Topic 6 - Nervous Coordination Flashcards
Do unmyelinated nerve fibres contain nodes of Ranvier?
No
What is the speed of transmission in myelinated nerve fibers?
High speed of transmission
What is the speed of transmission in unmyelinated nerve fibers?
Low speed of transmission
Where are myelinated nerve fibers located?
Central and peripheral nervous system
Where are unmyelinated nerve fibers located?
In the central and peripheral nervous system in the group C nerve fibers.
What is impulse conduction like in myelinated nerve fibers?
Do not lose the impulse during conduction.
What is impulse conduction like in myelinated nerve fibers?
Can lose the nerve impulse during conduction.
What is the length of myelinated axons?
Long
What is the length of unmyelinated axons?
Short
What is the myelin?
Lipid substance produced by Schwann cells
What are Schwann cells?
Special cells that create myelin in the peripheral nervous system
What are the nodes of Ranvier?
Gaps in myelin sheath with sodium channels
What is saltatory conduction?
When the impulse ‘jumps’ from one node of Ranvier to the next, resulting in rapid conduction.
Do myelinated nerve fibres contain nodes of Ranvier?
Yes
What do neurones coordinate?
Neurones coordinate the activities of sensory receptors and effectors
What is the sheath in a myelinated motor neurone made from?
The sheath is made up of myelin made by specialised Schwaan cells, sheath is made when Schwaan cells wrap themselves around the axon along its length.
What are Schwann cells?
Special cells that create myelin in the peripheral nervous system
What are the nodes of ranvier?
Gaps in myelin sheath with sodium channels
What is saltatory conduction?
When the impulse ‘jumps’ from one node of Ranvier to the next, resulting in rapid conduction.
What is the axon of a myelinated motor neurone insulated by?
A fatty sheath with small uninsulated sections along its length (nodes of ranvier.)
In what 3 ways are motor neurones adapted to their function?
Motor neurones have:
1) A large cell body at one end, that lies within the spinal cord or brain.
2) A nucleus that is always in its cell body.
3) Many highly branched dendrites extending from the cell body, providing a large surface area for the axon terminals of other neurones.
What is the resting potential?
Resting potential is the potential difference across the axon membrane and this keeps the neurone in a state of readiness. The value is -70mV
What is the potential difference caused by?
Potential difference is due to an unequal distribution of charge on either side of a plasma membrane. Fluid on the inside of the axon is negative compared to the outside.
How is a resting potential established?
1) Resting potential is maintained by a sodium potassium pump, involving active transport and the use of ATP.
2) The pump moves 2K+ in and 3Na+ ions out.
3) This movement of ions creates an electrochemical gradient and results in K+ diffusing out and Na+ diffusing in, however because the membrane is more permeable to K+, more are moved out resulting in a negative resting potential of -70mV.
How is the membrane more permable to K+ than Na+?
1) The membrane contains more K+ ion channels than Na+ ion channels.
2) K+ ion channels are almost always open but Na+ channels are closed and open when a high enough voltage is reached.
What is an action potential?
An action potential is when the neurone’s voltage increases beyond a set point from the resting potential and generates a nervous impulse.
What is depolarisation?
Process of sodium influx causing axon activation
What are the 5 stages of the generation of an action potential?
1) Detection of stimulus.
2) Depolarisation.
3) Repolarisation.
4) Hyperpolarisation.
5) Resting State
What happens in depolarisation in the stages leading to the generation of an action potential?
1) The excitation of the neurone cell causes the Na+ channels to open, making it more permeable to Na+ ions.
2)Na+ diffuse into the axon down their electrochemical gradient, making inside the axon less negative (-55mV)
3) When the threshold of -55mV is reached, even more Na+ channels open eventually giving a potential difference of +40mV.
What happens in repolarisation in the stages leading to the generation of an action potential?
1) Sodium channels close and potassium ions open.
2) The potassium ions diffuse out of the neurone down the concentration gradient and eventually the resting potential is restored.
What happens in hyperpolarisation in the stages leading to the generation of an action potential?
The closing of the potassium ion channels is slightly delayed which causes the potential of the neurone to decrease below the resting potential of the neurone to decrease below the resting potential, to around -80mV. This causes the refractory period.
How is the resting state established after the generation of an action potential?
The resting potential is achieved with the help of the sodium potassium pump which returns the potential difference to -70mV.
What is the refractory period?
When the membrane can’t be stimulated because Na+ channels are recovering and can’t be opened.
Why is the refractory period important?
1) Ensures that no action potentials overlap.
2) Ensures that action potentials travel in one direction.
3) it limits the number of impulse transmission.
What is the all-or-nothing principle?
If the depolarisation does not exceed -55mV then an action potential and the impulse are not produced (nothing). Any stimulus that does trigger depolarisation to -55mV will always peak at the same maximum voltage (all).
How does myelination and saltatory conduction affect the speed of conductance?
Schwann cells form the myelin sheath which is a lipid and does not allow charged ions or the impulse to pass through it therefore increasing the speed on conductance. Action potential moves in saltatory conduction which means the action potential travels along the axon faster as an action potential doesn’t need to be generated along the entire length - only at the nodes of Ranvier
How does axon diameter affect the speed of conductance along a motor neurone?
With a wider diameter the speed of conductance increases. A wider diameter means that there is less leakage of ions and therefore action potentials travel faster.
How does temperature affect the speed of conductance along a motor neurone?
A higher temperature increases the speed conductance as the ions diffuse faster and the enzymes involved in respiration work faster therefore there is more ATP for active transport in the Na+ and K+ pump.
What are three characteristics of a myelinated motor neurone?
1) Neurones coordinate the activities of sensory receptors and effectors.
2) The sheath is made of myelin made by specialised Schwaan cells, made when Schwaan cells wrap themselves around the axon along its length.
3) The axon of a myelinated motor neurone is insulated by a fatty sheath with small uninsulated sections along its length (nodes of Ranvier).
