Neurons
Nerve Tissue Cells
You may know that electric current can be generated in a circuit. Similarly, nerve cells have the ability to generate electrical currents, though these are very weak. The main functional cells of nerve tissue are called neurons. Other types of supporting cells in the nervous system, called glial cells, help neurons function properly.
A neuron includes a nucleus and most organelles located in an expanded area called the cell body. It has short extensions called dendrites, and a longer projection called the axon, which carries nerve impulses from the cell body and transmits them outward. The axon ends in branches that connect to other neurons or tissues.
A long bundle of axons surrounded by protective tissue is called a nerve fiber. If the impulse travels from the sensory organs to the central nervous system, it's called a sensory neuron. If the impulse travels from the central nervous system to muscles or other body parts, it's called a motor neuron.
Motor neurons carry commands from the central nervous system to body parts like hands and feet, while sensory neurons transmit incoming signals to the brain and spinal cord.
Important Concept
A neuron has three main parts: dendrites (which receive signals), the cell body (which processes them), and the axon (which sends the signal to the next cell or tissue).
Common Mistake
It's a common misunderstanding to think that nerves and neurons are the same. In fact, a nerve is made up of many axons from different neurons bundled together — not a single nerve cell.
Questions
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A neuron consists of dendrites (which receive signals), the cell body (which processes the signals), and an axon (which transmits the signals to other cells or tissues).
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A neuron is a single nerve cell, while a nerve is a bundle of axons from many neurons wrapped in connective tissue.
Nerve Impulse
You may have played with dominoes before. When one tile is pushed over, it knocks down the next, and the effect continues in a chain reaction. A nerve impulse travels through a neuron in a similar way.
When a neuron is stimulated, it generates an electrical signal called a nerve impulse. This impulse travels down the length of the neuron until it reaches the axon terminals, where it can be passed to the next neuron or target cell.
The nerve impulse is transmitted via the axon to the axon terminals. From there, it may pass to another neuron or to effectors such as muscles or glands. The ability of a neuron to generate and conduct impulses is vital for communication within the nervous system.
In addition to electrical signaling, special chemical compounds are released at the axon terminals. These neurotransmitters help transmit the nerve signal to the next cell.
Did You Know?
Certain drugs and chemicals can interfere with neurotransmitter function, disrupting nerve impulse transmission. This may lead to abnormal heart rate, mood swings, fatigue, joint pain, and unusual behavior.
Important Concept
A nerve impulse is an electrical signal that travels along a neuron. It is triggered by stimulation and travels to the axon terminal, where it may pass to another cell via neurotransmitters.
Common Mistake
Many students think that nerve impulses jump from one neuron to the next automatically. In fact, electrical signals stop at the axon terminal and require neurotransmitters to cross the gap (synapse) and continue to the next cell.
Questions
Show Answer
A nerve impulse is an electrical signal generated when a neuron is stimulated. It travels along the axon to the axon terminals, where it may be passed to another cell using neurotransmitters.
Show Answer
Neurotransmitters are chemicals released from the axon terminal that carry the nerve signal across the synapse to the next neuron or target cell.