Book cover for Fundamentals of Anatomy & Physiology

Fundamentals of Anatomy & Physiology

Frederic H. Martini, Judi L. Nath, Edwin F. Bartholomew

ISBN #9780321928610

10th Edition

867 Questions

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Homework Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

This chapter provides a comprehensive overview of neural tissue by explaining the structural and functional divisions of the nervous system, including the roles of neurons and neuroglia. Key electrophysiological processes, such as the resting membrane potential, graded potentials, and action potentials, are examined alongside factors affecting neural signal propagation like myelination and axon diameter. The chapter highlights the fundamental aspects of synaptic communication, emphasizing the importance of neurotransmitters and neuromodulators in neuronal integration and the all-or-none nature of action potentials.

Learning Objectives

1

Explain the structure and function of neural tissue, including the roles of neurons and neuroglia in intercellular communication.

2

Differentiate between the anatomical divisions (CNS and PNS) and functional subdivisions (afferent vs. efferent systems) of the nervous system.

3

Describe key electrophysiological processes such as resting membrane potential, graded potentials, and the all-or-none action potential mechanism.

4

Understand factors influencing neural signal transmission, including myelination and axon diameter.

5

Identify the functions of synapses and the roles of neurotransmitters and neuromodulators in neural communication.

Key Concepts

CONCEPT

DEFINITION

Neuron

A nerve cell specialized for receiving, processing, and transmitting information through electrical and chemical signals.

Neuroglia

Support cells in the nervous system that protect, nourish, and support neurons.

Central Nervous System (CNS)

The brain and spinal cord, responsible for integrating and processing sensory data and coordinating function.

Peripheral Nervous System (PNS)

All neural structures outside the CNS, responsible for carrying sensory and motor information to and from the CNS.

Afferent System

The component of the nervous system that carries sensory signals toward the CNS.

Efferent System

The component that transmits motor commands from the CNS to peripheral effectors (muscles and glands).

Resting Membrane Potential

The baseline electrical charge difference across a neuron's membrane, maintained mostly by ion gradients and selective permeability.

Graded Potentials

Local, varying changes in membrane potential that are scaled in magnitude and can summate to trigger an action potential.

Action Potential

A rapid, all-or-none electrical impulse generated when a neuron’s membrane potential reaches a threshold, propagating along the axon.

Synapse

A junction between neurons or between a neuron and another cell where communication occurs via chemical or electrical signals.

Myelination

The insulation of axons by myelin sheaths which increases the speed and efficiency of electrical signal transmission.

Axon Diameter

The thickness of the axon, which, along with myelination, affects the speed of electrical signal propagation.

Neurotransmitters

Chemical messengers released at synapses that influence the activity of receiving neurons.

Neuromodulators

Substances that modify the efficacy or strength of synaptic transmission by interacting with multiple neurons over extended areas.

Example Problems

Example 1

Label the structures in the following diagram of a neuron. (a) ___________ (b) ___________ (c) ___________ (d) ___________ (e) ___________ (f) ___________ (g) ___________ (h) ___________ (i) ___________

Example 2

Regulation by the nervous system provides (a) relatively slow, but long-lasting, responses to stimuli, (b) swift, long-lasting responses to stimuli, (c) swift, but brief, responses to stimuli, (d) relatively slow, short-lived responses to stimuli.

Example 3

In the CNS, a neuron typically receives information from other neurons at its (a) axon, (b) Nissl bodies, (c) dendrites, (d) nucleus.

Example 4

Phagocytic cells in neural tissue of the CNS are (a) astrocytes, (b) ependymal cells, (c) oligodendrocytes, (d) microglia.

Example 5

The neural cells responsible for the analysis of sensory inputs and coordination of motor outputs are (a) neuroglia, (b) interneurons, (c) sensory neurons, (d) motor neurons.
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Step-by-Step Explanations

QUESTION

How does an action potential propagate along a neuron's axon?

STEP-BY-STEP ANSWER:

Step 1: The neuron receives a stimulus that causes depolarization, reaching the threshold level.
Step 2: Voltage-gated Na+ channels open, allowing sodium ions to enter the cell, further depolarizing the membrane.
Step 3: The depolarization initiates a chain reaction along the axon as adjacent voltage-gated channels open.
Step 4: Repolarization follows as voltage-gated K+ channels open, letting potassium ions exit the neuron.
Step 5: The action potential completes its cycle and returns to the resting membrane potential.
Final Answer: The action potential is a self-propagating electrical impulse that travels along the axon through a sequence of depolarization and repolarization events, following the all-or-none principle.

Action Potential

QUESTION

What mechanisms establish the resting membrane potential in a neuron?

STEP-BY-STEP ANSWER:

Step 1: Ion concentration gradients are maintained by the sodium-potassium pump, which actively transports Na+ out and K+ into the cell.
Step 2: The cell membrane is selectively permeable, allowing more K+ to leak out than Na+ to enter.
Step 3: The differential distribution of ions creates a voltage difference between the inside and outside of the cell.
Final Answer: The resting membrane potential is established by ion pumps that maintain gradients and the membrane’s selective permeability, leading to a stable, negative internal environment relative to the outside.

Resting Membrane Potential

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Common Mistakes

  • Confusing graded potentials with action potentials; graded potentials vary in magnitude, while action potentials follow an all-or-none response.
  • Misunderstanding the effect of myelination; it increases signal speed rather than the strength of the action potential.
  • Overlooking the role of neuroglia, assuming that neurons operate independently without support.
  • Failing to distinguish between the anatomical (CNS vs. PNS) and functional (afferent vs. efferent) subdivisions of the nervous system.
  • Assuming that synaptic transmission is purely electrical, ignoring the significant role of chemical neurotransmitters and neuromodulators.