Biological Psychology Notes Chapters 1-4 PDF

Contents Contents.................................................................................................................................................. 2 Introduction - Overview and Major Issues................................................................................................

Contents Contents.................................................................................................................................................. 2 Introduction - Overview and Major Issues.............................................................................................. 5 The Biological Approach to Behavior.................................................................................................. 5 Biological explanations of Behavior.................................................................................................... 6 Career Opportunities.......................................................................................................................... 6 The Use of Animals in Research.......................................................................................................... 9 Summary............................................................................................................................................. 9 Chapter 1 - Nerve Cells and Nerve Impulses......................................................................................... 11 The Cells of the Nervous System....................................................................................................... 11 Neurons and Glia................................................................................................................... 11 The Blood-Brain Barrier......................................................................................................... 15 Nourishment of Vertebrate Neurons.................................................................................... 17 Summary............................................................................................................................... 17 The Nerve Impulse............................................................................................................................ 18 Introduction.......................................................................................................................... 18 The Resting Potential of the Neuron..................................................................................... 18 The Action Potential.............................................................................................................. 21 Propagation of the Action Potential...................................................................................... 24 The Myelin Sheath and Saltatory Conduction....................................................................... 24 Local Neurons........................................................................................................................ 26 Summary............................................................................................................................... 26 Chapter 2 - Synapses............................................................................................................................. 28 The Concept of the Synapse............................................................................................................. 28 Properties of Synapses.......................................................................................................... 28 Relationship among EPSP, IPSP, and Action Potentials.......................................................... 29 Summary............................................................................................................................... 31 Chemical Events at the Synapse........................................................................................................ 32 The Discovery of Chemical Transmission at Synapses.......................................................... 32 The Sequence of Chemical Events at a Synapse................................................................... 32 Hormones.............................................................................................................................. 42 Summary............................................................................................................................... 44 Chapter 3 - Anatomy and Research Methods....................................................................................... 46 Structure of the Vertebrate Nervous System.................................................................................... 46 Terminology to Describe the Nervous System...................................................................... 46  The Spinal Cord..................................................................................................................... 49 The Autonomic Nervous System........................................................................................... 50 The Hindbrain........................................................................................................................ 51 The Midbrain......................................................................................................................... 52 The Forebrain........................................................................................................................ 53 The Ventricles........................................................................................................................ 56 Summary............................................................................................................................... 57 The Cerebral Cortex.......................................................................................................................... 58 Introduction.......................................................................................................................... 58 Organization of the Cerebral Cortex..................................................................................... 59 The Occipital Lobe................................................................................................................. 61 The Parietal Lobe................................................................................................................... 61 The Temporal Lobe................................................................................................................ 62 The Frontal Lobe................................................................................................................... 63 How Do the Parts Work Together?........................................................................................ 64 Summary............................................................................................................................... 64 Research Methods............................................................................................................................ 65 Introduction.......................................................................................................................... 65 Effects of Brain Damage........................................................................................................ 65 Effects of Brain Stimulation................................................................................................... 66 Recording Brain Activity........................................................................................................ 66 Correlating Brain Anatomy with Behavior............................................................................ 68 Summary............................................................................................................................... 68 Chapter 4 - Genetics, Evolution, Development, and Plasticity.............................................................. 71 Genetics and Evolution of Behavior.................................................................................................. 71 Mendelian Genetics.............................................................................................................. 71 Heredity and Environment.................................................................................................... 76 The Evolution of Behavior..................................................................................................... 78 Summary............................................................................................................................... 79 Development of the Brain................................................................................................................. 80 Maturation of the Vertebrate Brain...................................................................................... 80 Pathfinding by Axons............................................................................................................. 83 Determinants of Neuronal Survival....................................................................................... 84 The Vulnerable Developing Brain.......................................................................................... 86 Differentiation of the cortex................................................................................................. 87  Fine-Tuning by Experience.................................................................................................... 88 Brain Development and Behavioral Development................................................................ 89 Summary............................................................................................................................... 90 Plasticity after Brain Damage............................................................................................................ 92 Brain Damage and Short-Term Recovery.............................................................................. 92 Later Mechanisms of Recovery............................................................................................. 93 Summary............................................................................................................................... 97 Introduction - Overview and Major Issues The Biological Approach to Behavior Biological psychologists try to explain behavior in terms of its physiology, development, evolution, and function Consciousness So far, no one has offered a convincing explanation of consciousness o Chalmers and Rensch proposed that we regard consciousness as a fundamental property of matter However, saying it is a fundamental property doesn't mean that there is no reason The field of biological psychology Biological psychology: the study of the physiological, evolutionary, and developmental mechanisms of behavior and experience o Approximately synonymous with the terms; biopsychology, psychobiology, physiological psychology, and behavioral neuroscience Neuroscience includes more detail about anatomy and chemistry Biological psychology deals mostly with brain activity According to biological psychology; o We think and act as we do because of brain mechanisms We evolved those mechanisms because ancient animals built this way survived and reproduced Three main points from this book 1. Perception occurs in your brain o When something touches your hand, your hand sends a message to your brain You feel it in your brain, not your hand The brain can produce the experience of a hand without a hand, a hand has no experience 2. Mental activity and certain types of brain activity are inseparable o Monism: the idea that the universe consists of only one type of being The opposite is dualism, the idea that minds are one type of substance and matter is another According to monism, your thoughts are the same thing as your brain activity Brain activity doesn't cause thoughts and thoughts do not direct brain activity, thoughts are brain activity Nearly all neuroscientists and philosophers support the position of monism  3. We should be cautious about what is an explanation and what is not o Avoid overstating the conclusions from any research study Biological explanations of Behavior Type of Example from Birdsong Explanation Physiological A particular area of a songbird brain grows under the influence of testosterone; hence, it is larger in breeding males than in females or immature birds. That brain area enables a mature male to sing. Ontogenetic In certain species, a young male bird learns its song by listening to adult males. Development of the song requires certain genes and the opportunity to hear the appropriate song during a sensitive period early in life. Evolutionary Certain pairs of species have similar songs. For example, dunlins and Baird’s sandpipers, two shorebird species, give their calls in distinct pulses, unlike other shorebirds. The similarity suggests that the two evolved from a single ancestor. Functional In most bird species, only the male sings. He sings only during the reproductive season and only in his territory. The functions of the song are to attract females and warn away other males. Career Opportunities A research position ordinarily requires a PhD in psychology, biology, neuroscience, or other related field People with a master's or bachelor's degree might work in a research laboratory but would not direct it Many PhD researchers also do teaching Anyone who pursues a career in research needs to stay up to date on new developments by; o Attending colleagues o Reading research journals If you pursue a career on the outskirts of neuroscience, such as clinical psychology, school psychology, social work, or physical therapy, you should also stay up to date on the current major developments Magazine - Scientific American Mind Dana Foundation - www.dana.org Specialization Description Research Fields Research positions ordinarily require a PhD. Researchers are employed by universities, hospitals, pharmaceutical firms, and research institutes. Neuroscientist Studies the anatomy, biochemistry, or physiology of the nervous system. (This broad term includes any of the next five, as well as other specialties not listed.) Behavioral neuroscientist Investigates how functioning of the brain and (almost synonyms: other organs influences behavior. psychobiologist, biopsychologist, or physiological psychologist) Cognitive neuroscientist Uses brain research, such as scans of brain anatomy or activity, to analyze and explore people’s knowledge, thinking, and problem solving. Neuropsychologist Conducts behavioral tests to determine the abilities and disabilities of people with various kinds of brain damage, and changes in their condition over time. Most neuropsychologists have a mixture of psychological and medical training; they work in hospitals and clinics. Psychophysiologist Measures heart rate, breathing rate, brain waves, and other body processes and how they vary from one person to another or one situation to another. Neurochemist Investigates the chemical reactions in the brain. Comparative psychologist Compares the behaviors of different species (almost synonyms: and tries to relate them to their ways of life. ethologist, animal behaviorist) Evolutionary psychologist Relates behaviors, especially social behaviors, (almost synonym: including those of humans, to the functions sociobiologist) they have served and, therefore, the presumed selective pressures that caused them to evolve. Practitioner Fields of Require a PhD, PsyD, or master’s degree. In Psychology most cases, their work is not directly related to neuroscience. However, practitioners often need to understand it enough to communicate with a client’s physician. Clinical psychologist Employed by hospital, clinic, private practice, or college; helps people with emotional problems. Counseling psychologist Employed by hospital, clinic, private practice, or college. Helps people make educational, vocational, and other decisions. School psychologist Most are employed by a school system. Identifies educational needs of schoolchildren, devises a plan to meet the needs, and then helps teachers implement it. Medical Fields Require an MD plus about four years of additional specialized study and practice. Physicians are employed by hospitals, clinics, medical schools, and in private practice. Some conduct research in addition to seeing patients. Neurologist Treats people with brain damage or diseases of the brain. Neurosurgeon Performs brain surgery. Psychiatrist Helps people with emotional distress or troublesome behaviors, sometimes using drugs or other medical procedures. Allied Medical Field Ordinarily require a master’s degree or more. Practitioners are employed by hospitals, clinics, private practice, and medical schools. Physical therapist Provides exercise and other treatments to help people with muscle or nerve problems, pain, or anything else that impairs movement. Occupational therapist Helps people improve their ability to perform functions of daily life, for example, after a stroke. Social worker Helps people deal with personal and family problems. The activities of a social worker overlap those of a clinical psychologist. The Use of Animals in Research Four reasons to study nonhumans 1. The underlying mechanisms of behavior are similar across species and sometimes easier to study in a nonhuman species 2. We are interested in animals for their own sake 3. What we learn about animals sheds light on human evolution 4. Legal or ethical restrictions prevent certain kinds of research on humans Degrees of opposition "Minimalists" o Tolerate certain types of animal research but wish to limit/prohibit others depending on the probable value of the research, the amount of distress to the animal, and type of animal (e.g., insect vs chimpanzee) "Abolitionists" o See no room for compromise, all animals have the same rights as humans Animals cannot consent --> wrong to use them in every case The legal standard emphasizes "the three R's" o Reduction of animal numbers (using fewer animals) o Replacement (using computer models or other substitutes for animals when possible) o Refinement (modifying the procedures to reduce pain and discomfort) In the US, every college and institution that receives government research funds is required to have an Institutional Animal Care and Use Committee o Composed of veterinarians, community representatives, and scientists o Evaluates the proposed experiments, specifies procedures to minimize pain and discomfort Summary Two profound, difficult questions; Why the universe exists Why consciousness exists Three key points; 1. Perception occurs in your brain, not in your skin or the object you see 2. Brain activity is inseparable from mental activity 3. It's important to be cautious about what is or isn't an explanation of behavior  Biological psychologists address four types of questions about any behavior Physiological: how does the behavior relate to the physiology of the brain and other organs? Ontogenetic: how does it develop within the individual? Evolutionary: how did the capacity for the behavior evolve? Functional: why did the capacity for this behavior evolve? Many careers relate to biological psychology, including various research fields, medical specialties, counselling, and psychotherapy Researchers study animals because the mechanisms are sometimes easier to study in nonhumans, because they are interested in animal behavior for its own sake, because they want to understand the evolution of behavior, and because certain kinds of experiments are difficult/impossible with humans Using animals in research is ethically controversial However, some questions can only be investigated through animal research Animal research today is conducted under legal and ethical controls that attempt to minimize animal distress Chapter 1 - Nerve Cells and Nerve Impulses The Cells of the Nervous System Neurons and Glia The nervous system consists of two kinds of cells; o Neurons: receive information and transmit it to other cells There are around 86 billion neurons in an adult human brain o Glia: supports and protects neurons by maintaining homeostasis, forming myelin, and assisting in signal transmission Santiago Ramón y Cajal o In the late 1800s, Santiago Ramón y Cajal used a newly developed staining technique to show that a small gap separated the tip of a neuron's fiber from the surface of the next neuron The structures of an animal cell o Plasma membrane The surface of a cell A structure that separates the inside of the cell from the outside environment Most chemicals cannot cross the membrane Protein channels in the membrane permit a controlled flow of water, oxygen, sodium, potassium, calcium, chloride, and other important chemicals o Nucleus All animal cells (excluding mammalian red blood cells) have a nucleus Structure that contains the chromosomes (DNA) o Mitochondrion (mitochondria) Structure that performs metabolic activities, providing the energy that the cell uses for all activities Contains separate genes from those in the nucleus Mitochondria differ from one another genetically Overactive mitochondria --> burns fuel rapidly and overheats, even in cool environments Underactive mitochondria --> predisposed to depression and pains Mutated mitochondrial genes are a possible cause of autism o Ribosomes The sites within a cell that synthesize new protein molecules Some float freely in the cell, others are attached to the endoplasmic reticulum (ER) o Endoplasmic reticulum (ER) A network of thin tubes that transport newly synthesized proteins to other locations The structure of a neuron o All neurons include a soma (cell body) Most also have dendrites, an axon, and presynaptic terminals The tiniest neurons lack axons, and some lack well-defined dendrites Dendrites: branching fibres that get narrower near their ends; its surface is lined with specialized synaptic receptors, at which the dendrite receives information from other neurons The greater the surface area of a dendrite, the more information it can receive Dendritic spines: short outgrowths that increase the surface area available for synapses Soma (cell body): contains the nucleus, ribosomes, and mitochondria In many neurons, the cell body is like the dendrites - covered with synapses on its surface Axon: a thin fibre of constant diameter; conveys an impulse toward other neurons, an organ, or a muscle Can be more than a meter in length Spinal cord to your feet Myelin sheath: sheaths of insulating material that cover axons; increases the speed of transmission through the axon through the use of gaps (Nodes of Ranvier) Invertebrate axons do not have myelin sheaths Presynaptic terminal (end bulb or bouton): the end point of an axon; where the axon releases chemicals that cross through the junction between that neuron and another cell o Motor neuron: with its soma in the spinal cord, receives excitation through its dendrites and conducts impulses along its axon to a muscle --> contraction o Sensory neuron: specialized at one end to be highly sensitive to a particular type of stimulation (light, sound, touch) o Afferent neuron: brings information into a structure (A as in Admit; sensory neurons are afferent to the nervous system) o Efferent neuron: carries information away from a structure (E as in Exit; motor neurons are efferent to the nervous system) o Intrinsic (inter-) neuron: the dendrites and axon are entirely contained within a single structure (an intrinsic neuron of the thalamus has its axon and all its dendrites within the thalamus) Variations among neurons o Neurons vary enormously in size, shape, and function The shape determines its connections with other cells and thereby determines its function The widely branching dendrites of the Purkinje cell in the cerebellum enable it to receive input from up to 200,000 other neurons Some neurons receive input from as few as two other cells Glia (neuroglia) o Outnumber neurons in the cerebral cortex, but neurons outnumber glia in many other brain areas (e.g., cerebellum) o Types of glia: Astrocytes Star-shaped Wraps around the synapses of functionally related axons o Shields them from chemicals circulating in the surroundings Takes up the ions and transmitters released by axons and then releases them back o --> Helps synchronize closely related neurons, enabling their axons to send messages in waves o --> Important for generating rhythms (e.g., breathing) Dilates the blood vessels to bring more nutrients into brain areas that have heightened activity Triparte synapse hypothesis: the tip of an axon releases chemicals that cause the neighbouring astrocyte to release chemicals of its own --> magnifies or modifies the message to the next neuron o Possible contributor process to learning and memory Responds to hormones and thereby influences neurons Microglia Act as parts of the immune system, removing viruses and fungi from the brain Proliferate after brain damage, removing dead or damaged neurons Contribute to learning by removing the weakest synapses Oligodendrocytes (in the brain and spinal cord) and Schwann cells (periphery of the body) Build the myelin sheaths that surround and insulate some neurons Also supply an axon with nutrients necessary for proper functioning Radial glia Guide the migration of neurons and their axons and dendrites during embryonic development When embryological development finishes, most radial glia differentiate into neurons o A smaller number differentiates into astrocytes and oligodendrocytes  The Blood-Brain Barrier Many chemicals cannot cross from the blood to the brain Why we need a blood-brain barrier o When a virus invades a cell, mechanisms within the cell extrude virus particles through the membrane so that the immune system can find them The immune system kills the virus and the cell that contains it Works fine if the virus-infected cell is a skin cell or a blood cell, as they are easy to replace With few exceptions, the vertebrate brain does not replace damaged neurons o The body lines the brain's blood vessels with tightly packed cells that keep out most viruses, bacteria, harmful chemicals Certain viruses do cross the blood-brain barrier (e.g., rabies) How the blood-brain barrier works o The blood-brain barrier depends on the endothelial cells that form the walls of the capillaries Outside the brain, such cells are separated by small gaps In the brain, they are joined so tightly that they block viruses, bacteria, and other harmful chemicals from passage o The barrier keeps out useful chemicals (all fuels and amino acids) as well as harmful ones What can freely cross through the cell walls:  Oxygen Carbon dioxide Fat soluble molecules o Vitamins A and D o Drugs that affect the brain (anti-depressants, heroin, etc.) How fast a drug takes effect depends largely on how readily it dissolves in fats --> how easily it crosses the blood-brain barrier Water crosses through special protein channels in the wall of the endothelial cells For other chemicals, the brain uses active transport (a protein-mediated process that expends energy to pump chemicals from the blood into the brain) What is pumped actively: o Glucose (the brain's main fuel) o Amino acids (building blocks of proteins) o Purines o Choline o A few vitamins o Iron Possibly insulin and certain other hormones also cross the blood-brain barrier, but the mechanism is unclear  Nourishment of Vertebrate Neurons Vertebrate neurons depend almost entirely on glucose (a sugar) for nutrition o Most other cells use a variety of carbohydrates and fats Cancer cells and the testis cells that make sperm also rely on glucose o Metabolizing glucose requires oxygen --> neurons need a steady supply The human brain is only 2% of the body's weight, but uses about 20% of its oxygen, and 25% of its glucose o To use glucose, the body needs vitamin B1, thiamine Prolonged thiamine deficiency (common in alcoholics), leads to death of neurons and a condition called Korsakoff's syndrome Marked by severe memory impairments Summary Neurons receive information and convey it to other cells o The nervous system also contains glia; cells that enhance and modify the activity of neurons in many ways In the late 1800s, Santiago Ramón y Cajal used newly discovered staining techniques to establish that the nervous system is composed of separate cells, now known as neurons Neurons contain the same internal structures as other animal cells Neurons have these major parts: o Soma (cell body) o Dendrites o An axon with branches o Presynaptic terminals Neurons' shapes vary greatly depending on their functions and their connections with other cells Blood-brain barrier o Because of the blood-brain barrier, many molecules cannot enter the brain The barrier protects the nervous system from viruses and many dangerous chemicals o The blood-brain barrier consists of an unbroken wall of cells that surround the blood vessels of the brain and spinal cord A few small, uncharged molecules (e.g., water, oxygen, carbon dioxide) cross the barrier freely  Fat soluble molecules also do Active transport proteins pump glucose, amino acids, and a few other chemicals into the brain and spinal cord Certain hormones, including insulin, also cross the blood-brain barrier Neurons rely heavily on glucose o Glucose is the only nutrient that crosses the blood-brain barrier in large quantities o They also need thiamine (vitamin B1) to use glucose The Nerve Impulse Introduction Why don't axons use electrical conduction? o They could transfer information at a velocity approaching the speed of light However, given that your body is made of water and carbon compounds and not copper wire, the strength of an impulse would decay rapidly as it travelled A touch on your shoulder would feel stronger than a touch on your abdomen Axons regenerate an impulse at each point o Signal strength doesn't weaken o Is a lot slower than electrical conduction (from less than 1m/s to about 100m/s) The Resting Potential of the Neuron Messages in a neuron develop from disturbances of the resting potential Membrane o All parts of a neuron are covered by a membrane (8nm thick) Composed of two layers of phospholipid molecules (containing chains of fatty acids and a phosphate group) Embedded among the phospholipids are cylindrical protein molecules through which certain chemicals can pass Resting potential o When at rest, the membrane maintains an electrical gradient (polarization) = There is a difference in electrical charge between the inside and outside of the cell The electrical potential inside the membrane is slightly negative with respect to the outside Mainly because of negatively charged proteins inside the cell  The difference in voltage is called the resting potential o Microelectrodes (fine glass tube with a salt solution) can be used to measure the resting potential o A typical level is -70 millivolts (mV) Forces acting on sodium and potassium ions o The membrane has selective permeability = some chemicals pass through it more freely than others Some molecules cross freely through channels that are always open: Oxygen carbon dioxide Urea Water Some molecules cross through membrane channels (or gates) that are sometimes open and sometimes closed: Sodium Potassium Calcium Chloride o When the membrane is at rest, the sodium and potassium channels are closed Permits almost no flow of sodium and only a small flow of potassium Stimulation can open these channels, permitting freer flow of either/both ions o Sodium-potassium pump The sodium-potassium pump, a protein complex, repeatedly transports three sodium ions out of the cell while drawing two potassium ions into it --> 10x more sodium ions outside the membrane than inside --> More potassium ions inside than outside Active transport --> requires energy o When the neuron is at rest: Two forces act on sodium, both trying to push it into the cell Electrical gradient: sodium is positively charged and the inside of the cell is negatively charged, opposite charges attract Concentration gradient: the difference in distribution of ions across the membrane; sodium is more concentrated outside than inside, sodium is more likely to enter the cell than to leave it (laws of probability) Sodium would enter rapidly into the cell if it could Two forces act on potassium, one pushing it in, the other pushing it out of the cell Electrical gradient: potassium is positively charged and the inside of the cell is negatively charged, opposite charges attract Concentration gradient: potassium is more concentrated inside the cell than outside, so the concentration gradient tends to drive it out o The concentration gradient counteracts the attraction The forces are almost in balance, but not quite (some potassium leaks out)  The sodium-potassium pump continues pulling potassium into the cell, counteracting the ions that leak out o Negative proteins and ions Negative proteins sustain the membrane's polarization Negative chloride ions are mainly outside the cell When the membrane is at rest, the concentration gradient and electrical gradient balance o Opening chloride channels would produce little effect Why a resting potential? o The resting potential prepares the neuron to respond rapidly Excitation opens channels that allow sodium to enter the cell rapidly The Action Potential Action potentials: messages sent by axons The all-or-none law o Any subthreshold stimulation produces a small response that quickly decays o Any stimulation beyond the threshold produces a big response (action potential) o All action potentials of any given neuron are approximately equal in amplitude (intensity) and velocity The amplitude and velocity of an action potential are independent of the intensity of the stimulus that initiated it Action potentials can vary across neurons Thicker axons convey axon potentials at greater velocities (and more action potentials per second) The timing can vary A taste axon shows one rhythm of responses for sweet tastes and a different rhythm for bitter tastes The molecular basis of the action potential o Three principles behind the action potential: 1. At the start, sodium ions are mostly outside the neuron, and potassium ions are mostly inside 2. When the membrane is depolarized, sodium and potassium channels in the membrane open 3. At the peak of the action potential, the sodium channels close o A neuron's membrane contains cylindrical proteins, that allow a particular type of ion to cross the membrane Sodium channel (or gate): a protein that allows sodium to cross Potassium channel (or gate): a protein that allows potassium to cross o The channels are voltage-gated - their permeability depends on the voltage difference across the membrane The channels open when the membrane becomes depolarized Of the total number of sodium ions near the axon, less than 1% cross the membrane during an action potential o Even during the peak, sodium ions are still far more concentrated outside the neuron At the peak of the action potential, the sodium gates snap shut The potassium gates remain open The role of potassium: At first, opening the potassium channels makes little difference After many sodium ions have crossed the membrane, the inside of the cell has a slight positive charge o At this point, both the concentration gradient and the electrical gradient drive potassium ions out of the cell o As they flow out, they carry with them a positive charge Enough potassium ions leave to drive the membrane beyond its resting level to a temporary hyperpolarization o At the end of the process, the membrane has returned to its resting potential, but the inside of the neuron has slightly more sodium ions and slightly fewer potassium ions than before The sodium-potassium pump restores the original distribution of ions (takes time) After an unusually rapid series of action potentials, the pump cannot keep up --> sodium accumulates within the axon --> toxic to a cell o Happens during a stroke or after using certain drugs o Action potentials require the flow of sodium and potassium Local anaesthetic drugs (Novocain and Xylocaine) attach to the sodium channels of the membrane Prevents sodium ions from entering Your receptors might be screaming in pain, but the signal doesn't go to your brain  Propagation of the Action Potential During an action potential, sodium ions enter a point on the axon o That spot becomes temporarily positively charged in comparison to neighbouring areas along the axon Positive ions flow within the axon to neighbouring regions Slightly depolarizes the next area of the membrane, causing it to reach its threshold and open its channels Then the membrane regenerates the action potential at that point --> travels along the axon At its start, the action potential "back-propagates" into the cell body and dendrites o The cell body and dendrites don't conduct action potentials, but they passively register the electrical event that started in the nearby axon o When an action potential back-propagates into a dendrite, the dendrite becomes more susceptible to the structural changes responsible for learning Action potential 1. When an area of the axon membrane reaches its threshold of excitation, sodium channels and potassium channels open. 2. At first, the opening of potassium channels produces little effect. 3. Opening sodium channels lets sodium ions rush into the axon. 4. Positive charge flows down the axon and opens voltage gated sodium channels at the next point. 5. At the peak of the action potential, the sodium gates snap shut. They remain closed for the next millisecond or so, despite the depolarization of the membrane. 6. Because voltage-gated potassium channels remain open, potassium ions flow out of the axon, returning the mem brane toward its original depolarization. 7. A few milliseconds later, the voltage-dependent potassium channels close. The Myelin Sheath and Saltatory Conduction Myelinated axons are covered with layers of fats and proteins o Interrupted periodically by short sections of axon (nodes of Ranvier) Sodium channels are virtually absent between nodes A myelinated axon admits sodium only at its nodes After an action potential occurs at a node, sodium ions enter the axon and diffuse, pushing a chain of positive charge along the axon to the next node, where they regenerate the action potential The distance between the nodes is generally at least 100x as long as a node In multiple sclerosis, the immune system attacks myelin sheaths An axon that has lost its myelin sheath is not the same as an axon that never had one  o An axon that lost its sheathe doesn't have sodium channels where the sheaths used to be --> most action potentials die out between one node and the next o Saltatory conduction: the jumping of action potentials from node to node The refractory period o As a result of the sodium gates shutting at the peak of the action potential, the cell is in a refractory period during which it resists the production of further action potentials Prevents the action potential from going back in the opposite direction o Absolute refractory period The first part of the refractory period The membrane cannot produce another action potential 1ms long o Relative refractory period A stronger-than-usual stimulus is necessary to initiate an action potential 2-4ms long  Local Neurons Local neurons: small neurons that have no axon; exchange information with only their closest neighbours o Do not follow the all-or-none law When a local neuron receives information from other neurons, it has a graded potential (a membrane potential that varies in magnitude in proportion to the intensity of the stimulus) The change in membrane potential is conducted to adjacent areas of the cell, in all directions, gradually decaying as it travels Those various areas of the cell contract other neurons, which they excite or inhibit o Local neurons are difficult to study because it is almost impossible to insert an electrode into a tiny cell without damaging it Summary The action potential transmits information without loss of intensity over distance o The cost is a delay between the stimulus and its arrival in the brain The inside of a resting neuron has a negative charge with respect to the outside o This is mainly because of negatively charged proteins inside the neuron The sodium-potassium pump moves sodium ions out of the neuron, and potassium ions in Resting potential o When the membrane is at rest, both the electrical gradient and the concentration gradient would act to move sodium ions into the cell, except that its gates are closed o The electrical gradient tends to move potassium ions into the cell, but the concentration gradient tends to move it out The two forces almost balance out, but not quite Net tendency for potassium to exit the cell All-or-none law: for any stimulus greater than the threshold, the amplitude and velocity of the action potential are independent of the size of the stimulus that initiated it Action potential o When the membrane is sufficiently depolarized to reach the cell's threshold, the sodium and potassium channels open. Sodium ions enter rapidly, reducing and reversing the charge across the membrane. o After the peak of the action potential, the membrane returns toward its original level of polarization because of the outflow of potassium ions. o The action potential is regenerated at successive points along the axon as sodium ions flow through the core of the axon and stimulate the next point along the axon to its threshold. The action potential maintains a constant magnitude as it passes along the axon. o Immediately after an action potential, the membrane enters a refractory period, curing which it is resistant to starting another action potential. In axons that are covered with myelin, action potentials form only in the nodes that separate myelinated segments o Transmission in myelinated axons is faster than in unmyelinated axons. Local neurons are small, with no axon o Local neurons convey information over short distances. Contrary to a popular belief, people use all of their brain, not some smaller percentage o However, we do not use all of it at once Chapter 2 - Synapses The Concept of the Synapse Properties of Synapses Chemicals are the main way that neurons communicate o Neurons transmit chemicals at specialized junctions (synapses) Charles Scott Sherrington physiologically demonstrated that communication between one neuron and the next differs from communication along a single axon o Introduced the term synapse to describe the gap between neurons o Studied reflexes: 1. Reflexes are slower than conduction along an axon --> some process (synapse) slows down conduction Reflex arc: the circuit from sensory neuron to muscle response 2. Several weak stimuli presented at nearby places or times produce a stronger reflex than one stimulus alone Graded potentials can be either depolarizations (excitatory) or hyperpolarizations (inhibitory) o A graded depolarization is known as an excitatory postsynaptic potential (EPSP) Results from a flow of sodium ions into the neuron If an EPSP doesn't cause the cell to reach its threshold, the depolarization decays quickly Temporal summation: several impulses from one neuron over time Spatial summation: impulses from several neurons at the same time Temporal and spatial summation ordinarily occur together  o A neuron might receive input from several axons in close succession 3. When one set of muscles becomes excited, a different set becomes relaxed Flexor muscles: draw an extremity toward the trunk of the body Extensor muscles: move an extremity away from the body A dog raising one leg needs to extend the other legs to maintain balance A pinch on the foot sends a message along a sensory neuron to an interneuron (intermediate neuron) that excites the motor neurons connected to the flexor muscles of that leg and the extensor muscles of the other legs o The interneuron sends messages to inhibit the extensor muscles in that leg and the flexor muscles of the three other legs At inhibitory synapses, input from an axon hyperpolarizes the postsynaptic cell (=increases the negative charge within the cell, moving it farther from the threshold) o Decreases the probability of an action potential o Inhibitory postsynaptic potential (IPSP): temporary hyperpolarization of a membrane Resembles an EPSP Occurs when synaptic input selectively opens the gates: For potassium ions to leave the cell (carrying a positive charge with them) For chloride ions to enter the cell (carrying a negative charge) Relationship among EPSP, IPSP, and Action Potentials When neuron 1 excites neuron 3, it also excites neuron 2, which inhibits neuron 3 o The excitatory message reaches neuron 3 faster because it goes through just one synapse Results in a burst of excitation (EPSP) in neuron 3, which quickly slows or stops  How the nervous system controls the outcome; o The axon from either cell A or cell B stimulates cell X with +1 unit If the threshold of cell X is +1, then cell X responds to A or B If the threshold of cell X is +2, then cell X responds to A and B Differences between synapses: o Some synapses produce fast, brief effects, others produce slow, long-lasting effects  The effect of two synapses at the same time can be more than double the effect of either one, or less than double The strength of a synapse can vary from one time to another o Most neurons have a spontaneous firing rate, a periodic production of action potentials even without synaptic input The EPSPs increase the frequency of action potentials above the spontaneous rate 10 action potentials per second --> 15+ The IPSPs decrease the frequency of action potentials below the spontaneous rate 10 action potentials per second --> 5 or fewer Summary The synapse is the point of communication between two neurons o Charles S. Sherrington's observations of reflexes enabled him to infer the existence of synapses and many of their properties Because transmission through a reflex arc is slower than transmission through an equivalent length of axon, Sherrington concluded that some process at the synapses delays transmission Graded potentials (EPSPs and IPSPs) summate their effects o Temporal summation: summation of graded potentials from stimuli at different times o Spatial summation: summation of graded potentials from different locations Inhibition is more than just the absence of excitation, it is an active brake that suppresses excitation o For effective functioning of the nervous system, inhibition is just as important as excitation Stimulation at a synapse produces a brief graded potential in the postsynaptic cell o EPSP: an excitatory graded potential (depolarization) Occurs when gates open to allow sodium to enter the neuron's membrane o IPSP: an inhibitory graded potential (hyperpolarization) Occurs when gates open to allow potassium to leave or chloride to enter The EPSPs on a neuron compete with the IPSPs o The balance between the two increases/decreases the neuron's frequency of action potentials Chemical Events at the Synapse The Discovery of Chemical Transmission at Synapses Sympathetic nervous system: a set of nerves that accelerates the heartbeat, relaxes the stomach muscles, dilates the pupils of the eyes, and regulates other organs History - the discovery that synapses are chemical o Sherrington assumed that synapses were electrical, not chemical T. R. Elliott found that applying adrenaline directly to the surface of the heart, the stomach, or the pupils produces the same effects as those of the sympathetic nervous system --> suggested that the sympathetic nerves stimulate muscles by releasing adrenaline or a similar chemical Otto Loewi experimented by stimulating the vagus nerve, thereby decreasing a frog's heart rate Collected fluid from around that heart, transferred it to a second frog's heart o Found that the second heart also decreased its rate of beating Stimulated the accelerator nerve to the first frog's heart, increasing the heart rate o Collected fluid from that heart and transferred it to the second frog's heart o --> its heart rate increased --> stimulating one nerve released something that inhibited heart rate, and stimulating a different nerve released something that increased heart rate --> realized that he was collecting and transferring chemicals, not loose electricity --> concluded that nerves send messages by releasing chemicals The Sequence of Chemical Events at a Synapse Major events: 1. Neuron synthesizes chemicals that serve as neurotransmitters Smaller neurotransmitters in the axon terminals Neuropeptides in the cell body 2. Action potentials travel down the axon At the presynaptic terminal, an action potential enables calcium to enter the cell Calcium releases neurotransmitters from the terminals and into the synaptic cleft Synaptic cleft: the space between the presynaptic and postsynaptic neurons 3. The released molecules diffuse across the narrow cleft, attach to receptors, and alter the activity of the postsynaptic neuron Mechanisms vary for altering that activity 4. The neurotransmitter molecules separate from their receptors 5. The neurotransmitter molecules may be taken back into the presynaptic neuron for recycling or they may diffuse away 6. Some postsynaptic cells send reverse messages to control the further release of neurotransmitter by presynaptic cells Types of neurotransmitters o Neurotransmitters: the chemicals that neurons release that affect other neurons A hundred or so are known Glutamate is the most abundant neurotransmitter in the nervous system Neurotransmitter Type Examples Amino Acids glutamate, GABA, glycine, aspartate, maybe others  A Modified Amino Acid acetylcholine Monoamines (also indoleamines: serotonin; modified from amino catecholamines: dopamine, acids) norepinephrine, epinephrine Neuropeptides (chains of endorphins, substance P, amino acids) neuropeptide Y, many others Purines ATP, adenosine, maybe others Gases NO (nitric oxide), maybe others o The oddest transmitter is nitric oxide (NO) Not to be confused with nitrous oxide (N2O) Nitric oxide is poisonous in large quantities, yet many neurons contain an enzyme that enables them ti make it efficiently Many neurons release nitric oxide when stimulated Nitric oxide also dilates the nearby blood vessels, thereby increasing blood flow to that brain area Synthesis of transmitters Nearly all neurotransmitters are synthesized from amino acids (obtained from proteins in the diet) Increasing serotonin levels Your serotonin levels rise after you eat foods richer in tryptophan (soy) and fall after something low in tryptophan (maize) Tryptophan competes with other amino acids  One way to increase tryptophan entry to the brain is to decrease consumption of phenylalanine, another is to eat carbohydrates o Carbohydrates increase the release of insulin, which takes several competing amino acids out of the bloodstream and into body cells --> decreases competition against tryptophan Storage of transmitters Most neurotransmitters are synthesized in the presynaptic terminal, near the point of release The presynaptic terminal stores high concentrations of neurotransmitter molecules in vesicles, tiny nearly spherical packets Nitric oxide is an exception, as it is released as soon as it forms The presynaptic terminal also maintains much neurotransmitter outside the vesicles Neurons that release serotonin, dopamine, or norepinephrine contain an enzyme, MAO (monoamine oxidase), that breaks down these transmitters into inactive chemicals, thereby preventing the transmitters to accumulate to harmful levels The first antidepressant drugs were MAO inhibitors --> increase the brain's supply of serotonin, dopamine, and norepinephrine Release and diffusion of transmitters At the end of an axon, an action potential itself doesn't release the neurotransmitter Depolarization opens voltage-dependent calcium gates in the presynaptic terminal Within 1-2ms after calcium enters the terminal, it causes exocytosis Exocytosis: bursts of release of neurotransmitter from the presynaptic terminal An action potential often fails to release any transmitter, and even when it does, the amount varies A single action potential can release a neurotransmitter After its release from the presynaptic cell, the neurotransmitter diffuses across the synaptic cleft (0.01ms over 20-30 nanometres) to the postsynaptic membrane where it attaches to a receptor Differences between neurons Some neurons release two transmitters at the same time Some neurons release one neurotransmitter at first and another one slowly later Some neurons release different transmitters from different branches of its axon Some neurons change their transmitter (one in summer, a different one in winter)  Activating receptors of the postsynaptic cell The effect of a neurotransmitter depends on its receptor on the postsynaptic cell When the neurotransmitter attaches to its receptor, the receptor may: Open a channel - exerting an ionotropic effect Produce a slower but longer effect - a metabotropic effect Ionotropic effects Corresponds to a brief on/off effect Begin quickly (sometimes less than 1ms after the transmitter attaches) Decays quickly with a half-life of about 5ms Most of the brain's excitatory ionotropic synapses use the neurotransmitter glutamate Acetylcholine is another transmitter at many ionotropic synapses o Excitatory in most cases Most of the brain's inhibitory ionotropic synapses use the neurotransmitter GABA (gamma-aminobutyric acid) GABA opens chloride gates, enabling chloride ions, with their negative charge, to cross the membrane into the cell more rapidly than usual Glycine is another common inhibitory transmitter o Found mostly in the spinal cord Ligand-gated (transmitter-gated) channel: a channel that is opened by a chemical that binds to something When the neurotransmitter binds to an ionotropic receptor, it opens the receptor just enough to open its central channel, letting a particular type of ion pass through Metabotropic effects and second messenger systems Neurotransmitters exert metabotropic effects by initiating a sequence of metabolic reactions that start slowly but last longer than ionotropic effects Metabotropic effects emerge 30ms or more after the release of the transmitter Typically lasts up to a few seconds, sometimes longer Metabotropic synapses use many neurotransmitters Dopamine, norepinephrine, and serotonin... Sometimes glutamate and GABA too When a neurotransmitter attaches to a metabotropic receptor, it bends the receptor protein that goes through the membrane of the cell The other side of that receptor is attached to a G protein  o G protein: a protein coupled to guanosine triphosphate (GTP), an energy-storing molecule Bending the receptor protein detaches that G protein, which is then free to take its energy elsewhere in the cell o The result of that G protein is increased concentration of a second messenger (such as cyclic adenosine monophosphate (cyclic AMP), inside the cell) o The second messenger communicates to areas within the cell May open or close ion channels in the membrane or activate a portion of a chromosome An ionotropic synapse has effects localized to one point on the membrane, whereas a metabotropic synapse (through its second messenger), influences activity in much or all of the cell and over a longer time Ionotropic and metabotropic synapses For vision and hearing, the brain needs rapid, up-to-date information --> ionotropic synapses needed Taste, smell, and pain are enduring effects, where the exact timing isn't important --> metabotropic synapses Metabotropic synapses are also important for arousal, attention, pleasure, and emotion Neuropeptides Feature Neuropeptides Neurotransmitters Place Cell body Presynaptic terminal synthesized  Place released Mostly from Axon terminal dendrites, also cell body and sides of axon Released by Repeated Single action depolarization potential Effect on They release the No effect on neighbouring neuropeptide too neighbours cells Spread of Diffuse to wide Effect mostly on effects area receptors of the adjacent postsynaptic cell Duration of Minutes Milliseconds to effects seconds Neuropeptides are often referred to as neuromodulators Neuropeptides are synthesized in the cell body and released mainly by dendrites (also by the cell body and the sides of the axon) Requires repeated stimulation to release (as opposed to neurotransmitters that can be released by a single action potential) After a few dendrites release a neuropeptide, the released chemical primes other nearby dendrites, including those on other cells, to release the same neuropeptide also Neurons with neuropeptides don't release them often, but when they do, they release substantial amounts Neuropeptides diffuse widely, slowly affecting many neurons in their region of the brain Effects often last 20min+ (because many alter gene activity) Neuropeptides are important for: Hunger Thirst Other long-term changes in behavior and experience  Variation in receptors Receptors for a given transmitter differ in their: Chemical structure Responses to drugs Roles in behavior A given receptor can have different effects for different people, or even in different parts of one person's brain This is because of differences in the hundreds of proteins associated with the synapse o Genetic variations in synaptic proteins have been linked to variation in anxiety, sleep, and other aspects of behavior Drugs that act by binding to receptors A drug that chemically resembles a neurotransmitter can bind to its receptor Many hallucinogenic drugs (that distort perception, such as LSD), chemically resemble serotonin o They attach to serotonin type 2a (5-HT) receptors and provide stimulation at inappropriate times or for longer-than-usual durations o LSD increases the connections among brain areas that ordinarily do not communicate much with one another Nicotine stimulates a family of acetylcholine receptors (known as nicotinic receptors) o As nicotinic receptors are abundant on neurons that release dopamine, nicotine increases dopamine release (associated with reward) The brain produces its own neuropeptides (endorphins - a contraction of endogenous morphines), that bind to the same receptors that opiates like morphine, heroin, methadone bind to Inactivation and reuptake of neurotransmitters Neurotransmitters don't linger at the postsynaptic membrane, as they could continue exciting or inhibiting the receptor Neurotransmitters are inactivated in different ways Acetylcholine o After acetylcholine activates a receptor, the enzyme acetylcholinesterase breaks it into two fragments (acetate and choline) Choline diffuses back to the presynaptic neuron, which takes it up and reconnects it with acetate already in the cell --> forms acetylcholine again o Takes time, doesn't reabsorb every molecule it releases  A rapid series of action potentials can deplete the neurotransmitter faster than the presynaptic cell replenishes it Slows/interrupts transmission Serotonin and catecholamines (dopamine, norepinephrine, epinephrine) o Do not break down into inactive fragments at the postsynaptic membrane They simply detach from the receptor Reuptake: the presynaptic neuron takes up much/most of the released neurotransmitter molecules intact and reuses them o Occurs through special membrane proteins called transporters The activity of transporters varies among individuals and from one brain area to another Stimulant drugs (amphetamine and cocaine) inhibit the transporters for dopamine, serotonin, and norepinephrine --> decreases reuptake -- > prolongs the effects of the neurotransmitters Increases accumulation of dopamine in the synaptic cleft --> COMT breaks down the excess dopamine faster than the presynaptic cell can replace it A few hours later, a user has a deficit of dopamine and enters a withdrawal state (reduced energy, motivation, and mild depression) Methylphenidate (Ritalin) is another stimulant drug prescribed for ADHD Works similarly but instead of a rapid increase in dopamine, there is a gradual increase over an hour or two, followed by a slow decline Most antidepressants also block reuptake of one or more neurotransmitters, but more weakly than amphetamine and cocaine do o Any transmitter molecules that the transporters don't take, are instead broken down by an enzyme called COMT (catechol-o-methyltransferase) The breakdown products wash away and eventually show up in the blood and urine Neuropeptides are not inactivated, they simply diffuse away Negative feedback from the postsynaptic cell Many presynaptic terminals have receptors sensitive to the same transmitter they release Autoreceptors: receptors that respond to the released transmitter by inhibiting further synthesis and release  Some postsynaptic neurons respond to stimulation by releasing chemicals (e.g., nitric oxide) that travel back to the presynaptic terminal to inhibit further release of transmitter Certain cells in the retina emit hydrogen ions (protons) to inhibit further transmission Two other reverse transmitters are: Anandamide (from the Sanskrit word anana, meaning "bliss") 2-AG (sn-2 arachidonylglycerol) Cannabinoids bind to anandamide or 2-AG receptors on presynaptic neurons, indicating "the cell got your message, stop sending it" --> the chemicals in marijuana decrease both excitatory and inhibitory messages from neurons that release glutamate, GABA, and other transmitters --> decreased anxiety Electrical synapses A few special-purpose synapses operate electrically, where synchrony between two cells is important Cells that control your rhythmic breathing are synchronized by electrical synapses (that you inhale on the left side at the same time as on the right) At an electrical synapse, the membrane of one neuron comes into direct contact with the membrane of another (gap junction) Pores of the membrane of one neuron line up precisely with similar pores in the membrane of the other cell Large enough for sodium and other ions to pass readily, and remain open constantly Whenever one of the neurons is depolarized, sodium ions from that cell pass immediately into the other neuron and depolarize it too Drugs and their effects (table) Drugs Main Synaptic Effects Amphetamine Blocks reuptake of dopamine and several other transmitters Cocaine Blocks reuptake of dopamine and several other transmitters Methylphenidate Blocks reuptake of dopamine and others, (Ritalin) but gradually MDMA (“Ecstasy”) Releases dopamine; Releases serotonin Nicotine Stimulates nicotinic-type acetylcholine receptor, which (among other effects)  increases dopamine release in nucleus accumbens Opiates (e.g., heroin, Stimulates endorphin receptors morphine) Cannabinoids Excites negative-feedback receptors on (marijuana) presynaptic cells; those receptors ordinarily respond to anandamide and 2AG Hallucinogens (e.g., Stimulates serotonin type 2A receptors LSD) (5-HT₂A) Hormones Many chemicals serve both as hormones and as neurotransmitters Hormone: a chemical secreted by cells in one part of the body and conveyed by the blood to influence other cells Hormones are particularly useful for coordinating long-lasting changes in multiple areas of the body Protein and peptide hormones attach to membrane receptors --> activate a second messenger within the cell Two types of hormones Protein hormones Longer chains Peptide hormones Shorter chains Hypothalamus Controls the pituitary gland Neurons in the hypothalamus synthesize the hormones oxytocin and vasopressin (also known as antidiuretic hormone) Those hormones migrate down axons to the posterior pituitary Secretes releasing hormones, which flow through the blood to the anterior pituitary Pituitary gland Attached to the hypothalamus Has two parts Anterior pituitary Composed of glandular tissue Synthesizes six hormones o The hypothalamus controls their release Posterior pituitary  Composed of neural tissue Can be considered an extension of the hypothalamus o Releases oxytocin and vasopressin Organs, hormones, and their functions Organ Hormone Hormone Functions (partial) Hypothalamus Various releasing Promote/inhibit release of hormones hormones from pituitary Anterior Thyroid- Stimulates thyroid gland pituitary stimulating hormone Luteinizing Stimulates ovulation hormone Follicle-stimulating Promotes ovum hormone maturation (female), sperm production (male) ACTH Increases steroid hormone production by adrenal gland Prolactin Increases milk production  Growth hormone Increases body growth Posterior Oxytocin Uterine contractions, milk pituitary release, sexual pleasure Vasopressin Raises blood pressure, decreases urine volume Pineal Melatonin Sleepiness; also role in puberty Adrenal cortex Aldosterone Reduces release of salt in the urine Cortisol Elevated blood sugar and metabolism Adrenal Epinephrine, Similar to actions of medulla norepinephrine sympathetic nervous system Pancreas Insulin Helps glucose enter cells Glucagon Helps convert stored glycogen into blood glucose Ovary Estrogens and Female sexual progesterone characteristics and pregnancy Testis Testosterone Male sexual characteristics and pubic hair Kidney Renin Regulates blood pressure, contributes to hypovolemic thirst Fat cells Leptin Decreases appetite, increases activity Summary The majority of synapses operate by transmitting a chemical neurotransmitter from the presynaptic cell to the postsynaptic cell Otto Loewi demonstrated chemical transmission by stimulating a frog's heart electrically and then transferring fluids from that heart to another frog's heart Many chemicals are used as neurotransmitters Most are amino acids or chemicals derived from amino acids  An action potential opens calcium channels in the axon terminal, and the calcium enables release of neurotransmitters Ionotropic and metabotropic synapses At ionotropic synapses, a neurotransmitter attaches to a receptor that opens the gates to allow a particular ion, such as sodium, to cross the membrane Ionotropic effects are fast and brief Most excitatory ionotropic synapses use glutamate Most inhibitory ionotropic synapses use GABA At metabotropic synapses, a neurotransmitter activates a second messenger inside the postsynaptic cell, leading to slower but longer-lasting changes Neuropeptides Neuropeptides diffuse widely, affecting many neurons for a period of minutes Neuropeptides are important for hunger, thirst, and other slow, long- term processes Several drugs including LSD, antipsychotic drugs, nicotine, and opiate drugs exert their behavioral effects by binding to receptors on the postsynaptic neuron After a neurotransmitter (other than a neuropeptide) has activated its receptor, many of the transmitter molecules re-enter the presynaptic cell through the use of transporter molecules in the membrane This process (reuptake), enables the presynaptic cell to recycle its neurotransmitter Stimulant drugs and many antidepressants inhibit reuptake of certain transmitters Postsynaptic neurons send chemicals to receptors on the presynaptic neuron to inhibit further release of neurotransmitter Cannabinoids mimic these chemicals Hormones travel through the blood, affecting receptors in many organs Their mechanisms of effect resembles that of a metabotropic synapse Chapter 3 - Anatomy and Research Methods Structure of the Vertebrate Nervous System Terminology to Describe the Nervous System Brain areas have specialized functions, but they perform those roles by means of connections with other areas Terminology to describe the nervous system Central nervous system (CNS): the brain and spinal cord Peripheral nervous system (PNS): the nerves outside the brain and spinal cord Connects the brain and spinal cord to the rest of the body Somatic nervous system: axons conveying messages from sense organs to the CNS and from the CNS to the muscles Autonomic nervous system: controls the heart, intestines, and other organs Has some of its cell bodies within the brain or spinal cord and some in clusters along the sides of the spinal cord Terms to describe location: Dorsal: toward the back (up) Ventral: toward the stomach (down) Horizontal: a plane that divides into upper and lower Superior (up): toward the top Inferior (down): toward the bottom Sagittal: a plane that divides into left and right Medial: toward the midline / in the middle Lateral: away from the midline / by the sides Coronal: a plane that divides into front and back Anterior (front): toward the front Posterior (back): toward the back Term Definition Dorsal Toward the back (up), away from the ventral (stomach) side. Ventral Toward the stomach (down), away from the dorsal (back) side. Anterior Toward the front end Posterior Toward the rear end Superior Above another part Inferior Below another part Lateral Toward the side, away from the midline Medial Toward the midline, away from the side Proximal Located close (approximate) to the point of origin or attachment Distal Located more distant from the point of origin or attachment Ipsilateral On the same side of the body (e.g., two parts on the left or two on the right) Contralateral On the opposite side of the body (one on the left and one on the right) Coronal plane (or A plane that divides into front and frontal plane) back Sagittal plane A plane that divides into left and right Horizontal plane (or A plane that divides into upper and transverse plane) lower  Terms referring to parts of the nervous system Term Definition Lamina A row or layer of cell bodies separated from other cell bodies by a layer of axons and dendrites Column A set of cells perpendicular to the surface of the cortex, with similar properties Tract A set of axons within the CNS, also known as a projection. If axons extend from cell bodies in structure A to synapses onto B, we say that the fibers "project" from A onto B. Nerve A set of axons in the periphery, either from the CNS to a muscle or gland or from a sensory organ to the CNS Nucleus A cluster of neuron cell bodies within the CNS Ganglion A cluster of neuron cell bodies, usually outside the CNS (as in the sympathetic nervous system) Gyrus (pl.: A protuberance on the surface of the brain gyri) Sulcus (pl.: A fold or groove that separates one gyrus from sulci) another Fissure A long, deep sulcus The cranial nerves Number and Name Major Functions I. Olfactory Smell II. Optic Vision III. Oculomotor Control of eye movements; pupil constriction IV. Trochlear Control of eye movements V. Trigeminal Skin sensations from most of the face; control of jaw muscles for chewing and swallowing VI. Abducens Control of eye movements VII. Facial Taste from the anterior two thirds of the tongue; control of facial expressions,  crying, salivation, and dilation of the head’s blood vessels VIII. Statoacoustic Hearing; equilibrium IX. Taste and other sensations from throat and Glossopharyngeal posterior third of the tongue; control of swallowing, salivation, throat movements during speech X. Vagus Sensations from neck and thorax; control of throat, esophagus, and larynx; parasympathetic nerves to stomach, intestines, and other organs XI. Accessory Control of neck and shoulder movements XII. Hypoglossal Control of muscles of the tongue The Spinal Cord The spinal cord is part of the CNS The spinal cord communicates with all the sense organs and muscles except those of the head Is a segmented structure, where each segment has on both the left and right sides a sensory nerve and a motor nerve The cell bodies of the sensory neurons are in clusters of neurons outside the spinal cord, called the dorsal root ganglia In most cases, a neuron cluster outside CNS is called a ganglion, and a cluster inside CNS is called a nucleus The cell bodies of the motor neurons are inside the spinal cord Each segment of the spinal cord sends sensory information to the brain and receives motor commands from the brain  The Autonomic Nervous System The autonomic nervous system consists of neurons that receive information from and send commands to the heart, intestines, and other organs Sympathetic nervous system Sympathetic nervous system ("fight or flight"): a network of nerves that prepare the organs for a burst of vigorous activity Prepares the organs for "fight or flight" Increases breathing and heart rate Decreases digestive activity Consists of chains of ganglia just to the left and right of the spinal cords central regions (the thoracic and lumbar areas) These ganglia have connections back and forth with the spinal cord The sweat glands, adrenal glands, the muscles that construct blood vessels, and the muscles that erect the hairs of the skin have sympathetic input but no parasympathetic input The sympathetic nervous system's axons release norepinephrine onto the organs A few, e.g., those onto the sweat glands, use acetylcholine Parasympathetic nervous system Parasympathetic nervous system ("rest and digest"): facilitates vegetative, nonemergency responses Decreases heart rate, increases digestive activity, promotes sexual arousal (e.g., erection), in general conserves energy Also known as the craniosacral system Consists of the cranial nerves and nerves from the sacral spinal cord The ganglia in the parasympathetic system are not arranged in a chain near the spinal cord Long preganglionic axons extend from the spinal cord to parasympathetic ganglia close to each internal organ o Shorter postganglionic fibres then extend from the parasympathetic ganglia into the organs themselves o Because these ganglia are not linked to one another, they act more independently The parasympathetic nervous system's axons release acetylcholine onto the organs Because the sympathetic and parasympathetic nervous systems use different transmitters, certain drugs excite or inhibit one system or the other  The Hindbrain The brain has three major divisions Hindbrain (rhombencephalon): the medulla, pons, and cerebellum Responsible for basic life functions; breathing, heart rate, balance Midbrain (mesencephalon): tectum and tegmentum Involved in functions such as vision, hearing, motor control, sleep/wake cycles, and arousal (alertness) Forebrain (prosencephalon): cerebral cortex, thalamus, hypothalamus, basal ganglia Responsible for complex behaviors, cognitive processes, emotion regulation, and sensory processing Area Also Known as Major Structures Forebrain Prosencephalon (“forward-brain”) Thalamus, hypothalamus Diencephalon Cerebral cortex, (“between-brain”) hippocampus, basal ganglia Telencephalon (“end- brain”) Midbrain Mesencephalon Tectum, tegmentum, (“middle-brain”) superior colliculus, inferior colliculus, substantia nigra Hindbrain Rhombencephalon Medulla, pons, cerebellum (literally, “parallelogram-brain”)  Medulla The medulla can be regarded as an enlarged extension of the spinal cord Controls vital reflexes: Breathing Heart rate Vomiting Salivation Coughing Sneezing The head and the organs connect to the medulla and adjacent areas by 12 pairs of cranial nerves (of each pair, one is for the right side, the other for the left) Pons Axons from each half of the brain cross to the opposite side of the spinal cord so that the left hemisphere controls the muscles of the right side of the body, the right controlling the left Cerebellum Contributes to the control of movement, balance and coordination Important for attention shifting, timing, learning and conditioning The Midbrain Tectum The roof of the midbrain The swellings on each side of the tectum are the superior colliculus and the inferior colliculus, which are important for sensory processing Inferior colliculus: important for hearing Superior colliculus: important for vision Tegmentum Lies under the tectum Covers several other midbrain structures Substantia nigra: gives rise to a dopamine-containing pathway that facilitates readiness for movement  The Forebrain Consists of two cerebral hemispheres (left & right) Each hemisphere is organized to receive sensory information, mostly from the contralateral (opposite) side of the body It also controls muscles, mostly on the contralateral side Cerebral cortex The outer portion of the forebrain Under the cerebral cortex are other structures (e.g., the thalamus and basal ganglia) Limbic system Several interlinked structures, known as the limbic system, form a border (or limbus) around the brainstem Includes: The olfactory bulb: processes scent information from the nose Hypothalamus: essential for control of eating, drinking, temperature control, and reproductive behaviors Hippocampus: essential for learning and spatial navigation Amygdala: most central for evaluating emotional information, especially regarding to fear Cingulate gyrus of the cerebral cortex: involved in emotion processing, decision making, and linking behavioral outcomes to motivation  Thalamus, hypothalamus and the pituitary gland The thalamus and hypothalamus form the diencephalon, a section distinct from the telencephalon (the rest of the forebrain) Thalamus A pair of structures (left & right) in the center of the forebrain Most sensory information goes first to the thalamus Processes it and sends output to the cerebral cortex o The cerebral cortex sends information back to the thalamus Prolongs and magn