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Ch. 14 (15)

The Nervous System III: The Peripheral Nervous System (PNS)

PNS consists of the nervous system structures outside the brain and spinal cord
the nerves thread through almost every part of the body
nerves cord-like organs in the PNS consisting of many axons arranged in parallel bundles which are enclosed by successive wrappings of CT
epineurium external tough fibrous CT sheath surrounding a whole nerve, which consists of several fascicles and blood vessels
fascicles bundles of neuronal axons
perineurium CT surrounding each fascicle
the perineurium forms the nerve-blood barrier
endoneurium delicate CT fibers that surround the individual axons of fascicles
most nerves are mixed, carrying both sensory and motor axons
the CNS is connected to the PNS via cranial and spinal nerves
the PNS is further subdivided into two divisions sensory and motor divisions
the sensory (afferent) division contains somatic and visceral sensory areas
the motor (efferent) division contains somatic, branchial, and visceral motor areas
the visceral motor areas comprise the autonomic nervous system (ANS) and the brachial motor division
the ANS is further categorized into two functional divisions that serve most of the same organ but generally cause opposing or antagonistic effects
the divisions of the ANS are parasympathetic and sympathetic
parasympathetic rest and digest
sympathetic fight or flight division
basic structural components of the PNS sensory receptors, motor endings, nerves, ganglia
peripheral sensory receptors pick up stimuli from inside and outside the body then initiate impulses in sensory axons
the two main categories of peripheral sensory receptors dendritic endings of sensory neurons and complete receptor cells
complete receptor cells = specialized epithelial cells or small neurons that transfer special senses info
receptors may be classified by the location of their stimuli, they type of stimuli detected and their structure
peripheral motor endings axon terminals of motor neurons that innervate effectors
effectors are muscles and glands
innervation of skeletal muscles - neuromuscular junctions are also known as motor end plates and are one junction associated with each muscle fiber
ACh is the neurotransmitter that diffuses across the synaptic cleft and binds to receptors on the sarcolemma
ACh induces impulses which signal the muscle cell to contract
motor unit a motor neuron innervating muscle fibers
innervation of visceral muscle and glands - simpler arrangement near the smooth muscle or gland cells that are innervated, a motor axon swells into a row of VARICOSITIES(knobs) which contain synaptic vesicles filled with neurotransmitters
peripheral nerves and ganglia cranial nerves and spinal nerves
ganglion cluster of peripheral cell bodies
dorsal root ganglion PNS ganglion containing the cell bodies of sensory neurons
spinal nerves 31 pairs of spinal nerves arise from and span the length of the spinal cord
31 pairs = 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
the first branch of each spinal nerve in the thoracic and upper lumbar regions become the...which contains...that continue to an white ramus ... myelinated PREganglionic axons...autonomic ganglion
two groups of...exit the dorsal root ganglion which are.... unmyelinated fibers...gray ramus and the autonomic nerve
gray ramus carries axons that innervate glands and smooth muscles in the body wall or limbs back to the spinal nerve
autonomic nerve carries fibers (axons) to internal organs
rami communicates the white and gray rami, which collectively carry visceral motor fibers to and from a nearby autonomic ganglion associated with the sympathetic division of the ANS
T1-L2's spinal nerves have four branches white ramus, gray ramus, dorsal ramus, ventral ramus
each spinal nerve connects to the spinal cord via a dorsal root and a ventral root
a dorsal root contains sensory fibers arising from cell bodies in a dorsal root ganglion
a ventral root contains motor fibers arising from cell bodies in the anterior horn of the spinal cord
together these sensory and motor fibers converge and exit the vertebral column as spinal nerves, which branch out as the dorsal ramus and the ventral ramus
dorsal ramus supplies dorsum of the neck and trunk and specific segment of the skin
ventral ramus supplies anterior and lateral regions of neck and trunk and all regions of the limbs
together the dorsal and ventral rami supply somatic regions from the neck inferiorly
each pair of spinal nerves monitors a specific region of the body surface (dermatome)
dermatome an area of skin innervated by the cutaneous branches from a single spinal nerve
dermatomes are clinically important because damage to either a spinal nerve or DRG will produce a characteristic loss of sensation in specific areas of the skin
nerve plexuses are complex, interwoven networks of nerves formed by the ventral rami only
nerve plexus occurs as pairs in the cervical, brachial, lumbar, and sacral regions
nerve plexus primarily serves the limbs
cervical plexus neck, is buried deep in the neck, under the sternocleidomastoid muscle
the cervical plexus is formed by the ventral rami of C1-C4 and some fibers of C5
cutaneous nerves of the cervical plexus supply only the skin of neck, back of head and most superior region of shoulder
the phrenic nerves of cervical plexus supply the diaphragm
the brachial plexus upper extremity/limb
brachial plexus lies partly in the neck and in the axilla
brachial plexus formed by the ventral rami of C5-T1
brachial plexus innervates the pectoral girdle and upper extremity
the bracial plexus is composed of five consecutive groups of stems and branches, including the nerves they form
the roots of the ventral rami of C5-T1 converge to form the trunks
trunks (superior, middle, inferior) -each of which divides into an anterior division and posterior division
division - each division then converge to form cords
cords lateral, medial, posterior
lateral cord is formed from the anterior division on the superior and middle trunks
medial cord is formed by a continuation of the anterior division of the inferior trunk
posterior cord is formed by the union of all three posterior divisions of the superior, middle, and inferior trunks
nerves arise from one or more trunks or cords whose names indicate their positions relative to the axillary artery which supplies the upper limb
the median nerve is formed by the lateral and medial cords
musculocutaneous nerve is formed exclusively by the lateral cord
ulnar nerve is formed by the medial cord
axillary nerve is formed by the posterior cord
radial nerve is formed by the posterior cord
lumbar plexus lower extremity/limb
lumbar plexus lies within the psoas major muscle in the posterior abdominal wall
lumbar plexus is formed by the ventral T12-L4
the lumbar plexus innervates the anterior thigh
femoral nerves innervate anterior thigh muscles, including quadriceps femoris
obturator nerves innervate adductor muscle group and some skin on superomedial thigh
sacral plexus lower extremity/limb
sacral plexus lies immediately caudal to the lumbar plexus
sacral plexus is formed by the ventral rami of L4-S4
the sacral plexus innervates the butt, lower limb, pelvis, and perineum
sciatic nerve is the thickest and longest nerve in the body
sciative nerve innervates all of the lower limb except anterior and medial thigh regions
the sciatic nerve is composed of two nerves wrapped in a common sheath
tibial nerve innervates almost all muscles in posterior lower limb
common fibular nerve innervates anterolateral aspect of lower limb
superior/inferior gluteal nerves innervate gluteal muscles
pudendal nerve innervates muscles and skin of perineum
cranial nerves attach to the brain and pass through various openings or foramina in the skull
CN I - XII rostral to caudal
CN I attaches to the forebrain
CN II-XII attach to the brain stem
CNs serve only head and neck structures, except for CNX which extends into the abdomen
CNs contain sensory and motor fibers that innervate the head
cell bodies of sensory neurons lie either in receptor organs or within cranial sensory ganglia which lie along CN V, VII-X just external to the brain
cell bodies of motor neurons occur in CN nuclei in ventral gray matter of the brain stem
purely sensory nerves I, II, VIII
purely sensory nerves consist of special somatic sensory fibers for smell, vision, hearing and equilibrium
primarily or exclusively motor nerves III, IV, VI, XI, XII
primarily or exclusively motor nerves contain general somatic motor fibers to skeletal muscles of the eye and tongue
mixed nerves V, VII, IX, X
mixed nerves consist of (1) general somatic sensory fibers to the face
mixed nerves consist of (2) general visceral sensory fibers to the mouth, viscera and taste buds
mixed nerves consist of (3) branchial motor fibers to all pharyngeal arch muscles
CN I olfactory
CN II optic
CN III occulomotor nerves
CN IV trochlear nerves
CN V trigeminal nerves
CN VI abducens nerves (adducts eye)
CN VII facial nerves
CN VIII vestibulocochlear nerves
CN IX glossopharyngeal nerves
CN X vagus nerves
CN XI accessory nerves
CN XII hypoglossal
olfactory nerves carry afferent impulses for sense of smell
olfactory nerves arise from olfactory receptor cells located in the olfactory epithelia of the nasal cavity
olfactory nerves project as olfactory nerve filaments which pass through the cribriform plate of ethmoid bone
anosmia partial or total loss of smell caused by fractured ethmoid bone or lesions of olfactory fibers
optic nerves carry afferent impulses for vision
optic nerves have ...fibers that arise from each... contralateral and ipsilateral...retina to form the optic nerves
optic nerves pass through optic foramina of the orbits and converge to form the optic chiasma
optic nerves form the optic tracts that enter the thalamus and synapse onto the LGN of the thalamus
optic nerve fibers then project from thalamix nuclei as thalamic fibers to the occipital cortex
anopsias visual defects
damage to the CNII results in blindness in the eye served by the nerve
damage to the visual pathway, distal to the optic chiasma, results in partial visual loss
oculomotor nerves carry efferent fibers which pass through superior orbital fissure, from ventral midbrain to eye
oculomotor nerves innervate 4/6 extrinsic eye muscles that help direct the eye and raise the upper eyelid
autonomic nervous system efferents to constrictor muscles of the iris and to the ciliary muscle (lens shape for focusing)
proprioceptor afferents from the 4 extrinsic muscles to the midbrain
oculomotor nerve paralysis eye cannot be moved up or inward
at rest, they eye turns laterally, upper eyelid droops (ptosis), double vision and trouble focusing on close objects
trochlear nerves carry somatic efferents to and proprioceptor afferents from the superior oblique muscle
trochlear fibers emerge from the... dorsal midbrain and course ventrally around the midbrain to enter the orbits of the eyes via superior orbital fissures of the sphenoid, along with CNIII
CN IV trauma or paralysis double vision and reduced ability to rotate eye inferolaterally
trigeminal nerves carry afferents for touch, temp, and pain from the face
trigeminal nerves also carry branchial efferents for chewing muscles
ophthalmic division (VI) afferent fibers run from the face to the pons via supeior orbital fissure of the sphenoid
ophthalmic division innervates skin of anterior scalp, upper eyelid, and nose
ophthalmic division contains afferents from nasal cavity mucosa, cornea, and lacrimal gland
maxillary division (V2) afferent fibers run from the face to the pons via foramen rotundum of the sphenoid bone
maxillary division: afferents from nasal cavity mucosa, palate, upper teeth, skin of cheek, upper lip and lower eyelid
mandibular division V3 afferent fibers run from the face to pons and pass through the skull via foramen ovale of the sphenoid bone
mandibular division; afferents from anterior tongue, lower teeth, skin of chin and temporal region of scalp
mandibular division; efferents...and afferents... to...from muscles of mastication
tic doloureux (trigeminal neuralgia) unknown factors cause CN V inflammation, but may reflect pressure on CN V root
tic doloureux causes symptomatic tics, which involves excruciating, stabbing pain that occurs -100x/day
abducens nerves carry mainly efferent fibers to and some proprioceptor afferents from the lateral rectus muscle of the eye
abducens nerve fibers leave the inferior pons and enter the orbit of the eye via superior orbital fissure
CN VI paralysis eye cannot be moved laterally, at rest, affected eyeball turns medially
facial nerves carry mixed fibers which are the chief motor nerves of the face
facial fibers arise from the...enter... pons...temporal bone via internal acoustic meatus and run within temporal bone before emerging through stylomastoid foramen
facial fibers then course to lateral aspect of the face
5 major branches of the face temporal, zygomatic, buccal, mandibular, cervical and proprioceptor...from the... efferents...afferents...skeletal muscles of face for facial expression
ANS effeents to lacrimal, nasal, palatine, submandibular and sublingual glands
afferents from taste buds of anterior 2/3 of the tongue and from tiny patch of skin on ear
bell's palsy paralysis of facial muscles on affected side and parital loss of taste sensation
bell's palsy is caused by herpes simplex viral infection which causes inflammation and swelling of CN VIII
vestibulococlear nerve carries afferent impulses for hearing and equilibrium
cochlear division of vestibulocochlear nerves carry afferents from hearing receptors located within the inner ear of temporal bone, pass through internal acoustic meatus
cochlear division afferents enter brain stem at pons-medulla border
vestibular division (vestibulocochlear) carry afferents from equilibrium receptors
lesions of CN VII or cochlear receptors cause central or nerve deafness
damage to vestibular division causes diziness, rapid involuntary eye movements, loss of balance, nausea and vomiting
glossopharyngeal nerves carry mixed fibers which innervate part of the tongue and pharynx
glossopharyngeal nerve fibers emerge from medulla and leave skull via jugular foramen to run to throat
(glossopharyngeal) and properiocetpor...from the efferents...afferents...stylopharyngeus muscle which elevates the pharynx during swallowing
ANS efferents of glossopharyngeal to parotid gland
afferents of glossopharyngeal conduct taste and general sensory impulses from pharynx and posterior tongue
glossopharyngeal afferents from chemoreceptors in carotid bodies and pressure receptors of carotid sinus
glossopharyngeal afferents also innervate small area of skin on external ear
CN IX damage impairs swallowing and taste on posterior 1/3 of tongue
vagus nerves carry mixed fibers that serve the pharynx, larynx, heart, lungs, abdominal viscera
vagus nerves; this is the only CN to extend beyond the head and neck region
vagus nerve fibers emerge from medulla, pass through skull via jugular foramen, and descend through neck into thorax and abdomen
brnachial efferents of vagus to skeletal muscles of pharynx and larynx for swallowing
ANS efferents of vagus innervate heart, lungs, and abdominal viscera
vagus afferents from thoracic and abdominal viscera, carotid sinus, carotid and aortic bodies, taste buds of posterior tongue, mucosa of larynx and pharynx
vagus nerves also innervate tiny area of skin on external ear and some of membrane lining middle ear
proprioceptor afferents (vagus) from muscles of larynx and pharynx
CN X paralysis hoarseness or loss of voice, difficulty swallowing, impaired GI mobility
total destruction of both CN X is fatal because these ANS nerves are crucial in maintaining the normal state of visceral organ activity
accesory nerves contain cranial roots and spinal roots
cranial roots carry branchial efferents from lateral aspect of medulla to larynx, pharynx and soft palate
spinal roots carry branchial efferents from superior region of spinal cord to trapezius and sternocleidomastoid muscles
spinal root injury of one CN XI causes head to turn toward injury side due to sternocleidomastoid paralysis, shrugging of the shoulder on the injured side is difficult
hypoglossal nerves carry efferents to intrinsic and extrinsic muscles of tongue
hypoglossal nerve fibers arise by a series of roots from medulla, exit from the skull via hypoglossal canal to travel to the tongue
somatic efferents (hypoglossal nerves) to tongue muscles allow food mixing and manipulation by tongue during chewing
somatic efferents of hypoglossal also allow tongue movements that contribute to swallowing and speech
CN XII damage causes difficulties in speech and swallowing, tongue deviates toward affect sides, paralyzed side eventuaolly beings to atrophy
both CNII damaged = cannot protrude tongue
Created by: handrzej



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