Exercise 6 Flashcards
2.What is meant by the term resting potential?
The resting potential is the difference in charges on either side of the plasma membrane of the cell due to the unequal distribution of ions. At rest, or when the axon is not conducting an impulse, the inside of the membrane is negative and the outside of the membrane is positively charged.
What are ions? What two ions are involved in neural transmission, and where are they found when the neuron is at rest?
Ions are charged atoms. Atoms that have lost an electron are positively charged and atoms that have gained an electron are negatively charged. The two ions involved in neural transmission are sodium ions (Na+) and potassium ions (K+). At rest, potassium ions are found within the cell and sodium ions are found outside the cell.
What is the cause of the unequal distribution of these ions? Which ion is the membrane more permeable to?
The cause of the unequal distribution of these ions is due to the action of the sodium-potassium pump. Because of this pump there is a greater concentration of sodium ions outside the membrane and a greater concentration of potassium ions on the inside of the membrane. The membrane is also more permeable to potassium ions than to sodium ions so there are more positive ions outside the membrane than inside. The net result is that the inside of the membrane is negative compared to the outside. This difference in charge is referred to as polarity.
Define the term action potential.
Action potential is defined as the nerve impulse. It is an electrochemical change that takes place across the membrane of the axon or we can say a change in polarity across the axomembrane.
What are the two types of gated channel proteins that the action potential depends on?
The two types of gated channel proteins are referred to as the sodium gate which allows sodium to flow through the membrane, and the potassium gate which allows potassium to flow through the membrane.
Which gated channel opens first, and briefly describe what happens?
The sodium gate opens first allowing sodium ions to flow into the axon. This movement of sodium ions causes a change in charge and now the inside of the cell is positive. This change in charge is referred to as depolarization.
What is the second gated channel to open, and briefly describe what happens?
The potassium gate opens next allowing potassium to flow to the outside of the axon. This movement changes the charge back to negative inside the axon and this is referred to as repolarization.
Describe how the impulse travels along the axon and explain why it travels in only one direction.
The neural impulse travels along the axon in a domino effect, depolarization and repolarization triggering the same effect at the next point along the axon. There is a short period of time called the refractory period, when the sodium gate from the previous point on the axon is unable to open and that ensures the impulse moves in only one direction and does not travel backwards along the axon.
What is the significance of myelin in terms of the speed of transmission of the impulse along the axon?
In a myelinated axon the gated ion channels are only found at the nodes of Ranvier. Because of this design feature, the impulse travels much faster as the gates function only at these points. The action potential is described as jumping from node to node
What is an axon terminal? What is a synapse? What is the synaptic cleft?
The axon terminal is a small swelling found at the end of the axon. It contains vesicles that produce chemicals called neurotransmitters.
The synapse is the region of close proximity or junction of the membrane of the first neuron, the membrane of the next neuron and the gap in-between.
The synaptic cleft is the small gap between these two membranes.
How is the nerve impulse transmitted from one neuron to another? What is the name given to molecules that help with the transmission of the impulse across the synapse?
An impulse travels from one neuron to another by crossing the synapse. Molecules called neurotransmitters help with the transmission of the electrochemical impulse across the synaptic cleft.
Name two well known neurotransmitters. Where are neurotransmitters produced? How and why are they destroyed? What effects do they have on nerve transmission?
The two most common neurotransmitters are acetylcholine and norepinephrine. Neurotransmitters are produced in the axon terminals and after diffusing from one neuron to the next they are destroyed by enzymes released by the post-synaptic membrane of the next neuron. Neuro-transmitters can help by either enhancing or inhibiting nerve transmissions.
Define nerve impulse.
A nerve impulse consists of an electrochemical change that occurs across the membrane of the neuron. It is the body’s way of transferring information from the internal or external environment to the CNS and back to the muscle or gland that will respond accordingly.
