3.6 Organisms respond to changes in their internal and external environments Flashcards
Describe the sequence of events involved in transmission across a cholinergic synapse.
Do not include details on the breakdown of acetylcholine in your answer
Depolarisation of presynaptic membrane
Calcium channels open and calcium ions enter (synaptic knob)
Calcium ions cause synaptic vesicles move to/fuse with presynaptic membrane and release acetylcholine/neurotransmitter
Acetylcholine/neurotransmitter diffuses across (synaptic cleft)
(Acetylcholine attaches) to receptors on the postsynaptic membrane
Explain how acetylcholine contributes to a synapse being unidirectional
Acetylcholine only produced released from presynaptic neurone
Receptors for acetylcholine to bind to are only found on the postsynaptic neurone membrane
Suggest two advantages of simple reflexes
Rapid and protect against damage to body tissues to help escape predators
Serotonin diffuses across the synaptic gap and binds to a receptor on the post-synaptic membrane.
Describe how this causes depolarisation of the post-synaptic membrane
Causes sodium ion channels to open
So sodium ions enter repolarise the
membrane
It is important that a neurotransmitter such as serotonin is transported back out of synapses. Explain why.
If not removed, they keep binding to receptors
keep depolarising membrane and causing more action
potentials
Explain how the release of acetylcholine at an excitatory synapse reduces the membrane potential of the postsynaptic membrane
acetylcholine binds to receptors on postsynaptic membrane
opens sodium ion channels
sodium ions enter and depolarise the membranes
Describe the sequence of events leading to the release of acetylcholine and its binding to the postsynaptic membrane.
action potential arrives and depolarisation occurs
calcium ions enter synaptic knob
vesicles fuse with membrane;
acetylcholine diffuses (across synaptic cleft)
binds to receptors
Explain what causes the conduction of impulses along a non-myelinated axon to be slower than along a myelinated axon
non-myelinated neurone every section of membrane along the whole length of axon needs to be depolarised so impulse travels along whole length
myelinated neurone = myelin sheath insulates preventing ion movement
so depolarisation only occurs at nodes of Ranvier
so saltatory conduction occurs where the
impulse jumps from node to node
A scientist investigated the effect of inhibitors on neurones. She added a respiratory inhibitor to a neurone. The resting potential of the neurone changed from –70 mV to 0 mV. Explain why.
less respiration = less ATP produced
so less active transport of sodium ions out and potassium ions in occurs
so electrochemical gradient is not maintained
what starts depolarisation in an action potential
sodium ion channels open
what requires the hydrolysis of ATP in an action potential
Active transport of sodium and potassium ions restores resting potential
When a neurone transmits a series of impulses, its rate of oxygen consumption increases. Explain why
using more oxygen = more respiration occurring, so more ATP produced for active transport of sodium and potassium ions by sodium-potassium pump
active transport requires ATP
After exercise, some ATP is used to re-establish the resting potential in axons.
Explain how the resting potential is re-established.
sodium pump actively transports sodium ions out of the axon and potassium in
Describe how the resting potential is established in an axon by the movement of ions across the membrane
Active transport of sodium ions out of axon and potassium ions in
diffusion of potassium ions out of axon and little diffusion of sodium ions into axon
sodium and potassium ions can only cross the axon membrane through proteins. Explain why.
Ions cannot pass through the phospholipid bilayer
because they are lipids insoluble or charged
