Topic 6: Nervous Coordination Flashcards
What is a neurone’s resting state?
The resting potential, when its not being stimulated so the outside of the membrane is more positively charged then the inside
What is the voltage at resting state or a neurone?
-70mV
What is voltage the measure of?
Difference in charge between the inside and outside of a membrane
What is a resting potential created and maintained by?
Sodium-Potassium pumps, potassium ion channels in a neurones membrane
What form of transport does sodium-potassium pump using?
Active transport
What do the sodium potassium pump use active transport to do?
Move 3 sodium ions out for every 2 potassium ions moving in (ATP needed)
What do potassium ion channels allow?
Facilitated diffusion of potassium ions out of the neurone, down their concentration gradient
Explain the 3 steps of creating and maintaining a resting potential?
1) Sodium-potassium pumps move sodium ions out of the neurone but the membrane isn’t permeable to sodium ions so they can’t diffuse back in. Creating electrochemical gradient more positive na+ outside than in
2) The sodium-potassium pump also moves potassium ions into the neurone
3) When the cell is at rest, more potassium ion channels are open. Meaning that the membrane is permeable to K+ ions so some diffuse back out through potassium ion channels
When does an action potential occur?
When a neurone is stimulated and other ion channels e.g Na+ open, if the stimulus is big enough it’ll trigger a rapid change in potential difference
When the neurone is stimulated what doe this cause the cell membrane to do?
Become depolarised
In terms of an action potential what does the stimulus do?
This excites the neurone cell membrane, causing sodium ion channels to open.
The membrane becomes more permeable to sodium so sodium ions diffuse into the neurone down the sodium ion electrochemical gradient making the neurone less negative
In terms of an action potential what happens at depolarisation?
If the potential difference reaches the threshold more sodium ion channels open, so more sodium ion diffuses into the neurone
In terms of an action potential what happens at repolarisation?
At a potential difference of -30mV the sodium ion channels close and potassium ion channels open
The membrane is more permeable to potassium so potassium ions diffuse out of the neurone
Starting to get the membrane back to its resting potential
In terms of an action potential, what happens at hyperpolarisation?
Potassium ion channels are slow to close so there’s a slight ‘overshoot’ where too many K+ ions diffuse out of the neurone
The potential difference becomes more negative than the resting potential
After the action potential what happens at the resting potential?
The ions reset, the Na-K pump returns the membrane to its resting potential by pmping sodium ions out and potassium in maintaining the resting potential until the membrane’s exited by another stimulus
After an action potential why can’t the neurone be stimulated again straight away?
As the ion channels are recovering and they can’t be made to open
When does the refractory period occur?
For Na+: during repolarisation when they are closed
For K+: during hyperpolarisation
What does the refractory process act as?
Time delay between one AT and the next, making sure they don’t over lap
How is a wave of depolarisation along a neurone caused?
When an AP happens, some of the sodium ions that enter the neurone diffuses sideways
Causing sodium ions channels in the next region of the neurone to open and Na+ diffuse into that part
When a wave of depolarisation occurs what happens?
The wave moves away from the parts of the membrane in the refractory period because these parts can’t fire an AP
What is the All-or-northing principle?
Once the threshold is reached, an AP will always fire with the same change in voltage, no matter how big the stimulus is
If the threshold isn’t reached, an AP won’t fire
In terms of action potentials, what does a bigger stimulus happen?
It won’t cause a bigger action potential but it will cause them to fire more frequently
What are the 3 factors that affect the speed of conduction?
Myelination (saltatory conduction), axon diameter and temprature
What is myelin sheath?
It is an electrical insulator
In the peripheral NS, what is the sheath made from?
Schwann cell
Between the Schwann cels what are the tiny patches of bare membrane called?
Nodes of Ranvier
What is concentrated at the Nodes of Ranvier?
Sodium ions
What is saltatory conduction?
In a myelinated neurone, the neurone cytoplasm conducts enough electrical charge to depolarise the next node, so the impulse ‘jumps’ from node to node it happens really fast
How does conduction occur in non-myelinated neurones?
The impulse travels as a wave along the whole length of axon membrane, so you get depolarisation along the whole length of the membrane, this is slower than saltatory conduction
How does axon diameter affect speed of conduction?
AP’s are conducted quicker along axons with bigger diameters because there’s less resistance to the flow of ions than in the cytoplasm of a smaller axon
With less resistance, depolarisation reaches other parts of the neurone cell membrane quicker
How does temperature affect speed of conduction?
The speed of conduction increases as the temperature increases too, because ions diffuse faster
The speed only increases up to around 40 degrees though after that the protein begin to denature and the speed decreases
What is a synapse?
Junction between 2 neurone’s or between a neurone and an effector cell
Whats a synaptic cleft?
The tiny gap between cells at the synaptic cleft
What does the presynaptic cleft have that the postsynaptic neurone doesn’t?
A swelling called synaptic knob
What does the synaptic knob contain?
Synaptic vesicles filled with chemicals called neurotransmitters
What the effect of an action potential?
It causes neurotransmitters to be released into the synaptic cleft and diffuse across the post-synaptic membrane and bind to specific receptors
When they bind an AP might be triggered causing muscle contraction or hormone secreted
Because receptors are only on the post-synaptic membrane what does that make the impulses?
Unidirectional, NT’s are removed from the left so the response doesn’t keep happening
What is Acetylcholine?
A neurotransmitter
What does Acetylcholine do?
Binds to cholinergic receptors
What are the synapses that use acetylcholine called?
Cholinergic synapses
Explain step 1 of how a nerve impulse is transmitted across a cholinergic synapse.
Arrival of an action potential: An AP arrives at the synaptic knob of the presynaptic neurone.
The AP stimulates voltage-gated calcium ion channels in the presynaptic neurone to open
Ca2+ ions diffuse into the synaptic knob
Explain step 2 of how a nerve impulse is transmitted across a cholinergic synapse.
Fusion of the vesicles: The influx of Ca2+ ions into the synaptic knob causes the synaptic vesicles to fuse with the presynaptic membrane
The vesicles release the NT acetylcholine (ACh) into the synaptic cleft by exocytosis
Explain step 3 of how a nerve impulse is transmitted across a cholinergic synapse.
ACh diffuses across synaptic cleft and binds to specific cholinergic receptors on the postsynaptic membrane causing Na+ ion channels in the postsynaptic neurone to open
The influx of Na+ ions into the post-synaptic membranes causes depolarisation
An AP on post mem is generated if the threshold is reache
ACh is removed from synaptic cleft so the response doesn’t keep happening
Broken down by enzyme AChE acetylcholinesterase and products are re-absorbed by he presynaptic neurone and used to make more ACh
What are the 2 types of neurotransmitters?
Inhibitory and Excitatory
What do Inhibitory NT do?
Hyperpolarise the postsynaptic membrane preventing it from firing an action potential
What do Exhibitory NT do?
Depolarise the postsynaptic membrane making it fire an action potential if the threshold is reached
What’s a synapse where inhibitory NT are released?
Inhibitory synpase
What is summation?
Where the effect of NT’s released from many neurons (or one neurone that’s stimulated a lot in a short time) is added together
What does summation mean can happen?
Means the synapse accurately processes info, finely tuning a response
What is spatial summation?
Where 2 or more presynaptic neurones release their NT at the same time onto the same postsynaptic neurone
The small amount of NT being released from these may be enough altogether to reach the threshold in the postsynaptic neurone and trigger an AP
In spatial summation, what is the effect if some neurones release inhibitory NT?
Total effect of all NT might be no AP
What is temporal summation?
Where 2 or more nerve impulses arrive in quick succession from the same presynaptic neurone, this makes an AP more likely because more NT is released into the synaptic cleft
What is a neuromuscular junction?
A specialised cholinergic synapse between a motor neurone and muscle cell
What NT do neuromuscular junctions use and what does it do?
Acetylcholine (ACh) binds to cholinergic receptors called nicotinic cholinergic receptors
How do neuromuscular junctions work?
Same way as cholinergic synapse, they both release ACh from vesicles in presynaptic membrane and the diffuse across the synaptic cleft and binds to cholinergic recpetors on postsynaptic mem
Name the 3 differences between neuromuscular junctions and a cholinergic synapse
At a neuromuscular junction:
1) Post-synaptic membrane has lots of folds that form clefts, these store AChE
2) Post synaptic membrane has more receptors that others
3) ACh is always exitatory
What is smooth muscle?
Controls without conscious control
Where is smooth muscle found?
In the walls of internal organ, e.g stomach, intestine and blood vessels
What is cardiac muscle?
Contracts without conscious control
Where is cardiac muscle found?
Heart only
What is skeletal muscle?
Type of muscle you use to move
Where is skeletal muscle found?
Bicep and tricep
How are skeletal muscles attatched to bones?
Tendons
What attaches 2 bones?
Ligaments
Name some properties of skeletal muscles
Skeletal muscles contact and relax to move bones at a joint, they are in compressible so act as a lever, giving the muscles something to pull against
What are antagonistic pairs?
Muscles that work together to move a bone, contracting muscle is called agonist and relaxing muscle is called antagonist
What are skeletal muscles made up of?
Large bundles of long cells called muscle fibers
What is the cell membrane of muscle fibre cells called?
Sarcolemma
Explain the structure of skeletal muscles?
Parts of the sarcoemma fold inwards across the muscle fibre and stick into the sarcoplasm, these folds are called transverse tubules and spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle
Network of internal membranes called sarcoplasmic reticulum runs throughout the sarcoplasm
What does the sarcoplamic reticulum store
Calcium ions that are needed for muscle contraction
What does muscle fibres contain a lot of?
Lots of mitochondria to provide that ATP needed for muscle contraction
Whats the name of the skeletal muscles structure?
Multinucleate and have lots
of long cylindrical organelles called myofibrils
What are Myofibrils made up off?
Proteins
What are myofibrils specialised for?
contraction
What do myofibrils contain?
Bundles of think and thin myofilaments that move past each other to make muscles contract
What is the thick myofilaments made of?
Protein myosin
What is the thin myofilaments made up of?
Actin
What is it called when actin and myosin overlap?
a-band
What is the band called that is only contain actin?
I-bands
What is a myofibril made up of?
Many short units called sarcomeres
What is the end of each sarcomere marked with?
Z-line
What is the middle of each sarcomere called?
m-line
What is the zone around M?
H-zone, only containing myosin
What is muscle contraction explained by?
Sliding filament theory
Explain sliding fiulament theory
Myosin and actin slider over each other to make sarcomeres contract, the myofilaments themselves don’t contract
The simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract and sarcomereds return to their orginal length as the muscle relaxes
