Muscle Structure and Function Flashcards
What are the three types of muscles? What are their functions? Are they under voluntary control?
Smooth: line hollow organs, not under voluntary control
Cardiac: in heart generates force to pump blood, not under voluntary control
Skeletal: applies force to bones to control posture and movements, under voluntary control
Skeletal Muscle: Structural features
Skeletal muscle fibres are huge multinucleate cells containing large amounts of protein
Connective tissues ensheath muscle fibres and connect fibres to bones
Skeletal muscle is richly supplied in blood vessels and nerve fibres
Muscle ______ are gathered into bundles called ______.
_______ are gathered into bundles called _______.
_______, ______ and ________ are each enclosed in __________ ______.
_________ ______ investments are gathered together to form _______ .
________ connect muscles to ________
Fibres, fascicles.
Fascicles, muscles.
Fibres, fascicles and muscles, connective tissue
Connective tissue, tendons
Tendons, bones
A ______ _____ is comprised of bundles called ________.
__________ are made of repeating units known as _________.
__________ are made of contractile proteins or ___________.
Two _________ are ____ (thin) and _______ (thick)
The organisation of these ___________ give muscle its ________ appearance
Muscle fibre, myofibrils
Myofibrils, sacromeres
Sacromeres, myofilaments
Myofilaments, actin, myosin
Myofilaments, striated
What are Transverse Tubules?
T-tubules are tubular extensions of the surface membranes. Their job is to conduct electrical signals deep into the core of the fibre
What is the Sacroplasmic Recticulum?
The SR is an extensive membranous tubular network associated precisely with the T tubules at regular intervals
The terminal chambers of each SR structure associate with the T-tubules to form a triad (membrane triplet)
What is SR’s job?
To take up and store calcium, then release calcium ions into cytoplasm along associated T-tubules
What is Actin?
Actin is a globular protein. It is a thin filament twisted stand of 2 rows
Each thin filament is a twisted strand of 2 rows of F-actin terminating at one end at the z-line
What is Myosin?
Myosin is a thick filament that has a thin tail and globular head
Formed from arrays of pairs of myosin molecules arranged with the tails pointing towards M line and forming complex double headed structure
What are muscle contractions?
Muscle contractions are triggered by electrical events (AP) which arise in brain and are conducted out of the CNS along motor axons to muscle fibres
What is the Neuromuscular Junction?
The myelinated axon of a motor neuron terminates at a single point on the muscle fibre - the NMJ
Each fibre receives contact from one motor neutron at one site
Arrival of AP initiates synaptic transmission resulting in AP muscle fibres triggering excitation contraction coupling
What is the motor unit in NMJ?
A whole muscle is a collection of motor units, big motor units develop lots of force but less control, smaller motor units develop less force but have more control
Cell bodies in the ventral part of spinal cord
What is recruitment?
When the amount of motor units activated is changed due to the amount of force produced
What is troponins function?
Troponin binds tropomyosin and actin and regulates interaction between actin and myosin during cross bridge cycle
What is Excitation-Contraction Coupling?
Term used to describe steps from plasma membrane excitation to calcium release to muscle a contraction
Steps of Excitation-Contraction Coupling
- Action potential triggers an AP in the muscle fibre
- The AP spreads over the sarcolemmas surface and invades T-tubular system
- Depolarisation triggers release of Ca2+
- Ca2+ release into cytoplasm promotes binding of Ca2+ to troponin molecule causing change in troponin shape, exposing actin binding site, myosin binds to actin, filaments slide, causes contraction
- Calcium pumped from intracellular space back to SR and unbinds from the contractile apparatus causing muscle to relax
What are the steps involved in the Cross Bridge Cycle?
- ADP bound myosin head is cocked and ready to bind to actin
- In presence of Ca2+, Ca2+ binds to troponin exposing binding sites for myosin
- The bound myosin rotates its head producing a ‘power stroke’, binds to site (cross bridge formed) - ADP released
- ATP molecule binds to myosin head (cross bridge broken)
- Actin and myosin detach - ATP hydrolysed
What does muscle tension depend on?
- The rate at which the muscle is stimulated at
- The number of muscle fibres recruited
How does a twitch in a muscle occur?
Single action potential results in pulse of Ca2+ release into cytoplasm developing a short period of tension
How does a tetanus occur?
Multiple action potentials cause rapid release of Ca2+ from SR causing sustained period of actin-myosin interaction and sustained period of contraction
Length-Tension relationship in muscles
Each muscle has an optimal length where it will be at its strongest, if it is longer or shorter than that length it will be weaker (less tension)
Muscle Structure: Smallest to Biggest
Myofilaments -> Sacromeres -> Myofibril -> Muscle Fibres -> Fasicles -> Muscle
What is endomysium, perimysium and epimysium?
Endomysium : surrounds each muscle fibre
Perimysiuem : surround each fascicle
Epimysium : surround entire muscle
Sliding filament theory
Contractile proteins develop force by trigger molecular interaction that allows association of the myosin head with the nearby thin actin filament followed by the flexing of the myosin head to allow it to walk along the thin filament
In this process the interlaced thick and thin filaments slide past each other
When activated the ends of the sacromere are brought closer together by flexing of myosin heads (Z lines drawn closer to M line)
