Muscle Physiology Flashcards
What are the 3 Major types of Muscle?
Smooth
Cardiac
Skeletal
Describe Smooth muscle?
- Lines tubular and hollow structures in the body
- Smooth muscle cells and gap junction
- Spindle shape with central nucleus
- Contractile cytoskeleton arranged diagonally
- Actin anchored to dense bodies arranged within intermediate fibres
- Myosin scattered throughout cell
Describe Cardiac Muscle?
- Striated with single branched cell
- Central nucleus and lots of mitochondria
- Specialised thickenings of sarcolemma (intercalated discs with desmosomes)
- Gap junctions for electrical signals
Describe Skeletal Muscle?
- Major muscle type 40% body weight
- Movement of bones
- Surrounded by connective tissue (epimysium) beneath muscle fasicle surrounded by perimysium
- Muscle fascicles composed of multinucleate fibres and myoblasts
- Satellite cells along muscle fibres
Describe Muscle Fibre?
- Consists of Myofibrils
- Myofibrils extend the length of the cell
- 2 forms; thin actin, thick myosin
Describe Excitable cells in muscle function?
- Membrane potential dependent on permeability of sodium
- RMP -95mv
- Depolarisation associated with opening ligand and voltage gated channels
- Depolarisation promotes release of calcium from SR
- Re-polarisation changes in potassium permeability
Describe coordination of Excitation?
Muscle fibres all have to contract simultaneously, achieved because signal to contract is distributed evenly to T-tubules
What are T-tubules?
Narrow tubes that extend from the sarcolemma into the sarcoplasm of the muscle fibre then around myofibrilshow Excitable cells Coordinate
What is the Mechanism of Excitable cells Coordinating?
T-tubules fill with extracellular fluid and allow a rapid conduction of potential changes throughout muscle, tightly bound to membrane of the SR
Describe the Sarcoplasmic Reticulum?
Forms tubular network around each myofibril either side of each T-tubule, the SR enlarges and fuse forming large chambers the terminal cisternae
What is a Triad?
Association between encircling T-tubule and a pair of terminal Cisternae
Where is Calcium stored?
Sarcoplasmic Reticulum
How is Calcium released from the SR?
When a muscle fires a AP that potential change is conducted along T-tubule allowing release of Calcium from SR into Sarcoplasm
What is the Sliding Filament model?
The contractile filaments actin and myosin are arranged into myofibrils, when they slide across each other when a muscle contracts
What are Sarcomeres?
Myofibril’s contractile units
What are each Sarcomere seperated by?
Thin line known as Z disc
What Thin Actin Sarcomere filament attached to?
I band
What band can be found between the I bands?
A band - Darker
What happens when Muscles contracts with the bands?
Actin filaments of the I band slide over myosin filaments of A band so Z discs move closer together
Describe Myosin?
- Protein with 2 identical heavy chains bound to a pair of light chains
- Amino terminal of heavy chain forms motor head domain, carboxyl end of heavy chain forms a helix tail, second heavy chain forms dimer
- Dimers polymerise into stable bipolar filaments with free head groups at either end
Describe Actin?
Consists of chain of globular actin molecule, each has a binding site for myosin head
- Actin helix coupled at every 7th molecule to 2 proteins tropomyosin and troponin
Describe Tropomyosin?
Rod shaped molecule that binds via troponin molecule to groove of actin helix where masks myosin binding site
Describe Troponin?
Bind the 4 Calcium ions, troponin goes through conformational change moving tropomyosin from myosin binding site
Describe 3 types of Troponin?
Troponin I - Actin
Troponin T - Tropomyosin
Troponin C - Calcium
Describe Muscle Contraction?
Contraction is a result of muscle cell excitation
- Stored Ca released from SR
- Ca binds to TC which creates conformational change in troponin complex
- Tropomyosin molecule moves away from actin binding sites which allows myosin head to bind
- Driven by conversion of ATP to ADP
Describe control of Skeletal muscle?
A single axon will branch within the perimysium and expand at ends to form synaptic terminals form apposing muscle fibre
Describe mechanism behind control of Skeletal muscle?
Synaptic terminal and cleft and sarcolemma (NMJunction) occur halfway down muscle fibre
- When depolarised ACh travels across synaptic cleft and binds to ACh receptors in sarcolemma triggers opening of sodium to AP
- Motor end plate rich in ACh of sarcolemma, folded to increase surface area and no of ACh receptors
Describe Length-Tension relationship?
Tension generated is dependant on number of cross bridges formed between actin and myosin - stretching muscle can modify this by overlap of filaments
- Relationship between degree of stretch and tension is positive and linear
- Cross bridges between filaments decrease the relationship becomes negative
Describe a Muscle Twitch?
Single stimulation of a muscle induces a single contraction
What are the 3 Main phases of a Twitch?
Latent period - 2ms
Contraction Phase - 15ms
Relaxation - 25ms
Describe Stimulus Frequency?
When a second stimulation arrive immediately after end of relaxation phase next contraction will be bigger, will happen for first 30-50 stimulation, because of increasing calcium
Describe Incomplete Tetanus?
Summation of contraction when second stimulus arrives after relaxation phase, subsequent stimulations at the same frequency will induce tension to rise until it reaches a max value
Describe Complete Tetanus?
Increasing stimulating frequency, eliminating relaxation phase muscle will contract smoothly upto max tension
Describe Motor units?
Muscle fibres are innervated by motor neurons - innervating 100’s of fibres by a single neuron called a motor unit
What is muscle tone?
Resting tension when muscle fibres/cells are always in a state of contraction even though muscle is at rest
What does Muscle tone enable?
Maintenance of posture
Diameter of tubular structures so resistance to flow
Describe Isotonic Contractions?
Equal tension when tension rises and muscles lengthen
What are the 2 types of Isotonic contractions?
Concentric
Eccentric
Describe Concentric Contractions?
Tension weight will move but tension in the muscle will remain
Describe Eccentric Contractions?
Weight cannot be moved but muscle lengthens
Describe Isometric Contractions?
Tension generated in muscle does not exceed the resistance to force - muscles maintain posture
