Goals: We will learn:

How info gets from your brain to the rest of your body,

How info gets from the rest of your body to the brain,

How reflexes work,

How our body detects and responds to stimuli.


axon, myelin, neuron, Schwann cells, synapse, neurotransmitter


Nerve cells (neurons) allow cells to communicate with each other.

Nerve cell axon stimulating muscle

The tree-like structure here is a neuron,

except for the red muscle fibers in the lower right.

Here we see a cell send an electrical signal,

down an axon to the muscle cells.

The muscle cells respond by contracting.

Different types 

Sensory/Afferent neurons – Carry info from different parts of your body to your brain.

smell, taste, vision, hearing, heat, pressure

Motor/Efferent neurons – Carry info from your brain to muscles and glands

control speaking, walking, breathing, and swallowing.

Interneurons – connect neurons from one part of your central nervous system to another part

* connects one part of your brain to another part of your brain

* connects your skin nerves, thru your spinal cord, to your muscles: This lets your body have automatic reflexes (muscle motions that don’t require you to think!)

How big are they?

Most nerves are microscopic- but not all! Some run from your brain to your toe.

longest-cell-in-andy-farke primary afferent sensory neuron

Image from svpow.com/2015/06/12/the-longest-cell-in-andy-farke/

Axons are insulated with myelin

Just like electrical wires have insulation, so do nerves.

Schwann cells grow along the axon, creating layers of insulation called myelin.

Nerve cell axon schwann cell myelin Nodes of Ranvier

Electrical signals travel faster in myelinated cells.

Saltatory-Conduction Nerve signaling on axon with myelin

from biologydictionary.net/myelin-sheath

How does the electric signal move?

Nerve cells generate an electrical signal, which then propagates down the axon? Read about action potentials.

The synapse

The electrical signal ends at a gap, called the synapse. The electrical impulse doesn’t cross it.

In the end of nerve we see vesicles: Little bags of lipids (fats) that contain chemical messengers (neurotransmitters)

When the signal arrives, some vesicles move to the end of the nerve:

They fuse,and dump their contents. Neurotransmitters float across the gap.

synapse neurotransmitter

from biologymad.com/ nervoussystem

Here we see the process in more detail:

Electrical signal arrives:

Vesicle moves to end of nerve cell and dumps out neurotransmitters

They cross the synapse

They connect to a membrane protein in their target, causing some action to occur.

Some neurotransmitters get recycled back at the other side.

Nerve synapse releasing neurotransmitter

Here are the labeled steps.




Nerves and the brain

The brain and the nervous system: CNS and PNS

Different types of nerves, Size of nerves, Myelin acts as an insulator, and how neurotransmitters cross the synapse

Action potentials: How nerves use ions to make electrical currents



Myths about the human brain

Nerves: Honors Bio

Cortical homunculus

Michelangelo’s Secret Message: A Juxtaposition of God and the Human Brain

How does the brain think? Textbook chapter

Nerves and evolution: laryngeal nerves

Did neurons evolve twice?


Learning Standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework

HS-LS1-2. Develop and use a model to illustrate the key functions of animal body systems: Emphasis is on the primary function of the following body systems (and structures): digestive (mouth, stomach, small intestine [villi], large intestine, pancreas), respiratory (lungs, alveoli, diaphragm), circulatory (heart, veins, arteries, capillaries), excretory (kidneys, liver, skin), and nervous (neurons, brain, spinal cord).

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