Chapter 12 Flashcards
skeletal muscle fiber characteristics
large, multinucleate cells that appear striped or striated under the microscope.
Cardiac muscle fiber characteristics
also striated but they are smaller, branched, and uninucleate. Cell sare joined in series by junctions called intercalated discs, which help transmit rapid signaling.
satellite cells
multi potent cells that eventually differentiate into muscle cells.
skeletal muscle breakdown
made of several muscle fascicles which are bundles of muscle fibers.
Muscle Cell ::___
muscle fiber
cell membrane ::__
Sarcolemma
Cytoplasm ::__
Sarcoplasm
Endoplasmic reticulum ::__
Sarcoplasmic reticulum
T Tubules
extensions of the cell membrane (sarcolemma)that associate with the ends (terminal cisternae) of thesarcoplasmic reticulum. brings actionpotentials into interiorof muscle fiber.
Sarcoplasmic reticulum
stores Ca2+
Thick filaments
~ 250 myosin molecules join to create a thick filament
Thin filaments
Actin is a protein that makes up thin filaments.
Multiple single actin molecules (G-actin) line up to form F-actin filaments; in skeletal muscle, 2 F-actin polymers twist together to create thin filaments
Myofibril structure
I band
Z disc is in the middle
contains actin only
from one myosin/actin overlap to another, with actin the only thing in the middle
A band
from I band to I band
edges contain actin and myosin overlap
H zone in the middle
H zone
Myosin only
in the middle of the sarcomere
edges are where myosin/actin overlaps are
M Line
Smack dab in the middle of the sarcomere
Myosin linked with accessory proteins
In the middle of the H band
Z disc
the Z shaped line that occurs when titin:Actin: titin connects with Actin:Actin
Titin
a giant accessory protein that spans the distance from one Z disc to the neighboring M line
Provides elasticity and helps align myosin
Nebulin
a giant accessory protein that lies along the thin filament and attaches to a z disc.
Does not extend to the M line.
It helps align actin
muscle tension
•force created by muscle contraction
Load
weight or force opposing contraction
Contraction
•creation of tension in muscle
(requires ATP)
Relaxation
•release of tension caused by a contraction
strucutre of sarcomere during contraction
sarcomere shortens during contraction, as actin and myosin slide past one another
the H zone and I band both shorten
The A band remains the same size
During relaxed state …
Myosin head is cocked
Tropomyosin partially blocks binding site on actin
Myosin is weakly bound to actin
In rigor state…
Myosin is bound to G protien on actin.
No ATP or ADP is bound to myosin
This is very brief!
Ends when ATP binds to myosin, which releases myosin from G protein
myosin head re-cocking
Myosin hydrolyzes ATP –> ADP. The energy released rotates the myosin head back to a cocked position, where it weakly binds/associates with the actin G protein.
Power stroke
myosin:ADP is weakly associated with actin G protien.
Ca signal comes in, and Ca binds to Troponin–> this makes tropomyosin shift, exposing the binding site on Actin
Myosin binds strongly to actin, and actin shifts.
This is the power stroke.
Myosin releases ADP at the end of the stroke.
Motor end plate
a
region of muscle membrane that
contains high concentrations of
ACh receptors.
The neuromuscular junction
consists of axon terminals, motor end plates on the muscle membrane, and Schwann cell
sheaths.
To end a muscle contraction, Ca2+ needs to be removed from the sarcoplasm…
- Ca-ATPase pumps Ca back into the sarcoplasmic reticulum
- overallt decreas of Ca concentration causes Ca to unbind from troponin
3.
Excitation- Contraction coupling
End plate potential–> twitch–> latent period
End plate potential
caused by depolarization at the muscle
Muscle twitch
A single contraction- relaxation cycle
latent period
•the short delay between the muscle action potential and beginning of muscle tension development
–this represents the time required for calcium release and binding to troponin
slow twitch fiber
•Rely primarily on oxidative phosphorylation
Darker in color, fatigue less easily.
Marathon runners have more slow twitch
fast twitch fiber
–Develop tension faster
Split ATP more rapidly
Rely primarily on anaerobic glycolysis
•Use oxidative and glycolytic metabolism
Lighter in color- fatigue more easily.
Sprinters have more fast twitch fibers.
Length- tension relationship
There is an ideal resting tension of the actin and myosin filaments. Anything greater or lesser than the optimal length is going to decrease the ability of the fiber to contract to its fullest potential.
Summation
Stimuli closer together do not
allow muscle to relax fully
unfused tetanus
many small rapid contractions are happening and summating to the point where they are at their maximum tension. There are small wave breaks.
complete tetanus
Muscle reaches steady tension. If muscle fatigues, tension decreases rapidly.
motor unit
one motor neuron and all the muscle fibers it innervates. A muscle may have many motor units of different types
contraction force
•Recruitment of additional motor units by the nervous system increases contraction force
•Asynchronous recruitment of motor units helps avoid fatigue
–Different motor units take turns maintaining tension
isotonic contraction
concentric action creates a shortening
eccentric action creates a lengthening
isotonic contraction creates a force to move a load
isometric contraction
the muscle isnt changing in size.
creates a force, without moving a load
bones form ___
levers
joints form ___
Fulcrums
relaxed phasic smooth muscle contraction graph
Example: esophagus
Cyclicly contracting phasic smooth muscle
like the intestines
Tonic smooth muscle that is usually contracted
ex: a sphincter that relaxes to allow material to pass
tonic smooth muscle with varied contraction
ex: vascular smooth muscle
Single unit smooth muscle cells
connected by gap junctions- allows muscles to act as one functional unit.
ex: Contracting uterus
multi-unit smooth muscle cells
are not electrically linked.
each cell has to be stimulated independently.
ex: eyeball
smooth muscle properties
acts slower
uses less energy
one nucleus
not arranged in sarcomeres
controlled by ANS
More actin, less myosin
no Troponin
No t-tubules–> caveolae
Ca2+ from the extracellular fluid initiates a cascade ending with phophorylation of myosin light chain and activation of myosin ATPase
