HUMAN BIOLOGY

The Nervous sysTem 263

Sections 13.5, 13.6 The brain and
spinal cord make up the central nervous
system. The peripheral nervous system
consists of nerves and ganglia in other body
regions.
The peripheral nervous system’s somatic nerves deal with
skeletal muscles involved in voluntary body movements and
sensations arising from skin, muscles, and joints. Its autonomic
nerves deal with the functions of internal organs.
Autonomic nerves are subdivided into sympathetic and
parasympathetic groups. Parasympathetic nerves govern
basic tasks such as digestion and tend to slow the pace
of other body functions. Signals from sympathetic nerves
produce the fight–flight response, a state of intense arousal
in situations that may demand increased activity.
Spinal cord nerve tracts carry signals between the brain and
the PNS. The cord also is a center for many reflexes.

Section 13.7 The brain is divided into
two cerebral hemispheres and has three main
divisions (Table 13.4). It and the spinal cord
are protected by bones (skull and vertebrae)
and by the three meninges. Both are
cushioned by cerebrospinal fluid. Specialized
capillaries create a blood–brain barrier that prevents some
blood-borne substances from reaching brain neurons.
In the forebrain the thalamus relays sensory information
and helps coordinate motor responses. The hypothalamus
monitors internal organs and influences behaviors related to
their functions (such as thirst). The limbic system has roles in
learning, memory, and emotional behavior.
Midbrain centers coordinate and relay some sensory
information. The midbrain, medulla oblongata, and pons make
up the brain stem.
The hindbrain includes the medulla oblongata, pons, and
cerebellum. It contains reflex centers for vital functions and
muscle coordination.

Section 13.8 The cerebral cortex
is devoted to receiving and integrating
information from sense organs and coord-
inating motor responses in muscles and
glands.
Sections 13.9, 13.10 States o f
consciousness vary between total alertness
and deep coma. The levels are governed
by the RAS, the brain’s reticular activating
system. It is part of the reticular formation in
the brain stem. Memory occurs in short-term
and long-term stages. Long-term storage depends on chemical
or structural changes in the brain.

Review QueStionS

1. Explain the difference between a sensory neuron, an
   interneuron, and a motor neuron.


2. What are the functional zones of a motor neuron?


3. Define an action potential.

Cerebrum Processes sensory inputs; initiates, controls

skeletal muscle activity. Governs thought,

memory, emotions

Olfactory lobe Relays sensory input from nose to olfactor

centers of cerebrum

Thalamus Relays sensory signals to and from cerebral

cortex; has role in memory

Hypothalamus With pituitary gland, a homeostatic control

center; adjusts volume, composition,

temperature of internal environment.

Governs organ-related behaviors (e.g., sex,

thirst, hunger) and expression of emotions

Limbic system Governs emotions; has roles in memory

Pituitary gland With hypothalamus, provides endocrine

control of metabolism, growth, development

Pineal gland Helps control some circadian rhythms; also

has role in reproductive physiology

Roof of In humans and other mammals, its reflex

midbrain centers relay visual and auditory sensory

input to the forebrain

Pons Some tracts bridge the cerebrum and

cerebellum; others connect spinal cord

with forebrain. With the medulla oblongata,

controls rate and depth of respiration

Medulla Its tracts relay signals between spinal

oblongata cord and pons; its reflex centers help

control heart rate, adjustments in blood

vessel diameter, respiratory rate, coughing,

other vital functions

Cerebellum Coordinates motor activity for moving limbs

and maintaining posture, and for spatial

orientation

Makes reflex connections for limb

movements. Its tracts connect brain,

peripheral nervous system

Forebrain

Midbrain

Hindbrain

Spinal cord

Brain stem

Table 13.4 Summary of the Central Nervous System

4. What is a synapse? Explain the difference between an
   excitatory and an inhibitory synapse.


5. Explain what happens during synaptic integration.


6. What is a reflex? Describe what happens during a
   stretch reflex.


7. Distinguish between the following:
   a. neurons and nerves
   b. somatic system and autonomic system
   c. parasympathetic and sympathetic nerves

Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).