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

2. 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

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

4. 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.

5. 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

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

7. 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

8. 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!!)

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

10. 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

11. 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)‏

12. 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

13. 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).

14. 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

15. 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