To label: The structures given in Fig 18.1
Concept introduction: Neurons are the fundamental functioning units of the nervous system. Neurons share many similar features with other body cells; only one different feature is that they can conduct signals throughout the body.
Answer to Problem 1.1BGL
Pictorial representation:
Fig 1: Transverse section displaying the coverings of a spinal nerve
Explanation of Solution
The spinal nerves function like “telephone lines” and bring back and forth messages between the body and the spinal cord to regulate motions as well as sensations. There are two roots in each spinal nerve; they are the ventral root and the dorsal root. An axon is a lengthy, slender projection that emerges from a nerve cell. The myelin sheath is formed of a fatty material that surrounds the nerve cells.
The dense and uneven connective tissue that surrounds the peripheral nerves is termed as the epineurium. This tissue envelops several blood vessels that supply blood to the nerves and nerve fascicles. The epineurium is abundantly seen in the regions of joints. Hence, they protect the nerves from injury as well as stretching.
A nerve fascicle is otherwise known as fasciculus. This structure is formed of a bundle of axons. These fascicles are present in the peripheral nervous system. They are bundled together with the blood vessels and fatty tissues.
Nerve fascicles are enveloped by a kind of connective tissue that is termed as the perineurium. The perineurium is formed of perineurial cells, and they are also referred to as myoepithelioid in some cases. The perineurium membrane is a smooth, tube-like transparent structure that could be easily detached from the fibers which it surrounds.
The connective tissue that surrounds the unmyelinated and myelinated axons is called the endoneurium. The endoneurium is otherwise known as the endoneurial channel or Henle’s sheath. It is delicate and surrounds the myelin sheath of every myelinated nerve fiber. The endoneurium is made up of endoneurial cells.
To label: The structures given in Fig 18.2
Answer to Problem 1.1BGL
Pictorial representation:
Fig 2: A transverse section photomicrograph through a spinal nerve fascicle
Explanation of Solution
An axon is a long, slim projection that emerges from a neuron. The myelin sac consists of a fat material that surrounds the cells of the nerves. The endoneurium is also known as the Henle’s sheath or endoneurial channel. It is fragile and surrounds every myelinated nerve fiber’s sheath. The endoneurium consists of endoneurial cells.
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Chapter 18 Solutions
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