Differences between synapse and neuromuscular
- neurone to neurone but neurone to muscle;
- no summation in neuromuscular synapse;
- some chlolinergic synapse can have different neurotransmitters e.g noradrenaline;
Describe the events that occur at the synapse during the delay between AP in the pre/postsynaptic neurone
- Voltage-gated Ca ion channels open
- Calcium ion enter
- vesicles fuse with preS memb
- exocytosis (release of neurotransmitter)
- these diffuse across cleft ;
- attach to receptors on postS memb
- this causes Na channels to open, allowing Na to diffuse in
Why is the impulse on transmitted in one direction
- Neurotransmitter only produced in pre-synaptic neurone;
- Receptor proteins for neurotransmitter only in post-synaptic membrane;
- Neurotransmitter diffuses from high conc to low
- Acetylcholinesterase is in the post-synaptic neurone
How is the resting potential re-established?
- Na-K pump
- 3 sodium actively transported out as 2 potassium in;
- ATP needed
Why does an increase in the length of myelination between nodes lead to an increase in the speed of conductance
- Impulse jumps from node to node
- Fewer jumps needed
what is a reflex?
Rapid** reactiom to stimulus which produces an **automatic** response. It is **innate
Why can’t another AP be created straight after?
- During refractory period
- Sodium ion channels closed;
- So Sodium ions cannot enter axon;
- Membrane potential becomes more negative than resting potential
- so threshold less likely to be exceeded
How is a new AP made? (2 M)
- Sodium ion channels open;
- Allowing rapid influx of sodium ions;
Why does a myelinated axon use less ATP to transmit a nerve impulse than an unmyelinated axon of the same diameter
- 3 Na+ actively moved out and 2 K+ in
- ATP required for active transport;
- Only at nodes in myelinated
- This occurs over whole length of axon in non-myelinated;
Criteria for a response to be a simple reflex action?
- Not involve conscious thought (brain isn’t used)
- Reaction is innate and not learned;
- Reaction is protective (prevent damage);
Function of energy released by the presynaptic mitochondria
- Synthesis of acetylcholine from acetyl + choline ;
- Movement of vesicles to membrane;
- Synthesis of enzyme acetylcholinesterase.
Why do people without mylein sheath have slower reflexes
- No saltatory conduction
- Depolarisation occurs over whole length of neurone
- This leads to slower transmission of AP
- Hence slowing down the arrival of impulses to muscle;
- So delay in muscle contraction
Explain why nervous transmission is delayed at synapses.
- Neurotransmitters need to diffuse across cleft
- Process of diffusion takes time
Why does a lower temp lead to a slower transmission?
- Slower diffusion;
- Of Na+ and K+ as less kinetic energy
Why do fewer AP pass along a myelinated neurone?
- Myelin insulates axon so ions can only pass through at gaps in myelin sheath;
- Gaps in sheath are called nodes of Ranvier;
How is the membrane repolarised?
- Sodium ion channels close and potassium ion channels open;
- Allowing efflux of potassium ions;
Define summation and lists the benefits
- addition** of many impulses which is directed onto a **single post synaptic neurone;
- spatial summation: allows integration** of stimuli from a **variety of sources
- temporal summation allows weak** background stimuli to be **filtered out before reaching the brain
How is the resting potential maintained at -65 mV
- Membrane more permeable to potassium ions than to sodium ions;
- So Potassium ions diffuse out faster than sodium ions diffuse in;
- Sodium-potassium pump uses ATP;
- 3 Na pumped out for every 2 K in
- Higher conc of +ve ions outside cell
All-or-nothing definition
- All action potentials are the same size;
- There’s a threshold value for action potential to occur
- Below it, no AP formed
After a reflex has occured, how do we know it has?
- impulses sent to brain
- sensory areas in brain interpretes and processes the impulse
Describe the formation of an AP
- Stimulus excites membrane, causing Na channels to open so Na+ enter;
- Down electrochemical gradient;
- If threshold met more Na+ channels open via +ve feedback
- At 40mV, Repolarisation occurs as Na channels close K channels open so K+ leave
- Down electrochemical gradient
- Hyperpolarisation occurs as K close slowly
- Sodium-potassium pump restores resting potential;
If acetylcholinesterase is inhibited how can this lead to death by affecting breathing?
- acetylcholine not broken down;
- it remains attached to receptor
- Na channels remain open, so Na depolarises axon
- would lead to continuous impulses, causing muscle spasms;
- no relaxation of intercostal muscle leads to fatigue
- stops breathing
Explain why the rate of oxygen consumption of a neurone increases when it conducts a high frequency of impulses.
- Oxygen used in respiration,
- Increase in respiration so more ATP made
- ATP used in sodium-potassium pump
- More Na+ actively moved out and more K+ actively moved in
- This is to maintain resting potential
Due to the refractory period, after a certain concentration of acid the brain can’t obtain information about the concentrations. Why
- Refractory period leads to discrete nerve impulses
- Refractory period limits the frequency of nerve impulses;
- When maximum frequency reached/exceeded, all higher concentrations of acid seem the same;
