Chapter 6 – Biological Bases of Mental Life & Behaviour

Learning Outcomes

• After mastering this chapter you should be able to …

  • 6.1 Describe the basic units of the nervous system

  • 6.2 Describe the major structures & functions of the endocrine system

  • 6.3 Explain subdivisions of the peripheral nervous system

  • 6.4 Describe major structures & functions of the CNS

  • 6.5 Explain relative roles of genetics & environment in psychological functioning

Big-Picture Concept Map

• Two biological message-systems

  • Nervous system: fast, electro-chemical, point-to-point

  • Endocrine system: slower, hormonal, broadcast via bloodstream

• Nervous system is split into

  • Central (CNS) → brain & spinal cord

  • Peripheral (PNS) → somatic & autonomic (sympathetic/parasympathetic)

• Behaviour arises from interaction of neurons, hormones, environment & genes

Case Anchor – Neale Daniher & Motor Neurone Disease (MND)

• Illustrates: motor neuron degeneration → loss of skeletal-muscle control

• Average survival ~ 27 months; Daniher lived far longer

• Ethical / philosophical angle: attitude & purpose may alter coping, perhaps progression; emphasises need to understand neural basis of behaviour

Neurons – Basic Units (LO 6.1)

Types of Neurons

• Sensory (afferent): receptor ⇒ CNS

• Motor (efferent): CNS ⇒ muscles/glands

• Interneurons: connect other neurons; majority in brain & spinal cord

Anatomy

• Dendrites: receive graded inputs

• Cell body (soma): nucleus w/ DNA

• Axon: conducts AP; may be >1 m long; branches (collaterals)

• Myelin sheath (lipid, nodes of Ranvier) → saltatory conduction, increase speed, decrease crosstalk

  • Developmental: unmyelinated in infants (poor motor control); demyelination (e.g., MS) → jerky movement

• Terminal buttons: hold synaptic vesicles

• Synapse: presynaptic membrane, 20-40 nm cleft, postsynaptic membrane

Electrical Events

• Resting potential ~ -70 mV (inside negative; maintained by Na+/K+ pumps)

• Graded potentials: small EPSPs (depolarisation) / IPSPs (hyperpolarisation); additive & decremental

• Threshold ~ -50 mV → Action potential: all-or-none spike to +40 mV, lasts < 2 ms

• AP propagates node-to-node in myelinated axons

Chemical Transmission

• AP triggers vesicle fusion → neurotransmitter release

• NT binds receptor → new graded potential

• Sequence: Rest → Depolarise → Graded → AP → NT → next cell (See Table 6.1)

Major Neurotransmitters

• Glutamate: main excitatory; LTP, learning; excess → excitotoxicity (Huntington’s, Alzheimer’s)

• GABA: main inhibitory; anxiety regulation; agonists = benzodiazepines, alcohol

• Dopamine (DA): movement (substantia nigra → basal ganglia); reward & addiction; high = schizophrenia; low = Parkinson’s; L-Dopa crosses BBB

• Serotonin (5-HT): mood, sleep, appetite; low = depression; SSRIs increase 5-HT

• Acetylcholine (ACh): muscle contraction, learning, memory; loss = Alzheimer’s; nicotine agonist

• Endorphins: endogenous opioids; pain relief, euphoria; ‘runner’s high’, acupuncture

• Epinephrine/NE: hormone & NT; arousal, fear; fight-or-flight

• Modulatory NTs: diffuse, prolong/inhibit other NT action

Endocrine System (LO 6.2)

• Nature: duct-less glands → hormones → blood → widespread receptors

• Pituitary (master): releases trophic hormones; interface w/ hypothalamus

• Thyroid: metabolism, growth; hypo-thyroid mimics depression

• Adrenals (above kidneys): adrenaline, cortisol; emergency energy mobilisation

• Pancreas: insulin/glucagon → blood glucose

• Gonads: testes → testosterone; ovaries → estrogens; drive, secondary sex features

• Oxytocin: neurotransmitter & hormone; bonding, lactation; possible social-deficit therapy

Peripheral Nervous System (LO 6.3)

Somatic Division

• Sensory input ↔ motor output to skeletal muscles

• Voluntary + posture adjustments; reflex arcs (2-neuron monosynaptic e.g., patellar)

Autonomic Division

• Sympathetic: threat → fight/flight; increase HR, dilated pupils, inhibits digestion

• Parasympathetic: routine maintenance; rest & digest; restores equilibrium

• Systems act antagonistically → homeostasis

Central Nervous System (LO 6.4)

Evolutionary Perspective

• Primitive brainstem = hindbrain + midbrain + forebrain nuclei

• Progressive layering: spinal reflexes → brainstem vital control → cerebellum (movement) → cerebrum & cortex (complex cognition)

Spinal Cord

• Segmental; dorsal sensory / ventral motor; 31 pairs spinal nerves

• Functions: reflexes, sensory relay to brain, motor commands from brain

• Lesion level predicts paralysis/anesthesia level

Hindbrain

• Medulla: heartbeat, respiration; decussation of motor/sensory tracts

• Pons: bridge; breathing rhythms, sleep & dreaming

• Cerebellum: coordination, balance, implicit learning; alcohol effects

• Reticular formation: arousal, consciousness; damage → coma

Midbrain

• Tectum: superior & inferior colliculi – orienting to visual/auditory stimuli; blindsight

• Tegmentum: includes substantia nigra (DA); movement, reward, aversion circuits

Forebrain

Diencephalon

• Hypothalamus: drives (hunger, thirst, sex), homeostasis, links endocrine via pituitary, stress response

• Thalamus: sensory relay & filter; attentional gateway; input from RF

Limbic System

• Septal area: reward, maternal defence, pain relief learning

• Amygdala: fear, emotional tagging of memories, recognition of threat; childhood trauma ↔ reduced volume

• Hippocampus: declarative memory encoding; H.M. case; neurogenesis site

Basal Ganglia

• Caudate, putamen, globus pallidus; initiate/inhibit movement; habits & automatic judgments; dysfunction → Parkinson’s, Huntington’s, motor tics & social-cognitive deficits

Cerebral Cortex

General Features

• 3-mm grey matter; gyri & sulci increase surface area

• Functions: sequence voluntary acts, fine sensory discriminations, symbolic thought

• Primary areas: raw sensory/motor

• Association areas: perception, ideas, planning (experience-dependent plasticity)

Lobes (both hemispheres)

• Occipital: vision; damage → cortical blindness

• Parietal: somatosensory cortex behind central fissure; touch maps; spatial cognition; neglect if damaged

• Frontal: motor cortex (anterior to central fissure), Broca’s area (speech production/grammar), executive functions, personality; lesions → apathy, disinhibition (Phineas Gage)

• Temporal: primary auditory cortex; Wernicke’s area (comprehension); ventral ‘what’ visual processing; right-temporal → music/faces; anterior temporal stores conceptual knowledge

Somato- & Motor Maps

• Cortical space is proportional to receptor / motor unit density → hands & face huge; back tiny

Neuroplasticity & Neurogenesis

• Brain rewires across lifespan; evidenced by:

  • Sensory deprivation/retraining studies

  • Recovery after injury; functional re-assignment

  • Adult hippocampal neurogenesis (Eriksson et al.)

• Applications: brain-based education, mindfulness, cognitive rehab, prosthetics & sensory substitution (cochlear implant, vision-to-touch devices)

• Debates: technology over-use & maladaptive plasticity; ethical aspects of stem-cell implants

Cognitive Neuropsychology

• Infers normal cognition from deficits (Broca, Wernicke, H.M.)

• Double dissociations map functions; guides rehab & models of reading, memory, etc.

Cerebral Lateralisation & Split-Brain Research

• Left: language, logic, analytic, positive affect

• Right: visuospatial, face/music, negative affect

• Corpus callosum connects; split-brain → independent hemispheric awareness (e.g., key flashed LVF → left hand picks up key but cannot name)

• Emotional laterality: left-frontal approach/positive, right-frontal withdrawal/negative

Genetics, Brain & Behaviour (LO 6.5)

Basic Genetics

• Humans: 46 chromosomes (23 pairs); genes encoded in DNA

• Genotype → hereditary blueprint; Phenotype → observable trait

• Degree of relatedness r: parent/child = 0.5; MZ twins = 1; DZ = 0.5; grandparent = 0.25

Behavioural Genetics Methods

• Twin, adoption, family & molecular studies

• Heritability coefficient (h^2): proportion of phenotypic variance due to genetic variance (population statistic, 0 <= h^2 <= 1)

• Findings:

  • IQ h^2 ~ 0.5

  • Personality traits h^2 = 0.15-0.5 (neuroticism, extraversion, etc.)

  • Divorce proneness, job satisfaction, religiosity show genetic components

• Gene–environment interaction: genes set potential; environment triggers/expresses; e.g., PKU diet, stress hormones & depression genetics

Human Genome Project

• Mapping 3 billion base pairs → identifies polymorphisms linked to schizophrenia, cancer, etc.

• Raises ethical, social, legal issues (privacy, discrimination)

Ethical, Philosophical & Practical Implications

• Can psychological states be reduced to neural events? No – insight comes from integrating biological with experiential levels

• Responsibility & brain damage: Phineas Gage, frontal injury patients – legal & moral debates

• Therapist use of brain-based explanations to motivate clients (neuroplasticity as empowerment)

Cross-Lecture / Real-World Connections

• Chapter 5: Neuroimaging techniques used to localise functions (PET, fMRI)

• Chapter 7: Blindsight, sensory processing streams

• Chapter 8/9: Dopamine & reward learning; classical & operant conditioning

• Chapter 13: Hypothalamic control of hunger, homeostasis, positive emotion

• Chapter 18/19: Neurotransmitters & psychopathology (schizophrenia ↔ DA/glutamate; depression ↔ 5-HT)

Key Numbers & Formulae

• Resting potential V_rest ~ -70 mV

• Threshold for AP V_th ~ -50 mV

• Action potential peak ~ +40 mV

• Heritability coefficient range 0 <= h^2 <= 1

• Degree of relatedness (examples):

  • Parent–child r = 0.5

  • MZ twins r = 1

  • Grandparent r = 0.25

Study Tips & Mnemonics

• "SAME" – Sensory =Afferent, Motor =Efferent

• "PAD THA(B)I LOBES" – Parietal, Auditory (Temporal), Dorsal (occipital behind), THAlamus, Basal ganglia, LIMBIC, OCCIPITAL, BRAINSTEM, ENDocrine

• For neurotransmitters: "Do SALEM GeNe" – Dopamine, Serotonin, Acetylcholine, (L-)Endorphins, Monoamines (Epi/NE), Glutamate, GABA

Recap Checklist

• [ ] Draw & label a neuron; annotate ionic changes during AP

• [ ] Compare sympathetic vs parasympathetic effects on 5 organs

• [ ] List four lobes & one key function each

• [ ] Explain L-Dopa rationale & side-effects

• [ ] Define heritability vs genetic determinism

• [ ] Describe split-brain key experiment & findings