Page 73 - 84 human physiolofy part-1

The Nervous System

ganglion, which acts on nicotinic receptors of the postganglionic nerve. The postganglionic nerve then
releases ACh to stimulate the muscarinic receptors of the target organ.

The three main types of muscarinic receptors that are well characterised are:

• The M1 muscarinic receptors are located in the neural system.
• The M2 muscarinic receptors are located in the heart, and act to bring the heart back to
normal after the actions of the sympathetic nervous system: slowing down the heart rate,
reducing contractile forces of the atrial cardiac muscle, and reducing conduction velocity of the
atrioventricular node (AV node). Note, they have no effect on the contractile forces of the
ventricular muscle.
• The M3 muscarinic receptors are located at many places in the body, such as the smooth
muscles of the blood vessels, as well as the lungs, which means that they cause vasoconstriction
and bronchoconstriction. They are also in the smooth muscles of the gastrointestinal tract (GIT),
which help in increasing intestinal motility and dilating sphincters. The M3 receptors are also
located in many glands that help to stimulate secretion in salivary glands and other glands of the
body.

Nervous Tissue

The nervous system coordinates the activity of the muscles, monitors the organs, constructs and
also stops input from the senses, and initiates actions. Prominent participants in a nervous system
include neurons and nerves, which play roles in such coordination.Our nervous tissue only consists of
two types of cells. These cells are neurons and neuroglia cells. The neurons are responsible for
transmitting nerve impulses. Neuroglia cells are responsible for supporting and nourishing the neuron
cells.

Types of Neurons

There are three types of neurons in the
body. We have sensory neurons, interneurons,
and motor neurons. Neurons are a major class of
cells in the nervous system. Neurons are
sometimes called nerve cells, though this term is
technically imprecise, as many neurons do not
form nerves. In vertebrates, neurons are found in
the brain, the spinal cord and in the nerves and
ganglia of the peripheral nervous system. Their
main role is to process and transmit information.
Neurons have excitable membranes, which
allow them to generate and propagate electrical
impulses. Sensory neuron takes nerve impulses
or messages right from the sensory receptor and
delivers it to the central nervous system. A sensory receptor is a structure that can find any kind of
change in it's surroundings or environment.

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