hormone, receptors

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CONTROL OF OESTRUS CYCLE

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    •  FSH stimulates follicle development
    • Follicle release s production of oestrogen
    • FSH stimulates ovaries to release oestrogen
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    • Rising concentration oestrogen so uterus lining to thicken
    • oestrogen inhibits FSH release from pituitary gland
    • High concentration stimulates pituitary glands to release LH and FSH
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MORE OESTROGEN CYCLE

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    • ovulation is stimulated by LH- follicle ruptures egg is released
    • LH stimulates ruptured follicle to turn into a corpus luteum
    • Corpus luteum releases progesteron
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    • progesterone inhibit FSH and LH
    • Uterus lining is maintained, corpus luteum breaks down and stop release of progesterone
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    • Fall concentration of progesterone
    • FSH and LH conf rise again
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CARDIOVASCULAR CENTRE CONTROL THE HEART

  • There are two seperate nerves for cardiovascular centre to SAN
    • Sympathetic nerve - speeds up
    • Parasympathetic nerve - slow down
  • Increase stroke volume
    • vasoconstriction increase blood pressure so more blood fills the heart at diastole
    • Decrease stroke volume cause vasodilation.
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STIMULI & REFLEX ARC

  • Stimulus - Change in an organisms environment that can be detected by receptor cells
  • Receptors - specialised cells that detect a stimulus and initiates a nerve impulse
  • Taxes and kinesis - Simple behavior response seen in organsims that can move
  • kinesis - change in speed of random movement in response to environmental stimulus e.g woodlice
  • Taxes - DIrect movement towards or away from a stimulus. There are positive and negative taxes. move towards- positive, moves away-negative
  • tropisms - they grow in a particular direction.

reflex arc

  • sensory neurone - nerve cells that carries impluse from a receptor to the central nerve system.
  • central nervouse system/relay neurones - The CNS processes incoming information and produce a response
  • motor neurones - nerve cells that carries implulse from CNS to effector
  • effector - organs thst bring a response- usually muscle or glands
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THE RETINE

  • Single layer of light - sensitive receptor cells (rodes and cones)
  • Rods and cones differ in sensitivity and visual acuity
  • sensitivity refers to the level of light needed for cells to function.
  • Acuity refers to their ability to precieve details
  • cones
    • detect colour
    • sensitive to hight light intensity
    • high visual acuity
    • concentrated at one point 'fovea;
  • Rodes
    • detects black and white
    • sensitive to low light intensity
    • low visual acuity
    • distributes evenly across retina
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RESTING POTENTIAL and ACTION POTENTIAL

  • How does the inside of the axon remain negative?
    • active transport, Na and K pumps will export three Na ions and import two K ions  there for it is more positively charges in the inside of the axon
    • More K channels in the membrane more K diffuses out due to difference in concentration gradient
    • There are negatively chraged anions e.g glucose, proteins and amino acids that cannot cross the membrane.

Action potential

  • Stimulus causes sodium voltage - gated channels in the axon membrane to open
    • sodium diffuse inside
    • positive charge move inside so more positive axon causing reveral charge(depolarisation)
    • More sodium channel open greater influx of sodium ions
    • when axon become to positive so sodium channel closes and potassium pumps opens so that positive ions are removed out.
    • K voltage - gate channels now open, increase in concentration stimulates more to open so more K ions diffuses out (repolarisation)
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The nerve impluse

  • Saltatory conduction
    • Action potential 'jumps' from one node to another
    • increase speed of transmission
    • Action potential, inlfux of Na ions causes the displacement of K ions down the axon
    • diffusion of K makes next node more positive and depolarises it until threshold is reached
  • all or nothing principle
    • impluse always has the same amplitude
    • threshold level of stimulation must be reached (generator potential) to intiate an action potential
    • high level of stimulation causes high frequency of impulses (more per ms)
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Synapse

  • action potential arrives at pre-synaptic neurone
  • Ca  channels open (voltage-gated)
  • Ca  influx (move in)
  • vesicles (containing neurotransmitter) move to pre-synaptic membrane
  • vesicles fuse with pre-synaptic membrane and neurotransmitter is released into synaptic cleft (exocytosis)
  • neurotransmitter diffuses across synaptic cleft
  • neurotransmitter binds to shape specific neuroreceptors
  • neurotransmitter binding causes Na  channe;s to open
  • Na  influx causes depolarisation
  • neurotransmitter must be removed from synaptic cleft to stop the synapse being permanently on. 
  • cholinesterase breaks down the neurotransmitter acetylcholine
  • Active process to reform acetlycholine into vesicles (endocytosis) -initiates an action potential.
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Nerve system

  • summation
    • Grand post-synaptic potential - sum of excitatory and inhibitory potential
    • spactial summation - sum of potential from different neurones coming into one synapses
    • temporal summation - sum of potential from one neurones building up over time
  • importance of synapses
    • integration of information (combinations)
    • enabls filtering out of non-essential information
    • nerve impulses are unidirectional
    • nerve impulses can be passed along seperate pathways
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RECEPTORS IN THE SKIN

mechanisms of skin recepltors

  • Pacinian corpuscles - mechanoreceptors
  • Detect strong pressure
  • each corpuscles consist of sensory neurone surrounded by a capsule layer of flattened schwann cells and fluid called lamellae
  • pressure distort the neurone cell membrane and opens mechanically - gated sodium channels
  • sodium ions diffuses in causing depolarisation called generator potential 
  • stronger pressure the greater the generatir potential intil threshold is reached.
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Neuromuscular junction

  • continue from synapse
  • How does action potential result in muscle contraction
    • action potential travel into t-tubules
    • this affects the sarcoplasmic reticulum which contains Ca
    • Ca  released into sarcoplasmic reticulum
    • The release causes the muscle contraction
    • (T-tubules is the post-synaptic neurones)
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Plant Responses

  • IAA causes plant cells to elongate
  • causes the plant to grow towards the light
    • cells in the tip of the shoot produces IAA, which is then transported down tbe shoot
    • light causes movement of IAA from the light side to the shaded side of the shoot
    • greater concentration of IAA on shaded side
    • cells in shaded side elongate more due to higher concentration of IAA
    • shaded side of plant grow faster causing the bend towards the light.
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Mucles

  • Cross bridge cycle
    • cross bridge (when myosin attached to actin) swings out from the thick filament and attaches to the this filament - actin
    • cross bridge changes shape adn rotates, this causes the filament to slide. Energy from ATP splitting is used for the 'power stroke' - pull actin towards the centre of the sacromere
    • New ATP molecule bind to myosin and cross bridge detaches from the actin
    • cross bridge changes back to original shape, while detached.
  • ATP needed for muscle to relax
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Mucles

  • Sliding filament theory - summary -
    • impuolse arrives down the motor terminates neuromuscular junction (modified synapse)
    • synapse secrets acetylcholine
    • acetylcholine fits into receptor site on motot end plate
    • binding causes change on permeability of the sarcoplasmic reticulum. So there is an influx of calcium ions which minds to troponin which then changes shape
    • troponin displaces tropomyosin so that myosin head can bind to actin
    • myosin head pulls backwards, actin is pulled over the myosin - power stroke
    • ATP molecule becomes fixed to the myosin head and causes it to detach from the actin
    • splitting the ATP to provide energy to move myosin head back to original position 'cocking the trigger' again
    • calcium actively removed from the sacroplasm.
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