Before we start looking at the neuron, here is a quick review for you!



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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

CNS or PNS?

Brain

........................

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








Response

b) Name 3 different reflexes found in animals.

Reflex 1..............................

Reflex 2..............................



Reflex 3..............................


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