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Chapter 14 NS PNS
I.
Student Notes
Functional Organization of the Peripheral Nervous System (pp. 396–397, Fig. 14.1).
A. The PNS is composed of nervous system structures outside the brain and spinal cord; basic structural
components of the PNS are the sensory receptors, motor endings that innervate effectors, nerves, and
ganglia; basic functional components are reviewed in Fig. 14.1 (pp. 396–397, Figs. 14.1–14.2).
B. Nerves are spinal nerves or cranial nerves; most nerves contain both sensory and motor axons and are
called mixed; some cranial nerves are purely sensory or purely motor in function.
II.
Peripheral Sensory Receptors (pp. 397–401, Figs. 14.3–14.4, and Table 14.1).
A. Sensory receptors detect stimuli (environmental changes) inside the body as well as outside the body;
classification is based on body location, stimulus detected, and structure (p. 397).
B. The three classes of sensory receptors based on location in the body are exteroceptors, interoceptors,
and proprioceptors (p. 397).
C. A second way to classify sensory receptors is by the kinds of stimuli that activate the receptors;
examples are mechanoreceptors, thermoreceptors, chemoreceptors, photoreceptors, and nociceptors
(p. 397).
D. The third way to classify general sensory receptors is by their structure (special senses are covered in
Chapter 16); the nerve endings of these receptors are structurally free nerve endings (unencapsulated)
or encapsulated nerve endings (pp. 397–401, Figs. 14.3–14.4, and Table 14.1).
1. Free, or naked, nerve endings are present everywhere in the body and respond
primarily to pain, temperature, and itch; various encapsulated nerve endings respond to
a wide variety of indivualized stimuli.
III.
Peripheral Motor Endings (pp. 401–403, Figs. 14.2 and 14.5–14.7).
A. Motor endings activate the effectors of the body; effectors are skeletal muscle, smooth muscle, and
glands (p. 401).
B. Skeletal muscle fibers are innervated at neuromuscular junctions, or motor end plates; a motor unit
consists of a motor neuron and all the muscle fibers it innervates (pp. 401–402, Figs 14.5–14.6).
C. Innervation of visceral muscle and glands is much simpler than innervation of skeletal muscle;
cardiac muscle cell innervation resembles that of smooth muscle (pp. 402–403, Fig. 14.7).
IV.
Cranial Nerves (pp. 403–411, Fig. 14.8, and Table 14.2–14.3).
A. Twelve pairs of cranial nerves attach to the brain and innervate the head and neck; vagus nerves are
the only pair that “wanders” into the thorax and abdomen (p. 403).
B. Cranial nerves are grouped according to function; some are purely sensory (I, II, and VIII); some are
primarily (or exclusively) motor (III, IV, VI, XI, and XII), and some are mixed (V, VII, IX, and X) (p.
404, and Table 14.2).
C. Four cranial nerves (III, VII, IX, and X) also contain general visceral motor fibers of the
parasympathetic division of the autonomic nervous system (ANS) (p. 404).
D. The name, number, and brief function summary are as follows:
I. Olfactory – smell
II. Optic – vision
III. Oculomotor – eye movement (four of the six extrinsic eye muscles)
IV. Trochlear – eye movement (superior oblique eye muscle)
V. Trigeminal – general sensation of the face
VI. Abducens – eye movement (lateral rectus eye muscle)
VII. Facial – chief motor nerves of the face
VIII. Vestibulocochlear – hearing and equilibrium
IX. Glossopharyngeal – innervates part of the tongue and pharynx for swallowing and taste
X. Vagus – innervates heart, lungs, and abdominal organs
XI. Accessory – moves structures associated with the head and neck (larynx, pharynx, soft
palate, trapezius, and sternocleidomastoid muscles)
XII. Hypoglossal – serves the tongue muscles
V.
Spinal Nerves (pp. 412–423, Figs. 14.9–14.17, and Tables 14.4–14.7).
A. Thirty-one pairs of spinal nerves attach to the spinal cord and names reflect point of issue from the
spinal cord. There are eight pairs of cervical spinal nerves (C1-C8), 12 pairs of thoracic spinal nerves
(T1-T12), five pairs of lumbar spinal nerves (L1-L5), five pairs of sacral spinal nerves (S1-S5), and one
pair of coccygeal spinal nerves (Co1) (p. 412, Fig. 14.9).
B. Roots are for attachment of a spinal nerve to the spinal cord; rami are branches of a spinal nerve (p.
412, Fig. 14.10).
C. Muscles and skin of the back (posterior portion of the trunk – from the neck to the sacrum) are
innervated by dorsal rami (p. 413, Fig. 14.10).
D. The anterior and lateral wall of the thorax and abdomen is innervated by ventral rami; thoracic ventral
rami do not form plexuses (p. 414, Figs. 14.9–14.10b).
E. A nerve plexus is a network of nerves (p. 414).
F. The cervical plexus (C1-C4) innervates the muscles and skin of the shoulder; the most important nerve
issued from the cervical plexus is the phrenic nerve (p. 414, Fig. 14.11 and Table 14.4).
G. The brachial plexus (C5-C8 and part of T1) serves the muscles and skin of the upper limb, including
the shoulder; the main nerves from the brachial plexus are the musculocutaneous, median, ulnar,
radial, and axillary (pp. 414–418, Figs. 14.12–14.14, and Table 14.5).
H. The lumbar plexus (L1-L4) innervates the muscles and skin of the anterior and medial thigh; the main
nerves issued from the lumbar plexus are the femoral and obturator nerves (pp. 418–420, Fig. 14.15,
and Table 14.6).
I. The sacral plexus (L4-S4) supplies muscles and skin of the posterior thigh and almost all of the leg; its
main branches are the sciatic nerve, tibial nerve, and common fibular nerve; other branches of the
sacral plexus innervate the pelvic girdle and perineum (pp. 420–422, Fig. 14.16, and Table 14.7).
J. Joints of the body are innervated by branches of the nerves of the muscles that cross the joint
(Hilton’s law) (p. 422).
K. The area of skin innervated by the cutaneous branches from a single spinal nerve is called a
dermatome (p. 422, Fig. 14.17).
VI.
Disorders of the Peripheral Nervous System (pp. 423–424).
A. Two disorders that involve sensory neurons are shingles and migraine headaches; disorders of motor
innervation are myasthenia gravis, polio, and postpolio syndrome (pp. 423–424).
VII.
The Peripheral Nervous System Throughout Life (pp. 424–425).
A. During embryonic development, each spinal nerve grows out between newly formed vertebrae to
provide the motor innervation of an adjacent myotome (future trunk muscle) and the sensory
innervation of the adjacent skin region (dermatome) (pp. 424–425).