Unit I: Biological Bases of the Brain

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Central Nervous System (CNS)

The CNS is the control center for all mental processes (memory, emotion, problem-solving) and voluntary/involuntary behaviors.

Central Nervous System (CNS) Spinal

The spinal cord carries messages between the brain and body and controls reflexes.

Central Nervous System (CNS) brain

The brain processes information, makes decisions, controls thoughts, emotions, and actions.

Peripheral Nervous System (PNS)

All nerves outside the brain and spinal cord.
Links the CNS to the rest of the body.

Connection to behavior:
Allows the body to sense the world and take action (movement, touch, pain, organ function).

Somatic Nervous System

Part of the PNS that controls voluntary movements and skeletal muscles.
Also carries sensory information (touch, pain, temperature) to the CNS.

Behavior connection:
Walking, writing, reaching, speaking, and all intentional movement rely on the somatic system.

Autonomic Nervous System (ANS)

Controls automatic, involuntary functions such as heart rate, breathing, digestion, and blood pressure.

Sympathetic Nervous System

Activates the body for fight-or-flight:

• increases heart rate

• dilates pupils

Parasympathetic Nervous System

Activates rest-and-digest:

• slows heart rate

• increases digestion

Endocrine System

A slow chemical communication system that uses hormones released into the bloodstream.

Connection to behavior:
Regulates mood, growth, metabolism, stress, sexual behavior, and long-term body processes.

Hypothalamus

A brain structure that links the nervous system to the endocrine system.
Controls hunger, thirst, body temperature, and triggers the pituitary gland.

Behavior connection:
Motivation (eating, drinking), stress regulation, and maintaining homeostasis

Pituitary Gland (“Master Gland”)

Controlled by the hypothalamus; releases hormones that regulate growth and control other endocrine glands.

Behavior connection:
Growth disorders, stress responses, reproductive behavior, and metabolism regulation.

Hormones

Chemical messengers released by glands into the bloodstream that influence emotion, behavior, mood, arousal, and development.

Adrenaline (Epinephrine)

Released by the adrenal glands during stress.
Increases heart rate, energy, and alertness.

Behavior connection:
Triggers fight-or-flight, heightens arousal, improves reaction time in danger.

Oxytocin

Released by the hypothalamus/pituitary.
Involved in bonding, trust, childbirth, and emotional connection.

Behavior connection:
Supports attachment, empathy, social bonding, and romantic/parental behavior.

Estrogen

Primary female sex hormone; regulates menstrual cycle and reproductive development.

Behavior connection:
Influences mood, sexual behavior, memory, and emotional regulation.

Testosterone

Primary male sex hormone (also present in females).
Linked to muscle development, sex drive, and aggression.

Behavior connection:
Affects risk-taking, competitiveness, motivation, and libido.

Glial Cells

Support cells that nourish neurons, remove waste, provide insulation (myelin), and help maintain the neural environment.

Neurons

Specialized nerve cells that receive, process, and transmit information through electrical and chemical signals.

Reflex Arc

A simple, automatic response that occurs without conscious brain involvement.
Sensory neuron → interneuron (spinal cord) → motor neuron → reflex movement.

Sensory Neurons (Afferent)

Carry incoming information from sensory receptors → CNS.

Motor Neurons (Efferent)

Carry outgoing instructions from CNS → muscles and glands.

Interneurons

Found in the brain/spinal cord; connect sensory and motor neurons and allow for processing and reflexes.

Neural Transmission

The process by which neurons send signals:

1. Electrical (action potential down the axon)

2. Chemical (neurotransmitters crossing synapse)

All-or-Nothing Principle

A neuron either fires completely or does not fire at all; intensity is based on the number of neurons firing, not strength.

Action Potential

A brief electrical impulse that travels down the axon when the neuron fires.

Depolarization

When positively charged ions (Na+) enter the neuron, making the inside less negative and triggering the action potential.

Refractory Period

A short recovery time after a neuron fires when it cannot fire again immediately.

Resting Potential

The neuron’s stable, negative charge when inactive

Reuptake

The process where neurotransmitters are reabsorbed by the presynaptic neuron after crossing the synapse.

Firing Threshold

The level of stimulation required to cause a neuron to fire an action potential.

Multiple Sclerosis (MS)

A disease in which the body’s immune system damages myelin, slowing communication and causing muscle weakness and coordination problems.

Myasthenia Gravis

An autoimmune disorder where the immune system attacks acetylcholine receptors, leading to muscle weakness and fatigue.

Excitatory Neurotransmitters

Excitatory: Increase the likelihood that the next neuron will fire.

Inhibitory Neurotransmitters

Inhibitory: Decrease the likelihood of firing.

Dopamine

Involved in movement, reward, motivation.
Too little → Parkinson’s
Too much → schizophrenia symptoms

Serotonin

Regulates mood, sleep, appetite.
Low levels → depression

Norepinephrine

Controls alertness, arousal, stress response.
Low levels → depression
High → anxiety

Glutamate

Major excitatory neurotransmitter; involved in memory and learning.
Too much → migraines, seizures

GABA

Major inhibitory neurotransmitter; reduces anxiety, stops overactivity.
Low levels → anxiety, seizures

Endorphins

Natural painkillers; produce euphoria and reduce pain.

Substance P

Transmits pain signals to the brain.

Acetylcholine (ACh)

Involved in muscle movement, memory, learning.
Deficits → Alzheimer’s disease
Blocked → paralysis

Agonist

A drug that mimics or enhances a neurotransmitter by binding to its receptor.

Antagonist

A drug that blocks neurotransmitters from binding.

Reuptake Inhibitors

Drugs that block reuptake pumps, leaving more neurotransmitter in the synapse (e.g., SSRIs for serotonin).

Psychoactive Drugs

Substances that alter perception, mood, consciousness, and behavior by affecting neurotransmission.

Stimulants

Increase neural activity and arousal.
Examples: caffeine, nicotine, cocaine, amphetamines.
Effects: alertness, energy, elevated heart rate.

Depressants

Slow down the CNS.
Examples: alcohol, barbiturates, benzodiazepines.
Effects: relaxation, slowed reaction time, reduced inhibitions.

Hallucinogens

Distort perception and cause sensory distortions.
Examples: LSD, psilocybin, marijuana (THC).
Effects: altered consciousness, hallucinations.

Brainstem

The oldest part of the brain; responsible for basic survival functions such as heart rate, breathing, and arousal.

Medulla

Controls vital autonomic functions: breathing, heart rate, blood pressure.
Damage = death.

Reticular Activating System (RAS)

A network in the brainstem that controls alertness, arousal, and sleep–wake cycles.
Damage → coma.

Reward Center (Nucleus Accumbens)

Part of the limbic system that produces pleasure and reinforcement through dopamine release.

Cerebellum

Coordinates balance, posture, voluntary movement, and is important for automatic motor learning (e.g., riding a bike).

Cerebral Cortex

The outer layer of the brain; responsible for thinking, planning, language, memory, and consciousness.

Hemispheres

The left and right halves of the brain; each performs specialized functions but normally work together.

Limbic System

Includes the amygdala, hippocampus, hypothalamus; regulates emotion, memory, motivation, and drives.

Thalamus

The brain’s sensory relay station—sends incoming sensory information to the correct cortex (except smell).

Hypothalamus

Controls hunger, thirst, body temperature, sex drive, and regulates the endocrine system through the pituitary gland.

Pituitary Gland

The “master gland” of the endocrine system; releases hormones that regulate growth and influence other glands.

Amygdala

Processes fear, aggression, and emotional memories.

Hippocampus

Forms new explicit memories (facts & events).
Damage → anterograde amnesia.

Corpus Callosum

A thick band of fibers that connects the two hemispheres and allows communication between them.

Occipital Lobes

Responsible for visual processing (primary visual cortex).

Frontal Lobes

Involved in decision-making, planning, impulse control, personality.

Prefrontal Cortex

Controls judgment, reasoning, planning, and inhibition.

Motor Cortex

Controls voluntary movement.

Temporal Lobes

involved in hearing, language comprehension, memory, and face/object recognition.

Parietal Lobes

Process touch and body sensations.

Somatosensory Cortex

Registers touch, temperature, pressure, and pain.

Split Brain Research

Studies conducted on people whose corpus callosum was severed to reduce seizures. Revealed independence and specialization of hemispheres.

Specialization of Right Hemispheres

spatial ability, facial recognition, creativity, patterns.

Specialization of Left Hemispheres

language, logic, analytical thinking.

Broca’s Area

Controls speech production.
Damage → Broca’s aphasia (broken speech).

Wernicke’s Area

Controls language comprehension.
Damage → Wernicke’s aphasia (fluent but meaningless speech).

Aphasia

Language impairment resulting from brain damage (usually left hemisphere).

Test with Split Brain Patients

Information presented to the right visual field → processed by left hemisphere → can say what they saw.
Information to the left visual field → processed by right hemisphere → can draw or point, but not verbalize.

Contralateral Organization

The left brain controls the right side of the body, and vice versa.

Plasticity

The brain’s ability to reorganize or strengthen neural connections after trauma or learning. Greater in children.

EEG

Measures electrical activity of the brain. Useful for sleep studies and detecting seizures.

fMRI

Shows brain structure and activity by detecting changes in blood flow. Provides detailed real-time images.

Lesioning Procedure

Deliberate or accidental destruction of brain tissue to study its function.

Nature and Nurture

Nature = genes and biology
Nurture = environment and experience
Behavior reflects interaction between both.

Genes

:Units of heredity that code for traits.

Genome

: The complete set of genetic instructions for an organism.

Heredity

Passing of traits from parents to offspring through genes.

Mutation

A random genetic change that may be harmful, neutral, or beneficial.

Interaction

The idea that genes and environment work together to shape behavior.

Epigenetics

Environmental factors turn genes on or off without altering DNA sequence.

Behavior Genetics

The study of how genes and environment influence behavior.

Twin Studies

Compare identical (monozygotic) and fraternal (dizygotic) twins to estimate genetic influence on traits.

Adoption Studies

Compare adopted children to their adoptive vs. biological parents to separate environmental and genetic influences.

Genetic Predisposition

An increased likelihood of developing a trait or disorder due to inherited genes.

Evolutionary Perspective

Behavior is shaped by genes that improved survival and reproduction in our ancestors.

Eugenics

A harmful, unethical movement advocating controlled breeding to “improve” human genetics; rejected by modern psychology.

Natural Selection

The evolutionary process where traits that increase survival and reproduction become more common in a population.