Stimuli And Response Flashcards
Phototropism
Cells in tip of shoot produce IAA
IAA travels down shoot and increases in concentration on the shades side
Promotes cell elongation
Causing the shoot to bend towards the light
Tropism
The growth of a plant in response to a directional stimulus
Positive vs negative responses
Positive- growth/ movement towards
Negative- growth/ movement away
Gravitropism
IAA produced by cells in shoot tip IAA transported down shoot into root IAA increases in conc on the lower side of roots Inhibits cell elongation Roots curve downwards towards gravity
Define a stimulus
A detectable change in an organism’s environment that leads to a response
Importance of a reflex arc
3 neurones, few synapses so rapid
Automatic does not involve the brain, does not have to be learnt
Response able to be carried out quickly, protect against harm
Taxes
Directional response ( movement towards or away) made by simple mobile organisms to a stimulus
Kineses
Non- directional responses by simple mobile organism to a non- directional stimulus
altering their speed or direction of movement
Benefits of taxis/ kinesis
Increases changes of finding a favourable environment to increase chances of survival
How a pacinian corpuscle produces a generator potential
Mechanical stimuli deforms lamellae and stretch meditated sodium-ion channels
Opens sodium ion channels
Sodium ions diffuse into sensory neurone, depolarising it
Forming a generator potential
If threshold reached- action potential
Rod cells
Black and white vision
One type
Low visual acuity
Highly sensitive to light
Where are rod cells found?
Periphery of the retina
None at fovea
Why do rod cells have the high sensitivity to light?
Many rod cells are connected to one bipolar neurone
Spatial summation occurs! Many impulses converge to one bipolar neurone
More likely to collectively reach the threshold and cause an action a potential
Why do cone cells have high visual acuity?
One cone cell connected to one bipolar neurone
If 2 adjacent cones are stimulated the brain will receive 2 discrete different impulses
Therefore able to distinguish between two different sources of light
Resting potential
Sodium potassium pump Active transport 3 NA+ out 2 K+ in Membrane more permeable to K+ K+ diffuses out via facilitated diffusion down electrochemical gradient Polarised
Generation of an action potential
Stimulus detected,
Membrane becomes more permeable to NA+, NA+ channels open
NA+ diffuse in down electrochemical gradient through facilitated diffusion
Depolarised
If pd threshold reached, action potential generated
Voltage gated NA+ channels open
Influx of NA+ into axon
Then voltage gated K+ channels open, membrane becomes more permeable to K+, NA+ begin to shut
K+ diffuse out of axon
Repolarised, becoming more negative
Hyper polarisation occurs as K+ channels are slow to close, so slight overshoot in number of K+ that leave
Refractory period- during which non action p can be gen ( uni, discrete impulses)
Restring potential then restored by sodium-potassium pump
Effect of myelination
Faster nervous transmission as depolarisation only has to occur at nodes of ranvier
Saltatory conduction, impulses jump
Depolarisation does not need to occur across the whole length of the axon
Cone cells
Coloured vision 3 types, dependant on wavelength of light Low sensitivity High visual acuity One cone to one bipolar neurone Found at fovea
Where are rods distributed?
Periphery of retina, except fovea and blind spot
Where are cones found?
High concentration around fovea
How is resting heart rate maintained
Cardiac muscle myogenic
SAN acts as a pacemaker and sends out regular waves of impulses
Impulse reached SAN, causes atria to contract simultaneously
Impulse travels to AVN
Impulse is delayed
Impulses travel down bundles of his and purkyne fibres
Ventricles contract from the bottom upwards
Where in the brain is in charge of controlling heart rate?
Medulla, cardio-vascular centre
Role of sympathetic neurones
Increase frequency of impulses sense to SAN
When bp is too low / CO2 con too high
How bp is increased
Low bp detected by baroreceptors in the aorta
More freq impulses sent to medulla
More freq impulses sent to SAN via sympathetic neurones
More frequent impulses sent from SAN
Cardiac muscle contracts more frequently
Response to high blood ph ( low CO2)
Chemoreceptors in Aorta detect
Increased frequency of impulses sent to medulla
Increased frequency of impulses sent to SAN via parasympathetic neurone
SAN sends out impulses less frequently
Cardiac muscles contract less frequently
Effect of temperature on speed of nervous transmission
Increased temperature= increased rate of impulse transmission
K+ and Na+ ions move faster as more kinetic energy
Active transport quicker as faster rate of respiration, faster rate of ATP production
Temp gets too high- proteins like sodium potassium pump denature- rate slows
Effect of axon diameter on rate of nervous transmission
Bigger the diameter
Faster the rate of transmission
Bigger so less leakage of ions
Neuromuscular junction vs normal synapse
Neuro neurone to muscle, nor neurone to neurone
Neuro always excitatory
Neuro has more receptors on post synaptic membrane
Neuro’s post synaptic membrane if highly folded into clefts
Role of acetylcholine
Excitatory neurotransmitter
Released from neuromuscular junctions
Role of AchE
Enzyme released from post-synaptic membrane to break down acetylcholine
So the neurotransmitter cannot keep binding to receptors
So response does not keep occurring
Refractory period
Period it takes to restore resting potential after hyper polarisation
No action potentials can be generated
Ensures impulses are uni directional and discrete
Unidirectionality due to synapses
Neurotransmitter only released from pre-synaptic neurone
Neurotransmitter receptors only found on post-synaptic membrane
Inhibition by synapses
Hyperpolarise post-synaptic neurone
K+ diffuse out
Cl- diffuse in
No action potentials can form as depolarisation cannot occur/ reduces effect of any sodium ions entering sp reaching of pd threshold for ap less likely
Use of the refractory period
period in which no action potentials can be generated
makes nervous impulses discrete and unidirectional
lists frequency of impulses
once maximum frequency of impluse reached any further increase in the strength of the stimuli will not lead to a stronger response- all seem the same
What is the purpose of the refractory period?
limits frequency of impulses, thus intensity of response
ensures impulse are unidirectional, action potential can not be propagated in a hyper polarised region
implies are discrete, action ponytails cannot overlap
the passage of an action potential along a non-myelinated neurone
action potential passes along as waves of depolarisation
the influx of sodium ions into one region causes the voltage-gated sodium ion channels of the adjoining region to open
causing sodium ions to diffuse into the neurone and depolarise it
