skeletal muscle

Question 1

Three major types of muscle

Answer 1

Skeletal muscle - voluntary, attached to bone.

Cardiac muscle - involuntary, not attached to bone. Specialized form of skeletal muscle.

Smooth muscle - involuntary, not attached to bone. Myocytes with a ‘fusiform’ shape.

DIFFERENCES IN CELL STRUCTURE, SHAPE AND ARRANGEMENT WITHIN EACH MUSCLE

Question 2

TENDONS

Answer 2

Bundles of collagen fibres that attach muscle to bone

Question 3

MUSCLE

Answer 3

skeletal muscle made from bundles of multinucleated muscle cells

Question 4

MYOFIBRIL

Answer 4

each muscle cell formed form bundles of actin and myosin filaments organized into myofibrils

Question 5

sarcoplasmic reticulum

Answer 5

Six actin filaments surround a single myosin filament

Sarcoplasmic reticulum homologous to endoplasmic reticulum in other cells: Ca2+ store in skeletal muscle

T-Tubules: propagates action potentials into the interior of the myofibril from the surface

Question 6

The Sarcomere

Answer 6

The sarcomere is the functional unit of skeletal and cardiac muscle

Runs from Z line to the next Z line

Functional unit of skeletal muscle (Z disk/line to Z disk/line)

Question 7

Thin filaments

Answer 7

Thin filamements are made from globular actin proteins (G-actin)

G-actin forms protein chains termed filament-actin (F-actin)

Question 8

A Band

Answer 8

Thick filaments (myosin) found as a dark band at the centre of the sarcomere

Question 9

I Band

Answer 9

Contains thin filaments (actin) that do not overlap with the thick filaments. Found either side of the A band with the Z disc in the centre.

Question 10

M line/disc

Answer 10

proteins that link the central regions of the thick filaments

Question 11

H Zone

Answer 11

light area found between the ends the thin filaments; found in the centre of the sarcomere.

Question 12

Z line/disc

Answer 12

Network of proteins that anchor the thin filaments

Question 13

The Sliding Filament Mechanism

Answer 13

Contraction means the development of force rather than shortening
Myofilaments remain the same length, however they overlap to a greater extent

Question 14

CROSS BRIDGE CYCLING

Answer 14

RESTING MUSCLE:
- Energized myosin molecule bound to ADP and Pi
- Tropomyosin covers and masks the ‘myosin binding sites’ on the actin filament (prevents interaction between the two filaments)

2. ACTIVATION OF CONTRACTION:
   
   • Muscle stimulated and cytosolic calcium levels increase
   • The calcium binds to the troponin complex
   • Calcium-bound troponin moves troopomyosin and unmasks the myosin binding sites on actin
   • Energized myosin molecule (+ADP) binds to actin
   • Cross bridge formation causes the release of ADP and Pi and movement of the crossbridge
3. TERMINATING CROSS BRIDGE:
   
   • ATP binds myosin and breaks the actin-myosin cross bridge
   • ATP converted to ADP and myosin returns to the energized position

Question 15

4. The Neuromuscular Junction (NMJ)

Answer 15

Myelin sheath that surrounds the motor neuron ends near the surface of the muscle fibre
Axon terminals contain vesicles that contain acetylcholine (Ach)
Region of the muscle fibre directly under the terminal portion of the axon is the motor end plate
Axon terminal + motor end plate = neuromuscular junction

Action potential in the motor neuron depolarizes the axon terminal leading to opening of a voltage dependent calcium channel
Intracellular calcium increase triggers the release of Ach containing vesicles
Ach diffuses to the motor end plate and activates the nicotinic Ach receptors (ionotropic receptors)
Depolarizes the motor end plate = end plate potential

Question 16

Five key points from this lecture

Answer 16

There are three major types of muscle
Skeletal muscle has a highly organized structure
The functional unit of skeletal muscle is the sarcomere
Skeletal muscle is under voluntary control where contraction is initiated at the neuromuscular junction
Calcium is stored in the sarcoplasmic reticulum and released to activate contraction