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