ANEQ 305 week 5 notes
ANEQ 305 week 5 notes ANEQ305
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This 9 page Class Notes was uploaded by Andrew Everitt on Sunday September 25, 2016. The Class Notes belongs to ANEQ305 at Colorado State University taught by Dr. Hyungchul Han in Fall 2016. Since its upload, it has received 37 views. For similar materials see Functional Large Animal Anatomy/Physiology in Animal Science at Colorado State University.
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Date Created: 09/25/16
ANEQ305 9-19-16 Chapter 4.3 Velocity of Action Potential Propagation - Nerve conduction velocity ranges from 0.7 m/sec (small unmyelinated fibers) to 120 m/sec (large myelinated fibers) Synapse - A specialized junction between a neuron and a target cell - Presynaptic neuron is the signaling cell - Postsynaptic cell (neuron, gland, or muscle) is the target - Electrical synapses signal via gap junctions - Chemical synapses signal via neurotransmitters released into the synaptic cleft o Slower than electrical synapses (synaptic delay) o Operate in only 1 direction o Allow for various kinds of signaling events Chemical synaptic transmission (“fast” synapses) - Neurotransmitter is stored in synaptic vesicles in synaptic knob of presynaptic neuron - Action potential reaches axon terminal of presynaptic neuron - Opens voltage-gated Ca2+ channels in the synaptic knob, allowing Ca2+ to enter - Neurotransmitter is released by exocytosis - Neurotransmitter diffuses across the synaptic cleft and combines with receptors on the sub-synaptic membrane - Binding triggers opening of chemically-gated ion channels in sub-synaptic membrane Excitatory Synapses - Binding of neurotransmitter open non-specific cation channels (Na+ and K+) - Electrochemical gradients favor inward movement of Na+ leading to depolarization - Excitatory postsynaptic potential (EPSP) Inhibitory synapses - Binding of neurotransmitter opens specific K+ or Cl- channels - Outward movement of K+ or inward movement of Cl-leads to hyperpolarization - Inhibitory postsynaptic potential (IPSP) Each neurotransmitter-receptor combo always produces the same response Neurotransmitters are quickly removed from the synaptic cleft - Diffuse away from the synaptic cleft or - Inactivated by a specific enzyme or - Transported back into the axon terminal by reuptake carriers Neurotransmitters in “slow” synapses activate intracellular second messengers - Responses take longer and last longer than “fast” synapses Neuromuscular junction is a synapse between a motor neuron and a skeletal muscle fiber - Terminal button of axon terminal fits into a shallow depression in the muscle cell membrane (motor end plate) - Acetylcholine (ACTH)*** is stored in synaptic vesicles in terminal button - Norepinephrine – know this *** Neuromuscular transmission - Action potential reaches axon terminal of presynaptic neuron - Opens voltage-gated Ca2+ channels in the terminal button, allowing Ca2+ to enter - ACTH is released by exocytosis - ACTH binds to cholinergic receptors on the motor end plate - ACTH binding opens chemically-gated ion channles in the motor end plate, leading to depolarization - Initiates an action potential, which spreads throughout the muscle cell membrane by contiguous conduction - Action potential intiates contraction of the muscle fiber An EPP in a muscle fiber is much larger than an EPSP in a neuron - There are multiple terminal buttons in the neuromuscular junction - More neurotransmitter molecules are released at each terminal button - Motor end plate has a larger surface area with a higher density of receptors - Many more receptor-channels open - A single EPP is sufficient to initiate an action potential ACTH binding is reversible and can be terminated - ACTH binds briefly to cholinergic receptors, then detaches - ACTH is inactivated by acetylcholinesterase - Acetylcholinesterase is an enzyme located in the motor end plate - Removal of ACTH terminates the EPP EPSPs and EPSPs are graded potentials that can be summed - Temporal summation – sum of EPSPs produced by repeated firing of a presynaptic neuron - Spatial summation – sum of EPSPs originating simultaneously from several different presynaptic inputs - EPSPs and IPSPs cancel each other out - Composite of all EPSPs and IPSPs occurring at about the same time is the grand postsynaptic potential (GPSP) The Action potential is initiated at the axon hillock - High density of voltage-gated Na+ channels - Lower threshold than dendrites or cell body - Action Potential initiated at the axon hillock is propagated to the end of the axon Neuropeptides - 2-40 amino acids - Synthesized in the cell body and delivered to axon terminals by axonal transport - Packaged in large dense-core vesicles - Released by Ca2+ - induced exocytosis - May be co-secreted along with neurotransmitters - Function as neuromodulators Pre-synaptic inhibition and facilitation - Presynaptic axon terminal may be innervated by another axon terminal - Presynaptic inhibition reduces neurotransmitter release o Inhibitory neurotransmitter reduces Ca2+ influx into axon terminal - Presynaptic facilitation enhances neurotransmitter release Complexity of the nervous system - A neuron may have thousands of neurons synapsing on it (convergence) - Through branching ox axon terminals, a neuron synapses on many other cells (divergence) - The human brain has 100 billion neurons and 10^14 synapses Synthetic and natural toxins can alter resting potentials and action potentials - Useful as research tools - Tetrodotoxins blocks v-gated Na+ channels - Tetraethylammonium blocks gated K+ channels - Ouabain stops the Na-K pump Most drugs that influence the nervous system alter synaptic transmission - Alter synthesis, axonal transport, storage or release of a neurotransmitter or - Modify neurotransmitter interaction with postsynaptic receptor - Influence neurotransmitter reuptake or destruction or - Substitute for a deficient neurotransmitter Drugs that alter synaptic transmission - Prozac inhibits serotonin reuptake - Cocaine inhibits dopamine reuptake - Caffeine blocks adenosine receptors - Ethyl alcohol stimulates inhibitory GABA receptors Neurotoxins that alter synaptic transmission - Strychnine competes with inhibitory neurotransmitter, glycine, at postsynaptic receptors - Tetanus toxin prevents release of GABA from inhibitory presynaptic axons - Both toxins cause unchecked excitation, muscle spasms and death Alteration of the neuromuscular junction - Black widow venom causes explosive release of ACTH - Curare block ACTH receptors - Both cause muscle paralysis and death - Myasthenia gravis is an autoimmune disease in which antibodies attack ACTH receptors, leading to muscle weakness - Neostigmine inhibits acetylcholinesterase, prolonging the activity of ACTH in the synapse Chapter 5 – Nervous Systems Vertebrate brain size is related to body size (with a few exceptions) - Expensive-tissue hypothesis o Cost of maintaining a larger brain is offset by a smaller intestinal tract o Carnivores are large-brained with high-quality diets o Herbivores are small-brained with low-quality diets requiring a larger digestive tract - Maternal-energy hypothesis o Brain size depends on the allocation of maternal resources to fetal and postnatal development Organization of the vertebrate nervous system - Central Nervous System (CNS) o Brain o Spinal cord - Peripheral Nervous System (PNS) o Nerve fibers extending to other parts of the body o Afferent division: carries information from sensors to CNS o Efferent division: transmits instructions from CNS to effector organs - Afferent neurons o Sensory receptor at peripheral end o Peripheral axon extends from sensory receptor to cell body o Cell body in dorsal root ganglion outside of CNS o Central axons extends from cell body into spina cord - Efferent neurons o Dendrites and cell body in CNS o Axon projects to effector organ - Interneurons o Lie entirely within the CNS o Integration of peripheral responses to peripheral information - Autonomic nervous system o Regulates visceral activities o 2 divisions: sympathetic and parasympathetic o Most visceral organs are innervated by both sympathetic and parasympathetic nerve fibers (dual innervation) o 2 divisions exert opposite effects o Sympathetic – excitation o Parasympathetic – relaxation Cranial – bottom of skull Thoracic – chest Lumbar – lower back Sacral – lowest part - Sympathetic system o Preparation for strenuous physical activity in emergency situations (fight or flight) Heart rate increases Respiratory airways open Glycogen and fat stores are broken down Blood vessels supplying skeletal muscle dilate Pupils dilate - Parasympathetic o General housekeeping activities in relaxed situations Digestion Emptying the urinary bladder Autonomic pathway consists of a 2-neuron chain - Preganglionic fibers extend from CNS to autonomic ganglion - Postganglionic fibers innervate effector organ - Sympathetic nerve fibers originate in thoracic and lumbar regions of spinal cord - Sympathetic ganglia form a chain alongside the spinal cord - Parasympathetic nerve fibers arise from brain (cranial) and sacral region of spinal cord - Parasympathetic ganglia (terminal ganglia) lie in or near effector organs Neurotransmitters - Sympathetic and parasympathetic preganglionic fibers release Acetylcholine - Parasympathetic postganglionic fibers release ACTH (cholinergic fibers) - Sympathetic postganglionic fibers release norepinephrine (NE) (adrenergic fibers) - Terminal branches of postganglionic fibers have varicosities for diffuse release of neurotransmitters - Adrenal Medulla is a modified sympathetic ganglion o Releases NE and epinephrine into the blood o Ad- close to o Renal – kidneys o So Adrenal = close to kidneys Different receptor types are available for each autonomic neurotransmitter - Cholinergic nicotinic receptors o On postganglionic cell bodies in all autonomic ganglia o Open nonspecific cation channels when ACTH binds o More Na+ enters than K+ leaves, resulting in depolarization - Cholinergic muscarinic receptors o On effector cells of parasympathetic system o Five subtypes linked to G proteins that activate second-messenger systems when ACTH binds - Adrenergic receptors o On effector cells of sympathetic system o Epinephrine of NE binding coupled to G proteins o Alpha1 receptors: bind to NE, excitatory response o Alpah2 receptors: bind to NE, inhibitory response o Beta1 receptors: bind equally to epinephrine and NE, excitatory response o Beta2 receptors: bind to epinephrine, inhibitory response Skeletal muscle is innervated by motor neurons - Cell bodies are in ventral horn of spinal cord or in brainstem - Axons terminate on skeletal muscle - Axon terminals release ACTH, which stimulates excitation and contraction of skeletal muscle fibers - Skeletal muscle is controlled by motor regions of the cortex, basal nuclei, cerebellum, and brainstem o Motor neurons are the final common pathway Glial cells (neuroglia) serve as the connective tissue of the CNS - Occupy half the brain volume - Do not initiate or conduct nerve impulse - Maintain composition of the ECF environment surrounding neurons - Modulate synaptic function - Important in learning and memory Types of glial cells - Astrocytes o Most abundant o Support neurons - Oligodendrocytes o Myelin sheaths - Ependymal Cells o Form cerebrospinal fluid - Microglia o Immune defense of CNS Protection of the CNS - Bony structures o Cranium (skull) encases brain o Vertebral column surrounds spinal cord - Meninges o 3 membranes between bone and nervous tissue - Cerebrospinal fluid (CSF) o Formed by selective transport across choroid plexus - Blood – brain barrier o Tight junctions between capillary endothelial cells Brain is highly dependent on a constant blood supply - Brain cannot produce ATP in the absence of oxygen - Brain uses only glucose (and ketone bodies during starvation) for fuel o Small amount of glycogen is stored in astrocytes - Brain damage results if brain is deprived of oxygen for more than a few minutes Neurogenesis: reproduction of neurons - Uncommon in adult brain - Hippocampus o Formation of spatial memory and development of cognitive skills - Sub-ventricular zone o Regeneration of sensory cells of olfactory epithelium - Hypothalamus o Cell division occurs in relation to environmental signals Chapter 8 – Muscle Physiology Muscle Cells - Specialized to produce force and do work - Utilize a highly developed microfilament system - Can shorten and develop tension - Convert chemical energy of ATP into mechanical energy that can act on the environment - 3 types of Muscle – skeletal, cardiac and smooth Contraction of Muscles Permits - Purposeful locomotory movement - Manipulation of external objects - Propulsion of contents through hollow internal organs - Emptying the contents of certain organs into the external environment - Production of heat - Production of sound Skeletal Muscle - Makes up the muscular system - Skeletal muscle cells (fibers) are large, elongated and cylindrical o Formed by fusion of many myoblasts during embryonic development: have multiple nuclei o Lie parallel to each other and are bundled together by connective tissue o Extend the full length of the muscle Myofibrils - Specialized contractile elements - Typically make up 90% of muscle volume - Cylindrical intracellular organelles extending entire length of muscle fiber - The greater the density of myofibrils, the greater the force that can be generated - Muscle fibers with a low percentage of myofibrils cannot generate much tension, but can contract at high frequency or for prolonged periods of time Myofibrils have a regular arrangement of thick and thin filaments - Thick filaments o 12-18 nm in diameter o Composed of the contractile protein, myosin Tails are intertwined with globular heads projecting out at one head Each globular head has an actin binding site and an ATPase - Thin filaments o 5-8 nm in diameter o Composed of the contractile protein, actin Has sites for attachment to myosin o Tropomyosin forms strands that cover actin binding sites when muscle is relaxed o Troponin is a protein complex with 3 subunits 1 subunit binds tropomyosin, 1 binds actin and 1 binds with Ca2+ When not bound to Ca2+, troponin stabilizes tropomyosin in its blocking position - Binding sites on actin blocked by tropomyosin o Calcium comes and binds to troponin and troponin pulls tropomyosin away, exposing binding site o Thick filament then binds o Action potential from motor neuron Key Highlighted = extra lecture information Underlined = important info Bold= slide header Bold and underlined = chapter title
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