◼ muscle properties
◼ muscle contraction
◼ membrane potential
◼ spread of AP and neuromuscular
transmission
◼ comparison of skeletal and cardiac
muscle
◼ model organism
◼ experiment
MUSCLE PROPERTIES (ALL 3 TYPES)
 Irritation (nerve and muscle cells)
 Conductivity – action potential (AP)
 Ability to contract
muscle movement is based on ATP consumption →
muscle cells specialize in the conversion of energy contained in
ATP into contractile movement (by-product is heat)
Heart:
• Automation - independence from the CNS
• Rhythmicity - heart rate is controlled by pacemaker = source
of excitations, AP generator
-
+
Rest and action potential
 Polarization- negative charge inside,
positive charge outside
 When an electrical signal is received, Na
flows inside the cell+→membrane
depolarization
 overshoot from - to + values =origin of AP
 Restoration, out flow K+→membrane
repolarization (hyperpolarization)
 refractory period
-
+
Neuromuscular disc
 Nerve - axon with myelin (Schwann)
sheath, Ranvier incisions → AP
spreads saltatory (after notches)
1. AP in the presynaptic nerve ending→
release of Ach from the vesicles to
the synaptic cleft
2.ACh binding to receptorsin the
subsynaptic membrane
(sarcolemma), degradation by
acetylcholinesterase → release of
receptors for other APs from the
neuron
3.increased membrane permeability for
Na + and K + ions (by opening ion
channels), the emergence of socalledplate
potential- it always
triggers an AP that spreads in both
directions along the surface of
the muscle fiber
Nerve:
electric path
Synaptic
cleft:
chemical
pathway
Sarcolemma:
AP, electric
road
video
Block of neuromuscular transmission
 Local anesthetics- dampens
Na+channels;muscle relaxants- operations,
etc.
 Botulinum toxin- blocks the release of
acetylcholine
 Kurare, snake venoms(cobra) - binds to Ach
receptors (more strongly than acetylcholine
alone) but does not induce ion channel
opening; death occurs by suffocation due to
respiratory muscle arrest
 Organophosphates (pesticides)- they block
cholinesterase, the disc is permanently
depolarized, neuromuscular transmission is
blocked
Muscle building
Muscle cell - myofibril
 length 1-400 mm; widthka 10-100
µm
 muscle fascia, membrane -
sarcolemma,
sarcoplasmic ER (sER),
mitochondria - sarcosomes
Innervation:
 1 neuron can innervate more
muscle fibers (1 end for each
muscle fiber)
 motor unit - muscle fibers +
motoneuron, which innervates
them, 1 muscle 10-1000 motor
units
 short refractory period (ms)
◼ myofibril - own propulsion equipment
 sarcometers - individual functional sections, Z-lines
 actin, myosin, troponin, tropomyosin, ...
Contraction
Relaxation
MUSCLE MULTIPROTEIN COMPLEX
http://www.edcenter.sdsu.edu/cso/paper/image005.jpg
video
Muscle contraction cycle
rigor mortis - postmortem stiffness:
depletion of ATP stores (actinmyosin
binding and Ca release2+
from the sarcoplasmic reticulum)
about 3-6 hours after the end of
delivery O2, muscle relaxation occurs
only after decomposition of
myofibrils (48-60h)
EXPERIMENT
spatial summation (addition of individual pulses, change of
pulse size)
- with increasing tension (irritation of more muscle fibers) the
contraction of the muscle increases → graduated answer at
the stimulus (at the heart "all or nothing")
subthreshold, threshold and above-threshold stimuli
 time summation (2 stimuli in quick succession) - pulse
frequency changes; the muscle cannot return to its original
position and vibrates at the topcorrugated and smooth
tetanus (tetanic contraction = permanent muscle
contraction)
 superposition - two stimuli later in a row
Conclusion: Demonstration of phenomena characterizing skeletal
muscle.
wavy tetanus smooth tetanus calf skeletal muscle irritation
HEART
 endocardium (inner membrane)
 myocardium (own muscle layer of the heart)
 epicardium (outer membrane)
 pericardium - covers the heart
Heart muscle
 the mechanism of contraction is the same as for skeletal muscle
 of mononuclear forked cells, functional syncytium
 cells separated intercalary discs (stair partitions)
 spreading irritation through nexus (gap junctions), responds to
hormones (eg adrenaline)
 many sarcosomes (Ca2+) and less myofibrils
 automation(contains natural pacemakers - SA and AV nodes) HF
Stannius
 long refractory period (min. 250 msec)
Cardiac muscle innervation
 afferent innervation- nerves perceive contraction or
filling of the heart compartments; pain (during a heart
attack)
 efferent innervation- controls the frequency and
strength of contractions, the speed of conduction in the
heart, the irritability of the heart:
 parasympathetic (n. vagus- innervates the SA- and AVnodes)
mediator acetylcholine, which muffles heart activity
 sympathetic(accelerating nerve cordis,innervates the whole
heart) mediator norepinephrine, encourages heart activity;
adrenaline from the adrenal medulla has a similar effect
 tachycardia- accelerated heart rate
 bradycardia- slower heart rate
 fibrillation- rapid chaotic superficial contractions of the
heart muscle, the heart does not pump blood
XENOPUS LAEVIS
 laboratory amphibian (jumpers, toads -
protected)
 females 10-15 cm, males 1/3 smaller
 flattened body without neck and tail, strong hind
legs, no front membranes on the front, smooth
skin, pale belly
 comes from South and South Africa
 stagnant waters, ponds, swamps, limestone lakes
 exclusively aquatic animal
 hormone choriogonadotropin causes egg laying
in the claws - embryology, pregnancy tests (early
human embryo and placenta produce hCG, it is
then in the blood and urine - blood is injected
into the frogs, they lay eggs in the morning =
pregnancy)
 hibernation for up to 10 months
NATURAL HEART AUTOMATION CENTERS
- contain cells that spontaneously depolarize with a certain frequency
 sino-atrial node = Keith-Flack = SA node (sinus venosus - venous rafting);
the main pacemaker, is the superior, responsible for rhythmicity, controls
mainly the activity of the vestibule
 atrio-ventricular node = Aschoff-Tawar = AV node = atrial node (atrium
cordis - atrium, ventriculum cordis - ventricular chamber) - he would not
keep the rhythm alone, he mainly controls the activity of the ventricles
CARDIAC CONDUCTION - www.medicoapps.org
Experiment - heart muscle
In situ
- stunning, decapitation, brain removal (CNS) and spinal cord
disruption (reflexes), the heart beats independently of the
CNS
 Heart muscle contractions
systole (contraction), diastole (release) of the heart muscle
1. SA node → atrium → 2. AV node → chamber
Normal heart activity
Ventricular
systole
Atrial systole
 1. Stannius's ligature(ligation, strangulation) = interruption of
conduction from the SA node by strangulation of the hall
immediately behind the node, the heart stops, or we register
only weak contractions sinu venosu(SA node → cardiac
arrest)
 2. Stannius's ligature- constriction at the site of the AV node,
mechanical irritation of the AV node (AV node → the chamber
is retracted)
 after a while the heart stops beating, external stimulation el.
current
Experiment - heart muscle
1. 2.
Normal - two pacemakers = two rhythms
Is it possible to change the force of the
contraction?
 1. spatial summation - change the size of the
pulses - the heart is either contracted or relaxed regardless
of the increase in the intensity of the
stimulus → answer "All or nothing"
Cardiac activity
Stimulus intensity
 2. time summation- pulse frequency change → wavy
tetanus (fibrillation) - period 0.5 s; smooth tetanus cannot
be induced in the heart - long absolute refractory period
 extra systoly - two stimuli in a row
Conclusion: Demonstration of phenomena characterizing the heart
muscle
What are the functions and use of myostimulator?
Transcutaneous Electrical Nerve Stimulator. The electrical impulses generated by
the device penetrate the body through adhesive electrodes placed on the surface
of the skin.