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responses and reflex, control of heart rate - Coggle Diagram
responses and reflex
A stimulus is a change in the environment (light, pressure) detected by receptors (each receptor responds to a specific stimuli). Responding to a stimuli by various mechanisms (taxes & kinesis) increases the chance of an organisms' survival, by keeping the organisms in favourable environments/conditions (light/dark, moist)
pacinian corpuscle
in order for a receptor (pacinian corpuscle, rod cell and cone cells) to create a response to a stimuli a generator potential must be created. When the stimulus is large enough to open the stretch-mediated sodium channels, creating an influx of sodium ions into the neurone, which becomes depolarised, creating a generator potential. When there are more positive sodium ions inside than outside, it can exceed the threshold and the generator potential in turn will create an action potential (nerve impulse which passes along neurones to the CNS). If it goes from -70 to -55 millivolts it has reached a threshold and action potential will occur
if there is no stimulus, therefore no pressure is applied on the pacinian corpuscle, that means there are no deformatives on the connective layers and on the plasma membrane of the sensory neurone. The stretch-mediated sodium channels will be too narrow, for any sodium ions to diffuse into the sensory neurone - the resting potential is maintained
human retina
the rod and cone cells (photoreceptors) are found in the retina, these act as transducers which convert light energy into an electrical energy (nerve impulse)
rod cells
- do not distingush different wavelenghts of light (colours) , instead it processes images in black and white
- can detect light at low light intensities, due to retinal convergence
- rod cells absorb light intensity
- the protein rhodopsin is found within the rod cell
- if enough light intensity is absorbed to break down the protein/pigment rhodopsin within the rod cell, an action potential will be generated
- if enough pigment is broken down for the threshold to be met in the bipolar cells, which are the cell that link the rod cell to the sensory neurone, creating a generator potential than an action potential will occur
the rod cells still function at very low light intensity, because of retinal convergence - multiple rod cells connected to one bipolar cell - so even if small amount of pigment is broken down as they are connected to one bipolar cell they add up reaching the desired threshold generating an action potential (spatial summation).
This is an advantage because it allows us to see in black and white even at low light intensities (survival mechanism)
The disadvantage is that it provide low visual acuity (not accurate vision at low light intensities), this is because multiple rod cells are connected to a bipolar cell which is connected to a sensory neurone, which cannot distinguish between different light sources.
cone cells
there are 3 different types of cone cells which each contain different types of iodopsin pigments : red; green; blue. Each cone cell absorbs different wavelenghts of light, which is why when is processed we can distinguish between the red, green and blue. Depending on the proportion of different cone cells which are stimulat<ed we perceive a range of coulours.
iodopsin is only broken down at high light intensity, which is why we can't see colour in the dark as not enough light intensity is present to break down the pigment and generate an action potential. This is because each cone cell is connected to a separate bipolar cell, thereofre there is no spatial summation and no retinal convergence.
cone cells provide a high visual acuity as each cone cell is connected to a separate bipolar cell, the brain can distinguish between separate sources of light
the distribution of rod and cone cells throughout the retina is uneven. The fovea is directly opposite to the lens and therefore receives the highest light intensity in the eye, which is why the number of cone cells are highest at the fovea. Rod cells are found further away from the fovea at the peripheris of the retina, as they can still trigger an action potential even at low light intensity
the blind spot is part of the reitna which has no rod cells and no cone cells. In this part light intensity cannot be detected at this point in the retina.
taxes & kinesis are simple responses that can maintain a mobile organism in a favourable environment
TAXES --> is a simple response where an organisms movement of direction is determined by the direction of the stimulus.
e.g. earthworms tend to move away from light towards a favourable environment (dark) which helps them avoid dehydrations and away from predators --> negative phototaxis
KINESIS --> this is when an organism changes the speed of movements and the rate it changes direction.
if an organism is completely placed in an unfavourable environment the rate of changes in direction decreases, to make the organism move in a straight line in order to allow the organism find a favourable condition
When an organism is taken from a favourable environment and placed into an unfavourable environment but it's only justa across a boundary, the organism will have an increase in the rate it changes the direction, as this allows the organism to find the favourable conditions more quickly and move back into it again.
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responses and the nervous system (the ability for an organism to respond to a change in their environment increases their survival rate)
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nervous system
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peripheral nervous system: receptors, sensory neurones, motor neurones
generator potential
the receptors/transducer converts/transducers the stimulus (change) in the form of energy into a form (e.g. nerve impulse) which can be understood by the body
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control of heart rate
structure
the sinoatrial node (SAN) is a pacemakes located in the right atrium of the heart which is a tissue, which releases a wave of electricity or depolarises the cardiac muscle causing it to contract
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the bundle of HIS is a conductive tissue which is found in the septum and in the walls of the ventricles
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the autonomic nervous system controls the involuntary activities of internal muscles and glands. The coordinator centre is the medulla oblingata in the brain which controls the heart rate of the brain. There are nerves directly connecting the brain to the heart which allows to control how quickly the waves of depolarisation are released from the SAN
sympathetic nervous system/sympathetic nerve : any impulses sent through this nerve will trigger the SAN to release the wave of depolarisation more slowly, increasing the heart rate
parasympathetic nervous system/parasympathetic nerve : any impulses sent through this nerve will trigger the SAN to release the wave of deplarisation more slowly, decreasing the heart rate
a stimuli that can change the heart rate is the pH level, which is detected by chemoreceptos, and blood pressure, which is detected by pressure receptors (baroreceptors). Both of them are found in the aorta and in the carotid artery (artery which branches out of the aorta to the rst of the body)
change in pressure
causes: stress, anxiety, diet, genetics
effects:
HBP stretched the blood vessels, stretching the pressure receptors, which triggers the action potential along the sensory neurone.
Can cause damage to the lining of the walls of the arteries which can cause blood clots, heart attacks and stroke.
LBP walls of the aorta and pressure receptors are not stretches.
May be caused by insufficient supply of oxygenated blood to repiring cells causing and build up of waste and therefore toxins.
change in pH
during high respiratory rates the pH of the blood will decrease, as CO2 and lactic acid are products of respiration. These products can build up in the blood if the heart rate doesn't increase to get the blood to the lungs for the CO2 to be removed, or to get the blood to the liver to break down the lactic acid.
If these products are not removed they can create acidic conditions in the blood causing proteins, enzymes and haemoglobin molecules found in the blood to denature
decrease in pH:
- detected by chemoreceptors in the walls of the aorta and carotid artery
- more impulses are sent to the medulla oblingata
- more impulses are sent via the sympathetic nervous system to the SAN (effector)
- the SAN tissue in the cardiac muscle is the effector which will receive the increased amount of electrical impulses, creating more depolarisation waves,
-increased in contraction, heart rate, to deliver the blood to the lungs to remove the CO2 more rapidly
the cardiac muscle is myogenic, which means it can contract and relax without the need of a stimulus as it is an involuntary muscle. However the rate at which it contracts and relaxes is controlled by nervous imupulses sent by the nervous system
- the SAN will release a wave of depolarisation which will cause atrial systole, both atrias will contract
- the AVN will produce a second wave of depolarisation, which will not reach the ventricels due to the presence of non.conductive layers of tissue between the atrias and the ventricles
- the second depolarisation wave cannot directly move downwards into the ventricles, instead it passes through a conductive tissue in the septum , the bundle of HIS, so it goes down the septum and the bundle the wave depolarisation passes through the purkyne fibres in the outer walls of the ventricle which will branch and deliver the wave into all the walls of the ventricle
- the apex (the bottom of the heart) will contract first as the depolarisation wave travels down the septum
- this forces the maximum amount of the heart to be pumped out of the heart
the non-conductive tissue causes a slight delay from the atria conductive and the depolarisation wave to reach the ventricles, causing the ventricles to contract. This is an advantage as it allows enough tiem for the atria to contract and pump all the blood into the ventricles, so that they are full before they contract.
resting potential maintaines- membrane more permeable to K+ than Na+, more Na+ is pumped out than K+