Cardiac and Skeletal Muscle Flashcards
What are the main three types of muscle ?
Cardiac, smooth, skeletal
Is skeletal muscle voluntary/involuntary ? Striated/non-striated ?
Voluntary
Striated
What are the defining characteristics of skeletal muscle cell ?
- Multinucleated
- Striated
- Many mitochondria
- Transverse Tubules (T Tubules)
- Myofibrils & sarcomeres
- Intracellular structures: Sarcolemma (=plasma membrane), sarcoplasm (= cytoplasm), sarcoplasmic reticulum (= smooth ER)
Is skeletal muscle attached to bone ?
Yes
What structures give skeletal muscle its characteristic striated appearance ?
Myofibrils (due to the orderly arrangements of thick and thin filaments)
Which kind of muscle is cardiac muscle most similar to structurally ? Functionally ?
Skeletal
Smooth
What is the activity of cardiac muscle dependant upon ?
- Intrinsic properties
- Hormones
- Autonomic nervous system
What are the defining characteristics of cardiac muscle cell ?
- One to two nuclei, centrally located
- Striated
- branching cells with intercalated discs with desmosomes and gap junctions
Which kind of mechanism do cardiac muscle cells use to contract ?
Sliding filament mechanism
What are nodal cells ?
Cardiac muscle cells which have the ability to stimulate their own action potentials. Called automaticity or auto-rhythmicity.
What is the absolute refractory period of cardiac muscle cells ? Why is it necessary ?
About 250ms
Because it prevents tetanic contractions which would interfere with the heart’s ability to pump.
What are intercalated discs ?
Mechanical and electrical connection between adjacent cardiac muscle cells
What are the subunits of gap junctions ?
6 connexins acting as a channel called a connexon
What is the electrical significance of gap junctions ?
They are sites of low electrical resistance between cells
Critical to the heart’s ability to be electrically coupled.
Where do the neurons which synapse on the motor neuron, in the grey matter of the ventral horn, originate from ? Where does the motor neuron then project/what does it do ?
From the primary motor cortex in the brain
Projects to the periphery and activates skeletal muscle
What is a motor unit defined as ?
Motor neuron + the skeletal muscle fibers it innervates
Can a motor neuron innervate more than one muscle fibre ? Can a muscle fibre be innervated by more than one motor neuron ?
Yes
No
Within one muscle, do you find one, a few, or many motor units ?
Many
Give an example of an action using muscles relying on motor units with relatively few fibres, and an action using muscles relying on motor units with more fibres.
Typing (fine motor movement in general)
Actions using legs
How many branches of motor neurons innervate a muscle fibre ?
Just one branch of motor neuron per muscle fibre
What is the overall mechanism by which action potential is initiatied in skeletal muscle ?
Stimulation of the nerve fibres to a skeletal muscle
What is the name of the nerve cells whose axons innervate skeletal muscle fibres ? Where are the cells of those nerve cells located ?
Motor neurons or somatic efferent neurons
In either the brainstem or spinal cord
What is the myelination/diameter status of the axons of motor neurons ?
What is the effect of this on velocity of action potential propagation ?
Myelinated, and largest-diameter axons in the body
Propagate action potentials at high velocities
Do the axon terminals of a motor neuron contain vesicles similar, or different, to the vesicles found at synaptic junctions between two neurons ?
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