5.1.3 Neuronal Communication Flashcards
What are communication systems needed for?
- detect stimuli
- coordinate information
- respond in order to survive
what are the three key features of neurones?
- Cell body- Contains large amounts of smooth ER for synthesising neurotransmitters
- Dendrons- Extensions which transmit impulses towards cell body
- Axons- Transmit impulses away from cell body contain a small amount of cytoplasm
What are pacinian capsucules and where are they found?
Pressure sensors found in skin
How do pacinium capsucules detect pressure?
- Have a capsule which deforms under pressure
- Causes Na+ and K+ ion channels to open
- This causes it to reach threshold potential
What are the features of a sensory neurone?
- 1 dendron 1 axon
- Transmit impulses from receptors to relay
What are the features of a motor neurone?
Many short dendrites with only one dendron
Transmit impulses from relay/sensory to effector
What are the features of a relay neurone?
Many short axons and dendrons
Transmit impulses between neurones
What are the features of an axolemma membrane at rest?
Na channels are closed
Membrane is leaky to K+ ions
At resting potential
What voltage is resting potential?
-70 mV
What is a generator potential?
- Small change in potential difference
- Caused by Na+ channels opening
- Higher strength of stimuli means more channels open
What is threshold potential?
50 mv
The minimum potential needed for an action potential to take place
What is a refractory period and what does it prevent?
Short period of time where it is impossible for another action potential to be formed
Stops actionpotentials from travelling in different directions
What happens at the membrane when threshold potential is reached?
-More voltage gated Na+ channels opendepolarising membrane to +40mv
What happens at a membrane after 40mv are reached?
Na channels close and K+ channels open causing K+ to diffuse out
What is hyperpolarisation?
Where Potential difference has overhsot slightly and needs to be fixed by the Na+/K pump
What the three steps in the transmission of an action potential?
1.Voltage gated Na channels open and Na+ diffuse in
2.Na+ in a igh concentration where they diffuse in so move to an area of low concentraton via diffusion in a local circuit
3. P.D altered across membrane where Na + have moved to therefore more Na channels open and action potential has moved
What are the features of myelination?
- Insulating layer of Schwann cells meaning action potential cannot occur within it
- Nodes of ranvier - Places of no myelination
What are the advantages of myelination?
Speeds up transmission of action potentials as elongates local circuits and means saltatory conduction can occur
Why is the width of an axon important?
Larger diameter = faster conduction
Greater area of membrane which ionic exchange can occur
What is acclimatisation?
- Repeated stimulation will cause synapse to run out of neurotransmitter vesicles meaning no more action potentials can be transferred
What are the roles of synapses?
- Ensures all action potentials are unidirectional
- Several stimuli warning us of danger
- One signal can be transmitted all over the body
- Filters out low level signals
What is summation?
Where low levels of stimulation can cause a reaction if persistent
What is spacial summation?
Where two or more synaptic knobs act simultaneously
What is temporal summation?
Where several action potentials arrive in great succession
What are the steps involved in the transmission across a synapse?
- Action potential arrives at end of presynaptic neurone
- Voltage gated Ca 2+ channels open
- Synaptic vesicles fuse with presynaptic membrane
- Acetylcholine released by exocytosis and diffuses across cleft
- Acetylcholine bind to receptors on Na channels
- Na channels open and Na+ diffuses into post synaptic membrane
- Generator potential created
- Membrane reaches threshold potential
