Chemical and electrical coordination 1

All the various animal nervous sytems are fast-acting communication systems containging nerve cells, neurones. These convey information in the form of nerve impulses which are electrical in nature.
Neurones take various forms but each has a cell body, containing a nucleus, and nerve fibres (long extensions that transmits nerve impuses rapidly from one part of the body to the other) Fibres carrying impulses away from the cell body are called axons; those carrying impulses towards the cell body are called dendrons. Apart from the main nerve fibre, there may be small dendrons extending from the cell body.
In mammals, sensory neurones carry messages from pheripheral sense organs to a centeral nervous system (CNS) consisting of the brain and spinal cord. The CNS acts as an integration centre and processes information from many sources. Motor neurones convey intructions from the CNS to effector organs
The effect of a neurone on an effector depends on chemicals called neurotransmitters that are released by nerve endings directly onto target cells. Some neurones are excitatory- they secrete neurotransmitters that make an effector more active. Other neurones are inhibitory- they secrete neurotransmitters that make an effector more active. Whether excitatory or inhibitory, the effect of the neurotransmitters is usually rapid, short lived and localised.
Organisation of the mammalian nervous system. Structually, the mammalian nervous system consists of a CNS and the pherpheral nervous system. A nerve is a thread like structure containing a bundle of nerve fibres. A single nerve may contain both sensory and motor neurones.
Functionally, the mammalian nervous system is divided into the somatic nervous system and the autonomic nervous system
The somatic nervous systems includes sensory neurones which transmit impulses from pheripheral receptors to the CNS, and motor neurones which send impulses to skeletal muscles. It is sometimes called the voluntary nervous system (VNS) becuase many of its actions are under concious control
The autonomic nervous system (ANS) is sometimes called the involuntary nervous system because it usually enables internal organs to function properly without any concious control. It has two parts; the parasympathic nervous system, the sympathetic nervous system
These general act antagonistically, while the parasympathetic nervous system maintains the body in non-threatening situations, the sympathic nervous system prepares the body for aaction during periods of excitment or danger. Hence the vagus nerves slows down the heart rate and sympathetic speeds it up.

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Chemical and electrical coordination 1

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