Primary Tissue 4 : Muscle Flashcards
What is muscle tissue
-primary tissue which optimizes universal cell property of contractibility
Which components generate forces for muscle contraction
-actin and associated proteins ( Myosin )
Origin of muscle
-mesoderm
What are the key differentiations of muscle cells
- elongated cell
- production of abundance of contractile apparatus
Describe myofibril , myofilaments and
- bundles of sarcomeres
- the components of a sacromere ( actin and myosin )
The types of muscles
1 skeletal
2 cardiac
3 smooth
Cytoplasm, membrane and sER of muscle cells name !?
- sacrolemma
- sacroplasm
- sacroplasmic reticulum
Development of skeletal muscle
- mesenchymal cells of mesoderm called myeoblasts align and fuse into long multinucleated cyclindrical tubes myotube
- myotubes synthesize myofibrillar proteins and cross striations begin to appear
- continued synthesis of myofilaments displaces nuclei to peripheral of sacroplasm
What happens to undifferentiated myeoblasts
-become satellite cells which serve a regenerative function
How many Layers of CT surround the muscle and name them
Three
1 epimysium
2 perimysium
3 endomysium
Location and functions of the 3 layers surrounding skeletal muscle
1 epimysium- external dense sheath of CT surrounding entire muscle. Septa extends inwards dividing fascicles and bring large vessels and nerves to perimysium
2 perimysium- thin CT surrounding individual fascicles. Septa provides vessels and nerves to each endomysium
3 endomysium - thin delicate reticular fibers surrounding individual cells. Has blood and nerves to cells
What is a muscle fascicle
-a functional unit of bundles of muscle fibers which work together
Fascia and tendon location and function
- overlies endomysium and continuous with tendon
- continuous with tendon and connects muscle to bone or skin
Do individual fibers extend from one end of muscle or not !?
Do not
What does collagen of CT do
-transit mechanic forces from individual fibers
What are myofibrils and where are they found and what are they made of
- cyclindrical tubes parallel to long axis of cell.
- collection of myofilaments
-made of myofilaments ( actin and myosin )
Describe myosin 2 and formation, subunits and functions
- has 2 heavy chains which intertwine into tails
- 4 light chains make 2 globular heads with binding sites for myosin and ATP
Describe thick filaments structure
-numerous myosin molecules with tails intertwined and heads protruding at either end
Describe proteins attached to actin in muscle and their functions
1 tropinin- has three domains
- TnC binds to Ca2+ found at top
- TnT binds to tropomyosin found at bottom
- TnI found at middle and regulates actin and myosin interactions
2 tropomyosin - 40nm coil of 2 peptide chains intertwine in between grooves of actin
-make inaccessible active site of actin from myosin
Bands of myofibrill
1 A band - region has thick filaments with overlaying thin filaments
2 I band - region is thin filaments and titin only
3 H zone - region of thick filaments only
4 M line - line which dissects and holds thick filaments. Has m line proteins
5 Z disc - where Titin and actin are held
What is sacromere and where found and function
- region of filaments in between 2 discs
- is functional repetitive unit of myofibrill
What causes striations of muscle cells
-lateral arrangement of sacromeres of adjacent myofibrill’s
Describe titin, Z and M line proteins
- largest protein in body with a spring like domain
- bind thick filaments to Z disc
-has alpha actinini to hold actin filaments
- has myomesin to hold thick filaments to M line
- creatine kinase to catalyze transfer of phosphate from phosphocreatine to ADP supplying energy for contraction
Describe Nebulin proteins
-accessory proteins which hold actin filaments laterally to each other and anchors them to alpha actinin
What is phosphocreatine
-source of high energy phosphate groups
Where sER found in muscle and function
- surround myofibrills
- stores and releases Ca2+ during contraction
What is T-tubule and function
- invaginations in lemma which penetrate into plasma and encircle myofibrils
- allow for uniform and simultaneous muscle nerve to reach sER
Triad structure and function
- a T-tubule surrounded by 2 terminal Cisternae
- allows for muscle nerve at lemma to trigger sER to release Ca2+ simultaneously and uniformly
Events of contraction describe up to active site being exposed.
- nerve impulse triggers synoptic knob to release synoptic vessels into cleft which bind with Ach receptors on NMJ
- initiation of muscle impulse which spreads from lemma to triad and stimulates sER to release Ca2+ into plasm
- Ca2+ binds to TnC changing shape of troponin which moves tropomyosin and active site of actin are exposed
Events of contraction describe after active site exposed.
- myosin heads attach to active site forming crossbridge and using ATP hydrolysis heads pivot
- pivoting moves actin towards sacromere center
- another round of ATP causes head to regain pre-pivot state
- cycle of bind-pivot and pre-pivot continues moving filaments past each other and towards sacromere center
- sacromere shortens causing muscle to contract.
What keeps contraction cycle going
-as long as Ca2+ is bound to tropinin and tropomyosin active site is exposed
What happens to contracts when impulse stops !?
- Ca2+ is actively transported into sER
- tropomyosin hides active site and filaments passive slide back to normal state past each other
What is and causes of rigor mortis at death
/stiffening of muscle
-at death no ATP and actin myosin crossbridge is stable and rigid
How are individual muscle fibers innervated
- myelinated axons from perimysium branch out
- each branch has several unemyelinated twigs that pass through epimysium and form NMJ with individual muscle fibers
Describe NMJ structure, functions and adaptations
- synoptic Knob is in depression on lemma surface
- Schwann cells lemma at NMJ continues with sacrolemma
- are numerous foldings on sacrolemma to increase # of AcH receptors
Describe what is synoptic cleft and motor end
- space between knob and motor end
- surface on sacrolemma with numerous foldings and in contact with knob
Describe selectivity of Ach receptors and function and mode of action and what it makes
-it is non-selective
- upon binding to Ach its opens cation channels
- cations influx depolarizing membrane producing muscle impulse
How is prolonged contact of neurotransmitter and receptor prevented
- Ach quickly dissociates from receptor
- free Ach molecules removed by extra cellular enzyme acetylcholinesterase
How many NMJ can be formed by a single motor axon
- 1 or many
How to produce precise muscle control
-single muscle fiber innervated by single motor neuron / axon
What is a motor unit
-single axon and all muscle fibers in contact with its branches
How is force of contraction varied
-not all fibers in a fascicle contract at the same time
How much force will a single motor neuron generate when fired
-directly proportional to the number of muscle fibers it innervates
List components of mitotic spindle
- intrafusal muscle
- modified perimysium
- afferent nerves wrapped around modified muscle
- interstitial fluid
How do intrafusal muscle fibers differ from normal ones
- fewer myofibrills
- nuclei closely aligned ( nuclear chain fiber ) or piled in central dilation ( nuclear bag )
Where is mitotic spindle found , function and mechanism of action
- among fascicles
- provide CNS with info about stretch and tension of musculoskeletal system
- they detect changes in length of normal fascicles caused by bodily movements and sent to CNS
Describe stretch receptor and function
/afferent sensory receptors wrapped around intrafusal fibers in mitotic spindle
-ones that sent info to CNS
Describe function, structure and mode of action of Golgi body
- smaller structure wrapped around sensory nerves penetrating collagen at myotendinous joints
- detect tension of tendon during movement
-sent info to CNS
/inhibit motor activity if tension is excessive
List the skeletal muscle fiber types and list major criteria and other criteria
1 slow oxidative ( red
2 fast glycolytic ( white )
3 fast oxidative glycolysis ( pinkish )
1 ATP synthesis pathway ( oxidative phosphorylation or anaerobic glycolysis )
2 maximal rate Of contraction
1 number of mitochondria
2 number of capillaries
3 glycogen molecules
4 amount of myoglobin
What determines slow or fast maximal rate of skeletal muscle
Describe myoglobin Structure and function
- isoforms with diff max rate of ATP hydrolysis
- similar to hemoglobin has Fe bound to it and used for O2 storage In sER
Describe red skeletal muscle function, number of mito glycogen myoglobin capillaries , rate of fatigue oxidative phosphorylation and myosin-ATP activity contraction and where found
- slow contractions over time without much fatigue
- much mito
- sparse glycogen
- much capillaries
- slow to fatigue
- slow oxidative phosphorylation
- slow myosin-ATP activity
- slow speed of contraction
-Postural muscles of back
Describe White skeletal muscle function, number of mito glycogen myoglobin capillaries , rate of fatigue oxidative phosphorylation and myosin-ATP activity contraction and where found
- specialized for rapid short term contractions
- few mito
- high glycogen
- sparse myoglobin
- few capillaries
- high rate of fatigue
- relies on anaerobic glycolysis
- high myosin-ATP activity
- high rate of contraction
-extra ocular muscles
Describe Fast Oxidative-Glycolytic skeletal muscle function, number of mito glycogen myoglobin capillaries , rate of fatigue oxidative phosphorylation and myosin-ATP activity contraction and where found
- intermediate of the red and white
- numerous mito
- high myoglobin
- high capillaries
- fast contraction
- high ATP-myosin activity
- intermediate rate of fatigue
- major pathway is oxidative phosphorylation
-major muscles of the legs
Skeletal muscle characteristics
nuclei , tubule system , organization, location , function and what innervates
- multi nucleated found at peripheral of sacrolemma
- tubule at center or triad at A-I junctions
- epimysium,perimysium and endomysium
- skeletal muscle, tongue, diaphragm , eyes
- voluntary movements
- efferent motor innervation
Skeletal muscle method of regeneration, where contractions are triggered and special feature and striations
- limited to satellite cells
- at NMJ
- very organized SR and transverse tubule system
- is striated
How does the heart muscle form ( development )
-during embryonic development cells of primitive heart align as a chain like array and do not fuse
Describe cardiac muscle fiber , where and how they join
-cells branch and Join other fibers via junctions at intercalated discs
How does heart acquire characteristic wave contraction
-bundles of cells interweave in spiralling manner
Describe the CT layers of heart muscle cells
- endomysium delicate sheath rich in capillaries
- perimysium separates bundles of muscle fibers
Describe intercalated discs and their function
- transverse lines that cross fibers where myocardial cells join
- they interdigitate and have junctions to adhere cells ( desmosomes , gap and fascia adhesions ) and strengthen tissue
Nuclei and striations structures of myocardial cells
/single nuclei at the center
-has striations
Function of gap junctions in myocardial cells
- provide ionic continuity between cells
- serve as electrical synapses promoting rapid impulse conduction
Method of contraction of myocardial cells
-same as skeletal cells
What is major fuel source of myocardial cells and how stored
-FA stored as TRIG in small lipid droplets
Ventricle thicker than atrium
So !?
-pumps blood into circulation system
Describe T-tubule and SR of myocardial cells where found and organization
- T tubule well developed with large lumen ( not present at atrium)
- SR less developed
- organized as dyads ( 1 T tubule and 1 terminal Cisternae )
Where do myocardial impulses originate from
-initiated , regulated and propagated by locally by nodes of unique myocardial fibers specialized for impulse generation
What innervates the heart
Effect para and sympathetic has !?
-autonomic nervous system at nodes
/sympathetic increases
-parasympathetic decreases signal propagation
Regulatory function of the atrium and what it does
-release the hormone atrial natriuetic factor ( ANF ) that targets kidney affecting Na+ excretion
Regenerative capacity and response of myocardial to stimuli
- no regenerative capacity at all
- hypertrophy
Smooth muscle function, what innervates and where found
- specialized for steady contractions
- innervates by ANS
- at blood vessels , in digestive, urinary,reproductive and respiratory tract and their organs
Shape, striations and nuclei of smooth muscle
- tappers at the ends
- occurs singly and found at center ( widest part )
- no striations
Synonym for smooth muscle
-visceral
Endomysium of visceral
-delicate network of collagen 1 and 3
How is visceral cells closely packed and describe the fiber
- narrow parts ends adjacent to wide ends of adjacent cells
- single small closely packed fusiform cells
What happened to smooth cells during contraction
/become scalloped and nucleus distorted
How are visceral cells linked
-gap junctions
What is on lemma of visceral cells and their Function
- numerous invaginations called caveolae
- function to control release of Ca2+ from rudimentary SR ( no tubule )
How are contractile apparatus arranged and what controls contractions in visceral tissue
- crisscrossed sacroplasm obliquely
- calmodulin ( tropomyosin )
- myosin light chain kinase MLCK ( tropinin )
Describe dense body location and function
1 deep in cyto - have alpha actinin to bind to thin filaments
2 near lemma - has attachment sites for intermediate filaments at adhesion junctions
Function of myocardial cells
-involuntary contraction of the heart to pump blood throughout circulatory system
How does visceral function as a unit
-arrangement of cytoskeleton and contractile apparatus at dense bodies
What is intermediate filament of myocardial and visceral cells made of
-desmin
Where contractile force transmitted by dense bodies and how do they link adjacent cells
/have e-Cadherin proteins to link to intermediate filaments of adjacent cells via desmosomes
-transmit contractile forces throughout cell and tissue
Describe contractions of visceral tissue
-partial , slow , spontaneous wave like contractions
What innervates visceral tissue and how contractions propagated
ANS
-distant fibers via gaps junctions stimulate contractions
Describe CT organization of visceral, response to stimuli and regenerative capacity
- has delicate endomysium and less organized CT
- good regenerative capacity involving mitotis
- hypertrophy and hyperplasia
Secondary function of visceral
- supplements fibroblasts
- make collagen, proteoglycans and fibers
How do synaptic vesicles reach visceral tissue
-axons near smooth muscle has periodic swellings which releases Ach or norepinephrine which binds to receptors
Functions of muscle
1 produce movement
2 thermogenesis
3 maintain posture
Properties of muscle cells
1 excitable
2 contractible
3 elasticity
4 extensibility
Muscle glycogen and mitochondria
- glycosome
- sarcosome
