Download Muscle Physiology REF

Muscle Physiology
REF:
Principles of Anatomy and
Physiology, Tortora, 13th ed:
327-356. 12th ed: pp: 305329, 11th ed. p294-316, 10th
ed. p277-299
1- Skeletal Muscle Structure
– Muscle = group of fascicles
– Muscle fibers extend length of muscle from tendon to
tendon
Components of a muscle fiber
Fig. 10.04
Fig. 10.06
Fig. 10.07
Fig. 10.10
Fig. 10.07
Figure 12.18
Fig. 10.10
Fig. 10.15
Summation and tetanus
• Summation: Rapid sequence of stimuli muscle
twitches fuse into each other, each subsequent one
being stronger that its precedent (due to Ca++?)
• Tetanus: very rapid sequence of stimuli: no relaxation
Treppe
Figure 12.17
2 Types of Skeletal
Muscle Tension
(contraction)
• Isotonic contraction
• Isometric contraction
Isotonic Contraction
Figure 10–18a, b
Isometric/isotonic contractions
• Isometric: muscle
contraction without
movement  no
muscle shortening
• Isotonic: muscle
contraction with
movement  muscle
shortens
Basis for classification
• Velocity of contraction: slow vs fast
• Energy source: oxidative vs glycolytic
Oxydative
Slow
Primary energy through
oxidative
phosphorylation
– Many mitochondria
– Myoglobin (red)
– Small diameter
– Capable of prolonged ,
sustained contractions
– Resistant to fatigue
Glycolytic
Fast
Primary energy through
anaerobic glycolysis
– Fewer mitochondria
– Many glycolytic
enzymes
– High glycogen stores
– Use little oxygen—
anaerobic
– Large diameter
– Quick to fatigue
• Which types of meat
are chicken breast
and duck breast?
• Why the difference?
Motor Unit
All the muscle cells controlled by one
nerve cell
Pharmacology of the NMJ
• Botulinum toxin blocks release of neurotransmitter at
the NMJ so muscle contraction can not occur
– bacteria found in improperly canned food
– death occurs from paralysis of the diaphragm
• Nerve gas inhibits acetylcholinerestase present in the
synapse
• Curare (plant poison from poison arrows)
– causes muscle paralysis by blocking the ACh receptors
– used to relax muscle during surgery
• Neostigmine (anticholinesterase agent)
– blocks removal of ACh from receptors so strengthens
weak muscle contractions of myasthenia gravis
– also an antidote for curare after surgery is finished
36
Myasthenia Gravis
• Progressive autoimmune disorder that blocks the
ACh receptors at the neuromuscular junction
• The more receptors are damaged the weaker the
muscle.
• More common in women 20 to 40 with possible
line to thymus gland tumors
• Begins with double vision & swallowing difficulties
& progresses to paralysis of respiratory muscles
• Treatment includes steroids that reduce antibodies
that bind to ACh receptors and inhibitors of
acetylcholinesterase
37
Muscle fatigue
• Muscle fatigue: a decline in the
ability of the muscle to sustain
the strength of contraction
• Causes:
- rapid build-up of lactic acid
- decrease in oxygen supply
- decrease in energy supply
(glucose, glycogen, fatty-acids)
- Decreased neurotransmitter at
the synapse
- psychological causes
Muscle Tone
• The normal tension and firmness of a
muscle at rest
• Muscle units actively maintain body
position, without motion
• Increasing muscle tone increases
metabolic energy used, even at rest
Muscle Hypertrophy
• Muscle growth from heavy training:
– increases diameter of muscle fibers
– Increases mitochondria, glycogen reserves, and
number of myofibrils
Muscle Atrophy
– wasting away of muscles
– caused by disuse (disuse atrophy) or severing of
the nerve supply (denervation atrophy)
– the transition to connective tissue can not be
reversed
Abnormal Contractions
• Spasm = involuntary contraction of
single muscle
• Cramp = a painful spasm
• Tic = involuntary twitching of muscles
normally under voluntary control--eyelid
or facial muscles
• Tremor = rhythmic, involuntary
contraction of opposing muscle groups
• Fasciculation = involuntary, brief twitch
41
of a motor unit visible
under the skin
SMOOTH MUSCLE CELLS
Smooth Muscle
• Found in walls of hollow organs and tubes
• No striations
– Filaments do not form myofibrils
– Not arranged in sarcomere pattern found in
skeletal muscle
• Spindle-shaped cells with single nucleus
• Cells usually arranged in sheets within
muscle
• Have dense bodies containing same protein
found in Z lines
Two Types of Smooth Muscle
• Visceral (single-unit)
– in the walls of hollow
viscera & small BV
– autorhythmic
– gap junctions cause
fibers to contract in
unison
• Multiunit
– individual fibers with
own motor neuron
ending
– found in large arteries,
45
large airways, arrector
Calcium Activation of Myosin Cross Bridge in Smooth Muscle
Comparison of Role of
Calcium In Bringing About
Contraction in Smooth
Muscle and Skeletal Muscle
PROPERTIES OF SMOOTH MUSCLE
CONTRACTION
• SLOW CYCLING OF MYOSIN CROSS
BRIGDES
• LESS ENERGY REQUIRES TO SUSTAIN
• SLOWNESS OF ONSET OF CONTRACTION
AND RELAXATION
• LENGTH TENSION RELATION SHIP
• MORE FORCE THAN SK. M.
Factor affects SMOOTH MUSCLE
CONTRACTION
• Norepinephrine and acetylcholine are the main
neurotransmitter for SM
• Other hormones and neurotransmitter such as ,
epinephrine, angiotensin, endothelin,
vasopressin, oxytocin, serotonin, and histamine
Factor affects SMOOTH MUSCLE
CONTRACTION
• Lack of oxygen or excess carbon dioxide in the
local tissues causes smooth muscle relaxation
hence vasodilatation.
• Increased hydrogen ion concentration causes
smooth muscle relaxation hence vasodilatation.
• Adenosine, lactic acid, increased potassium
ions, diminished calcium ion concentration, and
increased body temperature can all cause local
vasodilatation.