Your brain contains roughly 86 billion neurons, each connected to thousands of others, forming a network of staggering complexity. Everything you think, feel, and do emerges from these cells passing signals to one another. This is how the brain actually communicates.
Learning Objectives
- •Understand the neuron and its parts
- •Learn how neurons signal across synapses
- •Meet neurotransmitters and glial cells
The neuron
A NEURON is a specialized cell built to receive, process, and transmit information. It has three key parts: DENDRITES (branching antennae that RECEIVE signals from other neurons), the CELL BODY (which integrates them), and the AXON (a long fiber that SENDS the signal onward to other neurons). With ~86 billion neurons each connected to thousands of others, the brain has trillions of connections — a network of almost unimaginable density.
The synapse and neurotransmitters
Neurons don't quite touch — they communicate across tiny gaps called SYNAPSES. When a signal reaches the end of an axon, the neuron releases chemical messengers called NEUROTRANSMITTERS that cross the gap and bind receptors on the next neuron, passing the message along. Different neurotransmitters carry different signals: GLUTAMATE excites, GABA calms, and others like DOPAMINE, SEROTONIN, and ACETYLCHOLINE modulate mood, reward, attention, and more.
An electrochemical signal
The signal is part ELECTRICAL, part CHEMICAL. Within a neuron, the message travels as an electrical impulse (an 'action potential') racing down the axon. To cross the synapse to the next neuron, it converts to a CHEMICAL signal (neurotransmitters). So a thought is, quite literally, electrical impulses and chemical messengers cascading across billions of cells.
NEURON A: dendrites(receive) → cell body → AXON (electrical impulse) → SYNAPSE: release NEUROTRANSMITTERS (chemical) across the gap → NEURON B: dendrites receive → and the message continues Electrical within a neuron; chemical between neurons.
Why so many medications target neurotransmitters
A huge share of drugs that affect the mind work on neurotransmitter systems: antidepressants adjust serotonin or other messengers; many anti-anxiety drugs boost GABA (the calming signal); stimulants affect dopamine and norepinephrine; and caffeine blocks adenosine. Even recreational drugs hijack these systems. Understanding neurotransmitters is understanding how much of psychiatry and pharmacology works.
Glial cells: the unsung support
Neurons get the glory, but the brain is also full of GLIAL CELLS — support cells at least as numerous as neurons. They insulate axons with MYELIN (speeding signals), supply nutrients, and act as the brain's immune cells (microglia). Far from passive 'glue', glia are now known to actively shape brain function. The brain is a team effort of neurons and glia.
Neurons & communication, by the numbers
- ▸The brain has roughly 86 billion neurons, each connected to thousands of others
- ▸Neurons signal across synapses using chemical neurotransmitters
- ▸Signals are electrical within a neuron, chemical between neurons
- ▸Glial cells (at least as numerous as neurons) insulate, nourish, and defend
We only use 10% of our brains.
The '10% of your brain' claim is a myth. Brain imaging shows essentially all of the brain is active over a day, and even simple tasks engage widespread regions. There's no vast dormant 90% waiting to be unlocked — the whole brain is in use.
Quick Check
How do neurons communicate with each other?
Quick Check
What do glial cells do?
True or False
The claim that humans use only 10% of their brains is a myth.
Summary
- →Neurons receive (dendrites), integrate (cell body), and send (axon) signals
- →They communicate across synapses using chemical neurotransmitters
- →Signals are electrical within a neuron and chemical between neurons
- →Glial cells insulate, nourish, and defend — the brain is neurons + glia
This network isn't fixed — it constantly rewires itself. Next: neuroplasticity.