Nerve impulses are transmitted between areas of the body via a network of nerve cells and fibres. This is called the Nervous system.
When you touch a hot object, you sense that it is hot and suddenly pull off your hands. Have you thought about how you recognise that the object is hot? How you can act so quickly? We will learn how humans respond to various stimuli around us.
All cells in our body have the ability to respond to stimuli. But, the cells of our nervous tissue are specialised for being stimulated and then transmitting this stimulus very fast from one part to another part in the body. Our brain, spinal cord, and nerves are composed of nervous tissue. The cells of nervous tissue are called Nerve cells or Neurons.
Structure of neuron
- Cell body– It consists of cytoplasm and a nucleus.
- Dendrite– From the cell body, short thin hair-like parts arise in the form of branches. These are called dendrites. They help in detecting the information from the environment.
- Axon– A long cylindrical structure emerging from the cell body. The information detected by the dendrites travels through the axon and reaches the next nerve and finally to the brain.
- Nerve ending– The ending of the axon is branched and they help in neurotransmission.
Fig: Structure of Neuron
Neurotransmission
The traveling of signals to the brain through the nerve cells is called Neurotransmission. These signals that are transmitted along the nerve fibre are known as an impulse. We can move our muscles when we want because of nerve impulses. The changes in the environment are detected by the dendrites in the form of information. They are present in the sense organs like the inner ear, the nose, the tongue, and so on. The gustatory receptors will detect taste while the olfactory receptors will detect the smell. The information acquired by the dendritic tip of a nerve cell triggers a chemical reaction which in turn creates an electric impulse. The electric impulse travels from the dendrite to the cell body and then along the axon to reach the nerve endings. Here the electric impulse sets off the release of chemicals.
The gap between two nerve cells is called the synapse. The chemicals pass through these synapses and start a similar electric impulse in the dendrite of the next neuron. This is how the nervous impulses travel in our bodies.
Reflex Action
It is a spontaneous, automatic, and sudden action in response to something in the environment. As we have discussed earlier, we do these reflex actions in our day-to-day life knowingly or unknowingly.
Example- Our mouth gets watery when we see a delicious dish.
Reflex arc
It is the pathway of the nerve involved in a reflex action. Reflex arc involves
- Receptors– They receive a message from the external environment.
- Sensory neuron– The message from the receptor is carried to the central nervous system by the sensory neuron.
- Central nervous system– It processes the message and sends an impulse to the concerned part of the body.
- Motor neuron– The message from the central nervous system is carried to the effector by the motor neuron.
- Effector– They produce an instant response to the stimuli.
Human Brain
An adult brain weighs between 1.0kg – 1.5kg on average. The central nervous system consists of our brain and the spinal cord. Our brain has three major parts- the fore-brain, mid-brain, and hind-brain.
Fig of Human Brain
Fore-brain
It is the main thinking part of our brain. Fore-brain consists of the Cerebrum, Thalamus, and Hypothalamus (an extension of the Thalamus). The cerebrum occupies the maximum space in our brain. It is responsible for controlling our IQ (intelligence quotient), willpower, thought and memory. Thalamus regulates our reflexes or feelings. We can feel pain, cold, heat, due to the thalamus. The hypothalamus controls the sweat, temperature, and hormonal secretions of our body. It is the centre of thirst and hunger. Our emotions like love, hate, anger, joy, etc are controlled by it.
Mid-brain
The central and smallest part of our brain. It controls both voluntary and involuntary action. It controls our vision and hearing power.
Hind-brain
It consists of Pons, Cerebellum, and Medulla Oblongata. Hind-brain controls the involuntary actions of our bodies. The involuntary actions including blood pressure, heartbeat, breathing, salivation, and vomiting are controlled by the medulla. The cerebellum is responsible for the precision of voluntary actions and maintaining the posture during walking, riding, swimming, etc. They control the balance of the body. Pons regulate our sleep cycles. It helps coordinate facial expressions, eye movements, chewing, and processes sound.