240 Chapter 8
Test Your Knowledge
- Which of these statements about the precentral gyrus is true?
a. It is involved in motor control.
b. It is involved in sensory perception.
c. It is located in the frontal lobe.
d. Both a and c are true.
e. Both b and c are true.- In most people, the right hemisphere controls movement of
a. the right side of the body primarily.
b. the left side of the body primarily.
c. both the right and left sides of the body equally.
d. the head and neck only.- Which of these statements about the basal nuclei is true?
a. They are located in the cerebrum.
b. They contain the caudate nucleus.Review Activities
c. They are involved in motor control.
d. They are part of the extrapyramidal system.
e. All of these are true.
Which of these acts as a relay center for somatesthetic
sensation?
a. The thalamus
b. The hypothalamus
c. The red nucleus
d. The cerebellum
Which of these statements about the medulla oblongata is
false?
a. It contains nuclei for some cranial nerves.
b. It contains the apneustic center.
c. It contains the vasomotor center.
d. It contains ascending and descending fiber tracts.
The epithalamus contains a choroid plexus, where
cerebrospinal fluid is formed. The pineal gland, which
secretes the hormone melatonin, is also part of the
epithalamus.
The hypothalamus forms the floor of the third ventricle,
and the pituitary gland is located immediately inferior to
the hypothalamus.
B. The hypothalamus is the main control center for visceral
activities.
The hypothalamus contains centers for the control of
thirst, hunger, body temperature, and (together with the
limbic system) various emotions.
The hypothalamus regulates the secretions of the
pituitary gland. It controls the posterior pituitary by
means of a fiber tract, and it controls the anterior
pituitary by means of hormones.
8.4 Midbrain and Hindbrain 228
A. The midbrain contains the superior and inferior colliculi,
which are involved in visual and auditory reflexes,
respectively, and nuclei that contain dopaminergic neurons
that project to the corpus striatum and limbic system of the
forebrain.
B. The hindbrain consists of two regions: the metencephalon
and the myelencephalon.
- The metencephalon contains the pons and cerebellum.
The pons contains nuclei for four pairs of cranial nerves,
and the cerebellum plays an important role in the
control of skeletal movements. - The myelencephalon consists of only one region, the
medulla oblongata. The medulla contains centers for the
regulation of such vital functions as breathing and the
control of the cardiovascular system.
C. The reticular activating system (RAS) is an ascending arousal
system consisting of interconnected neurons of the reticular
formation that extend from the pons to the midbrain.
1. Arousal is promoted by different neural tracts of
the RAS that release ACh, different monoamine
neurotransmitters, and a polypeptide neurotransmitter
known as orexin (or hypocretin-1).
2. The activity of the RAS is inhibited by GABA-releasing
neurons, and this activity is necessary for sleep.8.5 Spinal Cord Tracts 232
A. Ascending tracts carry sensory information from sensory
organs up the spinal cord to the brain.
B. Descending tracts are motor tracts and are divided into two
groups: the pyramidal and the extrapyramidal systems.
1. Pyramidal tracts are the corticospinal tracts. They begin
in the precentral gyrus and descend, without synapsing,
into the spinal cord.
2. Most of the corticospinal fibers decussate in the
pyramids of the medulla oblongata.
3. Regions of the cerebral cortex, the basal nuclei, and
the cerebellum control movements indirectly by
synapsing with other regions that give rise to descending
extrapyramidal fiber tracts.
4. The major extrapyramidal motor tract is the
reticulospinal tract, which has its origin in the reticular
formation of the midbrain.8.6 Cranial and Spinal Nerves 236
A. There are 12 pairs of cranial nerves. Most of these are
mixed, but some are exclusively sensory in function.
B. There are 31 pairs of spinal nerves. Each pair contains both
sensory and motor fibers.
1. The dorsal root of a spinal nerve contains sensory fibers,
and the cell bodies of these neurons are contained in the
dorsal root ganglion.
2. The ventral root of a spinal nerve contains motor fibers.
C. A reflex arc is a neural pathway involving a sensory neuron
and a motor neuron. One or more association neurons also
may be involved in some reflexes.