Ch. 21 Peripheral Nervous System
simultaneously reciprocal inhibition (turning off) of the antagonist
(nature of a reflex) muscle spindle
the sensory organ in the muscle that sends the message to the spinal cord, triggering protective contraction of agonist (muscle you tapped)
(nature of a reflex) muscle spindle
action that results from a nerve impulse passing over a reflex arc: predictable response to a stimulus
(nature of a reflex) reflex
involve a single motor neuron whose axon stretches from the cell body in the CNS all the way to the effector innervated by that neuron
(basic principles of somatic motor pathways) all the somatic motor pathways for fibers that originate in the spinal cord, this means that the axon extends from the anterior gray horn, through the ventral nerve root, and out to a skeletal muscle
stimulates effector cells by means of the neurotransmitter acetylcholine (ACh)
(basic principles of somatic motor pathways) the last somatic motor neuron
is the extension of the great toe, with or without the fanning of other toes, in response to stimulation of the outer margin of the sole of the foot
(clinically important somatic reflexes) babinski sign
present in normal infants until approximately 1/5 years of age (abnormal for older individuals)
(clinically important somatic reflexes) babinski sign
sensory organ in tendon that senses if muscle is contracted or stretched too much
(nature of a reflex) golgi tendon organ
triggers autogenic inhibition of the agonist (muscle being contracted/stretched)
(nature of a reflex) golgi tendon organ
CN X
Vagus; Phyrynx, Larynx (vocal folds), heart, digestive organs
CN VIII
Vestibulocochlear; vestibular nerve-balance, postural control cochlear nerve-hearing
innervate the muscles and skin of the neck, upper shoulders, and part of the head
individual nerves emerging from the cervical plexus
consists of either muscle contraction or glandular secretion
reflex
formed by intermingling fibers from L4-S4
sacral plexus
located in the pelvic cavity on the anterior surface of the piriformis muscle
sacral plexus
typically contains motor neurons
the ventral root
innervate the lower part of the shoulder and the entire arm
Individual nerves emerging from the brachial plexus
each individual nerve that emerges contains all the fibers that innervate a particular region of the body
plexus
network of nerves (or blood vessels)
plexus
spinal nerve fibers are rearranged according to their ultimate destination, reducing the number of nerves needed to supply each body part
plexus
branches distal to the nerve
ramus
coccygeal nerve pair
1
thoracic nerve pairs
12 (T1 through T12)
connect to the undersurface of the brain, mostly on the brainstem
12 pairs of cranial nerves
___ pairs of spinal nerves are connected to the spinal cord
31
lumbar nerve pairs
5 (L1-L5)
sacral nerve pairs
5 (S1-S5)
cervical nerve pairs
8 (C1 through C8) (7,12, 5 breakfast lunch and dinner pneumonic)
CN VI
Abducens; lateral rectus muscles
CN XI
Accessory; trapezius, sternocleidomastoid
CN XII
Hypoglossal; muscles and sensation (proprioception, touch) of the tongue
made up of ventral rami of C1-C4 and a branch of the ventral ramus of C5
Cervical plexus
CN VII
Facial; all facial muscles, closing of eye lid, taste buds of anterior two thirds of the tongue
CN IX
Glossopharyngeal; taste buds of the posterior third of the tongue, pharynx (part of your throat above vocal folds and below nasal cavity)
formed by intermingling fibers of ___
L1-L4
CN III
Oculomotor; Pupil constriction, opening of eye lid, extrinsic eye muscle
CN I
Olfactory; smell
CN II
Optic; vision
___ emerges between the last cervical vertebra and the first thoracic vertebra
The eight cervical nerve
____ emerges from the cord in the space above the fist cervical vertebra
The first pair of cervical nerves
CN V
Trigeminal; has 3 branches, muscles of mastication, sensation of the face
CN IV
Trochlear; superior oblique muscles of the eye
if the center of the reflex arc is in the brain, the reflex is called
a cranial reflex
is easily recognized by a swelling called the dorsal root ganglion, or spinal ganglion (collection of nerve cell bodies)
a dorsal root
if the center of the reflex arc is in the spinal cord, the reflex is called
a spinal reflex
are mixed nerves (sensory & motor components)
all spinal nerves
pass out of the spinal cavity horizontally through the intervertebral foramina below their respective vertebrae
all the thoracic nerves
what is another name for the last somatic motor neuron
anterior horn neuron or lower motor neuron
are either contractions of smooth or cardiac muscles or secretion by glands
autonomic reflexes
located deep w/in the shoulder
brachial plexus
made up of ventral rami of C5- T1
brachial plexus
located deep within the neck
cervical plexus
formed by the last sacral spinal nerve (S5) and a few fibers from S4, joining w/the coccygeal nerve
coccygeal plexus
are identified by name (which is determined ether by distribution or by function) or they are identified by number ( the order in which they emerge, anterior to posterior); sometimes they are identified by both name and number
craninal nerves
region of the skin surface area supplied by afferent fibers of a given spinal nerve
dermatome
at first glance, the distribution of spinal nerves does not appear to follow an ordered arrangement; however, detailed mapping of the skin surface has revealed a close relationship between the spinal origin of each spinal nerve and the region of the body that is innervates
dermatomes and myotomes
formed by intermingling fiber of L1 through L4
lumbar plexus
located in the lumbar region of the back near the psoas muscle
lumbar plexus
because of their close proximity and overlap of fibers, the lumbar and sacral plexuses are often considered together as the
lumbosacral plexus
contains axons of sensory and motor neurons
mixed cranial nerve
made up of bundles of axons
mixed cranial nerve
skeletal muscle or muscles supplied by efferent fibers of a given spinal nerve
myotome
cervical plexus ventral rami
shows how ventral rami of the first four cervical spinal nerves (C1-C4) exchange fibers in the cervical plexus, fund deep w/in the neck Notice that some fibers from C% also enter this plexus to form a portion of the phrenic nerve
brachial plexus
shows, from the five rami C5 through T1 , the plexus forms three "trunks" the divisional branches reorganize into three "cords" the cords give rise to the individual nerves that exit the brachial plexus
somatic effectors
skeletal muscles
although many of theses nerves are mixed nerves, containing both sensory and motro fibers, it is often convenient to consider the PNS as having 2 functional divisions:
somatic motor nervous system (afferent division, efferent division) & autonomic nervous system
includes all voluntary motor pathways outside the CNS
somatic nervous system
each attaches to the spinal cord by a ventral root and dorsal root (proxical to the nerve)
spinal nerve
includes the fibers present in the cranial nerves, the spinal nerves, and all their individual branches
the entire peripheral nervous system
in the thigh, the tibial and common fibular nerves from the largest nerve in the body, ___
the great sciatic nerve
its many branches suppply nearly all the skin of the leg, the posterior thigh muschles, and the leg and foot muscles
the great sciatic nerve
descend from their point of origin at the lower end of the spinal cord before reaching the intervertebral foramina of their respective vertebrae, through which the nerves emerge
the lumbar, sacral, and coccygeal nerve roots
includes all the nervous path ways outside the brain and spinal cord
the peripheral nervous system
exits the cervical plexus and innervates the diaphragm
the phrenic nerve
is one of several large branches formed after each spinal nerve emerges from the spinal cavity
the ramus
exit the sacral plexus and supply nearly all the skin of the leg, posterior thigh muscles, and leg and foot muscles
the tibial, common peroneal, and sciatic nerves