- The Sensory neurone
- The Motor neurone
- The Relay neurone ( Also referred to as the Connector neurone)
Diagram 2 – A Motor Neurone
Neurone Structure and Function
Neurones are the cells in the nervous system which are responsible for sending messages. They have three major purposes
- To gather and send information from the senses such as touch, smell, sight etc.
- To send appropriate signals to effectors cells such as muscles, glands etc.
- To process all information gathered and provide a memory and cognitive ability thus allowing us to take voluntary action on information received.
Neurones are divided into different regions each having a different function and are characterised as having:
- A cell body containing the nucleus and most of the organelles responsible for maintaining the cell.
- A long process or axon stretching out of the cell, sometimes over a very long distance which is responsible for transmitting signals from the neurone to other cells.
- Several short processes called dendrites which increase the surface area available for connecting with axons of other neurones.
specialised cell junctions called synapses between it's axon and other cells which allow for direct communication from one cell to another.
Homeostasis
Homeostasis is the active process by which an organism maintains and controls a constant internal environment despite external changes.
There are two major control systems involved in homeostasis, these controls centres are:
- Brain of the nervous system
- Glands of the endocrine system
Within the body it is important that several different factors must be regulated including:
- Temperature
- Heart rate
- Respiratory rate
- Blood pressure
- Water balance
- Blood sugar levels
- Detoxification
Thermoregulation
Thermoregulation is the process of keeping the body at a constant temperature.
Human work best at 37°C (body temperature). The temperature of the body is monitored by a part of the brain called the . If you are too hot or too cold the hypothalamus sends nerve impulses to the skin, which has three ways to either increase or decrease heat loss from the body's surface.
Osmoregulation
Osmoregulation is the process of keeping a constant amount of water and salts in the blood. The body needs to constantly replace the water being lost in breathing, sweating, urine and faeces, as cells cannot function without sufficient water. If there is too much water in the body, however, it will move by into the cells, which may swell or even burst. A balance is needed, and again it is the hypothalamus which maintains this balance.
Glucoregulation
Glucoregulation is the means by which a constant blood sugar level is maintained. A vital part is played by the hormone , which reduces the level of glucose in the blood.
Homeostasis also maintains a person’s blood pressure, pulse rate and a person’s respiratory rate.
Diagram 3 – Balances and in-balances of Homeostasis
Negative Feedback
In animals such as ourselves, the internal environment of our bodies must have certain conditions within tolerable limits to continue the healthy functioning of us.
This is done by a process called negative control, where various receptors and effectors bring about a reaction to ensure that such conditions remain favourable.
When a change occurs in the body, there are two general ways that the body can respond. In negative feedback, the body responds in such a way as to reverse the direction of change. Because this tends to keep things constant, it allows us to maintain homeostasis. On the other hand, positive feedback is also possible. This means that if a change occurs in some variable, the response is to change that variable even more in the same direction. This has a de-stabilizing effect, so it does not result in homeostasis. Positive feedback is used in certain situations where rapid change is desirable. The principle of negative feedback control is illustrated by the diagram below:
