Chapter 9- Muscle and Muscle Tissue Flashcards
Movement
Voluntary or involuntary
Body posture and position
muscles work to hold us up against gravity
joint stability
muscles and tendons reinforce joints
Maintaining body temperature
muscle contraction produces heat
Muscle characteristics
Excitability- Membrane potential changes in response to stimulus
Contractility- Muscle cells shorten
Extensibility- Muscles cells can lengthen/stretch
Elasticity- Healthy muscle cells return to their original shape
Types of muscle tissue
Skeletal
Smooth
cardiac
Skeletal Muscle Tissue
Voluntary
Striated
skeletal
adaptable
most force
multinucleate
Smooth muscle tissue
involuntary
no striations
moves fluids and substances through body
all hollow organs
uninucleate
Cardiac muscle tissue
involuntary
moves blood through body
striated
uninucleate
pacemaker cells set rate of contraction
innervation of skeletal muscle tissue
Each muscle receives 1 motor nerve
nerve ending controls activity
motor neuron stimulates muscle fibers to contract
neurotransmitter released- acetylcholine
Vascularization of skeletal muscle tissue
Each muscle receieve 1 artery and 1 or more veisn to bring in nutrients and remove waste
connective tissue sheaths of skeletal muscle tissue
supports muscle, holds it tg
3 layers:
endomysium- innermost (surrounds individual muscle fibers)
perimysium- middle layer (discrete bundles of muscle fibers grouped together - form fascicles
epimysium- outermost later (surrounds entire muscle and draws boundaries between different skeletal muscles together
Skeletal muscle types of attachments
- direct- epimuysium of muscle fuses directly to bone or catilage
- indirect- involves tensions - bands of dense fibrous connective tissue that connects a muscle to a bone (tendon more common bc thicker)
skeletal muscle points of attachment
- origin- where hte muscle attaches to a less movable bone (proximal)
- insertion- where the muscle attaches to a movable bone (distal)
Skeletal muscle cells
myocytes, muscle fibers
largest and longest in the body
Sarcolemma
plasma membrane of muscle fibers
Sarcoplasm
cytoplasm of fluid muscle fibers
contain high numbers of
1. glycosomes- organelles that store glycogen (polysaccharide that is converted to glucose for ATP production)
2. myoglobin- red pigment organelle that stores oxygen (for ATP production)
Myofilaments
protein filaments in muscle tissue
1. thick filament - myosin
thin filament - actin
they interact during muscle contraction
Myosin filaments
4 light chains
2 heavy chains
Myosin head found at end of each heavy chain
2 regulatory proteins associated with actin filaments
- tropomyosin- arranged along length of thin filament that blocks myosin binding sites on actin
- troponin- globular protein associated with tropomyosin (binds tropomyosin to position it on the actin filament)
Myofibrils
rod-like organelles of muscle cells
made up of bands of myofilaments
creates striations
Myofibril bands
A band- region of myofibril where actin and myosin filaments overlap (h xone at the center of A has only filaments)
I band- region of myofibriil with only actin filaments (z disc at center holds the actin filaments in place)
Sarcomere
A and I bands create thi
Other intracellular structures that regulate muscle contraction
T-tubules- extensionso fht esarcolemma that wrap around deeper muofibrils that increase surface area of muscle fiber sarcolemma (changes in membrane potential can reach myofibils not in direct contact with sarcolemma
Sarcoplasmic reticulum- smooth endoplasmic reticulum of muscle
Highly branched, wraps around myofibrils
Form terminal cisterns around T-tubules
(stores and releases intracellular ca2 for muscle relaxation and contraction
The Neuromuscular Junction
site of synapse between a somatic motor neuron and a muscle fiber
neurotransmitter released- Acetylcholine- affects voluntary movements
junctional folds
formed by folded Sarcolemma at synaptic cleft
increase surface
For stimulation of muscle fiber to occur, to following steps must take place:
1) Events at the neuromuscular junction
(ACh is released & binds to chemically-gated ion channels on the sarcolemma)
2. Generation of the action potential across the sarcolemma
ACh binds to and opens ion channels on sarcolemma to create end plate potential (EPP)
EPP is a graded potential specific to muscle tissue
EPP depolarizes sarcolemma
If strong enough → action potential generated on sarcolemma
3. Occurs when action potential spreads from sarcolemma to T-tubules
When action potential arrives at T-tubules → voltage-gated proteins in T-tubules change shape
Channels will open
When T-tubule proteins change shape → Ca2+ channels in terminal cistern forced open
Result: Ca2+ released from sarcoplasmic reticulum & flows into cytosol of muscle fiber
4. Cross Bridge Formation & Muscle Contraction
Temporary attachment between actin and myosin
Once Ca2+ enters cytosol → interaction between actin and myosin filaments can begin
Cross bridge: the attachment of myosin to actin
The Process of Cross Bridge Formation:
A) Ca2+ binds troponintroponin changes shape
B) Change in troponin shape causes tropomyosin to roll to the side
C) When tropomyosin is movedmyosin binding site on actin is exposed
Myosin head will bind to actin binding site with use of ATP
D) Myosin head splits ATP into ADP + Pi
This allows myosin head to bind to actin
E) ADP + Pi is released from myosin head, causing the myosin head to bend
Effect: myosin head “pulls” actin filament
This is called the power stroke
F) Myosin head binds to another ATP → myosin head detaches from actin binding site
G) The myosin head binds to a different actin binding site
Steps D-G repeat until muscle contraction ends or ATP/Ca2+ run short
Repeated formation/breaking of cross bridges between myosin and actin results in myosin “walking” along actin filament
Ending cross-bridge formation & muscle contraction
Motor impulses no longer sent to muscle fiber
Action potential to muscle fiber ends
Ca2+ is returned to sarcoplasmic reticulum
When Ca2+ levels in sarcoplasm drop, it can no longer bind to troponin
Troponin returns to original shape
Result: Tropomyosin movescovers actin binding sites
Sliding Filament Model of Contraction:
During contraction, actin filaments “slide” over myosin filaments –> the sarcomere shortens and generates tension in the muscle