Anatomy and Physiology I
Lecture 21: Muscle and Body Movement
Muscle Tension at the Fiber Level Tension Produc6on and the Timing of
The smallest muscle contrac=on is the Frequency of S6mula6on
muscle twitch is the response of a single Wave summa=on, unfused tetanus and
muscle fiber from a single ac=on poten=al fused tetanus
Twitch Contrac6on Wave Summa6on
• A muscle twitch can be produced by • Wave summa=on is the
direct electrical s=mula=on of a progressively greater tension of a
muscle fiber. muscle fiber when it is repeatedly
• An instrument records the twitch s=mulated.
and generates a myogram. • The amount of tension is dependent
• The muscle twitch has 3 phases: on the frequency of s=mula=on (no.
latent, contrac=on and relaxa=on =mes per second).
periods. • The SR pumps do not have enough
=me to pump the Ca2+ back into the
SR.
• As a result the [Ca2+] in the cytosol
increases with each s=mula=on.
• The more Ca2+ allow more cross
bridges to form to increase tension.
There are two types of wave
summa=on.
1. Unfused or incomplete tetanus.
2. Fused tetanus.
Refractory Period
A 5 ms interval aHer the latent period in
which the muscle cannot respond to
another s=mulus
• The refractory period is a property
of all excitable cells.
• Cardiac and smooth muscles have
refractory periods as long as their
contrac=ons.
• Skeletal muscle fibers have much
shorter refractory period that allow
a sustained contrac6on phase.
, Anatomy and Physiology I
Lecture 21: Muscle and Body Movement
The Length Tension Rela6onship Classes of Skeletal Muscle Fibers
The number of cross bridges depends on Muscle fibers are either fast twitch or slow
the length of the sarcomere prior to twitch fibers and classified as type I or type
contrac=on II
• The op6mal sarcomere length is the • Fast twitch fibers have higher
length that produces the most cross myosin ATPase ac=vity and have
bridges to generate almost 100% rapid contrac=on cycles.
tension. • They are found in muscles that
• The degree of overlap of the thin move body parts rapidly such as
and thick filaments is the zone of those that move the eyeballs.
overlap.
• Slow twitch fibers have lower
myosin ATPase ac=vity and have
slower contrac=on cycles.
• These are found in muscles that
require slow sustained contrac6ons
such as the postural muscles of the
back.
How Myofilament Sliding Leads to Whole
Muscle Contrac6on
Contrac=on of the sarcomeres will
increase the tension in the
sarcolemma and endomysium.
Lecture 21: Muscle and Body Movement
Muscle Tension at the Fiber Level Tension Produc6on and the Timing of
The smallest muscle contrac=on is the Frequency of S6mula6on
muscle twitch is the response of a single Wave summa=on, unfused tetanus and
muscle fiber from a single ac=on poten=al fused tetanus
Twitch Contrac6on Wave Summa6on
• A muscle twitch can be produced by • Wave summa=on is the
direct electrical s=mula=on of a progressively greater tension of a
muscle fiber. muscle fiber when it is repeatedly
• An instrument records the twitch s=mulated.
and generates a myogram. • The amount of tension is dependent
• The muscle twitch has 3 phases: on the frequency of s=mula=on (no.
latent, contrac=on and relaxa=on =mes per second).
periods. • The SR pumps do not have enough
=me to pump the Ca2+ back into the
SR.
• As a result the [Ca2+] in the cytosol
increases with each s=mula=on.
• The more Ca2+ allow more cross
bridges to form to increase tension.
There are two types of wave
summa=on.
1. Unfused or incomplete tetanus.
2. Fused tetanus.
Refractory Period
A 5 ms interval aHer the latent period in
which the muscle cannot respond to
another s=mulus
• The refractory period is a property
of all excitable cells.
• Cardiac and smooth muscles have
refractory periods as long as their
contrac=ons.
• Skeletal muscle fibers have much
shorter refractory period that allow
a sustained contrac6on phase.
, Anatomy and Physiology I
Lecture 21: Muscle and Body Movement
The Length Tension Rela6onship Classes of Skeletal Muscle Fibers
The number of cross bridges depends on Muscle fibers are either fast twitch or slow
the length of the sarcomere prior to twitch fibers and classified as type I or type
contrac=on II
• The op6mal sarcomere length is the • Fast twitch fibers have higher
length that produces the most cross myosin ATPase ac=vity and have
bridges to generate almost 100% rapid contrac=on cycles.
tension. • They are found in muscles that
• The degree of overlap of the thin move body parts rapidly such as
and thick filaments is the zone of those that move the eyeballs.
overlap.
• Slow twitch fibers have lower
myosin ATPase ac=vity and have
slower contrac=on cycles.
• These are found in muscles that
require slow sustained contrac6ons
such as the postural muscles of the
back.
How Myofilament Sliding Leads to Whole
Muscle Contrac6on
Contrac=on of the sarcomeres will
increase the tension in the
sarcolemma and endomysium.
