The nervous system is essentially a biological information highway, and is responsible for controlling all the biological processes and movement in the body, and can also receive information and interpret it via electrical signals which are used in this nervous system
It consists of the Central Nervous System (CNS), essentially the processing area and the Peripheral Nervous System which detects and sends electrical impulses that are used in the nervous system
The Central Nervous System (CNS)
The Central Nervous System is effectively the centre of the nervous system, the part of it that processes the information received from the peripheral nervous system. The CNS consists of the brain and spinal cord. It is responsible for receiving and interpreting signals from the peripheral nervous system and also sends out signals to it, either consciously or unconsciously. This information highway called the nervous system consists of many nerve cells, also known as neurones, as seen below.
The Nerve Cell
Each neurone consists of a nucleus situated in the cell body, where outgrowths called processes originate from. The main one of these processes is the axon, which is responsible for carrying outgoing messages from the cell. This axon can originate from the CNS and extend all the way to the body’s extremities, effectively providing a highway for messages to go to and from the CNS to these body extremities.
Dendrites are smaller secondary processes that grow from the cell body and axon. On the end of these dendrites lie the axon terminals, which ‘plug’ into a cell where the electrical signal from a nerve cell to the target cell can be made. This ‘plug’ (the axon terminal) connects into a receptor on the target cell and can transmit information between cells
The Way Nerve Cells Communicate
The "All-Or-None-Law" applies to nerve cell communication as they use an on / off signal (like an digital signal) so that the message can remain clear and effective from its travel from the CNS to the target cell or vice versa. This is a factor because just like electricity signals, the signal fades out and must be boosted along its journey. But if the message is either 1 or 0 (i.e.) on or off the messages are absolute.
Classification of Neurones
Interneurones – Neurones lying entirely within the CNS
Afferent Neurones – Also known as sensory neurones, these are specialised to send impulses towards the CNS away from the peripheral system
Efferent Neurones – These nerve cells carry signals from the CNS to the cells in the peripheral system
The next page elaborates on how the nervous system works…