T8 Flashcards
How to do plants and animals increase their chances of survival?
By responding to stimuli in their external environment.
What’s a stimulus?
Any change in the internal or external environment.
What’s the difference between receptors and effectors?
Receptors detect the stimulus and can be cells or proteins in cell surface membranes.
Effectors are cells that bring about a response to the stimulus to produce an effect and can be muscle cells and cells found in glands.
How do receptors communicate with effectors?
Via the nervous system or the hormonal system or sometimes both.
What is the nervous system?
It is made up of a complex network of cells called neurones that sends electrical impulses.
The 3 neurones are:
- Sensory neurones
- Motor neurones
- Relay neurones
What are sensory neurones for?
They transmit electrical impulses from receptors to the central nervous system (brain or spinal cord)
What are motor neurones for?
They transmit electrical impulses from the CNS to effectors.
What are relay neurones for?
They transmit electrical impulses between sensory neurones and motor neurones.
What’s another phrase used for “electrical impulses”?
Nerve impulses
Action potentials
What happens when an electrical impulse reaches the end of a neurone?
Chemicals called neurotransmitters take the information across to the next neurone.
This sends an electrical impulse.
How do the eyes respond to dim light?
1) Photoreceptors in your eyes detect dim light.
2) CNS process the information.
3) Radial muscles in the iris are stimulated by motor neurones.
4) Radial muscles contract to dilate pupils.
How do the eyes respond to bright light?
1) Photoreceptors in your eyes detect bright light.
2) CNS process the information.
3) Circular muscles in the iris are stimulated by motor neurones.
4) Circular muscles contract to constrict pupils.
Explain what is meant by a hormonal system?
It is made up of glands which are groups of specialised cells that secrete chemicals like hormones.
E.g. Pancreas secretes insulin.
Glands can be stimulated by another hormone or an electrical impulse.
How does the body respond to low blood glucose concentration?
1) Receptors in the pancreas detect low blood glucose concentration.
2) Pancreas releases hormone glucagon into the blood.
3) Target cells in the liver detect glucagon and convert glycogen into glucose.
4) Glucose is released into the blood so glucose concentration increases.
Explain the features of nervous communication.
Uses electrical impulses.
Faster response.
Localised response - specific cells.
Short-lived response - neurotransmitters removed quickly.
Explain the features of hormonal communication.
Uses chemicals
Slower response - travel at the speed of blood.
Widespread response - target cells can be all over the body.
Long-lived response - hormones aren’t broken down quickly.
Why might a cell membrane be referred to as polarised?
When a nervous system receptor is in its resting state, there’s a difference in charge between the inside and outside of the cell.
What is the potential difference of a membrane?
It is the voltage across the membrane.
It is generated by ion pumps and ion channels.
What happens to the permeability of the cell membrane when a stimulus is detected?
It changes (ions are stopped from moving).
This changes the potential difference.
What happens if the change in potential difference is late enough?
If the ‘threshold level’ is reached, it’ll trigger an action potential.
How do Photoreceptors detect light in your eyes?
1) Light enters through the pupil.
- amount of light that enters is controlled by the iris.
2) Lens focus light rays onto the retina which has fovea containing Photoreceptors cells.
3) Nerve impulses travel to brain via the optic nerve (bundle of neurones).
Where is the blindspot in an eye?
It area where there are no optic nerves as there aren’t any Photoreceptors.
This means it’s not sensitive to light.
How do Photoreceptors convert light into an electrical impulse?
1) Photoreceptors have light-sensitive pigments which absorb the light.
2) Light bleaches the pigments causing a chemical change.
3) This triggers a nerve impulse along a bipolar neurone.
4) Bipolar neurones connect Photoreceptors to the optic nerve which takes impulses to the brain.
What 2 receptors does a human eye have?
1) Rods
2) Cones
What are the features Rod cells?
They only give information in black and white (monochromatic vision).
Mainly found in the peripheral parts of the retina.
Contain light sensitive pigment called rhodopsin - 2 chemicals: retinal and opsin joined together.
What are the features of Cones?
They only give information in colour (trichromatic vision).
Found packed together in the fovea.
3 types of cones:
- Red sensitive.
- Green sensitive.
- Blue sensitive.
What happens to your Rods when it’s dark?
Rods aren’t stimulated in the dark.
1) Na+ are pumped out of the cell via active transport.
2) Na+ diffuse back into the cell through open sodium channels.
3) The inside of the cell becomes slightly negative.
4) This triggers the release of neurotransmitters which inhibit the bipolar neurone.
5) The bipolar neurone can’t fire an action potential so no information goes to the brain.
What happens to your Rod cells in the light?
1) Light energy causes rhodopsin to break apart into retinal and opsin - bleaching.
2) Causes Na* to close.
3) Na+ actively transported out of the cell.
4) Na+ build up outside the cell making the membrane more negative.
- membrane is hyper-polarised.
5) This stops releasing neurotransmitters so there’s no inhibition of the bipolar neurone so it depolarises.
What are extensions connect to other neurones?
Dendrites and dendrons - carry nerve impulses towards the body.
Axons - carry nerve impulses away from the body.
Describe the structure of motor neurones.
Many short dendrites carry nerve impulse from CNS to cell body.
One long axon carries nerve impulses from cell body to effectors.
Describe the structure of sensory neurones.
One long dendron carries nerve impulses from receptor cells to cell body.
One short axon carries nerve impulses from cell body to CNS.
Describe the structure of relay neurones.
Many short dendrites carry nerve impulses from sensory neurone to cell body.
All axon carries nerve impulses from cell body to motor neurones.
Why are neurone cell membranes polarised at rest?
There are more positive ions outside the cell than inside.
Thus, there’s a difference in charge.
What is the resting potential?
The voltage across the membrane at rest.
-70mV
How is the resting potential created and maintained?
It is created and maintained by sodium-potassium pumps and K+ channels in the neurone membrane.
1) Na-K pumps move Na+ out of neurone as the membrane isn’t permeable to Na+ so it can’t diffuse back in.
- This creates a Na+ electrochemical gradient as there more positive ions outside the cell.
2) Na-K pumps move K+ out of the membrane which is permeable to K+ so they can diffuse back out the K+ channels.
Thus, the outside is positively charged compared to the inside.
What happens to neurone cell membranes once it’s stimulated?
Membrane becomes depolarised as an stimulus triggers Na+ ion channels to open.
A large stimulus, triggers a rapid change in potential difference.
Explain the process of an action potential.
1) Stimulus
2) Depolarisation
3) Repolarisation
4) Hyperpolarisation
5) Resting potential
1) Stimulus excites neurone. Na channels open. Membrane permeable to Na+ so it diffuses down electrochemical gradient. Inside becomes less negative.
2) Depolarisation - if potential difference reaches threshold, more Na channels open so more Na+ diffuses into neurone.
3) Repolarisation - Na channels close. K channels open. Membrane is more permeable to K+ so it diffuses out. Membrane closer to resting potential.
4) Hyperpolarisation - K channels close slowly. Potential difference becomes more negative than resting potential.
5) Resting potential - Ion channels reset. Na-K pump returns membrane to resting potential. Maintains until another stimulus.
What is the refractory period?
When the ion channels recover so they can’t be made open.
It acts as a time delay between each action potential so they pass along as discrete (separate) impulses.
Also insures action potentials flow in one direction.
What happens when there is a bigger stimulus?
Bigger stimulus = More frequent impulses
When it reaches a threshold, an action potential will fire with the same charge in voltage irrelevant of how big the stimulus is.
Action potential won’t fire if threshold isn’t reached.
How are action potentials stopped?
Referring to local anaesthetics.
It works by binding to the Na+ channels in the membrane of neurones.
This stops Na+ from moving into neurones so their membranes will not depolarise.
So this prevents action potentials from being conducted so the information about pain won’t reach the brain.
What are the properties of myelinated neurones?
It is neurones that have a myelinated sheath - acts as an electrical insulator.
It is made of a cell called Schwann Cell.
Between the Schwann cells are tiny patches of bare membrane called “Nodes of Ranvier”. This is where Na+ channels are concentrated.
What is saltatory conduction?
It is when Depolarisation occurs at the nodes of Ranvier.
The neurone cytoplasm conducts an electrical charge to depolarise the next node so impulses “jump” from node to node.
Makes it faster.
What is the conduction velocity?
The speed at which an impulse moves along a neurone.
A high conduction velocity means a faster travelling impulse.
What is a synapse?
It is the junction between neurone and another neurone.
Or between a neurone and an effector cell.
Tiny gap between the cells at the synapse is called the synaptic cleft.
What is a synaptic knob?
It is swelling in the presynaptic neurone.
It has synaptic vesicles filled with chemicals called neurotransmitters.
