Nervous Tissue & Nervous System Overview
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friedpicklechips on October 30, 2011
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Basic Nervous System Notes
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39 terms
Terms | Definitions |
|---|---|
 Types of Neurons | Sensory (Afferent) Interneurons (Association Neurons) Motor (Efferent) Reflex Ark |
| Sensory Neurons | aka afferent neurons. Conduct impulses toward the CNS. Sensory receptors respond to various stimuli. |
| Interneurons | aka association neurons. Entirely within the CNS. Conduct impulses from sensory neurons to motor neurons. Interneurons have an integrative function. |
| Motor Neurons | aka efferent neurons. Conduct impulses away from the CNS and to the effectors (muscles or glands). |
| Reflex Arc | An example of the arrangement of sensory neurons, interneurons, and motor neurons. |
| Functions of Neurons | Excitability (Irritability) Conductivity Secretion of Neurotransmitters |
| Structure of Neurons | Soma Axon Dendrites Myelin Sheath |
| Soma | Cell body or Perikaryon |
| Axon | Conducts nerve impulses away from the soma; there is never more than on axon per neuron. (Some have none) |
| Dendrites | Receive impulses from other neurons |
| Myelin Sheath | Insulating layer (mostly lipid) around nerve fibers, formed by neuroglia cells. Not all nerve fibers are myelinated. Those that are myelinated comprise the white matter, unmyelinated fibers comprise the gray matter. |
| Classes of Neurons | Multipolar Neurons Bipolar Neurons Unipolar Neurons Anaxonic Neurons |
| Multipolar Neurons | One axon, multiple dendrites; most common type. |
| Bipolar Neurons | One axon, one dendrite |
| Unipolar Neurons | Single axon branches a short distance from the soma, on branch (peripheral fiber) carries impulse from source of sensation, the other (central fiber) carries impulse into the spinal cord. |
| Anaxonic Neurons | The have no axon, multiple dendrites. Examples in retina and brain. |
| Types of Neuroglia | Oligodendrocytes Protoplasmic Astrocytes Fibrous Astrocytes Ependymal Cells Microglia Schwann Cells Satellite Cells |
| Neuroglia | These cells are not neurons, but perform various supportive roles in the nervous system. |
| Oligodendrocytes | Form myelin sheath in CNS |
| Protoplasmic Astrocytes | Cover brain surfaces Formation of blood-brain barrier Remove neurotransmitters and potassium ions from intercellular fluid Regulate composition of cerebrospinal fluid |
| Fibrous Astrocytes | Form supportive network in CNS Replace damaged nerve tissue (scar tissue) |
| Ependymal Cells | Line cavities of brain and spinal cord Produce and circulate CSF |
| Microglia | Perform phagocytosis |
| Schwann Cells | Form myelin sheath in peripheral nervous sytem |
| Satellite Cells | Surround somas of neurons in ganglia |
| Initiation and Conduction of Nerve Impulses | Resting membrane potential --> Action potential |
| Resting Membrane Potential | Interior of nerve cell is negatively charged, relative to extracellular fluid. Cell is said to be polarized. Maintence of this state requires expenditure of energy (ATP). |
| Action Potential | 1) Na+ gate opens, allowing influx of sodium ions. K+ gate begins to open. Depolarization begins. 2) Na+ gate closes. K+ gate opens fully. K+ ions leave cell, bringing about beginning of repolarization. 3) Both Na+ gate and K+ gate closed, repolarization complete. |
| Depolarization | A nerve impulse travels along a nerve impulse as a wave of depolarization. |
| Refractory Period | For a short time after action potential, it is impossible to stimulate that region of a neuron to fire again. |
| Nodes of Ranvier | In myelinated nerve fibers, ions can be exchanged with the extracellular fluid only at the Nodes of Ranvier. Impulse appears to jump (saltate) from node to node. |
| All or Nothing Law | Action Potential follows an All or Nothing Law, are nondecremental (do not lose strength over a distance), and are irreversible. |
| Synaptic Transmission | Although nerve impulses are conducted electrically along a nerve fiber, a 20-40 nm gap (synaptic cleft) exists between neurons. This necessitates (in most cases) chemical communication between neurons. |
| Synaptic Structures | Synaptic Knob - pre synaptic neruon Synaptic Vesicles - (filled with neurotransmitters) in the pre-synaptic neuron Neurotransmitter Receptors - in the post-synaptic membrane. |
| Types of Chemical Synapses | Ionotropic Metabotropic |
| Ionotropic Synapses | Nerve Impulse reaches synaptic knob and causes Ca2+ gates to open. This triggers exocytosis of synaptic vesicles which allows diffusion of neurotransmitter into the synaptic cleft. These bind receptors in the post-synaptic membrane which open and allow passage of Na+ and K+ ions, producing post-synaptic potential. |
| Metabotropic Synapses | Binding of neurotrasmitter by receptors in post-synaptic cell activates cyclic AMP production. This can turn certain metabolic pathways on or off, activate genetic transcription, and open ion gates in membrane. |
| Classes of Neurotransmitters | Excitatory Inhibitatory Acetylcholine acts at the neuromuscular junction |
| Cessation of Signal @ the Synapse | The "turning off" of th esignal at the syapse is just as important as the stimulation of the post-synaptic cell. Accomplished by: 1) Reuptake of the neurotransmitter by the pre-synaptic neuron. 2) Diffusion of the neurotransmitter into the extracellular fluid, where astrocytes absorb it. 3) Degradation of the neurotransmitter in the synaptic cleft (the enzyme acetylcholinesterase breaks acetylcholine down into acetate and choline, which have no effect on the post-synaptic cell. Certain pesticides and nerve gases are acetylcholinesterase inhibitors). |
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