Biological Psychology PDF

Biological psychology Physiological Explanation Is the study of the physiological, relates a behavior to the activity of the brain evolutionary, and developmental and other organs. It deals with the mechanis...

Biological psychology Physiological Explanation Is the study of the physiological, relates a behavior to the activity of the brain evolutionary, and developmental and other organs. It deals with the mechanisms of behavior and experience. It machinery of the body emphasizes that the goal is to relate biology Ontogenetic Explanation to issues of psychology. describes how a structure or behavior develops, including the influences of genes, nutrition, experiences, and their interactions. Evolutionary Explanation reconstructs the evolutionary history of a structure or behavior. Functional Explanation describes why a structure or behavior evolved as it did. Three main points: 1. Perception occurs in your brain 2. Mental activity and Brain activity are inseparable a. Monism - the idea that the universe consists of only one type of being. b. Dualism - the idea that minds are one type of substance and matter is another. 3. We should be cautious about what is an explanation and what is not. a. avoid overstating the conclusions from any research study. Biological explanations of behavior Field of Specialization FOUR CATEGORIES Physiological Explanation relates a behavior to the activity of the brain and other organs. It deals with the machinery of the body  Neurons receive information and transmit it to other cells. Glia serve many functions that are difficult to summarize. The adult human brain contains approximately 86 billion neurons, on average Santiago Ramón y Cajal, a Pioneer of Neuroscience THE USE OF ANIMAL IN RESEARCH He managed to combine the two fields, Four reasons why they study nonhumans becoming an outstanding anatomical 1. The underlying mechanisms of behavior are researcher and illustrator. similar across species and sometimes His detailed drawings of the nervous system easier to study in a nonhuman species. are still considered definitive today. 2. We are interested in animals for their own the Italian investigator Camillo Golgi found sake. a way to stain nerve cells with silver salts. 3. What we learn about animals sheds light on Cajal used Golgi’s methods but applied human evolution. them to infant brains, in which the cells are 4. Legal or ethical restrictions prevent certain smaller and therefore easier to examine on kinds of research on humans. a single slide. DEGREE OF OPPOSITION structure of an animal cell the three “r’s” The surface of a cell is its membrane (or 1. Reduction plasma membrane), a structure that 2. Replacement separates the inside of the cell from the 3. Refinement outside environment. Nucleus - the structure that contains the Institutional Animal Care and Use Committee chromosomes. composed of veterinarians, community A mitochondrion (plural: mitochondria) is representatives, and scientists that evaluate the structure that performs metabolic proposed experiments, decide whether they activities, providing the energy that the cell are acceptable, and specify procedures to uses for all activities. minimize pain and discomfort. Ribosomes - are the sites within a cell that Minimalist synthesize new protein molecules. accepts the concept of studying animals as Endoplasmic reticulum - a network of thin long as no harm is done. tubes that transport newly synthesized Abolitionist proteins to other locations. rejects the concept of studying animals for research. STRUCTURE OF NEURON All neurons include a soma (cell body), and Nerve cells and Nerve impulses most also have dendrites, an axon, and presynaptic terminals. neurons and glia A motor neuron, with its soma in the spinal The nervous system consists of two kinds of cord, receives excitation through its cells, neurons and glia. dendrites and conducts impulses along its axon to a muscle.  A sensory neuron is specialized at one Synapse - (Synaptic gap) is the junction or end to be highly sensitive to a particular gap where neurons communicate type of stimulation, such as light, sound, or touch. MOTOR NEURON The axon - is a thin fiber of constant diameter. conveys an impulse toward other neurons, an organ, or a muscle. Axons can be more than a meter in length, as in the case of axons from your spinal SENSORY NEURON cord to your feet. Structure of a neuron Dendrites - are branching fibers that get narrower near their ends. The dendrite’s surface is lined with specialized synaptic receptors dendritic spines - short outgrowths that increase the surface area available for synapses The cell body or soma - contains the Many vertebrate axons are covered with an nucleus, ribosomes, and mitochondria. insulating material called a Myelin sheath Most of a neuron’s metabolic work occurs with interruptions known as nodes of here. Cell bodies of neurons range in Ranvier (RAHN-vee-ay). diameter from 0.005 millimeter (mm) to 0.1 mm in mammals and up to a millimeter in certain invertebrates.  Presynaptic terminal - also known as an end bulb or bouton At that point the axon releases chemicals that cross through the junction between that neuron and another cell. Charles Sherrington - pioneer of modern neuroscience atoms are anatomically seperated Reflexes - reaction to stimuli Reflex Arc by Cajal Presynaptic Neuron - delivers or send (axon terminal) Post synaptic Neuron - receive (dendrites) variation among neurons An afferent axon brings information into a structure; an efferent axon carries information away from a structure. If a cell’s dendrites and axon are entirely contained within a single structure, the cell is an interneuron or intrinsic neuron of Glia - (or neuroglia), the other components that structure. of the nervous system, perform many functions. The term glia, derived from a Greek word meaning “glue” reflects early investigators’  idea that glia were like glue that held the neurons together. Radial glia guide the migration of neurons and their axons and dendrites during types of glia embryonic development. The star-shaped astrocytes wrap around When embryological development finishes, the synapses of functionally related axons. most radial glia differentiate into neurons, According to a popular hypothesis known as and a smaller number differentiate into the tripartite synapse, the tip of an axon astrocytes and oligodendrocytes releases chemicals that cause the neighboring astrocyte to release chemicals of its own, thus magnifying or modifying Oligodendrocytes in the brain and spinal cord and Schwann cells in the periphery of the body build the myelin sheaths that surround and insulate certain vertebrate axons. They also supply an axon with nutrients necessary for proper functioning. THE BLOOD BRAIN BARRIER Why We Need a Blood–Brain Barrier When a virus invades a cell, mechanisms within the cell extrude virus particles  through the membrane so that the immune system can find them. Certain viruses do cross the blood–brain barrier, When the rabies virus evades the blood–brain barrier, it infects the brain and leads to death. The spirochete responsible for syphilis also penetrates the blood–brain barrier, producing long-lasting and potentially fatal consequences. When a virus invades a cell, mechanisms within the cell extrude virus particles through the membrane so that the immune system can find them. Certain viruses do cross the blood–brain barrier, When the rabies virus evades the blood–brain barrier, it infects the brain and leads to death. The spirochete responsible for syphilis also penetrates the blood–brain barrier, producing long-lasting and potentially fatal consequences. how blood brain barrier works Outside the brain, such cells are separated by small gaps, but in the brain, they are joined so tightly that they block viruses, bacteria, and other harmful chemicals from Nourishment of Vertebrate Neurons passage. Vertebrate neurons depend almost entirely For certain other chemicals, the brain uses on glucose, a sugar. active transport, a protein-mediated Although the human brain constitutes only process that expends energy to pump about 2 percent of the body’s weight, it uses chemicals from the blood into the brain. about 20 percent of its oxygen and 25 Chemicals that are actively transported into percent of its glucose the brain include glucose (the brain’s main To use glucose, the body needs vitamin fuel), amino acids (the building blocks of B1, thiamine. proteins), purines, choline, a few vitamins, Prolonged thiamine deficiency, common in and iron chronic alcoholism, leads to death of The blood–brain barrier is essential to neurons and a condition called Korsakoff’s health syndrome, marked by severe memory However, the barrier poses a difficulty for impairments. treating brain cancers, because nearly all the drugs used for chemotherapy fail to SUMMARY cross the blood–brain barrier. 1. Neurons receive information and convey it to other cells. 2. 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.  3. Neurons contain the same internal structures as other animal cells. 4. Neurons have these major parts: a cell body (or soma), dendrites, an axon with branches, and presynaptic terminals. Neurons’ shapes vary greatly depending on their functions and their connections with other cells. 5. Because of the blood–brain barrier, many molecules cannot enter the brain. The barrier protects the nervous system from viruses and many dangerous chemicals. 6. The blood–brain barrier consists of an unbroken wall of cells that surround the blood vessels of the brain and spinal cord. A When at rest, the membrane maintains an few small, uncharged molecules such as electrical gradient, also known as water, oxygen, and carbon dioxide cross the polarization barrier freely. So do molecules that dissolve ○ a difference in electrical charge in fats. Active transport proteins pump between the inside and outside of glucose, amino acids, and a few other the cell. chemicals into the brain and spinal cord. The difference in voltage is called the Certain hormones, including insulin, also resting potential cross the blood–brain barrier. 7. Neurons rely heavily on glucose, the only nutrient that crosses the blood–brain barrier in large quantities. They need thiamine (vitamin B1) to use glucose. THE NERVE IMPULSE The Resting Potential of the Neuron Messages in a neuron develop from disturbances of the resting potential. All parts of a neuron are covered by a membrane about 8 nanometers (nm) thick. The membrane is composed of two layers ○ Phospholipid molecules free to float relative to each other containing chains of fatty acids and a phosphate group Doesnt let anything large or charged The membrane has selective permeability. That is, some chemicals pass through it more freely than others do. When the membrane is at rest, the sodium and potassium channels are closed, permitting almost no flow of sodium and  only a small flow of potassium. Certain ACTION POTENTIAL types of stimulation can open these Messages sent by axons are called Axon channels, permitting freer flow of either or Potential. both ions When an axon’s membrane is at rest, the The sodium–potassium pump, a protein recordings show a negative potential inside complex, repeatedly transports three the axon. If we now use a different electrode sodium ions out of the cell while drawing to apply a negative charge, we can further two potassium ions into it. The increase the negative charge inside the sodium–potassium pump is an active neuron. The change is called transport that requires energy. hyperpolarization, which means increased 3 Sodium (Na) out polarization. 2 Potassium (K) in charge differenve of -70mv This creates Electrical Chemical Gradient Now let’s apply a current to depolarize the neuron—that is, reduce its polarization toward zero. If we apply a small depolarizing current, we get a result like this: With a slightly stronger depolarizing current, the potential rises slightly higher but again returns to the resting level as soon as the stimulation ceases: Stimulation beyond the threshold of excitation produces a massive depolarization of the membrane. The potential shoots up far beyond the strength that the stimulus provided:  Note that any depolarization that reaches or passes the threshold produces an action potential. Driven by both the concentration gradient and the the all-or-none law is that the amplitude electrical gradient, the sodium ions enter the cell and velocity of an action potential are rapidly, until the electrical potential across the independent of the intensity of the stimulus membrane passes beyond zero to a reversed that initiated it, provided that the stimulus polarity, as shown in the following diagram: reaches the threshold. THREE PRINCIPLES 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. The axon channels regulating sodium and potassium are voltage-gated channels. That is, their permeability depends on the voltage At this point both the concentration gradient and the difference across the membrane. electrical gradient drive potassium ions out of the cell. As they flow out of the axon, they carry with them a positive charge. Because the potassium channels remain open after the sodium channels close, enough potassium ions leave to drive the membrane beyond its usual resting level to a temporary hyperpolarization. THE ACTION POTENTIAL: When an area of the axon membrane reaches its threshold of excitation, sodium channels and potassium channels open. At first, the opening of potassium channels produces little effect. Opening sodium channels lets sodium ions rush into the axon. Positive charge flows down the axon and opens voltage-gated sodium channels at the next point. 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. Because voltage-gated potassium channels remain open, potassium ions flow out of the axon, returning the membrane toward its original depolarization. A few milliseconds later, the voltage-dependent potassium channels close. The Myelin Sheath and Saltatory Conduction To increase the speed more, vertebrate axon evolved a special mechanism: sheaths of myelin, an insulating material composed of fats and proteins. Myelinated axons, found only in vertebrates, are covered with layers of fats and proteins. The myelin sheath is interrupted periodically by short sections of axon called nodes of Ranvier, each one about 1 micrometer wide, The jumping of action potentials from node to node is referred to as saltatory conduction, from the Latin word saltare, meaning to jump  During the second part, the relative refractory period, a stronger than-usual stimulus is necessary to initiate an action potential. The refractory period depends on two facts: The sodium channels are closed, and potassium is flowing out of the cell at a faster-than-usual rate. The Local Neurons Axons produce action potentials. However, many small neurons have no axon. 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 REFRACTORY PERIOD at the peak of the action potential, the sodium gates snap shut. As a result, the cell is in a refractory period during which it resists the production of further action potentials. In the first part of this period, the absolute refractory period, the membrane cannot produce another action potential, regardless of the stimulation.