1.4 Biological Bases of Behaviour

Genetic Predisposition

Increased chances of developing a certain specific trait or condition due to genetic code.

  • Researchers try to determine how much of nature/nurture contributes to human traits

Every human cell has 46 chromosomes in 23 pairs.

  • They are made up of Deoxyribonucleic Acid (DNA)

  • Certain parts of DNA control production of specific proteins that control some human traits → “genes”

  • Can be dominant or recessive

    • Two recessive genes for a trait are expressed

    • In any other combination of genes, the dominant one’s trait is expressed

Identical twins, aka monozygotic twins

  • Share identical genetic material

  • Thomas Bouchard → 100+ identical twins

    • Correlation coefficient of IQ → 0.69 raised apart, 0.88 raised together

    • Environment has some effect, but still highly correlated, so genes have effect on IQ as well

    • Similar physical appearance → treated the same? → same psychological environment → attributed to genetic influence?

Chromosomal Abnormalities

  • Our sex is determined by our 23rd pair of chromosomes

    • Males → XY, females → XX

  • Sometimes chromosomes will combine/fail to combine

    • Turner’s syndrome → single X chromosome where there’s supposed to be XX/XY

      • Short stature, webbed necks, different physical sexual development

    • Klinefelter’s syndrome → extra X chromosome → XXY

      • Minimal sexual development and extreme introversion

      • Symptoms vary greatly

    • Down syndrome → extra chromosome on 21st pair

      • Rounded face, shorter fingers/toes, intellectual disabilities

Neurons

  • Dendrites are root/treelike parts of the cell that stretch from the cell body and receives signals

    • They grow to make synaptic connections with other neurons

    • Takes in info from other neurons

  • Cell body (soma) contains nucleus, and helps maintain the cell

  • Axon travels from the soma to axon terminals

  • Myelin sheath is a fatty covering that surrounds the axon of some neurons that speed up neuron impulses

    • Multiple Sclerosis (MS) occurs when the myelin sheath gets damaged or destroyed, which interferes with neural transmission and can result in poor coordination and numbness.

  • Terminal buttons are the branched end of the axon that contain neurotransmitters

  • Neurotransmitters are the chemicals contained in terminal buttons that enable neurons to communicate, they act as a chemical signal when binded

  • Synapses are the gaps between the terminal buttons of one neuron and the dendrites of the next neuron.

When a neuron is at rest/in its resting stage, it’s called a resting potential.

  • Overall slightly negative charge (-70 mV (megavolts)) because mostly anions are in the cell and mostly cations surround it.

  • The cell membrane is selectively permeable and works to maintain an approximately -70 mV charge.

A reaction begins when terminal buttons of neuron A are stimulated and release neurotransmitters into the synapse.

  • These neurotransmitters fit into receptor sites on the dendrites of neuron B. If enough neurotransmitters are received (threshold), then the cell membrane of neuron B becomes permeable. Positive ions rush int o the cell, which brings the charge within the ion to approximately +40 mV.

  • This change in charge speeds down the length of neuron B. This electric message is called an action potential, which is approximately 120 m/s.

  • Neurons either fire, or don’t. This is called the all-or-none principle.

A neuron’s impulse is the same everytime.

  • Depolarization: the cell’s original charge becomes “depolarized” when positive ions rush into the cell.

    • Changes overall charge from negative (-70 mV) to positive (+40 mV).

Neurotransmitters

  • Some neurotransmitters are excitatory (excite the next cell into firing) and some are inhibitory (inhibit the next cell into firing).

  • Dopamine

    • Motor movement, attention, alertness, emotion, learning

    • Deficit → Parkinson’s disease

    • Excess → Schizophrenia

  • Serotonin

    • Mood control, hunger, sleep, arousal

    • Deficit → Clinical depression

    • Excess → Hallucinations

  • Norepinephrine

    • Alertness, arousal

    • Deficit → Depression

    • Excess → Anxiety

  • Glutamate

    • Excitatory neurotransmitter, memory, learning

    • Excess → Migraines, seizures

  • GABA (Gamma-amino butyric acid)

    • Major inhibitory neurotransmitter

    • Deficit → Anxiety, epilepsy

    • Excess → Sleep disorders

  • Endorphins

    • Natural painkillers

    • Involved in addictions

  • Substance P

    • Pain perception

    • Intense or lack of pain perception

  • Acetylcholine (ACh)

    • Motor movement, muscle action

    • Deficit → Alzheimer’s, myasthenia gravis

Nervous Systemxt

Nervous System Organization

  • Sensory neurons (afferent neurons) take information from the senses to the brain

  • Motor neurons (efferent neurons) take information from the brain to the rest of the body

  • Interneurons (association neurons) take the information that reaches the brain/spinal cord and sends them elsewhere in the brain/on to efferent neurons

Central Nervous System

  • Contains the brain and the spinal cord

  1. Getting snack

  2. Stubs toe

  3. Sensory neurons in toe are activated

  4. Message sent up from a neuron to base of spine (afferent neurons)

  5. Spinal cord

  6. Brain’s sensory cortex

  7. Motor cortex sends signal down your spinal cord

  8. Muscles controlling leg and food (efferent neurons)

  9. “Ouch!”

  • Most sensory information and muscle movements are controlled by the above statement/process

  • Certain reactions occur the moment sensory impulses reach your spinal cord (reflexes)

    • Heat, cold, knee reflexes

    • Has adaptive value, helps us survive

Peripheral Nervous System

  • All the nerves in your body that aren’t part of the CNS

  • All nerves not encased in bone

  • Somatic nervous system controls voluntary muscle movements

  • Motor cortex of brain sends impulses to SNS, controls muscles

    • Playing sports, writing, anything you wnat to do

  • Autonomic nervous system controls the automatic functions of our body

    • Heart, lungs, internal organs, glands, stress

    • Sympathetic Nervous System (flight/fight) mobilizes our body to respond to stress

      • Accelerates some functions such as heart rate, blood pressure, respiration, and slows down some such as digestion

    • Parasympathetic Nervous System (rest and digest) slows us down, returns body to homeostasis after a stress response

      • The “break pedal”

      • Slows down heart rate and breathing, pupils constrict, blood flows to intenstine

Endocrine System

  • A system of glands that secrete hormones

  • Adrenaline (epinephrine) → activated during fight/flight, speeds up bodily processes

  • Leptin → involved in weight regulation, surpresses hunger

  • Ghrelin → motivates eating, increases hunger

  • Melatonin → triggers sleep/wakefulness responses

  • Oxytocin → “love hormone,” promotes trust, bonding, love, etc.

How Do Researchers Study the Brain?

  • Accidents (ex. Phineas Gage)

  • Lesions → the removal/destruction of part of the brain

    • We can examine and closely monitor the patient’s behaviour after

    • Ex. frontal lobotomy

  • Electroencphalogram (EEG) → electrodes on the scalp

    • Detects brain waves (alpha, beta, theta, delta); usually a series of lines with distinct patterns

    • Used to investigate sleep disorders, dreaming, seizures, epilepsy

  • Computerized Axial Tomography (CAT/CT Scan) → a sophisticated xray

    • Xray cameras that rotate around the brain

    • 3D picture of the brain’s structure, no function or activity

    • Exposed to carcinogenic radiation

CT Scan

  • Magnetic Resonance Imaging (MRI) → uses magnetic fields/radio waves to measure density and location of brain material

    • More detailed

MRI

  • Positron Emission Tomography (PET) → sees which parts of the brain are most active during certain tasks

PET

  • Functional MRI (fMRI) combines MRI and PET scans, and can show details of brain structure and blood flow information