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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 • Peripheral Nervous System
– Brain
– Spinal Cord
– 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 Neurotransmitters
Neurotransmitter
Nervous System Location
Examples of Functions
Acetylcholine
Throughout the Brain
Neuromuscular Synapses
Learning and Memory
Control of Muscles
Dopamine
Cerebellum, basal ganglia,
limbic system
Motor activity,
coordination
Emotion 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