The Nervous System Revision

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The Nervous System sends information as Nerve Impu

The nervous system is made up of a complex network of cells called neurones.

3 main types of neurone;

Sensory - transmit nerve impulses from receptors to the CNS (Brain, and spinal cord).

Motor - transmit nerve impulses from the CNS to effectors.

Relay - transmit nerve impulses between sensory and motor neurones.

Stimulus detected by receptor cells.
Nerve impulse sent along sensory neurone.
When impulse reaches end of neurone neurotransmitters take the information to next neurone which sends a nerve impulse.
CNS processes the information and sends impulses along motor neurones to an effector.

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Sensory Receptors and Energy Conversion

Different stimuli have different forms of energy, e.g. light or chemical.

The nervous system only sends information in the form of electrical nerve impulses.

Sensory receptors convert the energy of a stimulus into electrical energy.

Sensory receptors act as transducers - something that converts energy from one form to another.

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How Receptor Cells Communicate Information

When a nervous system receptor is in its resting state (not being stimulated) there is a difference in voltage between the inside and the outside of the cell.

This difference is called the potential difference.

This is being generated by the ion pumps and ion channels.

When a stimulus is detected, the cell membrane becomes excited and therefore more permeable thus allowing more ions to move in and out of the cell.

This alters the potential difference.

The change in potential difference due to a stimulus is the generator potential.

A bigger stimulus excites the membrane more causing a bigger movement of ions so a bigger change in potential difference so a bigger generator potential.

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How Receptor Cells Communicate Information cont.

 

If the generator potential is big enough, it will trigger an action potential (nerve impulse) along a neurone.

 

An action potential is only triggered if the generator potential reaches a certain level called threshold.

 

If the stimulus is too weak, the generator potential will not reach threshold (-55mV) so an action potential will not be produced.

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Motor Neurones

Motor neurones have many short dendrites. They carry nerve impulses from the CNS to the cell body.

The long axon carries nerve impulses from the cell body to effector cells.

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Comments

vyvyan

This is just a basic introduction. Good but not great. It doesn't explain hpw the nerve impulses work and how action potentials are transmitted from one part of the body to another.

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