Chapter 3



Chapter 3 Lecture Notes

Biological Bases of Behavior

Neural Communication

Neurons-

• The body’s information system is built from billions of interconnected cells called neurons (nerve cells). There are many different types of neurons. Each has a cell body and branching fibers called dendrite which receive information. The axon fibers pass information along to other neurons, muscles, or glands. (Dendrites are short, axons long… sometimes several feet)

• Motor neurons are the body’s largest (on scale would be 4 mile long as compared to a basketball)

• A layer of fatty tissue called the myelin sheath insulates the axons of some neurons and helps speed their impulses. (In Lorenzo’s Oil, the myelin was destroyed and Lorenzo lost the communication to his muscles and eventually muscle control.)

• The speed of the neural impulse ranges from 2-200 miles per hour. (Even at top speed it is still 3 million times slower than electricity through a wire.

• We measure brain activity in milliseconds (.0001) and we measure computer activity in nanosecond (.000000001) Think about your reaction time to a sudden event loud noise…Your brain is more complex than a computer but not as fast at executing simple responses

• A neuron fires an impulse when it receives signals from sense receptors stimulated by pressure, heat, or light, or when it is stimulated by chemical messages from neighboring neurons. The impulse is called the action potential—or the brief electrical charge that travels down the axon.

• Neurons generate electricity from chemical events like a battery. The chemistry-to-electricity process involves the exchange of electrically charged atoms, called ions. The fluid interior of a resting axon has an excess of negatively charged ions, while the fluid outside the axon membrane has more positively charged ions.

• This positive-outside/negative-inside state is called the resting potential.

• The axon’s surface is very selective about what it allows in, in a sense it is selectively permeable. For example, a resting axon has gates that block positive sodium ions.

• When a neuron fires the security parameters change. The first bit of the axon opens its gates, like manhole covers flipping over, and the positively charged sodium ions flood through the membrane channel. This depolarizes the part of the axon, causing the axon’s next channel to open, and then the next, each on tripping the next.

• During the refractory period or the recharging period, the neuron pumps the positively charged sodium atoms back outside…then it can fire again.

• In myelinated neurons, the action potential speeds up by hopping from one myelin sausage to the next.

• Neurons receive signals on its dendrites and cell body. Some signals are excitatory—like pushing a neuron’s accelerator. Other signals are inhibitory, more like pushing its brake.

• If excitatory signals minus inhibitory signals exceed a minimum intensity level, called the threshold, the combined signals trigger action potential. (So if there is more excitatory that inhibitory, the neuron will fire or trigger the action potential)

• Increasing the stimulus above the threshold will not increase the action potential’s intensity.

• The neuron’s reaction is an all-or-nothing response—like a toilet… it either flushes or it doesn’t.

• The strength of the stimulus does NOT affect the action potential’s speed.

• A strong stimulus can trigger more neurons to fire…but the stimulus can not trigger a stronger or faster impulse.

How Neurons Communicate

• A Spanish anatomist named Santiago Ramon y Cajal described gaps between individual nerve cells and concluded that the individual neurons must function as independent agents within the nervous system.

• British physiologist Sir Charles Sherrington noticed that neural impulses were taking a long time to travel a neural pathway; he inferred that there must be a brief interruption in the transmission. He called the gap which is less than a millionth of an inch wide the synaptic gap or synaptic cleft.

• When the action potential reaches the knoblike terminals at an axon’s end, it triggers the release of chemical messengers called neurotransmitters. Within 1/10,000th of a second, the neurotransmitter molecules cross the synaptic gap and bind to receptor sites on the receiving neuron- like a key fits a lock. For an instant, the neurotransmitter unlocks tiny channels at the receiving site. This allows ions to enter the receiving neuron, thereby either exciting or inhibiting its readiness to fire. Excess neurotransmitters are reabsorbed by the sending neuron in a process called reuptake…many drugs increase the availability of selected neurotransmitters by blocking the reuptake.

How Neurotransmitters Influence Us

Neurotransmitters - Neurotransmitters are endogenous chemicals that are released from the synaptic vesicles in the axon terminal of the presynaptic cell to hook up to a receptor on the dendrite of the postsynaptic cell. Neurotransmitters are like keys which fit into the receptor lock. The receptor will recognize only one type of receptor. When a neurotransmitter is received by a receptor it either excites (depolarizes) or inhibits (hyperpolarizes) the postsynaptic cell. When a neuron is depolarized the membrane becomes more permeable to Na+ and is closer to firing (action potential). When a neuron is hyperpolarized the membrane becomes impermeable to Na+ and is harder to fire

Acetylcholine- play a vital role in learning and memory and is the messenger at every junction between a motor neuron and skeletal muscle.

• When ACh is released to our muscles, the muscles contract. If the transmission of Ach is blocked, our muscles can not contract. (Curare, a poison that South American Indians put on there hunting darts occupies and blocks ACh receptor sites, leaving the neurotransmitters unable to affect the muscles. If you are struck you will become paralyzed. Botulin—a poison from improperly canned food causes paralysis by blocking ACh release from the sending neuron. (Botox injections (Botulin) smooth wrinkles by paralyzing the underlying facial muscles)

• By contrast the venom of the black widow spider causes a synaptic flood of ACh and the result is violent muscle contractions, convulsions, and possible death.

Endorphins- natural opiates, similar to morphine released in response to pain and vigorous exercise

• Natural painkillers, boost mood

Dopamine- influences movement, learning, attention, and emotion

• excess dopamine receptor activity linked to schizophrenia; when starved of dopamine—the brain produces the tremors and decreased mobility of Parkinson’s disease

Seretonin- affects mood, hunger, sleep and arousal

• undersupply linked to depression, Prozac and some other anti-depressants drugs raise serotonin levels

Norepinephrine- helps control alertness and arousal

• Undersupply can depress mood

Gammaaminobutric (GABA)- a major inhibitory neurotransmitter

• Undersupply linked to seizures, tremors and insomnia

Glutamate- a major excitatory neurotransmitter; involved in memory

• Oversupply can over-stimulate the brain, producing migraines or seizures (which is why some people avoid MSG, monosodium glutamate, in food)

How drugs and other Chemical Alter Neurotransmission

• If you flood the brain with morphine and heroin, the brain stops producing its own natural opiates. When the drug is withdrawn, the brain may be deprived of any form of opiates. The result is agony that persists until the brain resumes production of its natural opiates or receives more artificial opiates.

• Drugs affect communication at the synapse, often by exciting or inhibiting neurons’ firing.

• Agonists excite. An Agonist can be a drug molecule that is similar enough to the neurotransmitter to mimic its effects or that blocks a neurotransmitter’s reuptake.

• Some opiate drugs produce a temporary high by amplifying normal sensations of arousal or pleasure

• Antagonists inhibit. An antagonist can be a drug molecule that inhibits a neurotransmitter’s release. Or it may be enough like the natural neurotransmitter to occupy its receptor site and block its effect but not similar enough to stimulate the receptor (rather like foreign coins that fit into but won’t operate a candy machine) Remember… curare poison causes paralysis by blocking acetylcholine receptors that produce muscle movement.

• Designing drugs may be harder than it sounds. A blood-brain barrier enables the brain to fence out unwanted chemicals circulating in the blood, and some chemicals don’t have the right shape to slither through the barrier.

• Scientists know that the tremors of Parkinson’s disease result from the death of nerve cells that produce dopamine. But giving the patient dopamine doesn’t help because dopamine can not cross the blood-brain barrier. But L-dopa, a raw material the brain can convert to dopamine, can sneak through, enabling many patients to regain better muscle control.

The Nervous System

Our primary information system is our nervous system. The Brain and spinal cord form the central nervous system. The peripheral nervous system links the central nervous system with the body’s sense receptors, muscles, and glands. The sensory and motor axons carrying the PNS information are bundled into the electrical cables called nerves. (The optic nerve bundles a million axon fibers into a single cable carrying the information that each eye sends to the brain)

Three types of neurons send messages through the nervous system

• Sensory neurons- send information from the body’s tissues and sensory organs inward to the brain and spinal cord, which process information. (We have a few million)

• Interneurons- enable internal communication within the central nervous system (Billions and Billions)

• Motor neurons- sends instructions to the body’s tissues (A few million)

The Peripheral Nervous System

The Peripheral Nervous System has two components

• Somatic Nervous System- controls the movement of our skeletal muscles

• Autonomic Nervous System- controls the glands and the muscles of our internal organs. It operates on its own (autonomously) to influence our internal functioning, including our heartbeat, digestion, and glandular activity. It is a dual system that includes the sympathetic nervous system and the parasympathetic nervous system.

o Sympathetic- arouses us for defensive action. If you are alarmed or scared your sympathetic system will accelerate you’re your heartbeat, slow your digestion, raise your blood sugar, dilate your arteries, and cool you with perspiration, making you alert and ready for action.

o The Parasympathetic nervous system produces the opposite effect. It conserves energy as it calms you by decreasing your heartbeat, lowering your blood sugar, and so forth. In everyday situations, the sympathetic and parasympathetic nervous systems work together to keep us in a steady internal state.

The Central Nervous System

The Spinal Cord is the information highway connecting the peripheral nervous system to the brain.

• Reflexes- our automatic responses to stimuli

• A simple spinal reflex pathway is composes of a single sensory neuron and a single motor neuron. They communicate through an interneuron. (Ex: knee jerk… a headless warm body could do it)

• When your fingers touch a flame, neural activity excited by the heat travels via sensory neurons to interneurons in your spinal cord. These interneurons respond by activating motor neurons to the muscles in your arm. That’s why it feels as if your hand jerks away not by choice, but on its own.

• Because the simple pain reflex pathway runs through the spinal cord and out, you hand jerks from the candle’s flame before your brain receives and responds to the information that causes you to feel pain.

• Neurons cluster into groups called neural networks—in order to have short, fast connections.

• Learning occurs as feedback strengthens connections that produce certain results. Piano practice builds neural connections

The Brain

The Tools of Discovery

• Lesion- naturally or experimentally cause destruction of brain tissue

• Clinical Observations- the oldest method, observes the effects of brain disease and injury, (University of Iowa have the largest registry of brain damaged observations)

• The electroencephalogram (EEG) is an amplified tracing of such waves by an instrument called an electroencephalograph. The technician presents a stimulus repeatedly and has a computer filter out brain activity unrelated to the stimulus, one can identify the electrical wave evoked by the stimulus.

• CT Scan- (Computed tomography) examines the brain by taking x-ray photographs that reveal brain damage

• PET Scan- (positron emission tomography) depicts brain activity by showing each brain area’s consumption of its chemical fuel, the sugar glucose. Patients receive a low dose of short-lived radioactive sugar and detectors around the subject’s head pick up the release of gamma rays from the sugar, which has concentrated in the active brain areas. A computer translates the signals into a map of the brain at work.

• MRI scans(magnetic resonance imaging) this technique exploits the fact that the centers of atoms spin like tops. In MRI scans, the head is put in a strong magnetic field, which aligns the spinning atoms. Then a brief pulse of radio waves disorients the atoms momentarily. When the atoms return to their normal spin, they release detectable signals, which become computer-generated images of concentrations. The result is a detailed picture of the brain’s soft tissue. (MRI scans reveal enlarged fluid-filled brain areas in some patients who have schizophrenia)

Lower-Level Brain Structures

Our brain processes most information outside of our awareness

• The brainstem- the oldest part and central core of the brain, beginning where the spinal cord swells as it enters the skull; the brainstem is responsible for the automatic survival functions.

• Medulla- the base of the brainstem; controls heartbeat and breathing

• Reticular formation- a finger-shaped nerve network in the brainstem that plays an important role in controlling arousal. It extends from the spinal cord right up to the thalamus.

• Atop the brainstem is the brain’s sensory switchboard, a joined pair of egg-shaped structures called the thalamus.

o It receives information from all the senses except smell and routes it to the higher brain regions that deal with seeing, hearing, tasting, and touching.

o It also receives some of the higher brain’s replies, which it then directs to the cerebellum and medulla.

o It also coordinates the brain’s electrical oscillations, which slow during sleep and speed up to produce waking consciousness

• The cerebellum extends from the rear of the brainstem. It is the “little brain” attached to the rear of the brainstem; it helps coordinate voluntary movement and balance.

o The cerebellum enables one type of nonverbal learning and memory

o Its most obvious function is coordinating voluntary movement.

o If you injured your cerebellum, you would have difficulty walking, keeping your balance, or shaking hands. Your movements would be jerky and exaggerated.

• The Limbic System- a doughnut-shaped neural system between the brain’s older parts and its cerebral hemispheres. Includes the amygdala, the hypothalamus, the hippocampus (helps process explicit memories for storage), and the pituitary gland

• The Amygdala- two almond shaped neural clusters that influence aggression and fear. When researchers (Kluver and Bucy lesioned the amygdala of a monkey, the ill-tempered monkey turned into a mellow monkey)

o It is not the only control center for aggression and fear, though. Our brain does not neatly organize behavior into structures.

o How about humans? In a few cases involving patients who suffered abnormalities, it reduced fits of rage, though sometimes with devastating side effects on the patient’s day to day functioning.

o Drastic psychosurgery is rarely used.

• The Hypothalamus- lies just below (hypo) the thalamus, directs several maintenance activities. It contains neural clusters… some influence hunger, regulate thirst, body temperature, and sexual behavior.

• It also monitors blood chemistry and takes orders from other parts of the brain.

EX: thinking about sex (in the cerebral cortex) can stimulate your hypothalamus to secrete hormones.

• Controls the pituitary “master gland” which in turn influences hormone release by other glands, which the hypothalamus monitors.

• Note: there is interplay between the nervous and hormone systems: The brain influences the hormone system which in turn influences the brain. The powerful little hypothalamus also exerts control by triggering autonomic nervous system activity.

• The hypothalamus also includes pleasure centers or reward centers. In studies, rats (not humans) would do anything to trigger the pleasure center… walk across an electrified floor. In another study when allowed to trigger their own stimulation by pressing a pedal, the rats would do so at a feverish pace… up to 7000 times per hour—or until they dropped from exhaustion.

• Animal research has revealed that both a general reward system that triggers the release of the neurotransmitter dopamine and specific centers associated with the pleasures of eating, drinking, and sex. Animals, it seems, come equipped with built-in systems that reward activities essential to survival.

• In humans, neurosurgeons have used electrodes to calm violent patients. Some researchers believe that addictive disorders, such as alcoholism, drug abuse, and binge eating, may stem from a reward deficiency syndrome—a genetically disposed deficiency in the natural brain systems for pleasure and well-being that leads people to crave whatever provides that missing pleasure or relieves negative feelings.

The Cerebral Cortex

The cerebral cortex is an intricate covering of interconnected neural cells that forms a thin surface layer on your cerebral hemispheres. It is your body’s ultimate control and information-processing center.

• Frogs and other amphibians have small cerebral cortex and operate extensively on preprogrammed genetic instructions.

• The larger the cortex, the more adaptable

• The cerebral cortex is 1/8th of an inch thick and contains some 20 to 23 billion nerve cells. Supporting these billions of nerve cells are nine times as many glial cells or glue cells that guide neural connections, provide nutrients and insulating myelin, and mop up ions and neurotransmitters. Some researchers believe that glial cells also participate in information transmission and memory.

• The cerebral cortex is wrinkled and you can only see about 1/3 of it. The folds increase the brain’s surface area.

• Each brain is divided up into four regions, or lobes.

o Frontal Lobes (behind your forehead) involved in speaking and muscle movements and in making plans and judgments.

o Parietal Lobes (at the top and to the rear) include the sensory cortex.

o Occipital Lobes (at the back of your head) include the visual areas, which receive visual information from the opposite visual field.

o Temporal Lobes (just above your ears) receives auditory information primarily from the opposite ear.

Motor Functions

• The Motor Cortex- an area at the rear of the frontal lobes that controls voluntary movements.

• Try moving your right hand in a circular motion. Then move your right foot in the same motion. Now reverse the foot motion (but not the hand) Now try the right hand and the left foot. Easier on the opposite than the same because less interference.

• Over 50 years ago, Otfrid Foerster and Wilder Penfield mapped the motor cortex. They painlessly (brain has no pain receptors) stimulated different cortical areas and noted the body responses. They mapped the motor cortex according to the body parts it controlled. Areas of the body requiring precise control, such as fingers and mouth, occupied the greatest amount of cortical space.

• Brown University researchers implanted 100 tiny recording electrodes in the motor cortexes of three monkeys. As the monkeys used a joystick to move a cursor to follow a moving red target, the researchers recorded the neural firing pattern. Then they let their computer operate the joystick. When the monkey merely thought about the move, the computer responded by moving the cursor with nearly the same proficiency as the monkey. This raises the hopes of those trying to enable the human mind to control machines, hands-free.

Sensory Functions

• Penfield identified a cortical area that specializes in receiving information from the skin and senses and from the movement of body parts.

• The Sensory Cortex- an area at the front of the parietal lobes that registers and processes body sensations. It is located parallel to the motor cortex and just behind it at the front of the parietal lobes

• The more sensitive a body region, the greater the area of the sensory cortex devoted to it; lips project to a larger brain area than do your toes. (Rats have a large area of the brain devoted to its whiskers)

• If a human loses a finger, the region of the sensory cortex devoted to receiving input from that finger branches to receive sensory input from the adjacent fingers. They then become more sensitive.

• Well practiced pianists have larger-than-usual auditory cortex area that encodes piano sounds and that deaf people have an enhanced visual cortex with greater peripheral vision.

• The brain is not just genes but experience too.

• The occipital lobes at the rear of the brain receive input from the eyes.

• The auditory area of the temporal lobes receives information from the ears

• (MRI scans of people with schizophrenia reveal that auditory areas of the temporal lobe are active during auditory hallucinations.

Association Areas- areas of the cerebral cortex that are not involved in primary motor or sensory functions… instead they are involved in higher mental functions such as learning remembering, thinking, and speaking

• Neurons in the association areas integrate information and associate sensory inputs with stored memories—an important part of thinking

• Because the association areas do not trigger any observable response, we can’t neatly specify the functions of the association areas

• The association areas interpret, integrate, and act on information processed by the sensory areas.

• Association areas in the frontal lobes enable us to judge, plan, and process new memories. People with damaged frontal lobes may have intact memories, score high on intelligence tests, and bake a cake, but unable to plan ahead to begin baking a cake. Others will remember recipes, measurements, and techniques but can not decipher the steps in preparing the meal.

• Frontal lobe damage can alter personality. Sometimes people whose frontal lobes are damaged lose moral compass as in the story of Phineas Gage.

• Parietal lobes are involved in math and spatial reasoning (Einstein parietal lobes were abnormally large)

• An area on the underside of the right temporal lobe enable us to recognize faces

Language

• Intricate coordination of many brain areas is needed for language

• Aphasia- impairment of language, usually caused by left hemisphere damage to either Broca’s area (impairing speaking) or to Wernicke’s area (impairing understanding)

• Broca’s area- controls language expression… if damaged a person would struggle to form words while still being able to sing familiar songs and comprehend speech.

• Wernicke’s area- control’s language reception… if damaged a person could only speak meaningless words.

• Reading aloud…The angular gyrus receives the visual information from the visual area and recodes it into auditory form

When we read aloud

1. the words register in the visual area

2. are relayed to the angular gyrus that transforms the words into an auditory code

3. are received and understood in Wernicke’s area

4. sent to Broca’s area (which controls the motor cortex

5. and creates the pronounced word

• Depending on which link in the chain is damaged, a different form of aphasia occurs. Damage to the angular gyrus leaves the person able to speak and understand but unable to read. Damage to Wernicke’s area disrupts understanding. Damage to Broca’s area disrupts speaking

• Remember… the mind’s subsystems are localized in particular brain regions, yet the brain acts unified as a whole.

Brain Reorganization

• Plasticity- the brain’s capacity for modification, as evident in brain reorganization following damage and in experiments on the effects of experience on brain development

• Most severed neurons will not regenerate, but neural tissue can reorganize in response to damage.

• Neuroscientists severed the neural pathways for incoming information from a monkey’s arm. The area of the sensory cortex that formerly received this input gradually shifted its function and began to respond when researchers touched the animal’s face.

• If a laser beam damages a spot in a cat’s eye, the brain area that received input from that spot will soon begin responding to stimulation from nearby areas in the cat’s eye.

• Another experiment reconfigured the brain of newborn ferrets to feed information from their from their eyes to brain regions normally assigned to hearing. Tests later showed the animals could see lights with their auditory cortex.

• If a blind person uses one finger to read Braille, the brain dedicated to that finger expands. The sense of touch invades the part of the brain that normally helps people see. PET scans also reveal activation of the visual cortex when blind people read Braille.

• Among deaf people who communicate with sign language, it is the temporal lobe area normally dedicated to auditory information that waits in vain for stimulation…Finally it looks for other signals to process like those from the visual systems

• If a body part is amputated, sensory fibers that terminate on adjacent areas of the sensory cortex may invade the brain tissue that’s no longer receiving sensory input. When stroking the face of someone whose hand had been amputated, VS Ramachandran found the person felt sensations not only on his face but also on his nonexistent fingers.

• The brain is not hardwired like once thought. It changes with time and can rewire itself with new synapses or select new uses for its reward circuits.

• Our brains are most plastic when we are young children. Children are born with a surplus of neurons. If an injury destroys one part of a child’s brain, the brain will compensate by putting other surplus areas to work.

• Hemispherectomies- removing a hemisphere of the brain to eliminate seizures

Our Divided Brains

• The brain’s two sides serve differing functions. Accidents, strokes, and tumors in the left hemisphere generally impair reading, writing, speaking, arithmetic reasoning, and understanding. Similar lesions in the right hemisphere seldom have such dramatic effects.

Splitting the Brain-

• Vogel and Bogen speculated that major epileptic seizures were caused by an amplification of abnormal brain activity that reverberated between the two hemispheres. They thought they could reduce seizures in their patients with uncontrollable epilepsy by cutting the communication between the hemispheres. They cut the corpus callosum, the wide band of axon fibers connecting the two hemispheres.

• The seizures were all but eliminated and the patients with these split brains were surprisingly normal.

• Our visual wiring enabled researchers to send information to the patient’s left or right brain- by having the patient stare at a spot and then flashing a stimulus to its right or left.

• A few people who have had split-brain surgery have been for a time bothered by the unruly independence of their left hand.

• “Alien hand syndrome” a neurological disorder in which people experience one hand as operating with a mind of its own. One patient claimed that her hand would sometimes grasp her throat during her sleep.

The Endocrine System

Endocrine system- the body’s “slow” chemical communication system; a set of glands that secrete hormones into the bloodstream

• The endocrine system’s glands secrete another form of chemical messengers called hormones, which originate in the in one tissue and travel through the bloodstream and affect other tissues, including the brain.

• Some hormones are chemically identical to neurotransmitters. Unlike the speed of the neurons zipping through the body in fractions of a second, the endocrine system’s messages trudge along. Several seconds or more elapse before the bloodstream can carry a hormone from an endocrine gland to its target tissue.

• Hormones influence growth, reproduction, metabolism, mood—working to keep everything in balance while we respond to stress, exertion, and our own thoughts.

• In danger, the autonomic nervous system orders the adrenal glands on top of the kidneys to release epinephrine and norepinephrine (also called adrenaline and nonadrenaline) which increase heart rate, blood pressure, and blood sugar—providing us with a surge of energy.

• The most influential endocrine gland is the pituitary gland—a pea sized structure in the base of the brain, where it is controlled by an adjacent brain area called the hypothalamus.

• The pituitary releases hormones that influence growth and its secretions also influence the release of hormones by other glands.

• The pituitary is the master gland whose own master is the hypothalamus.

Everything psychological is simultaneously biological.

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