Chapter 11 questions

describe the location of cerebrospinal fluid within the meninges

Cerebrospinal fluid (CSF) is found between the arachnoid and pia mater of the brain and spinal cord in the space called the subarachnoid space.

explain the consequences of nerve fibers crossing over

Crossing over causes the impulses from one side of the body to be received and controlled by the opposite side of the brain.

37. Describe the structure of a spinal nerve.

Each spinal nerve emerges from the spinal cord by two short branches that lie within the vertebral column. The dorsal root is also called the posterior or sensory root. It can be identified by the dorsal root ganglion. This root conducts sensory impulses inward from the peripheral body parts. The ventral root is also called the anterior or motor root. It consists of axons from the motor neurons. The roots unite to form a spinal nerve, which extends outward from the vertebral canal through and intervertebral foramen. Each spinal nerve splits into three parts called the meningeal, posterior, and anterior branches. Spinal nerves in the thoracic and lumbar regions have a fourth or visceral branch, which supplies the autonomic nerve fibers.

Distinguish between normal and paradoxical sleep.

Normal sleep (slow wave or non-REM) occurs when a person is very tired and is caused by decreased activity of the reticular formation. It is restful, dreamless, and accompanied by reduced blood pressure and respiratory rate. Paradoxical sleep (REM sleep) is so named because some areas of the brain are active. It is identified by dreaming, rapid eye movement beneath the eyelids, and irregular respiratory and heart rates.

Distinguish between short-term and long-term memory.

Short-term memories are thought to be electrical in nature such that the neurons are connected in a circuit so that the last in the series stimulates the first. As long as the stimulation continues, the thought is remembered. When it ceases, so does the memory, unless it enters long-term memory. Long-term memories appear to change the structure or function of certain neurons that enhance synaptic transmission. The synaptic patterns must meet two requirements of long-term memory. First, there must be enough synapses to encode an almost infinite number of memories. Second, the pattern of synapses can remain unchanged for years.

Describe the location and function of the basal nuclei.

The basal ganglia (basal nuclei) are masses of gray matter found deep in the cerebral hemispheres. They are the caudate nucleus, the putamen, and the globus pallidus and are responsible for producing most of the inhibitory neurotransmitter dopamine. Impulses from the basal ganglia inhibit motor functions, controlling certain muscular activities.

36. Define cauda equina.

The cauda equina is so named because in the adult, the spinal cord ends between the first and second lumbar vertebrae. Because of this the lumbar, sacral, and coccygeal nerves must descend down the spinal column to the exit points resembling a horse's tail.

33. List four general types of nerve fibers.

The four general types of nerve fibers are: general somatic efferent fibers, general somatic afferent fibers, general visceral efferent fibers, and general visceral afferent fibers.

describe the location of the ventricles of the brain

The lateral ventricles (first and second ventricles) extend into the cerebra hemispheres and occupy part of the frontal, temporal, and occipital lobes. The third ventricle is found in the midline of the brain, below the corpus callosum, and connects the lateral ventricles through openings in the anterior ends. The fourth ventricle is found in the brain stem in front of the cerebellum. The cerebral aqueduct connects openings in its roof that lead into the subarachnoid space of the meninges.

Describe the functions of the cerebellum.

The main function of the cerebellum is to serve as the reflex center for control of body part positions in response to sensory information from various nerve centers. It is the primary area for control of the complex skeletal movements involved in posture and locomotion. To accomplish this, the cerebellum communicates with the body and brain via three pairs of nerve tracts: Inferior peduncles—This pair receives sensory information concerning limb, joint, and other body part positions. Middle peduncles—This pair sends impulses concerning the desired position of these body parts from the cerebrum to the cerebellum. Superior peduncles—This pair sends the newly integrated information through the pons, medulla oblongata, and spinal cord as motor impulses to the skeletal muscles concerned. Damage to the cerebellum will cause tremors, muscle tone loss, reeling walk, loss of equilibrium, and inaccurate muscle movements.

Describe the medulla oblongata and its functions.

The medulla oblongata is an enlarged continuation of the spinal cord at its superior end. It extends from the foramen magnum to the pons. Because of its location, all ascending and descending nerve fibers connecting the brain and the spinal cord must pass through it. Some of the nuclei in the gray matter relay ascending impulses to the other side of the brain stem and higher brain centers. Other nuclei control vital visceral activities and are called the cardiac center, the vasomotor center, and the respiratory center.

Explain the function of the corpus callosum.

The nerve fibers of the corpus callosum allow the dominant hemisphere to receive sensory information sent to the nondominant hemisphere for use in decision making by the general interpretive areas. It also allows the dominant hemisphere to control the motor cortex of the nondominant one.

Describe the pons and its functions.

The pons is a rounded bulge on the inferior side of the brain stem where it separates the midbrain from the medulla oblongata. The dorsal portion of the pons relays impulses between the medulla oblongata and the cerebrum. The ventral portion relays impulses from the cerebrum to the cerebellum. The pons also relays impulses from the peripheral nerves to higher brain centers. It also works with the medulla oblongata to regulate rate and depth of breathing.

14. Describe the location and function of the primary motor areas of the cortex.

The primary motor areas of the cerebral cortex lie in the frontal lobes along the anterior wall of the central gyrus. Large pyramidal cells are responsible for nerve impulses sent through the corticospinal tracts to voluntary muscles. Impulses from the upper parts of the motor areas control muscles in the legs and thighs; the middle portion control muscles in the shoulders and arms; and the lower portions control the muscles of the head, face, and tongue.

describe the structure of the spinal cord

The spinal cord is a long slender column of nerve fibers that begins at the foramen magnum of the skull and extends downward to a point near the first and second lumbar vertebrae. The cord is actually a group of thirty-one segments that give rise to pairs of spinal nerves. These nerves connect all of the body to the CNS.

39. Distinguish between the sympathetic and parasympathetic division of the autonomic nervous system.

The sympathetic division of the autonomic nervous system is concerned primarily with preparing the body for energy-expending, stressful, or emergency situations. The parasympathetic division is active under ordinary, restful conditions. It counterbalances the effects of the sympathetic division and restores the body to a resting state following a stressful experience.

describe a withdrawal reflex

When a person touches something painful, receptors in the skin send impulses to interneurons in a reflex center in the spinal cord. The reflex center sends impulses to the flexor muscles of the affected part causing the part to be moved away. At the same time this is happening, impulses to the extensor muscles of the affected part are inhibited, so that the flexors can work more effectively. A phenomenon, called a crossed extensor reflex, occurs simultaneously with the initial reflex that causes the extensors of the opposite limb to contract.