Exercise Physiology Chp 11 Part 2; Membrane, Graded and Action Potentials

On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?

The inside surface of the plasma membrane accumulates more negative charge because of the presence of Na+ and K+ gradients and the selective permeability of the membrane to Na+ and K+.

When one or more presynaptic neurons fire in rapid order it produces a much greater depolarization of the postsynaptic membrane than would result from a single EPSP; this event is called

temporal summation

Immediately after an action potential has peaked, which cellular gates open?

potassium

Which of the following will occur when an excitatory postsynaptic potential (EPSP) is being generated on the dendritic membrane?

A single type of channel will open, permitting simultaneous flow of sodium and potassium.

Multiple sclerosis (MS) is a disease in which the myelin sheaths are destroyed. What process does this interfere with, and what would be the consequence?

Demyelination interferes with saltatory conduction, which would result in a slowing down of nerve impulse propagation.

Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?

Leak channels for Na+ and K+ are ubiquitous, and they allow for the diffusion of these ions across plasma membranes.

What prevents the Na+ and K+ gradients from dissipating?

Na+-K+ ATPase

In multiple sclerosis, the cells that are the target of an autoimmune attack are the _________.

Oligodendrocytes; are a type of neuralgia cell that function to form the myelin sheath around the axons of neurons within the central nervous system.

The __________ is due to the difference in K+ and Na+ concentrations on either side of the plasma membrane, and the difference in permeability of the membrane to these ions.

Resting Membrane Potential At rest, the cell membrane is about 25 times more permeable to potassium than to sodium, and so more potassium ions diffuse out of the neuron down their concentration gradient than sodium ions diffuse into the neuron down theirs. The consequence is a cell membrane that has more positive charges (ions) along its external surface and relatively more negative charges along its internal surface. This separation of charges, or membrane voltage, is called the resting membrane potential.

What major ion currents occur at the point along the action potential phase labeled D?

The hyperpolarization phase (D) is characterized by the diffusion of K+ down its electrochemical gradient out of the axon. During this phase, voltage-gated Na+ channels are closed until another threshold event occurs.

The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors.

The presence of concentration gradients and leak channels

Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference?

The resting membrane potential is the baseline potential that can be recorded across the plasma membrane of an excitable cell prior to excitation.

The plasma membrane is much more permeable to K+ than to Na+. Why?

There are many more K+ leak channels than Na+ leak channels in the plasma membrane.

Which of the following is not true of graded potentials?

They increase in amplitude as they move away from the stimulus point.

Which ion channel opens in response to a change in membrane potential and participates in the generation and conduction of action potentials?

Voltage-Gated Channel

Which of the following membrane regions would have significant numbers of voltage-gated Na+ and K+ ion channels?

Voltage-gated Na+ and K+ channels allow for the triggering of an action potential at the axon hillock (C) and its propagation down the axon (D). Receptive regions of neurons are areas characterized by the presence of chemically gated ion channels and other neurotransmitter-binding receptors.

At which point of the illustrated action potential are the most gated Na+ channels open?

Voltage-gated Na+ channels open when the membrane potential reaches threshold and soon close when temporarily inactivated during the repolarization phase (C).

What type of stimulus is required for an action potential to be generated?

a threshold level depolarization; The axolemma must be depolarized to threshold in order to generate an action potential.

What is the role of acetylcholinesterase?

destroy ACh a brief period after its release by the axon endings

Which membrane potential occurs because of the influx of Na+ through chemically gated channels in the receptive region of a neuron?

excitatory postsynaptic potential; An excitatory postsynaptic potential, a type of graded potential, occurs because of the influx of Na+ through chemically gated channels in the receptive region, or postsynaptic membrane, of a neuron. Graded potentials are generated by chemically gated channels, whereas action potentials are produced by voltage-gated channels.

An inhibitory postsynaptic potential (IPSP) is associated with ________.

hyperpolarization