Muscles

Question 1

What is muscle?

Answer 1

Surrounded by EPIMYSIUM and has many bundles

Question 2

What is Fabciculi?

Answer 2

Surrounded by PERIMYSIUM and has many individual muscle cells

Question 3

What are Muscle Fibres?

Answer 3

Surrounded by ENDOMYSIUM and the myofibrils are divided into sarcomeres.

Question 4

What is the Sarcoplasmic Reticulum (SR)

Answer 4

Holds and stores calcium and has an important role in contraction.

Question 5

What are mitochondria?

Answer 5

Produces ATP which is energy for muscular contraction.

Question 6

What is titin?

Answer 6

Heaviest proteins
Functional and structural
Anchors thick and thin filaments to the line

Question 7

What is the thick filament?

Answer 7

Myosin
Two intertwined filaments with globular heads
Interacts with actin filaments for contraction
Stabilised by titin

Question 8

What is the thin filament?

Answer 8

Actin
Anchored at Z disk
Equally spaced out by titin
3 proteins
-Actin- myosin-binding site
-Tropomyosin- covers active site at rest.
-Troponin- Anchored to actin and moves tropomyosin

Question 9

What do alpha motor neurons do?

Answer 9

Innervate muscle fibres

Question 10

What is a motor unit?

Answer 10

Single and motor neurons and all fibres it innervates

Increased operating unites= increased contractile force.

Question 11

What is a neuromuscular junction?

Answer 11

A synapse between a motor neuron and muscle fibres

Question 12

What is the muscle fibre contraction: excitation-contraction coupling?

Answer 12

1. Action potential starts in the brain
2. AP arrives at the action terminal (at the end of the nerve) and releases ACETYLCHOLINE (ACh)
3. ACh crosses the synapse and binds to the ACh receptors on the plasmalemma.
4. AP travels down plasmalemma, T-tubules
5. This triggers Ca2+ release from the SR
6. Ca2+ enables actin-myosin contraction.

Question 13

What is the role of Ca2+ in muscle fibres?

Answer 13

1. AP arrives from the SR from T-tubule.
   The SR is sensitive to electrical charge which causes the mass release of ca2+ into the sarcoplasm
   2.Ca2+ binds to troponin on the thin filament
   At rest- tropomyosin covers myosin-binding site and blocks actin-myosin attraction.
   Troponin-Ca2+ complex moves tropomyosin
   Myosin binds to actin, contraction can occur.

Question 14

What is the Sliding Filament Theory?

Answer 14

RELAXED STATE
No actin-myosin interaction at the binding site
Myofilaments over laps a little.
CONTRACTED STATE
Myosin head pulls actin towards sarcomere centre (power stroke)
Filaments slide past each other
Sarcomere, myofibrils, muscle fibres all shorten.
AFTER POWER STROKE ENDS
Myosin detaches from the active site
Myosin head rotates back to the original position
Myosin attaches back to another active side further down

Question 15

What is muscle relaxation?

Answer 15

AP ends and electrical stimulation of the SR stops
Ca2+ is pumped backed into the SR and stored until the AP arrives (requires ATP)
Without Ca2+, troponin and tropomyosin return to resting conformation
-Covers myosin-binding site
-Prevents actin-myosin cross-bridging.