THE BIOLOGICAL BASES OF BEHAVIOUR

THE BIOLOGICAL BASES OF BEHAVIOUR

1. NERVOUS TISSUE: BASIC HARDWARE

   • The cells in the nervous system fall into two major categories: Glia and Neurons
     • Neurons are individual cells in the nervous system that receive, integrate, and transmit information
     • Glia's are cells found throughout the nervous system that provide various types of support for neutrons
   • Soma: (Greek for body) contains the cell nucleus and much of the chemical machinery common to most cells
   • Dendrites: (Greek for tree) are the parts of the neurone that are specialized to receive information
   • Axon: (Greek for axle) is a long, thin fibre that transmits signals away from the soma to other neurons or to muscles or glands
   • Myelin sheath is insulting material, derived from glial cells, that encases some axons
   • The axon ends in a cluster of terminal buttons, which are small knobs that secrete chemicals called neurotransmitters
   • Synapse: (Greek word for junction) is where information is transmitted from one neurone to another

2. THE NEURAL IMPULSE

   • The resting potential of a neurone is its stable, negative charge when the cell is inactive
   • When the neurone is stimulated, for an instant its charge is less negative, or even positive creating an action potential
   • Action Potential: very brief shift in the neurones electrical charge that travels along a axon
   • The absolute refectory period is the minimum length of time after an action potential during which another action potential cannot begin
   • Various neurones transmit neural impulses at different speeds.
     • EXAMPLE: thicker axons transmit neural impulses more rapidly than thinner ones do

3. THE SYNPSE: WHERE NEURONES MEET

   • Transmissions take place at special junctions, which depend on chemical messengers
   • Sending signals: chemicals as couriers
     • Synaptic cleft, a gap between the terminal button of one neurone and the cell membrane of another neurone
     • Signals have to cross the gap to permit neurones to communicate. The neurone that sends a signal across the gap is called the presynaptic neurone
     • The arrival of an action potential at an axons terminal buttons triggers the release of neurotransmitters (chemicals that transmit information from one neurone to another)
   • Receiving signals: Postsynaptic potentials
     • They vary in size and they increase or decrease the probability of a neural impulse in the receiving cell in proportion to the amount of change in voltage
   • When a neurotransmitter and a receptor molecule combine, reactions in the cell membrane cause a postsynaptic potential (PSP)
     • PSP: a voltage change at a receptor site on a postsynaptic cell membrane
   • Two types of messages that can be sent from cell to cell: Excitatory and Inhibitory
     • Excitatory psp: a positive voltage shift that increases the likelihood that the postsynaptic neurone will fire action potentials
     • Inhibitory psp: a negative voltage shift that decreases the likelihood that the postsynaptic neurone will fire action potentials

4. NEUROTRANSMITTERS

   • Acetylcholine: activates motor neurones controlling skeletal muscles
     • Contributes to the regulation of attention, arousal, and memory
       • Some ACh receptors stimulated by nicotine
   • Dopamine: contributes to control of voluntary movement, pleasurable emoticons
     • Decreased levels associated with Parkinson's disease
     • Overactivity at DA synapses associated with schizophrenia
     • Cocaine and amphetamines elevate activity at DA synapses
   • Norepinephrine: Contributes to modulation of mood and arousal
     • Cocaine and amphetamines elevate activity at NA synapses
   • Serotonin: involved in regulation of sleep and wakefulness, eating, aggression
     • Abnormal levels may contribute to depression and obsessive compulsive disorder
     • Prozac and similar depressant drugs affect serotonin circuits
   • GABA: serves as widely distributed inhibitory transmitter
     • Valium and similar anti anxiety drugs work at GABA synapses
   • Endorphines: resemble opiate drugs on structure and effects
     • Contribute to pain relief and perhaps to some pleasurable emotions
   • Glutamate: an amino acid that has both excitatory and inhibitory effects. It has been implicated in learning and memory

5. THE NERVOUS SYSTEMS

   • The peripheral nervous system: its made up of all those nerves that lie outside the brain and spinal cord. (It can be divided into the somatic nervous system and the autonomic nervous system)
   • The somatic nervous system: its made up of nerves that connect to voluntary skeletel muscles and to sensory receptors
   • The autonomic nervous systems: Its made up of nerves that connect to the heart, blood vessels, smooth muscles and glands (It can be subdivided into two branches)
     • The sympathetic branch mobilizes bodes recourses for emergencies
     • The parasympathetic branch generally conserves bodily recources
   • The central nervous system: consists of the brain and spinal cord
     • (its bathed in its own special nutritive soup called "the cerebrospinal fluid")

6. THE BRAIN

   • The hindbrain: it includes the cerebellum and two structures found in the lower part of the brain stem: the medulla and the pons
     • The medulla which attaches to the spinal cord, is in charge of largely unconscious but vital functions
     • The pons includes a bridge of fibres that connects the brainstem with the cerebellum
     • The cerebellum is a large and deeply folded structure located adjacent to the back surface of the brainstem (its critical to the coordination of movement and to the sense of equilibrium, or physical balance)
   • The midbrain: segment of the brainstem that lies between the hindbrain and the forebrain. It contains an area that is concerned with integrating sensory processes
   • The forebrain: largest and most complex region of the brain, encompassing a variety of structures, including the thalamus, hypothalamus,limbic system, and cerebrum
     • The thalamus: a structure through which all sensory information (except smell) must pass to get to the cerebral cortex
     • The hypothalamus: a structure that is involved in the regulation of basic biological drives related to survival
     • The limbic system: involved in the regulation of emotion, memory, and motivation, and recently it has been linked to the tendency of some people to be optimistic in their approach to life
     • The cerebrum: the brain areas that are responsible for the most complex mental activities, including learning, remembering, thinking, and consciousness itself

7. BASIC PRINCIPLES OF GENETICS

   • Chromosomes are strands of DNA molecules that carry genetic information
     • Every cell in humans (except sex cells) contain 46 chromosomes. They operate in 23 pairs, with one chromosome of each pair being contributed by each parent
   • Fertilization create a zygote: a single cell formed by the union of a sperm cell and an egg
   • Genes are DNA segments that serve as they key functional units in heredity transmission
   • A dominant gene one that is expressed when paired genes are different.
   • A recessive gene is one that is masked when paired genes are different
   • Genotype refers to a persons genetic makeup
   • Phenotype refers to the ways in which a persons genotype is manifested in observable characteristics
   • Polygenic traits, or characteristics are influenced by more than one pair of genes

8. INVESTIGATING HEREDITARY INFLUENCE: RESEARCH METHODS

   • Family studies: researchers assess hereditary influence by examining blood relatives to see how much they resemble one another on a specific trait
     • Family studies can indicate whether a trait runs in families
       • Can also offer useful insights about the possible impact of heredity
   • Twin studies: researchers assess hereditary influence by comparing the resemblance of identical twins and fraternal twins with respect to a trait
     • Identical twins emerge from on zygote that splits for unknown reasons
       • Fraternal twins result when two eggs are fertilized simultaneously by different sperm cells, forming two separate zygotes
   • Adoption studies: researchers assess hereditary influence by examining the resemblance between adopted children and both their biological and their adoptive parents
     • If adopted children reusable their biological parents in a trait, even though they were not raised by them, genetic factors probably influence that trait
     • If adopted children resemble their adoptive parents, even though they inherited no genes from them, environmental factors probably influence the trait