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topic 9:control systems - Coggle Diagram
topic 9:control systems
homeostasis
maintaining pH, temperature and water
potential in the body.
feedback
negative feedback:change is system detected, message sent to control unit, message sent to effectors, effectors bring about change in the opposite direction
positive feedback:change is system detected, message sent to control unit, message sent to effectors, effectors bring about change in the same direction
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mamalian nervous system
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spinal chord:
cylindrical structure, tiny central canal, inner grey matter, surrounded by white matter, protected by vertebrae and backbone>
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periphorousNS
voluntary NS
neurones to skeletal muscles, mostly under conscious control.
autonomic NS
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- neurones to muscles- cardiac muscles and glands not under conscious control>
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nervous transmission
- once the potential difference reaches +30mV, this initiates
repolarisation
- Na+ channels close
- K+ channels open leaving K+ to leak out
- this causes hyper polarisation when too much K+ leaks out
- The Na+/K+ pump restores the resting potential by pumping Na+ out and K+ back in
upon stimulation (depolarisation)
- Na+ channels open allowing Na+ ions in and once the inside of the nerve reaches
-55mV, other channels open
- K+ channels close
in resting potential,
- nerve cells are polarised with a
- 70mV charge,- Na+/K+ pumps Na+ out and K+ into the nerve cell
- K+ Chanel pumps K+ ions out of the cell
- Na+ Chanels closed
- outside of the cell is positively charged
an action potential is propagated along a nerve as a wave of depolarisation, Na+ ions move to the adjacent resting region where they trigger a change in potential difference triggering another action potential
speed of nervous impulse:
- nerves with a myelinated sheath( an insulator for axon made from Schwann cells)
- salutary conduction when impulse jumps between gaps in sheath into nodes of ranvier because myelin sheath is impermeable
- it is faster for impulse to jump from node to node than to to activate an action potential all along nerve
synapses
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function:
- upon arrival of action potential the presynaptic membrane depolarises causing Ca2+ channels to open allowing them to enter the neurone
- Ca2+ causes the fusion of synaptic vesicles with a particular neurotransmitter to the presynaptic membrane
- neurotransmitters released into synaptic cleft- neurotransmitter binds to receptor on post synaptic membrane
excitatory post synaptic potential
- opening of cation channels
- Na+ enters cell
- membrane depolarises
- action potential
inhibitory post synaptic potential
- opening of anion channels
- Cl- ions enter neurone
- hyperpolarisation of post synaptic membrane
- makes new action potential more difficult
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detection of light
rods
- 100 million rod cells in one human eye
- multiple rod cells connected to one bipolar neurone
- low resolution image- very sensitive to light
- most are found around the edges of the retina
- all contain rhodopsin
- see only in black and white
- retinal convergence
- summation:
- since loads of rods connect to a single bipolar neurone then the threshold for an action potential due to the breakdown op rhodopsin is more likely
rods in the dark:
- cis retinal rhodopsin
- Na+ channels open
- membrane depolarised
- neurotransmitter released
- inhibitory neuroreceptors open
- membrane hyperpolarised
- no neurotransmitter released
- no action potential
rods in the light:
- trans retinal rhodopsin
- Na+ channels closed
- membrane hyper polarised
- no neurotransmitters released
- inhibitory neuroreceptors closed
- membrane depolarised
- neurotransmitter released
- action potential
cones
- 6-7 million
- very high resolution
- no summation as there is no retinal convergence so only sensitive to high intensity light
- each cone cell connected to it s own bipolar neurone
- contains iodopsin (needs high intensity light to breakdown)
- found at the fovea where there is the most concentration of light
- there are 3 different types of cone cells
- with different forms of iodopdin which breakdown at different wavelengths of light so we can see different colours
control of heart rate
factors affecting heart rate:
- pH caused by CO2 in blood
- blood pressure
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chemoreceptors: sensory receptors that initiate an action potential in response to a change in their chemical environment
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(baroreceptors)stretch receptors: sensory receptors that initiate an action potential in response to changes in tension
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