LESSON 3: NEURONS AND BRAIN FUNCTIONING

Neurons

The Basic Unit of the Nervous System

Cell Body (Soma)

Contains the nucleus and keeps the cell alive; integrates information

Dendrites

Branching tree-like fiber; Receive signals from other neurons.

Axon

Transmits: long segmented fiber; transmit signals away from the cell body.

Myelin Sheath

Insulates axon, speeds up transmission.

Axon Terminals

Release neurotransmitters into synapses

Electrochemical Process

Neurons use both electricity and chemicals to send messages.

Neurotransmitters

When the electrical signal reaches the axon terminals, the neuron releases this into the synapse (the tiny space between neurons).

Resting Potential

At rest, the neuron’s inside is more negatively charged than the outside. It’s like a battery waiting to be used — ready but not active yet.

Threshold

• When the incoming signal is strong enough, it reaches a threshold.

• The neuron’s membrane opens, letting positive sodium ions rush in.

• This triggers the neuron to “fire” — starting the action potential.

Action Potential

This is the electrical spark or impulse that travels down the axon. The inside becomes temporarily positive, sending the impulse forward.

• It’s an “all-or-nothing” event — the neuron either fires completely or not at all.

• Speed enhanced by the myelin sheath

Refractory Period

After firing, the neuron needs a short recovery time. It resets its charge and can’t fire again immediately.

Nerve impulse

The process (the message being sent).

Electrical impulse/charge

The mechanism (the voltage change that makes the message possible).

Myelin Sheath

A fatty, insulating layer that wraps around sections of the axon. Speeds up the transmission of electrical impulses. Prevents signals from “leaking” out of the axon

Nodes of Ranvier

Small gaps between the myelin sheath segments along the axon. Allow the electrical impulse to “jump” from one node to the next.

Saltatory conduction

Jumping process in Nodes of Ranvier

Synaptic Transmission

1. Electrical impulse (action potential) travels down the axon.

2. Neurotransmitters are released into the synaptic gap.

3. Receptors on the next neuron receive the signal, continuing communication.

Neurotransmitter

• A chemical messenger that carries signals across the synapse between neurons.

• They travel across the synaptic space between the terminal button of one neuron and the dendrites of other neurons, where they bind to the dendrites in the neighboring neurons.

Synapse

The tiny space where one neuron’s axon end almost touches another neuron’s dendrite to pass signals.

Excitatory

Makes the next neuron more likely to send its own signal.

Inhibitory

Makes the next neuron less likely to send a signal.

Reuptake

A process in which neurotransmitters that are in the synapse are reabsorbed into the transmitting terminal buttons, ready to again be released after the neuron fires.

Agonist

A drug that has chemical properties similar to a particular neurotransmitter and thus mimics the effects of the neurotransmitter

Antagonist

Drug that reduces or stops the normal effects of a neurotransmitter.

Acethylcholine

• A neurotransmitter that enables communication between neurons and muscles; vital for memory, learning, and attention.

• How it works - It transmits signals from motor neurons to muscle fibers, causing contraction, and also facilitates cognitive processing in the brain.

• Strengthens memory pathways

Adrenaline

A hormone and neurotransmitter that prepares the body for immediate action in stressful or exciting situations.

Dopamine

A neurotransmitter that regulates motivation, pleasure, and movement.

Endorphins

Natural painkillers produced by the brain to reduce discomfort and promote pleasure.

GABA (Gamma-Aminobutyric Acid)

The main inhibitory neurotransmitter that reduces neuronal excitability.

Serotonin

A neurotransmitter that stabilizes mood, sleep, and appetite.

Dopamine and Norepinephrine

Regulate alertness.