Neurones and the Reflex Arc (NAT 5 ONLY) PUPIL NOTES

By the end of the lesson you will be able to ….. Describe how a neurone is suited to it’s function. Describe the flow of information through a reflex arc. National 5 only outcomes

We know that our nervous system helps us sense the world around us. How?

Neurones Our nervous system is made of nerve cells called neurones CELL BODY NERVE FIBRE (Axon)‏ Our nervous system is made of nerve cells called neurones Consist of a cell body attached to very long nerve fibre Electrical impulses carry messages along neurones.

Flow of Information Specialised cells called receptors pick up stimuli, e.g. pressure or heat receptors in the skin. Sensory nerves carry information back to CNS Brain interprets (or “sorts out”) this data

Flow of Information 4. CNS sends nerve messages (via electrical impulses) along motor nerves to appropriate muscles/glands – effector organs

Flow of Information CNS STIMULI RESPONSE e.g. touch/light SENSORY NERVES MOTOR NERVES RECEPTORS (e.g. sense organs) EFFECTORS (e.g. muscle & glands) STIMULI e.g. touch/light RESPONSE e.g. movement/ hormone release

SRM Reflex arc The neural pathway that controls a reflex action Involves 3 types of neurone: Sensory neurone Relay neurone Motor neurone SRM (MRS backwards!!)

Iris contraction Bright light – iris contracts – pupil contracts – less light enters eye Dim light – iris relaxes – pupil dilates – more light enters eye

Corneal (Blink) Reflex Clapping your hands in the face of someone (is rude) and causes rush of air into the eyes The head jerks backwards and blinking of both eyes

Reflex Actions Pharyngeal Reflex Gag reflex caused by touching soft palette at back of throat Removing hand from flame Rapid muscle movement removes hand from immediate danger Suckling reflex in infants Exploits every chance to feed Why does the body usually need reflex actions? Protective reactions / Postural readjustments (e.g. neck jerk reflex when asleep)‏

Rapid conduction of impulses through the reflex arc Sensory neurone Synapse Relay neurone Response: arm muscles contract and hand withdraws Pain receptors stimulated Motor neurone Effector: muscles of the arm Harmful stimulus from a hot object

Reflex Action The transmission of a nerve impulse through a reflex arc results in a reflex action. Reflex actions protect the body from damage. They can be a rapid action from a muscle (e.g. limb withdrawal) or a slower response from a gland (e.g. the release of a hormone).

Synapse There is a tiny space between two meeting neurones Space between sending neurone and receiving neurone is called a SYNAPSE When nerve impulse reaches end of axon, a chemical is released Triggers off an impulse in the receiving neurone

Synapse A synapse occurs between neurons. When a nerve impulse reaches the end of an axon, a chemical is released Chemicals diffuse across the space Triggers off an impulse in the receiving neurone