Neuronal communication 5.3 Flashcards
What is a Pacinian corpuscule?
A pressure sensor found in the skin that detects changes in pressure
What are sensory receptors?
Specialised cells that can detect changes in our surroundings
What is a transducer?
A cell that converts one form of energy into another
Where are Pacinian corpuscules found?
The skin
What kind of receptors are Pacinian corpuscules?
Mechanoreceptors
What is the structure of a pacinian corpuscule?
Oval shaped structure consisting of rings of connective tissue wrapped around the end of a nerve cell
What triggers an action potential in a pacinian corpuscule?
When pressure is applied which stretches the nerve cell membrane and causes a change in polarity
What energy transfer do photoreceptors do?
Light to electrical
What energy transfer do mechanoreceptors do?
Movement to electrical
What energy transfer do chemoreceptors do?
Chemical to electrical
What energy transfer do thermoreceptors do?
Heat to electrical
What is the resting potential (not the value)?
When the charge is negative on the inside and positive on the outside
Is resting potential polarised or depolarised?
Polarised
What is the permeability of the membrane like?
- more permeable to K ions so they leak out more
- less permeable to Na ions so few leak out
Is an action potential polarised or depolarised?
Depolarised
What do neurons consist of?
- myelin sheath
- schwann cells
- nodes of ranvier
- nucleus
- mitochondria
- ribosomes
What does a dendron do?
Transmits electrical impulse towards the cell body
What does an axon do?
Transmits electrical impulse away from cell body
What is the myelin sheath made up from?
Schwan cells
What is saltatory conduction?
When the action potential jumps from node of ranvier to node of ranvier
Why is saltatory conduction quicker?
- reduces energy expenditure
- reduces degradation of impulse
(can travel longer distances)
What causes quicker transmissions?
- bigger axon (higher SA)
- higher temp
- nodes of ranvier
(doesnt depolarise entire membrane)
What is depolarisation?
A change in polarity (Inside of cell becomes more positive)
What happens due to slow closing potassium channels?
Refractory period
What cannot occur during a refractory period?
An action potential
Why does the refractrory period happen?
Allows time for the cell to recover and ensures that action potentials only occur in one direction
What is happening during the refractory period?
Hyperpolarisation
What is the threshold potential?
The threshold needed to create an action potential (-50mV)
What is the refractory period?
The period after an action potential when another action potential cannot be reached
What causes the refractory period?
Hyperpolarisation of the membrane
What is the difference between a small stimulus and a strong one?
A weak stimulus only triggeres 1 action potential whereas a strong one triggers multiple
What is the voltage inside the cell at resting potential?
-60mV
What do sodium potassium pumps do?
Actively transport 3 Na+ out of the neuron for every 2 K+ moved in
What do non gated ion channels do?
Allow facilitated diffusion of K+ and Na+ down their diffusion gradients (more K+ channels than Na+)
How is an action potential created in pacinian corpescules?
- Pressure is applied
- Na gated channel open
- Na ions diffuse into cells
- causes small amount of depolarisation (generator potential)
- If voltage change is higher than -50mV threshold value an action potential will occur
What are the 6 stages of an action potential?
- resting potential
- stimulius
- depolarisation
- PD reaches +40mV
- repolarisation
- hyperpolarisation
What happens at resting potential?
- outside is positive and inside is negative
- 70mV difference in charge
- Na+ voltage gate ion channels are closed
- K+ non voltage gated channels mostly closed
- Na/K gated channel protein actively transport 3Na+ out for every 2K+ in
What happens when a stimulus appears?
- triggers some Na+ voltage gated channels to open
- Na+ diffuses into the neuron
- Inside of neuron becomes more positive
What happens at depolarisation?
- PD reaches threshold value of -50mV
- causes all Na+ voltage gated channels to open
- more Na+ diffuses into the neuron
- positive feedback loop so this keeps happening to increase voltage inside
What happens once PD reaches -40mV?
- Na+ voltage gated channels close
- K+ voltage gated channel proteins open
What happens during repolarisation?
- K+ diffuses out the neuron
- reduces PD
- inside is now more negative than the outside
What happens during hyperpolarisation?
- Lots of K+ diffuses out due to slow closing gates
- inside is now more negative than resting potential
- K+ voltage gated channels now fully close
- Ma/K pump moves Na out the neuron
- K+ diffuses back into neuron
- resting potential is now achieved
What is the all or nothing law?
The idea that once threshold value is reached an action potential will always fire with the same voltage no matter the size of the stimulus
What is a synapse?
A junction between two or more neurones or a neurone and an effector?
Why do synapses use chemical messages?
An action potential cannot bridge the gap so a neurotransmitter is used
What are the components of a cholinergic synapse?
Axon terminal, presynaptic knob, synaptic cleft, post synaptic cell, dendrites
How does a synapse pass on a message?
- action potential arrives at axon terminal
- depolarisation causes voltage gated Ca 2+ channels and Ca 2+ enters cell
- Vesicles release ACh (acetylcholine) into synaptic cleft by exocytosis
- ACh diffuses across synaptic cleft and binds to specific cholinergic receptors
- Na+ channels open and it diffuses in
- action potential continues
What happens to ACh after it binds to the receptors?
Enzymes (acetylcholinesterase) digest neurotransmitter and products are transported back to presynaptic nob
Why is the neurotransmitter digested?
- to recycle the neurotransmitter
- to prevent response from happening again
How do cholinergic receptors work?
2 acetylcholine molecules fuse to receptor site and sodium ion channel opens
What is an exitatory synapse?
- have receptors that are Na+ channels
- when open Na+ diffuses in
- causes a local depolarisation and make an AP more likely
- exitatory post synaptic cleft (EPSP)
What is the neuro transmitter for an exitatory synapse?
acetylcholine
What is an inhibitory synapse?
- has receptors that let Cl- ions in so make membrane potential more negative
- hyperpolarises membrane so inhibits an action potential
- impulse in one neuron can inhibit the impulse in the next
- inhibitory post synaptic potential (IPSP)
What is the neuro transmitter for an inhibitory synapse?
GABA (gamma aminobutyric acid)
What is the importance of synapses?
- unidirectional transmission
- convergence
- divergence
- spatial summation
- temporal summation
- Filtering out low level signals
- habituation
- memory
Why is unidirectional transmission important?
- ensures every impusle travels in one direction
- vesicles of neurotransmitter are only found in the presynaptic buld
- neurotransmitter receptors are only found in the post synaptic membrane
Why is convergence important?
Allows impulses from several neurones to be passed to a single neurone
Why is divergence important?
Allows impulses from a single neurone to be passed to multiple neurones
What is spatial summation?
- each stimulus causes the release of the same amount of neurotransmitter
- sometimes this causes a small depolarisation in the post synaptic neurone but not enough to trigger an action potential
- spatial summation is when when multiple neurones release neurotransmitters to combine to cause an action potential
- volume
What is temporal summation?
- where two or more impulses arrive in quick succession from the presynaptic neurone
- the quantity of neurotransmitter in a short period of time is enough to trigger an action potential
- frequency
Why is it important to filter out low level signals?
- to not become overwhelmed by every stimulus
- if a low level stimulus creates an AP in the presynaptic neurone, it is unlikely to pass across the synapse and will not cause another AP
What is habituation?
- after repeated stimulation a synapse might run out of vesicles of neurotransmitter
- nervous system no longer responds to the stimuls as it has become habituated
- prevents overstimulation and damage of effectors
Why is memory important?
- synaptic membranes are adaptable
- post synaptic membranes an be made more sensitive by adding more receptors
- and adapted post synaptic membrane is more likely tyo fire an action potential
- creates a specific pathway in response to a stimulus
