excitation contraction Flashcards
c. Motor unit
one ventral horn nerve cell and all of the muscle fibers
skeletal muscle contracts under nervous controls and is organized in ____ each with it’s own ______
i. Organized in long straight parallel fibers. Each fiber has its own synapse
Motor neurons are located in the
b. Motor neurons in anterior horns of the spinal cord
smaller muscles have more or less motor units?
ii. Smaller muscles (like in our hands) have the most motor units and are best for dexterity
i. If a muscle has smaller but more numerous motor units, its capable of more different types of speeds and strengths of contraction
Synapse on muscle fiber occurs at the _ where nerve and muscle come together
Synapse on muscle fiber occurs at the _ where nerve and muscle come together
another name for the post-synaptic membrane
b. Post-synaptic membrane, also called the motor end plate
Invagination of muscle membrane, also called the ________
c. Invagination of muscle membrane, also called the synaptic gutter
a. Nerve terminals descend into the muscle fiber but lie outside the plasma membrane which is also known as the
sarcolema
sub-nueral folds do what for the membrane
d. Sub-neural folds increase surface area
NT at motor neuron synapse
Ach
Ach is housed in these structures before it’s release in the NMJ
vesicles there are approximately 125
and they are released in response to the influx of Ca at the axon terminal which occurs after the transmission of a nerve impulse
Ach Binds Ach receptor on motor end plate/postsynaptic membrane and binds to the receptors
a. Binds Ach receptor on motor end plate/postsynaptic membrane and binds to the receptors
Chemically gated channels on the motor end plate require binding of how many NT in order to open the channel
c. Chemically gated channels requiring binding of 2 Ach molecules to the external surface in order to open the channel
what happens after AcH binds at the motor end plate
when it opens, you have a flux of Na/K down their concentration gradient (so Na is entering the cell and K is leaving)
how does the membrane potential differ in the motor end plate compared to the axon
b. EPPs normally increase membrane potential 50-75mV, more than enough to pass threshold to trigger Ap
b. Resting muscle membrane potential (-80-90mV) has a larger “pull” on sodium
where do we get choline in the NMJ
breakdown from cholinesterase
Choline is then actively transported back into the presynaptic neuron and can repackaged as Ach again
Autoimmune disease in which autoantibodies destroy Ach receptors.
VIII. Myasthenia Gravis
what type of channels do we have at the NMJ
chemically gated channel that requires bdining of 2 Ach molecules and is a positive ion channel
5 subunits
alpha beta 2 gamma and delta)
resting membrane potential of the muscle cell
-80 to 90
biggest player is sodium
EPP trigger
AP
botulism toxin and curare interferes with this
t tubules in cardiac and skeletal
only 1 t tubule in cardiac
2 in skeletal
muscle stays contracted as long as
there is calcium present in the sarcomere
how does atrophy of a muscle occur
lack of innervation
lack of activity
dystophies
genetic disorders
cause combination of atrophy
hypertrophy or pseudo hypertrophy and necrosis of muscle tissue depending on the pescific defect
insidious progressive disorders with the primary symptom being weakness
pseudo hypertrophy
fat and fibrosis
duchenne MD what is it
Hertible absence of dystrophin that is required for muscle structure
prevalence in Duchenne MD
males and females have 50%
prognosis of duchenne MD
progressive weakness leading to paralysis in 3-5 years
most loose the ability to walk by 12
usually heart and breathing muscles get weak and cause pneumonia or heart failure
becker MD
similar but less severe
pt produces dystrophin but it is not fully fucntional
fascioscapulohumeral MD
progressive disorder seen in adults
MC form is myotonic seen with cataracts and cardiac abnormalities
loss of trophic effect of lower motor neuron is characteristic of
Denervation atrophy
- slowly progressive disorder of face, arms, shoulder beginning in teens
a. Fascioscapulohumeral MD
MC adult form characterized by cardiac abnormalities and cataracts, swan neck (from inability to support the weight of the head), drooping eyelids
b. Myotonic adult MD
