Receptors Flashcards
Pacinian corpuscle
- Increased pressure deforms stretch-mediated sodium channel;
- Sodium ion channel proteins open and sodium ions diffuse in;
- Depolarisation leading to generator potential;
specific to pressure only.
Explain how pressure on the Pacinian corpuscle produces the changes in membrane potential recorded by microelectrode A.
- (Pressure) deforms / opens (sodium) channels;
- Sodium ions enter;
- Causing depolarisation;
- Increased pressure opens more channels / greater sodium entry;
- [Size of generator potential determines frequency of action potentials]
Describe how the Pacinian corpuscle propagates an action potential.
- (Pressure causes) membrane/lamellae to become deformed/stretched;
- Sodium ion channels in membrane open and sodium ions move in;
- Depolarisation leading to generator potential;
- Greater pressure more channels open/sodium ions enter;
TWO types of photo-receptor cell on the retina
RODS
- Evenly distributed throughout the macula
- Sensitive to all wavelengths of light
- High visual sensitivity to low levels of light intensity
- Low visual acuity, this means the image is unclear or poorly resolved.
- Retinal convergence due to several rods sharing a single BIPOLAR neuron.
- Generator potentials combine to reach threshold.
CONES
- Densely packed in the fovea
- Each cone detects a specific wavelength of light (R-G-B). There are three types of iodopsin.
- Each cone cell is sensitive to a specific wavelength.
- Iodopsin is less sensitive than rhodopsin so requires higher Light intensity of photons
- High visual acuity giving a sharp image.
- This is because Each Cone cell synapses / connected with a single BIPOLAR neuron.
- Cones send separate impulses to brain.
connecting to bipolar neurons
Rods
- LOW VISUAL ACUITY as several rod cells are connected to one bipolar neuron. This means that the light which falls on several rod cells will only generate one impulse to the brain. The brain cannot distinguish between the separate light sources that generated them.
- Rods are highly sensitive to low light intensities because of this arrangement. The stimulation of several rods results in enough NETS released to reach threshold value
- Retinal convergence leads to spatial summation.
- Generator potentials combine to reach threshold = action potential produced
- contain rhodopsin
CONES
- Provide HIGH VISUAL ACUITY as each cone synapses with an individual bipolar neuron.
- This means that light falling on two cone cells generates two electrical impulses to the brain and the brain can therefore distinguish between the light sources that generated them.
- However, each cone cell must release enough neurotransmitter to reach the threshold in the bipolar neuron and this is only likely to happen in bright light. This is an example of temporal summation.
In low light intensities there is not enough neurotransmitter to create an action potential in the bipolar neuron so cones only operate when light intensity is high. - contain iodopsin
Explain how the fovea increases the detail of an image
- High (visual) acuity
- Each / single cone is connected to a single bipolar/neurone
- Each cone sends separate impulse to the brain
Explain how the connection of several rods to a single bipolar cell (Retinal convergence) influences visual acuity
- (Spatial) Summation means cannot distinguish between stimuli from different rod cells linked to same bipolar cell;
- Decreases acuity;
Explain how the connection of several rods to a single bipolar cell (Retinal convergence) influences sensitivity
- (Summation of) sub-threshold stimuli produces threshold stimulation;
- Increases sensitivity;
People with red-green colour blindness are unable to distinguish between red and green, and also between other colours
Explain why.
- Cones that detect green light non-functional;
- Three different types of cone;
- Other colours (‘seen’) due to stimulation of more than one cone
Control of heart rate
The heart muscle is myogenic: it can initiate its own contraction
- Sino atrial node sends wave or electrical activity across both atria
- Both atria contract
- Layer of nonconductive tissue prevents wave reaching ventricles
- Wave of electrical activity reaches the atrio ventricular node
- 0.1 second delay allowing atria to empty fully of blood
- Wave of electrical activity sent from the atrioventricular node
- Down the bundle of His to the base of the ventricles
- Up the Purkinje fibres
- Causing the ventricles to contract from the apex of the heart upwards
autonomic nervous system controlling heart rate
- sympathetic
* stimulates effectors
* speeds up heart rate
* fight or flight
* Neurotransmitter is noradrenaline - parasympathetic
* inhibits effectors
* controls activity at rest
* Neurotransmitter is acetylcholine
The two branches are antagonistic- they have opposing effects.
Blood pressure increases above normal.
- Detected by Baroreceptors in walls of aorta & carotid arteries.
- More frequent impulses sent to medulla oblongata.
- More frequent impulses from inhibitory center in medulla to SA node via parasympathetic nerve.
- Decreases frequency of impulses from SA node across atria. (Acetylcholine)
- Heart rate decreases
Blood pressure decreases below normal.
Detected by Baroreceptors in walls of aorta & carotid arteries.
* Less frequent impulses sent to medulla oblongata.
* More frequent impulses from acceleratory center in medulla to SA node via parasympathetic nerve.
* Increases frequency of impulses from SA node across atria. (Acetylcholine)
* Heart rate increases
