Why does the membrane potential go from -70 mV to less negative values when the
ID: 3478021 • Letter: W
Question
Why does the membrane potential go from -70 mV to less negative values when the Na+ voltage-gated channels open? 14. 15. On what parts of the neuron do we find chemically-gated channels? 16. Match the channel type to its fiunction: A. Nongated channels B. Chemically-gated channels C. Voltage-gated channels are responsible for the generation of the action ii) are responsible for potentials generated at synapses are responsible for the resting membrane potential. potential (nerve impulses)-the outgoing signal from the neuron. I (synaptic potentials). 17. What does it mean to say that cells exhibit selective permeability with respect to ions?Explanation / Answer
14. The membrane potential becomes less negative when the Na+2 voltage-gated channels opens due to the depolarisation which occurs as a result of influx of Na+2 ions into the neuron.
To understand this phenomenon, let’s look at the process of depolarisation. At the initial stage, when there is no stimulus, a neuronal membrane is said to be at resting potential (i.e. it carries some charge, but, not enough to generate an action potential). This resting potential is defined to be -70mV, with K+ ions inside the membrane and Na+2 ions outside of the membrane. At this stage, there is more positive electric charge outside the cell than on the inside; thus, the membrane is polarised. Now, when a stimulus approaches a neuron, the voltage-gated Na+2 channels open to allow influx of Na+2 ions. This leads to increase in positive charge inside the membrane. This increase in positive charge inside of the membrane makes the membrane potential go from -70mV to less negative; a process called depolarisation.
15. The chemical- gated channels on a neuron are responsible for transmission of nerve impulses from one neuron to another across a synaptic cleft. Once a neurotransmitter is released from one neuron, it travels across the synapse and attaches to the receptor present on the dendrite of a receiving neuron (Chemical- gated transmission). Further response of the receiving neuron is based on the signal carried by the neurotransmitter. Thus, the chemical-gated channels exist on dendritic ends and cell body of a neuron.
16. (i) Voltage-gated channels are responsible for the generation of action potential (nerve impulses)- the outgoing signals from neuron.
As detailed in Ans. 14, the voltage-gated Na+2 channels of a neuron open up to allow an influx of Na+2 ions as a response to a stimulus . Now, each neuron needs to depolarise to a certain extent (called the threshold potential) to generate an action potential. Once the threshold potential is achieved, more Na+2 channels open, causing more Na+2 ions to enter the neuron, complete depolarisation of the neuron is achieved and action potential is generated.
(ii) Chemical-gated channels are responsible for potentials generated at synapses (synaptic potential).
At a synapse, the action potential carried from the cell body of a neuron causes depolarisation of axon membrane. The Ca+2 channels on the axon open up to allow entrance of calcium ions. With the influx of calcium ions, there is an efflux of chemical (neurotransmitter) into the synapse which transmits the signal. This chemical traverses across the synapse and attaches to the receptors present on the postsynaptic dendrites. These chemicals are responsible for either excitation or inhibition of the postsynaptic neuron. Thus, the difference in the voltage potential between outside and inside of the receiving (post-synaptic) neuron is modulated by chemical-gated (neurotransmitter receptor) channels.
(iii) Non-gated channels are responsible for resting membrane potential.
A resting membrane potential can be defined as the membrane potential of a neuron when it has not been stimulated. This has been defined as -70mV for any neuron with K+ ions inside the membrane and Na+2 ions outside of the membrane. Now, to maintain the neuron at this potential, a number of channels work conservatively. These channels donot respond to a difference in potential (voltage- gated) or a chemical signal (chemical-gated) and thus, are called non-gated channels. One such non-gated channel is Na/ K pump. This pump actively transports (ie.e expends ATP to carry out the function) 3 Na+2 ions outside the cell and 2 K+ ions inside, maintaining a positive difference across the membrane. Thus, it is responsible for maintaining the resting membrane potential of a neuron to -70mV.
17. The cell membrane is a lipid bilayer with membrane proteins. The membrane controls the movement of molecules (ions and other chemicals) to within and out of cell. This control is achieved by a number of different techniques such as osmosis, passive transport across conc. Gradient. But, the cell membrane can also regulate the movement of molecules (esp. ions) against the concentration/ voltage gradient. This is achieved by means of active transport (i.e. by expenditure of energy, ATP). A good example is use of NA/K pump by the neurons to maintain RMP (resting membrane potential). Thus, a cell exhibits selective permeability allowing ions to move in and out of cells according to their requirement.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.