Wk4 L2 - Muscles Flashcards
LO
- To know the definitive light microscope features of smooth, skeletal and cardiac muscle fibres as shown by the presence or absence of striations and intercalated discs and location and number of nuclei per cell.
- To know the locations of the three types of muscle: smooth muscle in gut, blood vessels, uterus and bladder and scattered other sites; skeletal muscle attached to the skeleton and under voluntary control; and cardiac muscle only found in the heart.
- To know the ultrastructure of skeletal muscle including the location and role of organelles, especially sarcoplasmic reticulum and t-tubules, and the relationship of the band pattern to the two sets of myofilaments. To know also, in outline, the role of the myofilament in the sliding filament mechanism of contraction. Skeletal muscles are striated.
- To know the ultrastructure of cardiac muscle and the differences and similarities between cardiac and skeletal muscle. To know that the fibres of the impulse conducting system of the heart are modified cardiac muscle fibres. Cardiac muscle fibres are also striated.
- To know the ultrastructure of smooth muscle: myofilaments, cytoplasmic densities and location of organelles.
Skeletal muscle
- Multinucleated
- Compound tissue
Contains lots of CT:
- Epimysium
- Perimysium
- Endomysium
Lots of blood vessels and nerves
Subclassification of skeletal muscle cells
Extrafusal:
- Red, slow, aerobic
- White, fast, anaerobic
Intrafusal:
- Bag & Chain
- Invloved in proprioception
Extrafusal skeletal muscle levels of organisation:
Muscle
Fascicle
Myofibres (cells)
Myofibrils (arranged sarcomeres)
Myofilaments (actin & myosin)
Sarcomeres:
- Found within myofibrils
- Serially organised
- Contractile unit
Myofibres:
- Surrouned by basement membrane
- CT involved (endomysium)
- Satelite cells give rise to cells in mature muscle, replace myofibres
Skeletal muscle fibres under LM
Can see capillaries
- Striations visible when longitudinal section
[heft]
Skeletal muscle under EM
Can see myofibrils
Z lines = dark verticle line
Sarcomere = Z line - Z line
A band = darker band (thick myosin filament)
I band = lighter band (thin actin filament)
During muscle contration:
- I band gets shorter
- A band stays the same length
Neuromuscular Junction
Where nerves come in and innervate the muscle at the synapse
Sarcolemma is the muscle membrane
- Where the sarcolemma meets the nerve synapse, there are folds and receptors
- Ac-CoA from nerve cell binds to receptors on sarcolemma
Inside a striated muscle fibre
- Parts of the sarcolemma descend down as a T-tubule
- T-tubules are part of the surface membrane of the muscle cell
- Surface of cell dips into the depth of the cell, the T-tubules following
sER in the cell, containing Ca2+, T-tubules sit adjacent to sER to form a network
- Triads are adjacent to A & I band
- T-tubule takes conduction from neuromuscular junction deep into the muscle
- Activates the Ca2+, causing the actin and myosin to couple
- Ca2+ pumps out quickly to allow contract again
Heart
More than just cardiac muscle:
Endocardium:
- (inner)
Myocardium:
- Cardiac muscle cells
- Purkinje cells
Epicardium:
- (Outer)
Cardiac muscle
Ling individial cells joined by collated disks with 1 nucleus
- Sarcomeres forming myofibrils
- Diads adjacent to z line
- Striations and branch with lots of capillaries
- contracts spontaneously
- Intercollated disks
[heft] LM Vs EM
Various connections at intercollated disks of Cardiac Muscle
Transverse: (hold int. disks together)
- Fascia adherens
- Macula adherens
Longitudinal:
- Macula adherens
- Gap Junctions (communication)
Cardiac muscle cell cross section
Myofibrils not as dense as skeletal muscle
[heft] EM
- Black dots = glycogen granules (stored when needed for prolongued activity)
Purkunje fibres
- A bit larger than cardiac muscle cells
- Not as many myofribrils (pale colour)
- Throughout walls of ventricles (SA node activates them)
- Have electrical properties, communicate to heart for increasing HR
Smooth muscle
- Cells are fusiform in shape and have a single central nucleus
- Actin and myosin contractile units, but NOT organised into sarcomeres
- Organised by ‘dense bodies’
- Contractile filaments run in all directions
- No branching, but can have gap junctions
- Activated by nerves and other molecules and mechanical systems
neuromuscular junctions:
* appear further from the muscle, forming vericosities
* Activated by diffusion, NOT direct contact
[heft]
