3.14 Anatomy Chapter 14

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3.14 Anatomy Chapter 14
2010-10-19 04:45:31
Peripheral Nervous System

Cranial and Spinal Nerves
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  1. The Peripheral Nervous System
    The PNS

    • the nervous system outside the brain and spinal cord

    • Provides vital links to the body and outside world

    • Nerves allow the CNS to receive information and initiate action

    Structures of the PNS: sensory receptors, nerves and ganglia, and motor endings
  2. Cranial Nerves
    "Obviously, Once One Takes The Anatomy Final, Very Good Vodka Alleviates Heartache"

    • •Attach to the brain and
    • pass through foramina of the skull

    •Numbered from I–XII

    • •Cranial nerves I and II
    • attach to the forebrain

    •All others attach to the brain stem

    • •Primarily serve head and
    • neck structures

    • •The vagus nerve (X) is the only cranial
    • nerve that extends into the abdomen
  3. Cranial Nerve I
    Olfactory Nerves: sensory nerves of smell

    • - Nerves arise from receptors in the nasal cavity and pass through the cribiform plate of the ethmoid bone to the olfactory bulb
  4. Cranial Nerve II
    • Optic Nerves
    • - Sensory Nerves of Vision
    • - Fibers arise from retina via optic nerve that passes through the optic canal of orbit, cross at the optic chiasma, synapse at the thalamus, and relayed to the occipital cortex
  5. Cranial Nerve III
    • Occulomotor Nerves
    • - Innervates four of the extrinsic eye muscles: inferior oblique, superior, inferior, and medial rectus
    • - also innervates the levator palpebrae superioris muscle that lifts the eyelid
    • - Fibers extend from ventral midbrain (near pons junction) and pass through the superior orbital fissure to the eye
  6. Cranial Nervel IV
    • Trochlear Nerve
    • - Innervates the superior oblique muscle (an extrinsic eye muscles)
    • - Fibers emerge from the dorsal midbrain and goes through the superior orbital fissure along with the oculomotor nerves to serve the eye
  7. Cranial Nerve V
    • Trigeminal Nerve
    • - Largest of the cranial nerves; Both sensory and motor (mixed nerve)

    • Has three divisions: Ophthalmic division (V1), Maxillary division (V2), Mandibular division (V3)

    • Cell bodies of sensory neurons located in the trigeminal ganglion

    • Mandibular division contains motor fibers that innervate the chewing muscles
  8. Cranial Nerve VI
    • Abducens Nerve
    • - Primarily Motor
    • - Abducts the eyeball; innervates the lateral rectus muscle
    • - Fibers come from inferior pons through the superior orbital fissure to the eye
  9. Cranial Nerve VII
    • Facial Nerves
    • •Innervates muscles of facial expression; Both sensory and motor
    • - Fibers come from pons, go through the internal acoustic meatus and nerve passes through the stylomastoid foramen to innervate the face
    • - Five major branches of motor nerves to the face: temporal, zygomatic, buccal, mandibular, cervical
    • - signals lacrimal gland, nasal and palatine glands, and submandibular and sublingual salivary glands
    • - transmits sensory information from taste buds of front 2/3rds of tongue
    • **Bell's Palsy = paralysis of facial muscles/ partial loss of taste; caused by viral infection leading to inflammation and swelling of facial nerve
  10. Cranial Nerve VIII
    • Vestibulocochlear Nerves
    • Sensory nerve of hearing and balance
    • - Fibers arise from vestibule within the inner ear and pass through the internal acoustic meatus to enter the brain stem at the pons/medulla border
    • - hearing receptors in cochlear make up cochlear division; equilibrium receptors in semicircular canals and vestibule make up vestibular division
    • **Nerve damage leads to deafness or dizziness, loss of balance, nausea
  11. Cranial Nerve IX
    • Glossopharyngeal Nerve
    • Both sensory and motor nerve that Innervates structures of the tongue and pharynx
    • - Fibers come from medulla and leave the skull through the jugular foramen to run to the throat
    • **damage leads to impairment of swallowing and taste on posterior 1/3 of the tongue
  12. Cranial Nerve X
    • Vagus Nerve
    • Both sensory and motor nerve

    • - the only cranial nerve that “wanders” into thorax and abdomen
    • - Parasympathetic innervation of organs
    • - fibers emerge from medulla, pass through the jugular foramen and descend through the neck
    • **damage leads to hoarseness/loss of voice; total destruction of nerve is fatal
  13. Cranial Nerve XI
    • Accessory Nerves

    • Unique among cranial nerves

    • Accessory nerves are formed from ventral rootlets of the spinal cord

    • Do not arise from the brainstem

    • - Motor nerve that supplies the trapezius and sternocleidomastoid to move the head and neck
    • - arise from the cervical region of the spinal cord and enter the skill via the foramen magnum and exit through the jugular foramen
    • **damage to nerve causes head to turn towards injury, shrugging shoulders becomes difficult
  14. Cranial Nerve XII
    • Hypoglossal Nerve
    • Motor nerve that runs inferior to the tongue; innervates tongue muscles
    • - allows manipulation of tongue aiding in food chewing as well as swallowing and talking

    • **damage to nerve leads to difficulty in swallowing and speech.

  15. Spinal Nerves
    • 31 pairs—contain thousands of nerve fibers

    • Connect to the spinal cord

    • • Named for point of issue from the spinal cord:
    • • 8 pairs of cervical nerves (C1–C8)

    • 12 pairs of thoracic nerves (T1–T12)

    • 5 pairs of lumbar nerves (L1–L5)

    • 5 pairs of sacral nerves (S1–S5)

    • 1 pair of coccygeal nerves (Co1)
  16. Spinal Nerves
    Functional Components
    • Dorsal root and Ventral root extend from the spinal cord (via rootlets)
    • - Dorsal root contains axons whose cell bodies lie in the dorsal root ganglion
    • - Ventral root cell bodies lie within the gray column of the spinal cord
    • *Spinal nerve lies at the junction of dorsal and ventral root
    • - dorsal root ganglion and spinal nerve lie within intervertebral foramen

    Each spinal nerve branches laterally into a dorsal ramus and a ventral ramus, which contain both sensory and motor fibers
  17. Innervation of the Back
    • Posterior part of the trunk and neck
    • - innervated by the dorsal rami
    • - follows a near, segmented pattern that branches to innervate a horizontal strip of muscle and skin in line with its emergence point from the vertebral column
  18. Innervation of Anterior Thoracic and Abdominal Wall
    • Ventral rami arranged in a simple, segmented pattern only in the thorax.
    • - thoracic ventral rami run anteriorly, one deep to each rib as the intercostal nerves
    • - supply the intercostal muscles, skin of the thorax, and most of the abdominal wall below the rib cage.
  19. Introduction to Nerve Plexuses
    • Nerve plexus: a network of nerves
    • - Ventral rami of all spinal nerves (except T2–T12) form nerve plexuses

    • - occur in the cervical, brachial, lumbar, and sacral regions and primarily serve the limbs

    • •Fibers from ventral rami crisscross and redistribute so:
    • 1. each branch of the plexus receives fibers from several spinal nerves
    • 2. fibers from each ramus travel to body parts via several routes
    • - each muscle receives its nerve supply from more than one spinal nerve
    • **so destruction of one spinal nerve cannot paralyze any single limb
  20. Cervical Plexus
    Most branches are cutaneous nerves, carrying sensory impulses from the skin of the neck, back of the head, and superior part of the shoulder

    • Phrenic Nerve: receives fibers from C3, C4, and C5; innervates the diaphragm
    • *hiccups result from reflex response of phrenic nerve to irritation of diaphragm or stomach
  21. The Brachial Plexus and Innervation of the Upper Limbs
    • From Lateral and Medial Cords:
    • 1. musculocutaneous nerve: innervates the biceps brachii and the brachialis; enables skin sensation on the lateral forearm
    • 2. median nerve: innervates anterior forearm muscles and lateral palm (including thumb)
    • *damage leads to "hand of benediction"
    • 3. ulnar nerve: innervates intrinsic hand muscles and skin of the medial hand
    • ** damage leads to "claw hand" (or tingly sensation in pinky after hitting the "funny bone"

    • From Posterior Cord:
    • 1. axillary nerve: innervates the deltoid and teres minor muscles
    • 2. radial nerve: largest branch of the brachial plexus; innervates the posterior side of the upper limb (triceps brachii)
    • **damage leads to "wrist drop"
  22. The Lumbar Plexus and Innervation of the Lower Limb
    • Arises from first four lumbar spinal nerves (L1-L4)
    • - Smaller branches innervate the posterior abdominal wall and psoas muscle
    • - Main branches innervate the anterior thigh
    • 1. femoral muscle: innervates anterior thigh muscles (incl. quadriceps femoris)
    • 2. obdurator nerve: passes through obdurator foramen; innervates adductor muscles
  23. The Sacral Plexus and Innervation of the Lower Limb
    • Arises from spinal nerves L4 to S4
    • - Half innervate the buttock and lower limb, rest innervates pelvis and perineum
    • sciatic nerve: largest nerve of sacral plexus; actually two nerves:
    • 1. tibial nerve - innervates most of posterior leg
    • 2. common fibular nerve - innervates muscles of the anterolateral leg