Biology Unit 5 Revision Notes

Some revision cards, with questions and answers; specifically for the SNAB course: Topics 7 and 8, Unit 5. I hope they help somebody (:

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  • Created by: VicC
  • Created on: 11-06-10 17:08
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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 contract
o Radial muscles relax
Constrict pupils

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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
If potential difference threshold is reached, more Na+ channels open
Voltage-dependent Na+ channels close
Voltage-dependent K+ channels open
K+ ions move out of axon, repolarising membrane
Hyperpolarisation of membrane occurs
Voltage-dependent K+ channels close
K+ ions…read more

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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…read more

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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…read more

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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 with receptor proteins on postsynaptic
membrane, causing:
o Cation channels to open; Na+ ions flow through channels
Postsynaptic membrane depolarises, initiating an action potential
When released, the neurotransmitter is either:
o Taken up across the…read more

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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
light…read more

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Sensitivity Intensity Wavelength…read more

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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 cell decreases while inner segment
continuously actively pumps out Na+ ions.
4. So inside of cell is more negative that outside
a. Causing membrane to be hyperpolarised (-90 mv)
5.…read more

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Explain what each lobe of the brain does.…read more

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o Sensation
o Calculation
o Some types of recognition
o Memory
o Processes auditory processes
Hearing, sound, speech…read more


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