PNS / spinal nerves Flashcards
PNS
12 pairs cranial 31 pairs spinal - 8 C1-C8 - 12 T1-T12 - 5 L1-L5 - 5 S1-S5 - 1 coccygeal
Spinal nerves
- lumbar, sacral, and coccygeal nerve roots descend from their point of origin at the lower end of spinal cord (level of L1)
Cauda equina
Describes the appearance of the lower end of the spinal cord and its spinal nerves as ia horse’s tail
Structure of spinal nerves
- . Each spinal nerve attaches to the spinal cord by a ventral root and a dorsal root
- the dorsal root is easily recognizable by the dorsal root ganglion
- the dorsal root includes sensory fibers that carry information from receptors in peripheral nerves
- the ventral root includes motor neurons that carry information from the CNS and toward effectors (muscles and glands)
- all spinal nerves contain both motor and sensory fibers (mixed nerves)
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Ramus
One of several large branches formed after each spinal nerve emerges from the spinal cavity
- each spinal nerve splits into a distinct ventral ramus and dorsal ramus
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Dorsal ramus
Supplies somatic motor and sensory fibers to several smaller nerves
- these smaller nerves innervate the muscles and skin of the posterior surface f the head, neck, and trunk
- the structure for the ventral ramus is more complex than that of the dorsal ramus
Ventral ramus
Motor (autonomic and somatic) and sensory fibers innervate muscles and glands in the extremities and in the lateral and ventral portions of the neck and trunk
- autonomic motor fibers split from the ventral ramus and head toward a ganglion of the sympathetic chain
Nerve plexus facts
- plexuses are complex networks formed by the ventral rami of most spinal nerves (not T2-T12) subdividing and then joining together to form individual nerves
- each Indy nerve that emerges contains all the fibers that innervate a particular region of the body
- in plexuses, spinal nerve fibers are rearranged according to their ultimate destination, reducing the number of nerves needed to supply each body part
- correspond to spinal cord areas of enlargement
Cervical plexus
- deep within the neck
- ventral rami of C1-C4 (and a branch of C5 ventral ramus)
- innervates: muscles and skin of neck, upper shoulders, chest, and part of head
- phrenic nerve exits cervical plexus and innervates the diaphragm (ventral rami C3, C4, and C5)
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Brachial plexus
- deep in shoulder
- ventral rami of C5-T1
- nerves from the brachial plexus innervate lower part of the shoulder and entire arm
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Lumbar plexus
- deep to psoas muscle
- fibers of ventral rami L1-L4
- femoral nerve exits the lumbar plexus and divides into branches, supplying the thigh and leg
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Sacral and coccygeal plexus
- in peeve cavity, typically anterior to piriformis mm
- intermingling fibers from L4-S4
- tibial and common peroneal/fibular nerves
- sciatic nerve exits the sacral plexus and supplies nearly all the skin of the leg, posterior thigh muscles, leg and foot mm
- often combined with the lumbar plexus and referred to as the lumbosacral plexus
Dermatomes and myotomes
Close relationship between the spinal origin of each spinal nerve and the region of the body it innervates
- clinical application: enables a health professional to identify the site of spinal cord or nerve abnormality from symptoms in an area of the body
Dermatomes
A region of the skin surface area supplied by afferent (sensory) fibers of a given spinal nerve
- skin section
- there is some overlap between adjacent dermatomes
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Myotome
Skeletal muscle innervates by 1+ efferent (motor) fibers of a given spinal nerve
- some skeletal muscle organs may be innervates by motor axon from more than 1 spinal nerve
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Cranial nerves
- 12 pairs connect to the undersurface of the brain (primarily the brain stem)
- both names and numbers used to identify
- their names suggest their distribution (to or from)
- their numerous indicate the Oder in which they connect to the brain from anterior to posterior
Mixed cranial nerves
Axons of sensory and motor neurons
Sensory cranial nerves
Axons of sensory neurons only
Motor cranial nerves
Mainly axons of motor neurons and a small number of sensory fibers (proprioceptors)
Olfactory nerve (I)
Composed of axons and neurons that lie in the nasal mucosa
- high up along the septum and conchae
- carries info about the sense of smell
- functional classification: sensory
Optic nerve (II)
Composed of axons form the innermost layer of sensory neurons of the retina
- carries visual information from the eyes to the brain
- functional classification: sensory
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Oculomotor nerve (III)
Fibers originate from cells in the oculomotor nucleus (ventral midbrain) and extend to some of the external eye mm (not superior oblique or lateral rectus)
- Superior branch innervates extrinsic eyeball mm that control movements of eyeball and upper eyelid
- Inferior branch supplies parasympathetic motor axons to intrinsic eyeball mm (smooth mm) that adjust the lens for near vision and contract the iris when bright light stimulates the eye
- Proprioceptors in the eye mm
- functional classification: motor
Trochlear nerve (IV)
Fibers originate in cells of the midbrain and extend to the superior oblique muscles (extrinsic mm) of the eye
- also contains afferent fibers from proprioceptors in the superior oblique mm of the eye
- responsible for eye movements (motor) and proprioceptors (sensory)
- functional classification: motor
Trigémino nerve (V)
- Ophthalmic nerve
- Maxillary nerve
- Mandíbular nerve
- sensory neurons carry afferent impulses from skin and mucosa of head and teeth to cell bodies in the trigéminal ganglion
- motor fibers extend to the mm of mastication through the mandibular nerve (chewing)
- functional classification: mixed/both
Abducen nerve (VI)
Fibers originate from a nucleus in the pons on the floor of the fourth ventricle and extend to the lateral rectus mm of the eye (abd of eye)
- contains some afferent fibers form proprioceptors in the lateral rectus mm
- functional classification: motor
Facial nerve (VII)
Fibers originate from a nucleus in the lower part of the pons and extend to superficial mm of the face and scalp: facial expression
- efferent fibers extend to submaxillary and sublingual salivary glands
- contains sensory fibers from taste buds of the anterior 2/3 of tongue
- functional classification: mixed/both
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Vestibulocochlear nerve (VIII)
- Vestibular nerve
- Cochlear nerve
- Damage to the cochlear nerve can cause deafness
- sometimes called the auditory or acoustic nerve
- functional classification: sensory
Vestibular nerve
Fibers originate in the semicircular canals in the inner ear and transmit impulses that results in sensation of equilibrium
Cochlear nerve
Fibers originate in the organ of corti in the cochlea of the inner ear and transmit impulses that result in sensations of hearing
Glossopharyngeal nerve (IX)
- composed of both sensory and motor neurons
- supplies fibers to the tongue, pharynx, and carotid sinus
- responsible for sensations of the tongue, swallowing, movements and secretion of saliva
- functional classificaiton: mixed/both
Vagus nerve (X)
- composed of sensory and motor fibers with many widely distributed branches
- vagus means “vagrant or wandering” distributed from the head and neck into the thorax and abdomen
- sensory fibers supply pharynx, larynx, trachea, heart, carotid body, lungs, bronchi, esophagus, stomach, small intestine, and gallbladder
- somatic motor fibers innervate the pharynx and larynx and are mostly autonomic fibers: peristalsis
- functional classification: mixed
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Accessory nerve (XI)
Conveys motor impulses to the sternocleidomastoid and trapezius mm to coordinate head movements
- sensory axons in the accessory nerve originate from proprioceptors in the SCM and trap, shoulder movements, turning movements of head
- functional classification: motor
Hypoglossal nerve (XII)
- fibers innervate the mm of the tongue (speech and swallowing)
- fibers from proprioceptors in mm of the tongue
- “under the tongue”
- functional classificaiton: motor
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