REFLEX ACTION AND REFLEX ARC

REFLEX ACTION

The involuntary functioning or movement of any organ or body part in response to a particular stimulus which occurs in very short duration of time(within a second usually) and does not involve will or any thinking of brain is called reflex action.

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REFLEX ARC

Reflex arc is the path followed by nerve impulses to produce the reflex action. It usually includes receptor organ, afferent nerve, nerve center, efferent nerve, effector organ or a muscle.

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DO REFLEX ACTIONS INVOLVE BRAIN???

 Reflex actions are sudden responses, which do not involve any thinking. For example, 

when we touch a hot object, we withdraw our hand immediately without thinking as 

thinking may take time which would be enough to get us burnt. The sensory nerves that detect the heat are connected to the nerves that move the muscles of the hand. Such a connection of detecting the signal from the nerves (input) and responding to it quickly (output) is called a reflex arc. The reflex arcs−connections present between the input and output nerves − meet in a bundle in the spinal cord. Reflex arcs are formed in the spinal cord and the information (input) reaches the brain. 

he brain is only aware of the signal and the response that has taken place. However, 

the brain has no role to play in the creation of the response.

DOES REFLEX ARC INVOLVE THE BRAIN???

 No,the brain  is only made aware of your reflex travels after the incident has occured, as the the thinking process would slow down  impulse and increase the risk of danger.The incident is stored surrounded by the brain afterwards for memory purposes and to prevent happening within the future.Reflex arcs materialize at the spinal column level, so don't involve the brain. 

SIGNIFICANCE OF SYNAPSE B/W THE NEURONS..

Synapse- A specialized junction where transmission of information takes place between a nerve fibre and another nerve cell, or between a nerve fibre and a muscle or gland cell. The term was introduced at the end of the nineteenth century by the British neurophysiologist Charles Sherrington, who argued, on the basis of his own observations of reflex responses and the studies of the great Spanish anatomist, Ramón y Cajal, that a special form of transmission takes place at the contact between one cell and the next.

Synapses serve as one-way communication devices, transmitting information in one direction only, from the fibre ending to the next cell. They come in two varieties, known as chemical and electrical, according to the mechanism by which the signal is transmitted from the presynaptic to the postsynaptic cell. 

At electrical synapses, which are relatively rare in vertebrates, the membranes of the two cells are in tight contact, producing electrical coupling, which enables a nerve impulse arriving at the presynaptic nerve ending to pass swiftly and reliably to the next cell. 

                                                 

Chemical synapses are more complex, because the presynaptic and postsynaptic cells are physically separated by a minute gap (the synaptic cleft), which prevents simple electrical 

transmission of the action potential to the postsynaptic cell. Instead, transmission is accomplished by the release of a chemical neurotransmitter substance from the presynaptic fibre.

IN A CHEMICAL SYNAPSE-

The cytoplasm of the presynaptic nerve terminal  is packed full of small vesicles, each containing a few thousand molecules of neurotransmitter. When an action potential arrives in the terminal it stimulates the opening of calcium channels in the nerve ending. As a consequence, calcium ions flood into the cell and cause the synaptic vesicles to release their contents into the synaptic cleft. The neurotransmitter molecules that are liberated diffuse across the cleft or gap  and interact with specialized protein receptor molecules in the postsynaptic neuron. The molecular structure of the neurotransmitter and its receptor are matched, so that they fit one another like a lock and key. At nerve–muscle synapses, and in many nerve–nerve synapses, the receptors have a double function, since they also serve as ion channels. Binding of a neurotransmitter molecule produces a change in the three-dimensional shape of the receptor that opens a tiny intrinsic pore in the protein.