The Neuron

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Neuron

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A nerve cell. The structural and functional unit of the Nervous System.

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Afferent Neurons

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Sensory. Nerve cells that send impulses from receptors to the central nervous system.

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Efferent Neurons

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Motor. Nerve cells that send impulses from the Central Nervous System to skeletal muscles, cardiac muscles, smooth muscles or glands.

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What are the Functional types of Neurons of the Periferal Nervous System?

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Afferent and Efferent

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What are the types of Neurons of the Central Nervous System?

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Interneurons, Internuncial Neurons, Association Neurons, and Commissural Neurons.

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Interneurons

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Nerve cells that are located in the spinal cord and are involved in a reflex arc. These nerve cells act as a bridge within the spinal cord to carry impulses from sensory neurons directly to motor neurons within the PNS.

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Internuncial Neurons

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Nerve cells that communicate between two other neurons conducting impulses that are ascending or descending in the spinal cord.

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Association Neurons

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Nerve cells that carry impulses between the Gyri (ridges) within the same cerebral hemisphere (same side of the cerebrum of the brain).

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Commissural Neurons

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Nerve cells that carry impulses from the Gyri in one cerebral hemisphere to the corresponding gyri in the opposite cerebral hemisphere.

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Multipolar Neuron

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Several dendrites and one axon.

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Bipolar Neuron

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One dendrite and one axon

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Unipolar Neuron

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Axon and dendrite fuse into a single process in the cell body then divides into two branches, one functioning as a dendrite and one functioning as an axon.

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What are the anatomical components of a neuron?

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Cell body, Dendrite, Axon.

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Neuron Cell Body

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Contains a nucleus, nucleolus, and other typical organelles. Inloved in metabolism, growth and repair of Neuron.

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Dendrite

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Cytoplasmic extension which is highly branched. Conducts impulses toward the cell body. Peripheral sensory neurons have receptors at the tips of the dendrites. May be myelinated or unmyelinated.

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Axon

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Cytoplasmic extension which may be as long as a meter in length or as small as a few millimeters. Conducts impulses away from cell body. Surrounded by a selectively semi-permeable membrane (axolemma). May be myelinated or unmyelinated. Branches, called axon collaterals are found near the end of the axon. Terminates into axon terminals.

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Axon Terminals

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Contains synaptic vesicles that store chemicals called neurotransmitters. Neurotransmitters are released from the axon terminal and migrate to the neiboring cells (muscle, fiber, gland, or another neuron, altering its activity.

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What cells produce Myelin?

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Produced by Neuroglia Cells. Schwann Cells in the PNS and Oligodendrocytes in the CNS.

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Myelin Sheath

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Wraps directly around the neural process. The outer portion is termed the Neurilemmal Sheath (only in PNS). Plays a role in nutrition of the axon and regeneration of an injured axon. Allows nerve impulses to conduct down the process faster.

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White Matter

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Myelinated processes of many neurons which run together and give a white appearance upon dissection.

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Grey Matter

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Non-myelinated neuron cell bodies which "clump" together and give a gray appearance upon dissection.

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Nodes of Ranvier

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Gap where the myelin sheath is interrupted. The axon/dendrite is exposed in this nodal region.

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Salutatory Conduction

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Impulses utilizing Nodes of Ranvier to speed the transmission. The impulse "hops" from node to node which is quicker than transmitting down the entire length of the axion.

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Synapse

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The junction between an axon terminal of one neuron with a muscle fiber, gland, or dendrite, axon or cell body of another neuron. The site where transmission of an impulse (action potential) occurs.

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What are the components of a Synapse?

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Presynaptic Terminal, Postsynaptic Terminal, Synaptic Cleft, Synaptic Vesicles, and Mitochondria.

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Presynaptic Terminal

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Distal end of the axon terminal, characterized by a bulb-like structure, of the neuron conducting the impulse to the next cell. Neurotransmitters are released from this location to activate the next cell.

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Postsynaptic Terminal

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The location on the cell receiving the impulse. This can be on the dendrites, cell body, or axon of a neuron, or a gland or muscle fiber. Receptors for the neurotransmitters are located on the membrane surface.

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Synaptic Cleft

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Region between the presynaptic terminal and the postsynaptic terminal. The neurotransmitters must cross this region in order to transfer the impulse (action potential) to the postsynaptic terminal.

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Synaptic Vesicles

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Vesicles (containers) containing neurotransmitters which are located in the presynaptic terminal.

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Mitochondria

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Supplies the necessary energy for migration of the synaptic veicles to the edge of the presynaptic terminal's axolemma and release the neurotransmitter from the synaptic vesicles into the synaptic cleft.

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What are the types of Synapses?

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Axodendritic, Axosomatic, Axoaxonic, Neuromuscular, Neuroglandular

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Axodendritic Synapses

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Junction between an axon terminal of one neuron with a dendrite of another neuron

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Axosomatic Synapses

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Junction between an axon terminal of one neuron and a cell body (soma) of another neuron.

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Axoaxonic Synapses

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Junction between an axon terminal of one neuron and an axon of another terminal.

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Neuromuscular Synapses

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Junction between an axon terminal of one neuron (efferent neuron) and a muscle fiber.

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Neuroglandular Synapses

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Junction between an axon terminal of a neuron and a gland.

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Sensory Receptors

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Distal end of a dendrite of a peripheral afferent neuron.

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What are the functions of Sensory Receptors?

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Structures located in various parts of the body that send information from the external and internal enviroment to the spinal cord and brain for processing. The sensory receptors convert a stimulus into an electrical impulse or action potential.

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What are the types of Somatic Sensory Receptors?

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Free Nerve Ending, Merkel's Tactile Disks, Meissner's Corpuscle, Pacinian Corpuscle, Golgi Tendon Organ, and Muscle Spindle.

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Free Nerve Ending

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Pain, temperature and crude touch. Epidermis/Dermis line

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Merkel's Tactile Disks

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Discrimitive touch. Epidermis

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Meissner's Corpuscle

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Simple touch. Epidermis/Dermis line

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Pacinian Corpuscle

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Pressure. Dermis (subpapillary plexus)

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Golgi Tendon Organ

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(Neuromuscular Spindle) responds to tension of the skeletal muscle fibers.

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Muscle Spindle

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(Neuromuscular Spindle) Responds to stretching of a muscle