nervous system - i

7/30/2019 Nervous System - I

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Medical English (ESP in Medicine)

Lecturer: Do Thi Thu Hang

Email: [email protected]

Chapter 14: Nervous system


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2. Anatomy and physiology

The nervous system senses physical and chemical changes in

the internal and external environments, processes them,and then responds to maintain homeostasis

Voluntary activities, such as walking and talking, andinvoluntary activities, such as digestion and circulation, are

regulated and coordinated, by the nervous system

The entire neural network of the body relies on thetransmission of nervous impulses

Nervous impu lses: are electrochemical stimuli that travelfrom cell to cell as they send information from one area ofthe body to another. Nervous impulses are almostinstantaneous


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Cellular Structure of the Nervous System

1. Neurons are cells that transmit impulses-Afferent: the direction is toward the brain or spinal

cord

-Efferent when the direction is away from the brainor spinal cord

2. Neuroglia are cells that support neurons

and bind them to other neurons or other

tissues of the body


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Neurons

The three major structures of the

neuron are the cell body, axon,and dendrites

1. The cell body is the enlarged

structure of the neuron thatcontains the nucleus of the cell

and various organelles.

2. Dendrites that carry impulses to

the cell body

3. Axons that carry impulses from

the cell body.


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Axons:Axons possess a white, lipoid covering called myelin sheath

which acts as an electrical insulator. It allows impulses totransmit quickly and efficiently along the nerve cells. If themyelin is damaged, the impulses slow down (e.x. Multiple

sclerosis)On nerves in the peripheral nervous system, myelin sheath is

formed by a Schwann cell. Its exterior surface forms a thintube called neurilemma, or neurolemma

The myelin sheath covering the axons in the central nervoussystem is formed by oligodendrocytes


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The vertebrate nervous system can also be divided into

areas called grey matter ("gray matter" in American

spelling) and white matter.

Grey matter (which is only grey in preserved tissue, and isbetter described as pink or light brown in living tissue)

contains a high proportion of cell bodies of neurons.

White matter is composed mainly of myelinated axons, and

takes its color from the myelin

Gray matter and white matter


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Synapse:

The functional connection between two neurons or between aneuron and its target (muscle or gland) is a gap or spacecalled a synapse.

Impulses must travel from the axon terminal of one neuron to thedendrite of the next neuron or to its target by crossing thissynapse

The impulse within the transmitting axon causes a chemicalsubstance called a neurotransmitter to be released at the end

of its axon


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Neurotransmitter:

The neurotransmitter diffuses across the synapse andattaches to the receiving neuron at specialized receptorsites.

When sufficient receptor sites are occupied, it signals anacceptance message and the impulse passes to thereceiving neuron. The receiving neuron immediatelyinactivates the neurotransmitter, and prepares the sitefor receiving another stimulus


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Chemical transmission of a nerve impulse at the synapse. The arrival of the nerve

impulse at the presynaptic terminal stimulates the release of neurotransmitter into the

synaptic gap. The binding of the neurotransmitter to receptors on the postsynaptic

membrane stimulates the regeneration of the action potential in the postsynaptic neuron


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Neurogl ia

The term neuroglia literally means nerve gluebecause these cells were originally believed toserve only one function: to bind neurons to eachother and to other structures.

They are now known to supply nutrients andoxygen to neurons and assist in other metabolicactivities.

They also play an important role when the nervoussystem suffers injury or infection.


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Four types of neuroglia.


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The blood brain barrierkeeps large molecular substances from entering the

delicate tissue of the brain. Even so, small molecules, such as water, carbon

ioxide, oxygen, and alcohol, readily pass from blood vessels through the barrier

and enter the interstitial spaces of the brain

Astrocytesform tight

sheaths

around the

capillaries of

the brain


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nervous system - i

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