6.1 Nervous Communication Flashcards
What two things can organisms detect change in?
- Internal environment
- External environment
What detects a change in the environment?
Receptors
What initiates a response to the change in the environment?
Effectors
What is the change in the environment called?
Stimulus
Tropism definition
The growth of a plant in response to a directional stimulus
What is phototropism?
Growth in response to the direction of light
Are shoots positively or negatively phototropic?
Positively - they grow towards light
Are roots positively or negatively phototropic?
Negatively - they grow away from light
What is gravitropism?
Growth in response to the direction of gravity.
Are shoots positively or negatively gravitropic?
Negatively - they grow upwards, away from gravitational pull
Are roots positively or negatively gravitropic?
Positively - they grow downwards, towards gravitational pull.
What is hydrotropism?
Growth in response to water
What type of auxin controls cell elongation?
IAA (indoleacetic acid)
How does a directional stimulus distribute IAA?
Unevenly
How does IAA create positive phototropism in shoots?
If a shoot is exposed to an uneven light source, IAA is transported to the more shaded part.
A higher concentration of IAA in the shaded parts cause cells in the shaded area to elongate.
Cell elongation causes the shoot to bend towards the light.
How does IAA create negative phototropism in roots?
If a root is exposed to an uneven light source, IAA is transported to the more shaded part.
A higher concentration of IAA in the shaded parts inhibits cell elongation on the shaded part.
The root bends away from the light.
How does IAA cause negative gravitropism in shoots?
If a shoot is exposed to an uneven gravitational pull, IAA is transported to the underside (closer to the pull of gravity).
A higher concentration of IAA in the underside cause cells in the underside to elongate.
Cell elongation causes the shoot to bend away from the gravitational pull.
How does IAA cause positive gravitropism in roots?
If a root is exposed to an uneven gravitational pull, IAA is transported to the underside (closer to the pull of gravity).
A higher concentration of IAA in the underside inhibits cell elongation on the lower side.
The root bends towards the gravitational pull.
What are taxes?
A taxis is a simple response whose direction is determined by the direction of the stimulus. (Whole body is moved towards a favourable stimulus or away from an unfavourable one.)
What are kineses?
A kinesis is a form of response in which the organism does not move away from or towards a stimulus. It is a non-directional response. The organism changes the speed it moves at and the rate at which it changes direction.
What is the order of neurones in a reflex arc?
- (Receptors)
- Sensory neurone
- Relay neurone
- Motor neurone
- (Effectors)
What do pacinian corpuscle respond to changes in?
Mechanical pressure
Structure of pacinian corpuscle?
Rings of connective tissue which surround a single sensory neurone.
How are generator potentials produced in pacinian corpuscles?
- At resting potential, the stretch-mediated sodium channels in the sensory neurone surrounding membrane are too narrow for sodium to enter.
- When pressure is applied, the membrane is deformed and stretched.
- Stretch-mediated sodium channels are widened allowing sodium ions to diffuse into the neurone.
- The membrane becomes depolarised and a generator potential has been produced.
- This generator potential in turn produces an action potential if the threshold value is reached.
How sensitive are rod cells to light?
Highly
How sensitive are cone cells to light?
Less than rods
What is visual acuity?
The ability to distinguish between close objects or two points.
What is the visual acuity of rod cells?
Low
What is the visual acuity of cone cells?
High
How numerous are rod cells and how are they distributed?
- Highly numerous
- Evenly distributed across the retina but absent in the fovea
How numerous are cone cells and how are they distributed?
- Less than rod cells
- Mainly found in the fovea
Pigment used by rod cells?
Rhodopsin
How many wave lengths of light can rod cells detect?
1 - sees black and white
How many wavelengths of light can cone cells see?
3 - can see in colour
How many bipolar neurones do cone cells synapse to?
One
How many rod cells synapse to a bipolar neurone?
Several
What is spatial summation?
Several rod cells synapse with the same bipolar neurone. This means that the cumulative stimulation of more than one rod cell can create an action potential in the bipolar neurone.
What is the pigment in cone cells?
Iodopsin
How are generator potentials created in rod and cone cells?
Threshold value has to be exceeded which breaks down pigments in rods and cones. Rods synapsing with the same neurone need to all be stimulated to create a generator potential.
What does cardiac muscle being myogenic mean?
It is self-stimulating
Where is the sinoatrial node located?
Wall of the right atrium
What causes atrial contraction?
Sinoatrial node (SAN) sends electrical waves causing the atria to contract forcing blood into the ventricles.
What causes a delay before ventricles contract and why is it needed?
There is non-conducting tissue between the atria and ventricles which stops the electrical waves from the SAN from reaching the ventricles. This creates a delay which is needed to ensure atria have emptied before ventricles contract.
How does the electrical activity from the SAN pass to the ventricles causing them to contract?
It passes through the atrioventricular node (AVN) to conducting tissue called the bundle of His. This tissue conducts the electrical activity to the bottom of the heart and around ventricle walls along fibres called the purkyne fibres. This causes the ventricles to contract.
What do chemoreceptors detect in relation to the heart?
Changes in CO2 concentration
What do baroreceptors detect in relation to the heart?
Changes in blood pressure
Where do chemoreceptors and baroreceptors send signals to if stimulated?
A region of the brain called the medulla oblongata
What happens to heart rate if blood pressure is too high and how is it initiated?
Detected by baroreceptors.
Impulses are sent from the medulla along parasympathetic neurones to the sinoatrial node (SAN.)
Acetylcholine is released (a neurotransmitter).
Heart rate slows down and blood pressure decreases.
What happens to heart rate if blood pressure is too low and how is it initiated?
Detected by baroreceptors.
Impulses are sent from the medulla oblongata along sympathetic neurones to the SAN.
Noradrenaline is released (a neurotransmitter).
Heart rate rises and blood pressure increases.
What happens to heart rate is CO2 concentration is too low and how is it initiated?
Detected by chemoreceptors.
Impulses are sent from the medulla along parasympathetic neurones to the SAN.
Acetylcholine is released (a neurotransmitter).
Heart rate slows down and CO2 levels increase/O2 levels decrease.
What happens to the heart rate is CO2 concentration is too high and how is it initiated?
Detected by chemoreceptors.
Impulses are sent from the medulla along sympathetic neurones to the SAN.
Noradrenaline is released (a neurotransmitter).
Heart rate rises and O2 levels increase/CO2 levels decrease.
What does acetylcholine do?
Slow down heart rate
What does noradrenaline do?
Speeds up heart rate
Which neurone is used to slow down heart rate?
Parasympathetic neurone
Which neurone is used to speed up heart rate?
Sympathetic neurone
