Neuroscience Classification of Axons

Questions and Answers

What are the three major groups of axons?

A fibers (correct)

B fibers (correct)

C fibers (correct)

D fibers

What are the classifications of nerve fibers based on?

amount of myelination, diameter, propagation speeds

What are the four characteristics of A fibers?

largest diameter, myelinated, have a brief absolute refractory period, conduct nerve impulses at speeds of 12 to 130 m/sec

What are some examples of A fibers?

sensory neuron axons for touch, pressure, position of joints, and some thermal and pain sensations; motor neuron axons to skeletal muscles Signup and view all the answers

What are the four characteristics of B fibers?

diameters of 2-3 mm, myelinated, longer absolute refractory period than A fibers, exhibit saltatory conduction at speeds up to 15 m/sec Signup and view all the answers

What do B fibers do?

conduct sensory nerve impulses from the viscera to the brain and spinal cord Signup and view all the answers

What do B fibers constitute?

all axons of the autonomic motor neurons that extend from the brain and spinal cord to autonomic ganglia Signup and view all the answers

What are the four characteristics of C fibers?

smallest diameter, unmyelinated, longest absolute refractory period, propagate nerve impulses from 0.5 to 2 m/sec Signup and view all the answers

What do the unmyelinated axons of C fibers do?

conduct some sensory impulses for pain, touch, pressure, heat, and cold from the skin; and pain impulses from the viscera Signup and view all the answers

What are some examples of C fibers?

autonomic motor fibers that extend from autonomic ganglia to stimulate the heart, smooth muscle, and glands Signup and view all the answers

What are some examples of motor functions of B and C fibers?

constricting and dilating pupils, increasing and decreasing heart rate, and contracting and relaxing the urinary bladder Signup and view all the answers

Study Notes

Classification of Axons

Three major groups of axons: A fibers, B fibers, C fibers.

Classification Criteria

Axons are classified based on myelination amount, diameter, and propagation speeds.

Characteristics of A Fibers

Largest diameter among nerve fibers.
Myelinated, allowing for faster impulse conduction.
Brief absolute refractory period enhances rapid signal transmission.
Conduct nerve impulses at speeds ranging from 12 to 130 m/sec.

Examples of A Fibers

Sensory neurons for touch, pressure, joint position, and some thermal/pain sensations.
Motor neurons transmitting impulses to skeletal muscles.

Characteristics of B Fibers

Medium diameter around 2-3 mm.
Myelinated, but with a longer absolute refractory period compared to A fibers.
Exhibit saltatory conduction, enabling speeds up to 15 m/sec.

Functions of B Fibers

Conduct sensory nerve impulses from visceral organs to the brain and spinal cord.

Role of B Fibers in the Autonomic Nervous System

Make up axons of autonomic motor neurons connecting the brain and spinal cord to autonomic ganglia.

Characteristics of C Fibers

Smallest diameter among the three fiber types.
Unmyelinated, resulting in slower impulse conduction.
Longest absolute refractory period, slowing down nerve response.
Propagate impulses at speeds between 0.5 to 2 m/sec.

Functions of C Fiber Axons

Conduct sensory impulses for pain, touch, pressure, heat, and cold from the skin, as well as visceral pain signals.

Examples of C Fibers

Autonomic motor fibers extending from autonomic ganglia, stimulating the heart, smooth muscle, and glands.

Motor Functions of B and C Fibers

Regulate pupil constriction and dilation, heart rate changes, and urinary bladder contraction and relaxation.

Description

This quiz explores the classification of axons, focusing on A, B, and C fibers. Learn about their characteristics, functions, and propagation speeds. Test your knowledge on how these fibers contribute to sensory and motor functions in the nervous system.