Biophysiology

• • • • Did everyone in the class describe the same objects in the same way?

Did everyone guess the same object?

The nervous system underlies everything we do. Understanding biology is fundamental to understanding behaviour.

We need to know the mechanics of sensation before we can understand perception.

Is the center spinning?

Which intersections have white dots and which are black?

Is it rotating?

Ignore the word and say the color

Are the horizontal lines parallel?

Which center dot is bigger?

Are the horizontal lines straight?

Count the spirals

Star or square?

COUNT THE F’S

• FINISHED FILES ARE THE RE SULT OF YEARS OF SCIENTIF IC COMBINED WITH THE EXPERIENCE OF YEARS.

Straight or parallel?

Which center line is longer?

The Biological Bases of Behaviour

• • In order to understand the mind, psychologists must first understand how the body works and is constructed. Before becoming a software engineer, you must first know how a computer is put together and how it works.

The basic hardware

• • • • The nervous system is composed of billions of cells called neurons.

Neuron – individual cells that receive, integrate, and transmit information.

Humans are born with a fixed number of neurons, Between 10 and 100 million. We lose an average of 10,000 per day, but over a lifetime, that amounts to less than 2% of the total.

Neurons

• • • Receptors – specialized structures capable of turning stimuli in the environment into electrical impulses in the body.

Afferent nerves – nerves that transmit signals into the brain.

Efferent nerves – nerves that carry signals from the brain to the muscles.

Brain Impulse Stimulus Receptor Afferent nerve Efferent nerves Impulse Impulse Muscle

• • • • • Sensory neurons carry signals from the outer parts of your body (periphery) into the central nervous system. Motor neurons (motoneurons) carry signals from the central nervous system to the outer parts (muscles, skin, glands) of your body. Receptors sense the environment (chemicals, light, sound, touch) and encode this information into electrochemical messages that are transmitted by sensory neurons. Interneurons connect various neurons within the brain and spinal cord. The simplest type of neural pathway is a monosynaptic (single connection) reflex pathway, like the knee-jerk reflex. When the doctor taps the the right spot on your knee with a rubber hammer, receptors send a signal into the spinal cord through a sensory neuron. The sensory neuron passes the message to a motor neuron that controls your leg muscles. Nerve impulses travel down the motor neuron and stimulate the appropriate leg muscle to contract. The response is a muscular jerk that happens quickly and does not involve your brain. Humans have lots of hard-wired reflexes like this, but as tasks become more complex, the pathway "circuitry" gets more complicated and the brain gets involved.

• • When a sensation reached the threshold – the minimum strength required – a signal is triggered in the dendrites of the neuron.

Threshold – the minimum intensity required to trigger a chain reaction in a neuron.

Synaptic Transmission

• • • Scientists had always believed that there was some mechanism connecting two neurons together. This was finally proven in 1920 by Otto Loewi.

Lowei’s experiment proved that the transmission from one neuron to the next involved a chemical substance.

Synapse

• Synapse – the gap between the axon terminals of the transmitting neuron and the dendrites of the receiving neuron.

Synaptic Transmission

• • As the impulse reaches the axon terminals, tiny sacs of specialized proteins called synaptic vesicles rupture at the surface of the terminal.

These vesicles pop and release a chemical into the synapse called a neurotransmitter.

Neurotransmitters

• Neurotransmitter – chemical substance that is released at the terminal end of the neuron that travel across the synapse and have an excitory or inhibitory effect on the adjacent neuron.

Receptors

• • • As each neurotransmitter crosses the synapse, it lands on specialized receptor cells on the dendrites of the next neuron.

The receptors then lower the action potential of the neuron.

As each neurotransmitter reaches a receptor, the action potential is lowered more and more until the threshold is reached and an impulse is triggered.

Lock and Key Model

• Each neurotransmitter is paired with the special receptor at the end of the post synaptic neuron. Each receptor can only be activated by it’s paired neurotransmitter.

Reuptake

• • • Excess neurotransmitter in the synapse is removed to prevent prolonged stimulus and interference in two ways: Enzymes located in the synapse break down the chemicals into smaller component parts.

The axon terminal will reabsorb excess back into the neuron cell.

The Nervous System

• The nervous system constantly monitors, controls and maintains an optimal state in the body called homeostasis.

The nervous system has two parts: • • The Central Nervous System – the brain and spinal cord. The spinal cord consists of a large bundle of nerve fibres that run down the back and transmit signals between the body and the brain.

The Peripheral Nervous System – includes the smaller nerves that branch out from the spinal cord. These nerves take information from the body’s organs to the central nervous system and return information to the organs.

The peripheral nervous system is divided into two functions: • • Somatic division – concerned with the control of the skeletal musculature and the transmissions from the sense organs.

Autonomic division – serves the structures that are concerned with basic life processes such as heart beat, contraction of the stomach and intestines, and genital organs.

Brain structures

• • • Where the spinal cord meets the brain is the brain stem, attached to the brain stem are two structures; the cerebral hemispheres, which totally envelope the brain stem the cerebellum which is attached further down and is much smaller.

The brain itself can be divided into three portions: • • • The forebrain The mid-brain The hindbrain

The Hindbrain

• • What two structures are located in the hindbrain?

The medulla and the cerebellum.

• •

What are the functions of the two parts of the hindbrain?

The medulla controls heartbeat, circulation, respiration, and other vital functions.

The cerebellum controls balance and muscular coordination.

The Midbrain

• • What is the dominant structure in the midbrain?

The reticular formation.

How is the midbrain related to sleep?

• It is related to activation of other parts of the brain and when it is deactivated regulates sleep.

The Forebrain

• • What is the function of the thalamus?

It coordinates and regulates information from sensory organs and motor centers to the cerebral cortex.

What is your guess as to the effect of overstimulation of the hypothalamus? Why?

• Because the hypothalamus controls behaviours related to basic biological urges, overstimulation would probably lead to someone who eats, drinks, and sleeps too much and is probably inappropriate frequently.

What is meant by “functional summit”?

• Functional summit refers to the most complex, most capable, and most sophisticated part of the human body. It is the part of the body that is capable of the most significant and powerful actions.

What are the four lobes of the cerebral hemisphere?

• Frontal, parietal, occipital, temporal lobes.

What is the function of the cerebral cortex? Why do scientists believe that is a recent development in evolution?

• The cerebral cortex is the location for higher brain functions like thinking, memory, and planned and voluntary action. Scientists believe it is a recent evolutionary adaptation because many organisms lack one like fish, and many have only the beginnings of one like reptiles, and birds.

What do you think happened to Leonard’s brain based on these notes?

• Leonard must have suffered damage to his basal ganglia when he was young because it is the location of dopamine circuits and Leonard’s condition improved after taking synthetic dopamine.

Why do you think the limbic system called the “old cortex”? What does this mean about “human” behaviour?

• Because the limbic system is involved in motivation and emotion, it is linked to more primitive and basic functions whereas the cerebral cortex is involved in rationality, thinking, memory, and planning.

• This would lead us to believe that, based on biology and brain functioning, what makes us human is our higher brain functions. What makes us more “advanced” is our rationality, our thinking, and our premeditation; not our emotions or our basic motivations.

The Cerebral Cortex

• • The cerebral cortex is the key to human intelligence.

Without it, there can be no planning, no complex speech, no complex sequence of movement, no organizational perception.

Function zones

• • • The cortex is divided into two zones based on their function: Projection areas – serve as receiving areas for sensory information and as dispatching centers for motor commands.

Association areas – the remaining 2/3rds of the cortex is devoted to higher mental functions like planning, perceiving, remembering, thinking, and speech.

Projection areas

• • Motor projection areas of the cortex are linked with control parts of the body.

These can be mapped with a high degree of accuracy to create a motor homonculus, or a schema of the body as it is represented on the cortex.

Motor homunculus

Sensory areas

• • Each part of our body also has a designated area of the cortex devoted to sensation – called the somatosensory area. This map can be used to create a sensory homunculus of the region of the brain devoted to sensation.

Sensory homunculus

Sensory areas

• • Other parts of the cortex are devoted to the different senses. These are the visual cortex, and the auditory cortex.

Association Areas

• • Association areas are related to complex mental functions like speech, thinking, and remembering.

The precise locations of these activities can be discovered through lesions (damaged tissue) in the brain.

Association Areas

Studying Localization

• • • • • The location of these lesions results in the loss of a specific function.

Lesions can be discovered through: PET scan – Positron Emission Tomography CAT scan – Computerized Axial Tomography MRI scan – Magnetic Resonance Imaging

Localization - Phineas Gage

• • • • •

Author: Damasio et al. 1994 Type: Case Study, single subject, non-random sample, instrumental – it sought to construct/confirm a hypothesis regarding localization of inhibition in the brain as well as explaining the phenomena of his changed behaviour by what his brain injury turned out to be once they could perform an autopsy.

Aims: To discover the nature of the injuries to Gage’s brain and correlate those injuries with the changes in his behaviour reported from the period – disinhibition Method: Using modern technology, researchers reconstructed the injury to Gage’s skull and compared those to historical accounts of his behaviour before and after the injury.

Conclusions: The reconstructed injury based on the skull of Gage indicated damage to the pre-frontal lobe of the brain which corresponds with prior knowledge of the localization of inhibition in the brain. This correlates positively with the changes in behaviour of the subject described by the historical accounts.

What do we know?

• • Localization of brain function is not set, continually under study and subject to revision as new information comes available.

https://www.youtube.com/watch?v=dFs9WO2B8uI

Neurotransmitters and behaviour

• We must remember how the nerve functions

Impulse

• • Once the threshold is achieved in the cell body, the protein “gates” of the axon open and Na+ ions rush in.

For 1 millisecond, the outside of the axon body becomes – and the interior becomes +.

Propagation • • • • • The polarity of the axon body is reversed as the threshold is achieved.

Gates in the cell membrane open briefly to let Na+ ions rush in.

These gates quickly close and K+ ions slowly leak out and the cell begins to actively pump Na+ ions back out. This returns the cell to it’s resting state.

The depolarization of the cell produces electric currents that stimulate the threshold value in neighboring regions as the impulse travels down the axon.

All or None Law

• • • Once the impulse is triggered, the intensity of the signal is constant. All or None Law – the stimulus does not provide the energy of the nervous impulse. This means that a stronger sensation is caused by a greater number of neurons being stimulated, not a stronger impulse.

Pain

• • • • • The All or None Law is important for the study of sensations like pain.

Intense sensation can be caused by two factors: A strong stimulus will trigger a higher NUMBER of neurons to fire A strong stimulus will trigger a greater FREQUENCY in the neuron impulse.

The highest frequency in the human body is 1,000 impulses/second

Neurotransmitters

• The list: 1.

2.

3.

4.

5.

6.

7.

8.

9.

Ach 5HT GABA NE DA Amphetamines Curare Endorphins SSRIs 10. MAOIs 11. Cocaine 12. Benzodiazepines

You will be numbered by me

• • • Your assignment: Research and record the function of the neurotransmitter/drug that corresponds to your number.

You will trade, compare and copy notes from your classmates.

A short quiz will follow

The Endocrine System

• • Closely related to neurotransmitters, hormones are chemical substances that have an effect on structures elsewhere in the body.

While neurotransmitters work across the synaptic cleft 1/10,000mm wide, hormones work across the entire body. They can have an immediate and important impact on behaviour.

Role of hormones

• Hormones are released by endocrine glands and have specific effects on the body based on the body’s need to maintain homeostasis. They are vital to human development and behaviour.

Master gland

• • The hypothalamus regulates the pituitary gland which sends out a variety of hormones for growth and development. It is the “central command” for other endocrine structures.

Eg. Gonadotrophins – direct the formation of external sexual organs in the developing fetus.

The Endocrine glands

• • • •

Glands and their function

Anterior pituitary Posterior pituitary Thyroid Islets in the pancreas • • • • Often called the body’s master gland because it triggers hormone secretion in many of the other endocrine glands.

Prevents loss of water through kidney Affects metabolic rate Affects utilization of glucose

• Adrenal cortex • Adrenal medulla • Ovaries • Testes

Glands and their function

• • • • • Various effects on metabolism; some effects on sexual behaviour Increases sugar output of liver; stimulates various internal organs in the same direction as the sympathetic branch of the ANS.

One set of hormones (estrogen) produces female sex characteristics and is relevant to sexual behaviour. Another hormone (progesterone) prepares uterus for implantation of embryo.

Produces male sex characteristics. Relevant to sexual arousal.