Nervous System Flashcards
Need for Nervous system
1) Controls and harmonizes all voluntary muscular activities, and involuntary activities
2) Enables us to think recollect, reason and think
3) Allows us to perceive our surroundings through sense organs
Neuron
1) Structural and functional unit of the nervous system
2) Three main parts - cyton (cell body), dendrites and axon
Neuron - Cyton
1) Cell body of the neuron or perikaryon
2) Contains a well-defined nucleus surrounded by a granular cytoplasm
3) Has all the cell organelles except centrosome as the nerve cells have lost the ability to divide
Neuron - Dendrite
1) Branched cytoplasmic projections of the cell body
2) Conduct nerve impulses to the cyton
Neuron - Axon
1) Long process from the cell body
2) Varies from few millimetres in length to more than a metre
3) Surrounded by an insulating sheath called the myelin sheath
4) Some axons may have side branches called collaterals
5) Swollen bulb-like endings which store chemicals called neurotransmitters
6) Axon terminals closely placed near dendrites of one or more neurons but not connected
Neuron - myelin sheath
1) Outer white insulatory sheath covering the axon
2) Covered by an outermost thin shetah called the neurilemma
3) Shows gaps throughout the length which are called Nodes of Ranvier
Stimulus
agent or sudden change in the external or internal environment that results in a change in an organism or any of its body parts
Response
change in the organism resulting due to a stimulus
Impulse
a wave of electrical disturbance that sweeps over the nerve cells
Receptors
specialised epithelial cells which set up a wave of impulses on receiving stimulus
Effectors
muscles or glands which perform a specific action in response to the stimulus on receiving impulses from the brain or the spinal cord, such as contracting or secreting a substance
Synapse
Point of contact between the terminal branches of the axon of a neuron and the dendrite of another neuron separated by a fine gap
Neurotransmitter
A chemical substance released by the terminal ending of an axon at the synapse between two neurons which sets in motion an impulse in the dendrite of the adjacent neuron
E.g. - acetylcholine, dopamine, adrenaline
Transmission of Nerve impulses
1) Conduction of nerve impulses
At the synapse between two neurons a chemical neurotransmitter is released
2) It sets a new impulse in the dendrites of the adjacent neuron
3) The neurotransmitter is soon broken down by an enzyme to make the synapse ready for the next transmission
