Stimulus.
The senses that evoke responses in organisms are called stimuli. There are two types,
External stimuli : Sound, touch, heat, chemicals, pressure, cold, radiations.
Internal stimuli : Hunger, touch, infection, pressure variation, thirst, exhaust.
Function of nervous system is to generate and coordinate responses according to external and internal changes.
The following are the parts included in our nervous system
Neurons are the structural and functional units of the nervous system. They consist of a cell body, dendrites, and axon.
Structure of a model neuron.
A neuron has mainly the following parts
The senses that evoke responses in organisms are called stimuli. There are two types,
External stimuli : Sound, touch, heat, chemicals, pressure, cold, radiations.
Internal stimuli : Hunger, touch, infection, pressure variation, thirst, exhaust.
Function of nervous system is to generate and coordinate responses according to external and internal changes.
The following are the parts included in our nervous system
- Brain
- Spinal cord
- Nerves
- Receptors
Neurons are the structural and functional units of the nervous system. They consist of a cell body, dendrites, and axon.
Structure of a model neuron.
A neuron has mainly the following parts
- Cyton / cell body
- Dendrite : Branches of Dendron. Part that receives impulses from adjacent neuron.
- Dendron : Short filament from the cell body. Carries impulses from dendrites to the cell body.
- Schwann cell : Encircles the axon.
- Axon : Longest filament from the cell body. Carries impulses from the cell body to outside.
- Axonite : Branches of axon. Carries impulses to the synaptic knob.
- Synaptic knob : Tip of axonite. Secretes neurotransmitter.
The protective covering of nerve fibres is Myelin sheath.
Myelin sheath's. main functions are
- Provide nutrients and oxygen to the axon.
- Accelerate impulses.
- Act as an electric insulator.
- Protects the axon from external shocks.
- Gives white appearance ('white matter') to the neural parts.
The part of nerve, where myelinated neurons are present in abundance,is called as the white matter.
The part of nerve where the cell bodies and nonmyelinated neurons are present, is called as the grey matter.
These nerve cell and its functions:
- Dendrite : Receives impulses
- Dendron :Carries impulses from dendrite to the cell body
- Cyton / Cellbody :Passes impulses to the axon.
- Axon :Carries impulses from the cell body to outside.
- Schwann cells : Protects the axon and increases the speed of impulse
- Axonite : Carries impulses to the synaptic knob
- Synaptic knob : Secretes neurotransmitter
Swollen ends of axon is Synaptic knobs, and this Secretes
neurotransmitter.. When electric impulses from the axon reach the synaptic knob,
certain chemical substances are secreted from there to the synaptic cleft. These chemical
substances are called neurotransmitters.
Acetylcholine and dopamine are some examples of
neurotransmitters.
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