hormone, receptors

• 1
  •  FSH stimulates follicle development
  • Follicle release s production of oestrogen
  • FSH stimulates ovaries to release oestrogen
• 2
  • 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

• 4
  • ovulation is stimulated by LH- follicle ruptures egg is released
  • LH stimulates ruptured follicle to turn into a corpus luteum
  • Corpus luteum releases progesteron
• 5
  • progesterone inhibit FSH and LH
  • Uterus lining is maintained, corpus luteum breaks down and stop release of progesterone
• 6
  • Fall concentration of progesterone
  • FSH and LH conf rise again

• 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.

• 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

• 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

• 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)

• 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)

• 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.

• 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

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.

• 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)

• 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.

• 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

• 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.