Coordination

Different parts of the body need to be able to pass information between each other so that their activities are coordinated. There are communication systems within animals that coordinate the activities of receptors and effectors. The information they receive comes from the internal and external environment so there are receptors that detect stimuli inside the body and receptors that detect stimuli in the surrounding environment

In animals, there are two types of information transfer that are used to coordinate the body's activities:

• nerves that transmit information in the form of electrical impulses
• chemical messengers called hormones that travel in the blood

Glands that secrete hormones make up the body's endocrine system. Coordination in plants also involves use of electrical impulses for fast responses and hormones for coordinating slower responses to stimuli

Nervous communication

The mammalian nervous system is made up of:

Cranial nerves are attached to the brain and spinal nerves to the spinal cord. Information is transferred in the form of nerve impulses, which travel along nerve cells at very high speeds

Nerve cells are also known as neurones, and they carry information directly to their target cells. Neurones coordinate activities of sensory receptors such as those in the eye, decision-making centres in the CNS, and effectors such as muscles and glands

Neurones

There are 3 types of neurone, each with a different function:

• sensory neurones transmit impulses from receptors to the CNS
• intermediate neurones (relay or connector neurones) transmit impulses from sensory neurones to motor neurones
• motor neurones transmit impulses from the CNS to effectors

A motor neurone transmits impulses from the brain or spinal cord to a muscle or gland

• its cell body lies within the spinal cord or brain
• nucleus of a neurone is always in its cell body
• dark specks can be seen in the cytoplas, which are often small regions of rought endoplasmic reticulum that synthesise proteins
• thin cytoplasmic processes extend from the cell body
• some are very short and often have many branches - these are dentrites
• a motor neurone has highly branched dendrites to give a large surface area for the endings for other neurones
• the axon is much longer and conducts impulses over long distances
• a motor neurone with its cell body in your spinal cord might have its axon running all the way to one of your toes, so axons may be extremely long
• within cytoplasm of an axon are some organelles such as mitochondria
• the ends of branches of the axon have large numbers of mitochondria, together with many vesicles containing chemicals called transmitter substances 
• these vesicles are involved in passing impulses to an effector cell such as a muscle cell or a gland

A sensory neurone has same basic structure as a motor neurone but it has one long axon with a cell body that may be near the source of stimuli or in a swelling of a…