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How is the pupil size controlled in BRIGHT light?

STIMULUS: bright light
Detected by photoreceptors in the retina
Sends nerve impulses along optic nerve
Along sensory neurone
o Information is processes
Impulses are sent along parasympathetic motor neurones
EFFECTORS: circular muscles of iris are stimulated
o Circular muscles…

Page 2

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How is the impulse propagated along a myelinated axon?

Neurone is stimulated, causing voltage-dependent Na+ channels to open
Na+ ions diffuse into axon
Depolarisation of membrane increases (to +40mv)
Action potential is generated at Node of Ranvier
Local circuit is produced
Second action potential is generated by the first

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A time delay between one action potential and the next

Lasts until all voltage-dependent K+ and Na+ channels close, returning to
normal resting potential state

Ensures the impulses are UNIDIRECTIONAL: travel in just one direction

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How are impulses passed along a MYELINATED neurone?

Depolarisation occurs at Node of Ranvier

Local electric current occurs between nodes

Potential difference is reduced at the next node, initiating another
action potential

Impulses `jump' from one node to the next by SALTATORY CONDUCTION

Page 5

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How do Synapses transmit an impulse?

An action potential arrives at the presynaptic membrane
Membrane depolarises, causing:
o Calcium ion channels to open; calcium ions enter neurone
Increased calcium ion concentration causes synaptic vesicles (containing
neurotransmitter) to fuse with presynaptic membrane
Neurotransmitter released into synaptic cleft by EXOCYTOSIS
Neurotransmitter binds…

Page 6

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List some differences between Rods and Cones

Rods Cones
Numbers in Retina 2
Where in Retina All over Retina but not ONLY fovea
Light-sensitive Rhodopsin Iodepsin
Vision Only black & white Colour vision
vision ONLY in bright light
Both dim & bright

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Sensitivity Intensity Wavelength

Page 8

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How does light reaching a rod cell result in an action potential in the optic
nerve to the brain?

1. Light energy breaks rhodopsin opsin + retinal
2. Opsin binds to the membrane of the outer segment
a. Causes Na+ channels to close
3. Influx of Na+ ions into rod…

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Explain what each lobe of the brain does.

o Decision making
o Reasoning
o Planning
o Forming association: info ideas
o Includes primary motor cortex:
Stores info

OCCIPTAL LOBE: (visual cortex)
o Processes info from eyes
Vision, colour, perspective
o Orientation

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o Movement
o Sensation
o Calculation
o Some types of recognition
o Memory

o Processes auditory processes
Hearing, sound, speech


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