Muscle + Physiology Flashcards
Muscle cells are also called
Muscle fibres
Three types of muscle
-skeletal
-smooth
-cardiac
Muscle cells are specialized to contract via
Myofilaments (actin and myosin)
What is structurally related to haemoglobin and seen especially in skeletal and cardiac fibres?
Myoglobin
Myoglobin stores ___ and releases to ____
Oxygen; working muscle
In muscle cells, what are the terms used for:
-cytoplasm
-Endoplasmic reticulum
-plasma membrane
-cytoplasm = sarcoplasm
-Endoplasmic reticulum = sarcoplasmic reticulum
-plasma membrane = sarcolemma
___ muscle is voluntary while ___ muscle is involuntary
Skeletal; Smooth
Skeletal Muscle (5)
-multinucleated
-long
-Voluntary
-striated
-maintains body temperature via shivering
Endomysium (2)
-found in skeletal muscle
-fibres surrounded by reticular connective tissue
Four parts to skeletal muscle (from inner to out)
-muscle fiber/cell
-endomysium
-perimysium
-epimysium
Perimysium
Fascicles (groups of muscle fibres) are separated by dense connective tissue
Epimysium
Enveloping the entire muscle in a thick layer of dense connective tissue (ie. fascia)
Skeletal muscle fibres develop from chains of
Myoblasts (immature cells)
Myoblasts fuse to form a fibre called ___
Myotube
True or False: skeletal muscle cells can divide
False. Growth of skeletal muscle is via Hypertrophy
Satellite Cells (4)
-Mesenchymal stem/stromal cells
-able to differentiate into muscle cells
-growth in young animals
-repair in adults
Three types of skeletal muscle fibres
-red fibres (Type I)
-white fibres (Type IIX)
-intermediate fibres (Type IIA)
Red Fibres (Type I): (5)
-slow oxidative fibres
-rich in myoglobin and mitochondria
-extensive blood supply
-aerobic respiration
-slow, powerful and sustained contractions
White Fibres (Type IIX): (6)
-fast glycolytic fibres
-poor blood supply
-rich in glycogen
-anaerobic respiration (glycolysis)
-rapid (twitch) contractions
-easily exhausted
Intermediate Fibres (Type IIA): (4)
-mix between red and white fibre properties
-extensive blood supply
-rich in myoglobin, mitochondria, and glycogen
-primarily oxidative but can switch to glycolysis
Myofibrils contain ___ and are laid down in ___
Myofilaments (Actin and Myosin); an orderly pattern
Dark A Band (3)
-myosin filament
-anisotropic (constant length)
-pale central H band bisected by dark M line (where myosin filaments join)
Light I Band (3)
-actin
-isotropic (change in size during contraction of muscle)
-bisected by dark Z line (where actin filaments join)
Sarcomere (2)
-region between Z lines (ie. where actin filaments join)
-contractile unit of the myofibril
Sliding Filament Theory
During contraction, actin filaments (attached to the Z line within the I band) slide over the myosin filaments (attached to the M line). This causes shortening of the sarcomere and I band
A Triad is
One T Tubule and two Cisternae
Sarcolemma (4)
-aka plasmalemma/membrane
-sends tubular extensions (T Tubules) into the muscle fibre
-surrounds each myofibril at the junction of the A and I bands
-continuous with extracellular environment
T tubules are
Tubular extensions into the muscle fibre
Sarcoplasmic Reticulum (3)
-aka Endoplasmic reticulum
-network that encircles myofibrils between the T Tubules
-forms a flattened terminal Cisternae on either side of the T Tubule
Calcium is stored in
Sarcoplasmic reticulum
What occurs when the sarcolemma becomes depolarized? (4)
-transmission sent throughout muscle fibre via T Tubule System
-depolarization causes the release of Calcium stored in the Sarcoplasmic Reticulum (especially Cisternae)
-release of Ca2+ into sarcoplasm that surrounds the actin and myosin filaments
-causes contraction
What provides the muscle energy for contraction?
Mitochondria located within the I Bands (ie. actin)
Innervation of skeletal muscles occurs via
motor nerves from CNS
Motor nerve branches end in a specialized synapse called
Neuromuscular Junction (Motor End Plates)
Sensory nerve endings of skeletal muscle (4)
-called Neuromuscular Spindle
-convey information TO the CNS
-control rate and extent of muscle stretch
-highly concentrated in the Tendon-Muscular Junction
Which of the three muscle types is the least specialized
Smooth Muscle
Smooth Muscle (5)
-found in viscera and walls of blood vessels
-spindle shaped
-short
-one central, oval/round nucleus
-can be found singly or in groups (ie. sheets/layers OR fasciculi)
Fasiculi (3)
-irregular branching of smooth muscle
-functions as a contractile unit (ie. they all contract together)
-fibres within are roughly parallel
Smooth muscle lack (2)
-myofibrils
-sarcomeres
Three types of Myofilaments found in smooth muscle are
-actin (thin)
-myosin (thick)
-intermediate filaments
In smooth muscle, actin is anchored at ___ which connect to ___
dense bodies; Intermediate Filaments
In smooth muscle, intermediate filaments
Spread the force of contraction throughout the cell
Innervation of smooth muscle: (3)
-is inherent
-coordinated via gap junctions between adjacent cells
-rate of contraction is modulated by the ANS and hormones
Smooth muscle surrounding blood vessels is regulated by
Vasomotor nerves
Cardiac Muscle: (3)
-chains of branching cells with 1-2 central nuclei
-form a 3D branching network
-striated (similar to skeletal muscle)
Intercalated Discs of Cardiac Muscle (4)
-specialized junction where cells join
-allow cells to be linked physiologically and mechanically
-rapid spread of contraction
-anchors Myofilaments
Cardiac differs from Skeletal muscle (3)
-T Tubules are larger, no triads present
-actin and myosin arranged like a fan and separated by sarcoplasmic reticulum
-cells connected via intercalated discs (allows for rapid passage of action potential between cells)
Innervation of cardiac muscle (2)
-inherent (ie. independent neural control, involuntary)
-modulated by neural signals
Four types of Cardiac Muscle
-ventricular muscle
-atrial muscle (lacks T Tubules)
-Conducting Fibres (form nodes in dense connective tissue and coordinate electrical events)
-Purkinje Fibres (modified conducting fibres in ventricle)
Which neurotransmitter is reasonable for the initiation of skeletal muscle contraction
Acetylcholine
Which molecule is bound to Myosin when the Myosin head binds to the Actin Site
ADP
Each muscle fibre is innervated by
One motor neuron
Shortening of actin filament length will result in (2)
-shortening of the sarcomere
-shortening of the muscle
The sliding filament theory essentially means
The sliding of actin past myosin generates muscle tension
Troponin Complex is made of (3)
-Troponin T (bound to Tropomyosin)
-Troponin I
-Troponin C (binds to calcium)
Calcium interaction of the Troponin Complex (3)
-calcium binds to Troponin C, causing a change in shape
-change in shape causes Tropomyosin to move off Actin’s active site
-Myosin head and Actin can now interact, forming a cross-bridge
Cross Bridge Cycling Steps (7)
- Myosin head binds to active site of Actin
- ADP binds to myosin head, causing a conformational change
- Myosin cross bridge rotates toward the center of the sarcomere creating a power stroke (release of ADP)
- ATP binds to Myosin head, causing a change in shape
- Myosin is released/detached from Actin
- Cleft closed around ATP and myosin head is displaced toward the positive end of actin
- Cycle repeats (as long as ATP and Calcium are available)
Acetylcholine binds to receptors and
Opens Sodium Ion Channels, leading to an action potential in the sarcolemma
What blocks the binding sites on Actin during muscle relaxation
Troponin
What enzyme is used to break down acetylcholine
Acetylcholinesterase
SIRCA (3)
-Sarcoendoplasmic Reticulum Calcium ATPase
-requires energy (ATP)
-pumps calcium against its concentration gradient (causes Tropomyosin to cover the active site of actin)
The motor unit includes
The alpha motor neuron and all the skeletal muscle fibres it innervates
ADP is released during the
Power Stroke
What receptor is activated by membrane depolarization within the T Tubule of a skeletal myocyte
Dihydropyridine Receptor (DHP)
Smooth muscle is found in (7)
-blood vessels
-lung airways
-ureter and bladder
-reproductive tracts
-eye
-kidney
-skin
Single Unit Smooth Muscle (2)
-act as a single unit via gap junctions
-example is the gut
Multi Unit Smooth Muscle (3)
-muscles act independently
-allows finer control and graded response
-example is Iris of the Eye
Sphincters are normally
Contracted (ie. high force is exerted
Blood vessels and airways are normally
Partially contracted (ie. some force is being exerted)
The stomach and intestines are
Constantly active (ie. mix of contraction and relaxation)
The esophagus and bladder are normally
Relaxed (ie. no/little force is exerted)
The structure of smooth muscle is maintained by
Intermediate Filaments
Smooth muscle uses ___ instead of Troponin to bind to calcium
Calmodulin
Intermediate filaments (2)
-non-contractile bundles of smooth muscle
-anchored to dense bodies
Smooth muscle contraction can occur in one of two ways
-CICR (Calcium Induced-Calcium Released) voltage gated channel
-Ligand-Mediated
In Calcium Induced-Calcium Released (CICR) Smooth Muscle Contraction (4)
-a change in membrane potential is innervated by the ANS
-calcium channels within the Caveolus open, causing a small influx of calcium
-influx of calcium activates the CICR channels in the sarcoplasmic reticulum
-calcium is released
In Ligand-Mediated Smooth Muscle Contraction (3)
-a ligand (hormone or neurotransmitter) binds to the G protein coupled receptor (GPCR)
-GPCR stimulates IP3 formation
-IP3 stimulates release of Calcium from the sarcoplasmic reticulum into cytosol
Skeletal vs Smooth Muscle Contraction
Skeletal/Striated Muscle:
-works on Actin, fast rate of contraction
Smooth Muscle:
-works on Myosin, slow rate of contraction
Calcium binds to __ in skeletal muscle and ___ in smooth muscle
-Troponin
-Calmodulin
Relaxation of smooth muscle occurs by two mechanisms:
-Pump Calcium out of the cell via Calcium ATPase OR Sodium-Calcium Exchanger
-Sequester Calcium back into the sarcoplasmic reticulum
Calmodulin (2)
-protein used to activate the myosin head in smooth muscle
-calcium binds to it
In cardiac muscle, gap junctions are present at
Intercalated discs which bind sarcomeres of adjacent cells together
___ motor units are recruited first
Smaller
The smaller the muscle unit, the
Finer the control of movement (ex. Eye)
Recruitment is the
Process of activating more motor units to increase the strength of the contraction
Multiple stimuli in a short interval will ___ the force of contraction
Increase
Tetany is
When multiple signals/stimuli come in rapidly (ie. sustained contraction of the muscle)
Refractory Period is
A brief period of time in which muscle cells will NOT respond to stimulus
Cardiac Muscle has a longer ____, which prevents it from going into ____
-refractory period
-tetany
Total muscle tension is a mix of
Active (# of motor units being used) and passive (muscle length) force production
