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IVMS Neurobiology Review | Overview Notes
 

IVMS Neurobiology Review | Overview Notes

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    IVMS Neurobiology Review | Overview Notes IVMS Neurobiology Review | Overview Notes Document Transcript

    • Neurobiology Review/Overview Notes|mic 08-13 Page 1 Part of IVMS Autonomics - Neurobiology and the 4 P's Series (For USMLE Step 1 Preparation)
    • Neurobiology Review/Overview Notes|mic 08-13 Page 2 Neurobiology Review| Overview Notes The Biology of Behavior 1. The Nervous System - comprised of the following subsystems which control all activity in our body. 1. Central Nervous System 1. Brain 2. Spinal Cord 2. Peripheral Nervous System - connections to muscles and organs of the body. 1. Somatic or Skeletal - controls our voluntary muscles. 2. Autonomic - Controls autonomic functions that we have no voluntary control over such as breathing, heart rate etc. 1. Sympathetic - Responds to stress or demands put upon the body. 2. Parasympathetic - Work in opposition to the sympathetic NS to return body to homeostasis. 2. How the System works and interacts 1. Neurons - Over 200 billion in our body. 1. Sensory, Motor and Interneurons 2. Historical Notes 1. Glavani: 1700's first demonstrated neural conductivity with use of frog legs, first concept of electrical conduction 2. Volta: Explained process as electrical conductance 3. Golgi: Developed a staining method that allowed entire neurons to viewed and studied 3. No two neurons are the same, over 200 billion cells in brain 4. Main components of the neuron 1. Cell body or Soma (Greek word for body) 1. Spherical or pyramidal in shape, contains the nucleus 2. Synthesizes enzymes for cell function, neurotransmitters and other nutrients 2. Dendrites 1. Branch from cell body, receive signals only, transfer them to the cell body 2. Receive this signal from other neurons or the environment 3. Axon 1. Extends from the cell body to other neurons in the brain 2. Longer and thinner than dendrites 3. Covered with Myelin Sheath
    • Neurobiology Review/Overview Notes|mic 08-13 Page 3 4. Glial Cells used for support 5. Neurilemma is the covering of axons which are outside the brain and spinal cord 6. Every mm or so is interrupted by a Node of Ranvier. These server to insulate and speed conductance Impulses pass from neuron to neuron but the cells never touch 4. Synapse 1. Site where information is passed from one neuron to another 2. The enlargement at the end of the axon is called the Terminal Button and extends into the synaptic cleft of the next dendrite 3. The button contains synaptic vesicles which contain the neurotransmitters that are eventually released to continue conductance of the impulse across the synaptic cleft 4. The release of the neurotransmitters that find and lock into a specific binding site on the dendrite of the neighboring neruon. This elicits an action potential in the dendrite and the process continues on from cell to cell 5. Neurotransmitters tend to be either excitatory or inhibitory in nature
    • Neurobiology Review/Overview Notes|mic 08-13 Page 4 5. Neurotransmitters 1. Over 50 identified, may recognize some such as acetylcholine, epinephrine, dopamine and serotonin 2. Transmitter secretion or re-uptake may be affected by drugs or environmental chemicals 3. Other chemicals act to mimic (agonistic) or block (antagonistic) the effect of neurotransmitters. 4. The chemical may affect concentration of the neurotransmitter by increasing secretion or reducing normal reuptake 5. Neuropeptides affect the actions of the neurons themselves, for example in the case of enkephalin, the natural painkillers produced in the brain, mimics the effect of opiates or pain medications. Most commonly known as an endorphins. 2. The Nerve Impulse or Action Potential 1. Neuron is in a resting state with negative charge on the outside. 1. K+ and Cl- ions on the inside 2. Na+ on the outside
    • Neurobiology Review/Overview Notes|mic 08-13 Page 5 3. This gives the outside a more negative charge than the positive inside 4. Result is a polarized condition. The resting state is called polarization 2. The cell membrane is semipermeable 3. In the presence of a stimulus that reaches the neuron's threshold the membrane opens and additional Na+ ions enter, depolarizing the cell 4. This change in charge results in a neural impulse called the Action Potential 5. As the process continues additional gates open to allow more + ions to enter along the cell and subsequent depolarization results in the impulse moving down along the cell, like a wave. This energy can be measured as electrical energy 6. This change in charge is what stimulates the ion gates to open and close along the cell allow ions to move 7. The action is "all or none," the impulse itself remains constant 8. After the action potential a small refractory period exists as the ion pumps work to restore the cell to its original polarized state. No firing can take place until this process is complete (Relative Refractory Period) 9. The whole process may be repeated again upon a stimulus of sufficient threshold
    • Neurobiology Review/Overview Notes|mic 08-13 Page 6 3. Divisions of the Nervous System 1. Central Nervous System 1. Brain - Hindbrain, Midbrain, and Forebrain 1. Hindbrain 1. Controls autonomic functions of the body 2. Medulla ("Marrow or Core") - controls breathing, heart rate, blood pressure and reflex actions 3. Pons ("bridge") - Some control over hearing, sleeping and waking functions 4. Cerebellum ("little brain") - coordinates voluntary movement and balance 2. Midbrain 1. Reticular Formation ("Net Like") - control over alertness and sleepiness 2. Affects reflexes associated with the senses 3. Forebrain 1. Complex network of neurons covered by the cerebral cortex ("rind or shell") 2. White Matter - mass of neuron axons which are covered with myelin and appears a white color 3. Grey Matter - The cortex area that appears grey in color 4. Cerebral Cortex - 2 lobes or hemispheres separated by the longitudinal fissure and connected by the Corpus Callosum. The center of brain functions. The
    • Neurobiology Review/Overview Notes|mic 08-13 Page 7 ridges and valleys you see increase the surface area of the brain 5. Hypothalamus - Controls body temperature, hunger functions, thirst, sex drive, motivations and emotions. 6. Thalamus - Relays sensory input (except smell) to the cortex 7. Limbic System ("Border or Edge") - many areas forming a ring around the lower forebrain, connecting the hypothalamus and cortex 1. Hippocampus 2. Amygdala 3. Hypothalamus 4. Septal Area 5. Fornix 6. Cingulate Gyrus 7. Thalamus 4. Cerebral Cortex in more detail 1. Frontal Lobe 1. Control personality, social control, attention and planning. Remember the accident of Phineas Gage 2. Olfactory information present 3. Motor cortex 2. Parietal Lobe 1. Anterior part is concerned with somatosensory (body senses) function 2. Posterior controls motor function 3. Occipital Lobe
    • Neurobiology Review/Overview Notes|mic 08-13 Page 8 1. Processes visual information 4. Temporal Lobe 1. Mostly concerned with speech and hearing 2. Left side most often site of speech. Aphasia results for stroke or trauma to area 3. Right side trauma results in Amusia 4. Wernicke's area - changes sounds into recognizable words, allows association of meaning 5. Boca's Area - Involved in the process of articulating speech 6. Most of the cortex is known for being area of association. 5. Peripheral Nervous System 1. Somatic or Skeletal 2. All nerves are both afferent or sensory, efferent or motor, in function 1. Messages only can travel in one direction across a synapse 2. The Reflex Arc is a part of this system 1. Impulse from afferent neurons are processed first in the vertebrae and sent out to efferent neurons to produce a
    • Neurobiology Review/Overview Notes|mic 08-13 Page 9 response. By responding this way without involving the brain immediately responses are much faster 3. Autonomic Nervous System 1. The stress response 2. Carry messages to and from glands and visceral organs. 3. Affect messages to skeletal muscles during stress 1. Sympathetic Nervous System 1. The Stress Response or GAS 2. Prepares body to respond to stressor 2. Parasympathetic Nervous System 1. Reverses effect of sympathetic system 2. Maintains Homeostasis 3. Only the sexual response is invoked by both systems 6. Endocrine Glands ("to secrete within") 1. An additional system for sending chemical messages throughout the body. 1. The chemical messengers are called hormones 2. Pituitary - The Master Gland 1. Primarily for the growth hormone 2. Also involved in continued growth and in the menstrual cycle 3. Thyroid 1. Produces thyroxin for control of metabolism 2. Over or under secretion may result in emotional and physical symptoms 4. Parathyroid Gland 1. Secrete parathormone that affects excitability of the nervous system by regulating ion levels in the neuron
    • Neurobiology Review/Overview Notes|mic 08-13 Page 10 5. Adrenal Glands 1. Produces adrenaline and noradrenaline from cortex of Adrenal Gland on top of the kidneys 2. Adrenaline is a strong stimulant that is used to stimulate the heart in heart attacks and to reduce inflammations from acute anaphylactic shock. The chemical found in sting kits carried by those allergic to stings 6. Islets of Langerhans 1. Secretes Glucagon that causes liver to convert stored sugar or starch into blood sugar 2. Secretes insulin that helps cells effectively utilize blood sugar for energy 7. Gonads 1. Male and Female sex organs that secrete estrogen and testosterone 8. Pineal Gland 1. Effects activity levels over the course of a day. Secrets melatonin, the chemical touted as a health supplement to help induce sleep 7. Right/Left Brain Research 1. Fechner originally reasoned we have 2 brains since we have 2 hemispheres. Tried to prove with surgery to sever the 1/4 inch band of 200 million nerve fibers called the Corpus Callosum. Technology in the 1800's could note complete such procedures 2. Others like McDougal reasoned that it appeared we had 2 brains we only have one mind. Didn't believe there would be any effect to severing the Corpus Callosum 3. Later research suggested localization of function 1. 1836 - Dax found that Aphasic patients suffered damage on left side of brain 2. 1861 - Boca coined the term Aphasia to indicate patients who could not articulate ideas. Also found damage to left side of brain 3. 1952 - Sperry and Meyers discovered that when the Corpus Callosum was severed that the hemispheres acted independently 4. Early experiments used cats to test effects. Found learning with only one uncovered eye resulted in learning in only one hemisphere. Even so the cat still acted like a cat with no other deficits observed 5. In the 1950's the procedure called a commissurotomy was used to treat epileptic seizures. 1. It worked without loss of mental facilities or change in personality or IQ 2. Found with testing that learning when patient focuses on center of split screen with images flashed to sides that
    • Neurobiology Review/Overview Notes|mic 08-13 Page 11 learning took place in the hemisphere where the image was flashed. Each hemisphere was better at specific function. 3. Language seemed centered in left hemisphere and kinesthetic senses in the right. When object was seen in the right hemisphere the patient could not identify by label but could identify it by touch 4. Hemispheric Function 1. Language for most people is in the left hemisphere 2. Left hemisphere is better at language, reading, math, writing, spelling and math tasks 3. Right is better for spatial, symbolic, and creative ideas Key Terms Neuron The neuron, or nerve cell, is the basic building block of the nervous system. Dendrites The dendrites of a neuron are the bushy, branching extensions that receive messages from other nerve cells and conduct impulses toward the cell body. Axon The axon of a neuron is the extension that transmits messages to other nerve cells, muscles or glands. Myelin Sheath The myelin sheath is a layer of fatty cells that covers many axons and helps speed neural impulses. Action Potential An action potential, or neural impulse, is a brief electrical charge that travels down an axon similar to the motion of a wave. It is generated when a stimulus to a nerve cell reaches the cells threshold causing the axon to depolarize as the Na+ ions enter the axon. This depolarization causes the electrical charge. It is an all or none response. Threshold A neuron's threshold is the level of stimulation that must be exceeded in order for the neuron to fire or generate an electrical impulse. Synapse A synapse is the junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. The tiny gap at this junction is called the synaptic gap or cleft. Neurotransmitters Neurotransmitters are chemicals that, when released into synaptic gaps, transmit neural messages from neuron to neuron. Endorphins Endorphins are natural, opiate like neurotransmitters linked to pain control and to pleasure. Nervous System The nervous system is the body's electrochemical communication system, consisting of all the nerve cells of the peripheral and central nervous systems.
    • Neurobiology Review/Overview Notes|mic 08-13 Page 12 Central Nervous System The central nervous system consists of the brain and spinal cord; it is located at the center, or internal core, of the body. Peripheral Nervous System The peripheral nervous system connects the central nervous system to the rest of the body; it is at the periphery of the body relative to the brain and spinal cord. Nerves Nerves are bundles of neural axons that connect the central nervous system with muscles, glands, and sense organs. Sensory Neurons Sensory neurons carry incoming information from the sense organs to the central nervous system. Interneurons Interneurons are the neurons of the central nervous system that link the sensory and motor neurons in the transmission of sensory input and motor output. Motor Neurons Motor neurons carry information and instructions for action from the central nervous system to muscles and glands. Skeletal Nervous System The skeletal nervous system is the division of the peripheral nervous system that controls the body's skeletal muscles. Autonomic Nervous System The autonomic nervous system is the division of the peripheral nervous system that controls the glands and the muscles of internal organs and thereby controls internal functioning; it regulates the automatic behaviors necessary for survival. Sympathetic Nervous System The sympathetic nervous system is the division of the autonomic nervous system that arouses the body to react to demands put upon it. Parasympathetic Nervous System The parasympathetic nervous system is the division of the autonomic nervous system that calms the body, conserving its energy and restores homeostasis. Reflex A reflex is a simple, automatic, inborn response to a sensory stimulus; it is governed by a very simple neural pathway that does not involve the brain. Endocrine System The endocrine system, the body's "slower" chemical communication system, consists of glands that secrete hormones into the bloodstream. Hormones Hormones are the chemical messengers of the endocrine system; they are secreted by endocrine glands and circulate through the bloodstream to their target tissues, on which they have specific effects. Brainstem The brainstem, the oldest part of the brain, is an extension of the spinal cord and is the central core of the brain; its structures direct automatic survival functions. Medulla Located in the brainstem, the medulla is involved in the regulation of breathing and heartbeat. Electroencephalogram (EEG) An electroencephalogram (EEG) is an amplified recording of the waves of electrical activity of the brain. Encephalo comes from a Greek word meaning "related to the brain." CAT (Computerized The CAT (computerized axial tomograph) scan is a series of x-ray
    • Neurobiology Review/Overview Notes|mic 08-13 Page 13 Axial Tomograph) Scan photographs of the brain taken from different positions and analyzed by computer, creating an image that represents a slice through the brain. PET (Positron Emission Tomograph) Scan The PET (positron emission tomograph) scan measures the levels of activity of different areas of the brain by tracing their consumption of glucose. MRI (Magnetic Resonance Imaging) MRI (magnetic resonance imaging) uses magnetic fields and radio waves to produce computer-generated images that show brain structures more clearly. Reticular Formation Also part of the brainstem, the reticular formation is a nerve network that plays an important role in controlling arousal. Thalamus Located atop the brainstem, the thalamus routes incoming messages to the appropriate cortical centers and transmits replies to the medulla and cerebellum. The Grand Central Station of the Brain. Cerebellum The cerebellum assists in the coordination of voluntary movement and balance. Limbic System A doughnut-shaped neural system, the limbic system plays an important role in the regulation of emotions and drives such as those for food and sex. (From the Latin word limbus, meaning "border"); the limbic system is at the border of the brainstem and cerebral hemispheres. Amygdala Part of the limbic system, the amygdala is linked to the emotions of aggression and fear. Hypothalamus Also part of the limbic system, the hypothalamus regulates hunger, thirst, and body temperature and contains the so-called pleasure centers of the brain. It also helps govern the endocrine system through the pituitary gland. Cerebral Cortex The cerebral cortex is the outer covering of the cerebral hemispheres. The seat of information processing, the cortex is responsible for those complex functions that make us distinctively human. (Cortex in Latin means "bark." As bark covers a tree, the cerebral cortex is the "bark of the brain.") Frontal Lobes Located at the front of the brain, just behind the forehead, the frontal lobes contain the motor cortex and are involved in making plans and judgments. The accident of Phineas Gage helped psychologists understand the role of the frontal lobes in personality. Parietal Lobes Situated between the frontal and occipital lobes, the parietal lobes contain the sensory cortex. Occipital Lobes Located at the back and base of the brain, the occipital lobes contain the visual cortex, which receives information from the eyes. Temporal Lobes Located on the sides of the brain, the temporal lobes contain the auditory areas, which receive information from the ears. Motor Cortex Located at the back of the frontal lobes, the motor cortex controls voluntary movements. Sensory Cortex The sensory cortex is located at the front of the parietal lobes, just behind
    • Neurobiology Review/Overview Notes|mic 08-13 Page 14 the motor cortex. It receives information from the skin and muscles. Association Areas Located throughout the cortex, association areas of the brain are involved in higher mental functions, such as learning, remembering, thinking, and speaking. Most of the brain consists of association areas of the cortex that are involved in integrating, or associating, information from different areas of the brain. Aphasia Aphasia is an impairment of language as a result of left-hemisphere damage, either to Broca's area or to Wernicke's area . Broca's Area Broca's area is located in the left frontal lobe and is involved in controlling the motor ability to produce speech. Wernicke's Area Wernicke's area is located in the left temporal lobe and is involved in language comprehension. Plasticity Plasticity refers to the ability of the brain to reorganize itself in order to compensate for the destruction of brain tissue. The plasticity of the brain diminishes with age. Corpus Callosum The corpus callosum is a wide band of axon fibers that links the right and left cerebral hemispheres. Without this band of nerve fibers, the two hemispheres could not interact. Split Brain Split brain is a condition in which the major connections between the two cerebral hemispheres (the corpus callosum) are severed, literally resulting in a split brain. Early experimenters believed this surgery would eliminate the seizures of epilepsy.