Flashcards in Neuronal Communication Deck (72)
Describe the mechanoreceptor.
1) Stimulus - pressure and movement.
2) Example - Pacinian corpuscle.
3) Example of sense organ - skin.
Describe the chemoreceptor.
1) Stimulus - chemicals.
2) Example of receptor - olfactory receptor (detects smells).
3) Example of sense organ - nose.
Describe the thermoreceptor.
1) Stimulus - heat.
2) Example of receptor - end-bulbs of Krause.
3) Example of sense organ - tongue.
Describe the photoreceptors.
1) Stimulus - light.
2) Example of receptor - cone cell (detects different wavelengths).
3) Example of sense organ - eye.
Name 4 sensory receptors.
Define the term “sensory receptor".
Specialised cell which detects a stimulus.
Define the term “transducer”.
A device that converts one type of energy or signal into another. I.e. in sensory receptors they convert a stimulus into a nerve impulse.
Define the term “stimulus”.
Detectable change in the internal or external environment of an organism, which is detected by the nervous system and can cause a response.
State 3 characteristics of sensory receptors and for each explain why they are important.
1) They are specific to a single type of stimulus .
2) They act as a transducer - they convert a stimulus into a nerve impulse.
Acting as a transducer is important as it means that information can be passed round the nervous system and eventually an effector, to initiate a response.
Specific because you do not want stimulus to trigger multiple receptors, because the initiated may not be suitable to bringing the conditions back to the norm.
Draw and label a diagram showing the structure of a Pacinian corpuscle.
- The end of the sensory neurone is found within the centre of corpuscle, surrounded by layers of connective tissue.
- A blood capillary runs around the outside of the connective tissue, followed by a layer called a capsule.
- Within the membrane of the neurone there are Na+ channels which are responsible for transporting Na+ ions across the membrane.
- The neurone ending in a Pacinian Corpuscle has a special type of Na+ channel called a stretch-mediated Na+ channel. When these channels change shape (i.e. they stretch) their permeability to Na+ changes too.
Explain how a Pacinian corpuscle converts mechanical pressure into a nerve impulse. Give the process.
1) In its normal state (resting state), the stretch-mediated Na+ channels in the sensory neurones membrane are too narrow to allow Na+ to pass through them. Corpuscle is at resting potential.
2) When pressure is applied to the Pacinian corpuscle, the corpuscle changes shape. This causes the membrane surrounding its neurone to stretch.
3) When the membrane stretches, the Na+ channels widen. Na+ now diffuse into the neurone.
4) The influx of positive Na+ changes the potential of the membrane. It becomes depolarised. This results in a generator potential.
5) In turn, the generator potential creates an action potential (a nerve impulse) that passes along the sensory neurone.
6) The action potential will then be transmitted along neurones to CNS.
Outline the steps in a stimulus-response pathway and identify the role of the sensory, relay, and motor neurones in this pathway.
Known as the reflex arc.
1) Receptor - detects stimulus and creates an action potential in the sensory neurone.
2) Sensory neurone - carries impulse to spinal cord.
3) Relay neurone - connects sensory neurone to motor neurone within the spinal cord or brain.
4) Motor neurone - carries impulse to the effector to carry out the appropriate response.
Draw and label a diagram of a motor neurone.
- Have a one long axon and many short dendrites. No dendrons.
- Cell body at the end of the axon on the left.
- Nucleus in the centre of the cell body.
- The unmyelinated gaps are called nodes of ranvier.
Draw and label a diagram of a relay neurone.
- Many short axons and dendrons which branch off into dendrites.
- Cell body and nucleus are in the centre with dendrons branching off it.
- Myelin sheath surrounding the axons.
Draw and label a diagram of a sensory neurone.
- They have one dendron (on the right), which carries the impulse to the cell body.
- The cell body is in the centre.
- They have an axon which carries the impulse away from the cell body.
- The dendron branches into dendrites
- The unmyelinated gaps are called nodes of ranvier.
Define the term “dendrite”.
Dendrites are projections of a neurone that receive signals from other neurones. They conduct electrical messages to the neurone cell body for the cell to function
Define the term “dendron”.
Dendrons are short extensions from the cell body . These extensions divide into smaller and smaller branches called dendrites. They are responsible for transmitting electrical impulses towards the cell body.
Define the term “axon”.
Singular, elongated nerve fibres that transmit impulses away from the cell body. These fibres can be very long, for example, those that transmit impulses from the tips of toes and fingers to the spinal cord.
The fibre is cylindrical in shape and has a very narrow region of cytoplasm surrounded by a plasma membrane.
Define the term cell body.
This contains the nucleus surrounded by the cytoplasm. Within the cytoplasm there are also large amounts of endoplasmic reticulum and mitochondria which are involved in the production of neurotransmitters.
What are neurotransmitters?
Chemicals which are used to pass signals from one neurone to the next.
Define the term myelinated sheath.
Membrane rich in lipid which surrounds the axon of some neurones, speeding up impulse transmission.
Define the term “Schwann cell”.
Schwann cells form a lipid material called myelin, which wraps around the axon.
Define the term node fo ranvier.
Nodes of Ranvier are the gaps between each adjacent Schwann cell. With the myelin sheath, they allow for a faster speed of transmission.
Describe and explain the advantage of myelination.
- The myelin sheath is made of many layers of plasma membrane, Schwann cells produces these membranes by growing many times around the axon.
- The myelin sheath acts as an insulating layer and allows these myelinated neurones to conduct the electrical impulse at a much faster speed than unmyelinated neurones.
- Between each adjacent Schwann cell there is a small gap known as the node of Ranvier. This creates a gap in the myelin sheath.
- In myelinated neurones, the electrical impulses jump from one node to the next as it travels along the neurone.
- Called saltatory conduction and massively increases the speed of transmission.
Explain why some neurones are myelinated and others are unmyelinated.
- When the stimulus is non-urgent (i.e. a dull pain or a small temperature change), the response does not have to be fast.
- When the stimulus is urgent myelination is necessary for a fast transmission to protect body from danger.
Explain the role of sodium ions, potassium ions, organic anions, the sodium/potassium ion pump and potassium ion channels in establishing and maintaining the resting potential.
- Sodium/Potassium pump in the membrane of the axon is working constantly, actively transporting 2K+ inside the cell for every 3Na+ out.
- This creates a high concentration of Na+ outside the cell and a build of positive charge.
- K+ ion concentration builds up inside the cell but there are less positive ions inside compared to outside so the potential difference of the cell membrane with respect to the outside is negative (-70mv).
- This resting potential is maintained because the voltage-gated sodium ion channels are closed at this potential difference so sodium ions cannot diffuse back into the cell.
- The potassium ion channels are open, so some potassium ions diffuse out of the cell down their concentration gradient, but not many because of the positive charge outside of the cell that repels them.
- Potassium ions remain in higher conc inside the cell than out.
Describe what resting potential in the axon is.
- When a neurone is not transmitting an impulse, the potential difference across its membrane is known as resting potential.
- In this state, the outside of the membrane is more positively charged than the inside of the axon.
- The membrane is said to be polarised as there is a potential difference across it.
- The potassium ion channels (mainly those that are not VG) are open, and the VG sodium ion channels are closed.
- Sodium/potassium pump is working. Pumping out 3 sodium ions for every 2 potassium ions in.
Explain why a neurone is active when it is said to be resting.
Because it still carrying out active transport of ions in order to maintain the resting potential.
Define the term “resting potential”.
The potential difference across the membrane of the axon of a neurone at rest (i.e. when an impulse is not being transmitted).