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APHY 101 Exam 5c
Ch. 13 Peripheral Nervous System
| Question | Answer |
|---|---|
| what is a nerve? | cordlike organ of the PNS consisting of peripheral axons enclosed by connective tissue |
| what connective tissues cover a nerve? | endoneurium (closest to axon), perineurium, epineurium (farthest from nerve) Fig. 13.26b |
| what is endoneurium? | loose connective tissue that surrounds axons |
| what is perineurium? | coarse connective tissue that bundles fibers into fascicles |
| what is epineurium? | tough fibrous sheath around a nerve |
| what is the most common type of nerve? | mixed (sensory and motor) |
| how are nerves classified? | sensory and motor divisions where sensory, afferent nerves ARRIVE to the CNS and motor, efferent nerves EXIT the CNS; mixed nerves do both |
| what impulses do mixed nerves carry? | somatic and autonomic (visceral) impulses |
| what are the 4 types of mixed nerves? | somatic afferent (sensory), somatic efferent, visceral afferent (stomachache), and visceral efferent |
| from where do peripheral nerves originate? | from the brain or spinal column |
| does the regeneration of nerve fibers happen in the CNS or PNS? | PNS only - if the soma of a damaged nerve remains intact, damage in the PNS can be repaired |
| why is damage to nerve tissue serious? | because mature neurons are amitotic (don't divide) |
| why can't damage be repaired in the CNS? | because the CNS has no neurilemma or regeneration tube for repair |
| what 3 kinds of cells/parts coordinate activity to regenerate nervous tissue in the PNS, and what do they do? | macrophages remove debris, Schwann cells have neurilemma that form regeneration tube and secrete growth factors, and axons regenerate the damaged part Fig. 13.27 |
| how can neurilemma be compared to a toothpaste tube? | if the toothpaste tube is the neurilemma, the thin "tail" of the tube that doesn't have toothpaste in it anymore is the myelin wrapping around |
| how many pairs of cranial nerves arise from the brain? | 12, they have sensory, motor or both functions |
| what is the mnemonic for the 12 names of the cranial nerves? | Only One Of The Two Athletes Felt Very Good, Victorious, And Healthy |
| what are the names of the 12 cranial nerves? | olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, hypoglossal |
| which 4 cranial nerves carry parasympathetic fibers that serve muscles and glands? | 3, 7, 9 and 10 see Fig. 13.28a |
| (starred info) what is the mnemonic for the 12 cranial nerves' being sensory, motor, or both? | Some Say Marry Money But My Brother Says/Boasts Big Brains Matter Most (Fig. 13.28b) |
| what does cranial nerve 1 do? | sensory. olfactory. carries afferent impulses for the sense of smell (olfaction) |
| why is "uncus stunkus" a good mnemonic for cranial nerve 1? | the olfactory tract carries smell information directly to the primary olfactory cortex, which is located in the UNCUS of the temporal lobe |
| what does cranial nerve 2 do? | sensory. optic. carries afferent impulses for vision. amazingly, vision is processed in the occipital lobe even though eyes are in front of head. |
| what does cranial nerve 3 do? | motor. oculomotor. part of the 3, 7, 9, 10 parasympathetic group. raises the eyelid, directs the eyeball, constricts the iris, and controlls lens shape. 4 of 6 eye muscles. |
| note to not get trigeminal nerve and facial nerves mixed up | the trigeminal nerve is primarily sensory for face (touch, pain, temperature) and chewing muscles [muscles of mastication], while the facial nerve controls muscles of facial expression and taste. both of them have sensory and motor functions |
| what does cranial nerve 4 do? | motor. trochlear. directs the eyeball; named for the loop of connective tissue above the eyeball called the trochlea (Table 13.2 figure IV) |
| what does cranial nerve 5 do? | both (mixed). trigeminal. conveys sensory impulses from various areas of the face V1-3, and supplies motor fibers for mastication V3 |
| what is trigeminal neuralgia? | a chronic, neuropathic pain condition affecting the fifth cranial nerve, characterized by sudden, severe, electric shock-like facial pain, usually on one side. Known as *tic douloureux* |
| what does cranial nerve 6 do? | motor. abducens. primarily a motor nerve innervating the lateral rectus muscle - turns eye outward (abducts eye) |
| what does cranial nerve 7 do? | both (mixed). facial. part of the 3, 7, 9, 10 parasympathetic group. facial expression (nostril flare), and the transmittal of autonomic impulses to lacrimal & salivary glands. sensory: taste from anterior 2/3rds of the tongue |
| what causes Bell's palsy? | motor dysfunction at the 7th cranial nerve (facial paralysis on one side) |
| what is another name for the mandibular branch of the facial nerve (nerve 7)? | mental branch (at chin) |
| what does cranial nerve 8 do? | sensory. vestibulocochlear. two divisions of fibers - cochlear (hearing) and vestibular (balance) - functions are solely sensory for equilibrium and hearing |
| what does cranial nerve 9 do? | both (mixed). glossopharyngeal. part of 3, 7, 9, 10 parasympathetic group. motor: part of tongue & pharynx, and fibers to the parotid salivary gland; swallowing. sensory: taste for posterior 1/3 tongue, general sensory impulses for tongue, pharynx |
| which cranial nerve is the only one that extends beyond the head and neck? | |
| what does cranial nerve 10 do? | both (mixed). most motor fibers are parasympathetic fibers to the heart, lungs, and visceral organs; its sensory function is minor taste in the throat |
| if you take the parasympathetic group (3, 7, 9, 10) and exclude cranial nerve 3, what function is related to the rest? | taste |
| what does cranial nerve 11 do? | motor. accessory. supplies fibers to the larynx, pharynx, and soft palate; innervates the trapezius and sternocleidomastoid(!), which move the head and neck |
| what does cranial nerve 12 do? | motor. hypoglossal. innervates both extrinsic and intrinsic muscles of the tongue, which contribute to swallowing and speech |
| which cranial nerves innervate the tongue? | 12, 5, 7, 9 (recognize on multiple choice) |
| what are the abbreviated functions for the 12 cranial nerves? | 1. smell 2. vision 3. eye mvt, iris constrict 4. eye mvt 5. upper face sensation 6. eyeball movement 7. facial movement, taste 8. hearing, equilibrium 9. swallowing, taste 10. parasympathetic to viscera 11. head/neck/shoulder movement 12. tongue movements |
| which cranial nerves are responsible for eyeball movement? | 3, 4, 6 |
| how many pairs of mixed nerves arise from the spinal cord to supply all parts of the body besides the head? | 31 pairs, including 8 cervical (remember 7 cervical vertebrae), 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal |
| what are the 4 plexuses you need to know for spinal nerves? | cervical, thoracic, lumbar, sacral |
| what to know about spinal nerve roots? | each spinal nerve connects to the spinal cord via 2 medial roots and each root forms a series of rootlets that attach to the spinal cord |
| what is the placement of roots on the spinal cord? | ventral roots arise from the anterior horn and contain motor (efferent) fibers; dorsal roots arise from sensory neurons in the dorsal root ganglion and contain sensory (afferent) fibers |
| in summary, spinal nerve roots placements where? | sensory @ back, motor @ front of vertebrae (Fig. 13.30a) |
| what is a ramus/rami? | a branch off the spinal nerve |
| what is the anatomy of the spinal nerves' rami? | the short spinal nerves branch into 3 or 4 mixed, distal rami: small dorsal ramus, larger ventral ramus, tiny meningeal branch, and rami communicantes at the base of the ventral rami in the thoracic region |
| nerve plexuses are formed by what? | all ventral rami except nerves T2-12 form interlacing nerve networks called plexuses, which are found in the cervical, brachial, lumbar, and sacral regions |
| why is it significant that each resulting branch of a plexus contains fibers from several spinal nerves? | if one is damaged, the other fibers still work (Fig. 13.35 dermatomes) |
| how do nerve plexuses work anatomically? | fibers travel to the periphery via several different routes, each muscle receives a nerve supply from more than one spinal nerve, so damage to one spinal segment cannot completely paralyze a muscle |
| how is the back innervated? | dorsal rami via several branches |
| how is the thorax innervated? | ventral rami T1-12 work as intercostal nerves, and intercostal nerves also supply muscles of the ribs, anterolateral thorax, and abdominal wall |
| what forms the cervical plexus? | ventral rami of nerves C1-4, with most branches being cutaneous nerves of the neck, ear, back of head, and shoulders |
| what is the most important nerve of the cervical plexus? | THE PHRENIC NERVE, the major motor and sensory nerve of the diaphragm --> hiccups (and see Fig. 13.31) |
| how is the brachial plexus formed? | nerves C5-C8 and T1 (C4 and T2 may also contribute to this plexus), gives rise to the nerves that innervate the upper limb |
| which is the most involved of all plexuses? | brachial plexus (!) |
| what are the 4 major branches of the brachial plexus? | roots (5 ventral rami C5-T1), trunks (upper, middle, and lower, which form divisions), divisions (anterior and posterior serve the front and back of the limb), cords (lateral, medial, and posterior fiber bundles) (Fig. 13.32a) |
| what are the nerves of the brachial plexus? | axillary, musculocutaneous, median, ulnar, and radial |
| what does the brachial plexus' axillary nerve innervate? | axillary means armpit; innverates the deltoid and teres minor |
| what does the brachial plexus' musculocutaneous nerve innervate? | sends fibers to the biceps brachii and brachialis |
| what does the brachial plexus' median nerve innervate? | branches to most of the flexor muscles of forearm |
| what does the brachial plexus' ulnar nerve innervate? | supplies the flexor carpi ulnaris and part of the flexor digitorum profundus |
| what does the brachial plexus' radial nerve innverate? | innvervates essentially all extensor muscles (Fig. 13.32c) |
| how is the lumbar plexus formed? | arises from L1-4 and innervates the thigh, abdominal wall, and psoas muscle |
| what are the major nerves of the lumbar plexus? | the major nerves are the femoral and the obturator (Fig. 13.33) |
| how is the sacral plexus formed? | arises from L4-S4 and serves the buttock, lower limb, pelvic structures, and the perineum |
| what is the major nerve of the sacral plexus? | the major nerve of the sacral plexus is the sciatic nerve, the longest and thickest nerve of the body |
| what 2 nerves comprise the sciatic nerve? | the tibial and the common peroneal (fibular) nerves |
| what is the area of skin called that's innervated by the cutaneous branches of a single spinal nerve? | dermatome - all spinal nerves except C1 participate in dermatomes |
| what is a reflex? | a rapid, predictable motor response to a stimulus |
| what characteristics do a reflex have? | they may be inborn (intrinsic) or learned (acquired), may involve only peripheral nerves and the spinal cord, and involve higher brain centers as well |
| what are the 5 components of a reflex arc? | receptor, sensory neuron, integration center, motor neuron, and effector |
| what does the sensory neuron do in a reflex arc? | transmits the afferent impulse to the CNS |
| true or false, the integration center of a reflex arc may be either monosynaptic or polysynaptic within the CNS | true |
| what is the difference between the motor neuron and the effector in a reflex arc? | the motor neuron is what conducts efferent impulses from the integration center to an effector, while the effector is another name for the muscle fiber or gland that responds to the efferent impulse |
| what two conditions must be in place for skeletal muscles to perform normally? | the golgi tendon organs (proprioceptors) must constantly inform the brain to the state of the muscle, and stretch reflexes initiated by muscle spindles must maintain healthy muscle tone |
| what are muscle spindles? | they are encapsulated, stretch-sensitive mechanoreceptors located within the belly of skeletal muscles that detect changes in muscle length and the speed of stretch |
| what is the anatomy of a muscle spindle? | 3-10 intrafusal muscle fibers that lack myofilaments in their central regions, are noncontractile, and serve as receptive surfaces (Fig. 13.37) |
| what 2 types of AFFERENT endings wrap muscle spindles? | Ia annulospiral fibers (primarily), and type II flower-spray fibers, innervated by gamma efferent fibers, as opposed to contractile muscle fibers that are extrafusal and innervated by alpha efferent fibers |
| what happens to the muscle spindle when muscles stretch? | it activates the muscle spindle, and there is an increased rate of action potential in Ia fibers (Fig. 13.39) |
| what happens to the muscle spindle when muscles contract? | it reduces tension in the muscle spindle and there is a decreased rate of action potential on Ia fibers |
| true or false, afferent impulses from the spindle result in inhibition of the antagonist | true |
| how does the patellar reflex work? | tapping it stretches the quads and starts the reflex action; the quads contract and the antagonistic hamstrings relax |
| what is the opposite of the stretch reflex? | the Golgi tendon reflex |
| how does the Golgi tendon reflex work? | contracting the muscle activates the Golgi tendon organs, and afferent Golgi tendon neurons are stimulated. neurons inhibit the contracting muscle, and the antagonistic muscle is activated, contracting while the initial contracting muscle relaxes |
| what is the importance of the Golgi tendon reflex? | it prevents a strongly contracting muscle from pulling a tendon out of bone (aka avulsion fracture) |
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