The Nervous System  The nervous system controls our bodies and helps us respond to external stimuli.  The nervous system works by sending electrical impulses along neurones (nerve cells).

The Nervous System  There are two main parts: Central nervous system – brain and spinal cord A network of nerves

Reflex Arc  A chain of events occurs in order for us to respond to a stimulus Stimuli = changes in surroundings Receptor = detect the changes Co-ordination = decides what to do Effector = action Response = reaction to change

Example – reflex arc  Example: sitting on a drawing pin ○ Stimuli ○ Receptor ○ Co-ordination ○ Effector ○ Response  Information from the receptors pass along neurones to the brain, the brain then co- ordinates a response.

Reflex Action  Some responses to stimuli are automatic and rapid these are called reflex actions.  In a reflex action three types of neurone are involved sensory, relay and motor neurones.

In a reflex action: 1. Impulses from a receptor pass along a sensory neurone to the central nervous system. 2. At a junction (synapse) between a sensory neurone and a relay neurone in the CNS, a chemical is released which causes an impulse to be sent along a relay neurone.

3. A chemical is then released at the synapse between a relay neurone and a motor neurone in the CNS. This causes impulses to be sent along a motor neurone to the organ (effector), which brings about the response. 4. Effector is either a muscle or a gland. A muscle responds by contracting, a gland by releasing chemical substances.

Reflex Arc

More about Co-ordination  Read all information given on the sheet.  Answer questions 1 & 2  Using your knowledge MI 11 Answer questions (a) and (b)

Synapse  A synapse is the small gap between neurons, when an impulse reaches the end of an axon a chemical is produced. The chemical diffuses across the gap; it starts off an impulse in the next neuron.  Only one end of a neuron can make this chemical, so synapses make sure the impulse can only travel in one direction.

Synapse

Synapses are easily affected by drugs:  Can block them  Can make them work too quickly  Alcohol can affect synapses, which can slow down peoples ’ reactions.

Drugs and the nervous system  There are 4 main categories of drugs which can affect our nervous system: Sedative slow down the brain making you feel sleepy. Stimulants speed up the action of the brain making you more alert. Hallucinogens cause hallucinations Painkillers suppress the part of the brain that senses pain.

The Eye Sight is one of our most important senses. The eye lies in a socket in the skull, and is moved by the action of three pairs of eye muscles, which swivel the eye in their sockets.

Structure of the Eye  The sclera is the tough, white protective layer which surrounds the eye.  The cornea is the transparent region at the front of the sclera. The cornea allows light to enter the eye.  The iris surrounds the pupil controlling its size and the amount of light which enters the eye.

Structure of the Eye  The lens changes shape to focus light onto the retina, it is held in place by ciliary muscles and suspensory ligaments.  The retina contains receptors cells which are sensitive to light. There are two types of receptor cells Rods – work in dim light Cones – detect colour and details

Seeing Things  Light enters the eye through the cornea  It passes through the lens  It is focused on the retina  Receptor cells in the retina send impulses to the brain along sensory neurones along the optic nerve  The brain interprets the impulse to make a picture

The Iris Reflex  The Iris reflex prevents too much light entering the eye and damaging the retina  Increased light reaches the retina Light sensitive cells in retina send impulses along a neurone to the brain Brain sends impulses along another neurone to the iris muscles Size of pupil decreases

The Iris Reflex  Stimulus  Receptor  Sensory neurone  Brain  Motor neurone  Effector  Response

Iris Reflex

The Eye

Focusing  When light rays enter the eye they are refracted by the cornea and the lens.  Ciliary muscles and suspensory ligaments control the shape of the lens.

Looking at a near object  Ciliary muscles contract  Slackens suspensory ligaments  Elastic lens goes fatter  Near object is focused on the retina

Hearing and Balance

Hearing  Having two ears rather than one makes judging the direction of sound more accurate

 ear drum thin membrane which picks up the vibrations of sound waves  bones of the middle ear (hammer, anvil & stirrup) amplify the vibrations and pass them on to the cochlea  cochlea long coiled tube in the inner ear filled with fluid it picks up the vibrations and changes them to electrical signals

 auditory nerve connects the inner ear to the brain it carries the electrical signals from the cochlea  semi-circular canals detect movements of the head help control balance and tell us which way up we are

Balance  The semi-circular canals are 3 tubes at right angles to each other - they pick up movements of the head by detecting movements of the fluid they contain

 These movements are turned into electrical signals since there are 3 canals at right angles the brain can use these signals to give 3- dimensional information to help control balance and tell us which way up we are.

The Brain

The brain  The brain is at the top of the spinal cord and is protected by the skull.  Cerebrum Controls memory, personality, imagination and reasoning  Cerebellum Controls muscle coordination and balance  Medulla Controls heart rate and breathing