6.1 Stimulus and Response Flashcards
What is a tropism?
directional growth towards (positive) or away (negative) a stimulus
What is phototropism?
a directional growth in response to light
What is gravitropism?
directional growth in response to gravity
Where is IAA produced?
in the tips of roots and shoots
What is the effect of high conc of IAA in the shoots?
causes cell elongation and promotes growth
What is the effect of high conc of IAA in the roots?
inhibits growth
How does IAA cause positive phototropism in shoots?
- IAA is produced in the tip of the shoot
- light causes the movement of IAA
- IAA diffuses to the shady side of the shoot - a greater conc builds up on the shaded side
- IAA promotes cell elongation and growth occurs more on this side
- the shoot bends towards the light = positive phototropism
How does IAA cause positive gravitropism in roots?
- cells in the tip of the root produce IAA
- gravity influences the movement of IAA from the upper side of the root to the lower side of the root
- a greater conc of IAA builds up on the lower side
- IAA inhibits elongation of cells, the cells on the lower side grow less than the upper side
- causes the root to bend downwards towards gravity = positive gravitropism
What does a plant do in response to light when the shoot tip is removed?
it has no response to light = no IAA present in the shoots for phototropism
What is a taxis?
a directional response to a stimulus - the whole org either moves away (negative) or towards (positive) the stimulus
What is a kinesis?
non-directional movement response, the rate that an organism changes direction is affected by the intensity of the stimulus to find a more favourable environment
What are reflexes?
rapid involuntary responses
they are effective from birth and they do not need to be learned
Why are reflexes important to an organism?
protect against damge to body tissues
enables homeostatic control
enables escape from predators
What is the advantage of the reflex arc only having 3 neurons?
limits the number of synapses
What do sensory neurons do?
carry electrical nerve impulses from the receptor to the CNS
What are immediate neurons?
they synapse with the sensory neurone and the motor neurone - usually the coordinator
What are the stages of the reflex arc?
stimulus - receptor - sensory neurone -relay neurone - coordinator (immediate neurone) - motor neurone - effector - response
What are the features of all recpetors?
they respond to one specific stimulus
they act as a transducer - creating a generator potential
they convert energy of the stimulus into nervous impulses - generator potential
What is the structure of the pancinian corpuscle?
- single sensory neurone at the centre of layers of tissue (lamellae)
- each layer is separated by a gel
- capsule surronds the layers
- sensory neurone has strech mediated sodium channels in its membrane
What stimulus does the pacinian corpuscles respond to?
mechanical stimuli - changes in pressure
Describe how a pancinian corpuscle produces a generator potential in response to a specific stimulus
- increased pressure deforms the lamella
- deforms the strech-mediated sodium ion channels in the membrane of the sensory neurone
- sodium ion channels open
- sodium ions diffuse in
- causes the inside of the neurone to become more positive = depolarisation
- generator potential is produced
What pigment is in rod cells?
Rhodopsin
What pigment is in cone cells?
iodopsin
Which pigment from rod and cone cells is sensitive to low light intensity?
Rhodopsin - rod cells
Why do rod cells have low visual acutiy?
multiple rod cells are connected to a single bipolar neurone
it will generate a single impulse to the brain regardless of how many neurones are stimulated
Why do Rod cells have an increased chance of reaching threshold value?
many rod cells synapse with 1 bipolar cell - greater chance that threshold is reached through spatial summation
Why are images black and white from rod cells?
rhodopsin cannot distinguish different wavelengths = it is broken down by all wavelengths of light
only 1 type
How do rod cells create a generator potential?
rod cells absorb light energy and rhodopsin is broken down by the light energy
there is enough energy from low-intensity lght to cause the breakdown of rhodopsin
if enough pigment has been broken down = the threshold is met in the bipolar cell
Why can the threshold be reached by rod cells in low light intensities?
many rod cells are connected to a single bipolar cell = spatial summation
What is the issue with many rod cells joined to 1 bipolar cell?
low visual acuity = the brain cannot distinguish between the separate sources of light that stimulated the 1 bipolar cell
What are the 3 different colours of iodopsin?
red
green
blue
How are we able to see all colours due to iodopsin?
there are 3 types and each responds to different wavelengths of light
Why cant you see colours in the dark?
not enough light energy to break down iodopsin and overcome the thresold to generate an action potential
1 cone cell is conncted to 1 bipolar cell so there is no spatial summation
What part of your eye recieves the highest light intensity?
the fovea
Where are cone cells located in the eye?
the fovea
Why do cone cells have a high visual acuity?
each cone cell is connected to a single bipolar neurone
the brain recieves separate impulses from each cone cell
Describe cone cells sensitivity to light?
iodopsin can only be broken down in bright light
stimulation of each cone cell can also not be combined to reach threshold = each has their own bipolar cell
Why are cone cells sensitive to colour?
there are 3 types of iodopsin
each is sensitive to different wavelengths of light
What is a stimulus?
any detectable change in the environment that leads to a response
What is the role of a coordinator?
formulates a suitable response
What are the 2 effectors?
muscles and glands
What is the role of IAA in plants?
controls plant cell elongation
What are the 2 coordinators?
the brain and spinal cord
What is the NS divided into?
the central NS
the peripheral NS
What is the peripheral NS divided into?
sensory pathways and motor pathways
What do sensory pathways of the peripheral NS do?
carries impulses from receptors to the CNS
What do motor pathways of the peripheral NS do?
carries impulses away from the CNS to the effectors
What is the motor pathway divided into?
somatic NS and autonomic NS
Is the autonomic NS involuntary or voluntary?
involuntary
What is the autonomic NS divided into?
sympathetic division and parasympathetic division
What is the process of a reponse generated from the refelx arc?
- stimulus
- receptor in skin
- sensory neurone pases nerve impulses to spinal cord
4.intermediate neurone passes impulses across the spinal cord - motor neuron passes impulses to effector
- effector reponds
- response
What does a transducer do?
changes 1 form of energy to another form
Do you have more rod cells or cone cells?
rod cells
Where are rod cells located?
the periphery of the retina
What is an advantage of plants having positive phototropisms?
for more photoionisation of chlorophyll = more light absorbed
What is the advantage of plants positive gravitropism?
more anchoring in the soil
What is the role of the sino atrial node (SAN)?
it initiates the rhythm of the heart as a pacemaker
What does it mean that the SAN is myogenic?
it is independant of the nervous system and doesnt require nervous stimulation to contract
Where is the SAN located?
in the wall of the right atrium
Describe how the SAN causes the atria to contract
- the SAN sends out broad waves of depolarisation across both atria
- this stimulates atrial systole
- blood is pushed into the ventricles through the open AV valves
Why is there a delay of electriacl activity between atrial systole and ventricular systole?
allowing time for the ventricles to completely full before ventricular systole
What is the role of the atrioventricular node (AVN)?
initiates ventricular systole
Describe how the AVN causes ventricular systole
- AVN picks up wave of depolarisation from SAN
- transmits electrical activity as an impulse down the apex of the heart through the bundle of his
- impluses reaches the apex and spreads up the purkinje fibres
- spreads up through the walls of the ventricle
- ventricles contract upwards to force blood up to the arteries
What motor pathway is the control of heart beat part of?
the autonomic nervous system
What is the role of the sympathetic NS?
speeds up and stimulates effectors
What is the role of the parasympathetic NS?
inhibits glands to release hormones and slows the activity of effectors when resting
Describe the role of the sympathetic NS in controlling heart rate
- increased resp in cells increases CO2 conc so pH falls
- detected by chemoreceptors in the carotid arteries
- sends impulses to the cardiac centre in the medulla’s cardio-acceloratory centre
- acceleratory centre in the medulla sends more impulses to SAN by sympathetic nervous system
- increase in impulses sent out by the SAN = increase atrial systole
Why does caffeine increase heart rate?
more action potentials along sympathetic nervous system pathway
to the SAN increasing the heart rate
Describe the role of receptors and the nervous system in increasing heart rate
- chemoreceptors detect rise in CO2 / fall in pH
- Sends impulses to cardiac cente in medulla
- by sympathetic nervous system
- more impulses sent to SAN (higher frequency)
Explain how both the ventricles contract at the same time after the initiation of the heartbeat by the SAN
- electrical activity only through Bundle of His
- wave of electrical activity passes over / through both ventricles at the same time
Describe how the parasympathetic nervous system reduces heart rate
- decreased respiration in cells decreased CO2 conc in blood, increase in pH
- detected by chemoreceptors
- sends more impulses to the cardio-inhibitory centre in the medulla
- cardiac centre sends more impulses to the SAN by parasympathetic NS
- inhibits the SAN to intiate the heart beat
What is the role of the cardio-acceleratory system?
responsible for speeping up heart rate
What is the role of the cardio-inhibitory centre?
responsible for slowing down heart rate
What is a baroreceptor?
a pressure receptor
What happens when a baroreceptor deters high blood pressure?
the medulla sends impulses along the parasympathetic neurons to reduce heart rate
What happens when a baroreceptor deters low blood pressure?
medulla sends impulses along sympathetic neurones to increase heart rate
What happens when a chemoreceptor detects a low pCO2 / high pH?
medulla sends impulses along parasympathetic neurones to reduce heart rate
What happens when a chemoreceptor detects a high pCO2 / low pH?
medulla sends impulses along sympathetic neurones to increase heart rate
where are the chemoreceptors and the baroreceptors found?
in the wall of the carotid arteries
How does the SAN coordinate both ventricles to contract at the same time?
electical activity passes down the bundle of His
waves of electrical activity pass over both ventricles at the same time
How do rod cells allow orgs to see in the dark?
they have a high sensitivity
multiple rod cells are connected to a single bipolar neurone
so the threshold is reached/ overcome by spatial summation
What are the 2 types of muscles in the eye?
radial muscle and circular muscle
How do radial muscles and circular muscles in the eye cause the pupil to contrict (narrow)?
circular muscles around the iris contract so the iris is constricted
the radial muscles relax so that the circular muscles can contract
