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Neurons Carry Signals as Electrical Impulses · Control and Coordination · MS-LS1-8 · neurons

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Neurons Carry Signals as Electrical Impulses

with Medi

A detailed cross-section of the human brain glows with branching blue electrical sparks while Medi, a curious young guide in a lab coat, traces a signal pathway along an enormous neuron diagram mounted on the wall, pointing excitedly at the branching dendrites.

Identify the three main parts of a neuron and describe the function of each part.
Explain how an electrical signal travels from one neuron to the next across a synapse.
Compare the roles of sensory neurons, motor neurons, and interneurons in a reflex arc.
Predict what would happen to body coordination if signal transmission between neurons were disrupted.
Describe how the structure of a neuron is specialized for rapid, long-distance communication.

Key terms

Neuron: A specialized cell built to carry electrical signals through the body.
Axon: The long cable-like extension that carries a signal away from the cell body.
Synapse: The microscopic gap between two neurons crossed by chemical messengers.
Neurotransmitter: A chemical messenger released to carry a signal across the synapse.
Action potential: An all-or-nothing electrical impulse that travels down the axon.

How a Signal Crosses the Gap

A neuron carries its message electrically, but neurons do not actually touch, so the signal must cross a tiny space called the synapse. An action potential cannot leap that fluid-filled gap on its own. Instead, when the impulse reaches the axon terminal, it triggers the release of chemical messengers called neurotransmitters. These chemicals drift across the synapse and bind to the next neuron's dendrites, where they spark a brand new electrical signal. This electrical-then-chemical-then-electrical relay is how a message travels from one neuron to the next without the cells ever joining together.

Three Neurons Make a Reflex

Coordination depends on three neuron types working in a fixed order, easy to remember as sense, process, act. Sensory neurons carry information inward from receptors in the skin, eyes, and ears toward the spinal cord and brain. Interneurons, located inside the central nervous system, process that information and decide on a response. Motor neurons then carry the decision outward to muscles or glands so the body can act. In a reflex like pulling your hand off a hot pan, this chain runs through the spinal cord so fast that you move before the pain even reaches your awareness.

Worked examples

Trace the reflex when you touch a hot pan

Heat receptors in the skin detect danger and fire a signal into a sensory neuron.
The sensory neuron carries the impulse inward to interneurons in the spinal cord.
Interneurons process the signal and immediately activate motor neurons.
Motor neurons release neurotransmitters onto arm muscles, which contract to pull the hand away.

Answer: Sensory then interneuron then motor; the hand moves before pain reaches the brain.

Hey there! I'm Medi, and today we're going inside the fastest communication network in your body — your nervous system. The basic unit is called a neuron, a specialized cell built to carry electrical signals. Every neuron has three key regions. First, the dendrites — these are short, branching extensions that receive incoming signals from other neurons or from sense organs. Think of dendrites as the neuron's antennae, always listening. Second, the cell body (also called the soma) — this is the control center that contains the nucleus and keeps the cell alive. Third, the axon — a long, cable-like extension that carries the signal away from the cell body toward the next neuron or toward a muscle. Some axons are wrapped in a fatty layer called the myelin sheath, which acts like insulation on an electrical wire and makes signals travel many times faster — unmyelinated fibers carry signals at roughly 1 meter per second, while myelinated fibers can reach 70 meters per second or more. When a neuron is stimulated strongly enough, it fires an action potential — a rapid, traveling change in electrical charge that races down the axon. This is an all-or-nothing event: the signal is always the same strength, no matter how strong the original stimulus was. At the end of the axon are tiny bulbs called axon terminals. Between one neuron's axon terminal and the next neuron's dendrite is a microscopic gap called the synapse. The electrical signal cannot jump this gap directly. Instead, the arriving signal causes the axon terminal to release chemical messengers called neurotransmitters. These chemicals diffuse across the synapse and bind to the next neuron, triggering a new electrical signal there. There are three types of neurons working as a team. Sensory neurons carry signals from your skin, eyes, ears, and other sense organs toward the brain and spinal cord. Interneurons (found inside the brain and spinal cord) process the information and decide on a response. Motor neurons carry the decision signal outward to muscles or glands, causing them to act. Hint: to remember the order, think SENSE → PROCESS → ACT — sensory, interneuron, motor.

Activity

Drag each station into the correct order to show the path a signal travels from a touch on the skin all the way to a muscle movement.

Practice

Identify the dendrite, cell body, and axon on a neuron and state the job of each part.

Order the events when a signal reaches an axon terminal and moves to the next neuron.

Common mistakes to avoid

The electrical signal jumps the synapseNeurotransmitters carry the signal across the synapse because electricity cannot cross the gap.
A stronger stimulus makes a bigger impulseAction potentials are all-or-nothing, so a stronger stimulus only makes them fire more often.

Check your understanding

A signal traveling down a neuron reaches the axon terminal. What happens NEXT to move the signal to the following neuron?

You accidentally touch a hot pan and pull your hand away before you even feel pain. Which sequence of neuron types is responsible for this reflex?

A student says: 'A stronger pinch must create a stronger electrical signal in the neuron.' Is this correct?

Recap

A neuron carries an all-or-nothing electrical impulse down its axon, releases neurotransmitters to cross the synapse to the next neuron, and three neuron types in the order sense, process, act let the body detect and respond rapidly.

Reflect

How might your daily life change if the neurotransmitters in your synapses stopped being released?