What is a fascicle?
A bundle of muscle fibers.
What is a muscle fiber? (list the layers)
A single muscle cell containing many myofibrils.
Name the connective tissue sheaths from smallest to largest.
Endomysium → around muscle fiber
Perimysium → around fascicle
Epimysium → around whole muscle
What is the functional role of connective tissue sheaths?
They transmit force and contribute to passive tension.
What increases when more sarcomeres are arranged in series?
Greater shortening range
Greater contraction velocity
NOT force.
What increases when more sarcomeres are arranged in parallel?
Greater force production.
This links to hypertrophy and cross-sectional area.
What is titin and why is it important?
Elastic protein connecting myosin to Z line; contributes to passive tension and recoil.
This explains passive tension increase in outer range.
What does and does not shorten in muscle contraction?
Z | actin → → ← ← actin | Z
myosin in middle (M line)
When contracting:
Actin slides inward
Z lines move closer
Myosin does NOT shorten
What is a myofibril?
A long chain of sarcomeres arranged in series.
What Changes During Contraction?
During concentric contraction:
Sarcomere length ↓
Z lines move closer
I band ↓
H zone ↓
A band stays the same
If you remember only one thing:
A band never changes length.
What is the A band?
Entire length of thick filaments (includes overlap zone).
What is the H zone?
Area containing only thick filaments.
What is the I band?
Area containing only thin filaments.
What is located at the M line?
Structural proteins anchoring thick filaments (myosin) at the center of the sarcomere
What attaches to the Z line?
Thin filaments (actin).
What is a sarcomere?
The functional contractile unit of muscle, defined from Z line to Z line.
What do troponin and tropomyosin do?
Tropomyosin blocks binding sites on actin.
Calcium binds to troponin → shifts tropomyosin → exposes binding sites.
What part of myosin binds to actin?
The myosin head (cross-bridge).
The head flexes and pulls actin.
There are 2 types of main filaments, what are they and what are they made of?
Name the order of unit in a muscle
Myosin & Actin (protein filaments)
→ Sarcomere (functional unit)
→ Myofibril (chain of sarcomeres)
→ Muscle Fiber (cell)
→ Fascicle (bundle of fibers)
→ Whole Muscle
