Chapter 13 : Neuronal Communication Flashcards
What does the structure of a sensory neurone look like ?
a sensory neurone consists of dendrites, dendron, cell body, axon and axon terminals (it is myelinated)
what are dendrons and axons
dendrons transmit impulse towards the cell body
axons transmit impulses away from the cell body
where is direction of impulse
facing towards the axon terminals (to the right)
What is the dendrites of a sensory neurone attached to ?
a sensory receptor (which it receives impulses from)
Where is the relay neurone found and what does its structure look like ?
the relay neurone is found in the CNS and it consists of short branched axons and dendrites from the cell body
What is the role of the sensory neurone ?
to carry impulse from the receptors (which have detected a stimulus) to the CNS
What is the role of the motor neurone ?
to carry impulse from the CNS (relay neurone) to the effectors (muscles/glands) so that the response can be carried out
What does the structure of the motor neurone look like ?
consists of dendrites, cell body, axon then axon terminals
What is a myelin sheath, how is it formed and what neurones have one?
a myelin sheath is a layer of plasma membranes acting as an insulating layer and allowing conduction of impulses at a faster speed
it is produced by Schwann cells
only sensory and motor neurones have one
What are the nodes of Ranvier and why are they essential ?
the nodes of Ranvier are the unmyelinated sections where the impulse jumps between.
this is where action potential is generated
faster conduction of impulse
What are sensory receptors and what do they act as?
sensory receptors are specialised cells specific to a single type of stimulus and they act as transducers
What are transducers
transducers convert one form of energy into another
(converting energy provided from a stimulus to an electrical impulse)
How does the Pacinian corpuscle work ?
The Pacinian corpuscle detects changes in pressure and movement (stimulus) converting it into an electrical impulse/nerve impulse
Step 1: high concentration of sodium ions outside of the neurone and stretch mediated sodium ions channels are closed (membrane is polarised)
Step 2: pressure is applied causing the stretch mediated sodium ions channels to change shape and open and sodium ions diffuse down a electrochemical gradient into neurone
Step 3: membrane becomes depolarised (more positive inside) + action potential is triggered along sensory neurone —> CNS
What does generator potential mean ?
the process of the membrane becoming depolarised and initiating action potential in response to a stimulus (Only if the threshold is passed)
What is meant by resting potential and how many mV ?
This is when the cell is at rest
outside of the membrane of the axon is more positively charged than inside the axon (more negative)
it is -70 mV
why does the resting potential occur
it happens due to:
- sodium/potassium pump (intrinsic protein) pumps out 3 sodium ions and takes in 2 potassium ions (requires ATP)
- voltage gated sodium channel is closed (preventing re-entry) but non voltage gated potassium channels open allowing K+ ions to diffuse out
- therefore there are more positively charged ions outside the axon
how is action potential generated ?
- stimulus is detected which must surpass the threshold of -55mV to produce action potential
- voltage gated sodium channels open due to a stimulus (membrane is more permeable to Na+) inside of the neurone becomes less negative
- this change in charge causes a positive feedback response and more sodium ions diffuse into the axon down their electrochemical gradient
- influx of positively charged sodium ions causes the membrane potential to become less negative (depolarize) and moves towards +40 mV.
what happens in repolarisation and why ?
when potential difference reaches +40mV voltage gated sodium channels close and voltage gated potassium channels open
membrane is more permeable to K+ ions which diffuse out of the axon down their electrochemical gradient + this reduces positive charge
occur so that seizures do not happen and a continuous wave of depolarisation (transmit nerve impulses along constantly)
what is hyperpolarisation ?
Potassium channels remain open for a short time after the membrane potential has returned to around -70 mV.
leads to an overshoot, membrane potential becomes even more negative than the resting potential, decreases to around -80 mV.
how is a return to resting potential created ?
Voltage gated potassium ion channels are closed
The sodium-potassium pump restores the original distribution of sodium and potassium ions, pumping sodium ions out and potassium ions back in.
This process restores the resting potential, readying the neuron for another action potential
what is saltatory conduction ?
process where electrical impulses are transmitted in myelinated axons (much faster + energy efficient)
depolarisation only occurs at the nodes of Ranvier (contains voltage gated sodium and potassium ion channels)
large localised circuits between adjacent nodes (action potential jumps from one node to adjacent node)
what is the refractory period ?
after an action potential there is a short period of time where axon can not be excited again
voltage gated sodium ion channels remain closed preventing movement of Na+ into axons
why is the refractory period important
ensures that action potentials only travel in one direction (unidirectional) and that they do not overlap: occurring as discrete impulses
Define threshold
The minimum stimulus required to trigger an action potential
depolarisation above a certain level occurs initiating action potential
Describe the all or nothing principle
the power of the stimulus is not proportional to the power of the action potential.
the action potential will either occur or it won’t depending on if it passes the threshold
What does a large stimulus mean and what is the relationship between action potential frequency and size of stimulus
more frequent action potentials generated in neurone
the larger the stimulus the more frequent the action potentials generated in a given time (directly proportionate)
What is a synapse ?
the junction between two neurones where impulse is passed from one neurone to another (via neurotransmitters)
what is the role of a synapse
to ensure impulses are unidirectional and they can only travel from pre –> post synaptic neurone
How does the structure of a cholinergic synapse look like
consists of presynaptic neurone ending (with vesicles of acetylcholine and voltage gated calcium channel)
synapse,
post synaptic neurone (with voltage gated sodium ion channels and ACh receptors)
How is impulse transmitted across a cholinergic synapse ?
Step 1: action potential reaches the presynaptic neurone ending causing voltage gated calcium ion channels to open
step 2: calcium ions rush into the presynaptic neurone down the electrochemical gradient causing depolarisation of synaptic knob (action potential generated)
step 3: presence of calcium ions cause the synaptic vesicles with acetylcholine to move and fuse with the pre synaptic membrane
step 4: ACh is released into synaptic cleft and diffuses across the synapse to post synaptic neurone
step 5: ACh binds to receptor sites on post synaptic sodium ion channels causing them to open
step 6: sodium ions diffuse into post synaptic neurone down electrochemical gradient –> depolarisation of post synaptic membrane triggering new action potential
ACh is removed from the receptor and broken down by acetylcholinesterase
what is acetyl choline broken down into by acetylcholinesterase + why?
acetate (ethanoic acid) and choline
To prevent permanent depolarisation of post synaptic membrane
what happens to the products of enzyme breaking down acetylcholine
these products diffuse back into the presynaptic neurone (acetate and choline)
ATP released from the mitochondria can combine acetate and choline into acetylcholine (inside presynaptic neurone)
define summation
when the amount of neurotransmitter builds up to reach the threshold and then an action potential is triggered (in next neurone)
because amount of neurotransmitter from a single impulse may not be enough to trigger action potential in postsynaptic neurone
what is spatial summation
when a number of presynaptic neurones connect to one post synaptic neurone
each releases neurotransmitters until eventually they build up to a high enough level to trigger an action potential in the post synaptic neurone
passing the threshold potential
what is temporal summation
when a single presynaptic neuron releases neurotransmitters in rapid succession (due several action potentials)
high concentration of neurotransmitters build up and trigger an action potential in post synaptic neurone (passing the threshold)
what are the 2 types of neurotransmitters
- excitatory neurotransmitter (acetylcholine) triggering action potential in post synaptic neurone
- inhibitory (GABA)- does not trigger new action potentials in post synaptic
