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”
Central Nervous System
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!
Peripheral Nervous System
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
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
o Coil of wrapped membranes enclosing axon
o 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
o 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
o 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
o Interoceptors (internal environment)
o Exteroceptors (external surface of body)- Pressure, pain, temperature
o Proprioceptors (muscles, tendons, & joints)- Control equilibrium, posture, and
own movements
o Send information to brain on body position
Grouped by structure
o Free nerve endings – dendrites sense pain, usually in skin
o Encapsulated – capsule/knob at end of dendrites
o Separate, specific cells – cell takes info and stimulates neuron
i.e. photoreceptors (rods/cones) – cell stimulates neurons to take information to
brain
Grouped by stimuli (selective/specific)
o Stimulus produces potential if threshold met!
o mechanoreceptors (mechanical stimuli)
o 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
o 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
o Less and less integration occurs
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
o Positive ions inside cell: K+ (potassium)
o Positive ions outside cell: Na+ (sodium)
o Membrane relatively impermeable to both ions
o 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
Resting Potential
Polarized= Negative inside/ Positive outside
Will continue resting until receives stimulus (from environment or from another neuron)
o Typically is a neurotransmitter
o If enough received, neuron will depolarize and “fire”
Action Potential
1. Stimuli excite neurons
2. Gates of sodium channels in membrane open with stimulation
o Na+ diffuses into the cell (high concentration  low)
o Depolarization: polarity of neuron’s membrane reversed as sodium diffuses
o More negative outside, positive inside
3. If threshold potential reached, neuron activated to initiate & transmit an action potential (nerve
impulse)
o all-or-none response
o Depolarization (electrical impulse)
o happens along the axon at Nodes of Ranvier – jumps from node to node
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
o Fibers with myelin sheaths conduct impulses much faster
o Nerve impulse jumps from node to node along length of fiber (salutatory conduction)
Gaps allow ions to cross
All or none response
o Once threshold is met, neuron will fire
o Some mental illnesses involve neurons firing when they shouldn’t or not firing when
they should (bipolar, schizophrenia)
o Takes milliseconds to occur
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)
o Video Links on MBC
Neurotransmitters
o 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
o Certain neurotransmitters increase ion permeability (excitatory)
o Others decrease permeability (inhibitory)
o
Acetylcholine
o Abbreviated ACh
o most common neurotransmitter
o located in both the central nervous and peripheral nervous system
o first neurotransmitter be identified in 1914
o acts on basic autonomic and muscular functions
o Sarin gas (chemical warfare nerve agent) disrupts its ability to function and often leads to
death
Glutamate
o Excitatory neurotransmitter
o Plays a role in cognition, learning, and memory
o Main neurotransmitter in CNS of mammals
o Must be in correct balance in right place at right time! Excess glutamate in extracellular
space can damage neurons
o “overexcites” neurons and causes them to open channels, letting substances into
cells that shouldn’t be there
o released with stroke & head trauma and causes damage
o Researching drugs to help prevent damage
o Malfunction of glutamate has also been associated with Alzheimer's Disease
GABA (gamma-aminobutyric acid)
o GABA is the most important and common inhibitory neurotransmitter
o Fine-tunes neurotransmission
o Stops the brain from becoming overexcited
o Too much may cause hallucinations
o Also responsible for regulation of muscle tone
Dopamine
o Generally involved in regulatory motor activity
o In the basal ganglia of the brain, involved in mood, drives, pleasurable feelings, sensory
perception, and attention
o Produced when “feeling good,”
o also causes addictions (caffeine, cigarettes, drugs, etc.)
o With addictive substances, dopamine is increased
o More released
o Less broken down
o More received by receptors
o Drugs can mimic dopamine (i.e. marijuana – “dope”)
Epinephrine
o Also known as adrenaline (when released as hormone)
o Causes the feeling of being “revved up” or on edge
o Activates a “fight or flight” reaction in the autonomic nervous system
o Excitatory neurotransmitter – stimulates nerves to fire
o Counteracts with norepinephrine/noradrenaline
Serotonin
o Attention and other complex cognitive functions (drives), such as sleep (dreaming),
eating, mood, pain regulation
o Neurons which use serotonin are distributed throughout the brain, stomach and spinal
cord
Mood disorders
o 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
o 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
o Reflexes are rapid, predictable, and involuntary responses to stimuli
o 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
o (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
Central Nervous System
o Brain & spinal cord
o 100 billion multipolar neurons
o First appears as simple tube during embryonic development (neural tube)
o 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
o Collectively called the cerebrum
o Higher brain function
o Gyri (gyrus): elevated ridges of tissue separated by shallow grooves called sulci
o Fissures: deeper grooves which separate large regions of the brain
o 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
o Functions: speech, memory, logical and emotional response, consciousness, interpretation
of sensation, voluntary movement
Gray matter – cell bodies
o Highly ridged and convoluted, providing more room for thousands of neurons found here
Primary somatic sensory area: parietal lobe
o Interprets impulses traveling from the body’s sensory receptors (except for special
senses)
o Pain, coldness, light touch
Primary motor area: frontal lobe
o Consciously move skeletal muscles (voluntary)
o Sends impulses down motor tracts
Association areas (throughout cerebrum)
o 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)
o Parietal – compose speech, touch sensation
o Temporal – understand speech, reading, music, memories
o 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)
Somatosensory Areas on Cerebral Cortex
o can map somatosensory areas (lips and hands large area, trunk and limbs small area)
Cerebral White Matter
o Fiber tracts (commissures) carrying impulses to, from, or within the cortex
o Corpus callosum: fiber tract that connects cerebral hemispheres
o Communication between hemispheres
Basal Nuclei
o “islands” of gray matter within the white matter of the cerebral hemisphere
o Also called basal ganglia (caudate nucleus, putamen, globus pallidus)
o 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)
o 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
Diencephalon
o Enclosed by cerebral hemispheres
o Three major structures:
Thalamus: relay station for sensory impulses passing upward to the sensory cortex
Hypothalamus: (“under thalamus”) – primitive brain
o Autonomic nervous sytem center: regulates body temperature, water/ion
balance, glandular secretions, and metabolism (maintains homeostasis)
o Center for many drives and emotions- thirst, appetite, sex, pain, pleasure,
sleep
o Regulates pituitary gland & secretes hormones
o Mammillary bodies: reflex centers involved in olfaction
Epithalamus
o Pineal gland: secretes melatonin (broken down as you sleep)
o Choroid plexus: forms cerebrospinal fluid
The Limbic System- emotional experiences (amygdale hijack)
Brain Stem
o Pathway for ascending and descending tracts (white matter) connecting cerebrum &
diencephalon to spinal cord
o 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
o Provides the precise timing for skeletal muscle activity and controls balance and
equilibrium, posture, language processing & long-term learning
o Provides smooth and coordinated body movements
o Fibers reach cerebellum from inner ear, eye, proprioceptors
o Monitors body position and amount of tension in various body parts and sends message
to correct when necessary
o When damaged by head trauma or stroke, or sedated by alcohol, produces “ataxia” (loss
of coordination)
Evolution of the Brain
Lizard Brain
Basic functions
Mammalian Brain
More complex feelings & reactions
Human Brain
Logic & reasoning
Electroencephalogram (EEG)- measures brain acrivity (waves)
Protection of CNS
o Control center of body – needs good protection from damage (impact, friction, etc.)
o Skin/hair
o Bone (skull & vertebral column)
o Meninges: protective lining
o Dura mater – “tough mother”; hard, leathery, tough outer layer
o Arachnoid mater – “web-like”; middle layer, contains blood vessels
o Pia mater – “tender/soft mother”; inner layer
o Cerebrospinal fluid
o Blood-brain barrier
o Meninges
Cerebrospinal Fluid (CSF)
o provides protection, maintains proper ion concentration for the CNS, and provides a
pathway to the blood for waste
o helps maintain homeostasis, cushioning
o Made in choroid plexus
o In constant motion
o Small drains for CSF to drain out (constantly made, flows, and drains)
o Too much CSF increases pressure (hydroencephalus)
o Ventricles (openings), canals & aqueducts
Blood-Brain Barrier
o Keep blood & CNS separate (only certain molecules can cross into CNS)
o Can cross: small molecules (i.e. water), some viruses (i.e. polio, shingles), anything lipid
soluble because can go through cells (i.e. alcohol)
o 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
o Approximately 17 inches long
o Two-way conduction pathway to and from the brain
o Major reflex center (spinal reflexes)
o Enclosed within vertebral column, extends from foramen magnum of skull to first or
second lumbar vertebra (just below ribs)
o Cushioned and protected by meninges (extend beyond end of spinal cord)
o 31 pairs of spinal nerves arise from cord and exit vertebral column
o Cauda equina – collection of spinal nerves at inferior end of vertebral canal
Gray Matter of Spinal Cord
o Dorsal (posterior) horns: posterior projections
o Contain interneurons
o Sensory neuron fibers enter through dorsal root; cell bodies in dorsal root
ganglion
o Ventral (anterior) horns: anterior projections
o Cell bodies of motor neurons of somatic nervous system (voluntary)
o Motor neuron axons exit through ventral root
Dorsal & ventral roots fuse to form spinal nerves
Surrounds central canal (contains CSF)
White Matter of the Spinal Cord
o Myelinated fiber tracts
o Conduct impulses from brain to cord or one side of spinal cord to other
o Sensory (afferent) tracts: axons carrying sensory impulses to the brain
o Dorsal columns, ascending
o Motor (efferent) tracts: axons carrying impulses from the brain to the skeletal muscles
o Lateral & ventral tracts (ascending and descending motor tracts)
o
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
o Mixed nerves: carry both sensory & motor fibers (spinal nerves)
o Sensory (afferent) nerves: carry impulses toward CNS
o Motor (efferent) nerves: carry only motor fibers
Cranial Nerves
o 12 pairs of nerves serving head & neck (primarily); one pair extends to thoracic and
abdominal cavities
o Parasympathetic nervous system (autonomic)
o Numbered in order
o Most are mixed nerves
o Table 7.1 page 258-259; Figure 7.24 page 260
Spinal Nerves and Nerve Plexuses
o 31 pairs of human spinal nerves
o Formed from combination of ventral and dorsal roots of spinal cord
o Each spinal nerve divides into dorsal & ventral rami (spinal nerves only about ½
inch long)
 Rami contain both motor & sensory fibers
o Form plexuses: tangled networks of axons serving particular parts of the body
Autonomic Nervous System
 Motor subdivision of PNS that controls body activities automatically
o Main input from autonomic sensory neurons (interoceptors); monitoring internal
environment (i.e. chemoreceptors regulating CO2 levels)
o Controlled by hypothalamus and brain stem (integration centers)
o Regulates cardiac muscle, smooth muscles, and glands
o Homeostasis depends largely on ANS; lots of fine-tuning!
o Also called involuntary nervous system
o Function somewhat even if nerve supply damaged (“running around like a
chicken with its head cut off”)
o Hard to consciously control (i.e. lie detector, yoga)
Somatic vs. Autonomic NS
Somatic division:
o Effector organs: skeletal muscle
o Only one motor neuron
Cell bodies inside CNS
Axons (in spinal nerves) extend to skeletal muscles
o Neurotransmitter used is acetylcholine (ACh)
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
o 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
o preganglionic motor neurons arise in the spinal cord.
o pass into sympathetic ganglia which are organized into two chains that run parallel to
and on either side of the spinal cord.
ParasympatheticNS
o main nerve is the tenth cranial nerve, the vagus nerve.
o originates in the medulla oblongata
o 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
o 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
o Tangled networks of axons from sympathetic & parasympathetic neurons
o 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