Neuroscience Foundations: Brain Structure, Function, and Neurotransmission

Neurons: The Brain’s Communicators

Overview of Neurons

Neurons are specialized nerve cells that serve as the fundamental building blocks of the nervous system. They transmit information via electrical signals known as action potentials.

• Communication: Neurons interact with each other to process and relay information throughout the brain and body.

• Action Potentials: Electrical impulses that travel along neurons, enabling rapid signaling.

Neural Components

• Cell Body (Soma): Contains the nucleus and builds new cell components.

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

• Axons: Long tails that transmit information away from the cell body.

• Axon Terminal: End of the axon where synaptic vesicles filled with neurotransmitters are located.

• Synapse (Synaptic Cleft): The space between neurons where neurotransmitters are released and received.

Example: Dendrites listen, axons speak!

Glial Cells

Glial cells support and protect neurons, playing a vital role in psychological functioning.

• Functions: Provide structural support, nourish neurons, and produce myelin.

• Myelin: Fatty insulation from glial cells surrounding axons, enabling faster signal transmission.

• Bodyguards: Protect and insulate neurons.

Myelin Sheath

• Function: Insulates axons, speeding up electrical signal transmission.

• Multiple Sclerosis: Loss of myelin causes erratic signals and neurological symptoms.

Action Potentials and Neural Firing

Electrical Impulse: The Action Potential

Neurons transmit signals via action potentials, which are rapid changes in electrical charge across the cell membrane.

• Step 1: Resting Potential

  • Neuron is polarized (negative inside, positive outside).

  • Sodium-potassium pump allows sodium ions (Na+) to pass through.

• Step 2: Neuron Fires

  • Action potential is triggered, sending an electrical charge down the axon.

  • Neurotransmitters are released at the axon terminal.

  • Depolarization occurs (Na+ rushes in).

  • Frequency and intensity of firing depend on stimulus strength.

• Step 3: Repolarization

  • Potassium ions (K+) flow out, restoring resting potential.

Neurotransmitters and Synaptic Transmission

Neurotransmitter Release and Action

Neurotransmitters are chemical messengers that help neurons communicate across synapses.

• Excitatory: Increase the likelihood that the receiving neuron will fire.

• Inhibitory: Decrease the likelihood of firing.

Types of Neurotransmitters

• Dopamine: Pleasure, reward, voluntary movement, attention.

  • Deficit: Parkinson’s disease

  • Excess: Schizophrenia symptoms

• Serotonin: Mood regulation, sleep-wake cycles, appetite, emotional memory.

  • Deficit: Depression, anxiety

• Acetylcholine: Control of movement, learning, and memory.

• GABA: Inhibitory, dampens neural activity.

• Glutamate: Excitatory, learning and memory.

Neurotransmitter Fate: Release, Reuptake, and Drugs

• Release: Action potential triggers neurotransmitter release into the synaptic cleft.

• Reuptake: Neurotransmitters are reabsorbed by the presynaptic neuron.

  • Some drugs (e.g., cocaine) block reuptake, prolonging effects.

• Agonists: Mimic or enhance neurotransmitter action.

• Antagonists: Block or dampen neurotransmitter action.

Glutamate and GABA

• Glutamate: Most common excitatory neurotransmitter in the CNS.

• GABA: Most common inhibitory neurotransmitter; less brain activity.

• Drugs:

  • Caffeine: Increases glutamate, decreases GABA.

  • Alcohol: Increases GABA, decreases glutamate.

Brain Structure and Function

Major Regions of the Brain

• Hindbrain: Controls basic functions like breathing and sleeping.

  • Medulla: Vital functions (breathing, heart rate).

  • Pons: Sleep and arousal.

  • Cerebellum: Motor coordination and timing.

  • Reticular Activating System: Regulates sleep and wakefulness.

• Midbrain: Relays information between the eyes, ears, and brain.

• Forebrain: Manages complex cognitive activities, sensory and associative functions, and voluntary motor activities.

  • Cerebral Cortex: Higher mental processes (reasoning, self-awareness).

  • Consists of two hemispheres (four lobes each) connected by the corpus callosum.

Cerebral Cortex: Lobes and Lateralization

• Frontal Lobes: Planning, executive functions, motor control.

• Broca’s Area: Language production.

• Motor Cortex: Controls voluntary movement.

• Prefrontal Cortex: Thinking, planning, judgment.

• Parietal Lobes: Sensory information, spatial awareness.

• Temporal Lobes: Hearing, language, autobiographical memory.

• Occipital Lobes: Vision processing, recognition of complex shapes.

Left vs. Right Hemisphere Functions

Left Hemisphere	Right Hemisphere
Fine-tuned language skills (speech, reading, writing)	Coarse language skills (simple speech, tone of voice)
Making facial expressions, motion detection	Visuospatial skills, face perception

Split Brain Surgery

• Procedure to sever the corpus callosum, often used to treat severe epilepsy.

Phineas Gage: Prefrontal Cortex Damage

• Railroad foreman injured in 1848; tamping iron passed through his head.

• Damage to prefrontal cortex led to changes in personality and judgment.

The Psychopathy Connection

• Prefrontal cortex damage linked to impaired judgment, emotional regulation, and empathy.

• Brain imaging shows reduced activity in PFC in people with psychopathic traits.

Neural Plasticity

Plasticity in Action

• Brain’s ability to change structure and function in response to experience.

• Observed in children of Holocaust survivors, Vietnam veterans, and trauma survivors.

• Trauma can affect brain structure and function across generations.

Limbic System and Emotional Processing

Limbic System Components

• Emotional Center: Involved in motivation, emotion, and memory.

• Amygdala: Triggers fear or aggression.

• Hippocampus: Forms new long-term memories.

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

Brain Mapping and Measurement Techniques

Polygraph

• Measures physiological responses (e.g., skin response, heart rate) to detect deception.

Brain Mapping Methods

• Phrenology: Early method using skull shape to infer brain size and cognitive function (discredited).

• Brain Damage Studies: Observing function loss in people with brain damage to infer brain function.

• CT Scan: Uses x-rays to create images of brain structures.

• PET Scan: Monitors brain activity using radioactive substances.

• MRI/fMRI: Uses magnetic fields to produce images and measure activity.

• EEG: Records electrical activity via scalp electrodes.

• Deep Brain Stimulation (DBS): Implants electrodes to modify brain function (used for Parkinson’s, depression).

• Transcranial Magnetic Stimulation (TMS): Uses magnetic fields to enhance or interrupt brain function.

Brain Injury and Disorders

Concussion

• A concussion is a traumatic brain injury that affects brain function.

Toxoplasmosis

• Caused by a parasite; can affect brain responses and personality.

Summary Table: Key Neurotransmitters

Neurotransmitter	Main Function	Associated Disorders
Dopamine	Pleasure, reward, movement	Parkinson’s (deficit), Schizophrenia (excess)
Serotonin	Mood, sleep, appetite	Depression (deficit)
Acetylcholine	Movement, learning, memory	Alzheimer’s (deficit)
GABA	Inhibitory, reduces activity	Anxiety (deficit)
Glutamate	Excitatory, learning, memory	Schizophrenia (excess)

Additional Info

• Neurotransmission is essential for all brain functions, including sensation, movement, emotion, and cognition.

• Brain plasticity allows for learning and adaptation throughout life, though it decreases with age.

• Brain mapping technologies are crucial for diagnosing and treating neurological disorders.