Biological Bases of Behavior

Monozygotic vs. Dizygotic

Monozygotic=identical twins; most share a placenta

Dizygotic=fraternal twins; no more different than siblings

Twin studies

• Helps with understanding of nature vs. nurture (monozygotic twin studies)

• Genetic findings: twins have more similarity in personality, tastes, abilities, attributes, higher concordance rates with mental health issues in monozygotic twins

• Many adoption studies done

• Environmental findings: parenting can impact some factors (attitudes, politics, education, faith, etc.); trauma/stress & poverty in the family matters

Interaction & Epigenetics

• Interaction between nature & nurture (ex.: genetics & stress’s impacts on mental health); risk, protective benefits, etc.

• Epigenetics=area of scientific research that studies how environment can influence genetic expression by “turning off or on” genes or impacting which are expressed/inhibited

Nervous System

Involved in EVERY function of human body

Soma

Part of a neuron; the cell body that contains DNA (NOT TESTED)

Dendrite

Part of a neuron; receives messages & can grow to make connections w/ other neurons (NOT TESTED)

Axon

Part of a neuron; sends a message (NOT TESTED)

Synapse

Part of a neuron; gaps between neurons (NOT TESTED)

Terminal

Part of a neuron; receives electrical impulses & sends chemical ones (electrical messages travel in neurons; chemical messages travel between neurons) (NOT TESTED)

Myelin

Part of a neuron; fatty substance that insulates & allows for faster transmission of messages (NOT TESTED)

Nodes of Ranvier

Part of a neuron; gaps of exposed axons where action potential is transmitted (NOT TESTED)

Neurotransmitters

Part of a neuron; chemical messages sent between neurons (NOT TESTED)

Multiple Sclerosis

Immune system attacks protective myelin sheaths that cover nerve fibers, causing communication issues between brain & body; eventually can cause permanent damage/deterioration of nerve fibers

Motor neuron

OUTPUT from brain & spinal chord to muscles & glands

Sensory neuron

INPUT from sensory organs to brain & spinal chord

Interneurons

Carry info between each other & found only in the brain & spinal chord; involved in complex functions such as the reflex arc; acts as a “go between” between sensory & motor neurons

Glial cells

Hold neurons in place & provide them w/ nutrients; acts as the “glue” of the nervous system; functions in myelination, cleaning up debris, structural/nutritional support, etc.; there are 10-50 glial cells per neuron

Neuron firing

Occurs when an electrical signal is passed along the axon, resulting in the release of neurotransmitters from terminal button

1. Neurotransmitter messages gathered by dendrites & cell body

2. Messages transmitted along axon in brief electrical impulse (action potential)

3. Causes release of chemicals (neurotransmitters) into synaptic gap where other neurons’ dendrites can receive it

4. Any excess neurotransmitter is reabsorbed in reuptake

Action potential

Electrical impulse that travels along a neuron’s axon

Reuptake

Process by which neurons can reabsorb excess neurotransmitter

Threshold

Lvl of stimulation needed to trigger a neural impulse

• Strength of stimulus does NOT affect impulse’s speed

• Strong stimulus can trigger more neurons to fire more often

• Thicker axons are faster

• Myelinated axons are faster (impulse jumps “bump to bump”)

Excitatory vs. Inhibitory signals

Excitatory=increases likelihood of neuron firing

Inhibitory=decreases likelihood of neuron firing

• Each type affects polarization

Polarization

Differential electrical charge inside & outside neuron

Stimulus threshold

When a neuron reaches its stimulus threshold, it is sufficiently stimulated & the axon depolarizes, beginning action potential; sodium ions rush in & potassium ions rush out, continuing down length of axon

Resting potential

While waiting for sufficient stimulation, neurons are at their resting potential

• Electrical charge of a neuron when it’s not active

• When not active, fluid inside & outside of neuron are not in balance

• Inside=negative ions; outside= positive ions

All or None Principle

A neuron fires or it does not

Refractory Period

Follows action potential; neuron is unable to fire and must re-polarize to establish resting potential

Acetylcholine (Ach)

Type of neurotransmitter; main functions include enabling muscle action, learning, memory

Alzheimer’s

Ach-producing neurons deteriorate

Myasthenia Gravis

Ach receptor sites are blocked, causing symptoms such as impaired movement, impaired vision, impaired breathing, excessive fatigue, etc.

Dopamine

Type of neurotransmitter; main functions include reward/pleasure & motivation

Parkinson’s

• Occurs when one has too little dopamine

• Symptoms include loss of control over muscle movement, etc.

Schizophrenia

• Occurs when one has too much dopamine

• Symptoms include hallucinations, delusions inappropriate emotions, etc.

• Antipsychotics are used to treat Schizophrenia, reducing dopamine levels, BUT this can lead to Parkinson’s-like symptoms

Serotonin

Type of neurotransmitter; main functions include links to emotional state, appetite, arousal, sleep, impulse control; related to depressive disorders (anti-depressants often increase serotonin levels)

Norepinephrine

Type of neurotransmitter; main functions include speeding heart rate, raising BP, involvement in general arousal; linked to bipolar/depressive disorders

Endorphins

Type of neurotransmitter; main functions include relieving pain & increasing sense of wellbeing; linked to runners high

GABA

Type of neurotransmitter; called Gamma Aminobutyric Acid; main functions are inhibitory; linked to anxiety & intoxication

Glutamine

Type of neurotransmitter; main functions are excitatory and include links to learning, strengthening synaptic connections; disruption leads to MS

Substance P

Type of neurotransmitter; main function includes pain perception

Agonists

Type of drug; enhances neurotransmitter function; increases neurotransmitter synthesis/release; mimics; blocks reuptake

Ex.: L-dopa releases dopamine (used to treat Parkinson’s); LSD mimics serotonin, causing abnormal brain cell activities, leading to hallucinations, perpeption distortion, etc.; black widow venom increases Ach release, causing violent muscle contractions

Antagonists

Type of drug; inhibits neurotransmitter function; blocks neurotransmitter synthesis/release; blocks receptor sites

Ex.: herbal poisons affect Ach and can cause paralysis; alcohol inhibits glutamine, making it hard for glutamine to excite nervous system (depressant)

Nervous system structure

Central Nervous System (CNS)

Brain & spinal chord

Peripheral Nervous System (PNS)

Transmits messages to/from CNS; without it, our brains would be isolated from the world; has 2 parts: somatic, autonomic

Somatic

Part of PNS; consists of sensory & motor neurons; transmits (sights, sounds, smells, body temp., body pos., etc.) & sends (purposeful body movements such as winking, running, posture, balance, raising hands, etc.) messages to/from body;

Autonomic

Part of PNS; deals with automatic functions (heartbeat, respiration, digestion, eye dilation, etc.); has 2 parts: sympathetic, parasympathetic (often have opposite effects/balance each other out)

Parasympathetic

Part of autonomic section of PNS; replenished energy (slows us down); promotes hunger, digestion, relaxation (decreases heart rate, BP, etc.), etc.

Sympathetic

Part of autonomic section of PNS; expends energy (fight or flight); promotes fear (increases heart rate, BP, etc.), inhibits digestion, etc.

Phineas Gage

A railroad worker who suffered major brain damage to his frontal lobe in a freak accident during which an iron rod pierced his skull; Gage survived but his personality had changed; Gage had become more irritable, profane, and dishonest, causing him to eventually lose his job

The Brain (interesting facts/details)

• Brain is about the size of a large grapefruit

• Weighs just over 3 lbs

• Consists of over 86 billion neurons

• Each neuron is linked to 10,000 other neurons

Forebrain

Outermost layer of brain (NOT TESTED)

Midbrain

Relay station processing visual/auditory info (NOT TESTED)

Hindbrain

Automatic functions (NOT TESTED)

Pons

Part of hindbrain; deals with sleep, left-right coordination

Medulla

Part of hindbrain; deals with vital life functions (breathing, heartbeat, etc.)

Cerebellum

Part of hindbrain; coordinates movement, balance, posture

Reticular Formation (Reticular Activating System)

Part of hindbrain; deals with attention, alertness, arousal

Cerebral Cortex

Part of forebrain; deals with sophisticated mental functions; devised into 4 lobes & 2 hemispheres (each hemisphere controls opposite side of body)

Corpus Callosum

Part of forebrain; thick band of axons connecting 2 hemispheres of cerebral cortex

Left Hemisphere

Left hemisphere of cerebral cortex; deals with language (speech, writing, etc.), logic, math, sequentiality, chronology, order, etc.

Right Hemisphere

Right hemisphere of cerebral cortex; deals with emotion, creativity, spatial relationships, pattern recognition, art, music, some math reasoning (geometry, etc.), etc.

Split brain

When the corpus callosum is severed (often done for people who get seizures from epilepsy or other diseases; prevents electrical signals from spreading to both hemispheres of the brain and lessens seizure prevalence); ultimately prevents the two sides of the person’s brain from communicating, making it so that each side of the body can appear to be controlled by a separate being in certain cases

Frontal Lobe

Lobe of cerebral cortex; deals in reasoning, planning, speech, movement, critical thinking

Temporal Lobe

Lobe of cerebral cortex; deals in hearing, memory

Parietal Lobe

Lobe of cerebral cortex; deals in perception of touch-based info (pressure, temp., pain, etc.)

Occipital Lobe

Lobe of cerebral cortex; deals in visual info

Motor Cortex

A strip located in frontal lobe; registers motor info/movement

Sensory Cortex

A strip located in parietal lobe; registers sensory info

Broca’s Area

Deals in speech production

Wernicke’s Area

Deals in understanding speech (interpreting auditory code)

Angular Gyrus & Visual Cortex

Deal in reading/seeing words

Aphasia

Partial/complete inability to articulate ideas/understand language due to brain injury/damage

Broca’s Aphasia

Inability to produce speech BUT ability to understand it

Wernicke’s Aphasia

Inability to understand speech BUT ability to say things; what people say often doesn’t make sense (“word salad”)

Limbic System

Deals in motivation, emotion, memory

Amygdala

Part of limbic system; almond-shaped structure; involved in emotion & memory (usually negative emotions such as anger, fear, etc.)

Hippocampus

Part of limbic system; wishbone-shaped structure; involved in forming new memories (long-term)

Hypothalamus

Part of limbic system; peanut-sized structure; maintains homeostasis; links endocrine system to brain; involved in motivation & emotional drives (hunger, thirst, sex, body temp. reg., etc.)

Thalamus

Part of limbic system; processes & integrates info from all senses EXCEPT smell & relays info to appropriate higher brain centers