1. With a neat labelled diagram explain the structure of nerve cell.
2. Write a flow chart which shows different nerve pathways.
3. Give an example of co-ordination in your body where both hormonal and nervous controls func-
tions together?
4. If we step on a sharp edged object we suddenly remove our leg. Here reflex action takes place.
Write a flow chart showing different steps involve in this action.
5. Write differences between (i) Stimulus and response (ii) Afferent and efferent nerves.
Answers
Answer:
1. Cell Body–Each neuron has a cell body with a nucleus, Golgi apparatus, endoplasmic reticulum, mitochondria and other components. Axon–Axon is a tube-like structure that functions by carrying an electrical impulse from the cell body to the axon terminals for passing the impulse to another neuron
3. The nervous system is responsible for sensing the stimuli and generate the responses as per the stimuli. The functions of the body are coordinated by the nervous system. One such type of coordination is done along with the endocrine system. The neurons act upon the endocrine glands and make them release the specific and the required hormone that will further regulate the activity of the organs. For example, under the stressed 'flight or fight' conditions, the nervous system acts upon the adrenal gland and makes it secrete the adrenaline hormone. The hormone prepares the body to face the emergency situation by increasing the breathing rate so that more oxygen can be drawn in, increasing the heart beat so that more oxygen can be supplied to the body etc.
4. Revise
Test
Page 3 of 5
Reflex arc
Reflex actions
There are three main types of neuron: sensory, motor and relay.
These different types of neurons work together in a reflex action. A reflex action is an automatic (involuntary) and rapid response to a stimulus, which minimises any damage to the body from potentially harmful conditions, such as touching something hot. Reflex actions are therefore essential to the survival of many organisms.
A reflex action follows this general sequence and does not involve the conscious part of the brain. This is why the response is so fast.
Neurones work together to make a reflex action
Reflex arcs
The nerve pathway followed by a reflex action is called a reflex arc. For example, a simple reflex arc happens if we accidentally touch something hot.
The nerve pathway in the arm
Receptor in the skin detects a stimulus (the change in temperature).
Sensory neuron sends electrical impulses to a relay neuron, which is located in the spinal cord of the CNS. Relay neurons connect sensory neurons to motor neurons.
Motor neuron sends electrical impulses to an effector.
Effector produces a response (muscle contracts to move hand away).
Organisms are able to modify a reflex action and overcome it, but this uses the brain and has to be learnt. For example, keeping hold of a hot object requires a nerve impulse to be sent to the motor neuron of the reflex arc to interfere with the normal reflex action to drop the object.
5. Afferent neurons are sensory neurons that carry nerve impulses from sensory stimuli towards the central nervous system and brain, while efferent neurons are motor neurons that carry neural impulses away from the central nervous systme and towards muscles to cause movement.
