The Neuron
"The aristocrat among the
structures of the body, with its
giant arms stretched out like
tentacles of an octopus to the
provinces on the frontier of the
outside world, to watch for
constant ambushes of physical
and chemical forces."
-Ramon y Cajal (Spanish
neuroscientist and artist)1871,
Nobel Prize 1906
"It is as if the Milky Way entered
upon some cosmic dance.
Swiftly the brain becomes an
enchanted loom where millions
of flashing shuttles weave a
dissolving pattern, always a
meaningful pattern though
never an abiding one; a shifting
harmony of subpatterns."
-Sir Charles Scott Sherington,
1906
Before we start looking at the neuron, here is a quick review for you!
1.
Indicate whether the following parts of the nervous system are part of the
Central Nervous System CNS) or the Peripheral Nervous System (PNS).
Part of nervous system
Brain
CNS or PNS?
........................
Autonomic nervous system
........................
Spinal nerves
........................
Spinal cord
........................
Cranial nerves
.........................
2.
Match the descriptions below with the parts of the nervous system in the list.
You may need
to use some terms more than once.
Autonomic nervous system; Central nervous system; Peripheral nervous
system; Parasympathetic nervous system; Sympathetic nervous system
Description
Part of the nervous
system
Part of the nervous system that is composed of the brain and
the spinal cord.
........................
Part of the nervous system that is composed of the cranial
and spinal nerves.
..........................
The part of the peripheral nervous system that regulates
the activity of the heart and smooth muscle.
...........................
The part of the autonomic nervous system that increases
heart and respiratory rates, increases blood flow to the
skeletal muscles and dilates the pupils of the eye.
............................
The part of the autonomic nervous system that increases gut
activity and decreases heart and respiratory rates.
............................
Now let’s get on to the neuron!
Nerve cells are called neurons. The human brain has about one billion neurons. Each
neuron is a cell that uses biochemical reactions to receive, process, and transmit
information. In simple terms, a neuron is a cell specialized to conduct and generate
electrical impulses and to carry information from one part of the brain to another.
Thanks to their numerous branch-like processes, neurons interconnect forming a
massive network of "wires" that extend throughout the body. By sending messages
across this network, the different parts of the human body interact and communicate
with each other.
How Neurons Communicate
Neurons communicate through an electrochemical process. Sensory receptors
interact with stimuli such as light, sound, temperature, and pain which is transformed
into a code that is carried to the brain by a chain of neurons. Then systems of neurons
in the brain interpret this information. The information is carried along axons and
dendrites because of changes in electrical properties which we call action potential. An
action potential is initiated when a messenger attaches itself to a receptor. When that
occurs, an electrical signal is triggered to be generated through the neuron. Once the
signal reaches the end of an axon, which is at the end of a neuron, a neurotransmitter
is released and the process repeats.
There are several different types of neurons. Sensory neurons carry signals from the
outer parts of your body into the central nervous system or CNS. For example, if
somebody puts ice on your hand, the sensory neurons send the message from your
hand to your central nervous system telling you the ice is cold. Motor neurons carry
signals from the central nervous system to the outer parts of your body doing the
opposite of sensory neurons. For example, if you were driving, the motor neurons
would take the message from your central nervous system to your hand telling you to
turn the key. Receptors sense the environment and encode this information into
electrochemical messages sent by sensory neurons. Inter neurons act as highways or
bridges connecting neurons within the brain and spinal cord.
Axons and Dendrites
Axons
Dendrites
Take information away from the cell
body
Bring information to the cell body
Have a smooth surface
Have a rough surface
Only one axon per cell
Many dendrites per cell
No ribosome
Have ribosome
Have myelin
No myelin
Branch far from the cell body
Branch near the cell body
Time to answer some questions!!
3.
There are three different kinds of neurons or nerve cells. Match each kind with
its function.
A. Motor neuron; B. Sensory neuron; C. Relay neuron;
Kind of neuron
Function
...................................
The nerve cell that carries impulses from a sense
receptor to the brain or spinal cord.
....................................
The nerve cell that connects sensory and motor
neurons
.....................................
The nerve cell that transmits impulses from the brain
or spinal cord to a muscle or gland
4. Terms that are related to the neuron are given below, along with their functions.
Using this information, see if you can label the diagram of the neuron that you were
given (separate sheet). The words to label are in bold
Term
Function
Axon
The long fibre that carries the nerve impulses.
Nerve
A bundle of axons.
Synapse
The connection between adjacent neurons.
Neurotransmitter
The chemical secreted into the gap between neurons at a
synapse.
Reflex
A rapid automatic response to a stimulus.
Myelin sheath
The covering of fatty material that speeds up the passage of
nerve impulses.
Axon terminal
The structure at the end of an axon that produces
neurotransmitters to transmit the nerve impulse across the
synapse.
Nerve impulse
The high speed signals that pass along the axons of nerve cells.
Dendrites
The branching filaments that conduct nerve impulses towards
the cell.
Sense receptor
The sense organ or cells that receive stimuli from within and
outside the body.
Response
The reaction to a stimulus by a muscle or gland.
Cell body (soma)
The part of the nerve cell containing the nucleus.
Nodes of Ranvier
Gaps that occur long the axon between the sections of myelin.
Allow signals to jump from node to mode and therefore travel
faster
Schwann cells
Associate (glial cells) that produce the myelin sheath on axons
5.
The diagram that you have been given shows a cross-section of the spinal cord
and the reflex arc. Add the following labels to the diagram and answer the
question below the diagram.
Central canal; White matter; Dorsal root; Grey matter; Ventral root; Skin;
Muscle; Sensory neuron; Relay neuron; Motor neuron; Pain receptors in skin
6.
a) List in order the 3 different neurons involved in a reflex arc from the stimulus
to the response.
Stimulus
b) Name 3 different reflexes found in animals.
Reflex 1..............................
Reflex 2..............................
Reflex 3..............................
Response