Which of the following statements about the structure and organization of peripheral nerves is not correct?

Introduction / Context:
Peripheral nerves are crucial communication cables that connect the central nervous system to the rest of the body. They carry sensory information from receptors to the brain and spinal cord and transmit motor commands from the central nervous system to muscles and glands. Exam questions often test detailed understanding of how nerves are organized structurally and functionally. This question asks you to identify which statement about the organization of peripheral nerves is not correct.

Given Data / Assumptions:

• We are dealing with peripheral nerves, not isolated neurons or central nervous tissue.
• Each option describes some structural or functional feature of nerves.
• One option must be incorrect, while the others accurately describe peripheral nerves.
• Knowledge of nerve connective tissue layers and types of fibres is assumed.

Concept / Approach:
Each peripheral nerve contains many axons running together, often both sensory and motor, along with blood vessels and connective tissue. The axons are grouped into bundles called fascicles. Around individual axons with their myelin is endoneurium, around each fascicle is perineurium, and the whole nerve is wrapped in epineurium. Nerves can be classified as sensory, motor, or mixed, but in humans most major peripheral nerves are mixed, containing both sensory and motor fibres. Therefore, any statement claiming that a nerve cannot contain both sensory and motor axons is incorrect.

Step-by-Step Solution:
Step 1: Evaluate option A: Axons make up the majority of the tissue mass in a nerve. This is essentially correct, because the core of a nerve consists of many axons plus their myelin and support tissue. Step 2: Evaluate option C: Nerves are covered by an outer sheath called the epineurium. This is correct; the epineurium is the tough outer connective tissue layer surrounding the entire nerve. Step 3: Evaluate option D: Nerves consist of parallel bundles of myelinated and nonmyelinated axons. This is also correct; both types of axons can be present, arranged in bundles. Step 4: Evaluate option E: A typical peripheral nerve contains many axons bundled together into fascicles. This is correct and matches standard histology descriptions. Step 5: Evaluate option B: Nerves are collections of axons of either sensory or motor neurons but not both. This is incorrect, because most peripheral nerves are mixed nerves, containing both sensory and motor fibres in the same nerve trunk. Step 6: Conclude that option B is the not correct statement concerning peripheral nerves.

Verification / Alternative check:
Histology and anatomy texts classify nerves as sensory, motor, or mixed. Major nerves such as the sciatic nerve, median nerve, and facial nerve are described as mixed, carrying both afferent (sensory) and efferent (motor) fibres. Textbook diagrams of peripheral nerve cross sections clearly show fascicles surrounded by perineurium and the entire nerve wrapped in epineurium, confirming that options A, C, D, and E match real anatomy. This leaves B as the only incorrect statement.

Why Other Options Are Wrong:
Option A: Correctly notes that the bulk of a peripheral nerve is formed by numerous axons plus their coverings, which justifies it as a true statement, not the incorrect one. Option C: Correctly identifies the epineurium as the outer connective tissue sheath surrounding the nerve, so it is accurate. Option D: Correctly states that nerves contain both myelinated and nonmyelinated axons running in parallel bundles, matching histological findings. Option E: Correctly describes how axons are grouped into fascicles within a nerve, making this a true statement as well.

Common Pitfalls:
Students often confuse individual neurons, which may be sensory or motor, with nerves, which are large bundles of many axons. This leads to the mistaken belief that a nerve must be purely sensory or purely motor. Another pitfall is ignoring that mixed nerves are the rule, not the exception, in most of the body. Remember that anatomical classification distinguishes between neuron type and the composition of an entire peripheral nerve trunk.

Final Answer:
The incorrect statement concerning nerves is: Nerves are collections of axons of either sensory or motor neurons but not both.