Chapter 7 The Nervous System

Which ion contributes most to the resting membrane potential of neurons?

Potassium

A neuron will generate an action potential only when

Threshold is reached

The rapid rising phase of an action potential occurs because

Sodium enters the cell

Repolarization primarily results from:

Potassium efflux

During the absolute refractory period

No stimulus can trigger another action potential

Which statement best describes the relative refractory period?

A stronger stimulus is required

Saltatory conduction occurs in

Myelinated axons

Increasing stimulus strength is often encoded by

Increased firing frequency

Recruitment refers to

Activation of additional neurons

The primary excitatory neurotransmitter in the CNS is

Glutamate

Which neurotransmitter is most responsible for inhibition in the brain?

GABA

Benzodiazepines exert their effects by enhancing

GABA activity

Strychnine toxicity occurs because it blocks receptors for

Glycine

Which neurotransmitters function as natural analgesics?

Endorphins and enkephalins

Endocannabinoids differ from most neurotransmitters because they

Travel from postsynaptic to presynaptic neurons

Nitric oxide is unique because it

Functions as a gaseous neurotransmitter

ATP and adenosine bind to

Purinergic receptors

Which event helps remove the magnesium block from NMDA receptors?

Prior depolarization of the membrane

Conduction without decrement means

Signal amplitude remains constant along the axon

Which statement about myelin is correct?

It allows impulses to jump between nodes of Ranvier

What is the resting membrane potential (RMP) of a neuron?

Approximately −70 mV.

What triggers the generation of an action potential?

Threshold, usually around −55 mV, must be reached.

What occurs during depolarization in an action potential?

Voltage-gated sodium channels open, allowing sodium to enter the cell.

What happens during repolarization?

Potassium channels open, leading to potassium leaving the cell.

Define the absolute refractory period.

A period during which no second action potential can occur because sodium channels are inactivated.

Define the relative refractory period.

A phase where some sodium channels have recovered; a stronger stimulus is needed to trigger another action potential.

How do action potentials conduct in unmyelinated axons?

Continuous conduction occurs, with every adjacent section of the membrane depolarizing.

How do action potentials conduct in myelinated axons?

Saltatory conduction occurs, where impulses jump between nodes of Ranvier.

What is the role of GABA in the CNS?

GABA functions as the major inhibitory neurotransmitter, causing hyperpolarization.

What is the function of Glycine in the CNS?

Glycine primarily inhibits neural activity in the spinal cord.

What are endocannabinoids?

Lipid neurotransmitters that function as retrograde neurotransmitters, modulating neurotransmitter release.

What is the significance of glutamate?

It is the major excitatory neurotransmitter in the CNS, producing depolarization.

How do benzodiazepines affect GABA signaling?

They enhance GABA activity, leading to sedation and reduced anxiety.