14. Muscles Flashcards
Myofibrils are composed of…
Protein bundles
A muscle fibre contains many….
Myofibrils
Sarcomeres are ….
Contractile unit of muscle fiber
What are neuromuscular junctions?
Synapse between motor neuron and muscle fibre
What is an EPSP?
An excitatory postsynaptic potential (depolarization)
What happens when the spike reaches the neuromuscular junction?
- Voltage gated Ca++ channels happens and let it flow into presynaptic terminal
- Increased Ca++ leads to fusion of synaptic vesicles containing neurotransmitter with presynaptic membrane (acetylcholine)
- Transmitter reaches receptor proteins on postsynaptic membrane via diffusion
- These receptors are ligand-gated ion channels (Na+), some Na+ flows into muscle cell, depolarizes it
- Voltage gated Na+ channels open and action potential is generated in muscle cell membrane, travels into depth of muscle fiber via T-tubules
- Acetylcholine is broken down to acetic adic and choline by enzyme acetylcholine-esterase (components taken back up into presynaptic terminal for re-use)
Motor neuron spikes drive…
Muscle contraction
Contraction of sarcomere is caused by…
Sliding of thick filaments (myosin) between thin filaments (actin)
At low Ca++, the myosin heads…
Can’t bind to the actin filaments
With elevated Ca++, the myosin binding sites of actin become exposed
Sliding-filament model of muscle contraction?
.
What changes occur in actin & myosin during contraction?
They overlap more - (length does not change)
To what is due rigor mortis?
The fact that actin and myosin cannot separate without ATP
A single spike in a motor neuron causes …….. and spike in the associated muscle fibers, followed by…
- A single EPSP
- A single twitch
What is a motor unit?
Neuron + muscle fibers (a group of muscle fibers that are innervated by the same motor neuron)
For vertebrate skeletal muscle, each muscle fiber is innervated by ….
A single motor neuron, but each motor neuron innervates many muscle fibers
