Solutions To Exercises Lesson

1. The neuron is also called a nerve cell. It is the conducting unit of the nervous system. It is specialized to be irritable and transmit signals, or impulses. (para 12-1)

2. The three major subdivisions of the human nervous system are the central nervous system, the peripheral nervous system, and the autonomic nervous system. (para 12-2)

3 A neuron is the nerve cell body plus all of its processes and coverings.

A nerve is a collection of neuron processes together and outside of the CNS.

A fiber tract is a collection of neuron processes together and within the CNS.

A ganglion is a collection of nerve cell bodies together and outside of the CNS.

A nucleus is a collection of nerve cell bodies together and within the CNS. (para 12-3)

4. The human nervous system is supplied with special junctions called synapses. (para 12-4a)

5. In general terms, the human nervous system can be compared to a computer. Sensory information is the input, which is collated along with previously stored information. Once a decision has been reached by the central portion, there is an output of commands to the effector organs (muscles and/or glands). (para 12-4b)

6. The brainstem is a primary coordinating center of the human nervous system.

The cerebellum is the primary coordinating center for muscle actions. Here, patterns of movement are properly integrated. Also, the cerebellum is very much involved in the postural equilibrium of the body.

The newest development of the brain is the cerebrum. (para 12-6)

7. The autonomic nervous system (ANS) is that portion of the nervous system concerned with commands for smooth muscle tissue, cardiac muscle tissue, and glands.

For most of us, the control of the visceral organs is automatic, that is, without conscious control. (para 12-10)

8. The ANS is organized into two major subdivisions--the sympathetic and parasympathetic nervous systems. The first of these is also known as the thoraco-lumbar outflow. The second is also known as the cranio-sacral outflow.

If one of these subdivisions stimulates an organ, the other will inhibit it. The interplay of the two subdivisions helps visceral organs to function within a stable equilibrium. This tendency is called homeostasis.

Under conditions of stress, the sympathetic nervous system mobilizes all of the energy-producing structures of the body. For example, it makes the heart beat faster. Later, as equilibrium is restored, the parasympathetic nervous system has the opposite effect. (paras 12-11 thru 12-13)

9. The neurons are alined in sequences to form circuits. The transmission of information along a neuron is electrochemical in nature. Crossing the gap between one neuron and the next is a chemical called a neurotransmitter. (para 12-14)

10. Neurons are able to concentrate negative ions inside and positive ions outside of the cell membrane. When the neuron is not actually transmitting, this process produces the resting potential. (para 12-15)

11. When the polarity of ions is disrupted by a stimulus, that location on the cell membrane is said to be depolarized. The restoration of the original polarity is called repolarization. At the same time, adjacent areas are depolarized. Thus, there is a wave of depolarization/repolarization along the length of the neuron. (para 12-16)

12. The speed of an impulse is proportional to the thickness of the neuron process. Transmission is fastest in the thickest neurons. (para 12- 17)

13. Together, the gap and the "connecting" membranes between two successive neurons are called the synapse. The gap itself is called the synaptic cleft. Containing specific amounts of neurotransmitter are synaptic vesicles in the terminal bulb of the first neuron. When an impulse reaches the bouton, the vesicles are stimulated to release their neurotransmitter. This substance passes through the presynaptic membrane, across the synaptic cleft, and to the postsynaptic membrane. Since this process consumes much energy, the bouton contains many well-developed mitochondria. (para 12-18)

14. The neuromuscular junction is the "connection" between a motor neuron and a striated muscle fiber. It is nearly identical to a synapse. However, the surface of the postsynaptic membrane is in a series of longitudinal folds. This greatly increases the surface area receptive to the ACH.

The group of striated muscle fibers innervated by one motor neuron is called the motor unit. Fewer muscle fibers per motor unit result in finer movements. More muscle fibers per motor unit result in coarser movements. (para 12-19)

15. The simplest reaction is called a reflex, defined as an automatic reaction to a stimulus. (para 12-20)

16. A pathway of the human nervous system is the series of neurons or other structures used to transmit an item of information. In general, we consider two major types of pathways--the general sensory pathways and the motor pathways.

At some specific level in the neuraxis, all of these pathways cross to the opposite side. Each crossing is called a decussation. Thus, the right cerebral hemisphere communicates with the left half of the body. The left cerebral hemisphere communicates with the right half of the body. (para 12-22)

17. The general senses include pain, touch, temperature, and proprioception ("body sense").

A general sensory pathway extends from the point where the stimulus is received to the postcentral gyrus (fold) of the cerebral hemisphere. This gyrus is the site of conscious sensation of a stimulus.

Corresponding to each location in the body, there is a specific location in the postcentral gyrus. (para 12-23)

18. Pain is an ancient protective mechanism which generally helps us to avoid injury. Endorphins are chemicals found naturally within the body which tend to block the sensation of pain.

The pain receptor is not a specific receptor organ. It is referred to as a free nerve ending. (para 12-24)

19. The body has two different mechanisms for sensing temperature. Detecting warmth and cold in the periphery of the body are specific sensory receptors. Special heat-sensitive neurons in the hypothalamus detect increases in the temperature of the blood. (para 12-25)

20. The pacinian corpuscles are typical of the receptors which detect deep pressure. (para 12-26)

21. Another term for muscle sense is proprioception. For this, there is a special receptor organ to monitor the stretch of the muscle. These receptor organs are called muscle spindles or stretch receptors. They detect relative muscle length.

Another stretch receptor associated with the skeletal muscle is the Golgi tendon organ. As its name implies, this organ is located within the tendon of the muscle. It detects relative muscle tension. (para 12-27)

22. The CNS receives information through the sensory pathways and collates this information against information stored in memory. This results in a decision. If the decision is to do something, then the CNS sends out commands through the motor pathways to the effector organs. (para 12-28)

23. We usually consider two general motor pathways--the pyramidal and the extrapyramidal motor pathways. (para 12-28b)

24. A pyramidal motor pathway is primarily concerned with volitional (voluntary) control of body parts, particularly with the fine movements of the hands.

The pyramidal motor pathway begins in the precentral gyrus of the cerebral hemisphere. As we have already seen, the neurons making up the precentral and postcentral gyri are arranged in a pattern corresponding to the various parts of the body to which they are connected.

Immediately below the pyramids, the axons cross to the opposite side of the CNS. Thus, the left cerebral hemisphere commands the right side of the body, and the right cerebral hemisphere controls the left side of the body. (para 12-29)

25. The extrapyramidal motor pathways are concerned with automatic (nonvolitional) control of body parts. This particularly includes patterned, sequential movements or actions. The cerebellum plays a major role in extrapyramidal pathways. The cerebellum is the major center for coordinating the patterned sequential actions of the body, such as walking. (para 12-30)

26. The human nervous system can be thought of as a series of steps or levels. Each level is more complex than the level just below. No level is completely overpowered by upper levels, but each level is controlled or guided by the next upper level as it functions.

The simplest and lowest level of control is the reflex arc. Producing a wider reaction to a stimulus are segmented reflexes. (paras 12-31, 12-32)

27. Nuclei in the medulla of the hindbrainstem control the visceral activities of the body, such as respiration, heart beat, etc.

The reticular formation of the brainstem has a facilitory area and an inhibitory area. This control area produces sleep or wakefulness.

The thalamus is a group of nuclei found together in the forebrainstem. The thalamus is the major relay center of sensory inputs.

The hypothalamus is a higher control center for visceral activities of the body. (para 12-33)

28. The cerebellum is the primary center for the integration and control of patterned, sequential motions of the body. (para 12-34)

29. In humans, the highest level of control is localized in the cerebrum. Localized at this level are conscious sensation and volitional motor activity.

The visceral level within the cerebrum is concerned with visceral activities of the body, as related to fight-or-flight, fear, and other emotions.

The second level of the cerebrum is concerned with stereotyped patterns of muscle activity.

The third level of the cerebrum is the volitional level. Here, cognition (thinking) occurs, and unique, brand-new solutions can be created. (para 12-35)

30. The precentral gyrus is Brodmann's area number 4 . The center for hearing is Brodmann's area number 41 . (para 12-36)

31. In right-handed individuals, the left cerebral hemisphere is said to be dominant over the right cerebral hemisphere. For most individuals, an injury to the left cerebral hemisphere is more serious. (para 12-37)

32. Memory is the faculty which enables an individual to store and retrieve factual items such as sensations, impressions, facts, and ideas. All sensory inputs are collated against these stored items in order to arrive at an appropriate decision for action. (para 12-38a)

33. There are at least two types of memory--short-term memory and long-term memory.

Short-term memory is usually limited to about seven bits of information.

A portion of the cerebral cortex is thought to be important in transferring information from short-term memory to long-term memory. It is called the hippocampus. What is the effect on learning if the hippocampus is nonfunctional? The individual can learn nothing, but previous long-term memory remains intact. (para 12-38b)

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