Nervous System: Course Notes Essay

1. Explain both the anatomical and functional divisions of the nervous system. Include the subdivisions of each. The nervous system’s function is to monitor stimuli occurring inside and outside the body, process and interpret this sensory input, and respond by activating effector organs. It consists of the Central Nervous System (brain and spinal cord), and the Peripheral Nervous System (neurons that carry messages to and from the CNS).

2. Describe the composition and function of the cell body. How are xons and dendrites alike? How do they (structurally and functionally) differ? The nerve cell body contains the nucleus, rough ER (Nissl bodies), and cytoplasm. It is the major biosynthetic center and the main body for the outgrowth of neuronal processes. Axons and Dendrites are both arm-like extensions from the cell body. Dendrites are short and extremely branched processes that function as the input regions of neurons. Axons are long branched processes that contain end bulbs, these bulbs secrete neurotransmitters, so axons function as the output.

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3. What is myelin? How does the myelination process differ in the CNS and PNS? Myelin sheath is a fatty covering around long axons that protect it and help increase the speed of nerve impulse transmission. In the CNS the oligodendrocytes form the myelin sheath, while in the PNS Schwann cells form it. Schwann cells create gaps, known as nodes of Ranvier, while oligodendrocytes completely cover the axon.

4. Since at any moment a neuron is likely to have thousands of neurons releasing neurotransmitters at its surface, how is neuronal activity (to fire or not to fire) determined? Once a stimuli has reached a certain threshold the neuron will fire, this is achieved through either graded potential signals or action potential signals. 5. Since all AP’s generated by a given nerve fiber have the same magnitude, how does the CNS know whether a stimulus is strong or weak? The CNS determines stimulus intensity by the frequency of impulse transmissions.

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