THE MUSCULAR SYSTEM

What types of muscles can be found in the body?

Smooth Muscle

Cardiac Muscle

Skeletal Muscle Fibers

Figure 6.1Pectoralis major•Draws arm forwardand toward the body

Biceps brachii•Bends forearm at elbow

Rectus abdominus•Compresses abdomen•Bends backbone•Compresses chest cavity

External oblique•Lateral rotation of trunk•Compresses abdomen

Trapezius•Lifts shoulder blade•Braces shoulder•Draws head back

Deltoid•Raises arm

Triceps brachi•Straightens forearmat elbow

Latissimus dorsi•Rotates and drawsarm backward andtoward body

Gluteus maximus•Extends thigh•Rotates thigh laterally

Gastrocnemius•Bends lower leg atknee

•Bends foot away fromknee

What is the contractile unit of a muscle?

Skeletal muscle microstructure.

Myofibril

Z-lineZ-line

Sarcomere

Myosin

Actin

Thin filament(actin)

Thick filament(myosin)

A closer view of a section of a myofibril showing that it is composed of sarcomeres joined end to end at theZ-line. An electron micrograph

cross section of a sarcomerein a region that contains bothactin and myosin.

Sarcomeres contain thin filaments of actin that attach to the Z-lines and thicker filaments of myosin that span the gap between actin molecules.

A transmission electron micrograph ( 11,300) of a longitudinal section of a sarcomere. The rounded red objects are mitochondria.

Microscopic View of Actin and Myosin

Exercise 9

Activity 1: Skeletal Muscle

• Has striated cells with multiple nuclei• Occurs in the muscles attached to skeleton• Functions in voluntary movement of body• Examine figure 1. • Identify the long, multinucleated fibers

arranged in a parallel fashion. How do you know the muscle fibers are striated?

Figure 1.

Activity 1

• Draw a sarcomere.• Identify and label the following structures:• Z-lines• Thick and Thin filaments

Identify the Following Structures: A, B, C, and D.

Activity 2.

• Examine the model of the neuromuscular junction.

• Examine the branching of the motor neuron to several muscle cells.

• Identify the motor neuron, synaptic cleft, sarcoplasmic reticulum and T- tubules.

• Draw the neuromuscular junction.

Figure 6.6

Motor neuron

Electricalimpulse

T tubule

Sarcoplasmicreticulum

Muscle cellplasmamembrane

Z-line

Myofibrils

Ca2

Acetylcholine

The release of acetylcholine at the neuromuscular junction causes anelectrical impulse to be generated in the muscle cell plasma membrane

The electrical impulse triggers the release of Ca2 from the sarcoplasmic reticulum

The electrical impulse ( ) is carriedto the cell’s interior by the T tubules

1

2

3

Questions

• How do a motor neuron and a skeletal muscle fiber join at a neuromuscular junction?

• What events occur at this neuromuscular junction?

Activity 3

• Examine the figure of a muscle cross section.• Identify the following structures: tendon,

fascicles, perimysium, epimysium.• Draw and label whole muscle.

Activity 4: observing the gross anatomy of skeletal muscles.

Figure 6.1Pectoralis major•Draws arm forwardand toward the body

Serratus anterior•Helps raise arm•Contributes to pushes•Draws shoulder blade forward

Biceps brachii•Bends forearm at elbow

Rectus abdominus•Compresses abdomen•Bends backbone•Compresses chest cavity

External oblique•Lateral rotation of trunk•Compresses abdomen

Adductor longus•Flexes thigh•Rotates thigh laterally•Draws thigh toward body

Sartorius•Bends thigh at hip•Bends lower leg at knee•Rotates thigh outward

Quadriceps group•Flexes thigh at hips•Extends leg at knee

Tibialis anterior•Flexes foot toward knee

Trapezius•Lifts shoulder blade•Braces shoulder•Draws head back

Deltoid•Raises arm

Triceps brachi•Straightens forearmat elbow

Latissimus dorsi•Rotates and drawsarm backward andtoward body

Gluteus maximus•Extends thigh•Rotates thigh laterally

Hamstring group•Draws thigh backward•Bends knee

Gastrocnemius•Bends lower leg atknee

•Bends foot away fromknee

Achilles tendon•Connectsgastrocnemiusmuscle to heel

Activity 4

• Complete table 9.4

Activity 5: Contraction of Skeletal Muscles

• Work in pairs• Obtain a gripper• Read the directions• Complete questions 1-3.

Due Date

• March 11-14

Introduction

Function of the muscular systemTypes of muscles and functionsBasic structure of skeletal musclesSkeletal muscles work in pairsName and actions of skeletal musclesLeave procedures out

Results

Include your results from each activity.Drawing, label your drawings see the following example.Complete table or box. Label the table and include a description of the table or box.

Figure 1. Motor neuron anatomy. Neurons are cells specialized to conduct nerve impulses.

Conclusion• Include motor neuron and motor unit.• Include all the components of a neuromuscular junction. How do a

motor neuron and skeletal muscle fiber join at a neuromuscular junction? What events occur at the neuromuscular junction? What is the function of ACh?

• Include the microscopic anatomy of a muscle fiber• Describe the sarcomere(include all the components in a sarcomere)• Describe the contraction cycle.• What are the roles played by calcium and ATP during muscular

contraction? • Explain cross-bridge, power stroke and the sliding filament model.• What is the function of ATPase?• Isometric and Isotonic contractions• Complete the questions page 113 and 114.