The synapse, as coined by Charles Sherrington in 1897, is one of the most influential discoveries in neurophysiology. Synapses are the junctions between a neuron’s axon and another neuron’s cell membrane, transmitting information about an action potential chemically or electrically. They are thus essential to neuronal function. The discovery occurred in part due to nineteenth century technological advances, such as the microtome, improved histological techniques, and the compound light microscope. Unfortunately, investigation into nervous system physiology at the time was divisive. Most notable was the debate between Golgi and Cajal on whether the nervous system was composed of discrete cells. Sherrington’s work on the synapse contributed to …show more content…
In the 1870’s, Camillo Golgi and Joseph von Gerlach became the first to propose the idea that the central nervous system consisted of a single continuous network. This implied that action potentials spread directly into adjacent neurons. Sherrington’s work challenged this view, supporting the notion, championed by Cajal, that individual cells made up the nervous system. Throughout the 1890’s, Sherrington studied spinal reflexes in animals by stimulating muscle and skin afferents. Owing to these experiments, Sherrington concluded that action potential conduction along axons and their transmission across axon terminals occurred via separate …show more content…
Through his research, Sherrington corroborated the findings of van Gehuchten in 1891, Lenhossek in 1893, and Cajal in 1895, whereby nerve impulses travelled in a single direction. Sherrington attributed the one-way conduction along the reflex arc to a “valve-like behaviour of the synapse”, later arguing that electrical conduction was unable to cross the synapse. This interpretation deviated from Cajal’s concept of ‘dynamic polarization’, or the one-way depolarization from dendrite to axon. Both Exner in 1894 and Sherrington in 1900 found delays in the reflex arc that conduction alone could not account for. Sherrington credited this delay to transmission across the synapse. Sherrington also differentiated between excitatory and inhibitory synapses via experiments on reciprocal inhibition in the reflex arc. Inhibitory transmission between neurons was hard to reconcile with reticularist theories, since a continuous network of action potential conduction could not produce inhibition. Sherrington’s conclusions contradicted the reticularist notions of neuron anastomoses and continuous action potential transmission along neurofibrils extending between neurons. Still, the mechanism of synaptic transmission remained
In the beginning phases of muscle contraction, a “cocked” motor neuron in the spinal cord is activated to form a neuromuscular junction with each muscle fiber when it begins branching out to each cell. An action potential is passed down the nerve, releasing calcium, which simultaneously stimulates the release of acetylcholine onto the sarcolemma. As long as calcium and ATP are present, the contraction will continue. Acetylcholine then initiates the resting potential’s change under the motor end plate, stimulates the action potential, and passes along both directions on the surface of the muscle fiber. Sodium ions rush into the cell through the open channels to depolarize the sarcolemma. The depolarization spreads. The potassium channels open while the sodium channels close off, which repolarizes the entire cell. The action potential is dispersed throughout the cell through the transverse tubule, causing the sarcoplasmic reticulum to release
Stone, J. (1972). Morphology and physiology of the geniculocortical synapse in the cat: The question of parallel input to the striate cortex. Investigative Ophthalmology & Visual Science, 11, 338-46.
Briefly explain the process of neurotransmission. Neurotransmission starts with the neuron, the most important part of the central nervous system. A neuron contains a cell body, axon, and dendrites. When a neuron receives an electrical impulse, the impulse travels away from the cell body down the axon. The axon breaks off into axon terminals. At the axon terminals, the electrical impulse creates a neurotransmitter. The neurotransmitter is released into the synapse, a space between two neurons. If the neurotransmitter tries to stimulate a response of another neuron, it is an excitatory neurotransmitter. If the neurotransmitter does not stimulate a response of another neuron it is an inhibitory neurotransmitter. If a response is generated, the second neuron or postsynaptic neuron will receive an action potential at the site of the dendrite and the communication process will continue on. If a response is not generated, neurotransmitters left in the synapse will be absorbed by the first neuron or presynaptic neuron, a process known as reuptake. Neurotransmitters control our body functions, emotions, and
Rowland, Lewis P. (ed.): Merritt's Textbook of Neurology, eighth edition. Lea and Febiger. Philadelphia, 1959, pp. 630--631.
The general point behind the homunculi-head introduces consideration to the possibility of brain functions being done by parts which could not together be conscious. Functionalism requires only similar machine instructions which serve out a set of outputs given a set of inputs. Block’s counter arguments shows such an account of
Hicks, Brain. The Holdouts. Smithsonian 41.11 (2011): 50-60. Academic Search Premier. Web. 8 Nov. 2013
Sperry, R. W. (1963, October 15). Chemoaffinity in the Orderly Growth of Nerve Fiber Patterns and Connection. Natioanl Academy of Science, 50(4), 703-710.
Action potentials are started at one end of the node, flow passively through the myelinated axon, and pop out the other side to jump to the next node. This jumping of action potentials is called saltatory.
Kandel, E. R., J. H. Schwarz, and T. M. Jessel. Principles of Neural Science. 3rd ed. Elsevier. New York: 1991.
Biology The brain consists of both neurons and glia cells. The neurons, which are cells housed in a cell body called a Soma, have branches which extend from them, referred to as dendrites. From these dendrites extend axons which send and receive impulses, ending at junction points called synapses. It is at these synapse points that the transfer of information takes place. At the heart of neuroplasticity is the idea of synaptic pruning.
...ical impulse, repeating the mechanism described above. The neurons received signal, they crumble up the information passed it down until they get to the last one.
The neuron plays an important role in the occupation of the brain (Rollin Koscis). A neuron is...
Dendrites are located on either one or both ends of a cell.The peripheral nervous system then takes the sensory information from the outside and sends the messages by virtue of neurotransmitters. Neurotransmitters are chemicals that relay signals through the neural pathways of the spinal cord. The neurotransmitter chemicals are held by tiny membranous sacs located in the synaptic terminals. Synaptic terminals are located at the ends of nerve cells. The release of neurotransmitters from their sacs is stimulated once the electrical nerve impulse has finished travelling along a neuron and reaches the synaptic terminal. Afterward, neurotransmitters travel across synapses thus stimulating the production of an electrical charge that carries the nerve impulse onward. Synapses are junctions between neighboring neurons. This procedure is reiterated until either muscle movement occurs or the brain picks up on a sensory reaction. During this process, messages are being transmitted from one part of the body onto the next. The peripheral and central nervous system are two crucial subdivisions of the nervous system. The brain and spinal cord make up the central nervous
Synaptic transmission is the process of the communication of neurons. Communication between neurons and communication between neuron and muscle occurs at a specialized junction called synapses. The most common type of synapse is the chemical synapse. Synaptic transmission begins when the nerve impulse or action potential reaches the presynaptic axon terminal. The action potential causes depolarization of the presynaptic membrane and it will initiate the sequence of events leading to release the neurotransmitter and then, the neurotransmitter attaches to the receptor at the postsynaptic membrane and it will lead to the activation of the postsynaptic membrane and continue to send the impulse to other neurons or sending the signal to the muscle for contraction (Breedlove, Watson, & Rosenzweig, 2012; Barnes, 2013).
[online] Available at: http://www.livescience.com/22665-nervous system.html [Accessed: 1 Oct 2013]. Reece, J. 2012. The. Campbell biology. San Francisco, CA. -.