Transcript The Nervous System - Castle High School

The Nervous System
Chapter 7
Functions of the Nervous System
• Master controlling and communicating system of the
body
• Maintains body homeostasis with electrical signals
• Provides for sensation, higher mental functioning, emotional
response
• Activates muscles and glands
• Three overlapping functions to
accomplish control:
•
•
•
•
Sensory input (stimuli)
Integration (process and interpret)
Motor/Output (effects a response)
Functions are integrated into a loop…
keeps modifying until homeostasis is reached or environmental
condition changes
Structural Classification
• Central Nervous System: brain & spinal
cord (all neurons & neuroglia within)
• Occupy dorsal body cavity
• Integrating and command center
• Peripheral Nervous System: outside the
CNS
• Consists of nerves extending from brain &
spinal cord
• Connects CNS to rest of body
• Spinal nerves & cranial nerves
• Carry impulses from sensory receptors to
CNS & CNS to effectors
Functional Classification
• Sensory (afferent) division: conveys impulses to the
CNS from sensory receptors
• Motor (efferent) division: carries impulses from the
CNS to effector organs (muscles and glands); effect
a motor response
• Somatic Nervous System
• Voluntarily controls skeletal muscles
• Skeletal muscle reflexes (involuntary)
• Autonomic Nervous System
• Regulates events that are automatic/involuntary
(activity of smooth & cardiac muscles and glands)
• Sympathetic (stimulates) & parasympathetic
(inhibits) nervous system
Nervous Tissue: Supporting Cells
• Neuroglia (a.k.a. glia or glial cells)
• generally support, insulate, and protect the delicate neurons
• Cannot transmit nerve impulses
• Never lose ability to divide
• Brain tumor = “glioma”
• Types:
• Central Nervous System
•
•
•
•
Astrocytes
Microglia
Ependymal cells
Oligodendrocytes
• Peripheral Nervous System
• Schwann cells
• Satellite cells
Astrocytes
• Star-shaped cells (“astro”)
• Most abundant (nearly half of
neural tissue)
• Braces and anchors neurons to blood
capillaries
• Aid in exchanges between the
neurons and the blood capillaries
(nutrient regulation)
• Protect neurons from
harmful substances in
blood
• Help control chemical
environment
• Form scar tissue
Microglia
• Phagocytes that monitor the health of nearby
neurons
• Dispose of debris (including dead brain cells &
bacteria)
Ependymal Cells
• Form epithelial-like membrane that covers parts of brain and
forms inner lining that encloses spaces within brain and
spinal cord (central canal)
• Help with blood/brain barrier
• Ciliated, help circulate cerebrospinal fluid
Oligodendrocytes
• Have processes wrapped around nerve fibers that
produce myelin sheaths (fatty insulating coverings)
in brain & spinal cord
• Myelin is important for conducting electrical impulses!
Supporting Cells of the PNS
• Schwann Cells
• form myelin
sheaths around
nerve fibers that
are found in the
PNS
• Satellite cells
• Protective,
cushioning cells
Neurons
• Nerve cells
• Specialized to receive information and transmit it to other
cells! (electrochemical message)
• Sensory/integrative/motor functions of nervous system!
• Common features of neurons:
• Cell body
• Metabolic center of the neuron
• Contains nucleus & organelles
• Nissl bodies (rough ER) & neurofibrils (maintain cell shape)
• Processes
• Also called “fibers”, can be microscopic or 3-4 feet long
• Dendrites: receive incoming impulses (can have many)
• Axons: generate nerve impulses & conduct away from cell body (each
neuron only has one)
• Arises from Axon hillock
• Neurilemma: cell membrane of neuron
Neurons
Myelin Sheaths
• Myelin: white, fatty (lipid-protein) material, waxy
appearance
• Protects and insulates fibers
• Increases transmission rate of nerve impulses
• Schwann cells myelinate axons in PNS and form myelin
sheath
• Coil of wrapped membranes enclosing axon
• Neurilemma: part of Schwann cell external to myelin sheath
• Nodes of Ranvier: gaps between myelin sheaths formed by
different Schwann cells
• Oligodendrocytes myelinate axons in CNS
• Can myelinate as many as 60 different fibers, no neurilemma
Nodes of Ranvier
• Spaces between myelin sheaths
• Give astrocytes something to hold on to and
provides easier transfer of nutrients & materials
• Ion transfer
• Impulse jumps from
node to node
Terminology of CNS
• Nuclei: clusters of neuron cell bodies,
well protected
• i.e. Caudate nucleus (region of brain)
• Tracts: bundles of nerve fibers
(neuron processes)
• Each sense has own tract
• Sensory tracts go towards brain, motor
tracts come from brain
• White matter: myelinated fibers
(tracts)
• Gray matter: unmyelinated fibers and
cell bodies (nuclei)
Terminology of PNS
• Ganglia: small collections of cell bodies outside CNS
• Nerves: bundles of nerve fibers (neuron processes)
Functional Classification of
Neurons
• Grouped according to the direction the nerve impulse is
traveling relative to the CNS
• Sensory/afferent neurons
• Carry impulses from sensory receptors (in the internal organs
or the skin) to the CNS (from environment to CNS!)
• Cell bodies found in ganglion outside the CNS
• Dendrites associated with specialized receptors
• Motor/efferent neurons
• Carry impulses from CNS to the viscera and/or muscles &
glands (tell them to do something in response to the stimuli)
• Cell bodies always located in the CNS
• Interneurons (association neurons)
• Connect motor & sensory neurons in neural pathways
• Cell bodies always in the CNS
Path of Travel
Sensory  interneurons  motor
Sensory Receptors
• Grouped by location
• Interoceptors (internal environment)
• Exteroceptors (external surface of body)
• Pressure, pain, temperature
• Proprioceptors (muscles, tendons, & joints)
• Control equilibrium, posture, and
own movements
• Send information to brain on body position
• Grouped by structure
• Free nerve endings – dendrites sense pain,
• usually in skin
• Encapsulated – capsule/knob at end of dendrites
• Separate, specific cells – cell takes info and
stimulates neuron
• i.e. photoreceptors (rods/cones) – cell stimulates
neurons to take information to brain
Sensory Receptors
• Grouped by stimuli (selective/specific)
• Stimulus produces potential if threshold met!
• mechanoreceptors (mechanical stimuli)
• Rapid adaptation: Meissner’s corpuscle, Lamellar
corpuscle, hair root plexus; slower adaptation:
Merkel disc, Raffini corpuscle
• thermoreceptors (heat)
• free nerve endings
• nociceptors (pain)
• free nerve endings, not adaptive
• photoreceptors (light)
• chemoreceptors (chemicals)
• pH, ions
• osmoreceptors (osmotic pressure)
Adaptation
• Receptors adapt to
stimuli that they are
continuously exposed to
(can be rapid or slow)
• i.e. smell & temperature
are quickly adapting, pain
is very slow
• Less and less integration
occurs
A dog (red line) tracks a pheasant (yellow line).
As the dog keeps leaving the odor to prevent
receptor adaptation, it zigzags.
Structural Classification of Neurons
• Page 235, Figure 7.8
• Based on number of processes extending from cell
body
• Multipolar neuron: several processes
• Motor & associated neurons, most common structural type
• Majority of interneurons in CNS are multipolar
• Bipolar neuron: two processes (axon & dendrite)
• Rare, found only in some special sense organs (eye, nose)
• Act in sensory processing as receptor cells
• Unipolar neurons: single process emerging from cell
body
• Sensory neurons found in PNS ganglia
Physiology of Nerve Impulses
• Two major functional properties
of neurons:
• Irritability: ability to respond to
a stimulus and convert it into a
nerve impulse
• Conductivity: ability to transmit
the impulse to other neurons,
muscles, or glands
• Neurotransmission: neurons
communicating with one
another!
How does it all work?
• Plasma membrane of a resting (inactive)
is polarized (resting potential)
• Fewer positive ions sitting on the inside than
outside of the membrane
• more negative inside = resting/inactive
• Positive ions inside cell: K+ (potassium)
• Positive ions outside cell: Na+ (sodium)
• Membrane relatively impermeable to both ions
• Ion channels closed when resting
• Neuron no longer at rest when sodium
enters the cell and then potassium leaves
•Neuron uses energy to maintain polarization
•Na/K pump keeps ions where they are “supposed”
to be when at rest
•Page 236, Figure 7.9 – Flow chart
neuron
on the
Resting Potential
• Sodium
• Potassium
Polarized
• Negative inside
• Positive outside
• Will continue resting until receives stimulus (from
environment or from another neuron)
• Typically is a neurotransmitter
• If enough received, neuron will depolarize and “fire”
Action Potential
1. Stimuli excite neurons
2. Gates of sodium channels in membrane
open with stimulation
• Na+ diffuses into the cell (high concentration
 low)
• Depolarization: polarity of neuron’s membrane
reversed as sodium diffuses
• More negative outside, positive inside
3. If threshold potential reached,
neuron activated to initiate &
transmit
an action potential (nerve impulse)
• all-or-none response
• Depolarization (electrical impulse)
happens along the axon
•Nodes of Ranvier – jumps from node to node
Action Potential
4. Na+ channels close and K+ channels open
• K+ diffuse out of neuron into tissue fluid rapidly
• Repolarization – restores electrical conditions at
membrane to the polarized (resting) state
• Neuron cannot fire again until repolarized
5. Sodium-potassium pump restores original
concentrations
• Sodium (goes in)
• Depolarized
• Potassium (goes out)
• Repolarized
Myelinated Axons
• Fibers with myelin sheaths conduct impulses much
faster
• Nerve impulse jumps from node to node along
length of fiber (salutatory conduction)
• Gaps allow ions to cross
Action Potential
Depolarization
Repolarization
• All or none response
• Once threshold is met,
neuron will fire
• Some mental illnesses
involve neurons firing when
they shouldn’t or not firing
when they should (bipolar,
schizophrenia)
• Takes milliseconds to occur
Hyperpolarization
Transmission of Signal at Synapse
• Electrical impulse becomes chemical signal
(“electrochemical” event) – page 238, Fig 7.10
• Neurotransmitter chemical crosses synapse to
transmit signal from one neuron to the next
1. Action potential reaches axon terminal &
electrical change opens calcium channels
2. Calcium causes vesicles containing
neurotransmitter to fuse with membrane &
openings form, releasing transmitter
3. Neurotransmitter molecules diffuse
across synapse and bind to receptors on membrane
of next neuron
4. If enough neurotransmitter released,
depolarization of next neuron occurs
5. neurotransmitter is removed from the
synapse (diffusion, reuptake into axon terminal,
or enzymatic breakdown)
Video Links on MBC
Neurotransmitters
• chemical messengers that carry signals between neurons as
well as other cells in the body
• released from the end of one neuron and cross the synapse
to receptor sites in the next neuron or effector
• Certain neurotransmitters increase ion permeability
(excitatory)
• Others decrease permeability (inhibitory)
Small Molecule Neurotransmitter Substances
Acetylcholine (ACh)
Dopamine (DA)
Norepinephrine (NE)
Serotonin (5-HT)
Histamine
Epinephrine
Amino Acids
Gamma-aminobutyric acid (GABA)
Glycine
Glutamate
Soluble Gases
Aspartate
Neuroactive Peptides - partial list!!
Nitric Oxide
(NO)
bradykinin
beta-endorphin
bombesin
calcitonin
cholecystokinin
enkephalin
dynorphin
insulin
gastrin
substance P
neurotensin
glucagon
secretin
somatostatin
motilin
vasopressin
oxytocin
prolactin
thyrotropin
angiotensin II
sleep peptides
galanin
neuropeptide Y
thyrotropinreleasing
hormone
gonadotropninreleasing hormone
growth hormonereleasing hormone
luteinizing
hormone
vasoactive
intestinal
peptide
Carbon
Monoxide
Acetylcholine
• Abbreviated ACh
• most common neurotransmitter
• located in both the central
nervous and peripheral nervous
system
• first neurotransmitter be
identified in 1914
• acts on basic autonomic and
muscular functions
• Sarin gas (chemical warfare nerve
agent) disrupts its ability to
function and often leads to death
Glutamate
• Excitatory neurotransmitter
• Plays a role in cognition, learning, and
memory
• Main neurotransmitter in CNS of
mammals
• Must be in correct balance in right
place at right time! Excess glutamate
in extracellular space can damage
neurons
• “overexcites” neurons and causes them
to open channels, letting substances into
cells that shouldn’t be there
• released with stroke & head trauma and
causes damage
• Researching drugs to help prevent damage
• Malfunction of glutamate has also been
associated with Alzheimer's Disease
GABA
• gamma-aminobutyric acid
• GABA is the most important and common inhibitory
neurotransmitter
• Fine-tunes neurotransmission
• Stops the brain from becoming overexcited
• Too much may cause hallucinations
• Also responsible for regulation of muscle tone
Dopamine
• Generally involved in regulatory motor activity
• In the basal ganglia of the brain, involved in mood, drives,
pleasurable feelings, sensory perception, and attention
• Produced when “feeling good,”
also causes addictions
(caffeine, cigarettes, drugs, etc.)
• With addictive substances,
dopamine is increased
•
•
•
•
More released
Less broken down
More received by receptors
Drugs can mimic dopamine
(i.e. marijuana – “dope”)
Epinephrine
• Also known as adrenaline (when released as hormone)
• Causes the feeling of being “revved up” or on edge
• Activates a “fight or flight” reaction in the autonomic nervous system
• Excitatory neurotransmitter – stimulates nerves to fire
• Counteracts with norepinephrine/noradrenaline
Serotonin
• Attention and other complex
cognitive functions (drives), such as
sleep (dreaming), eating, mood,
pain regulation
• Neurons which use serotonin are
distributed throughout the brain,
stomach and spinal cord
• Mood disorders
• Antidepressants are serotonin uptake
inhibitors (leave serotonin in synapse
longer!)
• i.e. Prozac was first a diet aid (limited
appetite), but also caused mood change
due to its affect on serotonin. Important
to understand balance! (for example,
Prozac would not be a good antidepressant
for someone with a history of anorexia.)
Neurotransmitter Balance
• Most functions in body isn’t just one
neurotransmitter – usually a balance
• Have to have right amount of each – any of them
off can cause mental illness
• hard to treat mental illness
with medication because don’t
know which is off
• have to use trial & error
Other Neurotransmitter Examples
• Nitric oxide: vasodilator
• Endorphins – stress or pain, “runners high”
Physiology: Reflexes
• Reflexes are rapid, predictable, and involuntary responses to
stimuli
• Occur over reflex arcs and in both CNS and PNS structures
• Somatic reflexes: all reflexes that stimulate the skeletal muscles
(pulling back from hot stove)
• Autonomic reflexes: regulate activity of smooth muscles, the
heart, and glands (salivary reflex, pupillary reflex)
• Five elements:
•
•
•
•
Sensory receptor – reacts to a stimulus
Effector organ – muscle or gland eventually stimulated
Sensory and motor neurons to connect the two
CNS integration center - synapse or interneurons between the sensory
and motor neurons
• Example: patellar (knee-jerk) reflex, pulling hand back (Fig
7.11)
• Spinal reflexes – without brain involvement
Reflexes
Figure 7.11
Central Nervous
System
Central Nervous System
• Brain & spinal cord
• 100 billion multipolar neurons
• First appears as simple tube during embryonic
development (neural tube)
• Brain formation begins in the fourth week
• Functional Anatomy of the Brain
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Cerebral hemispheres (cognitive function)
Diencephalon (glands)
Brain stem (autonomic)
Cerebellum (coordination)
Cerebral Hemispheres
• Collectively called the cerebrum
• Higher brain function
• Gyri (gyrus): elevated ridges of tissue
separated by shallow grooves called sulci
• Fissures: deeper grooves which separate
large regions of the brain
• Cerebral hemispheres separated by
longitudinal fissure
• Sulci and fissures divide cerebral hemispheres into lobes
• Frontal
• Parietal
• Temporal
• Occipital
• Insula
• Three basic regions:
• Cortex (gray matter)
• White matter (internal area)
• Basal nuclei (gray matter whithin white matter)
Cerebral Lobes
Cerebral Cortex
• Functions: speech, memory, logical and emotional response, consciousness,
interpretation of sensation, voluntary movement
• Gray matter – cell bodies
• Highly ridged and convoluted, providing more room for thousands of
neurons found here
• Primary somatic sensory area: parietal lobe
• Interprets impulses traveling from the body’s sensory receptors (except for
special senses)
• Pain, coldness, light touch
• Primary motor area: frontal lobe
• Consciously move skeletal muscles (voluntary)
• Sends impulses down motor tracts
• Association areas (throughout cerebrum)
• Frontal – concentration, problem solving, planning, language comprehension, word
meanings, memories, higher intellectual reasoning and socially acceptable behavior,
recognizing patterns and faces, morality, planning (Cerebral Palsy – damaged)
• Parietal – compose speech, touch sensation
• Temporal – understand speech, reading, music, memories
• Occipital – visual (photoreceptors send info here through thalamus)
• Broca’s area – speech & vocalization
Association Areas of Cerebrum
Sensory and Motor Homunculi
• Shows relative amount of cortical tissue devoted to
each function (Fig 7.14, page 243)
Link
Somatosensory Areas on Cerebral
Cortex
• can map somatosensory
areas (lips and hands large
area, trunk and limbs small
area)
Cerebral White Matter
• Fiber tracts (commissures) carrying impulses to,
from, or within the cortex
• Corpus callosum: fiber tract that connects cerebral
hemispheres
• Communication between hemispheres
Basal Nuclei
• “islands” of gray matter within the white matter
of the cerebral hemisphere
• Also called basal ganglia (caudate nucleus, putamen,
globus pallidus)
• Motor relay station: help regulate voluntary motor
activities by modifying instructions sent to the
skeletal muscles by the primary motor cortex
(particularly in relation to starting or stopping
movement)
• Huntington’s disease and Parkinson’s disease are examples
of issues with basal nuclei – individuals are unable to
carry out voluntary movements in a normal way
LINK
Basal Nuclei (Basal Ganglia)
Diencephalon
Figure 7.1, page 245
• Enclosed by cerebral hemispheres
• Three major structures:
• Thalamus: relay station for sensory impulses passing
upward to the sensory cortex
• Hypothalamus: (“under thalamus”) – primitive brain
• Autonomic nervous sytem center: regulates body temperature,
water/ion balance, glandular secretions, and metabolism
(maintains homeostasis)
• Center for many drives and emotions
• Thirst, appetite, sex, pain, pleasure, sleep
• Regulates pituitary gland & secretes hormones
• Mammillary bodies: reflex centers involved in olfaction
• Epithalamus
• Pineal gland: secretes melatonin (broken down as you sleep)
• Choroid plexus: forms cerebrospinal fluid
Diencephalon
Limbic System
• cerebral cortex interconnects with
the basal ganglia, the thalamus,
and the hypothalamus
• Center of brain
• “emotional-visceral brain”
• Controls emotional experience and
expression; regulates emotion
• Amygdyla (negative emotions –
fear) & hippocampus (memory)
• Primitive/impulsive
• Associated with functions:
•
•
•
•
Fighting
link
Fleeing
Feeding
Reproductive behaviors
The Limbic System
Brain Stem
• Pathway for ascending and descending tracts (white
matter) connecting cerebrum & diencephalon to spinal
cord
• Also has small nuclei (gray matter) that produce
autonomic behaviors necessary for survival, some
associated with cranial nerves and control vital activities
such as breathing and blood pressure
• Four main structures:
• Midbrain (upper) - reflexes
• Pons (middle) - breathing
• Medulla oblongata (lower) – heart rate, breathing, blood
pressure, swallowing, vomiting
• Reticular formation – consciousness, awake/sleep cycle, filters
sensory inputs from spinal cord; damage results in coma
(permanent unconsciousness)
Cerebellum
• Provides the precise timing for skeletal muscle
activity and controls balance and equilibrium,
posture, language processing & long-term learning
• Provides smooth and coordinated body movements
• Fibers reach cerebellum from inner ear, eye,
proprioceptors
• Monitors body position and amount of tension in
various body parts and sends message to correct
when necessary
• When damaged by head trauma or stroke, or
sedated by alcohol, produces “ataxia” (loss of
coordination)
Cerebellum
Evolution of the Brain
• Lizard Brain
• Basic functions
• Mammalian Brain
• More complex feelings &
reactions
• Human Brain
• Logic & reasoning
The Brain of a Zombie
• Zombie Traits
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•
•
•
Stagger
Appetite
Rage
Stupidity
Zombie Stagger
• Seem clumsy, bump into
things, hold out arms for
balance
• Cerebellum: involved in
coordination of movements
• Basal ganglia works with
frontal lobe and brain stem to
coordinate movement &
behavior
Zombie Appetite
• Always hungry, appetite never
satisfied
• Eat humans
• Hypothalamus: connects with
many other regions of brain
and is responsible for
controlling hunger, thirst,
emotions, body temperature
regulation, and circadian
rhythms
Zombie Rage
• Aggressive at all times
• Extremely violent, attack
humans in enraged state
• Dangerous and cannot be
reasoned with
• Amygdala: brain’s primal
emotional center; implicated in
the experience of negative
emotions like fear and rage
Zombie Stupidity
• often can’t figure out how to
open doors and rarely, if ever,
plan ahead
• terrible problem solvers, and
seem to lack any ability to
communicate except through
indistinguishable grunts
• Frontal lobe: located at front
of brain, associated with
reasoning, motor skills, higher
level cognition, expressive
language
Zombie Autopsies
Electroencephalogram (
)
Protection of CNS
• Control center of body – needs good protection
from damage (impact, friction, etc.)
• Skin/hair
• Bone (skull & vertebral column)
• Meninges: protective lining
• Dura mater – “tough mother”; hard, leathery, tough
outer layer
• Arachnoid mater – “web-like”; middle layer, contains
blood vessels
• Pia mater – “tender/soft mother”; inner layer
• Cerebrospinal fluid
• Blood-brain barrier
Meninges
Meninges
Cerebrospinal Fluid
• provides protection, maintains proper ion
concentration for the CNS, and provides a pathway
to the blood for waste
• helps maintain homeostasis, cushioning
CSF
• Made in choroid
plexus
• In constant motion
• Small drains for CSF
to drain out
(constantly made,
flows, and drains)
• Too much CSF
increases pressure
(hydroencephalus)
• Ventricles
(openings), canals &
aqueducts
Blood-Brain Barrier
• Keep blood & CNS separate (only certain molecules can
cross into CNS)
• Can cross: small molecules (i.e. water), some viruses (i.e.
polio, shingles), anything lipid soluble because can go through
cells (i.e. alcohol)
• Many medications have to breach the BBB somehow by
attaching to something lipid soluble or mixing with higher
concentration of sugar to dehydrate cells and make gaps to
pass through
Spinal Cord
• Approximately 17 inches long
• Two-way conduction pathway to and from the brain
• Major reflex center (spinal reflexes)
• Enclosed within vertebral column, extends from
foramen magnum of skull to first or second lumbar
vertebra (just below ribs)
• Cushioned and protected by meninges (extend
beyond end of spinal cord)
• 31 pairs of spinal nerves arise from cord and exit
vertebral column
• Cauda equina – collection of spinal nerves at inferior
end of vertebral canal
Gray Matter of Spinal Cord
• Dorsal (posterior) horns: posterior projections
• Contain interneurons
• Sensory neuron fibers enter through dorsal root; cell
bodies in dorsal root ganglion
• Ventral (anterior) horns: anterior projections
• Cell bodies of motor neurons of somatic nervous system
(voluntary)
• Motor neuron axons exit through ventral root
• Dorsal & ventral roots fuse o form spinal nerves
• Surrounds central canal (contains CSF)
White Matter of the Spinal Cord
• Myelinated fiber tracts
• Conduct impulses from brain to cord or one side of spinal
cord to other
• Sensory (afferent) tracts: axons carrying sensory
impulses to the brain
• Dorsal columns, ascending
• Motor (efferent) tracts: axons carrying impulses
from the brain to the skeletal muscles
• Lateral & ventral tracts (ascending and descending motor
tracts)
Peripheral Nervous
System
Peripheral Nervous System
• Nerves & scattered groups of neuronal cell bodies
(ganglia) found outside the CNS
• Structure of a Nerve
• Nerve: bundle of neuron fibers found outside the CNS
• Endoneurium: CT surrounding each neuron fiber
• Perineurium: CT surrounding groups of fibers, forming
fascicles
• Epineurium: CT surrounding fascicles to form nerve
• Classification of Nerves
• Mixed nerves: carry both sensory & motor fibers (spinal
nerves)
• Sensory (afferent) nerves: carry impulses toward CNS
• Motor (efferent) nerves: carry only motor fibers
Nerve
Structure
Link
Cranial Nerves
• 12 pairs of nerves
serving head & neck
(primarily); one
pair extends to
thoracic and
abdominal cavities
• Parasympathetic
nervous system
(autonomic)
• Numbered in order
• Most are mixed
nerves
• Table 7.1 page
258-259; Figure
7.24 page 260
I - Olfactory
II - Optic
III - Oculomotor
IV - Trochlear
V - Trigeminal
VI - Abducens
VII - Facial
VIII - Auditory
IX - Glossopharyngeal
X - Vagus
XI - Accessory
XII - Hypoglassal
Spinal Nerves and Nerve Plexuses
• 31 pairs of human spinal
nerves
• Formed from combination of
ventral and dorsal roots of
spinal cord
• Each spinal nerve divides
into dorsal & ventral rami
(spinal nerves only about ½
inch long)
• Rami contain both motor &
sensory fibers
• Form plexuses: tangled
networks of axons serving
particular parts of the body
Autonomic Nervous System
Autonomic Nervous System
• Motor subdivision of PNS that controls body activities
automatically
• Main input from autonomic sensory neurons (interoceptors);
monitoring internal environment (i.e. chemoreceptors
regulating CO2 levels)
• Controlled by hypothalamus and brain stem (integration
centers)
Regulates cardiac muscle, smooth muscles, and glands
Homeostasis depends largely on ANS; lots of fine-tuning!
Also called involuntary nervous system
Function somewhat even if nerve supply damaged (“running
around like a chicken with its head cut off”)
• Hard to consciously control (i.e. lie detector, yoga)
•
•
•
•
Somatic vs. Autonomic NS
• Somatic division:
• Effector organs: skeletal
muscle
• Only one motor neuron
• Cell bodies inside CNS
• Axons (in spinal nerves)
extend to skeletal muscles
• Neurotransmitter used is
acetylcholine (ACh)
• ANS:
• Effector organs: cardiac
muscle, smooth muscle,
glands
• Chain of two motor neurons
• Preganglionic axon (CNS):
leaves the CNS to synapse
with the second motor
neuron in a ganglion outside
CNS; myelinated;
acetylcholine
• Postganglionic axon (PNS):
extends to the organ it
serves; unmyelinated;
acetylcholine or
epinephrine/norepinephrine
See figure 7.27, page 265
Divisions of the Autonomic NS
• Sympathetic division (thoracolumbar division):
mobilizes body during extreme situations (fear,
exercise, rage… “fight or flight”)
• Shorter pre-ganglionic neuron synapses in sympathetic
trunk ganglion or collateral ganglion (i.e. celiac and
superior and inferior mesenteric ganglia)
• Parasympathetic division (craniosacral division): “rest
& digest,” allows body to relax and conserve energy
• Longer pre-ganglionic neurons, synapse close to the
effector organ at terminal ganglion
Anatomy of Autonomic Motor
Pathways
• Some preganglionic neurons extend to adrenal
medullae (hormones released) – “adrenaline rush”
• Sympathetic trunk ganglia: vertical row on either
side of vertebral canal
• Sympathetic division
• Innervate organs above diaphragm
• Prevertebral ganglia: anterior to vertebral canal
• Sympathetic division
• Innervate organs below diaphragm
• Terminal ganglia: close to or actually in wall of
organ (longer)
• Parasympathetic division
Anatomy of the
ANS
SNS
• preganglionic
motor neurons
arise in the
spinal cord.
• pass into
sympathetic
ganglia which
are organized
into two
chains that
run parallel to
and on either
side of the
spinal cord.
Parasympathetic
NS
• main nerve is the
tenth cranial nerve,
the vagus nerve.
• originates in the
medulla oblongata
• Other preganglionic
parasympathetic
neurons also extend
from the brain
(cranial nerves III,
VII, IX) as well as
from the lower tip
of the spinal cord.
Autonomic Functioning
• Organs receive fibers from both divisions
• Blood vessels, skin structures, some glands, adrenal medulla –
all only receive sympathetic innervation
• Divisions have antagonistic effects due to different
neurotransmitters released
• Dynamic balance – both have to make fine continual
adjustments
• Communicate using neurotransmitters
• Parasympathetic fibers: cholinergic fibers (release
acetylcholine)
• Sympathetic postganglionic fibers: adrenergic fibers (release
norepinephrine)
• All pre-ganglionic neurons release acetylcholine
• Agonist: neurotransmitter that activates receptors;
antagonist: neurotransmitter that blocks receptor
Physiological Effects of ANS
• Table 7.3, page 268
• Autonomic tone: balance between sympathetic &
parasympathetic divisions
• Regulated by hypothalamus
• Sympathetic dominates during physical or emotional stress
(rapid ATP production); “flight or fight: response
• “E situations” - exercise, emergency, excitement, embarrassment
• one sympathetic neuron can synapse with 20+ postganglionic neurons
(effect much of body simultaneously)
• Hormonal effects they provoke linger (need to “come down” after
stressful situation)
• Parasympathetic dominates “rest and digest” activities conserve and restore energy
• SLUDD (salivation, lacrimation, urination, digestion, defecation)
• “Housekeeping” system of the body
• Preganglionic neurons synapse with only 4-5 postsynaptic neurons
(more localized response)
Autonomic Plexuses
• Tangled networks of axons from sympathetic & parasympathetic
neurons
“wind
knocked out
of you”
• Cardiac (heart), pulmonary (lungs), celiac or solar (liver, gall
bladder, stomach, pancreas, spleen, kidneys, testes, ovaries),
superior mesenteric (small & large intestines), inferior mesenteric
(large intestine), renal (kidneys & ureters)
Autonomic Reflexes
• controlled conditions
• i.e. blood pressure
• reflex arc:
• Receptor  sensory neuron
 integrating center 
motor neuron  effector
• hypothalamus is major
control center
Autonomic Nervous System Recap
• What are the key things to know about the ANS?
• Differences between sympathetic & parasympathetic
divisions (anatomy, physiology, effects)
• Anatomy of autonomic pathways & associated
terminology
• What is a plexus?
• Agonist vs. antagonist (neurotransmitters)