PhysiolPsychLecture 3

PhysiolPsychLecture 3 - Physiological Psychology 3 The...

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Unformatted text preview: Physiological Psychology 3 The organism makes its way through life as an integrated system of specialized parts Integration is achieved: 1. Mechanically skeletal & muscular systems (posture, locomotioin, skilled actions, facial expressions) 2. Chemically circulatory & endocrine systems 3. Neurally regulates other systems, like the router or server for the computer system Neural Integration Receptors specialized cells with the capacity to respond to stimuli and transduce them to neural events Effectors cells with which the organism responds Muscles: striated (voluntary); smooth (involuntary); cardiac Glands: exocrine (GSR) and endocrine Connectors Neural Levels of Integration Simple Reflex arc, spinal cord Complex pathways to the brain From Marcello Malpighi (16281694) and the founding of microscopy to 1839 and Theodor Schwann's Cell Theory all organisms are composed of similar units of organization, called cells to 1873 and Camillo Golgi's staining methods and Ramn y Cajal's Neuron Doctrine to 1897 when Sir Charles Sherrington's named the synapse Golgi and Cajal shared the Nobel Prize in 1906 and Sherrington was awarded it in 1932 Neuron Doctrine: a. Nervous system is composed of cells, neurons, which are discrete units acting at synapses b. All nerve fibers are processes of neurons c. They do not form a reticulum i.e., there is nota fusion of axons and dendrites The Cells of the Nervous System Terms used to describe the neuron include the following: Afferent axon refers to bringing information into a structure. Efferent axon refers to carrying information away from a structure. Interneurons or Intrinsic neurons are those whose dendrites and axons are completely contained within a single structure. Nerve cells (neurons) are the structural units of the nervous system 100,000,000,000 neurons in the human NS 1,000,000 seconds = 11.5 days 1,000,000,000 seconds = 32 years 1,000,000,000,000 = past recorded history to the dawn of the human species (35 million years ago) Fig. 2-1, p. 28 Fig. 2-5, p. 30 The Cells of the Nervous System All neurons have the following major components: Dendrites. Soma/ cell body. Axon. Presynaptic terminals. Fig. 2-2, p. 29 Neurons are the building blocks of the NS. They have the same genes, same general organization, same biochemical apparatus as other cells, they have unique properties which include: 1. A distinctive cell shape 2. An outer membrane capable of generating the nerve impulse 3. A unique "structure," the synapse for transferring information from cell to cell. Fig. 2-5, p. 30 The Cells of the Nervous System Cell body/ Soma contains the nucleus, mitochondria, ribosomes, and other structures found in other cells. Also responsible for the metabolic work of the neuron. The Cells of the Nervous System Axon thin fiber of a neuron responsible for transmitting nerve impulses toward other neurons, organs, or muscles. Some neurons are covered with an insulating material called the myelin sheath with interruptions in the sheath known as nodes of Ranvier. The Cells of the Nervous System Dendrites are branching fibers with a surface lined with synaptic receptors responsible for bringing information into the neruon . Some dendrites also contain dendritic spines that further branch out and increase the surface area of the dendrite. Dendrite shape of dendrites vary and depend upon varying inputs. Fig. 2-7, p. 31 Unipolar neurons Bipolar neurons Multipolar neurons small soma < 3 m diam (insects) or m 40 (mammals) large 10 m (worms) or 50 m (whales) giant 8002000 m (squid) The Cells of the Nervous System Neurons vary in size, shape, and function. The shape of a neuron determines it connection with other neurons and contribution to the nervous system. The function is closely related to the shape of a neuron. Example: Pukinje cells of the cerebellum branch extremely widely within a single plane Fig. 2-9, p. 32 The Cells of the Nervous System Glia are the other major components of the nervous system that exchange chemicals with adjacent neurons. Astrocytes helps synchronize the activity of the axon by wrapping around the presynaptic terminal and taking up chemicals released by the axon. Microglia remove waste material and other microorganisms that could prove harmful to the neuron. Fig. 2-10, p. 33 The Cells of the Nervous System (Types of glia continued) Oligdendrocytes & Schwann cells build the myelin sheath that surrounds the axon of some neurons. Radial glia guide the migration of neurons and the growth of their axons and dendrites during embryonic development. The Cells of the Nervous System The bloodbrain barrier is a mechanism that surrounds the brain and blocks most chemicals from entering. The immune system destroys damaged or infected cells throughout the body. Because neurons in the brain generally do not regenerate, it is vitally important for the blood brain barrier to block incoming viruses, bacteria or other harmful material from entering. Fig. 2-12, p. 34 Active transport is the protein mediated process by which useful chemicals are brought into the brain. Glucose, hormones, amino acids, and vitamins are brought into the brain via active transport. Glucose is a simple sugar that is the primary source of nutrition for neurons. The Cells of the Nervous System Thiamine is a chemical that is necessary for the use of glucose. The Nerve Impulse A nerve impulse is the electro chemical message that is transmitted down the axon of a neuron. The impulse does not travel directly down the axon but is regenerated at points along the axon. The speed of nerve impulses ranges from approximately 1 m/s to 100 m/s. The Nerve Impulse The membrane of a neuron maintains an electrical gradient which is a difference in the electrical charge inside and outside of the cell. Fig. 2-13, p. 38 The Nerve Impulse At rest, the membrane maintains an electrical polarization or a difference in the electrical charge of two locations. The resting potential of a neuron refers to the state of the neuron prior to the sending of a nerve impulse. the inside of the membrane is slightly negative with respect to the outside. (approximately 70 millivolts) The membrane is selectively permeable, allowing some chemicals to pass more freely than others. Sodium, potassium, calcium, and chloride pass through channels in the membrane. When the membrane is at rest: The Nerve Impulse Sodium channels are closed. Potassium channels are partially closed allowing the slow passage of sodium. Fig. 2-14, p. 38 The Nerve Impulse The sodiumpotassium pump is a protein complex that continually pumps three sodium ions out of the cells while drawing two potassium ions into the cell. helps to maintain the electrical gradient. The electrical gradient and the concentration gradient (the difference in distributions of ions) work to pull sodium ions into the cell. The electrical gradient tends to pull potassium ions into the cells. Fig. 2-15, p. 39 The Nerve Impulse The resting potential remains stable until the neuron is stimulated. Hyperpolarization refers to increasing the polarization or the difference between the electrical charge of two places. Depolarization refers to decreasing the polarization towards zero. The threshold of excitement refers to a levels above which any stimulation produces a massive depolarization. The Nerve Impulse An action potential is a rapid depolarization of the neuron. Stimulation of the neuron past the threshold of excitation triggers a nerve impulse or action potential. Fig. 2-16, p. 41 The Nerve Impulse After an action potential occurs, sodium channels are quickly closed. The neuron is returned to its resting state by the opening of potassium channels. potassium ions flow out due to the concentration gradient and take with them their positive charge. The sodiumpotassium pump later restores the original distribution of ions. The Nerve Impulse The allornone law states that the amplitude and velocity of an action potential are independent of the intensity of the stimulus that initiated it. Action potentials are equal in intensity and speed within a given neuron. The Nerve Impulse After an action potential, a neuron has a refractory period during which time the neuron resists the production of another action potential. The absolute refractory period is the first part of the period in which the membrane can not produce an action potential. The relative refractory period is the second part in which it take a stronger than usual stimulus to trigger an action potential. During the spike the neuron is unresponsive to stimulation (absolute refractory period = .5msc/ relative refractory period = 1msc later super stimulus works) As the cell returns to resting potential it is easier to stimulate since half of the task of depolarizing is already done. All neural impulses are identical. Information then is represented by the number/unit time. The greater the magnitude of the stimulus = the faster the firing rate Spark school vs soup school. By 1950s it was realized that transmission is mostly chemical. Graded potentials are electrical. Types of Synapses Axodendritic Axosomatic Axoaxonic Dendritodendritic Axons with myelin sheaths are the rule in vertebrates. Nodes of ranvier occur every mm. Neural impulse jumps from node to node. Along the axon the membrane is specialized to propagate the impulse. At the terminal end it releases neural transmitters; the dendrites respond to those chemicals. The Nerve Impulse The myelin sheath of axons are interrupted by short unmyelinated sections called nodes of Ranvier. Myelin is an insulating material composed of fats and proteins At each node of Ranvier, the action potential is regenerated by a chain of positively charged ion pushed along by the previous segment. Fig. 2-18, p. 44 The Nerve Impulse Saltatory conduction is the word used to describe this "jumping" of the action potential from node to node. Multiple sclerosis is disease in which the myelin sheath is destroyed and associated with poor muscle coordination. Provides rapid conduction of impulses Conserves energy for the cell ...
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