Download 03. Neurons and Nerves

Neuron Type and Function
• The human body contains billions/trillions
of cells. Like other systems in the body,
the nervous system is composed of
specialized cells. Neuron cells are
designed to conduct nerve impulses.
Neurons carry messages using
electrochemical communication. There
are many kinds of neurons. They differ in
size, structure and function.
• Two types of cells are found in the nervous
system:
1. Glial cells – are non-conducting cells.
They are important for structural support and
metabolism of nerve cells. Schwann cell is a
type of glial cell that surrounds axons.
2. Neurons – are functional units of the nervous
system. They carry information from one location
to another. They are categorized into three
groups: sensory neurons, interneurons, and
motor neurons.
Fact
• The human brain contains 100 billion
neurons.
Target Cells
• Cells stimulated by nerve cells are called
target cells. These include:
• muscle cells: they may respond by
contracting or relaxing
• Glands: may respond by secreting various
substances
• Other neurons: may respond by
generating their own impulses
Types of Neurons
Sensory Neurons (afferent neurons) - pick up
information from the environment and carry it to
the CNS. Sensory neurons are located in
clusters called ganglia located outside the
spinal cord.
Interneurons (association neurons) – link
neurons together in the body. Found mainly in
the brain and spinal cord. They pass information
between sensory neurons and motor neurons.
• Motor Neurons (efferent neurons) –
carry information to effectors (muscles and
glands that cause things to happen).
Parts of Neurons
All neurons contain a plasma membrane,
cytoplasm (containing organelles), a
nucleus, axons and dendrites.
• Cell Body – nucleus and most of cytoplasm
• Dendrites – finely divided branches of a neuron
that carry impulses toward the cell
• Axon – long, thin branch of a neuron that carries
impulses away from the cell body
(** in human body, more than 100 axons can be
placed in a strand of hair).
• Myelin sheath – insulated covering over
the axon of the nerve cell.
• Schwann cell- found along the axon.
Produces myelin sheath.
• Node of Ranvier – gaps found between
myelin sheath.
• Neurilemma – delicate membrane that
surrounds the axon of some nerve cells.
Complete
P. 417 #1,2,3,5
Assigned Reading:
Pages 412-416