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Part Two: OCR UNIT
1…read more

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Sensory Receptors
Sensory receptors are specialised cells that detect changes in surroundings,
they are transducers, they change on form of energy to another. The change in
energy levels are the stimulus which are then converted into electrical energy....
Rods and cones (found in the retina): light intensity and colour.
Taste buds: presence of soluble chemicals.
Olfactory cells (found in nasal cavity): presence of volatile chemicals.
Cochlea (found inner ear): Vibrations in the ear.
Muscle spindles: length of muscle fibres.…read more

Slide 3

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Sensory and Motor neurones
Just motor
From CNS to effector.
Have their cell body in the
CNS and a long axon that
carries action potential to
It's long so the transmission
can be carried over long
Maintain a potential difference across
membrane. Always ready for transmission.
Lots of organelles such as mitochondria.
Lots of dendrites to connect to other cells.
Just sensory
Along dendron (not part of
CNS) carries action
potential to cell body.
Where the CNS and short
axon transmit potential to
intermediate neurones.…read more

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Resting and Action Potentials
Key terms to know:
Polarised Membrane: has a potential difference across it, this is when it is
Depolarisation: Loss of polarisation caused by the entry of Na+ ions into the
Generator potential: small depolarisation caused by Na+ entry.
Action potential: achieved when membrane is depolarised to +40mV. It is an all
or nothing response.
Voltage gated channels: allows the passage of charged ions which open as a
response to a potential difference of -50mV across a membrane.
Threshold potential: difference across a membrane of -50mV must be
reached before an action potential can be created.
Action potential: Depolarisation of the cell membrane so it is more positive
than the outside (a potential difference of +40mV). This is transmitted along the
axon.…read more

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How is a Resting potential established?
Na+/K+ pump actively transports (using ATP hence the large amount of
mitochondria) 3Na+ out of the cell for every 2K+ into the cell.
Large organic anions maintains a negative potential (-60mV) to create a
polarised membrane.
How is an Action potential generated?
The generator regions in the receptors are changed by the environment causing
depolarisation of the sensory receptors.
Na+ ions diffuse through open channels into the axon. Na+ quickly travels down
a concentration gradient.
If the depolarisation is big enough and reaches the threshold potential (-50mV)
voltage-gated channels will open. This is causes a large amount of Na+ to travel
down a concentration gradient. When reaching +40mV the action potential is
created and transmitted.…read more

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Interpreting graphs
1. Membrane in resting state(-60mv)2. Na+ channels open some Na+ diffuses into axon 3.
membrane depolarises and reaches threshold potential. 4. voltage-gated Na+ channels
open, more can diffuse into axon becomes more + charged 5. Reaches action potential
value 6. Na+ channels close and K+ channels open. 7. K+ diffuse out of the axon to
repolarise the membrane 8. Potential difference decreases too much (hyperpolarises) 9. The
resting potential is restored.…read more

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