neurons and nervous system

Neurons are individual cells in the nervous system that receive, integrate, and transmit information.
Most neurons communicate with other neurons; some pass information to and from other parts of the body.
Neurons are the basic units that enable neural signaling and behavior.

Soma (cell body): Contains the cell nucleus and chemical machinery common to most cells.
Dendrites: Branch-like structures that receive information from other neurons.
A x on blue part.: Long, thin fiber that transmits signals away from the soma to other neurons.
Myelin Sheath: Insulating material that encases axons, increasing transmission speed.
Terminal Buttons: Small knobs at the ends of axons that secrete chemicals called neurotransmitters.
Neurotransmitters: Chemicals that transmit information from one neuron to another.
Synapse: Junction where information is transmitted from one neuron to another.
Note: Figure references (e.g., Figure 3.1) illustrate these parts in textbooks.

Glia are cells found throughout the nervous system that provide support for neurons.
Functions include:
- Supplying nourishment to neurons
- Helping remove neurons’ waste products
- Providing insulation around many axons
- Additional supportive roles in the nervous system
Emerging research suggests Glia may also send and receive chemical signals, like neurons.
Glia may play roles in various disorders and bodily sensations, including schizophrenia, depressive symptoms, Alzheimer’s disease, chronic pain, stress responses, and epilepsy.

The neural impulse is an electrochemical reaction involving ions.
Ions involved include: positively charged sodium (Na⁺) and potassium (K⁺) ions; negatively charged chloride (Cl⁻) ions.
Ions flow across the neuronal membrane at different speeds, leading to a negative interior when at rest
Resting potential: The stable, negative charge inside a neuron when it is inactive.
When a neuron is stimulated, the cell membrane opens and positive ions enter, changing the charge.
Action Potential: A brief shift in a neuron’s electrical charge that travels along an axon. When cells need to send msg t more - less
Visual cue from slide: interior becomes positive during the spike, then returns to negative.
Notation: resting state is negative; during firing, the inside becomes more positive relative to the outside.

Neural impulse is all or nothing: a neuron fires fully or not at all.
Strength of stimulus does not change the amplitude of the action potential, but can affect firing rate.
Examples:
- A dim light may trigger about 5 impulses per second.
- A bright light may trigger about 200 impulses per second.
A neuron may receive signals from thousands of other neurons; it must integrate these signals before firing.
Integration process: Excitatory inputs add to the likelihood of firing; inhibitory inputs subtract from it.
The decision to fire depends on whether the net input reaches the threshold needed for an action potential.

A neural impulse must be transmitted to other cells via the synapse.
Synaptic Cleft: The microscopic gap between the terminal button of one neuron and the cell membrane of the next neuron.
Neurotransmitters: Chemicals that transmit information across the synapse.
Messages across the synapse can be:
- Excitatory: A positive shift that increases the likelihood that the receiving neuron will fire an action potential.
- Inhibitory: A negative shift that decreases the likelihood that the receiving neuron will fire.
Reuptake: The process by which neurotransmitters are absorbed and reused.
Visual cue: Figure 3.3 in the textbook illustrates the synapse and neurotransmitter action.

Neurons receive, integrate, and transmit information.
Neurons rest when the membrane is negative and fire when it becomes positive (action potential).
The message can be excitatory (increase firing likelihood) or inhibitory (decrease firing likelihood).
Neurotransmitters are released into the synapse, then reabsorbed for reuse via reuptake.
All of this occurs hundreds of times per second in the nervous system.

Neurons are highly specialized: specific neurons work with particular others to enable precise, efficient behavior.
Common neurotransmitters and their general roles:
- Acetylcholine: regulation of attention, arousal, and memory.
- Dopamine: voluntary movement; also part of the reward pathway.
- Norepinephrine: modulation of mood.
- Serotonin: regulation of sleep and wakefulness, eating, and aggression.
- GABA: major inhibitory neurotransmitter; regulation of anxiety.
- Endorphins: pain relief and stress response; also involved in eating regulation.

Myth: We only use 10% of our brain. This is false; the brain is highly active and various regions participate in even simple tasks.
Neurons work together constantly to keep information flowing.
The nervous system is extremely organized to be efficient.

Definition: Nerves that lie outside the brain and spinal cord.
Nerves: Bundles of neuron fibers routed together in the PNS.
Components:
- Somatic Nervous System: Connects to voluntary skeletal muscles and sensory receptors.
- Autonomic Nervous System: Connects to heart, blood vessels, smooth muscles, and glands; handles physiological arousal during emotions.
- Autonomic divisions:
- Sympathetic Division: Mobilizes the body