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U3-Neurons, Synapses
| Question | Answer |
|---|---|
| Neurons/Nerve cells | conduct electrical signals/action potentials. Billions in brain alone; Extreme longevity-can live as long as you live; mature ones do not divide; some stem cells capable; require continuous and abundant supplies of oxygen and glucose |
| Major structural components & activities of neurons | cell body (soma), dendrites, axon |
| Cell body (soma) | enlarged part of neuron; contains nucleus |
| Dendrites | numerous, highly branched processes (extensions) of a neuron that function as receptive sites; provide enlarged surface area for receiving signals from other neurons, then conduct those signals toward the cell body |
| Axon | singular process from cell body; transmits impulses away from the cell body of neuron to which it belongs and toward dendrites or cell body of another neuron, or toward muscle cell or gland cell. Varies in length. |
| Nerve fiber | long axon |
| Structural support of axons | protein-composed microtubules |
| Axonal transport | with the aid of microtubules, the transport of beneficial substances to and from the cell body in a neuron. Can also be used by viruses-namely the rabies virus and herpes zoster (chicken pox and shingles). |
| Axon terminals | axons split at their ends into numerous branches that end as knobs. When nerve impulses reach the end of these knobs, they stimulate the release of chemicals called neurotransmitters (NTs) from synaptic vesicles that are located within the terminals. |
| Neurotransmitters | chemicals released from synaptic vesicles of axon terminals that either excite or inhibit the neuron, muscle cell, or gland cell to which the axon terminals are adjacent. |
| Structure and function of a Synapse | Neuron that transmits impulses toward the synapse, and to which the axon terminals belong, is the presynaptic neuron; second neuron on other side of the synaptic cleft, and which is controlled by the first neuron, is the postsynaptic neuron. |
| Synapse | the junction at which the axon terminals of a neuron meet with another neuron, or a muscle or a gland cell. |
| Synaptic cleft | the very small gap between an axon terminal and adjacent cell |
| Presynaptic neuron | the neuron that transmits impulses TOWARD the synapse when two neurons are involved in a synapse and the neuron to which the axon terminals belong. It controls the postsynaptic neuron |
| Postsynaptic neuron | the second neuron on the other side of the synaptic cleft which is controlled by the first neuron |
| Myelin sheath | a fatty, white, lipoprotein wrapping of many nerve fibers/axons; insulates axons and thereby increases impulse speed conduction along the length of the cellular extension. |
| nodes of Ranvier | gaps in between the Schwann cells of an axon |
| What myelinates nerve fibers in the PNS | glial cells called Schwann cells these glial cells wrap around axons in a fashion such that two coverings are actually formed around many nerve fibers in the PNS – an inner wrapping called the myelin sheath and the outer wrapping called the neurilemma |
| Oligodedrocytes | glial cells that form myelin sheaths around nerve fibers in the CNS, but they wrap around axons differently than Schwann cells, and they do not form a neurilemma. |
| How does the amount of myelin effect the speed of axon conduction? | Not all axons are myelinated to the same degree (some are not myelinated at all). But among those that do have myelin sheaths, the more myelin, the faster an axon conducts impulses. |
| Multiple Sclerosis | autoimmune disease that involves the gradual progressive detruction of myelin sheaths that surround axons in the CNS. As this happens, impulses are not as efficiently transmitted, and subsequently the affected person may exhibit sensory problems and/or mu |
| Axon Regeneration | b/c mature neurons have no appreciable capacity for mitosis, there is no effective replacement of dead or damaged neurons and neural injuries tend to cause permanent dysfunction. However, some regeneration of axons in the PNS is possible after nerve inju |
| Structural classification | based upon the number of processes (dendrites and axons) that extend directly from the cell body. There are three structural types of neurons-unipoloar, bipolar, multipolar. Multipolar neurons have many dendrites and one axon. Structurally over 99% of |
| Functional classification | based on the direction nerve impulses travel through them relative to the CNS. Classes are Sensory/Afferent neurons, motor/efferent neurons, and interneurons/association neurons. |
| Sensory/afferent neurons | transmit impulses toward the CNS from sensory receptors |
| Motor/efferent neurons | convey impulses away from the CNS to effector organs (muscles and glands); motor neurons form synapses with muscle cells and gland cells, thereby enabling them to promote muscle contraction or glandular secretion. |
| Interneurons/association neurons | lie between sensory and motor neurons and are only located in the CNS. Immensely complex linkages formed between the billions of interneurons are largely responsible for the astonishing complexity of the nervous system, especially that of the human brain |
Created by:
mbtrimm
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