Nervous Coordination Flashcards
What are nerve cells adapted to do?
Rapidly carry electrochemical changes (nerve impulses)
What are dendrites?
Extension of the cell body
Carry impulses towards cell body
Increase SA
What is the cell body?
Contains nucleus + large amount of RER
So that it can make its own proteins for growth + repair
What is the axon?
Collect + carry nerve impulse away from cell body
Spreads nerve impulse
What is the myelin sheath?
Multiple cells wrapped around axon
Increase speed of impulse
What are schwann cells?
Individual cells
Protect the neurone
Provide electrical insulation
Aid in regeneration of damaged
What are nodes of Ranvier?
Gaps where there is no myelination
Increase speed
Describe motor neurone adaptations
Lots of dendrites = multiple messages from different places
Attached to muscle
Long axon
Describe sensory neurone adaptations
Attached to receptors in skin
Only few dendrites = as only sending one message
Long axon = send message long distance
Describe intermediate neurone adaptations
Lots of dendrites on both side
Short axon = no distance
Gathers + transfers lots of info
What is a nerve impulse?
Self-propagating wave of electrical disturbance that travels along the surface of axon membrane
What are the two states?
Action potential
Resting potential
Resting potential charge
Outside + inside of axon have opposite charge
Inside = negative
Outside = positive
What is an action potential?
Temporary reversal of charge
How are messages sent?
Electrochemically
What controls the movement of Na+ and K+?
Phospholipid bi-layer
Intrinsic proteins
Gated channels
How does the phospholipid bi-layer control the movement of ions?
Hydrophobic fatty acid tails repel charged molecules
How do intrinsic proteins control the movement of ions?
Allow only specific ions to pass through
How does gated channels control the movement of ions?
Na+ and K+ open and close to control amount of movement
What is the resting potential voltage?
-65mV
How is a resting potential formed?
NaK pump = 3Na+ out, 2K+ in
Chemical gradient created
Na+ try to move back in but Na+ gates shut
K+ gates open = K+ diffuses out
= electrical gradient
Some K+ move back down electrical gradient
Until equilibrium is reached
Electrical + chemical gradient = balanced
Both sides of axon = polarised
How is resting potential maintained?
Membrane relatively permeable
Na+ actively pumped out by NaK pump
Inside = negative compared to outside
What is the action potential charge?
+40mV
What is an action potential?
The outside of the membrane is negative, the inside is positive
What is the charge of a hyperpolarised membrane?
-70mV
How is an action potential formed?
Stimuli causes Na gated channels to open
Na+ diffuses in down electrochemical gradient
More Na channels open until +40mV is reached (depolarised)
At +40mV Na channels close + K gated channels open
Axon repolarised
Movement of K+ out causes an overshoot of electrical gradient (-7mV)
NaK pump restores resting potential = axon repolarised
Describe the passage along the axon
One region depolarised + A.P
= acts as stimuli for next
As section becomes depolarised, the previous becomes repolarised = resting potential
A.P passes along axon
Explain how an action potential is passed along an unmyelinated neurone
3Na+ out, 2K+ in
Polarised
Influx of Na+ via diffusion = reversal of charge
Act as stimuli for Na channels to open further along
Behind Na channels close, K channels open
Removal of K+ returns membrane back to resting potential
What does the myelin sheath do?
Acts as an electrical conductor
prevents action potential from forming
Where can an A.P only occur?
Nodes of Ranvier
What is node “hopping” called?
Salatory conduction
What is salatory conduction?
Action potential propagation along myelinated axons from one node of Ranvier to the next
Why is salatory conduction useful?
Speeds up A.P
At each point no energy is lost
Why at each node “hop” is no energy lost?
Each A.P is the same size
Describe salatory conduction
Stimuli causes Na channels to open
Na+ facilitatedly diffuses in = reversal of charge
Na+ diffuses along conc gradient
Voltage gated Na channels open further along axon
Na+ diffuse in
New A.P occurs
A.P moves along axon
What factors affect the speed of an impulse?
Myelination (salatory conduction)
Temperature
Diameter of axon
How does an increased temperature speed up an impulse?
Particles have more KE so diffuse quicker
Increased enzyme activity
More energy available fort active transport
A.P established quicker
How does a smaller axon slow down an impulse?
Ions leave easier
= harder to build up ions in axon
= harder to establish electrochemical gradient
Membrane potentials = difficult to maintain
A.P = slower
What is the refractory period?
The time that it takes for Na+ influx to be possible again
What is the refractory period on a graph?
The proportion of the graph that leads back to the resting potential
What can’t happen during the refractory period?
No A.P can occur
Because no A.P can occur during the refractory period what about A.P’s does this ensure?
One direction
Discrete (separate)
Limited in number at one time
How does the refractory period cause the A.P to be in one direction?
Area before A.P will be in refractory period
So new A.P must be further along axon
How is an A.P discrete?
Refractory period takes time so the messages sent to the brain are not muddled
Why is the number of A.P’s limited at one time?
A.P’s = fixed distance apart
Cannot occur behind one another
Axon fixed length
So only a certain no. of A.P’s will fit
Why is it important that it is one direction?
Prevents movement backwards
Ensures message towards brain/effector
Why is it important that it is discrete?
Correct message received/delivered
Correct response coordinated
Why is it important that it is in limited numbers?
Can respond to different intensities of stimuli
Iniate different responses
Explain why the refractory period limits the propagation of an action potential
A.P must be at rest (-65mV) for new A.P to be propagated
Due to electrochemical gradient controlling the opening + closing of voltage gated channels
What is the synapse?
The point where a neurone communicates with the dendrites of another effector
What are the organelles of the synapse?
Axon Myelin sheath Presynaptic neurone RER Mitochondria Ca2+ channels Vesicles (containing neurotransmitters) Synaptic knob Post synaptic neurone Na+ channels
What does the synaptic knob contain?
Many mitochondria
Large amount of ER
Vesicles with neurotransmitters
Why does the synaptic knob contain many mitochondria?
Release energy for movement of vesicles
Release energy for protein synthesis
Why does the synaptic knob contain large amount of ER?
Synthesise chemical messages
Why does the synaptic knob contain vesicles with neurotransmitters?
Package up neurotransmitter
Move neurotransmitter to membrane
What are neurotransmitters?
Chemical messages
Specific
Enable synaptic transmission
What does the response to the arrival of a neurotransmitter depend on?
The cells
The cell’s location
The neurotransmitter involved
What is a cholinergic synapse?
A synapse that relies on the neurotransmitter acetylcholine
What is acetylcholine made of?
Acetyl (ethanoic acid)
Choline
What does acetylcholine cause?
Depolarisation
Generation of A.P
Describe synaptic transmission
Depolarisation of presynaptic neuron Ca channels open Ca2+ diffuses into presynaptic knob Vesicles move Vesicles fuse with phospholipid membrane Neurotransmitters diffuse across synaptic cleft Acetylcholine bind to Na channels Na channels open Reverse of charge due influx of Na+ Now A.P generated If threshold met
What are neuroreceptors?
Chemical-gated ion channels in post synaptic neuron membrane
Describe neuroreceptors
Specific - binding site for neurotransmitter
Usually closed
Undergo conformational change when neurotransmitter binds
Causes influx of Na+
Describe acetylcholinesterase
Hydrolic enzyme
Located on membrane
Breaks up acetylcholine
What happens after hydrolysis of acetylcholine?
Acetyl + choline diffuse back across cleft into presynaptic neurone
Neurotransmitters recycled + repackaged
Generation of new A.P prevented
Why are chemical synapses useful?
Transmit impulses in one direction
Protect system from overstimulation
Single impulse transmitted to multiple neurones
No. of impulses combined at synapse
Why does a chemical synapse transmit impulses in one direction?
So goes towards effector/ coordinator/ next neuron
Why does a chemical synapse protect against over stimulation?
Limited number of neurotransmitters released
Prevents fatigue
Why does a chemical synapse transmit a single impulse to multiple neurons?
One stimuli = multiple responses
eg. Pain = verbal + muscular response
Why does a chemical synapse combine a no. of impulses at the synapse?
Additive effect
Reach threshold value
What is summation?
The additive effect of low frequency A.P’s to produce sufficient neurotransmitters to trigger an A.P across synapse
What are the two forms of summation?
Spatial
Temporal
Describe spatial summation
Different presynaptic neurones come together to trigger ONE A.P
How does spatial summation meet the threshold value?
Both neurones need to release neurotransmitters
Describe temporal summation
Single presynaptic neuron releases neurotransmitters many times over a short period to exceed threshold
How does temporal summation meet threshold value?
Neurotransmitters released multiple times over short period
High frequency = A.P
What factors affect the rate at which acetylcholinesterase works + its effects?
Mutations
drugs
Temperature (diffusion)
Inhibitory synapse
What is inhibitory synapse?
A synapse which the nerve impulse in a presynaptic cell results in a reduced likelihood of an A.P initiation in a post synaptic cell
What happens in an inhibitory synapse?
Neurotransmitter diffuses across
Causes Cl- channels in post synaptic euro to open
Cl- diffuse across post synaptic membrane
Membrane hyperpolarised
Inhibits further A.P’s generated
What are the effect of drugs?
Block receptors so can't be activated by NT Same shape as NT so mimic action Inhibit enzyme that breaks down NT Stimulate release of NT Inhibit release of NT
What does it mean if drugs are the same shape as NT?
More receptors activated
What does it mean if drugs block receptors?
Fewer receptors can be activated
What does it mean if drugs inhibit enzyme?
More NT in synaptic cleft to bind to receptors
What does it mean if drugs stimulate release of NT?
More receptors activated
What does it mean if drugs inhibit release of NT?
Fewer receptors activated
What do serotonin + GABA do?
Inhibit nervous responses
What is serotonin used for?
Antidepressant
What is GABA used for?
Relieving anxiety, improving mood, reducing PMS + treating ADHD
What is the all or nothing principle?
The intensity of the stimuli is independent to the strength of the response/A.P
