Transcript Nervous System - cloudfront.net

 Three
major functions:
› 1. Receive sensory input
 Gather info by monitoring changes or stimuli
from inside & outside body
› 2. Integration of input
 Process & interpret sensory input & determine
action
› 3. Motor output
 Carry out response decided by integration
usually by muscles (movement) or glands
(secretion)

Two major parts of nervous system:
› Central nervous system (CNS)
 Brain
 Spinal cord
› Peripheral nervous system (PNS)
 All nerves (spinal & cranial) outside of CNS
 Two components:
 Sensory (afferent) division
 Info going TOWARD CNS
 Motor (efferent) division
 Impulses EXIT from CNS
 Two subdivisions of motor (efferent):
 Somatic nervous system – voluntary
 Conscious control of skeletal muscles
 Autonomic nervous system - involuntary
 Controls smooth/cardiac muscle & glands
 Two subdivisions of autonomic that often
bring about opposite effects:
 Parasympathetic – stimulate rest & digest
activities
 Ex: stimulate flow of saliva
 Sympathetic – stimulate flight or fight
activities
 Ex: inhibit flow of saliva
 Classified
into two types of cells:
1. Neurons – transmit nerve impulses; no cell
division (amitotic)
2. Support cells (called neuroglia or glia) that
can not transmit nerve impulses; cell division
(mitotic)
a.
b.
c.
d.
e.
f.
Astrocytes
Microglia
Central nervous system
Ependymal cells
(CNS)
Oligodendrocytes
Satellite cells
Peripheral nervous system
Schwann cells
(PNS)
Also known as nerve cells
 Structure allows them to
receive & transmit
messages or impulses
 All have same basic
structures

› Cell body – usual cell organelles including
nucleus except no centrioles (no mitosis)
› Processes/fibers – arms that extend to/from
body
› To body = dendrites (1-100s)
› From body = axon (only 1)

Must know cell parts:
› Soma - cell body
› Nucleus – metabolic center of cell
› Dendrite(s) – one or more processes that conducts
impulses TOWARD cell body
› Axon hillock – where cell branches out to axon
› Axon – process that conducts impulses AWAY from
cell body
› Myelin – whitish, fatty substance found on long
axons in CNS; speeds up transmission rate
› Schwann cells – cells that myelinate axons in PNS
› Myelin sheath – membranes wrapped around
myelin
› Nodes of Ranvier – gaps in between Schwann cells
› Axon terminal – branched end of axon in which
neurotransmitters are stored in vesicles
 Large
concentrations of cell bodies in
CNS are in clusters & called nuclei
 Small concentrations are called
ganglia (pl) or ganglion (sing) – found
in CNS & PNS
 Bundles of nerve fibers in CNS called
tracts, but in PNS are called nerves
› Myelinated nerve fibers/tracts in
CNS called white matter
› Unmyelinated fibers and cell bodies
called gray matter

Three types of neurons based on function or direction
of nerve impulse:
› Sensory (afferent) neurons
 Carry impulses from sensory receptors TOWARD
CNS
 Nerve endings – pain & temperature receptors
 Meissner’s corpuscle – touch receptor
 Pacinian corpuscle – deep pressure receptor
 Proprioceptors – stretch or tension in tendons &
muscles
› Motor (efferent) neurons
 Carry impulses FROM CNS to organs or muscles
› Association neurons/interneurons
 Connect motor & sensory neurons
(afferent)
(efferent)

Three types of neurons based on structure or how
many processes extend from body
› Unipolar
 Single, very short process from cell body
 Immediately breaks into peripheral & central axon
 Unique: dendrites at peripheral end, so axon
conducts impulses away and TO cell body
› Bipolar
 One axon, one dendrite
 Very rare, only seen sense organs (eye & nose)
 Act as receptor cells
› Multipolar
 Several processes extend from cell body
 All motor neurons are multipolar so they are most
common
Star-shaped
 Account for ~ 50% of
neural tissue
 Form living barrier
between capillaries &
neurons therefore make
exchanges between
them

› Help protect neurons from harmful
substances
› Pick up extra ions
› Recapture released neurotransmitters
 Spiderlike
phagocytes (cell eaters)
› Dispose of debris like dead brain cells
& bacteria
Covered with cilia
 Line cavity of brain & spinal cord
› Beating of cilia help circulate
cerebrospinal fluid that fills brain & spinal
cord cavity
› Forms protective cushion around CNS

 Wrap
flat extensions tightly around
nerve fibers
› Produces fatty insulating covering of
axons called myelin sheaths in CNS

Form myelin around axons in PNS

Protective, cushioning cell body in PNS

neuron has two distinct properties that
differentiate it from any other cell in human
body:
› Irritability - ability to respond to stimuli & convert it to
a nerve impulse
› conductivity - ability to transmit an impulse to other
neurons, muscles, or glands
Most CNS neurons receive chemical stimulus at
plasma membrane (everywhere on neuron),
transmits it as electrical signal along axon, &
ends as chemical signal at axon terminals
 Most PNS neurons (sensory organs) receive
stimulus as light (eyes), sound waves (ears),
pressure (touch), or chemicals (taste & smell)

plasma membrane is where nerve impulse
begins
 Plasma membrane at rest is polarized

› fewer positive ions (K+) are inside cell than
positive ions (Na+) outside cell
› More negative (Cl-) ions inside cell than outside
-
+
Na
+
Na+ Na
+
Na
+
+
+
Na
Na Na
+
+
+
Na
Na
Na
Na+
-
-
-K+- K+ -K+ - - - -+ K+- - K+ K - - K+ - K+-+ K
+
+
+
+
Na +Na Na Na+ Na+ Na +Na+
- Na+ - Na
Na
a stimulus depolarizes
neuron’s membrane by
opening up Na+ gates
on membrane, allowing
Na+ inside
 initial exchange of ions is
a local depolarization
 Inside is more + than
outside
 Depolarization starts an
action potential in entire
neuron

Once action potential
(nerve impulse) starts,
it’s propagated over
entire axon (all or
nothing principle)
 K+ ions rush out of the
neuron after Na+ ions
rush in, which repolarizes
the membrane
 Na+/K+ pump on
membrane restores
original configuration by
shoving Na+ back out
and allowing K+ back in

› requires ATP
outsiders
INSIDERS
outsiders
INSIDERS
outsiders
INSIDERS
outsiders
outsiders
outsiders
INSIDERS
INSIDERS
INSIDERS
outsiders
outsiders
INSIDERS
Impulse travels faster when fibers have a myelin
sheath
 Once electrical action potential reaches axon
terminals, excites vesicles containing
neurotransmitters
 Vesicles move toward axon terminal
membrane & releases neurotransmitter into
synaptic cleft
 Neurons NEVER touch other neurons
 Neurotransmitters bind to receptors on
neighboring neuron’s dendrites
 New action potential will start on THAT one

The human body uses 50 different
neurotransmitters depending on the need
 Neurotransmitters either excite or inhibit
neurons

› Many drugs act to mimic the effect of
neurotransmitters on the brain
Name
Function
Result from
DEFICIT
Result from
EXCESS
Acetylcholine
Muscle action,
learning, memory
Alzheimer’s,
paralysis
Muscle spasms
Endorphins
Diminish pain
sensation, increase
pleasure
Emotionally
unstable,
depression
Addiction, little pain
sensation
Norepinephrine Alertness, arousal
(flight or fight)
Slight depression
Anxiety, panic attacks,
rapid heartbeat,
nausea, dizziness
Dopamine
Movement,
learning, attention,
emotion
Parkinson’s,
schizophrenia
Schizophrenia
Serotonin
Mood, hunger,
sleep, arousal
Depression,
anxiety, OCD
None
GABA
Inhibits nervous
system
Seizures, tremors,
Huntington’s,
insomnia
Increase blood
pressure & heart rate
Glutamate
Memory
Schizophrenia
Migraines, seizures, ALS

Much communication between neurons on
everyday basis is done via reflexes
› Reflex: rapid, predictable, involuntary responses
to stimuli

Reflex always occurs in same manner using
same neural pathways of both CNS & PNS
so they are called reflex arcs
 Two
types of reflexes:
› Somatic: stimulates skeletal muscles
 Ex: pull hand away from hot object,
blinking when air burst aimed at eyes
› Autonomic: regulate smooth & cardiac
muscles, & glands
 Ex: secretion of saliva, change in pupil size

Reflex arcs have at least 5 elements
involved in same arc or pattern:
1. Sensory receptor – react to stimulus
2. Sensory neuron – connect receptor & CNS
3. Integration center – connect neurons
4. Motor neuron – connect CNS & effector
5. Effector organ – muscle/gland to be stimulated
patellar (knee-jerk) reflex is simplest type of
reflex – two neurons involved
 Withdrawal reflex (remove from painful
stimulus) is more complicated – three neurons
involved utilizing association neuron

Average adult brain weighs 3 lbs
 Divided into 4 regions:

1. Cerebrum – largest region, broken into left &
right hemispheres
2. Diencephalon – interbrain atop brain stem
3. Brain stem – stalk on which brain sits, connects
to spinal cord
4. Cerebellum – bulbous projection at occipital
region, broken into two hemispheres
Made of two
hemispheres together
called cerebrum
 Encloses other three
parts of brain
 Entire surface made of
peaks and valleys

› Gyrus (gyri) – peaks of
ridges
› Sulcus (sulci) – shallow
valleys
› Fissures – deep grooves
separating large regions

Function of cerebrum is vast
› speech, memory, logical & emotional response,
consciousness, interpretation of sensation,
voluntary movement

Sulci & fissures divide cerebrum into lobes
(named after cranial bones)
› Parietal lobe
› Frontal lobe
› Temporal lobe
› Occipital lobe

Parietal Lobe
› Somatic sensory area located just posterior to
central sulcus receives & interprets impulses
from body’s sensory receptors (NOT special
senses)
 Pain, cold, light touch

Spatial map depicting region on body where senses
come from and how much brain power is devoted
to them is called sensory homunculus
Model depiction showing
areas of body given more
brain “power” than others
› Sensory pathways are crossed pathways,
meaning left side of brain receives impulses
from right side of body & vice versa
 Itch on right hand interpreted on left side of
somatic sensory area.
Occipital lobe
› Visual area located in posterior part
 Visual cortex – “sees”
 Visual association area – ties object to
memories, knowledge
 Temporal lobe
› Auditory area bordering lateral sulcus

 Auditory cortex – “hears”
 Auditory association area – ties sound to object or
knowledge
› Olfactory (smell) area deep inside

Frontal lobe
› Contains primary motor area, just anterior to
›
›
›
›
›
›
central sulcus, which allows us control of skeletal
muscles
Spatial map region called
motor homunculus
Broca’s area – located in
left hemisphere gives
ability to speak
Higher intellectual reason
Socially acceptable
behavior
Language comprehension
Gustatory complex (taste)

Two layers of cerebral hemisphere:
› Gray matter (cerebral cortex)
 Outermost layer made out of cell bodies of
neurons (no myelin)
 Ridges allow greater surface area, increasing
amount of neurons
 Several islands of gray matter that jut inward
called basal ganglia
› White matter
 Deeper cerebral layer made from fiber tracts
(bundles of nerve fibers)
 Major tract called corpus callosum connects right
& left cerebral hemisphere

AKA interbrain, made of 3 areas:
› Thalamus – relay station for sensory impulses
going up to sensory cortex
 Get rough idea if sensation will be pleasant or
unpleasant – sensory cortex figures it out
› Hypothalamus – regulates body temperature,
water balance (thirst), metabolism (appetite),
sex, pain, pleasure, pituitary gland
 Pituitary gland is attached & secretes hormones
› Epithalamus – pineal gland(secretes hormones)
& choroid plexus (knots of capillaries that form
cerebrospinal fluid)
Made of 3 structures:
› Midbrain – reflex centers for vision & hearing
› Pons – fiber tracts that control breathing
› Medulla oblongata – control heart rate,
blood pressure, breathing, swallowing,
vomiting
 Many small gray matter areas that control
breathing, blood pressure
 Running along length is reticular formation
which regulates consciousness, awake/sleep
cycles

› Damage here results in permanent unconsciousness
or coma

Two hemispheres & wrinkly (convoluted)
surface
› Outer cortex is gray matter while inner region is
white matter called arbor vitae (tree of life)

Provides timing for muscle activity, controls
balance & equilibrium
› Constantly monitors body position & makes
adjustments to keep balance
Structure
Cerebrum
Diencephalon
Brain Stem
Cerebellum
Subdivision
Function
Frontal Lobe
Speech, logic/reason, social behavior,
language comprehension, gustatory complex,
skeletal motor cortex
Parietal Lobe
Receives sensory input (pain, cold, light touch)
Temporal Lobe
Auditory cortex, olfactory cortex
Occipital Lobe
Visual cortex
Thalamus
Sensory impulse relay station
Hypothalamus
Regulates body temp, water balance,
metabolism, sex, pain, pleasure, pituitary gland
Epithalamus
Regulates pineal gland, choroid plexus
(cerebrospinal fluid)
Midbrain
Reflex center for vision & hearing
Pons
breathing
Medulla
oblongata
Controls heart rate, blood pressure, breathing,
swallowing, vomiting
none
Muscle coordination, balance, equilibrium
As nervous tissue is very soft and delicate,
injury to irreplaceable neurons can be
catastrophic
 Three methods of protection:

› Bony skull & vertebral column
› Membranes
› Cerebrospinal fluid

Three connective tissue membranes called
meninges cover & protect CNS
› Top: Dura mater (“tough
mother”)
 Periosteal layer (touches
skull)
 Meningeal layer
› Middle: Arachnoid mater
(“spider mother”)
 Looks like a cobweb
› Bottom: Pia mater (“gentle
mother”)
 Clings gently but tightly to
brain surface
Watery broth similar to blood plasma
 Constantly formed by choroid plexuses

› Little protein, lots of vitamin C, lots of ions

Always circulating among ventricles,
canals, & aqueducts in brain
› Spinal tap removes CSF from lumbar area
Brain can not handle tiniest fluctuations of
chemicals (all kinds) as other organs can
 As result, neurons are kept separated from
blood borne substances by “blood-brain
barrier” which is composed of least
permeable capillaries in human body

› Only water, glucose, essential amino acids, fats,
respiratory gases, and fat-soluble alcohols,
nicotine, caffeine, and anesthetics can pass
› Metabolic wastes (urea), toxins, proteins, most
drugs are prevented
› Nonessential amino acids & K, are always
pumped from brain
The other component of CNS, it’s a two-way
conduction pathway from PNS & brain
composed of neurons with long axons
 Reflex center where reflexes are determined

17” long spinal cord is
continuation of brain
stem ending at L2
 Starting at L3, branched
into 31 pairs of spinal
nerves exit vertebral
column called cauda
equina (horse’s tail)

› Cervical – 8 pairs
› Thoracic – 12 pairs
› Lumbar – 5 pairs
› Sacral – 5 pairs

Covered by meninges for
protection

Gray matter of spinal cord resembles
butterfly
› Posterior projections = posterior/dorsal horns
› Anterior projections = ventral/anterior horns
› Gray matter surrounds central canal which
contains CSF
› Spinal (nerve) fibers entering spinal cord

White matter composed of myelinated fiber
tracts
› Divided into three regions: posterior, lateral,
anterior columns
› Two types of tracts
 Sensory/afferent tracts: conduct sensory impulses
TO the brain
 Motor/efferent tracts: carry impulses FROM brain to
skeletal muscles
Consists of nerves &
scattered groups of ganglia
found outside CNS
 Nerve is bundle of neuron
fibers not in CNS

› Neuron fibers (processes)
surrounded by endoneurium
› Groups of fibers bound by
perineurium
› Whole bundles called
fascicles
› Fascicles bound together by
epineurium

Nerves carrying
both sensory &
motor fibers called
mixed nerves
› All spinal nerves are
mixed
› Sensory (afferent)
nerves – toward CNS
› Motor (efferent)
nerves – away from
CNS

Cranial nerves – 12
pairs that serve
head and neck

Spinal nerves – 31 pairs formed by both
dorsal & ventral roots of spinal cord
› Ventral rami (extension) forms four plexuses
(network of nerves) which are both sensory &
motor
 Four
nerves to know:
› Sciatic nerve
 part of sacral plexus
 Largest nerve in body
 Serves lower trunk &
posterior thigh/leg
 Inflammation or
damage causes
sciatica
› Median nerve
 Part of brachial
plexus
 Allows flexion of
forearm & some
hand muscles
 Pressure on nerve
from tendon causes
carpal tunnel
syndrome
 Inability to pick up
small objects, fine
motor control
› VII Facial nerve
 7th cranial nerve
 Serves muscles for facial expression, salivary
& lacrimal (tear ducts) glands, taste buds
 Weakening or paralysis causes Bell’s palsy
› Vagus Nerve
 X or 10th cranial
nerve
 Latin for
“wandering
nerve”
 Controls heart,
lungs, stomach,
large intestines,
spleen, kidney!
 Involuntary
motor branch of PNS that
controls smooth muscles, cardiac
muscles, glands
 Information from CNS activates nerves
that release neurotransmitters which
then signal appropriate muscle/gland
 Recall
two divisions of ANS that have
opposite effects:
› Sympathetic – extreme situations (fear,
exercise, rage)
› Parasympathetic – rest & conserve energy
 Three
neurotransmitters in ANS:
› Acetylcholine – both sympathetic &
parasympathetic
› Epinephrine – sympathetic division
› Norepinephrine – sympathetic division
 Formation
› Nervous system formed during first 4 weeks of
embryonic development
› Maternal infection or poor health habits may
cause permanent damage
 Measles causes deafness
 Smoking decreases oxygen causing low
birth weight, others
 Drugs (OTCs & illegal) can permanently
damage
 Maturation
› Last areas of CNS to mature is
hypothalamus
 Preemies have problems controlling
body temperature
› Throughout childhood, no neurons
grow but in fact become myelinated,
allowing neuromuscular control
 Aging
› Brain at maximum weight as young adult
› Next 60+ years, neurons get damaged &
die
 Other unused pathways can take over &
be developed
› Sympathetic nervous system becomes less
efficient
› Premature shrinking of brain occurs when
individuals accelerate normal process with
lifestyle
 Boxers, alcoholics, drug abusers

Huntington’s Disease
› Dominant genetic disease (one dominant allele
›
›
›
›
›
needed) for 50% chance of acquiring it
Strikes in middle age (around 50)
Massive degeneration of basal nuclei then cerebral
cortex
Initial symptoms are wild, jerky movements termed
chorea (Latin for dance)
Usually fatal within 15 years of onset
Treated with neurotransmitter (dopamine) blockers
 Parkinson’s
Disease
› Degeneration of dopamine-releasing neurons
in substantia nigra (in midbrain) so basal
nuclei dopamine targets becomes
overactive, causing tremors
› First sign is “pill-rolling” tremor of hand
› Treatment with L-dopa drugs helps some
symptoms, but after more neurons are
affected, it is ineffective
› Newer (albeit controversial) treatments
include transplanting embryonic substantia
nigra tissue, or genetically engineered (stem
cells), or cells from fetal pigs

Alzheimer’s
› Progressive degenerative disease that
results in dementia (mental deterioration)
› Nearly 50% of all people in nursing homes
have Alzheimer’s
› Begins with short-term memory loss, short
attention span, disorientation, loss of
language
› Result of shortage of acetylcholine &
structural changes in brain (areas of
cognition & memory)
› Microscopy of tissue shows abnormally large
deposits of protein
› About 5-15% of people over 65 will get this

Stroke (Cerebrovascular Accident/CVA)
› Blood circulation to brain area is blocked resulting in
tissue death
 Blood clot
 Ruptured blood vessel
› Area of tissue is initially located by looking at patient’s
symptoms
 Left cerebral hemisphere results in aphasia
(language impairment)
› Severe strokes kill 2/3 people almost immediately, and
remaining 1/3 die within 3 years
› Mild strokes do not cut off blood flow completely
 Called temporary brain ischemia or transient
ischemic attack (TIA)
 Not permanent but offer warning signs of CVA later
 Spinal
Cord injuries (SCI) &
Paralysis
› Any damage to the spinal cord resulting from
crushing or severing.
› Cervical injuries
 Cervical (neck) injuries usually result in full or
partial tetra/quadriplegia.
› Thoracic injuries
 Injuries at or below the thoracic spinal levels
result in paraplegia. There are about 11,000 new
cases of
spinal
cord injury
 T1 to T8 : inability to control
the
abdominal
in the U.S. every year.
muscles.
Males
account
of 82% of all
 T9 to T12 : partial loss of
trunk
and abdominal
muscle control.
spinal cord injuries and
females for 18%.
› Lumbar and sacral injuries
 Decreased control of the legs and hips, urinary
system, and anus.

Multiple Sclerosis
› Autoimmune disease in which
myelin sheaths around axon
fibers in CNS are gradually
destroyed by own immune
system
› Myelin converts to hardened
sheaths called scleroses
› Lack of insulation leads to
inability to control muscles
› Treatment today includes
hormone-like substance called
interferon
› Will result in complete
inability to function
 Meningitis
› Inflammation of
meninges due to viruses
or bacteria
› Can be life threatening
since can spread to
nervous tissue of CNS
› Diagnosed by spinal
tap to look at CSF

EEG (electroencephalogram)
› Assess electric activity of brain impulses
› Many electrodes are placed on scalp and
measurement of activity pattern is recorded
› Used to diagnose epileptic lesions, tumors

PEG (pneumoencephalography)
› Detection of hydrocephalus (water on brain)
› Cerebrospinal fluid is drained via spinal tap,
air is injected into subarachnoid space
› Provides clear picture of ventricles
› Extremely painful for patients – recovery
takes 2-3 months for CF to return back to
normal
› Not used since 1980s

Cerebral angiogram
› Used to assess condition of cerebral arteries
› Dye is injected into artery & disperses into
brain
› X-ray is then taken which highlights dye so
blood flow can be assessed
 Stroke victims

Computed (Computer- Aided) Tomography (CT
or CAT) scan
› Series of X-rays grouped together by a computer.
› Used to see tumors, lesions, MS or Alzheimer’s plaques,
infarcts (dead brain tissue)
› Important in mapping brain prior to surgery

MRI scan (Magnetic Resonance Imagery)
› Used to see tumors, lesions, MS or Alzheimer’s
plaques, infarcts (dead brain tissue)
› Similar to CT scan but 3D image capabilities

PET scan (Positron Emission Tomography)
› Used to determine sugar (glucose) uptake/usage
of cells
 Faster growing cells (cancer) use sugar faster
 Active brain areas also use sugar faster
 Alzheimer, Parkinson, epilepsy, tumors, dementia
› Patient drinks glucose solution, areas of fast
uptake show up on image