Question

A Diagram of a phenomenon of the nervous system is given alongside. Observe it carefully and answer the following:

1. Label the parts 1-11
2. What phenomenon does the diagram represent? Name it.
3. What is the difference between parts 3 and 11?
4. What is a synapse?

Answer 1

1. Labeling the diagram

1. The given image shows the pathway followed during a reflex action. A reflex action is a sudden, involuntary, unplanned response given to a stimulus.
2. It may or may not involve the brain. For a reflex action to occur, a sensory neuron, a connector or relay neuron, and a motor neuron is required.
3. Reflexes are divided into two categories- unconditioned and conditioned reflexes. Unconditioned reflexes are unspecific, inborn, and present since birth. Conditioned reflexes are acquired during one’s lifetime and change based on the individual.
4. In the given image, the sharp object is the external stimuli. When we touch it, the pain receptors on the skin are activated.
5. The sensory neurons carry messages in the form of electrical impulses to the relay neuron present in the spinal cord. The dorsal root ganglion houses a cluster of cell bodies of the sensory neurons.
6. The signal from the relay neuron is transmitted to the motor neuron through the ventral root which reaches the effector cells, tissues, organs, or glands.
7. On receiving the message, the effector produces an immediate response. In this case, the muscle contracts and pulls the hand away from the sharp object.
8. The brain and the spinal cord make up the central nervous system (CNS). Based on the appearance of the color, it is broadly divided into two substances- grey matter and white matter.
9. The grey matter comprises the neuronal cell body whereas the white matter comprises the nerve fibres (axons and dendrites). The white color is due to the myelination of the axonal fibres of the neurons.
10. In the spinal cord, these substances are arranged in a reverse fashion compared to the brain. The grey matter surrounds the central canal of the spinal cord, whereas the white matter is present on the outer side of the spinal cord.

2. The phenomenon represented by the diagram

1. The phenomenon represented by the diagram is an unconditioned reflex action.

3. Difference between part 3 and part 11

1. Part 3 labels a sensory neuron. It carries electrical impulses from the sensory receptors toward the central nervous system (spinal cord or brain).
2. Part 11 labels an effector organ (muscle). It receives impulses from the motor neurons and undergoes a change (contraction or relaxation) to bring about a movement.

4. Synapse

1. The synapse is a gap between two nerve cells where the electrical impulses are transmitted from one nerve cell to the next nerve cell by the release of neurotransmitters.