MD2002- Skeletal and Cardiac Muscle Flashcards
What are the three classifications of muscle?
Skeletal, smooth and cardiac
What are the characteristics of skeletal muscle fibre?
Multinucleated
Contains mitochondria
Has transverse tubules
Has myofibrils and sarcomeres
In skeletal muscle fibres what do each of these three terms refer to;
Sarcolemma
Sarcoplasm
Sarcoplasmic Reticulum
Plasma Membrane
Cytoplasm
Smooth ER
Describe the structure of skeletal muscles
Voluntary, striated
Attached to bone
Interaction of the body with the external environment
What are myofibrils?
The structure that give skeletal and cardiac muscle their characteristic striated appearance
How are striations formed?
Results from the orderly arrangements of thick and thin filaments
What three things are cardiac muscles dependent on?
Intrinsic properties
Hormones
Autonomic nervous system
What are the characteristics of cardiac muscles?
Have one or two nuclei, located centrally
Striated
Are branching cells with intercalated discs with desmosomes and gap junctions
What is the function of nodal cells?
To stimulate their own action potentials
Called automaticity or auto-rhythmicity
What is the absolute refractory period of cardiac muscle and what does this stop?
250ms
Prevents tetanic contractions which would interfere with the heart’s ability to pump
What are intercalated discs?
A mechanical connection between adjacent cardiac muscle cells (structural)
Electrical connection between adjacent cardiac muscle cells (functional)
Describe the structure of gap junctions?
Constructed from a hexagonal array of protein subunits- connexins
What are gap junctions the site of?
Low electrical resistance
What is the function of gap junctions?
Act as a communicating channel- connexon
Where are skeletal muscles innervated from?
Primary motor complex in the brain synapse on the motor neuron (located in the grey matter of the ventral horn)
What is a motor unit?
Defined at the motor neuron and the skeletal muscle fibres it innervates
What is the only way to stimulate a skeletal muscle?
By stimulating the nerve fibres which connect to it
What are the axons which stimulate skeletal muscles called?
Motor or somatic efferent neurons
Where are motor neurons located?
Either the brainstem or the spinal cord
What characteristics of motor neurons allow minimal delay when stimulating skeletal muscle fibres?
They are myelinated
Largest diameter
Propagate action potentials at high velocities
What enzymatically degrades ACh?
Acetylcholinesterase
What is myasthenia gravis?
An auto-immune disease
Muscle weakness that increases during periods of activity and improves after periods of rest
Paralysis of respiratory muscle
Eye and eyelid movement, facial expression, mouth movements especially susceptible
What causes myasthenia gravis?
Production of antibodies
Directed against the ACh receptor (nicotinic)
Some impair the ability of ACh to bind
Some lead to destruction of receptors
Explain myositis
Inflammation
Explain muscular dystrophy
Inherited disorders with progressive weakness
Explain myasthaenia
Fatigueable weakness (worse on exercise)
Explain myotonia
Sustained contraction/slow relaxation
Explain channelopathy
Ion channel disorders
Explain metabolic myopathies
Metabolic/enzyme defects