Download 11.4: The Peripheral Nervous System

Section 11.4: The Peripheral Nervous System
Section 11.4 Questions, page 541
1. (a) Answers may vary. Students should include the following: The somatic system is the
mainly conscious and voluntary part of the nervous system that controls body movements and
carries signals from the CNS to skeletal muscles. The somatic system consists of 31 sets of
spinal nerves. The autonomic system works with the endocrine system to react to changes in
internal and external environments. The autonomic nervous system works via motor nerves and
controls mostly involuntary processes such as digestion, secretion by sweat glands, circulation of
the blood, many functions of the reproductive and excretory systems, and the contraction of
smooth muscles in all parts of the body.
(b) Answers may vary. Students should include the following: Both the sympathetic division and
the parasympathetic division are part of the autonomic system. The sympathetic division
includes primarily the nerves of the thorax and abdomen, and the ganglia of the sympathetic
division occur as a chain just outside the spinal column. The parasympathetic division has
ganglia located in the brain, and the axons exit the brain as cranial nerves or as the posterior or
sacral parasympathetic nerves. The cranial nerves connect the brain directly to the head, neck,
and body trunk. Sympathetic and parasympathetic nerves differ in their structure. Sympathetic
nerves have short preganglionic nerves and long postganglionic nerves. Parasympathetic nerves
have long preganglionic nerves. The sympathetic division is active in situations involving stress,
danger, excitement, or strenuous physical activity. Signals from the sympathetic division
increase heartbeat, raise blood pressure, dilate air passages in the lungs, induce sweating, and
open the pupils wide. Activities that are less important in an emergency, such as digestion, are
suppressed by the sympathetic system. The parasympathetic division, in contrast, is active during
quiet, low-stress situations, such as relaxation. Under its influence, the effects of the sympathetic
division, such as rapid heartbeat and elevated blood pressure, are reduced, and “housekeeping”
(maintenance) activities such as digestion can take place.
2. At every level from the bottom to the top of the spinal cord, one ventral and one dorsal root
enter from each side of the body to form a spinal nerve. Dorsal roots contain sensory fibres and
carry sensory information to the CNS. Ventral roots contain motor fibres and carry motor
information away from the CNS to initiate movement. These spinal roots are considered the
beginning of the PNS.
3. Pain is an interpretation of sensory input received by specialized cells known as the substantia
gelatinosa (SG). Stimulated SG cells produce a neurotransmitter that communicates with the
injured region, and relays a message to the brain, causing our perception of pain. When the
natural painkillers known as endorphins attach to SG cell receptor sites, they prevent or reduce
the binding of the neurotransmitters that transmit the signal interpreted as pain. When the
neurotransmitters do not bind to the receptor sites, we do not feel pain. The neurotranmitters act
as natural drugs.
4. Answers may vary. Sample answer: Strenuous exercise is known to result in the production of
endorphins, and endorphins bind with pain receptors in the substantia gelatinosa, causing
reduced perception of pain. They can also cause feelings of well-being or euphoria. In addition,
increased production of naturally occurring opioids, such as endorphins, affects the prefrontal
and limbic regions of the brain, known to be important in processing emotions. It appears that
this can improve mood and reduce the incidence or severity of depression.
Copyright © 2012 Nelson Education Ltd.
Chapter 11: The Nervous System 11.4-1
5. The severity of a spinal cord injury depends on where the spinal cord was injured because
each region of the spine and spinal nerves controls different areas and functions of the body. An
injury to the spinal cord will affect all regions of the spine below the site of the injury, and all of
the functions carried out by that region will be affected. Therefore, the higher on the spine an
injury is, the more areas and the more functions are affected.
6. The sympathetic nervous system is the part of the ANS that prepares the body for action in
times of stress. Blood vessels to the skin and organs contract, blood vessels to the heart, brain,
lungs, and skeletal muscles expand (increasing blood flow to those areas), and heart rate and
breathing rate increase. After the threat is over the parasympathetic system reverses the actions
of the sympathetic nervous system calming the body, conserving energy, and allowing normal
body processes to resume.
7. The neurons in the CNS receive, interpret, and send signals to the PNS. The neurons in the
PNS detect stimuli from outside and inside the body and carry signals from the CNS to other
parts of the body to stimulate muscles and other target organs.
8. Endorphins and enkephalins are both natural painkillers. Both are morphine-like substances
whose functions are similar to those of opium-based drugs. When a person is injured, pain
impulses travel up the spinal cord to the brain. The brain then releases endorphins and
enkephalins. Enkephalins block pain signals in the spinal cord. Endorphins may block pain at the
brain stem.
9. Answers may vary. Sample answer: Opiorphin is a natural painkiller six times more powerful
than morphine. Because it is derived from a natural substance found in the human body, it may
spawn a new generation of natural painkillers that relieve pain as well as morphine but without
the addictive and psychological side effects that morphine has.
10. Answers may vary. Sample answer: Only Older Otters Tend To Allow Friendly Alligators
Gentle Velvet-Soft Hands.
11. Answers may vary. Sample answer: It is likely that the optic nerve is damaged, as well as one
or more cervical motor nerves. The motor nerves initiate most eye movements, so inability to
move the eye or eyelid may indicate damage to these nerves. The optic nerve constricts the pupil,
so a dilated pupil may indicate damage to it.
Copyright © 2012 Nelson Education Ltd.
Chapter 11: The Nervous System 11.4-2