The Nervous System
The nervous system detects stimuli such as light, sound, pressure, temperature, or chemicals and coordinates the body's response to such stimuli.
The human nervous system consists of the central nervous system (CNS) and the peripheral nervous system (PNS).
- The central nervous system includes the brain and the spinal cord.
- The peripheral nervous system is made up of nerves that carry electrical impulses between the CNS and all parts of the body.
Neuron
A neuron is a nerve cell that transmits electrical impulses. A neuron receives electrical impulses through the dendrite and passes on the impulse to other neurons through the axon. The direction of electrical impulse is always dendrite → axon in one neuron. After the impulse reaches the axon of one neuron, it is transmitted to the dendrite of another neuron.
When one neuron transmits impulse to another neuron, the two neurons do not actually touch each other. The small gap between the two neurons is called the synapse.
Since electrical impulses cannot be transmitted through the synapse, impulses are transmitted chemically through chemicals called neurotransmitters.
- When electrical impulse reaches the end of the axon, neurotransmitters are released to the synapse.
- The neurotransmitter diffuses across the synapse and binds to receptors on the dendrite of the second neuron.
- This stimulates the electrical transmission of impulse down the second neuron.
Pathway for Nerve Impulse
- A receptor detects a change in the environment, or a stimulus.
- The receptor changes the stimuli into an electrical impulse.
- The impulse is transmitted to the central nervous system through sensory neurons.
- Relay neurons transmit impulses within the central nervous system, where decision-making happens.
- When the appropriate response is chosen, motor neurons transmit the impulse from the central nervous system to the effector.
- Effectors are parts of body (such as muscles or glands) that can produce response to a stimulus.
Reflex Arc
Sometimes, the body needs to react quickly to some dangerous stimuli, such as touching a sharp object. There is no time for the impulse to go through the conscious part of the brain. Impulse will be processed in the spinal cord, instead of the brain, and sent to motor neuron. This kind of pathway is called the reflex arc.
While the reflex is being carried out, the brain will receive the impulse. The conscious analysis of the stimulus will only happen after the reflex action.