Control and Coordination in Humans
There are two types of coordination of activities in humans. These are:
In human beings, nervous system and endocrine system work together to control and coordinate all our activities such as our physical actions, our thinking processes and our emotional behavior.
Human Nervous System
Nervous system is composed of two main components:
Central nervous system(CNS): It includes brain and spinal cord
Peripheral system (PNS): It includes all the nerves arise from brain (cranial nerves) and spinal cord (spinal nerves).These nerves are present outside the CNS and connect brain and spinal cord to all parts of the body.
STRUCTURE OF A NEURON
Nervous system is made of special cells called neurons. The neurons carry messages in the form of electrical impulses or nerve impulses. A neuron has three components:
Cell body or cyton
Cell body or cyton
1. The cell body contains a nucleus and cytoplasm. In the cytoplasm are embedded different cell organelles like mitochondria, Golgi apparatus, endoplasmic reticulum etc. 2.From the cell body extend out two kinds of protoplasmic extensions the cell body – dendrites and axons.
Dendrites are short and branched processes. They carry the impulse towards the cell body.
1. It is a long process, may be several centimeters long. It conducts nerve impulses away from the cell body.
2. The axon has an insulating and protective sheath of myelin around it.
Neurons are of three types:
Sensory neurons: They carry nerve impulses from receptors to the central nervous system. They carry stimulus from receptors.
Receptors → CNS
Motor neurons: They take nerve impulses from CNS to effector organs that may be a muscle or gland.
CNS → Effector
Interneuron or relay neurons: They are found only in CNS and make links between sensory and motor neurons.
3. There is no physical connection between the neurons at synapse and so the impulse has to pass through the synapse to be passed on to other neurons.
How do we detect that we are touching a hot object?
All information from our environment is detected by the tips of dendrite of nerve cells. These receptors are usually located in our sense organs, such as the inner ear, the nose, the tongue, the skin and the eyes.
1. Hot object is a stimulus. When a stimulus acts on a receptor, a chemical reaction is set off that creates electrical impulse.
2.This impulse travels from the dendrite to the cell body and then travel along its axon.
3.At the end of axon synapse is present; a microscopic gap between two neurons, thus electrical impulse can not directly pass between two neurons.
4. At the end of axon, the releases small amount of a chemical substance called acetylcholine into the synapse. This chemical substance starts a similar electric impulse in the dendrite of the next neuron. As acetylcholine transmits impulse of one neuron to another so it is called as neurotransmitter.
5. In this way it can be transmitted to a third neuron and so on. Finally reaches to the brain. The motor neurons bring message from the brain in the form of electrical impulse to the effector organs like muscles and glands.