Question

Illustrate the structure and functions of the brain.

Answer 1

A human brain is formed of three main parts forebrain, midbrain and hindbrain.

1. Forebrain: The forebrain is formed of Cerebrum and Diencephalon. The diencephalon consists of the dorsal thalamus and ventral hypothalamus.

(a) Cerebrum: It is the largest portion and nearly forms two-third of the brain. The cerebrum is longitudinally divided into two halves, as of right and left cerebral hemispheres by a deep – cleft called median cleft. The two cerebral hemispheres are interconnected by a thick band of nerve fibres called the corpus callosum. The outer portion of each cerebral hemisphere is formed of grey matter and is called the cerebral cortex.

The inner or deeper part is formed of white matter and is called the cerebral medulla. The cortex is extremely folded forming elevations called gyri, with depressions between them termed as sulci, that increase the surface area. Each cerebral hemisphere is divisible into a frontal lobe, a parietal lobe, a temporal lobe and an occipital lobe. These lobes are also known as cerebral lobes.

(b) Thalamus: Thalamus present in the cerebral medulla is a major conducting centre for sensory and motor signalling. It acts as a relay centre.

(c) Hypothalamus: It lies at the base of the thalamus. It controls the secretions of hormones from the anterior pituitary gland.

2. Midbrain: It is located between the thalamus and the Hindbrain. The dorsal portion of the midbrain consists of four rounded bodies called corporaquadrigemina, which control visual and auditory (hearing) reflexes.

3. Hindbrain: It is formed of three parts Cerebellum, Pons and Medulla Oblongata.

• Cerebellum: It is the second-largest part of the brain formed of two large-sized hemispheres and a middle vermis.
• Pons: It is a bridge of nerve fibre that connects the lobes of the cerebellum. It relays signals between the cerebellum, spinal cord, midbrain and cerebrum.
• Medulla Oblongata: It is the posterior-most part of the brain, that connects the spinal cord and various parts of the brain.

Functions of Brain:

Structure	Functions
1. Cerebral cortex	Sensory perception, Intelligence, consciousness, control of voluntary functions, language, thinking, memory, decision making, creativity, reasoning and willpower.
2. Thalamus	Acts as Relay Station.
3. Hypothalamus	Temperature control, anger, thirst, hunger, urination, the important link between the nervous system and endocrine glands, sleep, sweating, sexual desire, fear, water balance, blood pressure.
4. Midbrain	Visual and Auditory reflexes.
5. Cerebellum	Maintenance of posture and balance, and coordinate voluntary muscle activity.
6. Pons	Respiration and Role in the sleep-wake cycle.
7. Medulla Oblongata	Cardiovascular, respiratory and digestive control centres, vasomotor centres to control heartbeat, contraction of blood vessels. It also regulates vomiting and salivation.