Chapter 15 - Nervous coordination Flashcards
What are cells call which cover neurones and what are their purpose?
They are call Schwann cells, and they myelinate the neurones, preventing the movement of ions from the cells which makes the rate of transmission faster between the start and end of a Schwann cell.
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What is a resting potential and how is it created?
A resting potential is where sodium potassium pump in the neurone which pumps out three Na ions per 2 potassium ions pumped in (through active transport). However, the neurone is “leaky” to potassium ions therefore they will move through diffusion out of the cell again, resulting in a negatively charged cell
What is an action potential?
An action potential is when a stimulus from further down the neurone causes sodium voltage-gated channels to open and sodium floods into the neurone, which causes more and more channels to open, thus described as an all or nothing principle. However at +40mV, Na channels shut and potassium voltage gated channels open and the cell begins to hyperpolarise to recover its resting potential
What is the refractory period?
There are two types of refractory periods. Absolute and relative, absolute is where it is impossible to cause another action potential because there are too many positive ions on the inside of the cell, and relative is where they have started to move out so it is possible to cause an action potential but would require a very large stimulus
Why is the refractory period important?
It allows neurones to not constantly have an action potential and instead deliver discrete potentials so they can be detected more easily, and the impusle can only travel in one direction
What three factors affect the speed of conductance?
Myelination - myelinated axons are around 3 times faster than non-myelinated ones
Axon diameter - wider axons lose less ions and therefore have an easier time with action and resting potentials
Temperature - faster enzymes (sodium potassium pump) and also faster movement of ions
How does synaptic transmission work?
Once an action potential reaches a presynaptic knob, the charge causes Calcium channels to open allowing calcium ions to enter. The presence of the calcium ions causes the vesicles containing neurotransmitters to bond with the neurone and release the neurotransmitter into the synaptic cleft, where they would bind with receptors specific to that transmitter on the postsynaptic neurone, allowing sodium ions to enter which causes an action potential
What are inhibitory neurotransmitters
They are neurotransmitters which can be released and bind with the postsynaptic knob which instead work to make it more difficult to induce an active potential
What is summation and how does it work
Summation is one of two things:
spatial summation where several different neurones come together in one synapse, and when they all have action potentials it is significantly easier to induce an active potential in the post synaptic neurone
Temporal summation where one neurone can repeatedly release large amounts of neurotransmitter due to frequent active potentials
What happens to acetylcholine in the synaptic cleft
Enzymes can be released into the cleft which breaks acetylcholine into ethanoic acid and choline which is reabsorbed by the presynaptic neurone and converted back into acetylcholine
Describe the structure of a muscle
A muscle is made up of many different cells which are fused to essentially form one cell, or a fibre, with shared nuclei and a cytoplasm, known as a sarcoplasm. The fibre itself is made up of two proteins known as actin and myosin
How does synaptic transmission in the neuromuscular junction expose actin molecules?
The acetylcholine diffuses out of the presynaptic knob into the synaptic cleft where it bonds onto a receptor on the muscle fibre, causing calcium ions to be released in the sarcoplasm of the muscle. These calcium ions will diffuse to tropomyosin molecules, which then change shape and slide away revealing the actin binding sites
How does the interaction between myosin and actin result in a contraction
The myosin heads contain ADP, which binds to the actin sites which have now been exposed and slide it across the myosin molecule. After this, the ADP is regenerated into ATP. This change releases the myosin head from the actin site and “recocks” the myosin head. The ATP molecule is hydrolysed into ADP which is able to rebind to the actin molecule again. This process is repeated for as long the tropomyosin is revealing the actin sites
What is the funtion of phosphocreatine?
Phosphocreatine is able to immediately regenerate ADP into ATP without the need for respiration, and does so in anaerobic conditions
