Friday, 16th March 2018
16 March 2018
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Brain – Anatomy

Brain – Anatomy

The nervous system is the chief controlling an coordinating system of the body. It adjusts the body to the surroundings and regulates all bodily activities both voluntary and involuntary. The sensory part of the nervous system collects information from the surroundings and helps in gaining knowledge and experience, whereas the motor part is responsible for responses of the body.

The average weight of adult brain in the air is 1500 grams. Since brain floats in cerebrospinal fluid, it only weights 50 grams which are comfortable.

There are about 200 billion neurons in an adult brain.

Divisions of Nervous System


It is divided into

Central Nervous System (CNS) comprises brain and spinal cord

Peripheral Nervous System (PNS) includes 12 pairs of cranial nerves and 31 pairs of spinal nerves.


Classification of Neurons

Multipolar neurons

Bipolar neurons

Pseudounipolar neurons

Unipolar neurons

Sensory Neurons

These are three types

Primary sensory neurons

Secondary sensory neurons

Tertiary sensory neurons

Motor Neurons

These carry impulses from CNS to the distal part of the body. These are two types

Somatic motor neuron

Autonomic neuron

Somatic motor neuron

Upper motor neurons

Lower motor neurons

Autonomic Neuron

Preganglionic neurons in CNS

Postganglionic neurons in sympathetic chain

Neuroglial Cells

Various types of neuroglial cells are as follows

Astrocytes are concerned with nutrition of the nervous tissue

Oligodendrocytes are counterparts of the Schwann cells. Schwann cells myelinate the peripheral nerves. Oligodendrocytes myelinate the tracks

Microglia behave like macrophages of the CNS

Ependymal cells are columnar cells lining the cavities of the CNS

Reflex Arc

A reflex are is the functional unit of the nervous system. In its simplest form, it consists of

  • A receptor e.g the skin
  • The sensory neuron
  • The motor neuron
  • The effector. e.g the muscle

In complex forms of the reflex arc, the internuncial neurons are interposed between the sensory and motor neurons. An involuntary motor response to a sensory stimulus is known as the reflex action. Only cortical responses are voluntary in nature. All subcortical responses are involuntary and therefore are the reflex activities. Reflex action is chief function of the spinal cord. Knee jerk and ankle jerk are monosynaptic reflex arcs.

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