Skeletal and Cardiac Muscle Flashcards
What are the 3 muscle tissue types?
+ Skeletal
+ Smooth
+ Cardiac
What is skeletal muscle also known as?
Voluntary muscle; striated muscle
What are the 5 characteristics of skeletal muscle cells/fibres?
- Multinucleated
- Contains many mitochondria
- Transverse (T) tubules
- Myofibrils and sarcomeres
- Specific names for some of the intracellular structures
In a skeletal muscle cell/fibre, what is the sarcolemma?
Plasma membrane
In a skeletal muscle cell/fibre, what is the sarcoplasm?
Cytoplasm
In a skeletal muscle cell/fibre, what is the sarcoplasmic reticulum?
Smooth ER
What are features of skeletal muscle?
+ Voluntary, striated
+ Attached to bone
+ Under voluntary control
+ Involved in interaction of the body with external environment
What are myofibrils?
The structures that give skeletal (and cardiac muscle) their characteristic striated appearance
What are striations a result of?
The orderly arrangements of thick and thin filaments
What are the structural features of cardiac muscle?
+ Striations
+ Muscle fibres
+ Intercalated discs
+ Nucleus
What are features of cardiac muscle?
+ Structurally like skeletal muscle
+ Functionally like smooth muscle
+ Activity dependent upon:
- intrinsic properties
- hormones
- ANS
How many nuclei do cardiac muscle cells have?
One to two nuclei, centrally located
What mechanism does cardiac muscle use to contract?
The sliding filament mechanism, as it is striated
Cardiac muscle is made up of branching cells with what other structures?
INTERCALATED DISCS with desmosomes and GAP JUNCTIONS
What are gap junctions critical to in cardiac muscle?
The heart’s ability to be electrically coupled
What ability do nodal cells have?
The ability to stimulate their own actions potentials - called automaticity or auto-rhythmicity
What is the absolute refractory period of cardiac muscle (cells)?
250ms
What is the purpose of a refractory period?
Prevents tetanic contractions which would interfere with the heart’s ability to pump
What is the structural relevance of intercalated discs in cardiac muscle?
Provides a mechanical connection between adjacent cardiac muscle cells
What is the functional relevance of intercalated discs in cardiac muscle?
Provides an electrical connection between adjacent cardiac muscle cells
What are features of gap junctions?
+ Constructed from a hexagonal array of protein subunits - connexins
+ Sites of low electrical resistance between cells
+ Act as communicating channels - connexon
What is the diameter of the central pore in a gap junction?
1.5 nm
What size of molecules can pass through the central pore in a gap junction?
Small molecules (<500 MW) pass through
How does skeletal muscle become activated?
Neurons from the primary motor cortex in the brain synapse on the motor neuron, which projects to the periphery and activates the skeletal muscle
Where is the motor neuron located?
In the grey matter of the ventral horn
What makes up a motor unit?
Axon and muscle fibres
What is a motor unit defined as?
The motor neuron and the skeletal muscle fibres it innervates
What is the link between motor neurons and muscle fibres?
One motor neuron innervates many muscle fibres, but one muscle fibre is innervated by only one motor neuron
What is the only mechanism by which action potentials are initiated in skeletal muscle?
By stimulation of the nerve fibres to a skeletal muscle
What are motor neurons also known as?
Somatic efferent neurons
What are some physical features of axons of motor neurons?
+ Myelinated
+ Largest-diameter axons in the body
Axons of motor neurons propagate action potentials at high velocities - what does this then allow?
Signals from the CNS to travel to skeletal muscle fibres with minimal delay
What do axon terminals of a motor neuron contain?
Vesicles similar to the vesicles found at synaptic junctions between two neurons
What do the vesicles found at the axon terminals contain?
Neurotransmitter - acetylcholine (ACh)
What region is known as the motor end plate?
The region of muscle fibre plasma membrane that lies directly under the terminal portion of the axon
What is the neuromuscular junction?
The junction of an axon terminal with the motor end plate
Once ACh is released into the synaptic cleft, where does it go?
Ach is rapidly degraded enzymatically by the action of acetylcholinesterase
What is the role of the nicotinic cholinergic receptor?
It binds (to) two ACh molecules, opening a nonspecific monovalent cation channel
What does the open nonspecific monovalent cation channel allow to pass?
Na+ and K+
What happens to acetylcholine (ACh)?
- Combines with nicotinic receptors
OR
- Metabolised by acetylcholinesterase (AChE)
What do action potentials arriving at the axon terminal do?
Open gated Ca2+ channels
What is myasthenia gravis?
An autoimmune disease that causes muscle weakness that increases during periods of activity and improves after periods of rest
What actions are especially susceptible in myasthenia gravis?
\+ Eye and eyelid movement \+ Facial expression \+ Chewing \+ Talking \+ Swallowing \+ respiration
How can myasthenia gravis affect the respiratory muscles?
Can cause paralysis of them
What is the result of the production of auto-antibodies?
+ Most commonly directed against NACh receptors
+ Some impair the ability of ACh to bind to receptors
+ Some lead to the destruction of receptors
What are some different types of muscle myopathies?
\+ Myositis \+ Muscular dystrophy \+ Myasthenia \+ Myotonia \+ Channelopathy \+ Metabolic myopathies
What is myositis?
Inflammation
What is muscular dystrophy?
Inherited disorders with progressive weakness
What is myasthenia?
Fatiguable weakness (worse on exercise)
What is myotonia?
Sustained contraction/slow relaxation
What is channelopathy?
Ion channel disorders
What are metabolic myopathies?
Metabolic/enzyme defects
