Muscle Tissue Study Guide

Muscle Tissue Identify the criteria used to classify muscle, then differentiate the three muscle types using these criteria. Criteria = striations, nervous control, number of nuclei. Skeletal striated, voluntary, multinucleated Cardiac striated, involuntary, one nucleus (intercalated discs, striations branch more) Smooth non-striated, involuntary, one nucleus (“spindle cells” because they taper at both ends) Describe the properties common to all muscle types.  Excitability = responds to a stimulus  Contractility = ability to shorten/thicken; no muscle will contract unless it is stimulated to contract impulse carried by nervous system, muscle reacts by contracting  Extensibility = can stretch, work in antagonistic pairs in skeletal muscle  Elasticity = can return back to resting state after shortening/thickening Explain the functions of muscle. Motion – any muscle contraction results in motion  Contraction of cardiac muscle moves blood  Contraction of smooth muscle propels food, releases urine  Contraction of skeletal muscle = locomotion Maintenance of posture – skeletal muscle contraction opposes gravity Stabilizing joints – muscles surround join are partially contracted to give strength Heat production – any muscle contraction produces heat Examine the gross anatomical features of skeletal muscle. Muscle = 100s-1000s of individual muscle cells  Skeletal muscle fibers  Blood vessels – deliver oxygen and glycogen  Nerve fibers – carry impulse for stimulation  Connective tissue Attachment – indirect or direct; tendons and aponeurosis Epimysium = connective tissue around the entire muscle; dense irregular connective tissue Fascicle = bundle of muscle cells, covered by the perimysium Perimysium = connective tissue covering fascicle Muscle fiber = muscle cell = myofiber Endomysium = connective tissue surrounding the individual musc cell; reticular connective tissue Describe the types of muscle attachments. Direct attachment = muscle fuses to periosteum Indirect attachment = tendon attaches muscle to bone  Tendon – rope-like extension of connective tissue  Aponeurosis – sheet of connective tissue (palmar aponeurosis) Origin = attachment of the muscle to the immovable bone Insertion = attachment to the movable bone Can have more than one origin/insertion Explore the microscopic anatomy of skeletal muscle and the specific arrangement of each element in relation to the others.  Myofibers – cells run the length of the muscle  Sarcolemma – plasma membrane of a muscle cell; given a special name because of change in the cell during embryonic development  Sarcoplasm – cytoplasm of a muscle cell; store their own glycogen for contraction o Myoglobin = pigment that stores oxygen in muscle  Nuclei – multiple per cell  Myofibrils – contractile components of muscle; myofibers contain myofibrils  Sarcoplasmic reticulum – modified ER, surrounds the myofibrils  T tubule – 1/3 of a triad, run longitudinally; interrupted by terminal cisternae (perpendicular channels, 2/3 of triad) Describe the structural arrangement of a sarcomere. Sarcomere = z line to z line Thin myofilaments connected to the Z line Myosin pointing away from M line = higher energy configuration Z line = ends of sarcomeres A band = where thick and thin are together I band = doesn’t have thick myofilaments H zone = only thick myofilament Identify the proteins associated with the myofilaments. Thick myofilaments = myosin  Actin binding site (connects thick and thin myofilaments)  ATP binding site  Two heads per myosin Thin myofilaments = actin  Tropomyosin wraps around to give strength  Troponin – always connected to tropomyosin o Troponin I – attaches to actin o Troponin T – binds to tropomyosin o Troponin C – binds to calcium disables troponin I so it can no longer be attached to actin Explain the sliding filament theory of muscle fiber contraction. Actin (thin) filaments slide past the myosin (thick) filaments, using the actomyosin crossbridge Describe the structural arrangement of the neuromuscular junction, and explain the mechanism of generation of an action potential across the sarcolemma.  One neuromuscular junction per fiber  No direct connection: synaptic cleft = small space between nerve and muscle cell  Synaptic vesicles contain neurotransmitters ACH = acetylcholine  Signal comes down the neuron, causes the vesicles to release ACH through exocytosis (caused by calcium fusing with vesicles), which bind to receptors on sarcolemma  Motor end plate o Ach receptors found at motor end plate only o Acetylchonesterase breaks down Ach  Ach triggers generation of action potential across sarcolemma and down T tubules o Opens sodium channels so sodium moves into, cell becomes depolarized o Action potential passes triads +30 mV o Terminal cisternae release calcium into sarcoplasm o Some calcium binds to troponin removes tropomyosin from active sites on actin o Myosin heads attach to actin and pull thin myofilaments toward center of sarcomere o Power stroke  Thick and thin myofilaments found through cross bridge  Myosin head changes from high energy to low energy configuration  Pulls thin myofilament toward H zone  ATP binds with myosin head  Myosin and actin separate  ATPase splits ATP and released energy returns myosin head to high energy position  Cycle repeats in presence of calcium and ATP Describe a motor unit, and explain how these can affect the strength of muscle contraction. Motor unit = motor neuron and all the fibers its stimulates  Not all motor units in a muscle fire at the same time, which allows it to stay active longer  Each muscle fiber has only one neural connection  Strength of contraction is determined by the number of motor units involved Muscle Contraction *no muscle will contract unless it is stimulated to contract* Describe the different types of muscle contraction, and explain how wave summation operates in these various types.  Twitch: single stimulus in response to a single stimulus o More motor units = more tension o Latent period = period of time between stimulation and the beginning of activity  Time of Ach to open sodium gates and going through tubules and releasing calcium o Relaxation phase – sodium goes back out o A second stimulus applied before complete contraction and relaxation won’t cause anything to happen  Refractory period = time in which a second stimulus will not evoke a response  Tetanus: second contraction due to second stimulus before complete relaxation o Must come during the relaxation phase, after the refractory period    o Incomplete tetanus = partial relaxation  Wave summation – second stimulus applied before complete relaxation; strength increases with each additional stimulus, to a maximum o Complete tetanus = no relaxation Treppe: muscle completely relaxes but contractions get stronger o More efficient process Isotonic: effort exceeds the load, muscle shortens and changes shape Isometric: load exceeds effort no movement Describe the mechanisms through which muscles are supplied with ATP.  Direct phosphorylation o Creatin phosphate couples with ADP to produce ATP o Occurs within cytoplasm of the cell o Power muscle up to 15 seconds o CP reserves replenished during inactivity  Anaerobic respiration – if oxygen isn’t present o Glycolysis breaks down glucose (cytoplasm) o Pyruvic acid converted to lactic acid o Lactic acid diffuses into bloodstream, travels to the liver, which turns to pyruvic acid, and turns into glucose o Power muscle up to 1 minute o Lactic acid shuts off ATP  Aerobic respiration o Glycolysis breaks down glucose o Produces lots of ATP o Pyruvic acid enters mitochondria for complete breakdown Explain the factors that can affect the force of a muscle contraction.  Number of fibers stimulated o More fibers/motor units = stronger contraction  Relative size of fibers o More storage in the cell = larger = greater strength  Frequency of stimulation o More frequent = stronger  Degree of stretch o More overlap = less force o No overlap = no force of contraction Differentiate the types of skeletal muscle fibers. Based on speed of contraction and how ATP is produced:  Slow oxidative fibers o Slow contraction o Aerobic (oxygen) o Very fatigue-resistant   o Ex: long distance runner Fast oxidative fibers o Fast contraction (split ATP quickly) o Aerobic (oxygen) o Relatively fatigue-resistant, but might run out o Ex: sprinter Fast glycolytic fibers o Fast contraction (split ATP quickly) o Anaerobic o Prone to fatigue, but get big burst of contraction o Ex: weightlifter Indicate the microscopic anatomy of smooth muscle cells, and compare this to skeletal muscle cells.  Smooth fibers smaller than skeletal fibers (shorter cells)  Lack connective tissue sheaths only endomysium (no peri or epi)  Organized into sheets o Longitudinal layer o Circular layer  Unstructured neuromuscular junction o Autonomic nerve activates smooth muscle from the involuntary part of the brain o Repeated bulbous swellings (variscosities) that contain vesicles that hold neurotransmitters o Variscosities release neurotransmitters into diffuse junctions entire surface of the muscle has neurotransmitter receptors  Less developed sarcoplasmic reticulum o No triad arrangement o Touches sarcolemma, but no organized pattern to the myofilaments o No sarcomeres o No T tubules  Caveoli – infoldings of sarcolemma that holds concentrated calcium in pouches so that it is available when the cell needs it  Myofilament arrangement o 10-15 thin myofilaments for each long, thick myofilament o Myosin heads found along entire length of thick myofilament o Tropomyosin associated with thin myofilament, but no troponin  Nothing to cover myosin binding sites, but cross bridges are in low energy configuration and can’t bind to them o Myofilaments arranged diagonally within fibers o Intermediate filaments – non-contractile element  Attach to dense bodies and stretch from one to another  Dense bodies attached to sarcolemma Describe the types of smooth muscle and identify their locations within the body. Visceral – contracts rhythmically as a unit  Peristalsis: wave-like contraction of smooth muscle  Cells are coupled with gap junctions, which makes it work as a unit  Found in the walls of hollow internal organs Multiunit  No gap junctions  Pupil and arrector pilli  Walls of large arteries Describe the mechanism and regulation of smooth muscle contraction. Mechanism:  Neurotransmitter stimulates production of action potential changes membrane permeability  Calcium released by caveoli  Calcium binds to calmodulin (smooth muscle doesn’t have troponin)  Activated calmodulin activates myosin light chain kinase  Activates kinase charges myosin cross bridges  Actin and myosin interact to shorten fibers In smooth muscle, actin is ready to go, but myosin isn’t (opposite of skeletal) Regulation:  Autonomic nerves release different neurotransmitters o Excitatory or inhibitory  Chemical factors o Hormones independent of neurotransmitters (uterine contractions) o Histamine (allergic response) o Excessive CO2 o Changes in pH Identify the embryonic development of muscle tissue, and outline the changes in muscle tissue that occur due to age. Muscle tissue develops from the mesoderm  Skeletal myoblasts (mesodermal cells) fuse long, multinucleated o Cardiac and smooth do not fuse; develop gap junctions instead shorter cells  Agrin clusters and maintains Ach receptors, only at the motor end plate  All myoblasts have neurotransmitter receptors over entire sarcolemma  Muscles change because of agrin (growth factors), which creates neuromuscular junction and neuro end plate, acetylcholine receptors remain at that site Muscle Mechanics Describe the origin, insertion and belly of a muscle, and explain how each function to invoke movement.  Origin – attachment to stationary bone   Insertion - attachment to movable bone Belly – fleshy, meaty part of the muscle (gaster) Define a lever, and describe the two forces acting on it.  Lever – rigid structure that moves about a fixed point called fulcrum o Joints = fulcrum, bones = rigid structures  Resistance (load) – force that has to be overcome for movement to occur  Effort – force exerted to overcome the resistance  If the load is closer to the fulcrum than the effort is, there is mechanical advantage, making it easier for things to be moved Differentiate the three classes of levers. 1) First class  Fulcrum between load and effort  Head on shoulders o Load = weight of head o Effort = contraction of muscles on back of neck 2) Second class  Resistance is between fulcrum and effort  Can have mechanical advantage – require less fibers  Standing on tip toes 3) Third class  Effort is between fulcrum and load  Mechanical disadvantage  Require more fibers to overcome mechanical disadvantage Describe the functional groups of muscles.  Agonist (prime mover) – muscle that is primarily responsible for bringing movement about  Antagonists – opposite movement of agonist  Synergists – accessory muscles that help to steady the movement; assist agonist  Fixators – stabilizes the origin of the agonist Identify the criteria used for naming muscle.  Location  Shape  Size o Oblique = diagonal o Rectus = parallel  Direction of muscle fibers  Number of origins  Location of attachment (origin comes first in naming)  Action (flexers, abductors) Indicate the most common arrangements of fasciculi in skeletal muscle.  Parallel o Sartorius o Parallel to longitudinal axis of the muscle  Convergent o Broad at origin but narrows at the insertion o All of the fasciculi are arranged toward the insertion  Pennate – tendon runs entire length of muscle, fibers are short and orient toward tendon o Unipennate: all fasciculi on same side o Bipennate: on both sides o Multipennate: multiple tendons  Circular – around an oris Long fibers = increased range of motion Short fibers = relatively small range of motion Power of muscle is determined by number of fibers that the muscle possesses Neurophysiology Identify the functions of the nervous system.  Sense change o First response to stress is through the nervous system (immediate) o Chemical response is secondary  Interpret change – central nervous system  Respond – based on the interpretation o Detect change interpret what it means send response List the structural and functional divisions of the nervous system, and describe their relationship to one another. Central Nervous System – receives all sensory information and initiates responses Peripheral Nervous System – connects CNS to everything; extensions off brain = cranial nerves; extensions off spinal cord = spinal nerves  Afferent division – carries sensory information to CNS  Efferent division – carries motor information away from CNS o Somatic nervous system – attaches to a skeletal muscle to innervate to cause contraction; under conscious control o Autonomic nervous system – motor neurons that innervate cardiac or smooth muscle; involuntary control  Sympathetic division – fight or flight, survival  Parasympathetic division – housekeeping tasks Discuss the anatomy of a neuron and the function of each structure. Neurons = structural and functional units of the nervous system; conduct nervous impulses; 50% of nervous tissue  Cell body – nucleus and all organelles o Perikaryon = soma = portion of the cell that contains all of the cellular components  Chromatic substance (Nissl bodies): specialized rough endoplasmic reticulum; proteins used for neural growth lots in embryo, and used for peripheral regeneration (fixing damage)  Neurofibrils: microtubules of cytoskeleton, function in support and to distribute nutrients  Lipofuscin: yellow-brown pigment (cell inclusion), not sure what it does, mostly accumulated in elderly  Dendrites – numerous short extension of cytoplasm  Axon – single, long extension away from the cell body o Axon hillock: point at which the axon leaves the cell body; attachment part o Telodendria: end of the axons o Synaptic knobs: vesicles on ends telodendria, contain neurotransmitters o Axon collaterals = branches o Myelin sheath: made of lipid, protects axon, speeds up conduction of impulse along axon Innervation is transmitted dendrites cell body axon (ONLY DIRECTION) Explain the physiological characteristics of mature neurons.  Longevity – function for lifetime, develop in embryo  Lose ability to divide – cannot replicate, always in G0  High metabolic rate – requires lots of energy and glucose Describe the types of glial cells, their functions and their locations in the nervous system. Neuroglia = all cells that nourish, protect, and support neurons CNS glial cells:  Astrocytes o Most abundant in body o Attach neuron to blood vessel o Anchoring component to hold things in place o Coordinate the exchange between the neuron and the bloodstream (BBB)  Regulates internal chemical environment of the neuron (prevent bacteria from getting into the brain from the bloodstream)  Oligodendrocytes o Produce the myelin sheath around the axons of the CNS  Microglia o Immune role o Get rid of pathogens (macrophages)  Ependyma o Form the epithelial lining of the brain and spinal cord PNS glial cells: Satellite cells o Exist between adjacent cell bodies o Many present o Function has not been identified  Schwann cells o Create myelin sheath around axons in PNS o Produce lipids that are exported and accumulate around the axon  Describe the anatomy and function of the myelin sheath, and differentiate between myelinated and unmyelinated neurons. In the PNS: made by Schwann cells, nodes of Ranvier = gaps in myelin sheath In the CNS: made by oligodendrocytes, wider nodes of Ranvier  Made of lipid  Protects axon  Speeds up conduction of impulse along axon o Faster because the ions skip down over the nodes of Ranvier Define the structural and functional categories of neurons. Structural classification is based on the number of processes coming off of the cell  Multipolar o Several short dendrites o One long axon o Most prevalent  Bipolar o One dendrite and one axon, which are on opposite ends of the cell body o Only found in special sense organs (vision, hearing, balance); receptors  Unipolar o Only have on process, which acts as both the dendrite and the axon o Mostly sensory Functional classification is based on the direction of impulse transfer (toward or away from CNS)  Sensory neuron o PNS CNS o Most are unipolar  Motor neuron o CNS PNS o To muscle or gland  Interneuron o Entirely in the CNS o Most are multipolar Reflexes go to the spinal cord for decoding Explain the resting membrane potential and how it is generated. Resting membrane potential is the polarization of the membrane when at rest. It is due to the movement of sodium and potassium ions  -70mv  Inside of the cell is negative in relation to the surrounding extracellular fluid Identify how changes in membrane potentials act as signals, and relate each type of signal to the generation of an action potential. Stimulus is applied to polarized neuron localized change in membrane permeability Depolarization = making the cell less negative Describe the threshold stimulus. Discuss how it related to graded potentials and the all-ornone behavior of axons. Threshold stimulus = minimum potential at which an action potential will be caused  All or nothing: no action potential if stimulus does not reach threshold; it either is reached or not reached, there is not intermediate  Graded potentials cause gated ion channels to open o Inflow of positive ions changes membrane potential in localized region, causes change in permeability in local regions o Produced by sensory neuron (temp, light) o Short term reversal in permeability that results in polarization or depolarization  Action potentials are initiated by graded potentials that cause depolarization of the resting neuron Neural Integration Define a synapse, and contrast a chemical synapse from an electrical synapse. Synapse:  Electrical: plasma membranes of adjacent cells fuse together, create connexons and gap junctions o Depolarization of one cell can cause depolarization of the adjacent, fused cell through the connexons o Not as common in adults o Seen when synchrony is needed cardiac muscle, visceral smooth muscle (stomach contracts as a unit) o High amount in embryos  Chemical: relies on neurotransmitters o Pre synaptic neuron has to store neurotransmitters o Post synaptic neuron has to have binding places for the neurotransmitters Differentiate continuous, saltatorial, and synaptic conduction of an action potential.  Continuous: action potential is transferred along entire length of unmyelinated axon o Occurs in a neuron that doesn’t have a myelin sheath  Saltatorial (jumping): impulse jumps from node of ranvier to node of ranvier o Myelinated axon o Because lipid is noncuductive, ions can’t transfer across so they jump Define the absolute and relative refractory periods. Absolute refractory period  If you apply a stimulus during the depolarization period, you won’t get another action potential because all of the sodium channels are already opened up Relative refractory period  A second stimulus during repolarization probably won’t cause another action potential unless the stimulus is strong enough to open more so threshold increases Identify the factors that affect the speed of impulse conduction.  Temperature  Axon diameter  Degree of myelination NOT stimulus strength Compare the classifications of nerve fibers. Based on size, myelination, and speed  Group A fibers o Largest in diameter, myelinated o Fastest fibers, ~130m/s o Large sensory neurons, visual information o Motor neurons that connect to skeletal muscle  Group B fibers o Medium diameter, myelinated o Intermediate speed, ~10m/s o Connecting skin to viscera, twitches  Group C fibers o Smallest diameter, no myelin o Slowest, ~0.5m/s o Sensory receptors in skin and visceral organs All can connect to each other Identify the types of synaptic junctions. Presynaptic is the one that releases the neurotransmitters, post synaptic receives message  Axodendritic – axon of pre synapses with dendrite of post  Axosomatic – axon of pre connects with cell body (soma)  Axoaxionic – axon connects with another axon o Fastest because there is less distance to be traveled to the end of the axon Describe the types of postsynaptic potentials, including what causes them and how they are summated by the postsynaptic cell.  Excitatory synapses o Depolarization of postsynaptic membrane o EPSP = excitatory postsynaptic potential  o Ex: influx of sodium ions Inhibitory synapses o Hyperpolarization of postsynaptic membrane (IPSP) Contrast the actions of the different types of neurotransmitter receptors.  Channel-linked receptors  G-protein linked receptors - indirect Discuss the actions of the functional classifications of neurotransmitters. More than 50 Function classification is based on how they work and what they do  Excitatory o Depolarizes the postsynaptic membrane  Inhibitory o Hyperpolarizes the postsynaptic membrane  Direct o Opens ion channels directly, ion moves in or out of cell  Indirect – neurotransmitter binds to the receptor receptor activates a secondary protein (G protein) G protein opens up a channel allows a change in membrane permability Describe neuronal pools and their functions. Neuronal pools – neurons linked to the same activity link together; specific group of neurons that perform the same homeostatic function  Discharge zone: center of the pool, most likely to be activated  Facilitated zone: along the edges of the pool, may or may not get activated; only activated when the stimulus is really strong Pools are arranged in circuits Name the various types of circuits.  Diverging o Single presynaptic neuron stimulates multiple postsynaptics, which continues and goes through a large area  Converging o Several presynaptics all stimulate a single postsynaptic  Reverberating o Single presynaptic neuron brings about a chain of events o Arm swings while walking, breathing while sleeping  Parallel after-discharge o First half is divergent, second half is convergent o Single stimulus goes over a large area of the body, and then comes back to the origin