PHGY 209 Muscle physiology.doc

98 views7 pages
17 Mar 2012
3 types of muscle:
-Skeletal muscle is used for posture and locomotion. This is the muscle that enables our arms and legs to contract,
under our conscious control.
-Cardiac muscle is responsible for the rhythmic contractions of the heart.
-Smooth muscle causes involuntary contraction in blood vessels, gut, bronchi and the uterus.
-Thin cells constituting muscles are called muscle fibers (can be 1 ft long)
-Muscle is attached at each end to tendons, which in turn attach to bone on both sides of a joint.
Contraction of skeletal muscle pulls on the tendons resulting in flexion of the joints.
-Muscle fibers are generated during development by the fusion
of a large number of small precursor cells called myoblasts.
Each myobast has a single nucleus, whereas the fiber is a
multinucleated cell.
-The striations within each myofibril are caused by alternating
light I-bands and dark A-bands. In the center of each light
band is a dark line called the Z-line. These structures
delineate the sarcomere, the contractile unit of skeletal
-Each sarcomere consists of two sets of parallel and partially
overlapping protein filaments: thick filaments extending
from one end of the A band to the other, and thin filaments,
attached to the Z lines and extending across the I band and
part way into the A band.
-Thin filaments are physically attached to Z lines.
-Thin filaments consist of actin. Each actin filament is formed
from two chains of globular actin subunits, twisted into a helix.
The myofibril is a lattice of thick and thin filaments.
Unlock document

This preview shows pages 1-2 of the document.
Unlock all 7 pages and 3 million more documents.

Already have an account? Log in
-Muscle contraction occurs when the thin filaments slide over the
thick filaments. Neither the thick or thin filaments change in length.
-The thin filaments are pulled over the thick filaments by
the myosin headgroups, which repeatedly grab, pull and
release the thin filaments. The reaction is driven by ATP
-Headgroups: Reach out – Grab - Pull – Release
-The sarcomere contracts when thin filaments slide over
thick filaments.
-Contraction of the sarcomeres shortens the entire
-Actin molecules have binding sites for
myosin headgroup
-When binded, change of conformation
occurs and leads to release of ADP+Pi.
-Power stroke is caused by the release
of ADP+Pi
-When headgroup binds ATP, it is able to
let go.
-Motor unit=motor neuron+all the
muscle fibers it innervates.
-Size varies: number of fibers innervated
by a single motor neuron may range from
10 (ex. extraocular muscles) to 100
(muscles of the hand) to several
thousand (large flexor&extensor muscles
of leg).
-Motor neurons are found in spinal cord
(arms, legs…) and the brain stem
Unlock document

This preview shows pages 1-2 of the document.
Unlock all 7 pages and 3 million more documents.

Already have an account? Log in

Get OneClass Notes+

Unlimited access to class notes and textbook notes.

YearlyBest Value
75% OFF
$8 USD/m
$30 USD/m
You will be charged $96 USD upfront and auto renewed at the end of each cycle. You may cancel anytime under Payment Settings. For more information, see our Terms and Privacy.
Payments are encrypted using 256-bit SSL. Powered by Stripe.