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Physiology 1021 December Exam.docx

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Western University
Physiology 1021

Physiology 1021 1 Physiology 1021 December Exam The Hypothalamus and Limbic System Pyrogens and Fear Virus produces endotoxins Bacteria are recognized by white blood cells as being foreign. White blood cells try to attack them (ones that are phagocytic) White blood cells produce interleukin I Interleukin I gains access to neurons in the brain, by crossing at circumventricular organs to get through the blood brain barrier Interleukin I reaches the hypothalamus To increase temperature, goes to the anterior hypothalamus, and changes the set point o Very few can withstand 41C Surface area is important for thermoregulation babies have smaller body, bigger surface area, so they can regulate better, and can withstand higher temperatures than adults Development of Heat Exhaustion Pass out due to heat: heat will activate ANS, body will want to thermoregulate sweat, dilation of blood vessels o Water from extracellular fluid (blood): decreased blood volume, hypovolemia o If alcohol in system, dehydrates and dilates blood vessels more (losing core heat) decreased cardiac output, making blood pressure drop o When blood pressure drops, less blood going to the brain, meaning less oxygen to the brain, so person passes out Heat stroke: the consequence of brain no longer being able to thermoregulate system is no longer functional (severe elevation of core temperature, impaired CNS function, organ and tissue damage) Treatment: apply cold compresses, use a fan, elevate feet (increase blood flow back to heart and brain), give water to increase blood volume Symptoms of heat stroke: hot, dry skin, high body temperature Symptoms of heat exhaustion: moist, clammy skin, normal temperature Olfaction 2004 Nobel Prize in Physiology or Medicine to Richard Axel and Linda Buck for their discovery of odorant receptors and the organization of the olfactory system The limbic system is for memory, emotion, behaviour, with the hypothalamus at its centre Sensory stimuli reaches the cerebral cortex, where integrated information is passed on to the limbic system o The limbic system creates emotion, and there is a feedback loop to the cerebral cortex which creates an awareness of these emotions This is passed on to the hypothalamus and brain stem, initiating o Somatic or motor responses (both voluntary and conscious) o Automatic responses o Endocrine responses, immune responses In the olfactory system, there are 5 million receptors, 1000 different types A molecule should have 3 characteristics for us to be able to smell it: o Volatile (vapourized) o Water soluble o Lipid soluble Physiology 1021 2 Total area of olfactory epithelium is 2.5cm sq. in each nasal cavity, 1% of which is lost yearly Life of sensory cells: 30 days The olfactory receptor: o Receptor attached to neuron, brings membrane potential to threshold o Problem: the smaller the receptor potential, the farther it has to travel, smaller it gets as it travels (so may not even bring membrane to threshold o Receptors are slowly adapting o Combination of a receptor and a neuron: the only part that is susceptible to odorant is the cilia (which causes the receptor potential Steps: 1. Odorants bind to receptors 2. Olfactory receptor cells are activated and send electric signals 3. The signals are relayed in glomeruli (terminate as bundles in the olfactory bulb) 4. The signals are transmitted to higher regions of the brain Vomero-nasal organ (Jacobsons Organ): a specialized accessory organ, involved in behavioural responses to pheromones Physiology 1021 3 Motor Systems One of the most important functions of the nervous system is to provide the organisms with the ability to move around the world it lives in Before any movement can be performed, the central nervous system needs information about the muscles it is about to move: o Which muscle group it will move (learned) o The present length of the muscles it will move o The present tension in the muscles it will move (GTO) The basic unit for all motor movements is the motor unit: o Motor neuron o Myofibrils o Muscle fibre A motor unit (somatic) differs from a sensory unit (automatic) in that there is no pre/post- synaptic ganglion cell, rather just one alpha-motor cell o Also, somatic = ACh (excitatory NT, causes contraction) Muscle length and muscle tension o The gamma motor neuron influences muscle spindle (not muscle itself) o Muscle spindle 1a afferent neuron, alpha motor neuron (muscle fibres made to contract by this neuron, influences fibre not the spindle) o Muscle tendon 1b afferent neuron, golgi tendon organ Proprioceptors (spinal reflexes): 1. Muscle spindle: spindle parallel to muscle fibres, 1a afferent, alpha motor neuron 2. Golgi tendon organ: 1b afferent neuron, spindle found in series to muscle and tendon fibres Summary of the motor unit: 1. Basic unit for movement is the motor unit 2. Neuron to muscle: alpha motor neuron 3. To perform movement, we need to know a. Which muscle to use b. Length of muscle spindles c. Tension 4. Muscle spindle: connective tissue enclosing group of intrafusal fibres, in parallel to extrafusal muscle fibres, information about length and change in length of skeletal muscle 5. Golgi tendon organ: located at junction of tendon and muscle, in series with tendon, information about tension within muscle, free nerve endings wrapped between collagen fibres inside connective tissue capsule The Reflex Arc 1. A reflex is an involuntary response to a stimulus which requires the integrity of the nervous system (end result is contraction or secretion) 2. Voluntary movement only involves skeletal muscle, while reflex activity may involve skeletal, cardiac, or smooth muscle 3. A reflex arc involves a receptor, an afferent neuron, a synapse, a motor neuron, and an effector 4. Reflex latency: time between the application of the stimulus and the beginning of the response depends on the length of the nerve pathway, the conduction time along the pathway, and the number of synapses in the pathway 5. Reflexes are influenced by the CNS (may be facilitatory or inhibitory). The motor neuron is the final common pathway as several neurons converge on it Physiology 1021 4 6. Spinal shock: all reflexes below a cut section of the spinal cord are lost for a period of time returned reflex arc is often exaggerated 7. The coordination of bodily movements involves two or more sets of muscles o Reciprocal inhibition: muscle groups work together for movement sensory impulses to the spinal cord which excite extensor motor neurons also inhibit flexor motor neurons Monosynaptic reflexes: a single synapse between the affere
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