Question

The diagram given alongside represents the human brain as seen from an external view. Study the same and then answer the questions that follow-

1. Name the parts labeled 1,2,3, and 4.
2. Mention the difference in the arrangement of the nerve cells in the parts marked ‘1’ and ‘4’.
3. What is the main function of the parts marked ‘3’ and ‘4’?
4. Name the sheet of nerve fibers that connect the two halves of the part labeled ‘1’.

Answer 1

1. Labeling the image

1. The given image is of the brain. It belongs to the central nervous system (CNS).
2. The cerebrum occupies two-thirds of the forebrain. It is divided into two hemispheres connected by the corpus callosum.
3. The cerebrum is associated with sensory, motor, and association areas of the brain. It helps in processing the impulses coming in from various sensory organs and sends appropriate responses to effector organs, glands, or muscles. It is associated with memory, intelligence, thinking, interpretation, and similar functions.
4. The cerebellum is a small region of the hindbrain situated below the cerebrum. It has an outer grey and an inner whitish furrow which makes it appear like a branching tree.
5. The cerebellum helps in the control and coordination of various voluntary activities by controlling the skeletal muscles.
6. The medulla oblongata controls various internal involuntary functions like sneezing, swallowing, breathing, heartbeat, etc. It also controls the activities of the cerebrum.
7. The spinal cord is a cylindrical tube made of nerve fibers and supporting tissues enclosed within the spine. It extends down from the medulla oblongata of the brain.
8. The spinal cord controls the spinal reflex actions and nerve impulse conduction to and from the brain.

2. Arrangement of nerve cells in parts 1 and 4

1. Label 1 denotes the cerebrum, a part of the brain, and label 4 denoted the medulla oblongata, a part of the hindbrain.
2. 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.
3. The grey matter comprises the neuronal cell body whereas the white matter comprises the nerve fibers (axons and dendrites). The white color is due to the myelination of the axonal fibers of the neurons.
4. In the brain, the outer cortex appears greyish and the inner portions appear white in color. Thus the brain has neuronal cell bodies arranged in the outer region and myelinated axons in the inner regions.
5. In the spinal cord, this arrangement is reversed; the outer portion appears white whereas the inner region appears greyish in color. Thus the spinal cord has myelinated axons in the outer region and neuronal cell bodies in the inner region.

3. Functions of parts marked 3 and 4

1. The medulla (part 4) oblongata modulates involuntary functions like breathing, sneezing, swallowing, heartbeat, sleep, consciousness, etc.
2. The spinal cord (part 3) controls the spinal reflex actions and nerve impulse conduction to and from the brain.

4. Sheet of nerve fibers connecting two hemispheres of the brain

1. The cerebrum is divided into two hemispheres. Both the hemispheres are connected by a nerve tract called the corpus callosum.
2. The corpus callosum helps both sides of the brain communicate and send signals.