Neuroscience Foundations: Neurons, Neurotransmitters, and Brain Structure

Neurons: The Brain's Communicators

Structure and Function of Neurons

Neurons are specialized nerve cells responsible for transmitting information throughout the nervous system via electrical and chemical signals.

• Cell Body (Soma): The central part of the neuron; contains the nucleus and builds new cell components.

• Dendrites: Branch-like structures that receive information from other neurons.

• Axons: Long, tail-like structures that transmit information away from the cell body.

• Axon Terminal: The end of the axon, containing synaptic vesicles filled with neurotransmitters (e.g., dopamine, serotonin).

• Synapse (Synaptic Cleft): The gap between neurons where neurotransmitters travel; the meeting place for neuronal communication.

Key concept: "Dendrite listens, axon speaks"—dendrites receive signals, axons send them.

Glial Cells

Glial cells, often called "glue cells," support and protect neurons, clean up waste, bring nutrients, and maintain neural health.

Myelin Sheath

The myelin sheath is a fatty insulation made from glial cells that surrounds the axon, speeding up neural transmission.

• Multiple Sclerosis: A disease where myelin is damaged, causing disrupted electrical signals and cognitive/motor disabilities.

• Loss of myelin leads to long-term cognitive damage and disabilities.

How Does a Neuron Fire?

Neurons communicate via electrical impulses called the action potential.

• Step 01: Resting Potential - Neuron is polarized (negative inside, positive outside). - Selectively permeable membrane allows sodium ions ($Na^+$) to pass during activation. - Positive charge rushes in during action potential; positive ions are pumped back out after firing.

• Step 02: Action Potential - Brief electrical charges travel down the neuron. - Signals are transmitted to other neurons, muscles, or glands. - Axon depolarizes (gates open, $Na^+$ rushes in).

• Step 03: Repolarization - Potassium flows out, restoring negative charge.

• Step 04: Returns to Resting Potential

• Step 05: Refractory Period - Brief period after firing when the neuron cannot fire again.

Electrochemical Communication

When the electrical signal reaches the axon terminal, it triggers the release of neurotransmitters into the synapse (chemical communication).

• Excitatory: Increases likelihood of neuron firing.

• Inhibitory: Decreases likelihood of neuron firing.

Neurotransmitters

Definition and Function

Neurotransmitters are chemical messengers that help neurons communicate. They influence emotions, mood, movement, sleep, alertness, learning, and memory.

• Imbalances can lead to mental illnesses (e.g., excess dopamine linked to schizophrenia).

Release	Re-uptake
Action potential triggers neurotransmitter release into the synaptic cleft; NT binds to receptors on postsynaptic neuron.	Excess NTs are removed by drifting away, being broken down, or reabsorbed. Reuptake: NTs are taken back into the presynaptic neuron (e.g., cocaine blocks reuptake, prolonging NT effects).

• Agonists: Mimic/enhance neurotransmitter effects.

• Antagonists: Block/impede neurotransmitter activity.

Most Common Neurotransmitters

• GABA: Inhibitory; reduces brain activity.

• Acetylcholine: Aids arousal, memory, sleep, selective attention. Drugs like benadryl and illnesses (e.g., Alzheimer's) disrupt acetylcholine, leading to memory loss and dementia.

• Dopamine: Pleasure, reward, voluntary movement, attention. Parkinson's disease involves lack of dopamine; schizophrenia involves excess dopamine.

• Serotonin: Made from tryptophan (an essential amino acid from food). Regulates mood, sleep, appetite, pain perception. Low levels linked to depression/anxiety.

The Brain

Cerebral Cortex

The cerebral cortex is the brain's outer layer, divided into four major lobes. It handles higher-order thinking and voluntary actions.

• Consists of two hemispheres (left and right), connected by the corpus callosum.

• Contralateral control: Each hemisphere controls the opposite side of the body.

Left Hemisphere	Right Hemisphere
Fine-tuned language skills: speech comprehension, production, reading, writing, etc. Actions: facial expressions, motion detection	Coarse language skills: simple speech, simple writing, tone of voice Visuospatial skills: perceptual grouping, face perception

4 Major Lobes of the Cerebral Cortex

• Frontal: Planning, executive function, motor control. Includes Broca's area (language production), motor cortex (body movement), prefrontal cortex (thinking/planning).

• Parietal: Sensation. Somatosensory cortex processes touch, pressure, pain, temperature.

• Temporal: Auditory. Hearing, understanding language, autobiographical memory. Contains Wernicke's area (language comprehension).

• Occipital: Vision. Processes visual information, recognizes shapes.

Subcortical Structures

• Forebrain: Higher cognitive functions, voluntary movement.

• Midbrain: Controls movement, transmits information for seeing/hearing.

• Hindbrain: Pons (sleep/arousal), cerebellum (motor coordination), medulla (vital functions).

Limbic System

Functions and Components

The limbic system, located underneath the cortex, is involved in emotion, motivation, and memory.

• Emotional Center

• Amygdala: Detects danger, triggers fear/aggression.

• Hippocampus: Forms new long-term memories.

• Thalamus: Sensory relay; sends signals to the right places.

• Hypothalamus: Regulates hunger, thirst, sleep, links emotions to physical reactions.

Toxoplasmosis: Infection by parasites that reduces fear response.

Peripheral Nervous System: Autonomic Nervous System

• Sympathetic: "Fight or flight"—prepares body for action.

• Parasympathetic: "Rest and digest"—calms the body.

Brain Plasticity and Trauma

Plasticity

The brain is adaptable and can change in response to experience.

• Myelination makes neurons faster, regions more efficient.

• Pruning removes unused connections.

• Plasticity decreases with age.

Intergenerational Trauma

Trauma can be passed down through generations, affecting brain structure, function, and chemistry. PTSD may be linked to inherited changes.

Brain Mapping and Measurement

Polygraph

Measures physiological responses (heart rate, blood pressure, breathing, skin conductivity) to assess truthfulness.

Brain Mapping Methods

• Phrenology: Skull shape reflects brain size/function (historical, not scientifically valid).

• Neuropsychology tests: Used to analyze cognitive function.

• CT Scan: X-rays to show brain tumors.

• MRI: Shows metabolic activity using magnetic fields; produces tissue images.

• EEG: Measures electrical activity via scalp electrodes; tracks amplitude/frequency.

• MEG: Measures magnetic fields from brain; identifies epilepsy locations.

• Deep Brain Stimulation: Stimulates dopamine production; treats Parkinson's, depression.

• Transcranial Magnetic Stimulation (TMS): Applies magnetic fields to the skull to enhance/interrupt brain function.

Summary Table: Major Brain Divisions and Functions

Division	Main Structures	Function
Forebrain	Cerebral cortex, thalamus, hypothalamus	Higher cognitive functions, voluntary movement
Midbrain	Reticular activating system	Movement, attention, arousal
Hindbrain	Pons, cerebellum, medulla	Sleep, arousal, motor coordination, vital functions

Additional info:

• Neurotransmitter imbalances are linked to various mental health disorders.

• Brain imaging techniques are essential for diagnosing and understanding neurological conditions.