Transcript 23 Comp Review 1

Comprehensive Review
Unit 1
Neurons
• There are hundreds of different types of neurons, each one is
specialized for a particular task
• Sensory nerves receive and transmit sensory information, and
there are several different types of them, with receptors for
touch, light, smell, etc.
• Motor neurons transmit signals for muscle contraction, etc.
• They all share certain characteristics.
–
–
–
–
Longevity (can last a lifetime)
High metabolic rate
Cannot divide to reproduce
Cannot survive without oxygen
Neuron Anatomy
Soma (cell body)
Axon (transmits signals)
Axon terminals
(stimulate
another cell)
Axon hillock
(trigger zone)
Dendrites (receive signal)
Neuron Anatomy
• DENDRITES function to receive the signal and carry the
nerve conduction toward the cell body.
• SOMA (cell body) is where the nucleus, ribosomes, and
most organelles are located
• AXON HILLOCK is the area on the soma where the action
potential of the neuron builds up before it transmits the
signal down the axon.
• AXON function is to transmit signals. Some cells have
many axons, some have one, some are short, and some
are long.
• AXON TERMINALS (also called terminal boutons or
synaptic knobs) contain a neurotransmitter which, when
released, stimulates another cell.
• A synapse is where one neuron touches another neuron.
Neurons may have a couple of synapses, or hundreds.
Structure of a Synapses
Chemical substances released
from the presynaptic
terminal:
•May inhibit or stimulate an
action in the postsynaptic cell
•May be broken down by
enzymes
Figure 12.8a, b
Cell Membranes
• What two conditions must be met for
diffusion of a substance across a
semipermeable membrane?
– Is the membrane permeable to it?
– Does it have a concentration
gradient?
• If the answer is yes to both questions,
then the substance will diffuse (Which
way? Down it’s gradient)
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• Each cell in our body is surrounded by a cell membrane
composed of a phospholipid BI-LAYER. That means that our cell
membranes have two layers: an outer layer, and an inner layer.
• The inside layer of each cell membrane in the body, (including
each neuron) has a charge (usually negative), and the outside
layer of each cell membrane has a charge (usually positive).
• The reason for the charge difference is that there are many
proteins inside of cells, and proteins are made of amino acids,
most of which have a negative charge. Because proteins are
negatively charged, the inside layer of the cell membrane has a
negative charge.
• Outside of the cell, there are many electrolytes, especially
sodium (Na+), which have a positive charge. They stay outside of
the cell because they cannot get in unless sodium channels in
the cell membrane are open, which they usually are not. That’s
why the outside of the cell membrane usually has a positive
charge.
• What is a sodium channel? Proteins embedded in the cell
membranes form channels which only allow certain ions to
cross the cell membrane.
• A sodium ion can only get into the cell by way of a sodium
channel. A potassium ion can only get in by way of a potassium
channel, etc.
• Charged ions, such as potassium (K+), sodium (Na+), calcium
(Ca++), and chloride (Cl-) are called electrolytes. When they
move from one side of the cell membrane to the other (when
their channels are open), they carry their electrical charge with
them.
• When sodium channels open during neuron stimulation, it
changes the overall charge of the inside and outside of the cell
membrane.
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Sidedness
“Sidedness” of the membrane
• Sidedness means that the electrical charges on one side of the
membrane (positive or negative) are different than on the other side.
Why does sidedness exist?
• The cell membrane has different permeabilities to each ion; for
instance the cell is more permeable to K+ than any other ion.
• Pumps exist which force particular ions into or out of the cell
• Channels made out of protein selectively allow particular ions into or
out of the cell. These channels may be open or closed at any given
time.
9
Not just separation of solutes, but
charges, too!
+
+
+
+
_ _ _ _
_ _ _ _
_ _ _ _
+
+
+
+
+
+
+
+
– Abundance of proteins,
which have a negative
charge
– The cell membrane is
very permeable (“leaky”)
to K+, so it can LEAVE
the cell whenever it
wants. That leaves the
inside of the cell more
negative.
+
+
+
+
• Inside of the cell is
negative due to :
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• Every cell has a positive charge on the outside of the membrane and a
negative charge on the inside of the cell membrane, when the cell is at
rest (not being stimulated).
• K+ constantly leaks out of the cell because it wants to diffuse down its
concentration gradient. That means it wants to go from its area of high
concentration (the inside of the cell) to an area where it is in low
concentration (the outside of the cell).
• But once it leaks out of the cell, the positive
•
charge of K+ is combined with the positive
charge of Na+, and this collection of positive
charges makes K+ want to go back into the cell,
since positive charges are attracted to negative
charges. Na+ wants to get into the cell, too, but
it’s channel is closed.
We use this electricity to do work. Blood
pressure, peristalsis of intestines, muscles, etc,
use this electricity for work.
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Because of this separation of chemicals and electrical
charges, every cell has a Resting Membrane
“Potential”
• There is a difference in electrical charge
across the membrane (a potential
difference)
• More negative inside; more positive
outside
• Our cells are like batteries and some cells
can tap into this “potential energy” to do
work (“kinetic energy”)
• What generates it?
– Mainly, ion concentration gradients and
differences in membrane permeability (leaky to
K+ but not to anything else)
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Resting Membrane Potential
• The resting membrane potential is how
negative or positive the charge of the cell
membrane is when it is not being stimulated
by a neuron
• Resting membrane potential is minus70 to
minus 90mV
• Why is the resting membrane potential
negative? Because K+ has leakiness, so it
constantly escapes with its positive charge,
leaving the inside of the cell more negative.
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• As K+ leaves the cell, it takes a positive charge outside with it,
so the inside is more negative.
• However, as the inside of the cell is becoming more negative,
the outside of the cell is becoming more positive, and the
positive charges will want to flow back inside of the cell since
they are attracted to the negative charges.
• This is what keeps K+ from just leaving the cell until it is in equal
numbers on both sides of the cell. Before it can reach such an
equilibrium, it gets pulled back into the cell because its positive
charges are drawn into the inside of the cell, where the charge
has become strongly negative (because proteins are on the
inside of the cell and they have a negative charge).
• Other positively charged ions, like Na+, want to go into the cell
also, but they are blocked by protein gates that only K+ can get
through.
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MEMBRANE POTENTIAL
• The MEMBRANE POTENTIAL (how negative or positive the charge of the
cell membrane is) is a number that is a reflection of the ion with the
greatest permeability.
• Our cells’ resting membrane potential is minus 70 mV because they are
most permeable to K+. Therefore, K+ will diffuse out its concentration
gradient, taking its positive charges with it, leaving the inside of the cell
more negative.
• What if the cell was more permeable to Na+?
• Sodium would diffuse down its concentration gradient to the inside of
the cell, taking its positive charges with it, making the inside of the cell
more positive.
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What if…..
• What if a membrane suddenly became
MORE PERMEABLE to Na+?????
• Even for just a moment in time…..
• What would Na+ do? (Ask yourself the 3
questions)
Which way is the electrochemical
gradient for Na+?
Electrical: inward
Chemical: inward
Answer:
Most definitely INWARD
Sodium WANTS IN!
ClNa+
Cl-
Na Cl
+
Na Cl
+
Cl-
Na+
Na+
++
++
--Na+
Na Cl
Cl-
+
-70 mV
What would happen to the membrane potential of
the cell when this event occurs?
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• What would happen to the membrane potential of the
cell when you open up a sodium channel?
• If we instantly increase sodium permeability, sodium will
enter the cell, changing the charge of the inside of the
cell so that it goes from negative to positive. The outside
layer of the cell membrane would then go from positive
to negative (the charges flip). This is called
DEPOLARIZATION.
• However, when this occurs, Na+ will be in higher
concentration on the inside of the cell, so it wants to
diffuse back out of the cell.
• Once it leaves the cell again, the membrane potential of
the inside of the cell membrane will return to a negative
charge. This is called REPOLARIZATION.
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Excitable Cells
• Cells that can experience a momentary change in
membrane voltage are “excitable” cells
• That temporary change in voltage is due to a momentary
change in permeability of Na+
• The membrane, for only a moment, becomes more
permeable to Na+ than to K+
• When the outside and inside of the cell membrane reverse
their charges (inside becomes positive and outside becomes
negative), and then reverts back to normal, this process
(depolarization + repolarization) is called an ACTION
POTENTIAL.
• The reversal of charges (action potential) is carried like a
wave down the length of the cell, and into the next cell
touching it, and so on.
ACTION POTENTIAL
• The action potential occurs when the membrane potential (how
negatively charged the inside of the cell is) reaches a certain
threshold.
• When the Na+ rushes into the cell, the membrane potential becomes
less and less negative. Eventually, it reaches zero charge, and as more
Na+ enters the cell, the inside of the cell becomes positively charged.
• At this threshold, when the inside of the cell membrane has become
positive, the outside of the cell membrane will become negative, and
this reversal of charges sweeps down the length of the cell
membrane, like a wave of electricity. This is the action potential. This
is how one neuron stimulates a cell (a muscle cell, gland, or another
neuron).
• If the neuron stimulates a muscle cell, it contracts. If it stimulates a
gland, it secretes. If it stimulates another neuron, the action potential
is carried further along the nerve pathway, until it reaches the target
organ.
Functional Classification of Neurons
• Neurons are grouped functionally according to the
direction the nerve impulse travels relative to the CNS.
• Sensoroy Neurons (afferent neurons) transmit impulses
toward the CNS. They originate in the PNS and terminate
in the CNS.
• Motor Neurons (efferent neurons) transmit impulses
from the CNS to effector organs (muscles and glands).
They originate in the CNS and terminate in the PNS.
• Interneurons (association neurons) connect sensory
neurons to motor neurons within the spinal cord and
brain. They originate and terminate in the CNS, and form
complex neuronal pathways. They make up 99.98% of
the neurons in the body, reflecting the vast amount of
information processed in the CNS.
Sensory Input and Motor Output
• Sensory (afferent) neurons are those that pick
up sensory signals from receptors in the fingers,
toes, etc
– Bundles of the same kind of sensory neurons travel
together as NERVES, and go from the PNS to the
CNS
• Motor (efferent) neurons originate in the brain,
and the signals are carried away from the CNS
and go to the muscles and glands.
Neurons Classified by Function:
Sensory vs. Motor Neurons
Sensory neurons enter the
spinal cord. Motor neurons
leave the spinal cord.
Interneurons connect the
sensory and motor neurons.
Figure 12.11
Neurons are only one type of cell; there are
others, which are supporting cells, with a
special name:
GLIA (neuroglia, meaning “nerve glue”) are the
supporting cells of the nervous system. These
are only brain cells that can reproduce. Since
cancerous cells are those that reproduce, all
brain tumors originate from glial cells.
There are four types of glial cells that we will
cover:
1. Oligodendrocytes
2. Schwann cells
3. Astrocytes
4. Microglia
Types of Glial Cells
1. OLIGODENDROCYTES (“few branches”). They
are found only in the CNS, are very large and
complex cells. Oligodendrocytes form MYELIN
SHEATHS. This sheath is a covering around an
axon to speed up the nerve conduction.
• The action potential jumps BETWEEN
Nodes of Ranvier (it skips the bare areas),
speeding up the overall nerve conduction.
• Therefore, a myelinated axon conducts
impulses faster than an unmyelinated
axon.
MULTIPLE SCLEROSIS is an autoimmune disease where
the oligodendrocytes (the myelin sheaths) are
destroyed (axon demyelination), interfering with the
neuron functions in the CNS. Oligodendrocytes
cannot regenerate.
MS is the most common neurological disease of young
adults. Starts to manifest in late teens and early 20’s.
It progresses to paralysis and sometimes death.
One in 1000 people get it. There are treatments, but no
cure.
2. SCHWANN CELL is another cell that forms
myelin sheaths, but in the PNS. Each cell
only forms one myelin sheath.
Difference between oligodendrocytes and Schwann cells
Found in CNS only
One cell may
form 3 nodes,
another cell may
form 2 nodes
Found in PNS only
One cell always
forms only one
node.
3. ASTROCYTE is another very large, complex
cell, in the CNS. Its function is to wrap
around capillaries while it also is physically
supporting and wrapping around neurons.
– Physically supports the neurons
– Transmits materials from capillaries to neurons
– Forms blood-brain barrier (BBB)
Supporting Cells in the CNS
Figure 12.12a
Blood-Brain-Barrier
• The BBB prevents a lot of certain types of materials from
leaving the blood and entering the brain (e.g. hormones,
drugs).
• The brain still gets its nourishment from the blood,
without the toxins.
• The continuous capillaries have leakage, but are
surrounded by astrocytes, so not everything can leak out.
• Certain antibiotics can’t cross the BBB, so they can’t be
used for brain infections.
• The only function of the blood-brain barrier is to help
protect the central nervous system.
4. MICROGLIA (one word, two errors!). These
are not micro, nor are they glia.
They are macrophages, the same size as
everywhere else in the body.
They are called micro because they are much
smaller than real glia cells.
They pick up bacteria and dead cell, etc.
Supporting Cells in the CNS
Figure 12.12b
TERMINOLOGY
•GREY MATTER: that portion of the CNS that is
unmyelinated (cell bodies of neurons, some types of glia
(neuroglia), and dendrites)
•WHITE MATTER: that portion of the CNS with myelinated
axons; the myelin makes the area look white.
•NERVE: collection of axons in the PNS. No cell bodies,
dendrites, or synapses; just axons.
•TRACT: collection of axons in the CNS e.g. conveys
information (axons) from the left to the right side of the
brain.
•SYNAPSES: Where information is processed. Most
synapses are in the CNS
TERMINOLOGY
•GANGLION: A collection of cell bodies in the PNS
•NERVE PLEXUS: A network of nerves (nerves don’t run
by themselves, they go in groups)
•MOTOR NEURON: Nerves that leave the CNS to effect a
muscle or gland
•SENSORY NEURON: goes from body to CNS, carrying
sensory information.
•INTERNEURON is a small neuron found only in the CNS;
it connects two other neurons. There is a large number of
interneurons in the CNS, this is what makes the CNS
complex.
• MAJOR ANATOMICAL REGIONS OF THE BRAIN
– Cerebrum
– Diencephalon
– Brain Stem
– Cerebellum
CEREBRUM
•The brain is divided into parts, and is bilaterally symmetrical.
•In general, the left side controls the right half of the body, and
the right side of the brain controls the left half of the body.
•The largest portion is the CEREBRUM, which makes up 80% of
the brain.
•The cerebrum controls logical thought and conscious
awareness of the environment.
•It is also the area responsible for the highest sensory and
motor activity.
•The cerebrum is made up mostly of grey matter (cell bodies,
dendrites, and unmyelinated axons).
The Cerebral Hemispheres and lobes
Central
sulcus
• The FRONTAL LOBE and
PARIETAL LOBE are
separated by the CENTRAL
SULCUS.
• The TEMPORAL LOBE is
between the parietal and
frontal lobe, separated by
the LATERAL SULCUS.
• The OCCIPITAL LOBE does
not have a real border; it’s
just a region.
• These are the anatomical
areas, but the functional
areas are more important.
Lateral
sulcus
CORPUS CALLOSUM
• The CORPUS
CALLOSUM is
the area that
connects the
right and left
halves of the
brain.
Diencephalon
Consists of two parts:
• Thalamus
• The superior portion of the diencephalon
• Processes sensory information according to importance
• Major relay station for sensory impulses to the cerebrum
• Hypothalamus
– The inferior portion of the diencephalon
– Provides homeostatic control over the body (maintains the
homeostasis of the body)
– Controls hunger/thirst body temperature
THALAMUS
•The THALAMUS functions to sort out all the
sensory information.
•It compares the input and determines what
information is worth sending to the cortex.
•Your body ignores most sensory information.
•Up until now, have you noticed the sound of the air
conditioner? It’s not important, so it goes
unnoticed.
•This area also compares information from the right
and left eyes for stereoscopic vision, and the right
and left ear to determine direction of sound.
Thalamus
Hypothalamu
s
Pituitary
gland
HYPOTHALAMUS
 This small area exerts more control over autonomic functioning
than any other part.
 Provides homeostatic control over the body (maintains the
homeostasis of the body)
• It maintains homeostasis by controlling the autonomic
nervous reflexes, glucose and hormone levels.
• It is also the main visceral control center, so it controls
body temperature, hunger and thirst, and blood
pressure.
 The hypothalamus is part of the limbic system, so that’s why a
painful memory can increase blood pressure.
• BRAIN STEM
– MIDBRAIN
– PONS
– MEDULLA OBLONGATA
Midbrain
• The top of the brain stem is the MIDBRAIN.
• It controls automatic behaviors (fight or flight)
• The midbrain also contains a pigmented area called the
substantia nigra.
• The Substantia nigra is involved in addictions and in initiating
body movement.
• The substantia nigra secretes the neurotransmitter dopamine.
• When the neurons in the substantia nigra become damaged,
dopamine levels decrease, causing Parkinson's Disease.
• Treatment is to replace the dopamine
Dopamine
• Remember that acetylcholine is the neurotransmitter that
functions to contract skeletal muscles?
• There are many other types of neurotransmitters as well. One is
called dopamine.
• Dopamine is the neurotransmitter that controls the flow of
information between various areas of the brain.
• Dopamine is lacking in Parkinson's Disease, in which the person
has muscular rigidity and tremors, so they lose the ability to
start movements. They need a service dog to help them get out
of a chair or to take a first step. They have a pill-rolling tremor
at rest.
Pons
Farther down the
brainstem is the
PONS, which relays
sensory information
between the
cerebellum and
cerebrum.
Midbrain
Pons
Medulla
Oblongat
Medulla Oblongata
• At the base of the brainstem is the MEDULLA
OBLONGATA, which contains areas for heart rate,
blood pressure, and breathing.
• Damage here causes coma. Swelling from an injury
causes pressure, which can damage this area, which
can cause a coma.
• Concussions cause nausea and a decrease in blood
pressure; patients with these symptoms need an MRI
to see if this is early signs of damage to medulla
oblongata
• Boxers who are knocked out can recover, but repeated
knock-outs can cause permanent brain damage.
PINEAL BODY
• The PINEAL BODY secretes melatonin.
• How much it secretes depends on the sensory
information it receives from the eyes about how
many hour of daylight are present.
• The amount of melanin secreted and circulating
in the blood then determines the circadian
rhythm, or the biological clock (cycles
influenced by light).
• Therefore, the pineal body detects the number
of hours of light and dark, and sets the body’s
24-hour clock.
Thalamus
Pineal body
Pineal body
CEREBELLUM
• The cerebellum is the second largest portion of
the brain, is responsible for balance and muscle
coordination, and is a comparator.
FUNCTIONAL REGIONS
• A. MOTOR AREAS
• B. SENSORY AREAS
• C. HIGHER FUNCTIONS
MOTOR AREAS
• PRIMARY MOTOR CORTEX
• PRIMARY MOTOR ASSOCIATION AREA
CORTEX AND ASSOCIATION AREAS
• Each area of the brain has a region where the
sensory information comes in, and another area
where the information is understood.
• The area where the information comes in is a
cortex, and the area where it is understood is the
association area.
• Therefore, there will be a motor cortex and
association area, a visual cortex and association
area, an auditory cortex and association area, and
a somatic (sense of touch) cortex and association
area.
MOTOR AREAS
• 1. PRIMARY MOTOR CORTEX
• 2. PRIMARY MOTOR ASSOCIATION AREA
2
1
PRIMARY MOTOR CORTEX
Contains UPPER MOTOR NEURONS, which
extend down the spinal cord and synapse on
LOWER MOTOR NEURONS which then leave the
spinal cord to innervate every skeletal muscle.
Some muscles have more motor units than others
(hands, eyes, etc).
Upper and Lower Motor Neurons
Lower motor neuron is here. The
upper motor neuron comes down
from the brain and synapses on
this neuron.
Figure 12.11
PRIMARY MOTOR ASSOCIATION AREA
Located just anterior to the primary motor cortex.
A. Learned motor skills: these are preprogrammed skills, like
when you know how to type or swing a golf club. You
practiced it so often, it’s now automatic.
– When someone asks you how to spell a word, but you
can’t do it until you write it out, it’s because that memory
is now a motor skill.
– The same happens when you know how to tie your own
shoelace or necktie, but can’t tie another’s; it initially is
learned by repetition.
– Then, to do it later triggers a series of information which
turns on those muscles in the right order.
PRIMARY MOTOR ASSOCIATION AREA
B. Planning movement: This is when you plan to
reach for a new item.
You have not rehearsed it, but you know to extend
your forearms, lift, etc.
A signal is sent to the primary motor cortex to turn on
specific motor units to do that.
Damage from a stroke= loose function to that area,
but you can compensate by using other muscles,
and re-learn that movement.
Pre-Central Gyrus
Pre-Central Gyrus
• Within the primary motor area of the brain, there is a structure called the
pre-central gyrus which contains a precise map of the different body parts.
• This map is called a motor homunculus (Latin: little man)
• All the neurons that innervate the lips would have their cell bodies in one
particular region in this area. All the neurons that innervate the hands have
their cell bodies in this area. All those that innervate the back have their cell
bodies here.
• However, we don’t have as many neurons innervating the back as we do for
the lips and hands.
• The homunculus is drawn to represent how many neuron cell bodies we have
that innervate each region of our body.
FUNCTIONAL REGIONS
• A. MOTOR AREAS
• B. SENSORY AREAS
• C. HIGHER FUNCTIONS
SENSORY AREAS
• PRIMARY SOMATOSENSORY CORTEX Somatic
= touch
• SOMATOSENSORY ASSOCIATION AREA
• PRIMARY VISUAL CORTEX
• VISUAL ASSOCIATION AREA
• PRIMARY AUDITORY CORTEX
• AUDITORY ASSOCIATION AREA
SOMATOSENSORY AREAS
1. Primary somatosensory cortex
2. Somatosensory association area
The primary somatosensory cortex receives
signals for touch and pressure.
1
The somatosensory association
area interprets the sensation.
When I put my hand in my
pocket, I know that is my keys I
am feeling.
2
VISUAL AREAS
1. Primary visual cortex
2. Visual association area
The primary visual cortex receives signals from
the optic nerves.
The visual association area
interprets the signals. When I
look at my keys, I can identify
them as keys.
2
1
VISUAL ASSOCIATION AREA
Within the visual association area is a region called Brodmann areas
18 +19.
Damage to this area results in an inability to recognize what one
sees.
The person can see a chair in their way, move around it, but they
can’t identify the object as a chair.
Some people with this damage can’t distinguish one person from
another because they can’t recognize their faces.
For more information on these types of brain damages, there’s a
book called The Man Who Mistook his Wife for a Hat.
HEARING AREAS
1. Primary auditory cortex
2. Auditory association area
The primary auditory cortex receives signals from
the ear.
The auditory association area
interprets the signals. When I
hear a sound, I can tell you what
it is that I am hearing.
1
2
Auditory Association Area
• The auditory association area contains two special regions
• BROCA'S AREA is a region of the brain that allows for speech.
– Injury (stroke) in this location causes impairment of
speaking certain words. They know what they want to say,
they just cannot get the words out. Not being able to
speak at all is called aphasia.
• WERNICKE’S AREA is the region of the brain that allows
understanding of words.
• It does not affect a person’s speech.
• They can say what they want to, but
they cannot comprehend
someone else’s speech.
FUNCTIONAL REGIONS
• A. MOTOR AREAS
• B. SENSORY AREAS
• C. HIGHER FUNCTIONS
• For a great video of a neurologist describing what it felt like
when she had a stroke:
http://www.ted.com/talks/lang/eng/jill_bolte_taylor_s_powerful_stroke_of_insight.html
HIGHER FUNCTIONS
1. PLANNING AND JUDGMENT
2. MEMORY
3. EMOTIONS
PLANNING AND JUDGMENT
• How much time do you need to be ready for the
test? This is calculated by the frontal lobe.
• Damage to the frontal lobe causes people to
become docile and do what they are told.
• 1930’s when people were overly aggressive,
they did a frontal lobotomy by going up the
eyelid, crack through the skull, and stirring up
the brain. The problem is that it permanently
altered their personalities.
• Stopped in 1960’s; we do it with drugs now
(Ritalin).
MEMORY: HIPPOCAMPUS
• We talked about motor memory. You can also
have memory of events.
• This is controlled by the HIPPOCAMPUS (“sea
horse”; that’s its shape). The hippocampus plays
a major role in storing and retrieving memories.
• But memories are not stored there or in any
other single site in the brain. They are stored
throughout the brain, especially in the cerebral
cortex.
Memory: Hippocampus
Hippocampus
Mammilary Bodies
• A pair of small round bodies at the anterior end of
the fornix
• Part of the diencephalon; they form part of the
limbic system.
• They relay information (recognition memory) from
the hippocampus. They also add the element of
smell to memories.
• Damage to the mammillary bodies due to thiamine
deficiency or alcohol causes Wernicke-Korsakoff
syndrome (anterograde amnesia)
Sheep
brain
Fornix
Mammilary
body
Fornix
Mammilary
body
Fornix
• Carries signals from the hippocampus to the
mammillary bodies.
ANTEROGRADE AMNESIA
• Damage to the mammillary bodies or
hippocampus; they remember things before the
injury occurred, but all new information is lost
within minutes.
• Nemo’s fish friend, Dori, has this type of amnesia.
• You can get around it by motor memory. Give an
amnesiac a new puzzle; they’ll do it in 30 mins.
The next day, they don’t recognize the puzzle, but
they do it in 20 mins, the next day in 10. Therefore,
they are learning by motor memory. They can
learn their route from home to the market by
repetition. But they can’t make a detour, and if
anything bumps them off track, they’ll be lost.
RETROGRADE AMNESIA
• Retrograde amnesia is a form of amnesia where someone is
unable to recall events that occurred before the development of
the amnesia.
• Retrograde amnesia is caused by trauma that results in brain
injury.
• Retrograde amnesia is often temporally graded, meaning that
remote memories are more easily accessible than events
occurring just prior to the trauma.
• Events nearest in time to the event that caused memory loss
may never be recovered.
• They can remember new things.
STROKES
• A hemorrhage in the brain (broken blood
vessel) deprives an area of the brain of oxygen.
• This is called a stroke.
• It is one of the most likely causes of amnesia.
• Amnesia that is caused by a blow to the head is
not cured by a second blow!
ALZHEIMER’S DISEASE
• Dementia is a symptom, not a disease. Dementia is
loss of memory.
• Alzheimer’s disease is the most common form of
dementia.
• About 10% of people over the age of 65 and 50% of
people over the age 85 suffer from it.
• It is irreversible, incurable, and fatal (6th leading
cause of death in the USA, surpassing diabetes).
The person dies because they can no longer eat,
swallow, etc. There are treatments to delay
symptoms.
EMOTIONS: LIMBIC SYSTEM
• The prefrontal lobe and the hippocampus are part
of a system of structures in the brain.
• The LIMBIC SYSTEM also includes the olfactory
nerves (sense of smell). Therefore, memory,
emotion, and smell are linked.
• Crayolas are created today with the same scent
because it reminds people of their happy times in
childhood.
• Why is the brain formed so that smell and
emotions are tied together?
• Because pheromones are tied to emotions and
behavior, so they need the link.
The Limbic System
(everything in orange)
Figure 13.23
Limbic System
• The limbic system includes the olfactory cortex
(sense of smell), and portions of the
diencephalon and cerebrum
• It influences emotions, motivations, and mood
• It is functionally associated with the
hypothalamus
• It initiates responses necessary for survival,
such as hunger and thirst.
MENINGES
• These are tissues that cover the entire CNS.
They are three layers that serve to protect and
cushion the brain.
Meninges
1. DURA MATER is the thickest and most superficial of the
meninges.
2. ARACHNOID MATER is the middle layer and is not nearly as
dense. It also does not go down into the sulci, it only covers
over the top of the gyri.
3. PIA MATER is the thin, shiny layer that DOES follow the brain
surface into the sulci.
• SUBDURAL SPACE is between the dura mater and the arachnoid
mater.
• The SUBARACHNOID SPACE is between the arachnoid and pia
mater, and is filled with CEREBRAL SPINAL FLUID (CSF).
1. DURA MATER (“Tough mother”)
Dense regular connective tissue.
It consists of two layers.
Under the skull is the first layer of dura mater, called the
PERIOSTEAL LAYER. Just under this is the second layer, called
the MENINGEAL LAYER. There are these two layers everywhere
except around the spinal cord, where it’s just one layer, the
meningeal layer of the dura mater; no periosteal layer.
Between the meningeal and periosteal layers of the dura mater are
DURAL SINUSES, which are filled with venous blood which is
drained from the brain.
Dural sinus and subarachnoid space
Clinical Significance
• In the spinal cord, between L3 and L4, a doctor can
inject anesthetic above the dura mater, so only the
nerves are affected. What is that called? Epidural.
 The dura and arachnoid mater both have lots of blood
vessels, which might rupture in an injury, called a
SUBDURAL or SUBARACHNOID HEMORRHAGE, which
is potentially fatal. Blood accumulates and squeezes
the brain.
 Treatment = drill a hole.
VENTRICLES OF THE BRAIN
• The brain and spinal cord are hollow, filled with CSF = ventricles They are
extensive. The names are simple.
• LATERAL VENTRICLE is the largest, extends throughout the cerebrum.
• THIRD VENTRICLE: in a sheep, it forms a figure “3” under the fornix and
around the corpora quadrigemina. In a human model, it looks like a cavity
between the fornix and a red arch.
• FOURTH VENTRICLE is at the base of the cerebellum; it is continuous with
the central canal of the spinal cord, and also with the subarachnoid space.
– CEREBRAL AQUEDUCT: connects the 3rd and 4th ventricles.
•
The ventricles, subarachnoid space , and cerebral aqueduct are filled
with CSF. The subdural space is NOT filled with CSF; it is filled with
venous blood.
VENTRICLES OF THE BRAIN (blue)
Figure 13.6a, b
CerebroSpinal Fluid (CSF)
• CSF is similar to plasma because it is derived
from plasma.
• CSF is made in the ventricles by a group of
capillaries called the CHOROID PLEXUS.
• The choroid plexus capillaries have holes that
allow the blood plasma to leak into the
subarachnoid space. It is now called
cerebrospinal fluid (CSF).
CerebroSpinal Fluid (CSF)
• The CSF that has been depleted of its nutrients is absorbed back
into the blood through the ARACHOID GRANULATIONS.
• Arachnoid granulations are small protrusions of the arachnoid
mater (the thin second layer covering the brain) through the
dura mater (the thick outer layer).
• They protrude into the venous sinuses of the brain, and allow
cerebrospinal fluid (CSF) to exit the brain, and enter the blood
stream.
• 800ml of CSF is made per day, but there is actually only 150 ml
there because the extra is continually absorbed in the dural
sinus through the arachnoid villa, which are valves that release
the CSF back into the blood.
PROBLEMS WITH MENIGES
• HYDROCEPHALY is accumulation of CSF inside the ventricles.
• It is usually congenital, caused by a blockage of the cerebral
aqueduct. The CSF is made but can’t leave, and the brain gets
expanded.
• The skull bones in a newborn can expand, so although it CAN
damage the brain, it does NOT cause mental retardation. The
head becomes enlarged.
• Treatment is to put in a tube to drain it.
• Hydrocephaly in adults can be caused by a tumor, and since the
skull no longer expands, it’s very dangerous.
MENINGITIS
• Meningitis is inflammation of the meninges.
• Can be caused from bacteria (can be fatal in 24 hours) or virus
(fatal in a week or more).
• The main symptom is a headache, so when this occurs in an
infant, they can’t say where they hurt.
• So when an infant presents with a high fever of 104˚ with no
other symptoms, they might test for meningitis, because if
they miss it, it’s fatal.
• The test is a SPINAL TAP, where a needle is inserted between
L4 and L5 because that is below the level of the spinal cord.
• They draw the CSF to look at. It it’s cloudy or bloody, it’s
usually meningitis. Untreated meningitis can lead to this next
one:
ENCEPHALITIS
• This is inflammation of the brain.
• It can be caused by mosquito-borne illnesses, or
bacteria.
• Why is infection of the brain so dangerous? The
swelling crushes the brain.
• Any injury may lead to brain swelling.
• Treatment is to remove a piece of the skull bone
to allow the swelling.
The 12 Pairs of Cranial Nerves
Figure 14.8
I. Olfactory Nerves
• Sensory nerves of smell
Table 14.2
II. Optic Nerve
• Sensory nerve of vision
Table 14.2
III Occulomotor Nerve
• This controls most of the extrinsic muscles of
the eye (that move the eyeball).
• They also have parasympathetic innervation in
the iris (pupil) and cilliary muscles (controls
the lens).
IV. Trochlear Nerve
• Innervates an extrinsic eye muscle
Table 14.2
V. Trigeminal Nerve
• This is the main sensory nerve of the face. It has a
large branch that passes through the foramen
ovale of the skull. It has three parts.
• When a dentist numbs the lower teeth, he injects
the mandibular branch. For the upper teeth, he
injects the maxillary branch.
• The superior branch is the opthalmic branch.
• Problems with CN-V are called TRIGEMINAL
NEURALGIA, which is excruciating pain in the face
from nerve inflammation.
V. Trigeminal Nerve
Table 14.2
VI. Abducens Nerve
• Abducts the eyeball
Table 14.2
VII Facial Nerve
•This innervates the muscles of facial expression.
•A person who cannot blink or smile may have damage to this
nerve.
•Someone with a damaged facial nerve can not easily taste
sweet, sour, or salty substances.
•It also supplies parasympathetic innervation to most salivary
glands.
•BELL’S PALSY is damage of the facial nerve causing paralysis on
one side. The nerves swell from infection by herpes simplex
virus, but only the motor nerves are involved, not the sensory, so
it’s painless. Needs to be distinguished from a stroke.
VII. Facial Nerve
• Innervates muscles of facial expression
Table 14.2
VIII. Vestibulocochlear Nerve
• Sensory nerve of hearing and balance
Table 14.2
IX: GLOSSOPHARYNGEAL
• Along with CN X, the Glossopharyngeal nerve
carries information from the baroreceptors in
the head and neck to the brainstem.
• Baroreceptors sense how much arteries are
being stretched, and use this to measure the
blood pressure so the brain can adjust BP as
needed.
• Signals the pharynx to constrict (along with
CN-X) during swallowing.
Baroreceptors
• Baroreceptors are sensors located in the blood vessels of the
human body. They detect the pressure of blood flowing
through them, and can send messages to the central nervous
system to increase or decrease total peripheral resistance and
cardiac output.
• Baroreceptors act immediately as part of a negative feedback
system (called the baroreflex) as soon as there is a change
from the usual blood pressure, returning the pressure to a
normal level.
• Baroreceptors detect the amount of stretch of the blood
vessel walls, and send the signal to the nervous system.
IX. Glossopharyngeal Nerve
• Innervates structures of the tongue and
pharynx
Table 14.2
X Vagus Nerve
•
•
•
•
(vagrant = “wanders”).
90% of all parasympathetic fibers are in this cranial nerve.
This is the only cranial nerve that travels into the abdomen.
This is the most important cranial nerve because it innervates
all of the organs in the thoracic and abdominal cavities: heart,
lungs, GI tract, etc, with parasympathetic innervation.
• It also moves the larynx during speech and signals the
pharynx to constrict (along with IX) during swallowing.
• The majority of the parasympathetic outflow from the head is
by the vagus nerve.
X. Vagus Nerve
• A mixed sensory
and motor nerve
The only cranial nerve
that “Wanders”
into thorax and
abdomen
Table 14.2
XI: ACCESSORY NERVE
• Enters the skull through foramen magnum and
leaves through the jugular foramen.
• It just supplies the shoulder muscles.
XI. Accessory Nerve
• An accessory part of the vagus nerve
XII. HYPOGLOSSAL NERVE
• Supplies the tongue.
• Damage causes impairment of speech.
XII. Hypoglossal Nerve
• Runs inferior to the tongue
– Innervates the tongue muscles
Table 14.2
Need to know all of the cranial nerves
• Hint: use the first letter of each nerve to make
a sentence: “OOOTTAFVGVAH”. OOO, Tommy
Turtle Always Finds Vegetable Gardens Very
Attractive, Heavenly!
Spinal Cord Cross Section
Dorsal root
ganglion
Dorsal root
Dorsal root
Dorsal horn
Ventral
root
Ventral
horn
Posterior median
sulcus
Central canal
Dorsal root ganglion
Dorsal root
Ventral
root
Dorsal horn
Ventral
horn
Anterior median
fissure
Grey matter
White matter
White Matter
• White matter of the nervous system forms conduction
pathways called NERVE TRACTS.
• The white matter in each half of the spinal cord is organized
into three columns:
– Dorsal (posterior) column
– Ventral (anterior) column
– Lateral column
• Each column has ascending tracts, which consist of axons
conducting impulses toward the brain and descending tracts,
which consist of axons conducting impulses away from the
brain.
1. Dorsal (posterior) column
2. Ventral (anterior) column
3. Lateral column
1
1
3
3
2
2
Terms
• GANGLION is the term for a group of neuron
cell bodies (both sensory and motor) found in
the peripheral nervous system only.
• SENSORY NEURONS come in (via the spinal
nerve) through the dorsal root; their cell body
is in the dorsal root ganglion, and its axon
goes into the dorsal horn and synapses in the
grey matter.
• It also sends a branch to an area of the white
matter called the DORSAL COLUMN
PATHWAY, which goes into the brain
(thalamus).
Neurons Classified by Function
Dorsal column
pathway
Upper
motor
neuron
Lower motor
neuron
Figure 12.11
Terms
• LOWER MOTOR NEURONS have their cell body in the ventral horn, their
axon goes out the ventral root, and synapses in a skeletal muscle.
Symptoms of a lower motor neuron disorder is when the patient has
paralysis including their reflexes.
• UPPER MOTOR NEURONS have their cell body in the brain, and they
synapse on a lower motor neuron. Symptom of an upper motor neuron
disorder is when the patient cannot move their hand (paralysis) but
reflexes work
• INTERNEURONS: These are found in the brain and spinal cord. The ones in
the spinal cord have their cell bodies in the dorsal half of the gray matter.
They receive signals from the sensory neuron and then synapse on the cell
body of the motor neuron. In this way, the interneurons (sometimes called
association neurons) transmit signals from the sensory pathways to the
motor pathways. The complexity of the CNS can be attributed to the
large number of interneurons in the CNS.
Spinal Cord Reflexes
• Stretch Reflex (knee-jerk; patellar reflex)
– Muscle contracts in response to a sudden stretch force
(with a reflex hammer).
– After a severe spinal cord injury, all spinal reflexes are lost
below the level of the injury for 2 weeks. Then the patellar
reflex returns but it is often exaggerated (hyper-reflexic),
indicating damage is still present.
• Withdrawal Reflex
– The body part is quickly removed from a painful stimulus.
– Sensory neurons carry the information to the spinal cord, and the
muscles remove the limb immediately, before the brain receives the
pain information.
Sensory Tracts
• Now the signal has to go to the brain via a TRACT.
• A tract is a collection of axons inside the central
nervous system.
• Sensory axons send a branch to the thalamus
portion of the brain.
• SENSORY TOUCH  SPINAL NERVE 
POSTERIOR ROOT  POSTERIOR ROOT
GANGLION  POSTERIOR HORN  TRACT 
THALAMUS
Tracts to the Brain
• These tracts have various names, depending
on what types of neurons are traveling within
them.
• For example, the SPINOTHALAMIC TRACT
transmits pain and temperature.
• The SPINOCEREBELLAR tract transmits signals
of balance and position to the cerebellum.
• There are many other tracts as well. Some
tracts send sensory information to the brain,
and some tracts send motor commands from
the brain to the muscles.
SOMATIC MOTOR NEURON
• Sends commands to the skeletal muscle to
contract.
• When the nerves leave the spinal cord, they
travel together in what is called a plexus. One of
these is known as the brachial plexus (in the
armpit; innervates the muscles of the upper
extremity).
• Starting at the spinal cord and preceding laterally,
the subdivisions of a plexus start out in the
ROOTS (RAMI), then form a TRUNK, which then
branches into DIVISIONS, which then become
CORDS, which become the plexus.
Upper and Lower Motor Neuron
Diseases
• Some diseases only effect the UMN, and some
only effect the LMN.
• Lower motor neuron disorders:
– Multiple Sclerosis
– Polio
• Upper motor neuron disorder:
– Cerebral palsy
• Upper and Lower motor neuron disease
– ALS
Amyotrophic Lateral Sclerosis (ALS)
•
•
•
•
•
•
•
•
Also known as Lou Gehrig's disease
Physicist Stephen Hawking also has this disease.
A progressive motor neuron disease.
The disorder causes muscle weakness and atrophy throughout the body as
both the upper and lower motor neurons degenerate, ceasing to send
messages to muscles.
The muscles gradually weaken, develop fasciculations (twitches) because
of denervation, and eventually atrophy .
Eye muscles are usually spared.
Cognitive function is generally spared.
Death usually occurs in 2-4 years, although Stephen Hawking has had it for
the longest period of time, almost 50 years.
PROPRIOCEPTION NEURONS
• Sensors within the muscles that measure the amount of force
and movement (sensory).
• Proprioception neurons travel up the spinocerebellar tract.
The brain can then interpret whether you are off balance,
then send a command to the muscles to contract and
straighten yourself up so you don’t fall.
• Note that this sense of balance is NOT the same as the sense
of balance from equilibrium in the ears. Proprioception
neurons are located within the muscles.
• During a physical exam, a doctor will test the patient’s
proprioception ability by telling them to close their eyes and
place their finger on their nose. This may indicate a lesion in
the cerebellum. Who else may ask you to do this test? Alcohol
disrupts the cerebellum.
•Sensory
receptors that
report on
internal events
in your muscles
and joints.
•They report on
muscle stretch
and joint
position.
•They generate
electrical
impulses that
will travel up
neurons to the
CNS.
Proprioceptors
Proprioception Disorders
• Damage to proprioceptors can occur from
consuming excess vitamin B6 (pyridoxine).
• Patients cannot tell where their body parts are
unless they look at them.
• They have difficulty with all motor tasks
including walking, eating, dressing, etc.
• They must use their vision to watch each body
part to make it move in the right direction.
Structure of a
Nerve
Each neuron is surrounded
by a sheath called the
endoneurium. Some axons
have an additional sheath
called myelin.
A bundle of neurons travel
together in a fascicle, and
are surrounded by
perineurium.
A bundle of fascicles is
surrounded by epineurium
Figure 12.16a
DAMAGE TO THE
NERVOUS SYSTEM
• If a person has a spinal cord injury in their
cervical region, they could have quadriplegia
(arms and legs paralyzed).
• If a person has a spinal cord injury in their
thoracic region, they could have paraplegia
(just legs are paralyzed).
SOME CLINICALLY IMPORTANT
PERIPHERAL NERVES:
• Note: an epidural nerve block during child birth
will numb the mother from her navel to her
knees.
• PUDENDAL NERVE: this is the nerve that can be
anesthetized during childbirth as an alternative to
an epidural (a pudendal nerve block is also called
a saddle block because the numb areas are
where you would be touching a saddle).
• PHRENIC NERVE: allows the diaphragm to
contract. If it gets severed, the person can no
longer breathe without assistance.
Nerve Plexus
A PLEXUS is a network of nerves that primarily
serves the limbs. There are four major plexi:
cervical, brachial, lumbar, and sacral.
1. CERVICAL PLEXUS comes out of the neck and
are cutaneous nerves (sensory input of the
skin) of the neck and back of the head.
BRACHIAL PLEXUS
2. BRACHIAL PLEXUS
• This is the major group of nerves that supply
the upper limbs. It runs through the axilla.
• If a person leans their armpits on their
crutches, they can damage this plexus and
lose the use of their arms.
• The nerves in the brachial plexus change
names as they go to different regions in the
arm.
Axillary
Musculocutaneus
Major Nerves
of the Upper
Extremity
Axillary Nerve
• Deltoid
Musculocutaneus Nerve
• Supplies anterior muscles of the arm
Median Nerve
• Supplies no muscles of the arm
• Supplies anterior forearm (except flexor carpi
ulnaris)
• Carpal Tunnel Syndrome
– Hand of benediction
Carpel Tunnel Syndrome
• The median nerve travels under the transverse
carpal ligament.
• The nerve is pinched in carpal tunnel
syndrome.
MEDIAN NERVE
• This is the nerve that gets cut when people try
to slit their wrists.
• The arteries are so small in the wrist; people
rarely die from this type of suicide attempt.
However, they live with a lot of tissue damage.
They are not able to move the thumb towards
the little finger, so it is hard to pick up small
objects. This is called “ape hand”.
Ulnar Nerve
• Supplies flexor carpi ulnaris
• “Funny Bone”
• Damage can cause claw hand; cannot adduct
or abduct fingers
Radial Nerve
• Supplies muscles on the posterior
arm and forearm
• Damage can cause wrist drop
Carpel Tunnel
Syndrome
Axillary, Radial, Ulnar,
Median Nerves
Figure 14.4
Brachial Plexus
• Damage to Brachial Plexus
– Klumpke’s paralysis (brachial plexus damaged during
birth)
– Acquired Brachial Plexus injuries
• Crutch paralysis (total upper extremity paralysis)
• Claw Hand / Ape hand
• Hand of benediction
• Wrist Drop (Waiter’s Hand)
LUMBAR PLEXUS
3. LUMBAR PLEXUS
• FEMORAL NERVE is the main nerve to the
anterior thigh.
Sacral Plexus
4. SACRAL PLEXUS
Some of the fibers from the lumbar plexus mix with the sacral
plexus, so these are often referred to together as the
lumbosacral plexus.
• SCIATIC NERVE is the largest branch of the sacral plexus and
the largest nerve in the body; it leaves the pelvis through the
sciatic notch.
• A short, thick muscle (Piriformis muscle) covers the sciatic
notch, and when it contracts, it can pinch the sciatic nerve,
causing a type of sciatica (sciatic nerve irritation) known as
piriformis syndrome.
• This can be alleviated by stretching exercises. However,
sciatica can also be caused if there is a herniated lumbar disc,
in which case stretching exercises make it worse.
Obturator
Femoral
Nerves of the
Lower
Extremity
The sciatic nerve supplies
the back of the thigh, then
branches out into the
TIBIAL and FIBULAR
(peroneal) nerves, which
supply the leg and foot.
The fibular nerve branches
into superficial and deep.
Lower Extremity Nerves
Obturator Nerve
Supplies adductor muscles
Sciatic Nerve
Supplies back of thigh, leg and foot
Femoral Nerve
Supplies anterior Thigh
Tibial Nerve
Supplies posterior leg and foot
Common Fibular Nerve
Superficial branch
Supplies lateral side of leg
Deep branch
Supplies anterior leg
Injury causes “Foot Drop”
Tibial Nerve
• Sometimes a small branch of the tibial nerve
in the foot gets pinched between the
metatarsal heads, and the irritation causes
nerve swelling and pain.
• It is called a neuroma (“nerve tumor”) and
manifests as pain in the ball of the foot, made
worse with high heels.
• An injury to the fibular nerve may result in
“foot drop”, where the foot cannot be
dorsiflexed.
AUTONOMIC NERVOUS SYSTEM
• We don’t have voluntary control over
these nerves.
• They are involved digestion, blood flow,
urination, defecation, glandular secretion.
• Therefore, the ANS supplies the glands,
smooth muscle, and cardiac muscle, but
NOT the skeletal muscle.
• For this reason, the ANS is also called the
general visceral motor system.
ANS
• All of the neurons of the ANS are motor
neurons (there are no sensory neurons in the
ANS).
• The ANS differs from the CNS reflex arc
because the ANS has two lower motor
neurons in the periphery (the cell body of one
is in the spinal cord and the cell body of the
other is in the periphery), whereas the CNS
has one lower motor neuron, and its cell body
is within the spinal cord, not in the periphery.
Ganglia
• The area where the two neurons come together
is the AUTONOMIC GANGLIA.
• The first neuron is the PRE-GANGLIONIC
NEURON.
• The second neuron is the POST-GANGLIONIC
NEURON.
• Some of these ganglia (those in the sympathetic
division of the ANS) are lined up along the
vertebral column, called a structure called the
sympathetic trunk ganglia.
ANS
• The ANS motor unit is characterized by
having more than one lower motor
neuron, the axons may be myelinated or
unmyelinated, conduction is slow, and
the axons are thin.
• The ANS has two divisions: sympathetic
and parasympathetic.
ANS has TWO lower motor neurons
Preganglionic
neuron
CNS has just one
lower motor neuron
Post-ganglionic
neuron
Ganglion (where the
cell bodies of the postganglionic neurons
are)
SYMPATHETIC DIVISION
• ↑heart rate and blood pressure,
• ↑metabolic activity (increased blood
glucose),
• decreased peristalsis (decreased food
digestion)
• dilation of bronchioles
• control of blood flow to the skin
• sweating
Sympathetic Division
• E.g. when running, ↑heart rate =
sympathetic.
• When hot  sweat = sympathetic.
• The term “Fight or Flight” is inaccurate; it
refers to the ↑ heart rate, etc, but the
sympathetic division is also active when
relaxing on a nice beach with a cool drink
on a hot day, because whenever you’re
sweating, that’s the sympathetic division.
ANATOMY OF THE SYMPATHETIC DIVISION
• The sympathetic neurons exit the spinal cord at
the thorax and lumbar regions.
• The axons of most pre-ganglionic neurons in the
sympathetic division are fairly short, and they
synapse quickly on a ganglia.
• All these ganglia together are the SYMPATHETIC
TRUNK (CHAIN) GANGLIA.
• Therefore, the postganglionic cell bodies of the
sympathetic nervous system are in the chain
ganglia.
• There are also nerves that connect the ganglia to
each other.
Sympathetic Division
In Sympathetic division,
preganglionic axons are
SHORT because they
terminate in ganglia that are
close to the spinal cord
That means the postganglionic axons are
LONG, because they
have to reach all the
way to the target
muscle.
Sympathetic Division
• The axons of POST-GANGLIONIC NERVES are
very long, and go to the target organs.
• Some pre-ganglionic neurons bypass the
sympathetic chain ganglia and go directly to
the abdomen.
• They create a group of ganglia in the abdomen
called the SOLAR PLEXUS (“sun”). When you
get punched in the abdomen, you are punched
in the solar plexus, and get the wind knocked
out of you.
PARASYMPATHETIC DIVISION
• Unlike the sympathetic division, the axons of
the preganglionic neurons of the
parasympathetic division are long, and the
axons of the postganglionic neurons are short.
• The nerve cell bodies (peripheral ganglia) of
the parasympathetic division are closer to the
organs being innervated than in the
sympathetic division.
• In fact, the cell bodies are either next to or
inside of the target organs. Therefore, they
have short post-ganglionic fibers.
Parasympathetic Division
In the Parasympathetic
division, preganglionic
axons are LONG
because they terminate
in ganglia that are
close to the target
organ
That means the postganglionic axons are
SHORT
PARASYMPATHETIC DIVISION
• Involved in vegetative activities, such as
digestion, urination, defecation
• Has postganglionic cell bodies in terminal
ganglia, located either near or within
target organs
• Has both preganglionic and postganglionic
neurons that secrete acetylcholine
• Has preganglionic cell bodies located in
the cranial and sacral areas.
Parasympathetic Division
• The function of this division is often
antagonistic (opposite) of the sympathetic, but
actually, they work together.
• The parasympathetic division inhibits cardiac
contraction, so there is: ↓heart rate,
constricts bronchioles, activates digestive
system, and causes salivation, urination, and
defecation.
• When you are lounging on the beach, the
heart rate decreases (parasympathetic), but
the sweat increases (sympathetic).
Vagus Nerve
• The parasympathetic neurons come out of
either the brain or the sacral region of the
spinal cord.
• The majority of the parasympathetic
outflow from the head is by the vagus
nerve.
Vasovagal Syncope (Fainting)
• The most common type of fainting.
• After a stressful trigger, the parasympathetic nervous
system is enhanced by the Vagus nerve.
• The heart rate speeds up, then suddenly drops.
• Then the blood pressure drops.
• Unconsciousness results.
• Treatment: elevate the legs above the heart for a few
minutes, and make sure the airway remains open.
• A cold, wet cloth on the forehead and back of the neck
may make the person feel better as they recover.
VISCERAL (“organ”) SENSES
• A visceral nerve innervates involuntary
effectors (smooth muscles in organs).
• A somatic motor nerve innervates
voluntary effectors (skeletal muscle).
– (don’t confuse this with a somatic sensory nerve for
the sense of touch; sensory nerves are not part of the
ANS)
VISCERAL (“organ”) SENSES
• Internal organs also have sensory nerves that
tell you when you have eaten enough or your
bladder is full. These are not part of the ANS
because they are sensory.
• Not all organs have sensory nerves, for
instance, you can’t feel when you have high
blood pressure.
• You can also have visceral reflexes, which
trigger the parasympathetic system to contract
the bladder when full, etc.
• Reflexes are hard to localize.
Referred Pain
• Pain in an organ may not be where the organ
is.
• Heart pain usually manifests in the left side of
chest, the left shoulder, arm, but not the
heart.
• This is REFERRED PAIN.
• Pain in the lungs usually shows up as neck
pain.
• These areas of referred pain are important to
know, but not for this class.