Nervous control in mammals

Essay summarising how the nervous system in mammals works

did this over easter break

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  • Created on: 24-04-11 20:08
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Nervous coordination in mammals
The nervous system performs the function of communication and coordination of all the actions of cells,
tissues and organs within the body in response to internal or external environment changes. There are
many different parts of a mammalian nervous system which consists of different cells to maximize
neurotransmission efficiency.
Within the mammalian nervous system there is the central nervous system which includes the brain and
spinal cord and the peripheral nervous system which includes everything else either sensory or motor.
This then splits further. The peripheral nervous system then breaks into two parts: the somatic and
autonomic nervous systems. The somatic nervous system is voluntary and receives inputs from sensory
organs and delivers outputs to skeletal muscles. The autonomic nervous system is involuntary and
receives inputs from internal receptors and delivers outputs to smooth muscles and glands. The
autonomic nervous system then splits into two parts: sympathetic and parasympathetic motor systems.
The sympathetic motor system controls the flight or fight response and the neurotransmitter
noradrenalin. The parasympathetic motor system controls the relaxing responses and the
neurotransmitter acetylcholine.
The nervous system has two main types of cell: neurones and neuroglia. Neurones are cells which are
adapted to carry nerve impulses whilst neuroglias are cells which provide structural support as well as
metabolic support to neurones. This includes swann cells. Every neurone consists of a cell body containing
the nucleus and organelles and endoplasmic reticulum. The cytoplasm surrounding the nucleus is known
as the perikaryon. Each also contains a long axon which stretches out of the cell which is responsible for
transmitting signals from the neurone to the effector cells. There are also several short dendrites which
are highly branched and increase the surface area available for carrying impulses from axons. Axons can
be surrounded by specialized cells called Swann cells. This layer of Schwann cells is called the myelin
sheath. The gaps inbetween each Schwann cell is called the node of ranvier. When an axon is myelinated
it allows a nerve impulse to jump from one node of ranvier to the next. This increases the rate at which an
impulse can travel and is known as salutatory conduction.
A nerve impulse can be defined as a wave of depolarization or an action potential. A nerve impulse
involves the movement of ions through the axon membrane. This means there is a change in the
concentration of this ion inside and outside of the axon. This change means the axons charge also
changes. An axon is said to have a resting potential which is when it is not conducting an impulse. The
axon has a negative electrical charge compared to outside of the axon and it has a greater concentration
of sodium ions on the outside than on the inside, however there is a greater concentration of potassium
ions inside. Any large negatively charged ions are found only on the inside of the axon. This is because
when the axon is in a resting state, the permeability of the membrane to potassium is relatively high due
to the presence of protein channels. These protein channels let potassium pass through and are
attracted by the negative charge inside the axon. The positively charged sodium ions are also attracted
the negatively charged axon. The permeability of the axon membrane to sodium is reasonably low and
so the inward movement of sodium is quite slow through the sodium channels. Once inside, the sodium is
pumped back out anyway through ion pumps. However for the negatively charged ions there are no

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There is a potential difference across the membrane of
around -70mV; this is known as the resting potential.
An action potential is the maximum positive charge generated within the axon as a result of a nerve
impulse. When a nerve impulse is generated the axon membrane briefly increases its permeability to
sodium ions. This means that sodium ions enter the axon membrane at a faster rate than they can be
pumped out which causes the potential difference to increase to a positive value.…read more

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