Sharpening of a pencil, grasping a door knob, walking or running, driving, and a few physical actions, all involve well-coordinated movements made with well balanced postures. In fact, whenever we move the three basic functions, such as movement, balance, and coordination they work together to perform purposeful motions of body parts.

This is actually quite a feat, because moving is a complex process for the body. Even standing upright is a  difficult challenge of balancing on just two feet with a narrow base. Yet, it is common for us not only to stand upright easily and apparently, effortlessly but also while keeping our balance to perform many other functions.

Responding to Stimuli

A response as an effect of a change in the environment of the organism or signals of change or ‘stimuli’.All living organisms respond to stimuli. The cat may be running because it saw a mouse. Plants grow towards the sunshine. We start sweating when it is hot and humid.

• The ability to react to a particular stimulus in a particular situation must be of great importance in ensuring the survival of the organism.
• There is a sequence of events that brings about responses. They start from detecting changes in the environment (both external and internal) or stimuli, transmission of the information, processing of the same. Finally, the response will detect and execute the appropriate action.

Integrating pathways - Nervous coordination

• The Greeks believed that all functions of the body were controlled by the brain since damage to that organ produced remarkable changes in behavior.
• They had very little idea on how such control could be exercised though Galen, a Greek physiologist (A.D. 129-200) made one notable observation.
• One of his patients, having suffered a blow on the neck when falling from his chariot, complained of loss of feeling in the arm while still retaining normal muscular control of its moment.
• Galen concluded that nerves were of two kinds – those of sensation and those of action. According to him the blow in the neck had damaged the nerves of sensation but had not affected it’s action 

Structure of nerve cell

Each nerve cell consists of a cell body with a prominent nucleus. There are fine projections mainly of two types extending from the cell body of the nerve cell.

• The small projections are  dendrites while a long one that extends to different parts of our body.
• The axon is surrounded by a specialized insulatory sheath called myelin sheath.
• This sheath is interrupted at regular intervals called nodes of ranvier. The myelin sheath is made up of Schwann cells and chiefly consists of fatty material. Axons not having the sheath are non-myelinated fibers.
• The covering also forms a partition between adjacent axons. The nerve cell body lies either in our brain or spinal cord or very close to the spinal cord in a region called dorsal or ventral root ganglion.
• In the brain or spinal cord, it is difficult to make out the difference between dendrites and axons on the basis of their length, often, the presence of the sheath helps us to find out but several axons here do not have the sheath.
• the nerve cell is the structural and functional unit of nervous system. Our nervous system consists of around about 10 billion of them, which communicate with each other in a specific manner.
• Dendrites of one nerve cell connect to the other or to the axons of the other nerve cell through connections called as a ‘synapse’.

• Synapse is the functional region of contact between two neurons, where information from one neuron is transmitted or relayed to another neuron.
• Though these are regions of minute gaps and essentially neurons do not have any protoplasmic connection between them yet information is passed from one nerve cell to the other through these gaps either in the form of chemical or electrical signals or both.
• These synapses are mainly found on the brain, spinal cord and around the spinal cord. Beyond these areas the axon carries the signals to respective areas in our body.

Pathways:

From stimulus to response In the holding stick activity you observed that there is coordination between eye and finger.

• Different pathways are taken by nerves to bring about this coordinated activity. On the basis of pathways followed, nerves are classified mainly into three different types.

Afferent neurons:

Afferent (or ferrying towards) which carry messages towards the central nervous system (spinal cord or brain) from nerve endings on the muscles of different sense organs that sense the change in surroundings are called stimulus detectors. These are also called ‘sensory’ nerves.

Efferent neuron:

Efferent (or ferrying away) which carry messages from the central nervous system to parts that shall carry out the response or the effectors (nerve endings). They are also called ‘motor’ nerves

Association nerves:

Association nerves, which link together the afferent and efferent nerves.