6.2 Nervous Coordination Flashcards
What is a neurone?
A single nerve cell
What is a nerve?
A bundle of axons surrounded by connective tissue which binds them together
What is the sensory neurone made up of? (In direction of nerve impulse)
Dendrites Dendron Cell body (in the middle) Axon Branches of axon Synaptic knob
Potentially with myelin sheath and nodes of Ranvier
What is the intermediate (multipolar) neurone made up of?
Cell body in the middle
Axons and dendrites, with branches of axon and dendrites attached, all around the cell body
What is the motor neurone made up of? (In direction of nerve impulse)
Cell body at the end (surrounded by dendrites)
One large axon
Branches of axon
Motor end plate (forms neuromuscular junction)
Potentially with myelin sheath and nodes of Ranvier
How to remember the direction of the impulse?
Dendrites - dick in
Axon - away
What do dendrites do?
Subdivisions of the dendron which transmits nerve impulses towards the cell body
What does the cell body contain?
A nucleus
Large amounts of rough endoplasmic reticulum- for production of proteins and neurotransmitters
What are the nodes of Ranvier?
Gaps between adjacent schwann cells where there is no myelin sheath
What is the myelin sheath?
Forms a covering to the axon
Made up of membranes of Schwann cells
What are the stages of an action potential?
Resting potential
Depolarisation
Repolarisation
Hyperpolarisation
What are the numbers we need to learn from the action potential?
Resting potential: -65mV
Threshold: -55mV
Height of depolarisation: +40mV
What is resting potential?
No impulse is being passed along
More positive ions outside the axon
-65mV
What is the threshold for an action potential to take place?
-55mV
It needs to exceed the threshold
Describe resting potential in terms of ions?
Na+/K+ pump actively transports 3Na+ out of the axon for every 2K+ in
The leakage channel is open and facilitated diffusion of K+ out of the axon down it’s conc gradient takes place
Na+ ion channel is closed
K+ ion channel
-65mV
Describe Depolarisation in terms of ions?
Na+/K+ pump actively transports 3Na+ out of the axon for every 2K+ in
The leakage channel is open and facilitated diffusion of K+ out of the axon down it’s conc gradient takes place
Na+ion channel is open - Na+ facilitated diffuses into axon down electrochemical gradient
K+ ion channel is closed
-65mV to +40mV
Describe Repolarisation in terms of ions?
Na+/K+ pump actively transports 3Na+ out of the axon for every 2K+ in
The leakage channel is open and facilitated diffusion of K+ out of the axon down it’s conc gradient takes place
Na+ ion channel closes
K+ ion channel opens - K+ facilitated diffuses out of axon down conc gradient and electrochemical gradient
+40mV to -65mV
Describe Hyperpolarisation in terms of ions?
Na+/K+ pump actively transports 3Na+ out of the axon for every 2K+ in
The leakage channel is open and facilitated diffusion of K+ out of the axon down it’s conc gradient takes place
Na+ ion channel closed
K+ ion channel open - too many +ions have diffused out (temporary overshot of the electrochemical gradient)
The Na+/K+ pump, pumps K+ ions back into the axon to restore resting potential
Which neurone is faster from a myelinated and unmyelinated neurone and why is it faster?
Myelinated is faster
As the fatty sheath of myelin around the axon acts as an electrical insulator preventing action potentials from forming
Action potentials only occur at the nodes of Ranvier where a localised current can form and the action potential ‘jumps’ from node to node
Called saltatory conduction
Which neurone is slower from a myelinated and unmyelinated neurone and why is it slower?
Unmyelinated is slower
Depolarisation has to take place across the entire axon as oppose to just small sections
What are the factors affecting nerve impulses?
Diameter of axon - increased = faster speed of conductance (due to less leakage of ions)
Myelin sheath - increases speed of conductance
Temperature - increased = speeds up the nerve impulse (due to enzymes being able to function faster and ATP formed faster for AT)
What are the refractory periods?
Absolute - from start of depolarisation through to partway through hyperpolarisation NO action potential can be generated
Relative - from mid way through hyperpolarisation to resting potential an action potential is inhibited but not impossible
What are the three purposes for the refractory period?
Ensures the action potentials only move in one direction
Produces discrete impulses
Limits the number of action potentials
What is the principal to do with action potentials?
All or Nothing
There is an action potential or not at all
It needs to exceed threshold of -55mV
The strength of the stimulus is determined by the frequency
What are the stages of synaptic transmission? P1
The action potential arrives at the synaptic knob
Ca+ ion channels open = Ca+ ions flow into the synaptic knob
Causing vesicles containing the transmitter to move to the presynaptic membrane
The vesicles fuse with the presynaptic membrane and release acetylcholine into the synaptic cleft (exocytosis)
Acetylcholine diffuse down conc gradient across the gap and bind to specific receptor sites on postsynaptic membrane
What are the stages of synaptic transmission? P2
Permeability of the postsynaptic membrane changes = Na+ ions flow inwards building up EPSP charge (e-excitatory)
If EPSP exceeds threshold = action potential some transmitters cause IPSP (i-inhibitory)
Acetylcholine is hydrolysed by acetylcholineresterase in the cleft
Choline and ethanoic acid are reabsorbed into the synaptic knob, which are resynthesised using energy from ATP
Na+ channels closed -absence of acetylcholine
What is summation? Types?
The build up of neurotransmitter in the synapse
Spatial
Temporal
What is spatial summation?
Where two or more action potentials arrive at the synapse at the same time down different neurones
So sufficient neurotransmitter is released to initiate the action potential in the postsynaptic neurone
What is temporal summation?
Where two or more action potentials arrive at a synapse in quick succession down the same neurone
So sufficient neurotransmitter is released to initiate an action potential in the postsynaptic neurone
How are some synapses inhibitory?
Neurotransmitter at synapses open K+ and Cl- channels rather than Na+
The resulting ion movement causes an IPSP which hyperpolarises the postsynaptic membrane
Why is it beneficial to have inhibitory synapses?
Particular pathways can be selected
Makes it more difficult for an action potential to be generated
How are synapses affected by morphine/codein?
It works agonistically
Has the same effect as endorphins
How are synapses affected by prozac or ecstasy?
Blocks the reuptake of serotonin
So there is a high concentration of serotonin in the synapse = feeling happy
How are synapses affected by valium?
It increases the efficiency of synaptic transmission
More Cl- channels are open to hyperpolarise the neurone = less excitable
How are synapses affected by beta blockers?
Reduces the transmission of nerve impulses by binding to the receptor on the second neurone
Stops the heart speeding up
