Chapter 7: The Muscular System

Chapter 7:The Muscular

System

Taylor: Structure and Function of the Human Body

Types of Muscle

The Muscular System

Skeletal Muscle Has Three Primary Functions:

•Skeletal movement

•Posture maintenance

•Heat generation

The Muscular System

Muscle Structure

•Fascicles

– Bundles of muscle cells (fibers) that make up a whole muscle

•Connective tissue

– Hold fascicles and whole muscle together

– Three layers

• Endomysium

• Perimysium

• Epimysium

•Tendons

The Muscular System

Muscle Cells in Action

•Motor unit: A single neuron and all the muscle fibers it stimulates

– Small motor units used for fine movements

– Large motor units used for broad movements

The Muscular System

•Neuromuscular junction (NMJ): The point at which a nerve fiber contacts a muscle fiber

– A type of synapse

– NMJ anatomy

• Motor neuron

• Neurotransmitter (acetylcholine; ACh)

• Motor end plate (on muscle fiber)

Contains acetylcholine receptors

The Muscular System

•NMJ allows motor neuron to stimulate muscle fiber to become electrically excited (action potential)

•Action potential stimulates muscle contraction

•Events at the NMJ

– Ach is released from motor neuron into synaptic cleft

– Ach diffuses across synaptic cleft towards motor end plate

– Ach binds to receptors on motor end plate and stimulates action potential

The Muscular System

•The sarcomere is the functional unit of contraction in the skeletal muscle fiber

•Sarcomere anatomy:

– Thick filaments (myosin)

– Thin filaments (actin)

– Regulatory proteins

• Troponin

• Tropomyosin

The Muscular System

•Sarcomeres contract via the sliding filament mechanism:

– Myosin heads bind to actin, forming cross-bridges

– Using stored energy, myosin heads pull actin filaments together within the sarcomeres and the cell shortens

– New ATP is used to detach myosin heads and move them back into position for another “power stroke”

Figure 7-4 Sliding filament mechanism of skeletal muscle contraction.

Sliding filament mechanism of skeletal muscle contraction.

The Muscular System

•Calcium regulates sarcomeric contraction within the muscle cell:

– Action potential from NMJ travels to sarcoplasmic reticulum (SR)

– SR releases calcium into cytoplasm

– Calcium shifts troponin and tropomyosin off of thin filament soit blocks the sites on actin filaments where cross-bridges form

– Muscle relaxes when stimulation ends and calcium is pumped back into SR

The Muscular System

Summary of Events in a Muscle Contraction

1.ACh is released from neuron ending into synaptic cleft at NMJ

2.ACh binds to motor end plate and produces action potential

3.Action potential travels to sarcoplasmic reticulum (SR)

4.SR releases calcium into cytoplasm

5.Calcium shifts troponin and tropomyosin so that binding sites on actin are exposed

The Muscular System

Summary of Events in a Muscle Contraction (continued)

6.Myosin heads bind to actin, forming cross-bridges

7.Using stored energy, myosin heads pull actin filaments together within sarcomeres and cell shortens

8.New ATP is used to detach myosin heads and move them back to position for another “power stroke”

9.Muscle relaxes when stimulation ends and calcium is pumped back into SR

The Muscular System

Energy Sources

•Muscle contraction requires ATP

•Skeletal muscle prefers to produces ATP via aerobic metabolism, which requires

– Oxygen

– Glucose

•Storage compounds ensure an adequate supply of oxygen and glucose for aerobic ATP metabolism

– Myoglobin

• Stores additional oxygen, located in muscle cells

– Glycogen

The Muscular System

Energy Sources

•During strenuous activity, muscle cells use anaerobic ATP metabolism which causes an oxygen debt and does not require ATP

– Breakdown of creatine phosphate

– Anaerobic glycolysis

• Lactic acid accumulation and oxygen debt

• Excess postexercise oxygen consumption

– After strenuous exercise, person takes in extra oxygen (via rapid breathing) to remove lactic acid and replenish energy stores

The Muscular System

Effects of Exercise

•Improved balance, joint flexibility

•Increased muscle size (hypertrophy)

•Improved muscle tissue

•Vasodilation

•Strengthened heart muscle

•Improved breathing and respiratory efficiency

•Weight control

•Stronger bones

The Muscular SystemTypes of Muscle Contractions

•Partial (muscle tone or tonus)

– Partially contracted state that is normal

•Isotonic

– No change in tension

– Muscle length shortens

– Movement

•Isometric

– Great increase in tension

– Muscle length unchanged

– No movement

The Mechanics of Muscle Movement

• Tendons attach muscles to bones.

– Origin: Attached to more fixed part of skeleton

– Insertion: Attached to more movable part of skeleton

Figure 7-6 Muscle attachments to bones.

Muscles Work Together

•Many muscles function in pairs

– Prime movers

• Movement by a muscle

– Antagonists

• Produces opposite movment

– Synergists

• helpers

Levers and Body Mechanics

•Musculoskeletal system as a lever system

– Lever—bone

– Fulcrum—joint

– Force—applied by muscle

•Three classes of levers

– First class

– Second class

– Third class—most body systems

Skeletal Muscle Groups

Characteristics for Naming Muscles

Muscles of the Head and Neck

Figure 7-10 Muscles of the head and neck.

Muscles That Move the Shoulder and Arm

Muscles That Move the Forearm and Hand

Muscles That Move the Forearm and Hand (continued)

Figure 7-11 Muscles that move the forearm and hand.

Muscles of the Trunk

Figure 7-12 Muscles of respiration.

Figure 7-13 Muscles of the abdominal wall.

Muscles That Move the Leg and Thigh

Muscles That Move the Leg and Thigh (continued)

Figure 7-15 Muscles of the thigh.

How many muscles make up the quadriceps femoris?

Muscles That Move the Foot

Figure 7-16 Muscles that move the foot.

Effects of Aging on Muscles

• Beginning at about age 40

• Gradual loss of muscle cells

• Loss of power

• Tendency to flex hips and knees

• Decrease in height

Chapter 7: The Muscular System

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