Ch 13 Answers to End-of-Chapter Questions
Multiple-Choice and Matching Question answers appear in Appendix H of the main text.
Short Answer Essay Questions
12. The PNS enables the CNS to receive information and carry out its decisions. (p. 484)
13. The PNS includes all nervous tissue outside the CNS, and consists of the sensory
receptors that detect specific stimuli, the peripheral nerves (cranial or spinal) that
conduct
impulses to and from the CNS, the ganglia that contain synapses or cell bodies outside
the CNS, and motor nerve endings that innervate effector organs. (p. 484)
14. Sensation is simply the awareness of a stimulus, whereas perception also understands
the meaning of the stimulus. (p. 484)
15. a. Central pattern generators (CPGs) control often repeated locomotion and motor
activities.
b. The precommand center, the cerebellum and basal nuclei, modify and control the
activity of the CPG circuits. (pp. 511–512)
16. For a diagram of the hierarchy of motor control, see Figure 13.14. (p. 512)
17. The cerebellum is called a precommand area because it integrates inputs from all
ascending tracts prior to these inputs reaching the cortical command centers. The basal
nuclei play a role in inhibiting cortical areas of the brain, preventing response until this
inhibition stops. (p. 512)
18. In the PNS, damaged fibers can be replaced or repaired by physical and chemical
processes directed by macrophages and Schwann cells. In the CNS, oligodendrocytes
do not aid fiber regeneration because they have growth-inhibiting proteins on their
surface,
allowing damaged fibers to collapse and die. (pp. 491–492)
19. See pp. 501–502.
a. Spinal nerves form from dorsal and ventral roots that unite distal to the dorsal root
ganglion. Spinal nerves are mixed nerves that contain both sensory and motor fibers.
b. The ventral rami, with the exception of those in the thorax that form the intercostal
nerves, contribute to large plexuses that supply the anterior and posterior body trunk
and limbs. The dorsal rami supply the muscles and skin of the back (posterior trunk).
20. a. A plexus is a branching nerve network formed by roots from several spinal nerves
that ensures that any damage to one nerve root will not result in total loss of
innervation to that part of the body. (p. 503)
b. See Figures 13.9 to 13.12, and Tables 13.3 to 13.6, pp. 503–509, for detailed
information about each of the four plexuses.
21. Ipsilateral reflexes involve a reflex initiated on and affecting the same side of the body;
contralateral reflexes involve a reflex that is initiated on one side of the body and affects
the other side. (p. 518)
22. The flexor, or withdrawal, reflex is a protective mechanism to withdraw from a painful
stimulus, leading to a loss of pain. (p. 518)
23. Flexor reflexes are protective ipsilateral and polysynaptic reflexes that are designed to
pull a part of the body away from a painful stimulus. Crossed-extensor reflexes consist
of an ipsilateral withdrawal reflex and a contralateral extensor reflex that usually aids in
maintaining balance. (p. 518)
24. The sensory input of a crossed-extensor reflex illustrates parallel processing, an ipsilateral
response to a stimulus. The serial processing phase consists of motor activity, the
contralateral response that activates the extensor muscles on the opposite side of the body.
(p. 518)
25. Reflex tests assess the condition of the nervous system. Exaggerated, distorted, or
absent reflexes indicate degeneration or pathology of specific regions of the nervous
system
often before other signs are apparent. (p. 514)
26. Dermatomes are related to the sensory innervation regions of the spinal nerves. The
spinal nerves correlate with the segmented body plan, as do the muscles (at least
embryologically). (pp. 509–510)
Critical Thinking and Clinical Application Questions
1. Precise realignment of cut, regenerated axons with their former effector targets is highly
unlikely. Coordination between nerve and muscle will have to be relearned.
Additionally, not all damaged fibers regenerate. (p. 491)
2. Damage to his common fibular nerve would result in problems dorsiflexing his right
foot, and his knee joint would be unstable (more rocking of the femur from side to side
on the tibia). (p. 508)
3. Damage to the brachial plexus occurred when he suddenly stopped his fall by grabbing
the branch. (p. 505)
4. The left trochlear nerve (IV), which innervates the superior oblique muscle responsible
for this action. (p. 495)
5. The region of motor and sensory loss follows the course of the sciatic nerves (and their
divisions); they must have been severely damaged by the shooting accident. (p. 508)
6. The specific ascending pathways of the fasciculus cuneatus carry discriminative touch
information from the upper limbs to the cortex. You must use feature abstraction and
possibly pattern recognition to identify a specific pattern feature such as the teeth of a
key or the fur of a rabbit’s foot. (pp. 487, 489)
7. Referred pain occurs because visceral and somatic pain fibers travel along the same
neural pathways. Mr. Jake felt pain in his left arm because the heart, located on the left
side of the thoracic cavity, would share pathways with the left arm. (p. 490)