The Nervous SystemChapter 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 TravelSensory 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) neuron is

polarized (resting potential)• Fewer positive ions sitting on the inside than on the

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 sodiumenters 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

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 Potential1. Stimuli excite neurons2. 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 Potential4. 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

• 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

Depolarization Repolarization

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 next1. Action potential reaches axon terminal &

electrical change opens calcium channels2. 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

Aspartate

Neuroactive Peptides - partial list!!

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 Ythyrotropin-releasing hormone

gonadotropnin-releasing hormone

growth hormone-releasing hormone

luteinizing hormone

vasoactive intestinal peptide

Soluble Gases

Nitric Oxide (NO)

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• 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

• Three basic regions:• Cortex (gray matter)• White matter (internal area)• Basal nuclei (gray matter whithin white matter)

• Occipital• Insula

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

patb

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 wayLINK

Basal Nuclei (Basal Ganglia)

Diencephalon• 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

Figure 7.1, page 245

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• Fleeing• Feeding• Reproductive behaviors

link

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• 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 (EEG)

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 theANS

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.

ParasympatheticNS

• 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

• 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)

“wind knocked out

of you”

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)