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KINESIOL 1A03 Final: Muscular System- Histology and Physiology

16 Pages
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Department
Kinesiology
Course Code
KINESIOL 1A03
Professor
Maureen Mac Donald

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Muscular System: Histology and
Physiology
Skeletal Muscle System Functions
- Body movement
o muscles are attached to bones, muscle attached to sclera of eye to help rotate eyeball,
muscle attached to skin in your face to help create facial expressions
oBones act as levers allowing body movement
- Maintenance of posture
o stabilize joints, maintain various body positions eg. Standing, sitting
oMuscles that maintain posture are always contracting
- Fainting – postural muscles relax and you can’t hold stay upright; sleeping – neck muscles relax
- Respiration – diaphragm, intercostal muscles help us breathe
- Production of body heat – main energy source is ATP, you get work out of it, majority of energy
is lost as heat during breakdown of ATP; muscles use so much ATP – main contributor to body
temperature – explains why exercise makes you hotter, why you shiver when you’re cold –
repeated contraction of muscles uses energy, produces heat to maintain body temp
- Communication
Properties of Muscle
-Contractility: the ability of a muscle to shorten forcefully
oShorten a muscle and create tension, that produces a force (tension is the force)
oMuscle attached to two bones , shortening it pulls on the bones, creates tension along
the length of the muscle and causes muscle to move the bone
-Excitability: capacity of muscle to respond to a stimulus; most cases we’re talking about
electrical excitability, electrical stimulus coming from the nervous system
oOn plasma membrane are voltage gated channels; when axon synapses with skeletal
muscle it sends a NT across which cause a change in resting potential and we can
propagate an AP across membrane
oCan respond to hormone, pH changes in addition to electrical impulse
1
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-Extensibility: muscle can be stretched beyond its resting length and still be able to contract
oEg. We can stretch muscles on anterior portion of joint beyond resting position but still
contract eg playing baseball swinging the bat
-Elasticity: ability of muscle to recoil to original resting length after its been stretched
- Muscle tissue can only be excited not inhibited, can contract or not, can`t inhibit it
2
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Skeletal Muscle Structure
- Composed of muscle cells (fibers), connective tissue, blood vessels, nerves
- Fibers are very long, cylindrical, multinucleated tube type of structure
- muscle fiber cell runs the length of the entire muscle in most cases
- nucleus is just under the plasma membrane
- nucleus is on the outside closer to plasma membrane because we don’t want it to interfere with
muscle protein properties which allow for contraction and are found on the inside
- striated appearance due to light and dark banding produced by proteins within muscle fiber
Picture 1
- outer layer – muscular fascia – fibrous sheath of CT surrounding muscle (very dense and thick_
- surrounds individual muslcles and sometimes groups with similar functions
- deep to fascia is the epimesium: dense, irregular connective tissue
- tightly adheres to fascia layer, also surroundsmuscle and is found on outer layer
-epimysium: bundles of muscle fibers (represented by red circles) are called fasiculus
- each fasiculus is surrounded by perimysium
- between muscle fibers in fasciululs is the endomysium – loose, areolar connective tissue which
fills in the spaces between muscle fibers in the fasiculus
- muscles have a very extensive blood and nerve supply –r every single muscle fiber has an
innervation by a nerve
- arteries and veins will penetrate all 3 layers to get into the level of the muscle fibres, when
arteries reach muscle fibers they form an extensive capillary bed network around the fibers
- as we train, we get more capillary beds so more O2 and oxygen  endurance improvement
- nerve supply enters the muscle, penetrate through -the connective tissue layers
- single axon divides up and innervates several muscle fibres
- single motor neuron and associated fibers is called the motor unit
3
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Description
Muscular System: Histology and Physiology Skeletal Muscle System Functions - Body movement o muscles are attached to bones, muscle attached to sclera of eye to help rotate eyeball, muscle attached to skin in your face to help create facial expressions o Bones act as levers allowing body movement - Maintenance of posture o stabilize joints, maintain various body positions eg. Standing, sitting o Muscles that maintain posture are always contracting - Fainting – postural muscles relax and you can’t hold stay upright; sleeping – neck muscles relax - Respiration – diaphragm, intercostal muscles help us breathe - Production of body heat – main energy source is ATP, you get work out of it, majority of energy is lost as heat during breakdown of ATP; muscles use so much ATP – main contributor to body temperature – explains why exercise makes you hotter, why you shiver when you’re cold – repeated contraction of muscles uses energy, produces heat to maintain body temp - Communication Properties of Muscle - Contractility: the ability of a muscle to shorten forcefully o Shorten a muscle and create tension, that produces a force (tension is the force) o Muscle attached to two bones , shortening it pulls on the bones, creates tension along the length of the muscle and causes muscle to move the bone - Excitability: capacity of muscle to respond to a stimulus; most cases we’re talking about electrical excitability, electrical stimulus coming from the nervous system o On plasma membrane are voltage gated channels; when axon synapses with skeletal muscle it sends a NT across which cause a change in resting potential and we can propagate an AP across membrane o Can respond to hormone, pH changes in addition to electrical impulse 1 - Extensibility: muscle can be stretched beyond its resting length and still be able to contract o Eg. We can stretch muscles on anterior portion of joint beyond resting position but still contract eg playing baseball swinging the bat - Elasticity: ability of muscle to recoil to original resting length after its been stretched - Muscle tissue can only be excited not inhibited, can contract or not, can`t inhibit it 2 Skeletal Muscle Structure - Composed of muscle cells (fibers), connective tissue, blood vessels, nerves - Fibers are very long, cylindrical, multinucleated tube type of structure - muscle fiber cell runs the length of the entire muscle in most cases - nucleus is just under the plasma membrane - nucleus is on the outside closer to plasma membrane because we don’t want it to interfere with muscle protein properties which allow for contraction and are found on the inside - striated appearance due to light and dark banding produced by proteins within muscle fiber Picture 1 - outer layer – muscular fascia – fibrous sheath of CT surrounding muscle (very dense and thick_ - surrounds individual muslcles and sometimes groups with similar functions - deep to fascia is the epimesium: dense, irregular connective tissue - tightly adheres to fascia layer, also surroundsmuscle and is found on outer layer - epimysium: bundles of muscle fibers (represented by red circles) are called fasiculus - each fasiculus is surrounded by perimysium - between muscle fibers in fasciululs is the endomysium – loose, areolar connective tissue which fills in the spaces between muscle fibers in the fasiculus - muscles have a very extensive blood and nerve supply –r every single muscle fiber has an innervation by a nerve - arteries and veins will penetrate all 3 layers to get into the level of the muscle fibres, when arteries reach muscle fibers they form an extensive capillary bed network around the fibers - as we train, we get more capillary beds so more O2 and oxygen  endurance improvement - nerve supply enters the muscle, penetrate through -the connective tissue layers - single axon divides up and innervates several muscle fibres - single motor neuron and associated fibers is called the motor unit 3 - only have to send signal down one neuron and it causes reaction from several fibers - every fibers has a synapse or a neuromuscular junction - each fiber only has one junction - don`t want to contract muscle fiber from diff ends at diff times so neuron can have several fibers but each fiber only has one neuron - 4 Picture 2: - muscle fibers, while they run the length, they end where the tendon is located - tendon is a continuation of the 3 connective tissue layers, attaches to bone - easy diffusion of nutrients and gases - sarcolemma: plasma membrane of muscle - nuclei - # of them located on length of muscle fiber - inside muscle fiber – transverse tubules (T tubules) - - evaginations of sarcolemma, fold sin on itself to produce tube network - Creates larger SA for AP to move along membrane - AP signalled propagates along sarcolemma in a little pore through transverse tubule… - Sarcoplasmic reticulum – smooth ER, stores calcium - Red region – muscle fiber, white region – tendon (3 connective tissue layers extending past where muscle fibres are to attach to bone) - 3 connective tissue layers: epimeysum, perimysium, endomysium - Endomysium – in between muscle fibers within the fasiculus - Perimysium - surrounds each individual fasiculus - Epimysium – just under muscular fsacia layer surrounds whole muscle - Extensive capillary bed for delivering nutrients – endurance training – more capillary beds - Along length of sarcolemma are invaginations /pores that lead to a tube system inside the muscle fiber itself called the transverse (T) tubules which are open to the outside / extracellular space which provide a greater surface area for AP’s moving along the sarcolemma - AP propagate along muscle fiber and moves down in through invagination and through the T tubule, creates / allows AP to reach the inside of the fiber at a similar time as the outside of the fiber  important b/c contractile properties of fiber are located throughout the fiber, want it to contract in a coordinated fashion - Smooth endoplasmic reticulum – sarcoplasmic reticulum – associated with T tubules, main job is to store calcium - Mitochondria within cytoplasm of muscle fiber located on outside and move through fiber close to where protein regions are located, depend son fiber type and # of mitochondria which produce ATP  more oxidative type of fiber, more mitochondria 5 - Within muscle fiber in cylindrical packages are myofibrils – bundles of protein filaments, contractile portion of muscle fiber (everything else is just associated with contractions, within myofibrils is what actually causes contraction) - Myofibrils also span entire length of muscle fiber - T tubules are repeated sections as we move down the muscle fiber, look like a cross section and on either side ewe have sarcoplasmic reticulum… - Myofibrils are what cause striped appearance of muscle, myofibrils are striated and a bunch together gives it a striped appearance Myofibrils - 2 Protein filaments; thin filament: actin myofilament, thick myofilament: Myosin myofilament - While the myofibril itself spans the entire length of the muscle, the myofilaments do not - They are contained in a very highly ordered unit within the myofibril called the sarcomere - Small myofilaments are much shorter, together a bunch of sarcomeres in series make up a myofibril - From one blue line to the next blue line is a sarcomere ( in the diagram) - Blue lines rep something called z disk - Z disk – disk like structure in zig zag formation , acts as ach - Actin myofilaments (thin filaments) – anchored /attached to the z disk on the lateral end - Whatever’s located between two z disks is referred to as a single sarcomere - Individual sarcomere is the distance from one z disk to another z disk - Space between actin myofilaments in the center - In the middle of the sarcomere – myosin myofilament (thick filament); between actin filaments, attached by delicate protein fibres at the M line (middle line) that hold center of myosin myofilament in place and connect adjacent myosin myofilaments together 6 - Myosin myofilament also held in place by titin filament , represented by grey structure - Titin: One of the largest proteins in the body, 2 in each sarcomere - Individual titin filament runs form z disk to m line but goes in either direction so winds up spanning the whole sarcomere but its two filaments put together - Close to z disk, titin filament is coiled which gives muscle its elasticity & extensibility properties (ability to contract beyond resting position and ability to return to rest position ) - When our myosin myofilaments binds to the actin myofilament we refer to this as a cross bridge (just the place where actin and myosin bind), allows muscle to shorten - Actin myofilaments - Made up of 3 protein components: o F(ibrous) actin molecules – make a strand, 2 coil together to form a double helix; made up of little purple circles o G(lobular) actin molecules – little purple circles, bunch of G actin molecules lined up together which form the F actin molecules o Active sites – each individual G actin has an active site – where myosin will bind to the actin and create the cross bridge - 2 other proteins associated: regulatory proteins – they regulate whether or not active sites are available to myosin for binding: o Tropomyosin (blue, string-like structure): coils around the F actin molecules and cover the active sites at rest; blocks active sites, not allowing myosin to bind to actin o Troponin: (red structure) – 3 subunits: 1 subunit binds to actin, 2 binds to tropomyosin (helps anchor tropomyosin onto actin molecule, holds tropomyonsin in rd place around F actin molecule), 3 binds to calcium – important for muscle contraction (calcium stored in sarcoplasmic reticulum); calcium released works its way to actin myofilament, bind to troponin, and troponin will move tropomyosin out of the way from actin sites allowing for myosin to bind to actin 7 Myosin myofilaments - Made up of a large number of myosin molecules (about 300 / myosin myofilament) - Individual myosin molecule looks like two golf clubs with shafts wrapped around each other - All lined up, Half pointing with head sin one direction half with heads in other direction - Structure of individual myosin molecule: - Green portion: 2 heavy chains of myosin – larger protein molecule of myosin molecule - coiled-portion form two α helices, portion that coiled together referred to as the rod of the myosin - head portion is also part of the heavy chain ; two heads on each myosin molecule - head is the region where we have the binding to the actin , heads bind to active site on actin - what allows for muscle contraction is the fact that the heads can move relative to the rod portion because of a hinge region on the myosin located between the rods and heads - as it attaches to the actin, the head pulls on the actin and moves the actin relative to the myosin - heads bind to the actin, located on lateral ends of myosin myofilaments - light chains of proteins: 4 located in the head region, not as important functionally - heads are region that require ATP for action / moving of head relative to the rod - when we use ATP, usually referred to as an ATPase – myosin ATPase (breaks down ATP) 8 - similar to sodium potassium pump, breaking down ATP to allow pumping action of sodium out of cell and potassium into cell - variety of myosin molecules in a circular fashion so heads are all projecting outwards and available for binding to actin which will surround this molecule Sarcomere Details - heads on lateral side, rods in center, actin molecule attached to z disk - always overlap between actin and myosin myofilaments – important or we can’t have muscle contraction; two regions always have a bit of overlap - I band: region around z disk on either side of z disk that contains only actin myofilaments - Light appearance because actin myofilaments are thin and don`t create density when stained - Make up little hexagons - M line: middle line of sarcomere, delicate fibers that hold myofilaments together, create hexagon pattern - A band: Region where we have entire myosin myofilament, wherever myosin myofilament is located - Within A band, regions of overlap between actin and myosin and some regions of just myosin - Actin and myosin overlapping looks similar to this.. hexagon around myosin, little things out of myosin are heads, surrounding each head is the actin myofilaments cause they’re right next to each other - H zone: Region where we have no actin and only myosin - Myosin bands are heavy, A bands always look darker and overshadow where you see overlap - Striated appearance:
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