construction of a model demonstrating neural pathways and reflex arcs

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I N N 0 V A T I 0 N S A N D I D E A S finger \ \ sensory receptor pain stimulus , cell body of sensory neuron FIG. 2. Example of a sensory neuron with its structures labeled. Tack is providing stimulus. This sensory neuron is receiving input from a sensory receptor in the finger. Sensory neuron is unique in that it only has an axon by which it transmits information. Information carried by this neuron continues in the body by way of a tract to reach the brain. functions. Efferent neurons cause an appropriate re- sponse to the sensory information received. An example of a motor neuron is shown in Fig. 3. Association neurons are also called interneurons. Interneurons are found between afferent (incoming sensory information) and efferent (outgoing motor information) neurons. Interneurons serve many functions and can have many connections. Interneurons are involved in information processing and are found only in the CNS. An example of an interneuron is shown in Fig. 4. dend rites of mot0 r neuron cell body of motor neuron motor neuron The site of transmission between two neurons is called a synapse. A synapse is an anatomic structure that involves two neurons and the space between them. The synaptic space is very small, and it can be seen best with an electron microscope. A synapse is different from synaptic transmission. Synaptic transmission is an event that occurs at the synapse; the synapse itself is a structure. A schematic of a synapse is shown in Fig. 5. 1) -+Name the three types of neurons. Are they afferent, efferent, or neither? axon hillock of motor neuron Nodes of Ranvier axon of motor \ target muscle FIG. 3. Motor neuron with structural components labeled. Motor neuron is shown with its target muscle. VOLUME 16 : NUMBER 1 - ADVANCES IN PHYSIOLOGY EDUCATION - DECEMBER 1996 s17
I N N 0 V A T I 0 N S A N D I D E A S syqapse I synapse :ov?E*> neuron neuron 2) *What are the components of the CNS? Central Nervous System FIG. 4. Example of an association neuron or interneuron. Note that the interneuron is placed between a sensory (afferent) neuron and a motor (efferent) neuron. Brain. The brain is made of neurons grouped together according to their function. For example, neurons dealing with vision are grouped together (sensory areas), and neurons moving specific muscle groups are placed together (motor areas). Although parts of the brain are sectioned off by function, areas of the brain are still interconnected so that the brain works as a whole unit. There are three main divisions of the brain: the forebrain (front brain), the midbrain (middle brain), and the hindbrain. These divisions are useful for locating specific structures of the brain (Table 1). In addition, Fig. 6, A and R, shows labeled structures of the brain that correspond to Table 1. neuron 1 synapse neuron 2 FIG. 5. Synapse between 2 neurons is shown. The cerebral cortex in the forebrain is the largest part of the human brain. “Knowing” or a “conscious awareness” of information is associated with the cerebral cortex. Sensory, motor, and association areas of the brain are found in the cerebral cortex. Associa- tion areas deal with higher brain functions and are often called ‘ ‘ silent’ ’ areas. They are involved in memory, reasoning, concentrating, problem solving, and many other complex functions. The cerebral cortex can be compared with the boss of a company who must be informed about everything going on. The boss makes most of the important decisions in the company, just as the cerebral cortex does in the body. The medulla in the hindbrain is anatomically the lowest part of the brain. It controls the subconscious activities of the body, which include heart rate, respiration, sleeping and waking, digestive functions, and electrolyte balance. Many of these functions are also controlled by a region of the forebrain called the hypothalamus. The hypothalamus is involved in body temperature control, water balance, and hor- monal control, along with other functions. TABLE 1 Structures of the brain Hindbrain Midbrain Forebrain H 1. Medulla M 1. Cerebral aqueduct F 1. Thalamus H2. Cerebellum F2. Hypothalamus H3. Pons F3. Cerebral cortex See Fig. 6 for schematic representation. VOLUME 16 : NUMBER 1 - ADVANCES IN PHYSIOLOGY EDUCATION - DECEMBER 1996 Sl8
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