Biological Bases

• Central Idea: Biological factors that influence human behavior

Main Branches:

1. Nervous System

• Central Nervous System

  • Consists of the brain and spinal cord

  • Receives, processes, interprets and stores incoming sensory information; sends out messages

• Peripheral Nervous System

  • Somatic

    • Connects to sensory receptors and to skeletal muscles

    • Afferent (incoming) nerves, Efferent (outgoing) nerves

  • Autonomic

    • Regulates the internal organs and glands

      • Sympathetic Nervous System

        • mobilizes bodily resources: increases output of energy, increase heart rate and diverts blood flow to muscles for exercise or emergency

      • Parasympathetic Nervous System

        • conserves bodily resources: conserves energy, promotes activity of digestive system and slows down heart rate

2. Neural Communication

Neurons

• a cell that conducts electrochemical signals

• Structure:

  • Dendrites: branching structures that receive signals from other cells

  • Cell Body (Soma): keeps the neuron alive and decides whether it will fire

  • Axon: extending fiber that conducts impulses away from the cell body to transmit to another neuron

  • Myelin Sheath: fatty insulation that surrounds the axon

  • Node of Ranvier: Gap between the myelin sheath on the axon

  • Axon Terminals: connect to other terminal buttons from another neuron, gap in between the buttons is the synapse (synaptic gap)

    • Synaptic Cleft: minuscule space between neurons

    • Synapse: the site where transmission of a nerve impulse from one nerve cell to another occurs

• Types:

  • Sensory: relay incoming information to nervous system

  • Motor: relay information from the brain to the muscles

  • Interneurons: internal communication

• Neural Impulse:

  • Resting Potential: neuron’s stable, negative charge when inactive

  • Action Potential: voltage spike that travels along axon

  • Absolute Refractory Period: brief time after action potential before another action potential can begin

  • All-or-None Law: a neuron either fires or doesn’t fire

Neurotransmitters

• a chemical substance that is released by a transmitting neuron at the synapse that alters the activity of a receiving neuron

• Examples:

  • Acetylcholine (ACT)

    • enables muscle action, learning, memory

    • Undersupply marks Alzheimer’s disease

  • Dopamine

    • influences movement, learning, attention, emotion

    • Oversupply linked to schizophrenia; undersupply linked to tremors and decreased mobility of Parkinson’s disease

  • Serotonin

    • affects mood, hunger, sleep, arousal

    • Undersupply linked to depression (antidepressant drugs can raise levels)

  • Norepinephrine

    • helps control alertness and arousal

    • Undersupply linked to depressed mood

  • GABA

    • a major inhibitory neurotransmitter

    • Undersupply linked to seizures, tremors, and insomnia

  • Glutamate

    • a major excitatory neurotransmitter, involved in memory

    • Oversupply can overstimulate brain, producing migraines or seizures

• Low levels of serotonin and norepinephrine associated with severe depression

• Abnormal GABA levels related to sleep and eating disorders and convulsive disorders such as epilepsy

3. Brain Structures and Functions

• Brainstem:

  • Stemlike portion of the brain; composed of midbrain, pons, medulla

  • Relays messages between spinal cord and brain; helps control heart rate, breathing rate, blood pressure; involved with hearing, taste, other senses

• Cerebellum:

  • Second largest part of the brain; located behind pons; composed of cerebral cortex, two lateral loves, central flocculondular lobes, medial vermis, some deep nuclei

  • Coordinates fine muscle movement, balance; processes sensory information

• Cerebral Cortex:

  • Outer layer of cerebrum; composed of gray matter and arranged in raised ridges (gyri), grooves (sulci), depressions (fissures)

  • Involved with most conscious activities for living

• Cerebral Lobes: Major divisions of cerebrum

  • Frontal: Primary motor cortex, control of emotional expressions and moral behavior

  • Parietal: Primary somatosensory cortex

  • Temporal: Primary auditory cortex; involved with equilibrium, emotion, memory

  • Occipital: Primary visual cortex

  • Limbic Lobe: Involved with emotions, behavioral expressions, recent memory, smell

• Cerebrum:

  • Largest part of the brain

  • Handles complex mental activities such as sensing, learning, thinking, and planning

• Corpus Callosum:

  • Bridge of nerve fibers that connects one cerebral hemisphere with the other

  • Connects cerebral hemispheres, relaying sensory information between them; allows left and right hemispheres to share information, helps to unify attention

• Medulla Oblangata:

  • Lowermost portion of brainstem; connects pons and spinal cord; site of decussation of descending direct corticospinal tract and an ascending sensory pathway from spinal cord to thalamus; emergence of cranial nerves 4 through 7; movement of cerebrospinal fluid from ventrical to subarachnoid space between subarachnoid and pie matter

  • Provide subarachnoid circulatory paths for cerebrospinal fluid, protective cushion; regulates unconscious functions such as breathing and circulation

• Pons:

  • Short, bridge like structure composed mainly of fibers that connect midbrain and medulla, cerebellar hemispheres, and cerebellum and cerebrum; lies anterior to cerebellum and between midbrain and medulla; site of emergence of cranial nerve

  • Involved with visual reflexes, movement of eyes, focusing of lens, dilation of pupils, sleep, and arousal

• Reticular Formation:

  • Complex network of nerve cells organized into ascending (sensory) and descending (motor) pathways; located throughout core of entire brainstem

  • Specific functions for different neuron, including involvement with respiratory and cardiovascular centers, regulation of brain’s level of awareness

• Substantia Nigra:

• Thalamus:

  • Composed of two separate bilateral masses of gray matter; located in center of cerebrum

  • Intermediate relay structure and processing center for all sensory information (except smell) going to cerebrum

• Hypothalamus:

  • Small mass below the thalamus; forms floor and part of lateral walls of third ventricle

  • Highest integrating center for autonomic nervous system; controls most of endocrine system through its relationship with the pituitary gland; regulates body temp, water balance, sleep-wake patterns, food intake, behavioral responses associated with emotion

• Limbic System:

  • Loosely connected network that contributes to emotion, memory, motivation

    • Amygdala:

      • Involved in learning of fear response (found to have shrunken in individuals who suffered traumatic events)

    • Hippocampus:

      • Contributes to memory