Muscles Flashcards
1
Q
Functions of Muscles
A
- Producing movement
– Through external environment
– Propulsion of items in body - Maintaining posture
- Stabilizing skeleton
- Generating heat
2
Q
Characteristics of Muscles
A
- Excitability
– Respond to stimulus - Contractility
– Use ATP to shorten forcibly - Extensibility
- Elasticity
3
Q
Note
A
make and study a types of muscle table
4
Q
Skeletal Muscle
A
- Muscle Fiber
– Long- Length of muscle
– Diameter; 5-100 μm
– Multinucleate
– Sarcolemma
– Sarcoplasm
– Myofibrils; parallel units in
fiber - Sarcomeres; repeated contractile units in
series within myofibril
- Length of muscle
5
Q
Sarcomere
A
functional unit of
striated muscle
6
Q
Myofilaments
A
- Thin filaments
– Actin
– Z disk – bounds each sarcomere; α-actinin- Thin filaments arise out of this structure
- Thick filaments
– Myosin
– Cross bridge with actin
7
Q
Sarcomeres
A
- A band – Interdigitated actin and myosin
– Each myosin surrounded by 6 actin filaments
– Includes H zone - I band – Portion with only actin (thin)
- H zone – Area with only myosin (thick)
– Also includes M line - M Line – Keeps myosin together
8
Q
Myofilaments Substructure
A
- THIN filaments structure – 3 proteins
– F-actin = Double stranded helix of G-actin- G-Actin- globular protein monomer
- Spherical protein with myosin binding site
– Tropomyosin = double stranded protein - Lie end to end along actin spiral
- Cover myosin binding sites
– Troponin Complex (three polypeptides) - TnI – Binds to actin; inhibitory subunit
- TnT – Binds to Tropomyosin; positions it on
actin - TnC – Binds calcium ions
9
Q
Myofilament Substructure
A
- Thick filaments
– Myosin protein
– Two regions- Entwined tail
- Globular heads
- Heads form cross
bridges
– Flexible
– Actin Binding Site
– Myosin ATPase
10
Q
Sacroplasmic Reticulum
A
- Modified endoplasmic reticulum
– System of tubules and cisternae that surround
myofibrils
– Calcium pump; removes Ca++ ions from the
sarcoplasm and stores it.
* Concentrates Ca++ by 2000 times - T Tubules
– Part of surface membrane of muscle fiber that
dips into fiber at junction of A and I bands
11
Q
Depolarization of T-Tubule
A
depolarizing signal goes down T-tubule to release calcium
12
Q
Sliding Filament Model
A
- Contractions
- Sarcomeres change length
– A-band stays constant
– I-band gets narrower
– H-zone gets narrower/disappears - Length-tension relationship: relates amount of
actin-myosin overlap to tension
13
Q
Length-tension relationship
A
- Total tension depends on
– Active component- actin/myosin interaction
– Passive component- elastic component
14
Q
Length-tension relationship cont
A
- If interactions between myosin and actin
are important for contraction, when should
active component of tension be greatest?
– Where the overlap between actin and
myosin heads in the greatest
– Active tension decreases as muscle
stretches beyond overlap of actin and
myosin
– Active tension decreases as actin bands
collide and begin to overlap
15
Q
Cross Bridge Cycle
A
- Cross Bridge attachment (4)
– Myosin heads undergo conformational change,
bending the head towards the actin filament - The Power Stroke (5,6,1)
– Provides the power to “slide” the actin filament- P released and power stroke is triggered
- ADP released but myosin head remains bound in
rigor
- Cross Bridge detachment (2)
– ATP binds to head and detaches it from actin - “Cocking” the myosin head (3)
– ATPase cleaves ATP and provides energy for
conformational change of head, “cocking” it.
