Ch 11 Check your Understanding

Which subdivision of the PNS is involved in (a) relaying the feeling of a "full stomach" after a meal, (b) contracting the muscles to lift your arm, and (c) increasing your heart rate?

(a) This "full stomach" feeling would be relayed by the sensory (afferent) division of the PNS (via its visceral afferent fibers). (b) The somatic nervous system, which is part of the motor (efferent) division of the PNS, controls movement of skeletal muscle. (c) The autonomic nervous system, which is part of the motor (efferent) division of the PNS, controls the heart rate.

How does a nucleus within the brain differ from a nucleus within a neuron?

A nucleus within the brain is a cluster of neuron cell bodies the nucleus within each neuron is a large organelle that acts as the control center of the cell

ACh excites skeletal muscle and yet it inhibits heart muscle. How can this be?

ACh interacts with more than one specific receptor type, and this explains how it can excite at some synapses and inhibit at others.

Which is bigger, a graded potential or an action potential? Which travels farther? Which initiates the other?

Action potentials are larger than graded potentials and travel farther. Graded potentials generally initiate action potentials.

An action potential does not get smaller as it propagates along an axon. Why not?

An action potential is regenerated anew at each membrane patch.

Which type of neuroglia controls the extracellular fluid environment around neuron cell bodies in the CNS? In the PNS?

Astrocytes control the extracellular environment around neuron cell bodies in the CNS satellite cells perform this function in the PNS

Which structural and functional type of neuron is activated first when you burn your finger? Which type is activated last to move your finger away from the source of heat?

Burning a finger will first activate unipolar (pseudounipolar) neurons that are sensory (afferent) neurons. The impulse to move your finger away from the heat will be carried by multipolar neurons that are motor (efferent) neurons.

Which two types of neuroglia form insulating coverings called myelin sheaths?

CNS: Oligodendrocytes PNS: Schwann cells

Why does a myelinated axon conduct action potentials faster than a nonmyelinated axon?

Conduction of action potentials is faster in myelinated axons because myelin allows the axon membrane between myelin sheath gaps to change its voltage rapidly, and allows current to flow only at the widely spaced gaps.

Why is cyclic AMP called a second messenger?

Cyclic AMP (cAMP) is called a second messenger because it relays the message between the first messenger (the original chemical messenger) outside of the cell and effector molecules that will ultimately bring about the desired response within the cell.

Which ions flow through chemically gated channels to produce IPSPs? EPSPs?

IPSPs result from the flow of either K+ or Cl− through chemically gated channels. EPSPs result from the flow of both Na+ and K+ through chemically gated channels.

If an axon receives two stimuli close together in time, only one AP occurs. Why?

If a second stimulus occurs before the end of the absolute refractory period, no AP can occur because sodium channels are still inactivated.

How is a myelin sheath formed in the CNS, and what is its function?

In the CNS, a myelin sheath is formed by oligodendrocytes that wrap their plasma membranes around the axon. The myelin sheath protects and electrically insulates axons and increases the speed of transmission of nerve impulses.

What is meant by "integration," and does it primarily occur in the CNS or the PNS?

Integration involves processing and interpreting sensory information, and making a decision about motor output. Integration occurs primarily in the CNS.

For which cation are there the largest number of leakage channels in the plasma membrane?

K+

Recall (from Chapter 9) that, at a neuromuscular junction, the AP in the muscle fiber is also triggered by a graded potential. Name that graded potential.

Recall (from Chapter 9) that, at a neuromuscular junction, the AP in the muscle fiber is also triggered by a graded potential. Name that graded potential.

Which types of neural circuits would give a prolonged output after a single input?

Reverberating circuits and parallel after-discharge circuits both result in prolonged output

What is the difference between temporal summation and spatial summation?

Temporal summation is summation in time of graded potentials occurring in quick succession at the postsynaptic membrane. It can result from EPSPs arising from just one synapse. Spatial summation is summation in space—a postsynaptic neuron is stimulated by a large number of terminals at the same time.

For an open channel, what factors determine in which direction ions will move through that channel?

The concentration gradient and the electrical gradient—together called the electrochemical gradient—determine the direction in which ions flow through an open membrane channel.

What pattern of neural processing occurs when we smell freshly baked apple pie and remember Thanksgiving at our grandparents' house, the odor of freshly cooked turkey, sitting by the fire, and other such memories?

The pattern of neural processing is parallel processing

What pattern of neural processing occurs when your finger accidentally touches a hot grill? What is this type of pathway called?

The pattern of neural processing is serial processing. The response is a reflex arc

Your patient, Ms. Young, has failing kidneys that cause an increase in her extracellular fluid K+ concentration. What would this do to the resting membrane potential of her neurons and muscle cells? Explain.

The resting membrane potential depends on both the concentration gradients of K+ and Na+ across the membrane and the permeability of the membrane to K+ and Na+. An increase in the extracellular K+ concentration will decrease the concentration gradient for K+ and this will decrease the resting membrane potential of neurons and muscle cells. In other words, the inside of these cells will become less negative (be depolarized).

What determines the size of a graded potential?

The size of a graded potential is determined by the strength of a stimulus

What structure joins two neurons at an electrical synapse?

gap junctions