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Bio 201: Chapter 13-The Peripheral
Nervous System & Reflex Activity 20242025
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abdominal reflexes - ANS-tests the spinal cord integrity from T8-T12
autonomic (visceral) - ANS-activate effectors (smooth or cardiac muscles or glands)
axillary nerve - ANS-innervates the deltoid and teres minor muscle and the skin and
joint capsule of the shoulder
BRACHIAL PLEXUS - ANS-gives rise to all nerves that innervate the upper limbs
-ventral rami of C5-C8 and most of the T1 ramus
cervical plexus - ANS-formed by the ventral rami of C1-C4
common fibular nerve - ANS-wraps the head of the fibula
-innervated the knee joint, skin of the lateral calf & dorsum of the foot
cranial nerves - ANSI
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optic: vision
III
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trochlear: "pulley" for the eye
V
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abducens: abducts the eye
VII
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vestibulocochlear: hearing & balance
IX
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vagus: head, neck, thorax & abdomen
XI
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hypoglossal: tongue movement
crossed-extensor reflex - ANS-accompanies the flexor reflex in weight-bearing limbs
-important in maintaining balance
dermatomes - ANS-the area of skin innervated by the cutaneous branches of a single
spinal nerve
dorsal roots - ANS-contain sensory (afferent) fibers that arise from sensory neurons i
the dorsal root ganglia and conduct impulses from peripheral receptors to the spinal
cord

encapsulated dendritic endings - ANS-all mechanoreceptors
-enclosed in a connective tissue capsule
femoral nrve - ANS-the largest, terminal nerve of this plexus
-innervates anterior thigh muscles
flexor/withdrawal reflex - ANS-initiated by a painful stimulus an causes automatic
withdrawal of the threatened body part from the stimulus
free or naked nerve endings - ANS-present everywhere in the body
-abundant in the epithelia and connective tissues
ganglia - ANS-collections of neuron cell bodies associated with nerves in the PNS
general sensory receptors - ANS- involved in tactile sensations
-proprioceptors
-either unencapsulated or encapsulated nerve endings
Golgi tendon organs - ANS-proprioceptors
-cause contracting muscles to relax
-encapsulated
golgi tendon reflexes - ANS- produce muscle relaxation and lengthening in response to
tension
hair follicle receptors - ANS-free nerve endings that wrap around hair follicles
-light touch receptors that detect the bending of hairs
Hilton's Law - ANS-any nerve serving a muscle that produces movement at a joint also
innervates the joint and the skin over that joint
intercostal nerves - ANS-the ventral rami of T1-T12
-supply the intercostal muscles lying between the ribs
Joint kinesthetic receptors - ANS-proprioceptors
-monitor stretch in the articular capsules that enclose synovial joints
-encapsulated
LUMBAR PLEXUS - ANS- arises from spinal nerves L1-L4
median nerve - ANS-innervates five intrinsic muscles of the lateral palm
Meissner's corpuscles or tactile corpuscles - ANS-found just beneath the epidermis
-numerous in hairless skin areas
-receptors for discriminative touch
-encapsulated

Merkel discs - ANS-lie deeper within the layers of the epithelium
-function as touch receptors
motor endings - ANS-the PNS elements that activate effectors by releasing
neurotransmitters
Muscle Spindles - ANS-detect muscle stretch and initiate a reflex that resists the stretch
-encapsulated
muscle spindles - ANS-each muscle spindle consists of 3-10 intrafusal muscle spindles
enclosed in a connective tissue capsule
-regions wrapped by type Ia fibers, which innervate the spindle center AND type II
fibers,which supply the spindle ends and are stimulated only by stretch
musculocutaneous nerve - ANS-provides cutaneous sensation for the lateral forearm
nerve - ANS-a cordlike organ that is part of the peripheral nervous system
-each nerve axon is surrounded by a endoneurium
-groups of fibers are bound into bundles, called fascicles, wrapped by the perineurium
-all fascicles are enclosed by the epineurium
neuromuscular junctios - ANS-formed by the terminals of somatic motor fibers that
innervate voluntary muscles
obturator nerve - ANS-innervates the adductor muscles
organization of the somatosensory system - ANS1
...
circuit level: ascending pathways
3
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exteroceptors: sensitive to stimuli arising outside
the body
2
...
proprioceptors: respond to internal stimuli, however their location is much more
restricted, occur in skeletal muscles, tendons, joints and ligaments
receptor classes by stimulus type - ANS1
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thermoreceptors:sensative to temperature changes
3
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chemoreceptors: resond to chemicals in solution or changed in blood fluid
5
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receptor: site of stimulus activity
2
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integration center: within the CNS
4
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effector: muscle fiber or gland cell that responds to the efferent impulses
tibial nerve - ANS-supplies the posterior compartment muscles of the leg and the skin of
the posterior calf and sole of the foot
-gives off to the sural nerve: serves the skin of the posterolateral leg
-sural nerve divides into the medial and lateral plantar nerves: serve the foot
ulnar nerve - ANS-supplies the flexor carpi ulnaris and the medial part of the flexor
digitorum profundus
varicosities - ANS-knob-like swellings containing mitochondria and synaptic vesicles
ventral roots - ANS-contain motor (efferent) fibers that arise from ventral horn motor
neurons and extend to and innervate the skeletal muscles
Abducens – ANS Fibers extend from pons through superior orbital fissures to lateral
rectus muscle; primarily motor nerve for lateral eye movement
Accessory - ANSFormed from ventral rootless from C1-C5 region of spinal cord;
rootless pass into cranium via foramen magnum and exit skull via jugular foramina;
motor to trapezius and sternocleidomastoid
Activation of sensory receptors - ANSResults in action potentials sent to the brain
Adaptation - ANSThere is a decreased sensitivity of receptors in response to constant
stimuli
Chemoreceptors - ANSRespond to chemicals (smell, taste, changes in blood chemistry)
Classification of nerves - ANSSomatic sensory/motor; visceral sensory/motor; pure
sensory or pure motor nerves are rare

Complex receptors - ANSVision, hearing, equilibrium, smell, and taste
Cranial nerves - ANS12 pairs extend from brainstem; most are mixed nerves
Encapsulated dendritic endings - ANSAll are mechanoreceptors
Exteroceptors - ANSRespond to stimulus outside the body
Facial - ANSFibers extend from pons through internal acoustic meatuses and emerge
on lateral aspect of the face; main motor nerves of face; motor functions include facial
expression; parasympathetic nerves control lacrimal glands, salivary glands; sensory
function is taste
ganglia - ANScontain neuron cell bodies; dorsal root ganglia contain somatic sensory
neuron cell bodies; autonomic ganglia contain visceral motor neuron cell bodies
Glossopharyngeal - ANSFibers extend from the medulla through jugular foramen to
throat; motor to tongue and pharynx for swallowing; parasympathetic to parotid salivary
glands; sensory for taste from posterior 1/3 of tongue and general sensory from throat;
sensory from carotid chemoreceptors and baroreceptors
Hypoglossal - ANSExtend from medulla through hypoglossal canal; motor to extrinsic
and intrinsic muscles of tongue; invovled in tongue movement; contribute to swallowing
and speech
Interoceptors - ANSRespond to stimuli arising from internal viscera and blood vessels
Magnitude estimation - ANSIntensity is coded in the frequency of action potentials
reaching sensory cortex
Mechanoreceptors - ANSRespond to touch, pressure, vibration, stretch, and itch
Nociceptors - ANSSensative to pain-causing stimuli
Oculomotor - ANSFibers extend through superior orbital fissures to the eye; motor fibers
to 4 of 6 extrinsic muscles; control most eye movements; parasympathetic fibers
constrict smooth muscle of iris decreasing pupil diameter; parasympathetic fibers
contract the ciliary muscles which control lens shape
Olfactory - ANSSmell; pass through cribriform plate of ethmoid; axons synapse at
olfactory bulb; olfactory tracts terminate in the primary olfactory cortex in temporal lobe;
purely sensory
Optic - ANSArise from retinas; pass through optic canals, converge and partially cross
over the optic chiasma; optic tracts continue to thalamus where they synapse; optic
radiation fibers extend to visual cortex in occipital lobe; purely sensory

Perception - ANSConscious interpretation of stimuli
Perception of pain - ANSWarns of tissue damage; stimuli include extreme pressure and
temperature; also include chemicals released from injured tissue
Peripheral Nervous System - ANSAll neural structurs outside of the brain
Phasic receptors - ANSQuickly adapt to stimuli
Photoreceptors - ANSRespond to light energy
Preceptual detection - ANSAbility to detect a stimulus
Processing at circuit level - ANSOccurs at synapses between 1st and 2nd order
neurons; occurs in spinal cord, brain stem, thalamus, and cerebellum
Processing at perceptual level - ANSOccurs in the sensory cortex
Processing occurs at - ANSReceptor level; circuit level; perceptual level
Proprioceptors - ANSRespond to stretch in skeletal muscles, tendons, joints, ligaments
and connective tissues of coverings of bones and muscles; inform brain of movement
and position
Receptors respond to - ANSSpecific stimuli
Referred pain - ANSVisceral pain afferents travel along the same pathway as somatic
pain fibers; pain stimuli arising in the viscera are perceived as somatic in origin
Regeneration of nerve fibers - ANSMature neurons are generally amitotic; if soma is
damaged axon regenerates; macrophages remove dead axon/debris; schwann cells
form regeneration tube; axons grow through regeneration tube; does NOT occur in CNS
Sensation - ANSAwareness of changes in environment
Sensation and perception - ANSAwareness of stimuli and intrepretation; occurs in the
brain
Sensation to perception - ANSSurvival depends on it
Sensory input - ANSRelayed toward brain and is processed along the way
Sensory receptors - ANSSpecialized to respond to changes in environment

Simple receptors - ANSTacticle sensations, temperature, pain, unencapsulated or
encapsulated dentritic endings
Spatial discrimination - ANSIdentifying the site of the stimulus depends on the location
of sensory cortex stimulated
Spinal nerves - ANS31 pairs: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
Structure of nerve - ANSBundle of axons enclosed by connective tissue; endoneurium,
perineurium, and epineurium
Thermoreceptors - ANSSensative to changes in temperature
Tonic receptors - ANSVery little or no adaptation
Transduction - ANSStimulus energy is converted into action potentials and sent along
sensory neuron
Trigeminal - ANSLargest cranial nerve; extends from pons to face through three skull
holes: ophthalmic, maxillary, and mandibular; sensory impulses from face and head,
motor to muscles of mastication
Trochlear - ANSFibers extend through superior orbital fissures to innervate superior
oblique muscle; motor nerve for inferior-lateral eye movement
Unencapsulated Dendritic endings - ANSThermoreceptors, light touch receptors,
nociceptors
Vagus - ANSExtends beyond head and neck; extend from medulla through jugular
foramen; parasympathetic nerves regulate activities of heart, lungs, liver, stomach, etc

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