12.15.1 Motor Control: Muscle Microstructure

Question 1

Motor Control: Muscle Microstructure

Answer 1

• A vertebrate skeletal muscle consists of a bundle of muscle fibers. Each muscle fiber consists of bundles of myofibrils. Each functional unit of a myofibril is called a sarcomere.
• A myofibril is made up of many thick filaments and thin filaments. Thick filaments are bundles of myosin molecules. Thin filaments consist of two strands of actin with associated proteins.
• When a muscle contracts, thick filaments slide along thin filaments, causing the entire sarcomere to decrease in length.

Question 2

skeletal muscle

Answer 2

• Skeletal muscles are made up of bundles of muscle fibers attached to bones. When skeletal muscles contract, they cause the motion of the bones.
• Each muscle fiber is a single multinucleated cell. The cell contains numerous myofibrilsthat enable the cell to contract. A myofibril is made up of both thin filaments and thick filaments.

Question 3

sarcomere

Answer 3

• A sarcomere, shown in the diagram to the left, is the
  functional unit of a myofibril. The thin filaments, composed of two strands of actin and associated proteins, are attached to Z lines, the borders of the sarcomere (not labeled in the diagram).
  The thick filaments, composed of bundles of myosin molecules, span across the middle of the sarcomere in between the thin filaments, and do not reach the Z lines.

Question 4

sliding-filament model

Answer 4

• The sliding-filament model describes muscle contraction. The thick and thin filaments slide past each other causing a shortening of the sarcomere and contraction of the muscle.

Question 5

A sarcomere is

Answer 5

• the basic functional unit of the muscle.
• bordered by Z lines.
• a group of overlapping actin and myosin filaments.

Question 6

Myofibrils are composed of which two kinds of microfilaments?

i. myosin (thick)
ii. myosin (thin)
iii. actin (thick)
iv. actin (thin)

Answer 6

• i, iv

Question 7

Human motion is the result of

Answer 7

• muscles contracting to pull against bones

Question 8

Muscle contraction occurs when _________ interacts with __________.

Answer 8

• actin, myosin

Question 9

The thick fiber of the myofibril is composed of _________.

Answer 9

• myosin

Question 10

According to the sliding filament model of muscle contraction:

Answer 10

• neither type of filament contracts, the actin and myosin filaments slide together during muscle contraction.