Response to stimuli

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  • Created by: r98
  • Created on: 21-03-16 13:20
What is a stimulus?
A detectable change in the internal or external environment of an organism that produces a response in the organism.
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What are stimuli detected by?
By cells or organs known as receptors.
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What do receptors do?
Transform the energy of a stimulus into some form of energy that can be processed by the organism and that leads to a response.
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What are effectors?
A range of cells, tissues, organs and systems that carry out the response.
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What's the definition of a taxis?
A simple response whose direction is determined by the direction of the stimulus.
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What's the term used for when the movement is towrds the stimulus?
Positive taxis.
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What's the term used for when the movement is away from the stimulus?
Negative taxis.
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What is kinesis?
A form of response in which the organism does not move towards or away from the stimulus. Instead, the more unpleasant the stimulus, the more rapidly it moves and the more rapidly it changes direction.
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What's a tropism?
A growth movement of part of a plant in response to a directional stimulus.
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What are the 2 major divisions of the nervous system?
The central nervous system (CNS) & the peripheral nervous system.
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What is the CNS made up of?
The brain and spinal cord.
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What is the PNS made up of?
Pairs of nerves that originate from either the brain or the spinal cord.
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How is the peripheral nervous system divided?
Into two; the sensory neurones and motor neurones.
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What's the role of the sensory neurones?
To carry nerve impulses from receptors towards the CNS.
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What's the role of the motor neurones?
To carry nerve impulses away from the CNS to effectors.
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What are the 2 subdivisions of the motor nervous system?
The voluntary nervous system & the autonomic nervous system.
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What's the role of the voluntary nervous system?
To carry nerve impulses to body muscles and is under voluntary (conscious) control.
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What's the role of the autonomic nervous system?
To carry nerve impulses to glands, smooth muscle and cardiac muscle and is involuntary.
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What is the name of an involuntary response to a sensory stimulus?
A reflex.
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The pathway of neurones involved in a reflex, what is this a definition of?
A reflex arc.
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What are the main stages of a reflex arc?
Stimulus --> receptor --> sensory neurone --> intermediate neurone --> motor neurone --> effector --> response.
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What are the two divisions of the autonomic nervous system?
The sympathetic nervous system & the parasympathetic nervous system.
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What does the sympathetic nervous system do?
It stimulates effectors, so speeds up any activity.
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What does the parasympathetic nervous system do?
It inhibits effectors, so slows down any activity.
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What region of the brain controls heart rate?
The medulla oblongata.
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How is the medulla oblongata split?
Into two centres; a centre that increases heart rate & a centre that decreases heart rate.
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What is the centre that increases heart rate linked to?
It's linked to the sinoatrial node by the symoathetic nervous system.
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What is the centre that decreases heart rate linked to?
It's linked to the sinoatrial node by the parasympathetic nervous system.
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Where are chemoreceptors found and what are they sensitive to?
They're found in the wall of the carotid arteries and aorta, and are sensitive to changes in the pH of blood, resulting from changes in carbon dioxide concentration.
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Where are pressure receptors found?
Within the walls of the carotid arteries and the aorta.
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What do pressure receptors do when blood pressure is higher than normal?
They transmit a nervous impulse to the centre in the medulla oblongata that decreases heart rate. This centre sends impulses via the parasympathetic nervous system to the SA node, which decreases the rate at which the heart beats.
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What is specific to a single type of stimulus and produces a generator potential by acting as a transducer?
A recpetor.
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Where can you find Pacinian corpuscles?
Deep in the skin, they're most abundant in the fingers, soles of the feet and the external genitalia. They also occur in joints, ligaments and tendons.
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What is the name of the special type of sodium channel in the plasma membrane of the sensory neurone of the Pacinian corpuscle?
Stretch-mediated sodium channel.
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Why are they called strech-mediated sodium channels?
Their permeability to sodium changes when the pacinian corpuscle change shape, e.g. by stretching.
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When is the neurone of the Pacinian corpuscle said to have a resting potential?
In its normal (resting) state, when the strech-mediated sodium channels are too narrow to allow sodium ions to pass along them.
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What happens to the Pacinian corpuscle when pressure is applied to it?
It changes shape and the membrane around the neurone becomes stretched. This widens the sodium channels and sodium ions diffuse into the neurone, this changes the potential of the membrane, producing a generator potential.
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What does the generator potential of a Pacinian corpuscle do?
Create an action potential (nerve impulse).
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What are the 2 main types of light receptors?
Rod cells and cone cells.
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How do rod and cone cells act as transducers?
By converting light energy into the electrical energy of a nerve impulse.
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Why do rod cells only prodyce black and white images?
Because they cannot distinguish between different wavelengths of light.
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To what light intensity do rod cells respond to and why?
Respond to low light intensity because many rod cells share a single sensory neurone.
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What is the pigment called in rod cells that needs to be broken down in order to produce a generator potential?
Rhodopsin.
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Why are rod cells said to have low visual acuity?
They can't distinguish between the separate sources of light that stimulated them, this is due to many rod cells linking to a single bipolar cell so light received by these rod cells only generates a single impulse.
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Why do cone cells only respond to high light intensities?
Each cone cell often have their own bipolar cell that's connected to a sensory neurone. So the stimulation of many cone cells can't be combined to exceed the threshold value amd so create a generator potential.
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Why do cone cells have good visual acuity?
Each cone cell is connected to a single bipolar cell, so if two adjacent cone cells are stimulated, the brain receives two separate impulses so it can distinguish between the two separate sources of light.
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Why is the concentration of cone cells high at the fovea?
Light is focused by the lens at the fovea, therefore this receives the highest intensity of light.
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Why is the concentration of rod cells high at the peripheries of the retina?
Light intensity is at its lowest at these places.
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Other cards in this set

Card 2

Front

What are stimuli detected by?

Back

By cells or organs known as receptors.

Card 3

Front

What do receptors do?

Back

Preview of the front of card 3

Card 4

Front

What are effectors?

Back

Preview of the front of card 4

Card 5

Front

What's the definition of a taxis?

Back

Preview of the front of card 5
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