The Nervous system

The Nervous System

• Brain• Spinal cord• Nerves

• Enables you to control your body

• Gives you feedback about the world

What does it do?

What are its component parts?

Look away if you’re squeamish…

A dissected brain, spinal cord and sections of major nerves.

The Cells of the Nervous System - Neurones

The route impulses take

The route impulses take

Effectors –

Sensory neurone

Motor neurone

Relay neurones (in brain or spinal cord)

The SpineYou don’t need to know any of these little details – just remember that the spinal cord carries messages to and from the brain.

The spine – the message motorway

Effects of a spinal cord injury on breathing

• With a spinal cord injury of C4 and higher, all the muscles which control breathing will be paralysed. These are the intracostal muscles, the diaphragm and the abdominal muscles. In order to breathe, the person will need a machine called a ventilator to breath for them. In order to cough, the person will need help by way of a carer performing an assisted cough procedure.

• Injuries between C4 and T6 will leave the person able to breathe on their own. However, because the intracostal muscles may be weakened or paralysed depending on the level of injury, breathing may be done solely or mainly by the diaphragm. Again, coughing may also be a problem.

• Injuries between T6 and T12 do not normally affect breathing. However the ability to cough will be impaired.

• It is only with injuries below T12 that normal breathing and cough reflexes are preserved.

Left: sensory neurone

Right: motor neurone

Above: Sensory NeuroneBelow: Motor Neurone

Diagrams and Drawings in Biology

Nerves – bundles of neurones

Close-up of a nerve

Single neurones in cross-section

How Impulses Pass from Neurone to Neurone – the Synapse

Synapses

Reflex Reactions – bypassing the brain for extra speed

Reflex Reactions

Can you think of any?

• Startle reflex – moving away, contraction of arm and leg muscles, blinking, breathing changes

• Withdrawal reflex – moving away from potentially harmful influences (e.g. high temperature)

• Iris reflex – pupil becomes smaller in bright light

Knee Jerk Reflex

Why the knee jerk reflex?

• This reflex is quite useful for walking. Every time you put weight on your foot, your muscles contract to support you. Without this reflex, we would all look silly staggering around, having to consciously think about working our muscles for each step, but with the muscles reacting too hopelessly late to be useful. Chewing gum at the same time would be out of the question.

Rod and Cone cells

Iris Reflex

Look at the difference between the two eyes

Accommodation of the eye