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Ch. 13 The Peripheral Nervous System and Reflex Activity
Marieb - Human Anatomy & Physiology 11th Edition
Marieb, Hoehn11th EditionHuman Anatomy & PhysiologyISBN: 9780136874034Not the one you use?Change textbook
All textbooksMarieb, Hoehn 11th EditionCh. 13 The Peripheral Nervous System and Reflex ActivityProblem 12
Chapter 13, Problem 12

(a) Define plexus.
(b) Indicate the ventral rami of origin of the four major nerve plexuses.

Verified step by step guidance
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(a) Begin by defining the term 'plexus' in the context of anatomy: A plexus is a network of intersecting nerves or vessels in the body, specifically referring to a complex branching and interconnecting of ventral rami of spinal nerves that serve a particular region.
(b) Identify the four major nerve plexuses in the human body: cervical, brachial, lumbar, and sacral plexuses.
For each plexus, specify the ventral rami of spinal nerves that contribute to its formation:
1. Cervical plexus: formed by the ventral rami of spinal nerves C1 through C4.
2. Brachial plexus: formed by the ventral rami of spinal nerves C5 through T1; 3. Lumbar plexus: formed by the ventral rami of spinal nerves L1 through L4; 4. Sacral plexus: formed by the ventral rami of spinal nerves L4 through S4.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Plexus

A plexus is a network of intersecting nerves or vessels in the body. In the nervous system, it refers to a complex branching of ventral rami of spinal nerves that combine and redistribute fibers to form peripheral nerves. Plexuses allow for the mixing of nerve fibers, providing multiple pathways for nerve signals.

Ventral Rami of Spinal Nerves

The ventral rami are the anterior branches of spinal nerves that carry motor, sensory, and autonomic fibers. They contribute to the formation of nerve plexuses by merging and redistributing fibers to innervate limbs and anterior body regions. Understanding their origin is key to identifying plexus formation.
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Four Major Nerve Plexuses

The four major nerve plexuses are the cervical, brachial, lumbar, and sacral plexuses. Each arises from specific ventral rami: cervical (C1-C4), brachial (C5-T1), lumbar (L1-L4), and sacral (L4-S4). These plexuses supply motor and sensory innervation to the neck, upper limbs, lower limbs, and pelvic region.
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Related Practice
Textbook Question

Characterize each receptor activity described below by choosing the appropriate letter and number(s) from keys A and B. 

_____    , _____  (1) You are enjoying an ice cream cone. 

_____    , _____  (2) You have just scalded yourself with hot coffee. 

_____    , _____  (3) The retinas of your eyes are stimulated. 

_____    , _____  (4) You bump (lightly) into someone. 

_____    , _____  (5) You are in a completely dark room and reaching toward the light switch. 

_____    , _____  (6) You feel uncomfortable after a large meal.

Key A:

a. Exteroceptor

b. Interoceptor

c. Proprioceptor

Key B:

(1) Chemoreceptor

(2) Mechanoreceptor

(3) Nociceptor

(4) Photoreceptor

(5) Thermoreceptor

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Textbook Question

The connective tissue sheath that surrounds a fascicle of nerve fibers is the

a. Epineurium

b. Endoneurium

c. Perineurium

d. Epimysium

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Textbook Question

Briefly describe the three stages of neuron development.

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