Exam 2 Terms To Know
Exam 2 Terms To Know AGR*143*001
Popular in Anatomy and Physiology of Livestock
Popular in Animal Science
This 14 page Study Guide was uploaded by Cassidie Cartwright on Monday September 19, 2016. The Study Guide belongs to AGR*143*001 at Morehead State University taught by Dr. Patricia Harrelson in Fall 2016. Since its upload, it has received 49 views. For similar materials see Anatomy and Physiology of Livestock in Animal Science at Morehead State University.
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Date Created: 09/19/16
EXAM 2 STUDY GUIDE NERVOUS SYSTEM Nervous system consists of: Brain Spinal cord Peripheral nerves o Primary functional cell type Neuron General Functions of the Nervous System o Initiate and/or regulate movement of body parts Does by contraction of muscles Smooth, skeletal, and cardiac o Regulate secretions from glands o Maintain state of consciousness o Gather information from the environment and the status of the internal environment Senses: sight, hearing, touch, balance, and taste Mechanisms to detect pain, temperature, pressure, and certain chemicals o Stimulate thirst, hunger, fear, rage, and sexual behaviors Two Acting Systems in Nervous System o Central nervous system (CNS) Includes brain and spinal cord Processes information Sends and receives information o Peripheral nervous system (PNS) Peripheral nerves Cranial and spinal nerves that are contacting body structures Responsible for getting information to and from CNS Peripheral Nervous System is divided into two systems: o Somatic Nervous System Transmits information from environment to CNS o Autonomic Nervous System Consists of sympathetic and parasympathetic nervous systems Sympathetic nervous system o Flight or fight response Parasympathetic o Important in vegetative functions o Normal body functions Sympathetic Nervous System o Most important in regulating circulation o Fibers leave spinal cord st nd Through all thoracic and 1 and 2 lumbar vertebrae o Fibers end at the adrenal medulla o Stimulates release of catecholamines into blood Epinephrine (mostly) Norepinephrine o Flight or fight response Prepares body for action o Stimulates: Circulatory system Respiratory system Skeletal and muscular systems Vision, sweating, metabolism Mental awareness o Inhibits Digestive system Reproduction system Renal system Peripheral circulation Parasympathetic Nervous System o Consists of: Cranial nerves Sacral spinal nerves o Majority of effects on digestive system are from vagus nerve (one of the cranial nerves) o Opposite effects of sympathetic nervous system o Fibers are cholinergic It uses acetylcholine as a neurotransmitter Chemical messenger o Stimulates: Digestion Increased salivation Increases tone and contraction of intestinal smooth muscle Contraction of bladder wall muscle Communication Between Neurons o Axon ending communicates with any part of a second neuron o Area between neurons is called the synapse Is the location where chemical messenger is released What starts the communication between neurons? o An action potential Impulse results from depolarizing and repolarizing the nerve cell membrane Done using Na+ and K+ (ions) to change the charge of the cell membrane and ultimately the cell What sends the communication from one neuron to another? o An action potential moves down the axon of the first neuron o The change in charge, causes voltage-gated calcium (Ca) channels to open o Causes neurotransmitter vesicles to move to presynaptic membrane (of first neuron) o Through exocytosis, neurotransmitter is released into the synaptic cleft Communication o Neurotransmitter binds a receptor on second (postsynaptic neuron) o Stimulates an action potential o The action potential is carried down second neuron until it causes release of more neurotransmitter o Creating another action potential on another neuron and so on…. Two types of drugs Antagonist o Prevents normal neurotransmitter from binding and thus blocks its effects Agonist o Binds to receptor and has similar effects Mimics effects of neurotransmitter Information Received o How are environmental stimuli detected? By sensory receptors They transmit nervous impulses via neurons Each receptor is highly specialized to detect a particular type of stimulus o Much less receptive to other types of stimuli Sensory Receptors o Sensation detected by the receptor is determined by the brain Based on where fibers terminate in the brain Regardless of stimulus, if pain fibers are activated, the animal will feel pain o Stimulus of receptor causes a change in membrane potential – thus starting action potential Mechanoreceptors o 5 main types Tactile Deep tissue Hearing Equilibrium Arterial pressure Thermoreceptors o Detect changes in temperature o Temperature change alters permeability to ions such as Na+ and K+ Types Warm receptors Cold receptors Nociceptors o Detect damage to a tissue Damage could be physical or chemical o Always results in pain impulse May be blocked by anesthetics o Generally are free nerve endings May detect any type of stimuli Perceived as pain because they terminate in pain center Electromagnetic Receptors o Detect light Alters directly or indirectly receptor membrane permeability to ions Example: Vision receptors o Rods – black and white vision o Cones – color vision Chemoreceptors o Detect chemical stimuli o May directly or indirectly alter membrane permeability to ions o Types Taste Smell Arterial oxygen Osmolality Blood CO 2 Blood glucose, amino acids, fatty acids Spatial summation o Number of receptors picking up stimulus and transmitting to brain Temporal summation o Frequency of firing of the receptors Spatial Summation o More receptors firing (numerous) o Each receptor has hundreds of free nerve endings within a few inches of area Known as field of receptors o Receptor fields overlap, so a large stimulus will be created and will excite several receptors at once o Creates perception of a large stimulus Temporal Summation o Increased frequency of impulses o Frequency increases to a point where the strength of the signal increases by building on the previous signal Reflex Arc o Basic functional unit of nervous system o Components Receptor Sensory nerve fiber CNS Motor nerve fibers Effector o Sensory nerve fiber Carries impulses from receptor to CNS o CNS Integrates, modulates, and properly relays impulse to proper motor output nerve fibers o Motor nerve fibers Carries impulse from CNS to proper target tissue o Effector Tissue that responds to the order caused by the impulse Spinal Reflexes o Reflex message enters the spinal cord and leaves directly without first going to the brain Message will eventually get to the brain The brain ALWAYS is kept apprised of the situation Because it may need to make further decisions regarding the original stimulus MUSCULAR SYSTEM • Skeletal muscle ▫ Striated ▫ Voluntary movement • Cardiac muscle ▫ Striated ▫ Involuntary movement • Smooth muscle ▫ Innervated by autonomic nervous system ▫ Involuntary movement Functional Grouping of Muscles • Flexor ▫ Muscle is on the side of the limb toward which a joint bends Decreases angle between the segments • Extensor ▫ Muscle opposite of the flexor Increases the angle Functional Grouping of Muscles • Adductors ▫ Muscles that pull a limb toward the median plane • Abductors ▫ Muscles that move the limb away from the median plane • Sphincters ▫ Muscles that surround an opening ▫ Can be striated or smooth • Cutaneous muscles ▫ Occur in superficial fascia between skin and deep fascia covering skeletal muscles ▫ Allow movement of skin Microanatomy of Skeletal Muscle • Epimysium ▫ Connective tissue covering of the entire muscle ▫ Each muscle is made up of hundreds of muscle bundles • Perimysium ▫ Connective tissue layer that covers bundles of muscle ▫ Each muscle bundle is made up of thousands of muscle fibers • Endomysium ▫ Connective tissue covering of each muscle fiber ▫ Muscle fiber is the skeletal muscle cell Contains the nuclei The number of nuclei increase as the fiber length increase Skeletal Muscle Fiber • Sarcolemma ▫ Membrane surrounding the muscle fiber ▫ It is an excitable membrane with an electrical potential • Sarcoplasm ▫ The cytoplasm of muscle • Sarcoplasm Reticulum (SR) ▫ Specialized form of endoplasmic reticulum that lies within each muscle fiber (just under sarcolemma) ▫ Composed of longitudinal tubules that parallel the muscle fiber These tubes terminate in flattened channels called terminal cisternae • Sarcomere ▫ Repeating units within muscle fibers ▫ Each muscle fiber is made up of approximately 20,000 repeating units ▫ Is the basic contractile unit of skeletal muscle Made up of thick and thin filaments called myofilaments ▫ Separated by the membrane like Z lines at each end Thin filaments attach to the Z lines ▫ * Has alternating light and dark bands I bands contain only thin filaments A bands contain both thick and thin filaments H zone only has thick filaments ▫ During muscle contractions, the sarcomeres shorten and the Z lines are pulled closer together Myofilaments DO NOT change length I bands shorten as myofilaments slide over each other The H zone disappears ▫ Thin filaments are made up primarily of actin Each actin filaments is composed of two strands of actin proteins Tropomyosin is wrapped around the two actin strands A third protein in the thin filament is troponin * It is made up of: • Troponin T • Troponin C • Troponin I ▫ Thick Filaments Thick filaments are composed of myosin Each thick filament is made up of several hundred myosin molecules Contains different myosin protein subunits Has a thick helical rod that terminates in a globular head Has two flexible regions • The swivel occurs between the helical rod and the globular head • The hinge is in the helical rod A myosin filament is formed by ordered tail-to-tail interactions Leaves hundreds of heads sticking out on both ends Globular heads of myosin have a high affinity for binding actin Myosin head also binds ATP and catalyzes its conversion to ADP + Pi • Arrangement of Thick and Thin Filaments ▫ Each thick filament is surrounded by six thin filaments ▫ Each thin filament is in contact with three thick filaments ▫ At Rest – Thick & Thin Filaments At rest: Actin and myosin are in close proximity but are not bound Myosin head is bound to ADP + Pi It is also at 90 degree angle to the actin filament Myoneural Junction • Nerve fibers that stimulate skeletal muscle generally originate within the somatic nervous system ▫ Large, myelinated fibers which branch several hundred times Called alpha motor neurons • The motor unit ▫ Each nerve ending stimulates a single muscle cell Thus, a single alpha motor neuron can stimulate hundreds of muscle cells ▫ Each muscle cell is only stimulated by a single nerve ending • The nerve fiber and muscle cells it stimulates make up the motor unit • The nerve fiber terminates at the motor end plate ▫ The sarcolemma has a large number of invaginations to increase the surface area These are called synaptic troughs How does a nerve complete an impulse? • Action potential ▫ Impulse results from depolarizing and repolarizing the nerve cell membrane ▫ Uses flow of Na+ and K+ to change the charge of the nerve cell membrane • The action potential travels down the alpha motor neuron and ends up at the motor end plate ▫ Results in release of acetylcholine into the synaptic cleft ▫ Acetylcholine binds to receptors in the muscle membranes ▫ An action potential is started Once action potential is started acetylcholine is rapidly broken down by acetylcholinesterase within the synaptic cleft Drugs in Synaptic Cleft • Target of many toxins and drugs ▫ Curare Acts as acetylcholine antagonist ▫ Botulinum toxin Acts as acetylcholine antagonist ▫ Nicotine Agonist • Many drugs inactivate acetylcholinesterase ▫ This allows the buildup of acetylcholine ▫ Person will smother due to laryngeal spasm Many military gases are based on this principle *Where does the action potential travel? 1. Sarcolemma 2. T-tubule 3. Terminal cisternae 4. Longitudinal tubule Action Potential – Muscle Contraction • Action potential causes the opening of Ca+ channel with membrane of the tubules ▫ Must open the voltage-gate Ca+ channel • Ca+ rapidly flows into the cell where it starts the process of contraction Molecular Mechanism of Contraction • Effects of Ca 2+ ▫ Depolarization causes rapid influx of Ca 2+from SR 2+ ▫ Ca effects are on the troponin complex Binds troponin complex to tropomyosin Troponin complex binds the actin filament Binds to four sites troponin complex Troponin/tropomyosin complex moves deeper into the grooves between the actin filaments Uncovers the myosin binding sites on actin Molecular Mechanism of Contraction • Once Ca+ is bound to troponin complex, the myosin head binds to actin ▫ ADP + Pi is released This causes a free energy change, resulting in rotation of myosin Rotates from 90 degrees relative to the actin to 45 degrees • Power Stroke • Rotation pulls the actin towards the center of the sarcomere ▫ Called “Power Stroke” • Results in the Z lines getting closer together • Each rotation of the myosin head pulls the actin filaments about 4-5 nm Relaxation State of Muscle Contraction • Myosin head binds ATP ▫ Loses affinity for actin ▫ The ATP is rapidly hydrolyzed to ADP + Pi Causes myosin head to move back to 90 degrees relative to actin Resulting in resting state • 1 step to relaxation = stopping the contraction nd • 2 step to relaxation = elongating the muscle (it may require force) • Without ATP, the myosin head binds almost irreversibly with actin ▫ This is the mechanism of rigor mortis Because ATP is depleted, more and more myofilaments become irreversibly bound Causes the characteristic rigidness of muscle Summary of Muscle Contraction • The action potential reaches the motor end plate ▫ Causes release of acetylcholine, which binds to receptors on the muscle cell membrane ▫ This initiates the action potential, which travels through the muscle cell membrane • Action potential is then transmitted through the cell, which causes depolarization of the SR 2+ ▫ Ca is released, binds to troponin complex Causes a conformational change in troponin/tropomyosin, which uncovers the myosin binding site on actin • Myosin binds to actin and releases its bound ADP + Pi • This free energy change causes the myosin head to rotate, pulling the actin fiber towards the center of the sarcomere • ATP binds to the myosin head, causing dissociation of actin and myosin • The bound ATP is hydrolyzed to ADP + Pi and the myosin head “recocks” to the relaxed position • The Ca 2+pump has removed the Ca 2+from the cell at this time and the myosin binding site on actin is now recovered by the troponin/tropomyosin complex Muscle Contraction – rate of contraction • As the load increases, the rate of contraction will decrease ▫ At some point, the rate will reach zero The amount of weight (load) equals the force of contraction Types of Whole Muscle Contractions • Isometric contraction ▫ When the muscle contract against a load, but does not shorten ▫ The force of the contraction equals the force of the load on the muscle ▫ Used in posture or any type of resistance to a load where movement doesn’t occur • Isotonic contraction ▫ The muscle shortens as it contracts ▫ Means that the force of contraction is greater than the force of the load ▫ Type of muscle contraction involved in movement
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