6.3 - Lecture - Muscle Flashcards
This is the syllabus lecture 6.3 as well as all of the notes from the slides (because one set of slides for both lectures)
Caveolae
- endocytoic vesicles in smooth muscle that shuttle calcium
- Are present in all types of muscle
- responsible for bringing calcium for sequestering in the SR until an electrical impulse is received
Sarcoplasmic reticulum (SR)
- fancy name for endoplasmic reticulum
= a modified ER in muscle - ends in tubular structures = called terminal cisterns
Transverse tubules
- in cardiac (and skeletal) muscle
= tubular extensions of the cell membrane - permeate into the cell creating an extracellular space adjacent to the membrane of the SR (adjacent to the terminal cisterns)
- called t-tubulues
- contain DHP receptors = voltage gated calcium channels
DHPRs interact with ryanodine receptors on SR
Terminal Cisterns
- tubular structures formed at the ends of the SR
Dyad
- in cadiac muscle
- formed by one t-tubule and one terminal cistern
- recognizable in EM
- specialized structure to increase the speed that electrical impulses can act on SR during contraction
Triad
- in skeletal muscle
- t-tubules weave along the region of actin-myosin overlap in the sarcomere just outside the myofibrils (not the same in cardiac)
- formed by two terminal cisterns surrounding either side of a transverse tubule
- even greater efficiency than in cardiac muscle
- specialized to increase the speed that electrical impulses can act on SR to cause contraction
Myosin
thick filament
Actin
- thin filament
- bound to sarcoskeleton
Dense bodes (dense plaques)
- in smooth muscle only
- bound to actin
- can be located intracellularly or bound to the sarcolemma
- also bind to intermediate filaments:
Desmin in visceral muscle and vimentin in vascular muscle
Desmin
- intermediate filaments that connect to dense bodies (plaques) in smooth muscle
- in skeletal muscle desmin connects the Z-lines of myofibrils with each other
- also connects to lateral sarcolemma via a complex of proteins (costamere)
- intermediate filaments have little importance in cardiac muscle? (says the syllabus)
Vimentin
- an intermediate filament in vascular muscle
- binds dense bodies (plaques)
Costamere
= complex of proteins (including dystrophin) that connect desmin to the lateral sarcolemma
Dystrophin
- part of the complex of proteins that makes up a costamere and connects intermediate filaments (desmin) to the lateral sarcolemma
- is lacking in muscular dystrophy
Skeletal muscle fibers are formed from….
syncytial embryonic myocytes - that come from a myoblast progenitor
Myoblast
the myocyte progenitor that will form the embryonic myocytes that form a syncytium to make a skeletal muscle fiber
Myosatellite cells
- some undifferentiated progenitor cells that remain intact in adult muscle
Myotubes
- formed from myocytes
- initially contain central nuclei and few peripheral myofibrils
- eventually grow into the myofibers of adult skeletal muscle
Describe the possible changes of an adult myofiber
- cannot increase in number
- may change in size (diameter) by addition or subtraction of myofibrils
Discuss ideal conditions for muscle regeneration and injury
Much like in axons of peripheral nerves:
- surrounding external membrane is intact (equivalent in structure and function the external membrane o nervous tissue and basement membrane of epithelia)
- myosatellite cells are present within
- supporting endoneurium is still in place
2 Types of Smooth Muscle
Unitary
Multiunit
2 Special types of cardiac muscle
Purkinje fibers
cardiac endocrine cells
3 Types of skeletal muscle
Type I = red
Type IIa = intermediate
Type IIb = white
General Features of smooth muscle
- reticular layer
- intermediate filaments
- dense bodies
- caveolae
- SR
Innervation of Smooth muscle
- by the ANS through second neuron in chain
- Epinephrine - if stimulated by Sympathetic Divison
- Ach - if stimulated by Parasympathetic division
Describe features of Myogenic Regulation of Contraction
= Single unit, visceral
- one axon –> many cells
- MANY gap junctions
- coordinated action
- responsive to hormones, etc.
- low ratio of nerve fibers to muscle cells
Describe features of Neurogenic Regulation of contraction
= multi-unit
- one axon –> few cells
- independent action
- found in iris, arrectar pili, large vessels, small airways of lungs
- high ratio of nerve fibers to muscle cells
Regulation of calcium in smooth muscle
- mainly through caveolae
Describe the general features of cardiac muscle
- T-tubules
- centralized nucleus
- sarcoplasmic reticulum
- dyads (at the z-line)
- intercalated disc
- fascia adherens
- GAP junctions
Fascia Adherens
- parallels zonular adherens of epithelial cells
- connects actin of 1 cell to neighboring actin of other cell
Describe the morphology of cardiac muscle
- cardiac myocytes (may be branched?)
- fiber size ~100 micrometeres long and 10-15 diameter
- one (sometimes 2) centralized nuclei per cell
- striated –> striateiion are more delicate than in skeletal muscle fibers
- many mitochondria and few myofibrils
- sarcoplasmic cone
- intercalated disc
Describe the intercalated disc
= distinct band-oriented perpindicular to the cell long axis
= complex of 3 intercellular JXNs:
1) Fascia adherens (connects to actin in terminal sarcomere)
2) GAP JXN
3) Desmosome
What are the two cardiac myocyte subtypes
1) Myocardial endocrine cell
2) Cardiac Conducting cell
Describe the myocardial endocrine cell
- mostly located in atria of heart
- cells have granules filled with atrial natriuretic peptide (ANP) which is released in response to stretch of atrial wall
What is ANP, where does it come from, what is its FXN
= atrial natriuretic peptide
- enclosed in granules of the myocardial endocrine cell
- is released in response to stretch of atrial walls
- promotes loss of sodium, potassium and water in kidneys –> decreases the body fluids to decrease blood pressure
What is a cardiac conducting cell
- cardiac myocyte modified for conducting electrical activity (increased size, # GAP JXNs, [glycogen] + decreased myofibrils)
= purkinje cell
What are the characteristic modifications to a cardiac myocyte that cause it to become a cardiac conducting cell
- increased size of cell
- incerased number of gap junctions
- increased glycogen content
- fewer myofibrils (because space is occupied by glycogen)
What is the conduction path of a cardiac conducting cell
1) SA node
2) AV node
3) Bundle of His
4) Purkinje Fibers
5) Ventricular fibers
What are the general features of skeletal muscle
- t-tubules
- myofibrils
- sarcomeres
- actin/myosin
- SR
- Triads ( at A-I interface)
- mitochondria
- peripheral nucleus
Describe Red/ Type I skeletal muscle and its characteristic staining
- slow-twitch
- oxidative
- capable of repeated contraction without fatigue
Staining: - least glycogen/PAS stain
- most mitochondrial activity (most cyto c oxidase staining)
Describe intermediate/ Type IIa skeletal muscle
- fast-twitch
- glycolytic-oxidative
- fatigue resistant
Describe White/ Type IIb skeletal muscle and its characteristic staining
- fast-twitch
- glycolytic
- strong + fast contraction
- fatigues easily
Staining: - most glycogen/PAS stain
- least mitochondrial activity (least cyto C oxidase staining)
Describe Skeletal muscle fiber developement
1) Skeletal muscle fiber myoblasts
2) primary myotubes form from the fusion of myoblasts
3) secondary myotubes from with the external membrane of primary myotubes + subsequently separate to from additional fibers of equivalent adult morphology
4) myoblast (some) persist beneath (within) the external membrane of adult fibers as satellite cells (not full stem cells- have limited regenerative abilities)
Describe general characteristics of Satellite cells and which muscle types if any will they not be present in
= muscle stem cells
- population of undifferentiated quiescent precursors that become activated to divide and differentiate in response to demands of growth + damage
- multipotential
- not present in cardiac muscle
describe the Function of satellite cells
= monitor the interface between muscle fiber and CT along the external membrane
- monitor the integrity of skeletal muscle fibers + clean up and repair these areas
- if external membane breaks - it is much harder for them to repair muscle tissue
Describe the neuronal regulation by afferent fibers
- muscle spindle = afferent fiber in parallel with the body of muscle (each comprising by itself a small fascicle) - positioned for supplying information on length of muscle
- golgi tendon organ - afferent fiber in series with muscle and tendon (between them) - positioned for supplying info of force being exerted by muscle
Describe the function and location of muscle spindle
- Afferent neuronal regulation in skeletal muscle
- sits in parallel with the muscle
- positioned for supplying information on length of muscle
Describe the function and location of the golgi tendon order
- afferent neuronal regulation in skeletal muscle
- sits in series between the muscle and tendon
- positioned for supplying information on the force being exerted by the muscle
Describe the morphology of the muscle spindle
- similar to the Golgi tendon organ
- contains bad and chain fibers = each is sensitive to different ranges of stretch
- receives efferent (gamma motor neurons) and generates afferent ( type Ia and II sensory) innervation
- surrounded by a capsule that is equivalent to perimysium
Describe the two broad functions of muscle spindle
1) Proprioceptive inputs to the nervous system
2) prevent over stretch of muscle
What does desmin do
- connects myofibrils with each other at z-line (holds them in register)
- important for transmission of force to body of muscle
What are costameres and what are their function
= Collection of intracellular protein binding desmin to sarcolemma at the z-line
- a protein complex that connects intermediate filaments that exist throughout the z-line of the sarcomere with the cell membrane
- mutation in costamere-associated protein dystrophin - has been implicated in muscular dystrophy
Describe the transmission of force to the tendon
- at the Myotendinous JXN - actin filaments are directly anchored to cell membrane in a similar structure to the fascia adherents
- the anchoring region is largely parallel to direction of force
Describe the External membrane of muscle: what it surrounds, its composition, and function in regards to repair
- surrounds skeletal muscle fibers, cardiac muscle cells, smooth muscle cells
- is analogous in structure + composition to basement membrane of epithelia
- can serve as scaffolding for the repair of damaged muscle fibers
Discuss the possibility of muscle repair as it relates to muscle fibers
1) a broken muscle fiber with an external membrane –> can be repaired
2) a broke muscle fiber with a broken external membrane –> cannot be repaired
