In the two previous articles [ NEUROLOGICAL BASIS OF BEHAVIOUR ] and [ THE CENTRAL NERVOUS SYSTEM AND BEHAVIOUR , I showed simple information about them.

In this article I complete simple information about NEUROLOGICAL BASIS ,then I will complete more in another article because I don’t want to make the article so long and appreciate the time of the readers.


The PNS consists of nerves in the head (cranial nerves), nerves from the spine (spinal nerves), a self-governing nervous system that deals with reflexes (the autonomic nervous system), and a system of glands that produce hormones in response to stimuli (the endocrine system). The PNS contains all the nerves outside the CNS and is therefore crucial in receiving sensory and other stimuli and transmitting messages to different parts of the body.


A neuron is a nerve cell capable of receiving and transmitting an impulse (message). These cells are joined to each other to form chains of neurons, some quite short and some long, along which nerve impulses travel.

Key terms

  • A)-Nucleus – The nucleus contains the nucleolus; this is the part of the cell which holds the genetic material, the chromosomes and chromatin which are concerned with reproduction of the cell.
  • B)-Dendrites – branches of the cell that receives and carries impulses towards the cell body.
  • C)-Cell body – The mass of cytoplasm containing the nucleus (i.e. close to the nucleus), distinct from long branches of cell which extend away from the proximity of the nucleus.
  • D)-Axon – The long process of a nerve cell that conducts impulses away from the cell body.
  • E)-Myelin sheath – A covering made up of layers of lipids and proteins covering Schwann cells and oligodendrocytes around axons of many neurones. Not all neurons have myelin sheaths.

Sensory neurons in the PNS receive messages from special receptors in the skin, muscles etc. and carry them to the spinal cord, which sends them to the brain. An example of an impulse carried in this sort of neuron would be the sensation registered by nerve ends in a finger when it is burnt by a flame.  The impulse is first received in the finger and then sent to the central nervous system for decoding. The impulse in a sensory neuron begins in the nerve ends then travels along the dendron to the cell body.  (A dendron is a filament that carries an impulse to a neuron).  The impulse now passes through the axon.  (An axon is a long nerve fibre that carries the impulse away from a neuron).  The impulse now moves onto the next sensory neuron on its way to the central nervous system.

Motor neurons carry messages from the brain and spinal cord to the different muscles, glands and organs, causing them to make and appropriate response. This sort of neuron receives a stimulus from the central nervous system that tells a muscle how to act.

Continuing with the above example, when the central nervous system has received a warning of pain from the nerve ends in the burnt finger, it sends a command back to the finger telling it to move away from the flame. 

Again, the stimulus passes through the dendrites and the cell body on its way to the axon.  The stimulus is finally received by the motor end plates which are embedded in a muscle and cause the muscle to act.

Sensory neurons conduct impulses towards the central nervous system while motor neurones conduct impulses away.  Sensory neurons are sometimes referred to as receptors (because they receive the stimulus) while motor neurones can be termed effectors (because they effect a change).

Parts of a NEURON

1)- Cranial Nerves

There are twelve pairs of cranial (head) nerves.  Of each pair, one nerve goes down one side of the body while the other nerve goes down the other side.  Depending on their jobs, cranial nerves are made up of sensory neuron, motor neuron or a mixture of both.

2)-Spinal Nerves

Spinal nerves emerge from the spinal cord.  One nerve goes to one side of the body and the other goes to the other side.  Each nerve contains both sensory and motor neurones which divide when they reach the spinal cord.  The sensory neurones enter the cord via the dorsal root while the motor neurones enter via the ventral root.  They connect up inside the spinal cord to form a reflex arc.  The spinal nerves serve various parts of the body and are connected to the brain through the spinal cord.

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