1.9 Nerves and sensitivity

Natural sciences

Grade 9

Life processes: healthy life

Module 10

Nerves and sensitivity

• Sensitivity involves your capacity to react to your changing (internal and external) environment.

1. Indicate the stimulus-reactor path for the process that follows when a bee stings you on the hand.

2. Add the captions to the illustrations of the brain and the neuron.

1. Write down the functions of the following:

Brain, spinal cord, motor neuron, sensor neuron

1. Write down the stimulus and sensation of each sense organ:

• Light rays penetrate the lens to fall on the retina
• Image is formed
• Cones and rods stimulated
• Impulse transmitted to brain via optic nerve

• Sound waves stimulate receptors in cochlea
• Impulse to brain via auditory nerve

• Gas molecule dissolves in mucus membrane
• Olfactory nerve transmits impulse to the brain

• Taste buds on the tongue sense only bitter, sweet, sour or salty (other tastes are perceived by the sense of smell)
• Impulse to brain

• Receptors in skin pick up mechanical, heat, touch, cold or pain stimuli.
• Impulses to brain

5. FIND OUT:

• Why :

a) you blink your eyes:

b) your nose runs when you have been crying:

c) your pupils dilate in a dark room:

d) food has no taste when your nose is blocked:

The effects of drugs and alcohol on the brain

When your body is in pain, painkillers mask the pain. You can control the nervous system’s capacity to feel. This means that medication can be applied usefully, but also that it can be misused.

Drugs are used in this way to provide excitement, but this is dangerous because it can lead to DEPENDENCY and result in TOLERANCE for particular levels of the drug. When this happens, more and stronger drugs are needed.

PAIN KILLERS :Morphine and heroin

• suppress pain

deaden the senses

STIMULANTS :Caffeine, nicotine, ecstasy anti-depressants

• enhance brain activity
• anxiety (it causes)

lead to depression

TRANQUILLISERS :Alcohol and sleeping tablets

• slow down brain activity
• willpower, judgement and self-control affected

Sluggishness and disturbances of the vision

HALLUCINOGENICS :Dagga and LSD

• feelings of wellbeing
• experiencing things that are not real

Schizophrenia

• Why do young people turn to drugs?

Assessment: APPLICATION

Could you apply your existing knowledge?

LO 2.4

Assessment

Learning Outcomes 2 : Constructing Science knowledge

The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.

We know this when the learner:

2.4 applies knowledge.

Memorandum

1. impulse/stimulus – receptor – impulse – cns – impulse – effector

2. labels: sketch brain + neurone

4. Complete the table on the senses:

5 a) reflex action to lubricate the eye with a lubricant

b) Tears drain the tear duct that opens at the back of the throat cavity – which is also the back of the nasal cavity

c) opening enlarges to allow more light

d) nasal receptors temporarily out of action; tongue only recognises sweetness, saltiness, acidity, and bitterness