The Nervous System: Neurons and Synapses

A 10-card study set covering the structure of the nervous system, resting membrane potentials, action potentials, axonal conduction, and synaptic transmission.

How is the Peripheral Nervous System (PNS) structurally divided in terms of nerve pairs?

The PNS consists of $12$ pairs of cranial nerves and $31$ pairs of spinal nerves.

What are groups of neuron cell bodies called in the Central Nervous System (CNS) versus the Peripheral Nervous System (PNS)?

In the CNS, groups of cell bodies are called nuclei; in the PNS, they are called ganglia.

What is the functional difference between dendrites and axons in a neuron?

Dendrites receive information and convey it to the cell body, whereas axons conduct impulses away from the cell body.

How are depolarization and hyperpolarization defined in terms of membrane potential?

Depolarization occurs when the membrane potential becomes more positive, while hyperpolarization occurs when the membrane potential becomes more negative than the resting membrane potential (RMP).

What ionic mechanism drives the rapid depolarization phase of an action potential from $-70\,\text{mV}$ to $+30\,\text{mV}$?

At threshold, voltage-gated $\text{Na}^+$ channels open and $\text{Na}^+$ is driven inward by its electrochemical gradient via a positive feedback loop.

How does the nervous system code for increased stimulus intensity?

Increased stimulus intensity causes a higher frequency of action potentials to be fired, while the size (amplitude) of the action potentials remains constant.

What causes the absolute refractory period compared to the relative refractory period?

The absolute refractory period is due to inactivated voltage-gated $\text{Na}^+$ channels, whereas the relative refractory period is due to continued outward diffusion of $\text{K}^+$ through open voltage-gated $\text{K}^+$ channels.

Why does saltatory conduction occur in myelinated axons?

Myelin prevents ions from flowing across the membrane and stops current leaks, causing the action potentials to skip from one Node of Ranvier to the next.

What are the diameter, conduction velocity, and primary function of the fastest mammalian nerve fibers listed in Table 7.4?

They have a diameter of $12\text{--}22\,\mu\text{m}$, a conduction velocity of $70\text{--}120\,\text{m/sec}$, and serve sensory function for muscle position.

What role does acetylcholinesterase (AChE) play at a synapse, and what drug is noted to block acetylcholine (ACh) action at the neuromuscular junction?

AChE is located in the synaptic cleft and inactivates ACh to terminate its action; curare blocks ACh action at the neuromuscular junction.