Topic 6A - Stimuli And Responses Flashcards
What is a taxis response
A directional response in the direction of a stimuli. E.g light
What is a kinetic response
A non directional movement in response to a stimulus. E.g. the intensity of a stimulus affects the response
What’s the difference between positive taxis and negative taxis response
Positive - moves toward the stimulus
Negative - moves away from the stimulus
What are the 3 neurones and what are there functions
- Sensory - transmit electrical impulse from receptors to the CNS
- Motor - transmit electrical impulse from the CNS to the effector
- Relay - transmit electrical impulse between sensory neurone and motor neurone
What is the pathway of nervous communication
Stimulus —> receptor —> CNS —> effector —> response
What is a simple reflex
A rapid, involuntary response to a stimulus
What is the purpose of simple reflexes
Protection - help organism avoid damage to the body as response happens so quickly
What is a tropism
A response of a plant to a directional stimulus
What is a positive and negative tropism
Positive - growth in response to a stimulus
Negative - growth away from the stimulus
What are the 2 types of tropism
Phototropism
Gravitropism
What is phototropism? What are the 2 types of phototropism?
Growth in response to light
Positive phototropism (growth towards light)
Negative phototropism (growth away from light)
What is gravitropism? What are the 2 types of gravitropism?
Growth in response to gravity
Positive gravitropism (grow downwards)
Negative gravitropism (grow upwards)
Which hormones speed or slow down plant growth
Auxins
Where are auxins produced?
In the tips of shoots (diffuse backwards to stimulate the cell just behind the tip to elongate)
What is indoloaecetic acid? Why does it move around the plant? How does it move across?
Important Auxin produced in the tips of shoots and roots.
It’s moved around the plant to control tropisms.
Moves via diffusion and active transport over short distances.
What is the resting potential? How is it generated
Is the potential difference when a cell is at rest
It is generated by ion pumps and ion channels
What is the generator potential
Change in potential difference due to a stimulus
What is an action potential? How is it generated?
An electrical impulse
If a generator potential is big enough
What is a pacinian corpuscles? Where are they found?
Nerve endings in skin, responsible for sensitivity to deep pressure touch and high frequency vibrations.
Are at the end of a sensory neurone wrapped in layers of lamellae
How does a pacinian corpuscle convert mechanical pressure into a nervous impulse
Mechanical pressure stimulates the layers of lamellae to stretch and become deformed.
This causes the axon membrane to also stretch.
The stretch mediated channels are open and sodium ions diffuse into the cell creating a generator potential.
If generator potential reaches the threshold then it causes an action potential.
What are photoreceptors?
A receptor in the eye that detects light.
How is something seen?
Light enters the eye through the pupil, the light rays are focused by the lens onto the retina. The retina contains photoreceptors.
Where are rods located
Periphery and the retina
How do photoreceptors work
Light enters the eye and hits the photoreceptors
It’s absorbed by light sensitive pigments, which causes a chemical change and alters the membrane permeability to sodium ions
This creates a generator potential, if it reaches the threshold then an action potential is sent along the bipolar neurone.
The bipolar neurones connect the photoreceptors to the optic nerve which takes impulses to the brain.
What is the structure of rods
Many rods to 1 bipolar neurone
What is the function of rods
See black and white (works in dim light)
High sensitivity
Low acuity
Where are cones located
Fovea
What are the different types of cones
Red
Green
Blue
What is the function of cones
Color vision
Low sensitivity
High acuity
How are we able to see in high visual sensitivity
Dim light stimulates each rod cell and rhodopsin breaks down
Several rods are connected to one bipolar neurone so there is a spatial summmation of ACh
This leads to a generator potential
The threshold is passed and impulses move along the shared bipolar neurone
Impulses reach the brain
Why are rods very sensitive to light
Many rods join one bipolar neurone, therefore many weak generator potentials combine to reach the threshold and trigger an action potential
Why are cones less sensitive to light
One cone joins one bipolar neurone, therefore it takes more light to reach the threshold and trigger an action potential
What is visual acuity
The ability to tell apart 2 points that are close together
Why do rods have low visual acuity
Many rods join the same bipolar neurone, this means light from 2 points close together cant be told apart
(Brain doesn’t get seperate information about the 2 points)
Why do cones have a high visual acuity
Because one cone joins one bipolar neurone and they are close together.
(When light from 2 points hits 2 different cones, 2 action potentials are generated and sent to the brain)
What does the term myogenic means
Heart will beat without an external stimulus
How are heartbeats controlled? (4)
- SAN sends electrical impulse across heart
- AVN delays the impulse by 0.1 second to allow the atria to finish contracting
- The bundle of HIS takes the electrical impulse to the base of ventricles
- The bundle splits into punkijne fibres which causes the ventricles to contract
What is a parasympathetic neurone
Neurone that sends low frequency of impulses
What is a sympathetic neurone
Neurone that sends high frequency impulses
Where are impulses sent when wanting to reach the heart
Medulla oblongata
How is heart rate slowed down?
Barrow receptors detect high blood pressure
Chemoreceptors can detect high blood pH
Impulses are sent down the sensory neurone to the medulla oblongata
Low frequency impulses are sent along the parasympathetic neurone to the heart.
This stimulates ACh to be released which binds to receptors in the heart.
Heart rate slows down
How does heart rate increase?
Barrow receptors detect low blood pressure
Chemoreceptors detect low blood pH
Impulses sent along sensory neurone to medulla oblongata
High frequency impulses are sent along SYMPATHETIC neurone to the heart
This stimulates noradrenaline to be realeased which binds to receptors in the heart
Heart rate increases
