B14 Response To Stimuli Flashcards
What are the photoreceptors in the eye called
Cone and rod cells
What is a stimuli
A detectable change in environment
What are stimuli detected by
Receptors
What are the 2 types of nervous systems
Peripheral - neurones and receptors
and
central - brain and spine
What does the stimulation of a receptor cell lead to
The establishment of a generator potential - can cause a response
What is the stimulus in a pacinian corpuscle?
Pressure
What do pacinian corpuscle respond to
Pressure changes
Where do pacinian corpuscle occur
Deep in skin e.g. fingers and feet
What does a pacinian corpuscle consist of
A singles sensory neurone wrapped with layers of tissue separated by gel
What do membranes surrounding sensory neurone have in pacinian corpuscle
Stretch mediated sodium channels
What happens to stretch mediated sodium channels in resting state
Channels too narrow for sodium ions to diffuse into sensory neurone - resting potential is maintained
What shape are rod cells
Rod shaped
What shape are cone cells
Cone shaped
What is the pigment in rod cells
Rhodopsin
What is the pigment in cone cells
Iodopsin
What colour images are formed by rod cells
Black and white images
What colour images are produced by cone cells
Coloured images
Why can we see even if it’s dark
Can see in black and white - survival mechanism
It doesn’t take a lot of light energy to break down rhodospin, so a generator potential can be established
What is visual acuity
The accuracy of vision in light intensity’s
What is the distribution if rod and cone cells in the retina
It’s uneven
Blind spot
Has no rod cells or cone cells, so there are no photoreceptors, no light can be detected at that particular point in the retina
What’s the steps in the reflex arc
Stimulus —> receptor —> coordinator —> effector —> response
What’s the advantage of responding to stimuli
Increase survival chances
What are the 2 types of nervous systems
Peripheral nervous system and central nervous system
What’s the peripheral nervous
Receptors
Sensory and motor neurones
What’s the central nervous system
Coordination centres
E.g. brain + spine
How can a response be triggered
each receptor respond only to specific Stimuli.
Stimulation of receptor cells leads to establishment of generator potential → can cause response.
What do pacinian corpuscle respond to
Pressure changes
What is the stimulus of a pacinian corpuscle
Pressure
Where do pacinian corpuscle occur
Deep in skin (e.g. fingers and feet)
What do pacinian corpuscle consist of
Single sensory neurone wrapped with layers of tissue separated by gel
Has special channel proteins in its plasma membrane, containing channel proteins that allow ion transportation
What do the membranes surrounding sensory neurones in pacinian corpuscle
Stretch mediated Na channels
What do stretch-mediated Na channels do in pacinian corpuscle
Open + allow Na+ to enter sensory neurone only when they’re stretched and deformed. ( pressure must be applied)
Are closed unless they’re stretched/pushed on to pull/stretch open the Na+ channels to allow Na+ to diffuse in
Why can’t Na+ be diffused into the Na+ channels in the pacinian corpuscle when no pressure is applied
In resting state, Na+ channels too narrow for Na+ to diffuse into sensory neurone only- resting potentials maintained.
What happens when pressure is applied to pacinian corpuscle
Pressure applied, deforms and stretches sensory neurone plasma membrane + widens Na+ channels, so Na+ diffuses in leading to establishment of a generator potential.
Enough Na+ diffuse in, so can exceed the threshold + a response can occur as it has generated an action potential.
What stimulus do rod + cone cells respond to
Light
Where are rod and cone cells found
On the human retina
Why do rod cells produce black and white images
They cannot distinguish between different wavelengths of light
Why can rod cells detect light at low light intensities
Because many rod cells connect to one sensory neurone wrapped- retinal convergence
What must happen in rod cells to generate an action potential
Rod cell absorb light
There’s enough light energy from low-intensity light to cause the breakdown.
enough pigment must be broken down for threshold in bi-polar cell to trigger action potential
What’s a bipolar cell
Cells that link rod cell to sensory neurone
Why can the threshold in a sensory neuron needed trigger an action potential be reached even in low light intensities.
Many rod cells are connected to a single bipolar cell - spatial summation
Also it doesn’t take a lot of light energy to break down rhodopsin
Why are we able to see in black and white in the dark
Survival mechanism
Retinal convergence - have multiple rod cells connecting to one bipolar cell
Advantage is special summation = each of rod cells in low light intensity, rhodopsin will be broken down + collectively, all broken down pigment will result in big enough stimulus to trigger and action potential.
Disadvantage of rod cells
Low visual acuity - don’t have very accurate vision in lower light intensities.
And because of Retinal convergence the brain cannot distinguish between the separate light sources that stimulate it
How many different types of Cone cells are there
3 - each differing but the colour pigment they have (red, green, blue)
All absorb different wavelengths of light
Why can we see more than the 3 colours of the 3 types of cone cells
Depending on proportion of each cone cell that’s stimulated we perceive colour images
Why can we only see in colours when it’s bright
Because iodopsin only broken down if theres high light intensity, so they require more light energy to break down the pigment
so action potentials can only be generated with enough light
In cone cells why is there no spacial summation or retinal convergence
Only 1 cone cell connects to a bipolar cell, no spacial summation occurs + cones can only respond to high light intensity, which is why we can’t see colour in the dark.
Advantage of cone cells
each cone cell is connected to 1 bipolar cell, so the brain can’t distinguish between separate sourced of light detected.
So cone cells have high visual acuity
What is the name of where light is focused by the lens on the retina
Fovea
Why does the fovea receive the high test intensity of light
As light is focused by lens on part of retina opposite pupil, which is the fovea
What is the explanation for the uneven distribution of rod and cone cells on the fovea
Most cone cells near fovea as they only respond to high light intensities
Rod cells further away as these can respond to low light intensities
At the fovea, what is the name of the highest number of photoreceptor cells
Cone cells
How quickly the SAN releases the wave of depolarisation is controlled by what system
The nervous system
What does SAN stand fro
Sino atrial node
Where is the SAN located and what is it also known as
Right atrium
Pace maker
Where are the purkyne fibres located
In the walls of the ventricles
Where does the bundle of HIS run through
Through the septum
Where is the AVN located
Located near the border of right + left ventricle within the atria still
What does AVN stand for
Atrio ventricular node
What is the rate of contraction controlled by
The wave of electrical activity
Why is the cardiac muscle described as myogenic
It contracts on its own accord
Where is the medulla oblongata located
In the brain
What does the medulla oblongata do and how does it do it
Controls the HR
Via autonomic nervous system
Sympathetic nervous system linked to SAN that increases HR
Parasympathetic nervous system that is linked to the SAN decreases HR
How does the heart control + coordinate the regular contraction of atria and ventricles
SAN releases wave of depolarisation (WOD) across the atria, causing atria to contract (atrial systole).
AVN will release another WOD when 1st WOD reaches it .
There’s a non-conductive layer between atria and ventricles which prevents WOD travelling down to ventricles.
Instead bundle of HIS running through the septum can conduct and pass a WOD down septum + purkyne fibres in walls of ventricles.
As result, apex + walls of ventricles contract.
There’s a shirt delay before this happens whilst the AVN transmits the 2nd WOD.
This allows enough time for atria to pump all blood into ventricles.
Finally, cells repolarise and cardiac muscle relaxes.
How CO2 conc is restored to normal in the blood
Increased exercise, causes increase in respiration
More CO2 produced by respiring tissues
Increased CO2 in blood
Blood pH decreases
Chemoreceptors in carotid arteries increases frequency of impulses that it sends to the medulla oblongata.
The centre in the medulla oblongata that increases HR increases freq that it sends impulses to SAN via sympathetic nervous system.
SAN increases HR, so there’s increased blood flow to lungs
More CO2 is removed faster
Normal conc of CO2 in blood returns to normal.
