Neuroscience and Behavior
Intro
Z Everything psychological is simultaneously biological. You relate to the world through your body
Z “In spite of our mechanical magnificence, if it were not for this continuous stream of motor impulses, we would COLLAPSE! Like a bunch of BROCCOLI!” –Gene Wilder in Young Frankenstein
Z Aristotle believed that the mind was located in the heart, but Plato correctly located it in the head
Z Phrenology = theory that bumps on the skull could reveal our mental abilities and character traits. Invented by Franz Gall in the early 1800’s. We now know that this is a wrongheaded theory (first bad joke in the module)
Neural and Hormonal Systems Intro
M Tiny cells à Our body organs (ex. Stomach, heart, brain) à Larger systems (ex. for digestion, circulation, information processes) à human being!
M Biological psychologists = people who study the links between biological activity and psychological events, applying this information to the understanding of topics such as sleep and dreams, stress and disease
M Fortunately for scientists, the information systems of humans and other animals act very similarly
Neurons and Neural Impulses
µ Neurons = nerve cells that serve as building blocks of the neural info system. Many different types, but all variations on the same theme. Consists of a cell body and its branching fibers
µ Dendrites and axons = types of fibers. Dendrites receive information, which the axon then passes along to other neurons or to muscles or glands. Unlike the short and bushy dendrites, axons are sometimes very long
µ Myelin sheath = layer of fatty tissue. Insulates the axons and helps speed their impulses
µ Multiple sclerosis = disease in which myelin sheath deteriorates. Eventual loss of muscle control due to decrease in communication speed
µ Action potential = a brief electrical charge that travels down the axon, like in Men in Tights when Robin Hood kicks one of the soldiers and they all fall down. This neural impulse can travel at speeds ranging from 2 mph to 200 mph, but even the top speed is 3,000,000x times slower than that of electricity through a wire
µ Like batteries, neurons generate electricity from chemical events. 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 polarization is called the resting potential and it occurs because an unmyelinated axon’s membrane is selectively permeable
µ When a neuron fires, the first bit of the axon opens its gates, and the positively charged sodium ions flood through the channel. That part of the axon is then depolarized, causing the axon’s next channel to open, and then the next (again, like the Men in Tights example). During the refractory period (a rest), the neuron pumps the sodium ions back outside, and then it can fire again. This electrochemical process repeats itself 100 times a second
µ Some of the signals that a neuron receives are excitatory and stimulate the neuron to fire; others are inhibitory and refrain the neuron from firing. If excitation signals minus inhibitory signals exceed a minimum intensity (called the threshold), the combined signals trigger an impulse. The action potential (electrical impulses) then transmits down the axon
µ The neuron’s reaction is an all-or-none-response; it either fires or not, and no increase in the stimulus above the threshold will affect the impulse’s intensity or speed
Neural Communication
{ The discoveries of Santiago Ramon y Cajal and Sir Charles Sherrington have helped us determine today that the axon terminal of one neuron is separated from the receiving neuron. This junction is called the synapse, and the gap is called the synaptic gap or cleft
{ When the action potential reaches the knoblike terminals at an axon’s end, it triggers the release of neurotransmitters (chemical messengers), which then cross the synaptic gap and bind to receptor sites on the receiving neuron, like a key in a lock, or like the sword Anduril in the hands of Aragorn son of Arathorn, but probably more like the first example. For an instant, the neurotransmitter unlocks tiny channels at the receiving site, allowing ions to enter the receiving neuron, and either exciting or inhibiting its readiness to fire. Many drugs increase the availability of selected neurotransmitters by blocking their reuptake (when excess neurotransmitters are reabsorbed by the sending neuron)
{ Most neurons fire randomly depending on the amount of excitatory messages as opposed to inhibitory ones
{ Neurotransmitters affect our motions and emotions. Some examples include dopamine, serotonin, norepinephrine, Gamma-aminobutyric acid (GABA), and acetylcholine (ACh)
{ Dopamine influences movement, learning, attention, and emotion; excess activity at receptors has been linked with schizophrenia
{ ACh is one of the best-understood neurotransmitters. It works on neurons involved in muscle action, learning, and memory; when a person has Alzheimer’s disease, the neurons that produce this chemical messenger deteriorate. ACh is also the messenger at every junction between a motor neuron and skeletal muscle. When ACh is released to our muscle cells, our muscle contracts, so if the transmission is blocked, our muscles cannot contract (ex. curare, a poison on the tips of hunting darts used by certain South American Indians, and botulin, a poison formed in improperly canned food, cause paralysis by blocking ACh release from the sending neuron).
The Endorphins
‡ As discovered by Candace Pert and Solomon Snyder in 1973, the brain contains “opiate receptors” in areas linked with mood and pain sensations that take up opiate drugs like morphine. Further research showed that the brain contains certain types of neurotransmitter molecules similar to morphine, endorphins, natural opiates that are released in response to pain and vigorous exercise. Endorphins help explain all sorts of good feelings, such as “runner’s high,” the painkilling effects of acupuncture, and the indifference to pain in some severely injured people
How Drugs and Other Chemicals Alter Neurotransmission
¥ Though it might seem like a splendiferous solution, flooding the brain with opiate drugs such as heroin and morphine may make the brain stop producing natural opiates, so when the drug is withdrawn, agony (no more happiness) persists until the brain resumes production of natural opiates, or receives more artificial ones
¥ Agonists excite the neuron by mimicking a particular neurotransmitter or blocking its reuptake. Agonists can be drug molecules that are similar enough to the neurotransmitter to mimic its effects
¥ Antagonists inhibit by blocking neurotransmitters or by diminishing their release. An antagonist can be a drug molecule that is enough like the natural neurotransmitter to occupy its receptor site and block its effect but not similar enough to stimulate the receptor, kind of like if Boromir stole Anduril from Aragorn. Boromir would be able to hold onto the sword, and therefore would block Aragorn from using it. Actually, like the book says, it’s probably more like fitting foreign coins into a candy machine, but you can’t get candy from it
¥ A blood-brain barrier (awesome alliteration!) enables the brain to cut out unwanted chemicals circulating in the blood, and some chemicals don’t have the right shape to make it through this barrier, which makes the designing of therapeutic drugs difficult
The Nervous System
§ The body’s primary information system is the nervous system. The brain and spinal cord form the central nervous system (CNS), and the peripheral nervous system (PNS) is comprised of everything else. The PNS links the central nervous system with the body’s sense receptors, muscles, and glands; the sensory and motor axons carrying this PNS information are bundled into nerves (like electrical cables)
§ There are three types of neurons through which information can travel. Sensory neurons send information from the body’s tissues and sensory organs inward to the brain and spinal cord, which then process the information. This processing involves interneurons, which enable internal communication in the CNS. (Our nervous system has far more interneurons than sensory or motor neurons.) The CNS then sends instructions out to the body’s tissues via the motor neurons
The Peripheral Nervous System
Ö Our peripheral nervous system has two components: somatic and autonomic. The somatic nervous system controls the movements of our skeletal muscles, while the autonomic nervous system controls the glands and the muscles of our internal organs. The autonomic nervous system may sometimes be consciously overthrown, but usually it operates independently (autonomously; hence the name)
Ö The autonomic nervous system is a dual system. The sympathetic nervous system arouses us for defensive action. If something scares or infuriates you, the sympathetic system works to accelerate your heartbeat, raise your blood sugar, slow your digestion (your digestion isn’t quite so important when you’re about to be beat up or something drastic like that), and cool you with perspiration. When the stress reduces, the parasympathetic nervous system produces opposite effects by conserving energy to calm you and lower your blood sugar. An excellent example is when Aragorn sees Lurtz trying to kill Boromir. Aragorn is infuriated, and his sympathetic nervous system kicks in (the fight-or-flight response) to attack Lurtz. When Aragorn has killed Lurtz, his parasympathetic nervous system reacts by calming him down, and he is able to go and speak with Boromir one last time
The Central Nervous System
® The central nervous system’s spiral cord is an information highway connecting the brain to the peripheral nervous system. The spinal cord’s work is illustrated by the neural pathways governing our reflexes. A simple spinal reflex pathway is composed of a single sensory neuron and a single motor neuron, which often communicate through an interneuron. Examples include the knee-jerk response and the pain reflex
® To illustrate the pain reflex, let’s pretend that after Gandalf hands Frodo the ring and says “Take it, it’s quite cool,” Frodo takes the ring and finds it burning hot. Neural activity excited by the heat would travel via sensory neurons to interneurons in his spinal cord (for the moment, we’re pretending that hobbits have nervous systems like humans). The interneurons would respond by activating motor neurons to the muscles in his arm, and Frodo would jerk back and probably drop the ring. His hand would jerk away before his brain received and responded to the information that caused the poor hobbit to feel pain. “GANDALF!”
® If the top of your spinal cord was severed, you would not feel pain or pleasure, because your brain would literally and figuratively be out of touch with your body. You would lose all sensation and voluntary movement in body regions whose sensory and motor neurons connect with the spinal cord below its point of injury (like Ah Like in the book The Tiger In The Well)
® The brain receives information, interprets it, and decides responses, functioning rather like a computing machine
® We have like 300 trillion cortical synaptic connections. Clearly, being human takes a lot of nerve (second bad joke in the module). Neurons cluster into work groups called neural networks; they network with nearby neurons with which they can have short, rapid connections. The cells in each layer of a neural network connect with various cells in the next layer. Given feedback, networks are strengthened or sometimes connections are inhibited, and learning occurs. New computer models can simulate neural networks
The Endocrine System
% The endocrine system is interconnected with the nervous system. In fact, they are kindred systems: both secrete molecules that activate receptors elsewhere (though endocrine messages are much slower than those of the nervous system; however, the effects of an endocrine message usually lasts longer than a neural message).
% The endocrine system’s glands secrete hormones, different forms of chemical messengers. Some hormones are chemically identical to neurotransmitters. Hormones originate in one tissue, travel through the bloodstream, and affect other tissues. When they act on the brain, they influence our interest in sex, food, and aggression. These hormones influence many aspects of our lives, working to keep everything in balance while we respond to stress, exertion, and our own thoughts. For example, when the cave troll appears in Moria, Sam’s autonomic system probably ordered his adrenal glands (located on top of the kidneys) to release epinephrine (adrenaline) and norepinephrine (noradrenaline). His heart rate, blood pressure, and blood pressure all increased, giving him a surge of energy. After the emergency passed and the cave troll was dealt with, the hormones and the feelings of excitement lasted for a while, so instead of collapsing, Sam was able to rush over to Frodo and see if he was okay
% The most influential endocrine gland is the pituitary gland, a pea-sized structure located in the base of the brain, controlled by the hypothalamus. The pituitary releases growth-influencing hormones, and its secretions also influence the release of hormones by other endocrine glands. It is therefore a sort of master (or mistress) gland, whose master (or mistress) is the hypothalamus
% This feedback system (brain à pituitary à other glands à hormones à brain) demonstrates how the nervous system directs endocrine secretions, which then affect the nervous system. In fact, the distinctions between the two systems, and between neurotransmitters and hormones, are sometimes blurred