Sinn 1.3

Soma

 (Cell Body): The life support center; contains the nucleus and genetic material

Dendrites:

Branching fibers that receive chemical information from adjacent neurons via receptor sites

Axon

 The longest part of the neuron; carries the electrical signal away from the soma toward the terminal branches

Myelin Sheath

 A layer of fatty tissue (produced by Schwann cells) that insulates the axon. It speeds up the signal and protects the axon

Myelin Sheath:Disorder Link: Multiple Sclerosis (MS)

Occurs when the myelin sheath is damaged, disrupting signal transmission

Nodes of Ranvier:

Gaps in the myelin sheath that help promote the action potential as it moves down the axon

Axon Terminals:

The endpoint where neurotransmitters are stored and released into the synaptic gap (the tiny space between neurons)

Neural Firing & Transmission

Communication within the neuron is electrical, while communication between neurons is chemical.

All-or-None Principle:

A neuron either fires at full strength or not at all; it only fires if it reaches the threshold (the minimum stimulation required)

Action Potential:

• Depolarization: Positive sodium ions flood into the cell, making it more positive and triggering the electrical charge [04:02].

• Refractory Period: A brief "recharging" phase where the neuron cannot fire again [04:15].

• Resting Potential: The stable, negative charge of a neuron when it is ready to fire but currently inactive

Reuptake:

After neurotransmitters are released, the sending neuron reabsorbs the excess chemicals from the synapse

Excitatory vs. Inhibitory:

• Excitatory: Increases the chance a neuron will fire

• Inhibitory: Decreases the chance a neuron will fire, often leading to hyperpolarization (making the cell more negative)

Acetylcholine (ACh):

Muscle action, learning, and memory. (Deficit linked to Myasthenia Gravis)

Dopamine:

Movement, learning, attention, and emotion.

Serotonin:

Mood, hunger, sleep, and arousal.

Norepinephrine:

 Alertness, blood pressure, and fight-or-flight response

GABAA:

 major inhibitory neurotransmitter; helps with sleep and slows the system down.

Glutamate:

 A major excitatory neurotransmitter; involved in memory.

Endorphins:

Pain control and pleasure.

Substance P:

Transmits pain signals to the CNS

Epinephrine (Adrenaline):

 Fight-or-flight, high-emotion memories

Melatonin:

Regulates sleep-wake cycles (circadian rhythm)

Leptin vs. Ghrelin:

 Leptin inhibits hunger (signals "full"); Ghrelin promotes hunger

Oxytocin:

The "love hormone"; promotes bonding and affection

 Psychoactive Drugs & The Synapse

Drugs alter perception and mood by affecting neurotransmission

Agonists:

Mimic or increase the effectiveness of a neurotransmitter. (e.g., Xanax increases GABA)

Antagonists:

Block or decrease the effectiveness of a neurotransmitter by blocking receptors. (e.g., Schizophrenia medication blocks dopamine)

Stimulants:

Excite neural activity (Caffeine, Nicotine, Cocaine).

Depressants:

Reduce neural activity (Alcohol, Sleeping pills).

Hallucinogens:

Distort perceptions (LSD, Marijuana).

Opioids:

Provide pain relief and are highly addictive (Morphine, Heroin).

 Reflex Arc

 It allows you to move (like pulling your hand from a stove) before the signal even reaches your brain for processing—a key survival mechanism!