BIO210Y5 Lecture Notes - Lecture 5: Neuromuscular Junction, Motor Neuron, Myocyte

1.) Each motor neuron innervates a finite number of musclefibers. We have referred to this set of muscle fibers as amotor unit. Do motor units vary insize?

a.) no, they average about the same throughout themusculature

b.) yes, fine control depends upon a motor unit with onlyseveral muscle fibers

2.) The cerebellar input that defines the status of the headoriginates within the left and right

a.) motor cortex b.)vestibular apparatus

3.) How are the muscle fibers within a motor unit arrangedspatially within a muscle fascicle?

a.) adjacent to one another

b.) scattered somewhat throughout the fascicle

4.) What is the resting membrane potential of a musclefiber?

a.) -90 mV

b.) -60 mV

5.)

In view of the difference between the resting membrane potentialof a motor neuron and a muscle fiber, which cell is more leaky tosodium ions?

a.)motor neuron

b.) muscle fiber

1.If the supply of ATP to a shortening muscle is completelydepleted, what will happen to the cross-bridge cycle? What is thename if the phenomenon that results from complet ATP depletion?

2.Order the following 10 events that summarize musclecontraction. Remember that a muscle contraction begins with thetransmission of a nerve impulse to a muscle fiber

a. the power stroke

b. Opening of ryanodine Ca2+ channels in the sarcoplasmicreticulum

c. Binding of mysosin cross-bridges to actin

d. release of acetylcholine into the neuromuscular junction

e. confromational change in tropomyosin troponin complex

f. binding of ca2+ to troponin

g. binding of atp to myosin cross-brisges

h. depolarization of the muscle fiber

i. hydrolysis of atp bound to myosin cross-bridges

j. action potential propagation along the transverse tubules

Instructions: Select 2 potential antidotes only from those listed in the box at the bottom.

More than 2 correct answers are possible. For credit you must submit this in class on TUES., Feb. 21 See the 2 sample answers for atropine & physostigmine.

POISON Mode of Action ANTIDOTE

Select 2 from those listed in the box below!

Atropine blocks neurotransmitter (2), (6)

(from belladonna) acetylcholine binding to

post-synaptic receptors

Nicotine mimics the action of acetylcholine

(from tobacco) in NMJ

Physostigmine inhibitor of acetylcholinesterase (4), (5)

(in calabar bean) (in NMJ)

Botulinum Toxin [Botox] blocks vesicles from releasing

(causes botulism) acetylcholine into NMJ

Digoxin inhibitor of Na⁺/K⁺ ATPase

(cardiac medication) pump in axon membrane

Black widow venom enhances release of acetylcholine into NMJ

(latrotoxin) by synaptic vesicles

Pufferfish toxin blocks closed Na⁺ gates of axon

(tetrodotoxin)

NMJ = neuromuscular junction (synapse between neuron & muscle cell)

POTENTIAL ANTIDOTES:

(1) atropine; (2) nicotine; (3) physostigmine; (4) botulinum toxin;

(5) digoxin; (6) black widow venom; (7) pufferfish toxin