Human Nervous System

Parts of Human Nervous System

Human nervous system consists of two parts, central nervous system and peripheral nervous system. The peripheral nervous system is a bridge between various body parts and the central nervous system. It picks up sensations and hands over the same to the central nervous system. On instructions from central nervous system, through voluntary or involuntary control, it brings about activity in various parts of the body. Spinal cord is also a communicating channel between brain and trunk part of the body. Brain is the major part of the nervous system that is involved in thinking, reasoning, memory, intelligence, emotions and will. The study of nervous system is called neurology. The study of structure, working and functioning of brain is called encephalology.

Human Brain

It is anterior walnut shaped large part of the nervous system that has a size of 1400 cc and weight of about 1.4 kg. It is pinkish grey in color. Brain is distinguished into three parts-fore-brain (thinking part), mid brain (relay part) and hind brain (involuntary part). Both mid brain and hind brain are also called reflex part.

  1. Olfactory Lobes. They are two club-shaped structures which lie on the inferior surface of cerebrum. Olfactory lobes relay sense of smell to temporal lobes of cerebrum.
  2. Cerebrum. It is the largest part of the brain that occupies nearly 80% of its volume. Cerebrum is formed of two closely placed cerebral hemispheres. They are attached to each other on the inferior surface by a thick band called corpus callosum.

Each cerebral hemisphere has a fluid filled cavity called lateral ventricle. The superior surface is convex and convoluted. The convolution is called gyri while the depressions are known as sulci. The left cerebral hemisphere controls the functioning of right side of the body while the right cerebral hemisphere has a control over left part of the body. The cerebral hemispheres are divisible into 4 parts – frontal, parietal, temporal and occipital.

Frontal Lobes. They constitute the anterior or front part of the brain. Frontal lobes have several nerve centre‚Äôs like motor area for controlling voluntary movements, premotor area for higher centre of involuntary and autonomic functions, intelligence, association area between sensation and movement and motor speech or Broca’s area.

Parietal Lobes. They are mid dorsal lobes which control some components of speech (in left lobe) but the major function is control of sensation of pain, touch, pressure, temperature and taste.

Temporal Lobes. They are lateral lobes of the cerebrum. Temporal lobes have centres for smell, hearing, audiovisual memory and some components of speech.

Occipital Lobes. They lie on the posterior side of the cerebrum. They possess centres for sensation of sight.

  1. Diencephalon. It lies on the undersurface of cerebrum. Diencephalon encloses a third ventricle which is connected with the lateral ventricles of the cerebral hemispheres. The roof of diencephalon is called epithalamus. It bears pineal body. The sides of diencephalon are called thalami. They function as relay station of sensory impulses except that of smell. The floor of diencephalon is called hypothalamus. It has control centres for body temperature, hunger, thirst, sleep, fatigue, sweating, emotional reactions. It secretes neurohormones for pituitary gland which lie at the inferior surface.
  2. Mid Brain. It has two tracts called cerebral peduncles or crura cerebri, four swellings or corpora quadrigemina and a narrow cavity called iter. Crura cerebri connect for brain with hind brain. The two superior corpora quadrigemina have centres for sight reflexes while inferior corpora quadrigemina have centres for auditory reflexes.
  3. Cerebellum. It lies above medulla oblongata, behind cerebrum. Cerebellum is the second largest part of the brain, with 12.5% volume of the total. It has three parts, two large cerebellar hemispheres on the sides and a central small worm-like vermis. Cerebellum maintains the equilibrium of the body while walking, riding, dancing, picking up articles from ground, etc. It also coordinates muscular activities of the body.

Differences Between Cerebrum and Cerebellum

CerebrumCerebellum
1. Size. It is the largest part of the brain.

2. Parts. Cerebrum has two parts known as cerebral hemispheres.

3. Position. Cerebrum forms anterior, superior and lateral parts of the brain.

4. Cavities. Cerebrum has two lateral ventricles.

5. Lobes. Each cerebral hemisphere has four lobes.

6. Function. Cerebrum is a seat of intelligence, memory, control of movements and sensation.

1. Cerebellum is the second largest part of brain.

2. Cerebellum has three components, two cerebellar hemispheres and a vermis.

3. Cerebellum forms the posterior part of the brain.

4. Cavities are absent.

5. A cerebellar hemisphere is without any lobes.

6. It maintains equilibrium and coordinates muscular activity.

 

  1. Pons Varolii (= Pons). It is crosswise band of nervous tissue that connects and relays information amongst cerebrum, cerebellum and medulla oblongata. It also possesses pneumotaxic centre of respiration.
  2. Medulla Oblongata. It is cylindrical conical hinder most part of brain which lies below the cerebellum. Medulla oblongata encloses a fluid filled cavity called fourth ventricle. It controls many involuntary actions. For this it has respiratory centre, cardiac centre, blood pressure centre, and reflex centre for coughing, sneezing, vomiting, salivation, swallowing and peristalsis.

Medulla oblogata, pons and midbrain are together called brain stem. Midbrain and hindbrain do not have thinking part. Instead they control reflexes and involuntary actions connected with them.