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.
COUNT THE F’S • FINISHED FILES ARE THE RE- SULT OF YEARS OF SCIENTIF- IC COMBINED WITH THE EXPERIENCE OF YEARS.
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.
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 Afferent nerve Receptor Impulse Efferent nerves 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.