The Biological Perspective

The Biological Perspective Chapter 2

What is Biological Psychology? • Neuroscience – science that deals with the structure and functioning of the brain and the neurons, nerves, and nervous tissue that form the nervous system • Biological Psychology or Behavioral Neuroscience – branch of neuroscience that focuses on the biological bases of psychological processes, behavior, and learning • How the nervous system works provides information about what is going on inside the body when you engage in a specific behavior, feel an emotion, or have an abstract thought

Overview of the Nervous System • Nervous system – a network of cells that carries information to and from all parts of the body (4 levels) • Central nervous system (CNS) – brain and spinal cord • Brain – interprets and stores information and sends orders to muscles, glands, and organs • Spinal cord – pathway connecting the brain and the peripheral nervous system • Peripheral nervous system – transmits information to and from the CNS • Autonomic nervous system – automatically regulates glands, internal organs and blood vessels, pupil dilation, digestion, and blood pressure • Parasympathetic division – maintains body functions under ordinary conditions; saves energy • Sympathetic division – prepares the body to react and expend energy in times of stress • Somatic nervous system – carries sensory information and controls movement of the skeletal muscles

Structure of the Neuron: The Nervous System’s Building Block • Neuron – the specialized cell in the nervous system that receives and sends messages within that system • One of the body’s messengers, therefore it has a very special structure • 3 main parts of a neuron • Dendrites – branchlike structures that receive messages from other neurons • Soma – the cell body of the neuron responsible for maintaining the life of the cell • Axon – tube-like structure that carries the neural messages out to other cells

Structure of the Neuron Dendrites Axon Soma

Structure of the Neuron • Neurons only make up 10% of cells in the brain • Other 90% is glial cells • Glial cells – cells that provide structure for the neurons to grow on and around, deliver nutrients to neurons, and produce myelin • Myelin – fatty substances produced by glial cells that coat the axons of neurons to insulate, protect, and speed up the neural impulse

Structure of the Neuron • 2 types of glial cells produce myelin for the neurons in the nervous system • Oligodendrocytes – produce myelin for the neurons in the brain and spinal cord (CNS) • Schwann cells – produce myelin for the neurons of the body (PNS) • Axons travel all over the body like cables, carrying messages • Myelin wraps around the axon forming a protective sheath (myelin sheath) • Nerves – bundles of axons coated in myelin that travel together through the body

Structure of the Neuron • How do neurons send messages? • When a neuron is at rest (not firing an impulse or message) it is actually electrically charged • Inside and outside the cell, charged particles called ions are in a semi-liquid (jelly-like) solution • The relative charge of ions inside the cell is mostly negative • The relative charge of ions outside the cell is mostly positive

Structure of the Neuron • Cell membrane is “semipermeable” meaning that tiny substances inside and outside the cell can pass through channels in the membrane • Inside the cell, there are smaller positively charged potassium ions and larger negatively charged protein ions • Negatively charged protein ions are too big to go through the channels when the cell is at rest, leaving the inside of the cell with a mostly negative charge • Outside the cell, there are lots of positively charged sodium ions and negatively charged chloride ions • Unable to go into the cell when it is at rest because the channels are closed

Structure of the Neuron • Positively charged sodium ions cluster around the outside of the cell because the inside of the resting cell is mostly negatively charged and opposite charges attract • This difference in charges creates an electrical potential • Resting potential – the state of the neuron when not firing a neural impulse • http://www.youtube.com/watch?v=YP_P6bYvEjE

Structure of the Neuron • When the cell receives a strong enough stimulation from another cell (meaning the dendrites are activated) the channels in the cell membrane open up all down the cell and allow the sodium ions to rush into the cell • Causes reversal in electrical charge - the inside of the cell becomes mostly positive and the outside becomes mostly negative (because many of the positive sodium ions are now inside the cell) • Sodium ions begin entering the cell through the first channel that opens up, the channel closest to the soma • The rest of the ion channels open up all down the axon in a kind of chain reaction • Change in electrical charge is called the Action Potential because the electrical potential is now in action, rather than at rest (like in resting potential)

http://www.youtube.com/watch?v=R0TdXkxBOkE&feature=related

Structure of the Neuron • During action potential, the cell becomes positive inside and negative outside • After the action potential passes, the cell has to return back to its resting potential, meaning it has to get the positively charged sodium ions out • Ion channels close immediately after the action potential passes • Then, the cell membrane literally pumps the positive sodium ions out • Meanwhile, small positively charged potassium ions inside the neuron move out rapidly helping to restore the negative charge inside the cell • http://www.youtube.com/watch?v=GTHWig1vOnY

Structure of the Neuron • To start an action potential, the neuron must receive a signal strong enough to break the threshold for firing • Neurons are receiving “Fire!” and “Don’t Fire!” messages from other neurons constantly • When the “Fire!” messages are great enough to cancel out the “Don’t Fire!” messages, the threshold is crossed and the neuron fires • Neurons fire in a sort of “all-or-none” fashion, either firing at full strength or not firing at all • Like a light switch, when its on, its on and when its off, its off…. No dimmer switch

Sending the Message to Other Cells: The Synapse • The end of the axon fans out into several short fibers that have swellings or little knobs on the ends called synaptic knobs or axon terminals • The synaptic knobs are filled with little saclike structures called synaptic vesicles • Synaptic vesicles are filled with chemical substances called neurotransmitters (the message carriers)

Sending the Message to Other Cells: The Synapse • Next to the synaptic knob is the dendrite of another neuron, in between them is a fluid-filled space called the synapse or the synaptic gap • Remember, in the synaptic knob are vesicles full of neurotransmitters • The dendrite next to the synaptic knob contains ion channels that have receptor sites • Receptor sites – proteins that allow only particular molecules of a certain shape to fit into it

Sending the Message to Other Cells: The Synapse • When the action potential reaches the synaptic knob, it causes the vesicles to release their neurotransmitters into the synapse • The neurotransmitters float across the synapse and many of them fit themselves into the receptor sites • This opens the ion channels and allows sodium ions to rush in, activating the next cell • The next cell may be another neuron, or a cell on a muscle or gland • http://www.youtube.com/watch?v=HXx9qlJetSU

Sending the Message to Other Cells: The Synapse • When neurotransmitters bind to receptor sites they have one of two possible effects (remember the “Fire!” and “Don’t Fire!” signals?) which depend on what kind of synapse they are release into • Excitatory synapse – ion channels open causing the next cell to fire • Inhibitory synapse – ion channels close causing the next neuron to stop firing • http://www.youtube.com/watch?NR=1&v=LT3VKAr4roo • Start a 1:07

Neurotransmitters: Messengers of the Network • At least 50 – 100 different types of neurotransmitters in the human body • Acetylcholine - 1st neurotransmitter to be discovered • Excitatory • Causes muscles to contract • Roles in cognition, particularly memory • GABA (Gamma Amino Butyric Acid) • Inhibitory • Decreases the activity level of neurons in the brain

Neurotransmitters: Messengers of the Network • Serotonin • Both excitatory and inhibitory • Linked with sleep, mood, and appetite • Dopamine • Both excitatory or inhibitory • Involved in control of movement and sensations of pleasure • Low levels have been found to cause Parkinson’s disease • Increased levels linked to schizophrenia • Endorphins • Special type of neurotransmitter called a neural regulator • Controls the release of other neurotransmitters • When endorphins are released in the body, the neurons transmitting information about pain are not able to fire action potentials

Neurotransmitters: Messengers of the Network • Some chemicals not naturally found in the body can either enhance or block the effects of neurotransmitters on receptor sites • Fit into receptor sites on target cells • 2 types • Agonists – mimic or enhance the effects of a neurotransmitter • Antagonists – block or reduce a cell’s response to the action of a neurotransmitter

Neurotransmitters: Messengers of the Network • Antagonist Example: Acetylcholine – neurotransmitter found at the synapses between neurons and muscle cells, causes muscles to contract • If acetylcholine receptor sites on the muscle cells are blocked, then the acetylcholine cant get to the site and the muscle will be incapable of contracting (meaning the muscle is paralyzed) • Curare a drug used on poison blow darts is just similar enough to fit into the receptor site without actually stimulating the cell • This blocks acetylcholine from its receptor sites causing paralysis

Neurotransmitters: Messengers of the Network • Agonist Example: Acetylcholine causes most muscles to contract, but actually slows the contraction of the heart muscle • Black widow spiders’ venom stimulates the release of excessive amounts of acetylcholine and causes convulsions and possible death

Reuptake and Enzymes • After neurotransmitters are released into the synapse they must be taken back into the axon they came from before the next stimulation can occur • Reuptake – process by which neurotransmitters are taken back into the synaptic vesicles • However acetylcholine which simulates muscles must be cleared out of the synapse more quickly (no time for the “sucking up” process) • A special enzyme specifically designed to break apart acetylcholine clears the synapse very quickly (called enzymatic degradation)

The Central Nervous System: The “Central Processing Unit” • CNS = brain and spinal cord • Brain – core of the nervous system • Spinal cord – long bundle of neurons • Divided into 2 areas that serve 2 vital functions • Outer area – composed mainly of myelinated axons and nerves • “Message pipeline” - Carries messages from the body up to the brain and from the brain down to the body • Inner area – mainly composed of cell bodies separated by glial cells • “Primitive brain” – responsible for certain reflexes, very fast, lifesaving reflexes

The Central Nervous System: The “Central Processing Unit” • Inside of the spinal cord contains 3 types of neurons that make up the reflex arc • Afferent (sensory) neurons – carry messages from the senses to the spinal cord • Ex. If you burn your finger, afferent neurons relay information about the sharp pain in your finger • Efferent (motor) neurons – carry messages from the spinal cord to the muscles and glands • Ex. Send command to pull your finger back from the painful stimulus • Interneurons – connect the afferent (sensory) neurons to the efferent (motor) neurons • Help coordinate signals between sensory neurons and motor neurons

The Central Nervous System: The “Central Processing Unit” • Neuroplasticity – the ability of the brain and spinal cord to change in structure and function • Can change the structure and function of many cells in response to experience and trauma • Stem cells – cells that can become other cells (blood cells, nerve cells, and brain cells) • Facilitate neuroplasticity • If stem cells can be successfully implanted into damaged areas in the spinal cord, the newly developed neurons may be able to assume the roles that the damaged neurons can no longer perform

The Peripheral Nervous System: Nerves on the Edge • Peripheral nervous system (PNS) – made up of all the nerves and neurons that are NOT in the brain and spinal cord • Includes all the nerves that connect to your eyes, ears, skin, mouth, and muscles • Allows the brain and spinal cord to communicate with these sensory systems • Divided into 2 major systems • Somantic nervous system – controls the senses and voluntary muscles • Autonomic nervous system – controls organs, glands, and involuntary muscles

The Somantic Nervous System • 2 parts • Sensory pathway – all the nerves carrying messages from the senses to the CNS (nerves containing afferent neurons) • Nerves from the body going to the CNS to relay information • Motor pathway – all the nerves carrying messages from the central nervous system to the skeletal of the body (nerves containing efferent neurons) • Nerves from the CNS going out to the body telling the body what to do

The Autonomic Nervous System • 2 systems • Sympathetic division – turns on the body’s fight-or-flight reactions, including increased heart rate, increased breathing, and dilation of your pupils • “fight-or flight system” • Active during times of stress • Parasympathetic division – controls the body when it’s in a state of rest to keep the heart beating regularly, to control normal breathing, and to coordinate digestion • “eat-drink-rest system” • Active most of the time

Distant Connections: The Endocrine Glands • Sort of the 2nd messenger system in the body • Endocrine glands – have no ducts and secrete chemicals called hormones directly into the blood stream • Hormones are carried by the blood stream to organs in the body • Compared to communication between neurons, the hormonal system is slower, and has more widespread effects on the body and behavior

The Pituitary: Master of the Hormonal Universe • Pituitary Gland – master gland, controls or influences all of the other endocrine glands • located in the brain just below the hypothalamus • Hypothalamus controls the glandular system by influencing the pituitary gland • Secretes the hormones that control milk production and salt levels in the body and growth from infancy to adulthood

The Pineal & Thyroid Glands • Pineal gland • Located in the brain, near the back, directly above the brain stem • Secretes melatonin – hormone that helps track day length and contributes to the regulation of the sleep-wake cycle in humans • Thyroid gland • Located in the neck • Secretes a hormone that regulates metabolism (how fast the body burns its available energy)

The Pancreas & Gonads • Pancreas • Controls the level of blood sugar in the body by secreting insulin and glucagons • Too little insulin = diabetes • Too much insulin = hypoglycemia • Gonads • Sex glands, secrete hormones that regulate sexual behavior and reproduction • Called ovaries in females • Called testes in males

Adrenal Glands • 2 Adrenal glands - located on the top of each kidney • Critical role in regulating the body’s response to stress • Adrenal glands are divided into 2 parts • Adrenal medulla – releases epinephrine and norepinephrine when people are under stress and aids in sympathetic arousal • Adrenal cortex – produces over 30 different hormones called corticoids • Most important is cortisol – released when the body feels both physical and psychological stress

Looking Inside the Brain: Deep Lesioning • How can psychologists find out about what parts of the brain do? • In animals – deliberately damage a part of the brain then test the animal to see what has happened to its abilities • Deep lesioning - a thin wire, insulated everywhere except the tip, is surgically inserted into the brain. Then an electrical current strong enough to kill off the target neurons is sent through the tip of the wire • In humans – study and test people who already have brain damage • Not ideal – no 2 injuries are exactly the same

Brain Stimulation • Electrical stimulation of the brain (ESB) • Less harmful than lesioning • Temporarily disrupt or enhance the formal functioning of specific brain areas through electrical stimulation • Invasive techniques – deep brain stimulation (DBS) • Surgically implant electrodes in specific deep-brain areas which are connected to an impulse generator that is surgically implanted under the collar bone • Used in treatment for Parkinson’s disease and seizure disorders • Noninvasive techniques – repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) • rTMS – magnetic pulses are applied to the cortex using special copper wire coils positioned over the head • tDCS – uses scalp electrodes to pass very low amplitude direct currents to the brain

Mapping Brain Structure • Computed Tomography (CT) – series of brain x-rays • Involves mapping slices of the brain using a computer • Magnetic Resonance Imaging (MRI) – uses a magnetic field to “take pictures” of the brain • More detail than CT scans MRI scan CT scan

Mapping Brain Function • Electroencephalogram (EEG) – provides a record of the electrical activity of groups of neurons just below the surface of the skull • Functional Magnetic Resonance Image (fMRI) – uses magnetic fields in the same way as an MRI, but goes a step further and pieces the pictures together to show changes over a short period of time • Positron Emission Tomography (PET) – involves injecting a person with a low dose of radioactive substance and then recording the activity of that substance in the person’s brain • Single Photon Emission Computed Tomography (SPECT) – similar to PET but uses somewhat different radiotracer technique PET EEG fMRI SPECT

From the Bottom Up: The Structures of the Brain • The brain can be roughly divided into 3 sections • Brainstem – lowest part of the brain that connects to the spinal cord • Cortex – outer wrinkled covering of the brain • Structures under the cortex (subcortical structures) – includes everything between the brainstem and the cortex

Brainstem • 4 important structures • Medulla – controls life-sustaining functions such as heart beat, breathing, and swallowing • Pons – influences sleep, dreaming, and coordination of movements • Reticular formation – plays crucial role in attention and arousal, such as attending to certain kinds of information in the environment • Cerebellum – controls all involuntary, rapid, fine motor movement (ex. People can sit upright in a chair because the cerebellum controls all the little muscles that keep you from falling out of the chair)

Structures Under the Cortex • Limbic system – involved in emotions, motivation, memory, and learning • Thalamus – round structure in the center of the brain • Hypothalamus – just below the front of the thalamus • Hippocampus – in the temporal lobes on each side of the brain • Amygdala – near the hippocampus • Cingulate cortex – in the cortex, right above the corpus callosum in the frontal and parietal lobes

The Limbic System • Thalamus – receives input from sensory systems, processes it, and then passes it on to the appropriate area • Hypothalamus – interacts with the endocrine system to regulate body temperature, thirst, hunger, sleeping, sexual activity, and mood • Hippocampus – critical in the formation of long-term memories and for memories of the locations of objects • Amygdala – involved in response to fear • Cingulate cortex – important role in emotion and cognition

The Cortex • Cortex – outermost part of the brain (wrinkly part) • Made up of tightly packed neurons and is actually only about 1/10 of an inch thick • Corticalization – refers to the fact that the cortex is wrinkled, allowing a much larger area of cortical cells to exist in the small space inside the skull • Divided into right and left sections called cerebral hemispheres • Cerebral hemispheres communicate with each other through the corpus callosum • Corpus callosum – thick bank of neurons (axons)

The Cortex • Each cerebral hemisphere can be roughly divided into 4 sections called lobes • Occipital lobes • Parietal lobes • Temporal lobes • Frontal lobes

Occipital Lobes • Visual information • Primary visual cortex – processes visual information from the eyes • Visual association cortex – helps identify and make sense of the visual information from the eyes • Example: a patient who had a tumor in the right occipital lobe area in the visual association cortex could see and even describe objects in physical terms but couldn’t identify them • Described a rose as a “red inflorescence” with a green tubular projection

Parietal Lobes • Process information regarding touch, temperature, body position, and possibly taste • Somatosensory cortex – processes information from the skin and internal body receptors for touch, temperature, and body position

The Biological Perspective