The Nervous System

Role and Functions

Sensory

To sense changes inside and outside the body (e.g. a change in temperature).

Integrative

To analyse and interpret incoming information

Motor

To respond to the interpretation by activating the relevant body system (e.g. to shiver or sweat and bring body temperature back to normal).

These functions of the nervous system enables the body to achieve a balance in order to operate effectively. This is known as homeostasis.

The achieve homeostasis in the body, the nervous system is divided into two main sections, central and peripheral.

Central Nervous System (CNS)

The brain and the spinal chord. The control center of the body. All of the information is collected and analysed here. The brain has sensory, motor and association areas. Sensory (eyes, ears, skin, mouth) receive impulses via the sense organs, via the peripheral nervous system. Association areas area connected with things such as thoughts and memories. Motor areas activate motor units via the spinal chord peripheral nervous system.

Peripheral Nervous System (PNS)

31 pairs of nerves extend from the spinal chord connect to motor units glands, blood vessels and organs. Somatic nerves are responsible for actions we have control over. Autonomic are responsible for things we don’t have control over, such as digestion and breathing. Sympathetic is the accelerator (brings heart rate up when needed), Parasympathetic is the break (brings the heart rate down after exercise)

The Structure of a Nerve Cell

All messages or impulses that pass via the nervous system are transmitted by nerve cells. These nerve cells are called neurons. Neurons are the wiring system of the body and are the functional units of the nervous system. Each neuron is made up of a main cell body, dendrites and one axon. The main cell body has nerve fibres extending from it. These nerve fibres can be microscopic or as long as 3-4 feet in length. The longest fibres are those from the lumbar spine to the big toe. The cell body is responsible for directing information. Dendrites are responsible for transmitting impulses towards the cell body. The axon is responsible for transmitting impulses away from the cell body.

The two main types of neurons are:

Sensory: These transmit the impulse messages from the sensory organs to the brain.

Motor: These transmit the impulse messages from the brain to the muscles and glands.

The conduction of information along nerves requires the involvement of neurotransmitters. These are chemicals produced by the nerve cells which allow the nerve signal to ‘jump’ from one nerve to the next. Neurotransmitters allow the brain to interpret signals from the periphery and to respond appropriately. They are also extremely important in less obvious functions, such as emotion, desire, blood pressure, pain and consciousness.

All the fibres within a motor unit are either on (contracting) or off (relaxing). The strength of a contraction depends on how many motor units are recruited. The two key factors that affect the strength of a muscle contraction are the frequency of nerve impulses and number of motor units.

  1. The strengthening or creation of new connections within the nervous system, leads to more ‘skilled’ movements.
  2. Speeding up the frequency of nerve impulses to motor units (neuromuscular pathways) leads to stronger contractions.
  3. Improving synchronous recruitment of motor units results in stronger muscle contractions.
  • Sensory nerves bring information from the body into the central nervous system
  • The spinal chord IS NOT a part of the peripheral nervous system. It is a part of the CENTRAL NERVOUS SYSTEM
  • When a motor unit is stimulated, ALL of the muscle fibres within the unit contract
  • The SOMATIC part of the peripheral nervous system is under voluntary control
  • With regular motor skills training, the nervous system adapts by growing new connections
  • The nervous system will recruit MORE motor units to lift a heavy weight
  • The SYMPATHETIC branch of the autonomic nervous system is responsible for speeding everything up.
  • Nerve impulses are conducted using chemical called neurotransmitters.

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