receptors + control of heart rate Flashcards
what is the role of receptors
-gather info from the environemnt and transmit it to the CNS via the sensory neurons
what is the generator potential
-to convert one form of energy to another
-the stimulus to electrical energy (nervous impulse)
what are the 3 specific examples of receptors that I need to know abt
-pacinian corpuscle
-rod cells
-cone cells
what does the pacinian corpuscle only respond to
-changes in mechanical pressure - it is a mechanoreceptor
where are pacinian corpuslces found
-the skin
-tendons
-muscles
-joints
OF MAMMALS
what does the pacinian corpuscle consist of
-single senosry neuron
-one end of which consits of a capsule made of rings of connective tissue that acts as a pressure-sensitive pad
-depolaristaion in the middle of the capsule
describe how the pacinian corpuscle works
1-the STRECH-MEDIATED SODIUM ION CHANNEL PROTEINS are too narrow to allow sodium ions through in their normal resting state - this is the neurones’ resting potential
2-application of pressure against the connective tissue deforms/stretches the stretch-mediated sodium ion channel proteins in the plasma membrane - making it wider so that Na+ can pass through
3- this causes an influx of positively charged Na+ ions into the sensory neuron- this reverses the potential difference across the plasma membrane - the inside becomes temporarily +ve - depolarisation
4- the electrical potential created by the stretching is proportional to the stimulus intensity - this graded potential is known as the generator potential
5- if the stimulus is above a critical level the graded potential is high enough to trigger the transmission of the nerve impulse along the sensory neurone - if the stimulus is below the critical level then no impulse is transmitted - all or nothing law
when does the pacinian corpuscle stop responding in a situation
-when it is given an unchanging stimulus - so that the sensory system is not overloaded with unnecessary info
what is sensory adaptation
-when there is a decline in the generator potential
-so nerve impulses transmitted in a sensory neuron become less frequent
-may eventually stop
what are the two types of photoreceptor in the retina of the eye
-rods
-cones
what is the structure of a cone cell
-outer segment -light sensitive
-membrane carrying pigment - iodopsin
connected to the inner segment by connecting cillia
-mitochondira
-nucleus
-end bulb - meet bipolar cells at synapses
what is the structure of a rod cell
-outer segement -light sensitive
-membrane carrying pigemt - rhodopsin
connected to the inner segment by connecting cillia
-mitochondira
-nucleus
-end bulb - meet bipolar cells at synapses
what are the differences bwt rod and cone cells
-different pigments rod = rhodopsin/ cone = iodopsin
-shape is different - rod are skinnier
rods
- more numerous in the retina than cones
-spread approx evenly across the retina although there are none in the fovea
-occurs only as one type of cell
-unable to detect colour
-sensitive to low light intensity
-provide low visual acuity because several rods share a connection to optic nerve
cone
-less numerous in retina than rod
-more numerous in the fovea than elsewhere in the retina
-occur as 3 types of cell each with a different form of iodopsin senstve to green,red and blue light
-able to detect colour
-are only sensitive to high light intensity
-provide high visual acuity bc each cine has its own connection to the optic nerve
how are rod and cone cells arranged
-conected to pugemented epitheilium
-end bulbs connect to bipolar neruones
-these connect to ganglion cells
-the axons of the ganglion cells form the optic nerve which carry impulses to the brain
what does a rhodopsin molecule consist of
-protein unit
-opsin
-retinal unit
how do rod cells maintain a resting potential
-sodium-potassium pump
-K+ ions in Na+ out
-gated Na+ channels open so Na+ flows back in
- down conc gradient
-net result is that the cell is +ve charged at rest (depolarised)
what is the effect of the neurotransmitter glutamate on the resting potential of a rod cell
-when resting the rods secrete a steady stream of glutamate
-diffuses across the synaptic cleft and prevent the bipolar neuron from becoming depolarised
what happens when light falls onto the rod cell
-rhodopsin absorbs the light and the energy causes the rhodopin to split into opsin and retinal
-causes Na+ channels to close
-Na+ ions can no longer move into the cells and the inside of the rod cell becomes -ve charges and is hyperpolarised
-the hyperpolarisation of the rod causes it to stop releasing glutamate
-bipolar neuron now becomes depoalrised and in turn causes the generation of an action potential in the ganglion cells
-the axon of which runs along the optic nerve and an impulses is sent to the brain
what happens in the rod cell when it is dark
-cell is not depolarised so no impulse via the optic nerve
-no transmitter substance produced by bipolar cell
-transmitter substance inhibits depolarisation so bipolar cell remains polarised
-transmitter substance released by rod cell
-rod cell depolarised
-gated Na+ channels open leading to the constant inflow of Na+ ions
what is bleaching
-when the rhodopsin splits into retinal and opsin
-these need to recombine to reform rhodopsin
-to restimulate the rod cell
why do rod cells only operate in low light intensities
-very sensitive to light - so even a single photon iks enough to trigger hyperpolarisation
what is dark adaptation
-when move from light area to dark area
-not able to see very well at first
-but then rhodopsin is gradually reformed and then are able to see easier
why is cone cells /iodopsin better in high light intensity
-only broken down by high intensity
-genrated much quicker than rhodopsin
what differes bwt the 3 types of cone cell
-each type absorbs more strongly in a different section of the visible spectrum
-red,green and blue sensitive pigments
what is the trichromatic theory
-brain perceives colour as a result of the relative stimulation of each type of iodospin
-so will show 3 peaks at different wavelengths
what cone cells are stimulated is the colours perceived by the brain are orange and yellow
-red sensitive and green sensitive
how does the eye discriminate bwt different cone types
-comapring the activity of different cone tyes
-overlap in the range of light wavelengths absorbed by different pigments
how does a white object appear white
-does not absorb light - reflects red ,green and blue light
-all types of cone cell are stimulated
-brain percives objects as white
why do plants appear green
-plant absorbs blue and red light
-thereofre green cones cells are stimulated
-brain perceives as green
what is colour blindness
-caused by a lack or deficiency in one or more of the iodopsin pigment
how do mutations affect colour blindness
-pigments are protein based then mutation in the genes coding for the proteins leads to colour blindness
-genes occur on X chromo (for red and green) - so more common in men - only need one copy of ressecive mutaion to be soon in pheno
how do cone cells have the greatest visual acuity
-most concentrated at a point called the fovea
-so can see in detail
-each individual cone cell in the fovea synapsyes with one bipolar neuron and the brain is able to distinguish individual stimuli hence more detail
-in bright light - more active - see in much more detail
why do rod cells have a weaker acuity and how is this beneficial for them
-several rod cells synapse with a single bipolar neuron
-this is called convergence
-allows weal stimuli to be amplified giving the rod cells great sensitivity and increasing the ability to detect a small amount of light
weaker acuity
-brain is unable to determine in which rod cell the stimulus originated from and is therefore unable to interpret in as much detail
-more active in dim light and provide low visual acuity - cannot see in as much detail in dim light
how can humans see more than 3 colours
-overlap in the wavelength of the light absorbed
describe how the heart rate is controlled
-electrical impulse is produced at the SAN and spreads out across the atria causing the atrial cell muscles to contract
-bringing about atrial systole
-electrical impulse is stopped by the non-conduncting tissue between the atria and venticles
-AVN stimulated
-electrical impulse spreads down the Purkyne fibres to the bundle of HIS ti the base of the ventricle where there is then a slight delay in transmission of the electrical impulse
-electrical impulse spreads up the ventricles
-ventricle contracts from the base upwards
-bringing about ventircular systole
how does exercise impact the extrinsic regulation of the heart
-increased rate of respiration - more CO2 - lower pH
-chemoreceptors in aorta/ carotid artery detect CO2/ low pH
-send nerve impulse to cardiac accelerator centre in medulla of brain
-send impulse down the sympathetic nerve
-to SAN
-increases SAN activity - increases the heart rate
-increases blood flow to tissues
-increased removal of CO2
what system is extrinsic regulation of the heart an example of
negative feedback
-blood deviates from norm
-detected
-effectors restore the norm
how does extrinsic regulation work to slow down the heart rate
-increased blood pressure
-baroreceptors in aorta/carotid artery detect high blood pressure
-send nerve impulse to cardiac inhibitory centre in medulla
-send impulse down parasympathetic nerve
-to SAN
-decreases SAN
-decreases heart rate
-decreases blood pressure
what do the non-conducting tissues help achieve
-a delay bwt atrial and venticular systole
how can fibrilation of the heart occur
-when the excitation wave becomes choatic whilst passing through the ventricles in all directions feeding back on itself
-restimulates areas that have just contracted
-caused by an electric shock or extensive damage to large areas of the heart
-can be fatal
how does heart block occur
-where conduction from the atria to the ventricles does not take place
-damage to the electrical conductivity of the tissue of the heart
-this can be treated by implanting an artificial pacemaker which stimulates normal functioning of the SAN
how does adrenaline work in heart regulation
-produced from adrenal glands
-hormone acts on the heart, blood vessels,liver and fat cells
-acts as the same way as the direct sympathetic stimulation increasing the heart rate and therefore increasing the cardiac output - impulse to SAN - increasing SAN activity - increasing blood flow
-increases blood flow to the muscles supplying it with vital oxygen and glucose
what 2 types of stimulus are there
-external
-internal
what does sensitivity mean in terms of stimuli
-ability to respond appropriately to sitmuli
what is the stimulus
-a change inside or outside an organism that brings a response in the organism
what is a receptor
-a cell that detects stimulus and initiates a nerve impulse
what is an effector
-a structure that responds to the arrival of a nerve impulse or hormone triggered by a receptor - usually muscles or glands
how are stimuli detected in large multicellular organims
-sense organs
-contain receptors that are particularly sensitive to specific stimuli
how is a coordinator required
-responses usually involve the coordinated actions if many different parts of the body
what is a taxis
-type of behaviour involving the movement of an animal towards or away from the stimulus
is a taxis directional or non-directional
-directional repsonse - the direction of the stimulus rather than the intensity of it determines the response
what are the two ways in which taxes are classified
-movement towards the stimulus - positive taxis
-movement away from the taxis - negative taxis
and also by the nature of stimulus
eg earthworms move away from the light (negative phototaxis) increasing the chances of survival by taking them deep into the soil where they are better able to conserve water, find food and avoid predators
-some species of bacteria move towards a region where glucose is in a higher conc (positive chemotaxis) increases chance of survival as they rely on glucose as a food source
what is kinesis
-type of behaviour involving the animal changing its speed of the movement and/or its rate of turning as a result of the intensity of the stimulus
is kinesis directional or non-directional
-non-directional response - the response depends on the intensity of the stimulus rather than the direction
how does the rate of turning change in an organism depending on its location
-if an organism crosses a sharp dividing line bwt a favourable and unfavourable enviro its rate of turning decreases
-this raises the chance of a quick return to the favourable enviro
-if it moves a considerable distance into an unfavourable enviro its rate of turning may slowly decrease so that it moves in a long straight line before it turns, often very sharply - this tends to bring the organism into a new region with favourable conditions
how are woodlice affected by kinesis
-move more rapidly and change direction more often when they move from a damp area to a dry one
-this increases their chance of moving back into a damp one
-once back in the damp area they slow down and change direction less often
-this means they are more likely to stay in the damp area - increasing their chance of survival
-in high humidity they move slowly and turn less often so they stay in that area
-as the air gets dryer they move faster and turn more often so move into a new condition
what is a tropism
plant response in which the direction of growth is determined by the direction of stimulus - it can be positive or negative
eg plant shoots grow towards the light ( positive phototropism) and away from gravity (negative gravitropism) so they can access more light for photosynthesis
-plant roots grow away from light ( negative phototropism) and towards gravity (positive gravitropism ) so the roots can absorb water and minerals
where are the receptors located that show an increase or decrease in blood pressure
-aorta
-carotid artery
what is IAA
-indoleacetic acid
-specific growth factor found in plants
-synthesised in the growing tips of roots and shoot eg in meristems where the cells are dividing
how does IAA control growth
by elongation
describe the process of IAA by controlling growth by elongation
-IAA molecules bind to specific, comp receptor proteins on the CSM
-IAA stimulates ATPase proton pumps to pump H+ from the cytoplasm into the cell wall
-acidifies the cell wall eg lowers pH
-activates proteins known as expansins which loosen the bond bwt cellulose microfibrils
-at the same time K+ ion channels are stimulated to pen
-leads to an increase in the K+ ion conc un cytoplasm which decreases the water potential of the cytoplasm
-causes cells to absorb water by osmosis - water enters through aquaporins - which is then stored in the vacuole
-increase internal pressure of the cell causing the cell wall to stretch
-cell elongates
how does phototropism affect the shoots and top of the stem
-grow towards the light
how does the conc of IAA affect the elongation of a plant
-conc of IAA determines the rate of cell elongation within the region of elongation
-if the conc of IAA is not uniform on either side of the root or shoot then uneven growth will occur
-in shoots higher conc of IAA results in a grater rate of cell elongation
how does the shoot bend towards the light due to IAA - phototropism
-cells in the tip of the shoot produce IAA, which is actively transported down the shoot
-the IAA is initially transported down the shoot evenly throughout all regions as it begins to move down the shoot
-light causes the movement of IAA from the light side to the shaded side of the plant - diffusion
-a greater conc of IAA builds up on the shaded side of the shoot rather than on the light side
-as IAA causes elongation of the shoot cells and there is a greater conc on the shaded side of the shoot, the cells on this side elongate more
-the shaded side elongates faster than the light side and the shoot tip bends towards the light
how does the conc of IAA affect the roots - gravitropism
-cells in the tip of the root produce IAA, which is then actively transported along the root
-the IAA is intilally transported to all sides of the root
-gravity influences the movement of IAA from the upper side to the lower side of the root
-a greater conc of IAA builds up on the lower side of the root
-as IAA inhibits the elongation of root cells, the cells on the lower side elongate less than those on the upper side
-the relatively greater elongation of cells on the upper side causes the root to bend downwards, towards the force of gravity
The retina of an owl has a high density of rod cells.
Explain how this enables an owl to hunt its prey at night.
Do not refer to rhodopsin in your answer
- High (visual) sensitivity;
- Several rods connected to a single neurone;
- Enough (neuro)transmitter to reach/overcome
threshold
OR Spatial summation to reach/overcome threshold
The fovea of the eye of an eagle has a high density of cones. An eagle focuses the image of its prey onto the fovea.
Explain how the fovea enables an eagle to see its prey in detail.
Do not refer to colour vision in your answer.
- High (visual) acuity;
- (Each) cone is connected to a single neurone;
- (Cones send) separate (sets of) impulses to
brain;
During hibernation, the heart rate and the metabolic rate of black bears decrease
(lines 3−5).
Use your knowledge of the nervous control of heart rate to describe how these are linked.
or in a question to show how decrease in CO2 effects control of heart rate
- (Lower metabolism so) less/low CO2 (in
blood); - (Detected by) chemoreceptors;
- (Chemoreceptors) located in aorta/medulla
OR
(Chemoreceptors) located in carotid artery; - Fewer impulses to cardiac centre;
OR
Fewer impulses to medulla (oblongata); - (More) impulses along parasympathetic/vagus
pathway/neurones/nerve
OR
Fewer impulses along sympathetic
pathway/neurones/nerve; - (To) SAN;
why is IAA useful to the plant roots in terms of gravitropism
-enable the plant to grow to find a water source deeper in the ground
-anchor the plant in the soil - stability
why is IAA useful to the plant shoot in terms of phototropism
-grow towards the light
-more photosynthesis
-more glucose for growth
how does IAA affect plant shoots
-greater conc of IAA on the lower side
-increases cell elongation on the lower side
-lower side cells elongate more so the shoot grows upwards away from the force of gravity
how does IAA affect the plasticity (ability to stretch) of the cell walls
-acid growth hypothesis
-hydrogen ions are actively transported from the cytoplasm into the spaces in the cell wall, causing it to become more plastic and enabling elongation
