Stimuli And Responses Flashcards
How do animals and plants increase their chance of survival?
By responding to changes in their external and internal environment - a stimulus.
Receptora detect…
Stimuli
Effectors are…
Cells that bring about a response to a stimulus e.g. muscle and gland cells
Neurones: (3)
Sensory neurone - impulses from receptors to the CNS
Motor neurone - impulses from CNS to effectors
Relay neurone - impulses between sensory and motor neurone
What is a reflex?
Where the body responds to a stimulus without making a conscious decision to respond - really quick.
What happens when an electrical impulse reaches the end of a neurone?
Neurotransmitters are secretes directly onto target cells - then they are quickly removed once they’ve done their job.
Features of plants? (3)
Sense the direction of light and grow towards it
Sense gravity so their roots and shoots grow in right direction
Climbing plans have a sense of touch so they can find things to climb up and reach sunlight
What is a tropism?
The response of a plant to a directional stimulus
Positive tropism:
Growth towards the stimulus
Negative tropism
Growth away from the stimulus
Phototropism is…
The growth of a plant in response to light
Shoots grow towards light
Roots away from light
Gravitropism is…
The growth of a plant in response to gravity
Shoots grow upwards
Roots grow downwards
How do plants respond to directional stimuli?
Through their growth factors which are produced in the growing regions of the plants.
What is Auxins?
Growth factors which stimulate the growth of shoots by cell elongation.
High conc of this inhibits it though
What is Indoleactic Acid? IAA
An auxin which is produced in the shoots in flowering plants
What does IAA do?
Moved around the plant to control tropisms - different concentrations of it means uneven growth of the plant.
Phototropism
What does IAA do?
Moves to the more shaded parts so the IAA conc increased on shaded side so cells elongate and the shoot bends towards light
IAA conc increased so growth inhibited and roots bend away from the light
Gravitropism
What does IAA do?
IAA moves to underside of shoots and roots so IAA conc increased on lower side so cells elongate and shoot grows upwards
IAA conc increased on lower side so growth inhibited so the root grows downwards
Simple mobile organisms have ….
Simple responses to keep them in a favourable environment
Taxes
Kineses
What are Taxes?
When the organisms move towards or away from a directional stimulus e.g. light
What is Kinesis?
When an organisms movement is affected by a non directional stimulus e.g. humidity
What happens when a nervous system receptor is in its resting state?
There’s a voltage across the membrane
This is known as its resting potential
What happens when a stimulus is detected?
The cell membrane is excited and becomes more permeable Allows more ions to move in and out
Altering the potential difference - the change is called the generator potential
A bigger stimulus…
Excites the membrane more so a bigger generator potential is produced
What happens if the generator potential is big enough?
It’ll trigger an action potential - electrical impulse along neurone.
What are Pacinian Corpuscles?
They detect mechanical stimuli - pressure receptors on skin
Structure of Pacinian Corpuscles:
- contain the end of a sensory neurone - sensory nerve ending
- sensory nerve ending wrapped in lamellar
What happens when a Pacinian Corpuscle is stimulated?
Lamellar are deformed and press on the sensory nerve ending - causes the sensory neurone’s cell membrane to stretch so sodium ion channels open
More sodium ions diffuse into cell creating a generator potential, could trigger an action potential
What are Photoreceptors?
Light receptors in your eye.
How does light enter your eye, what controls it?
Enters through pupil
Amount of light that enters is controlled by Iris muscles
Where is the photoreceptors cells?
Inside the retina
The fovea is an area inside the retina where there are lots of PR
How are nerve impulses carried to the brain?
From the retina to the brain via optic nerve - a bundle of neurones .
Where the optic nerve leaves the eyes is called…
A blind spot - there aren’t any photoreceptor cells - not sensitive to light.
The human eye has two types of photoreceptor:
Rods
Comes
Where are rods and cones found?
Rods - peripheral parts of retina
Cones - packed together in the fovea
What do rods and cones contain?
Different optical pigments making them sensitive to different wavelengths of light.
Which one is in black and white?
Rods
3 types of cones :
- red sensitive
- green sensitive
- blue sensitive
Which one is more sensitive to light?
Rods - because many rods join one neurone so many weak generator potentials combine to reach the threshold and trigger an action potential.
Which is less sensitive to light?
Cones because one coin joined one neurone so it takes more light to reach the threshold and trigger an action potential.
What is Visual Acuity?
The ability to tell apart points that are close together.
Which has a low visual acuity?
Rods Because many rods join the same neurone which means light from two points close together can’t be told apart.
Which has a high visual acuity?
Cones Because cones are close together and one cone joins one neurone - when light from two points hits two cones, two action potentials go to the brain so you can distinguish two points that are close together as seperate points.
The heart is myogenic, what does this mean?
It can contract and relax without receiving signals from the nerves - this creates a heartbeat.
What is the pacemaker?
Where is it?
Sinoatrial node - SAN
Right atrium wall
What does the SAN do?
Sets the rhythm of the heartbeat by sending out regular waves of electrical activity to the atrial walls.
What is the effect of the SAN sending out regular waves of electrical activity to the atrial walls?
Causes the right and left syria to contract at the same time.
These waves are then transferred from the SAN to the Atrioventricular node - AVN.
What does the band of non-conducting collagen tissue do?
Stops the waves of electrical activity from being passed directly from atria to ventricles - allows it to pass to the AVN.
What is the AVN’s role?
Responsible for passing the waves of electrical activity on to the bundle of His.
Why is there a delay before the AVN reacts?
To make sure the atria have emptied before the ventricles contract.
What is the bundle of His?
A group of muscle fibres responsible for conducting the waves of electrical activity between the ventricles to the apex (bottom of heart)
Where does the bundle of His lead to?
Muscle fibres in the right and left ventricle walls - Purkyne tissue.
What does the Purkyne tissue do?
Carries the waves of electrical activity into the muscular walls of the right and left ventricles causing them to contract.
What affects the rate at which the SAN fires?
The medulla oblongata - part of brain.
Pressure receptors in aorta and carotid arteries:
Baroreceptors
Chemical receptors in the aorta and carotid arteries and medulla:
Chemoreceptors
- monitor pH, oxygen conc and carbon dioxide conc
What are the Sympathetic Neurones?
They secrete noadrenaline which aims to increase something.
What are the Parasympathetic neurones?
They secrete Acetylcholine to decrease something.
Summarise steps for heart detecting stimuli:
- electrical impulse from receptors are sent to medulla along sensory neurone
- medulla sends impulses along parasympathetic/sympathetic neurones which seceretes acetylcholine/noadrenaline which binds to receptors on the SAN.
- causes a change = heart rate increases/decreases/slows down/ speeds up via cardiac muscles
