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PNS consists of the nervous system structures
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Ch. 14 (15)
The Nervous System III: The Peripheral Nervous System (PNS)
| Question | Answer |
|---|---|
| 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 |
| branchial...to 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) branchial...to 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 |
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handrzej
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