The Biological Perspective

Development of the Biological Perspective

• Develops in response to the Dualism attributed to Descartes circa 17th century– Dualism-mind and body distinct, can interact via

pineal gland in brain.• Biological perspective moves away from this

towards monism and materialism– Monism-mind and body a single entity– Materialism-all behavior has a physiological basis

• Shift begins away from dualism with Julien de La Mettrie, French Priest turned physician– Contracts fever and notes physical condition

affected both mental and physical state– Writes L’histoire naturelle de l’ame (The Natural

History of the Soul)• Argues mind and soul are the same and the mind is

part of the body.• Forced from France for his views

• A physician named Cabanis connected consciousness to the brain during the French Revolution– Argued guillotine victims were not conscious because this was

a function of the brain.• Paul Broca was the first to connect physiological

structures and behavior in 1861.– Meets man who lost ability to speak coherently after head

injury at insane asylum at Bicetre.– Post-mortem autopsy reveals injury to specific area of brain

• Proves localization of function, final step in progression of ideas• Localization of function-connects a specific behavior to a specific

brain area

• The role of heredity in behavior was another major aspect of the perspective– Heredity-the biological transmission of characteristics from one generation to another

• Original beliefs centered around creationist ideas in the Bible• Questions began to arise with catalogue of biologist Linnaeus in 1735

– Orderly categories suggested connections among species• French naturalist Lamarck produced first theory of evolution in 1809

– Variations develop through inheritance of acquired characteristics– Important even though discredited because it suggested hereditary basis for characteristics

• Charles Darwin’s Origin of the Species in 1859 was the absolute game changer– Variations occur by chance, but can be passed on– “Survival of the fittest” principle stated that variations which help individuals survive to

reproduce will be passed on– Leads to natural selection of the best characteristics from a survival standpoint

• Natural selection-the evolutionary process by which those random variations within a species which enhance reproductive success will lead to perpetuation of new characteristics,

– Mechanism for this was not explained until the work of Gregor Mendel was rediscovered– Darwin suffered a fate similar to La Mettrie in conflict with religious ideologies

• Still not formally resolved.

Nature of the Physiological System

• What is the mechanism of mind and body interactions?– Several physiological systems involved• Central Nervous System• Peripheral Nervous System• Endocrine System

– Important to note that “mind” or seat of consciousness may consist of all or several of these systems and not just the brain

• The Nervous System– Coordinates the activities of the many body

systems– Composed of specialized cells called neurons• Act as wires carrying an electro-chemical message• Connect to each other at junctions called synapses

– A synapse acts as the switch board sending the message to other areas

The Nervous System

• Central Nervous System– Consists of the brain and the

nerve pathways of the spinal cord

– Use interneurons to carry messages from peripheral to brain and back

– Brain integrates info and directs muscle activity

– Spinal cord acts as relay station (passes through vertebrate for protection)

– Cannot be repaired

• Peripheral Nervous System– All nerve pathways outside

of central nervous system– Carry outside messaged to

CNS through sensory neurons

– Initiate muscle direction using motor neurons which receive info from CNS

– Can be repaired

Nervous System

• Central Nervous System– Brain– Spinal Cord

• Peripheral Nervous System– Autonomic

• Sympathetic• Parasympathetic

– Somatic

Further Information

• Simple Breakdown of the Nervous System

Neurons• Basic units of the nervous system• Act like a wire passing an electric signal called a nerve impulse• Key components of neurons

– Dendrites- small branches that receive and transmit info between neurons

– Axon-cable like structure on which messages travel through neurons– Myelin- insulating sheath around the axon, made of tightly wrapped

Schwann cells, improve efficiency of conduction– Node of Ranvier-small gaps in the myelin sheath of an axon– Axon Terminals- branch like structures that extend from the end of the

axon pathway– Synapse- small gaps between dendrites and the axon of the next neuron– Neurotransmitters- chemicals released to bridge gaps at the synapse

Neurons

The Brain

• Consists of about 100 billion neurons (Estimate via extrapolation)

• Each neuron makes and receives connections with 100’s maybe 1000’s of other neurons– Creates network of 1 million-billion connections in

the cortex (Pink, wrinkled outer layer of brain which controls many higher functions)

Divisions of the Brain

• Cortex– Split into two hemispheres (left and right) which control opposite

sides of the body– Hemispheres broken into lobes by 2 major fissures

• Central-Splits brain in half roughly, front and back• Lateral-Runs along the side of each hemisphere

– There are 4 lobes with seeming localized function• Frontal-interpretation of emotion and experience/integrates activity from

other brain areas/controls voluntary movement of the muscles• Temporal-hearing, language and memory for objects • Parietal-related to touch senses• Occipital-devoted solely to vision

– Despite localization of functions in the brain it always functions as a whole

The Primitive Brain• Located beneath the cortex and linked by subcortical networks• Control fundamental aspects of behavior• Consists of

– Limbic system• Hypothalamus-regulates behavior associated with basic drives and regulates hormonal

functions• Hippocampus-important to memory function• Amygdala-plays a role in basic emotions

– Cerebellum • Contains 2 hemispheres• Directs movement and balance, particularly fine motor control activities

– Brain Stem• Medulla-regulates basic bodily processes• Pons- provides connections between the cortex and the cerebellum• Reticular formation-controls sensory inputs

Limbic System

Chemical Processes in Behavior

• Required for communication to work between neurons• Exchange of chemicals called neurotransmitters

bridges gaps at synapses• Approximately 100 chemicals used in this process• Some used to excite (Trigger activation) others used to

inhibit (Prevent neuron firing) still more are used to block or clear away these exciters and inhibitors

• If neurons are constantly stimulated they reduce their response, called habituation– Reason why we need hormones

How Neurotransmitters Work

Types of NeurotransmittersNeurotransmitter Nervous System Location Examples of Functions

Acetylcholine Throughout the Brain Neuromuscular Synapses

Learning and MemoryControl of Muscles

Dopamine Cerebellum, basal ganglia, limbic system

Motor activity, coordinationEmotion and Memory

Epinephrine Sympathetic Nervous System

Emotion, Stress

Gamma-aminobutyric acid Throughout the brain Anxiety, Arousal, Learning

Glutamate Throughout Nervous System

Anxiety, Mood

Serotonin Thalamus and Brain Stem Sensory Processing, Sleep, Arousal

Endocrine System• Secretes chemical called hormones into the bloodstream to regulate

bodily processes that require slower long term functions• Originally thought to be complementary to Nervous System • Now thought to instead be linked via pituitary gland and

hypothalamus– Chemical thought once to be hormones have now been found to also be

neurotransmitters and vice versa (i.e. norepinepherine, vasopressin)• Major difference between hormones and neurotranmitters

– Neurotransmitters used to send signals along neural pathways, relatively quick process

– Hormones send signals to internal organs and other areas in a more controlled and slower fashion via the blood stream

How hormones are received

Endocrine glands and their functions

Pineal Gland Melatonin (circadian rhythm)

Pituitary Gland Growth hormone, ACTH stress hormones for labor and milk production

Thyroid Metabolism

Parathyroids Calcium levels

Pancreas Insulin

Adrenals Stress response, Metabolism

Gonads Sex hormones

Sleep-Wake Cycle

Involvement of Endocrine System in Sleep-Wake Cycle

Basic Mechanisms of Heredity

• Genes- basic units of heredity made up of stings of amino acids– Humans possess about 80,000 different genes

• Each regulates a different process

– Genes split and recombine using genetic information from both parents to produce offspring• Chromosomes are the mechanism for this

– Chromosomes-thread-like genetic structures composed of double strands of DNA and proteins

– Humans contain 23 pairs of chromosomes

• Genotype- genetic code and individual carries in their DNA

• Phenotype- the observed characteristics of the individual

• Remember that genes function in pairs and various forms of genes (alleles) for a characteristic exist

• Mutations- change the genetic material of a cell possibly creating a new trait that can be passes on to descendants– Argument for evolution