Chapter 12 HW

Select all that are true regarding the resting membrane potential.

- It has a negative value. - It is measured in millivolts. - It can range from −40 to −90 millivolts.

Place the following labels in the proper position to designate the appropriate glial cells.

- Oligodendrocytes: Form the myelin sheath in the CNS - Ependymal Cells: Function in the production and circulation of cerebrospinal fluid. - Microglia: Cells of the lymphatic system. Macrophages of the CNS. - Astrocytes: Most abundant CNS glial cell. Involved with neurogenesis, scar formation, and blood-brain barrier maintenance. - Neurolemmocytes: Form the myelin sheath in the PNS - Satellite Cells: PNS cells that surround and insulate the somas.

Select all that are true of glial cells.

- They are smaller than neurons. - They may protect neurons. - They can undergo mitosis

Place the following labels in the proper position to designate action potential or local potential.

Action Potentials: - Require threshold - Important for transmissions over long distances Local potentials: - Decremental - Cause summation - Reversible - EPSPs - IPSPs

When threshold is reached, depolarization occurs with the same amplitude of potential change. This is known as

All-or-None principle

At resting membrane potential, voltage-gated potassium ion channels are open.

False

Place these neurons into the proper classification group.

Structural Classification: - Multipolar neuron - Bipolar neuron - Unipolar neuron Functional Classification: - Sensory neuron - Motor neuron - Afferent neuron - Efferent neuron - Association neuron - Interneuron neuron

Most researchers believe MS results from a combination of genetic and environmental factors. One peculiar observation regarding environment is the fact that the incidence increases as one gets further from the equator.

True

Pumps move substances ___ a concentration gradient, a process that requires energy.

against

Select all that are common features of most neurons.

axon, dendrite, soma

Acetylcholinesterase

catalyzes hydrolysis of ACh to remove it from the synaptic cleft.

The voltage-gated Na⁺ channels ___ when the cell reaches +30 mV.

close

Channels that are normally closed, but open in response to changes in ___ across the plasma membrane are voltage-gated channels. When open, they allow a specific ion to diffuse across the membrane.

electrical charge

On a graph of an action potential, the small depolarizations that lead to threshold are from

excitatory postsynaptic potentials (EPSPs).

Activation gates in the cell membrane for voltage-gated sodium ion channels open into the

extracellular fluid

An axon with a large diameter transmits an impulse ____ than an axon with a smaller diameter.

faster

Channels that are always open, allowing continuous diffusion of a specific ion from a region of ___ concentration to a region of ___ concentration are leak channels.

high; low

Myelin is critical to nervous system function since it provides insulation for the neuronal axons and facilitates rapid propagation of neural impulses.

it provides insulation for the neuronal axons and facilitates rapid propagation of neural impulses.

When K⁺ diffuses out of the cell, the cell becomes ___ depolarized.

less

When Na⁺ diffuses into the cell, the cell becomes ___ depolarized.

more

Depolarization is initiated by a stimulus that makes the membrane potential

more positive

Depolarization of a cell membrane occurs because

more sodium ions diffuse into the cell than potassium ions diffuse out of it.

K⁺ diffusing out of the cell has a ___ feedback effect on the initial polarization.

negative

• Channels that are normally closed that open in response to the binding of a ___ are chemically gated channels. When open, they allow a specific ion to ___ across the plasma membrane.

neurotransmitter; diffuse

The cells of the nervous system that produce myelin are the

oligodendrocytes

The voltage-gated Na⁺ channels ___ when the cell membrane reaches threshold level as a result of a stimulus.

open

Na+ diffusing into the cell causes more Na+ gates to open, which is a ___ feedback loop.

positive

When sodium enters the neuron via chemically gated sodium channels, the membrane will depolarize. Therefore, the membrane potential will become more

positive

Triggers of acute episodes of MS include

pregnancy, infections, stress

The symptoms of MS can come and go. This is because

the oligodendrocytes are constantly renewing the myelin sheathes, so they are able to temporarily repair some of the damage.

The negative value of the resting membrane potential means that

there are more negatively charged particles on the inside of the membrane than on the outside.

Channels instead provide the means to move a substance ___ a concentration gradient.

with