BIOB32H3 Lecture Notes - Lecture 3: Axon Hillock, Myelin, Extracellular Fluid

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5 Nov 2017

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The action potential (1: changes in membrane potential, properties of na and k channels, graded potentials: what they are, what they do, and how they do it (k and na channels, the action potential. Nerve and muscle cells are excitable cells: opening and closing of voltage-gated ion channels causes changes in membrane permeability, allows ions to move between the ic and ec compartments. Leads to changes in excitability of the cell. Change of ion movement =change in excitability in cell. In excitable cells vm changes in response to voltage: membrane potential difference = vm in relation to 0, towards 0 = depolarisation (less negative, more negative than rmp = hyperpolarisation, towards rmp when depolarised = repolarisation. So you have lear(cid:374)ed that 2 fa(cid:272)tors i(cid:374)flue(cid:374)(cid:272)e a (cid:272)ell"s (cid:373)e(cid:373)(cid:271)ra(cid:374)e pote(cid:374)tial (1) conc gradeints of different ions across the membrane; (2) permeability of the membrane to ions. If the (cid:272)ell"s per(cid:373)ea(cid:271)litiy to a(cid:374) io(cid:374) (cid:272)ha(cid:374)ges, the (cid:272)ell"s (cid:373)e(cid:373)(cid:271)ra(cid:374)e pote(cid:374)tial (cid:272)ha(cid:374)ges.

Related Questions

Why do ion channels not function like open pores?

What is membrane potential?

How do K⁺ leak channels work? Why is the membrane potential of a resting cell negative?

What is patch clamp recording? What is one of the major insights gained from patch clamp reporting experiments?

Compare and contrast the three types of gated ion channels.

Be familiar with the different parts of a neuron.

During an action potential, what happens to the membrane potential, voltage-gated Na⁺ channels, Na⁺ ions, voltage gated K⁺ channels, K⁺ ions, and Na⁺-K⁺ ion pumps?

When an action potential reaches a synapse, what happens to the Ca²⁺ channels, Ca²⁺ ions, neurotransmitters, transmitter-gated ion channels, and the post synaptic neuron?

What effect do excitatory or inhibitory neurotransmitters have on postsynaptic cells?

What is an example of a mechanically gated ion channel?

This is the peak depolarization in an action potential. At this point in an action potential two events start to happen.

1. Na+ channels begin to inactivate, which is equivalent to closing.

2. A majority of the K+ channels are beginning to open.

Determine what happens to the membrane potential when voltage-gated K+ channels are open simultaneously with voltage-gated Na+ channels (and the leak K+ channels which are still open). Increase the membrane permeability to K+ by increasing it to 115.

i. What happens to the membrane potential Em? __________________________

j. Why does the membrane potential change in this direction? __________________________ Now inactivate the voltage-gated Na+ channels by reducing the membrane permeability for Na+ back to 1. k. What is the new membrane potential? _____________

l. Is the new membrane potential less negative or more negative than the resting membrane potential listed in line âbâ of this section? _____________

m. Why? (hint: what 2 types of K+ channels are open now?) n. Under the current ionic concentrations given, what is the most negative value that the membrane potential could reach? _____________ (Increase the permeability of the membrane to K+ to confirm your answer.)

o. What equilibrium potential has the same value? _____________

p. At this point in the action potential, when the membrane potential is more negative than the resting potential, the membrane potential is said to be hyperpolarized. What happens to voltage-gated K+ channels (membrane permeability to K+) to bring the membrane potential back to its resting potential near -70mV?_____________

When the membrane potential became more negative than the Threshold potential, the inactivated voltage-gated Na+ channels became reactivated. After the voltage-gated K+ channels closed to enable the membrane potential to return to resting membrane potential they became ready to open again. Both channels are ready to open again in order to fire another action potentia

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1. The plasma membrane of rod and cone cells are

a) At resting potential in the dark and deploarized in thelight

b) At resting pootential in the dark and hyperpolarized in thelight

c) Depolarized in the dark and hyperpolarized in the light

d) Hyperpolarized in the dark and at resting potential in thelight

e) Hyperpolarized in the dark and depolarized in the light

2. The equilibrium potential of K+ ions in nerve cells is about-90mV. The membrane potential of a typical nerve cells at rist is-70mV. Therfore

a) Increasing the permeability of a resting neuronal membrane toK+ ions will increase the membrane potential (that is, make it morenegative, inside with respcect to outside)

b) In nerve cells at rest, there is a net diffusion of K+ ionsout of the cell

c) Increasing the membrane potential of a nerve cell would slowthe diffusion of K+ ions out of it.

d) K+ is not the only ion that is permeable at rest

e) All of the above

3. Which of the following is responsible for the replarizingphase of the action potential?

a) Voltage-gated Na+ channels are opened.

b) The Na+-K+ pump restores the ions to theri original restingstate.

c) The permeability to Na+ increases greatly.

d) ATPase destroys the energy supply that was maintaining theaction potential at its peak.

e) The permeability to K+ increases greatly while that to Na+decreases

4. The Relative refractory period of an axonm conincides withthe period of

a) Activation and inactivatioin of voltage-gated Na+channels

b) Increased Na+ flux into the cell

c) Increased K+ flux into the cell

d) Increased K+ flux out of the cell

e) Increased Na+ flux out of the cell

5. The plasma membranes of rod and cone cells are

a) At resting potential in the dark and epolarized in thelight

b) At resting potential in the dark and hyperpolarized in thelight

c) Depolarized in the dark and hyperoplarized in the light

d) Hyperpolarized in the dark and tat resing potential in thelight

e) Hyperpolarized in the dark and depolarized in the light

BIOB32H3 Lecture Notes - Lecture 3: Axon Hillock, Myelin, Extracellular Fluid

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