The central nervous system

This is made up of the brain and spinal cord.

The Brain

The structure of the Brain

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The brain is covered and protected externally by the skull (cranium) and internally by membranes called meninges.

Functions of the brain

  1. It receives impulses from all receptors and sends back impulses to the effectors.
  2. It integrates and coordinates all activities in the body such that the body works efficiently.
  3. It stores information.
  4. It is involved in cranial reflex actions but it does not initiate them.

The brain is divided into three major regions, that is;

  1. Fore brain
  2. Mid brain
  3. Hind brain
  4. The fore brain. It consists of:
    i) The cerebrum (cerebral hemisphere)
    This is the largest part of the brain.
    It is made up of 2 hemispheres i.e. the left and the right cerebral hemispheres. The right hemisphere controls the activities of the left side of the body while the left hemisphere controls the activities of the right side of the body. The 2 hemispheres are joined by a fibre known as corpus collosum.
    It controls all voluntary activities
    It is a center of memory and reasoning.
    It receives impulses from the sense organ of smell, touch, sight, taste and sound.

ii) The olfactory lobes:
These are paired lobes located ventrally at the base of the cerebrum.
They are small in size. They receive impulses from the olfactory nerves bringing about the sense of smell.

  1. The mid brain
    It consists of:
    i) Thalamus
    It integrates sensory impulses from the eyes, skin and ear and sends them to the cerebral cortex of the cerebrum.
    It also directs impulses from all parts of the body to particular areas of the brain.

ii) Hypothalamus
It is a centre of many activities. It is below the thalamus.
It controls involuntary activities e.g. water and salt balance (osmoregulation)
Controls body temperature, CO2, levels in blood, appetite, sleep, hunger, wakefulness, sex drive and produces hormones e.g. oxytocin and ADH which are stored in the pituitary gland.

iii) Pituitary gland
It secretes a number of hormones like the thyroid stimulating hormone, FSH, LH, ADH, etc. which control various activities.
It also controls other endocrine glands in the body thus called the master gland.

iv) Optic lobes
These are paired lobes. Their main function is to interpret sight.

  1. Hind brain
    It is made up of:
    i) Cerebellum
    This is concerned with maintenance of balance, locomotion and posture. It receives impulses from the skeletal muscles.
    ii) Medulla oblongata
    This controls involuntary actions like yawning, vomiting, blinking of the eye, etc. any injury to this region leads to instant death.