10/1/2013

1

CHAPTER 6: THE MUSCULAR SYSTEM

3 types of muscle tissue

Skeletal muscle structure • Each muscle fiber is wrapped

in connective tissue called an endomysium

• Several muscle fibers are then wrapped in a fibrous membrane called a perimysium to form a fascicle

• Another connective tissue called the epimysium wraps around the whole muscle

• The epimysium connects to tendons or aponeuroses, which attach muscles to bones

10/1/2013

2

Smooth muscle

• Not striated like cardiac or skeletal muscle

• Controls involuntary movements

• Cells tend to be arranged in layers running in different directions, as shown here

• Smooth muscle contraction is slow and occurs without fatigue

Cardiac muscle

• Only found in the heart

• Striated like skeletal muscle and involuntary like smooth muscle

• Arranged in bundles that allow the heart to act as a pump

Functions of muscle

• Producing movement

• Maintaining posture

• Stabilizing joints

• Generating heat

• Protect internal organs

• Regulate passage of substances through the body

10/1/2013

3

MICROSCOPIC ANATOMY OF SKELETAL MUSCLE & SKELETAL MUSCLE ACTIVITY

Anatomy of a muscle fiber

A myofibril is made up of repeating patterns of proteins called a sarcomere

10/1/2013

4

Sarcomeres are made from actin and myosin

Motor units

• The activity of muscle fibers is controlled by nerve cells called motor neurons

• A single motor neuron & all the muscle fibers it controls are called a motor unit

The neuromuscular junction

• The neuromuscular junction is where a motor neuron comes in close contact with a muscle fiber

• Electrical signals from the spinal cord travel through the motor neuron to the neuromuscular junction

10/1/2013

5

BUILDING MUSCLE

Skeletal muscle is built through training

• Muscle cells will become larger with exercise training

• Need amino acids and calories to build muscle

• Muscle atrophy will occur when training stops

10/1/2013

6

Hormones determine how much muscle mass you can build

• Testosterone and other androgens promote muscle growth

• This is why men build muscle tissue more easily than women

• Other hormones also play a role

Myostatin mutation

MUSCLE MOVEMENTS

10/1/2013

7

Muscle attachments

• All skeletal muscles have two or more connections to bone or other connective tissue

• The point of connection to the less movable bone is called the origin; the point to the more movable bone is called the insertion

Muscle movement

• All muscle movements are the result of muscles contracting

• Opposing muscle groups move limbs in opposite directions

• Flexors are muscles that bring two bones closer together when contracted (example: biceps)

• Extensors are muscles that bring two bones further apart when contracted (example: triceps)

• When the biceps contracts, the triceps relaxes, and vice versa

Flexion & extension

10/1/2013

8

Rotation

• Movement of a bone around its longitudinal axis

• Common for ball-and-socket joints

Abduction and Adduction

• Abduction moves a limb away from the midline

• Adduction is the opposite

Special movements

10/1/2013

9

Special movements

GROSS ANATOMY OF SKELETAL MUSCLES

Muscles of the head & neck • Facial muscles include:

– Frontalis: allows you to raise eyebrows & wrinkle forehead

– Orbicularis Oculi: allows you to close eyes & squint

– Orbicularis Oris: the “kissing muscle”

– Buccinator: flattens the cheek & helps with chewing

– Zygomaticus: the “smiling muscle”

10/1/2013

10

Muscles of the head & neck • Chewing muscles include:

– Masseter: closes the jaw by elevating the mandible

– Temporalis: helps the masseter close the jaw

• Neck muscles include:

– Platysma: helps pull the corners of the mouth down

– Sternocleidomastoids: move the neck

Muscles of the anterior trunk

• Pectoralis major: adducts and flexes the arm

• Intercostal muscles (not shown): found between the ribs and help expand the ribcage for breathing

Abdominal muscles

• Rectus abdominus: flex the vertebral column & compress abdominal contents during childbirth & defecation

• External obliques & internal obliques: Allow rotation and lateral bending of the trunk

• Transversus abdominus: compresses abdominal contents; deeper than other abdominal muscles

10/1/2013

11

Posterior muscles

• Trapezius: move the scapula and head

• Latissimus Dorsi: extend and adduct the humerus

• Deltoid: abduct the humerus; prime site for intramuscular injections (like a tetanus shot!)

Upper arm muscles

• Biceps brachii: flexes & supinates the forearm

• Brachialis: important for elbow flexion

• Triceps brachii (not shown here): main extender of the elbow (“boxer’s muscle”)

Anterior muscles of the legs

• Quadriceps (4 muscles): extensors of your lower legs (includes rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius)

• Adductor group: two muscles that adduct the thigh

10/1/2013

12

Posterior muscles of the legs • Gluteus maximus & gluteus

minimus help us stand upright and extending the leg, as in climbing

• Hamstring group: 3 muscles that control thigh extension and knee flexion (includes biceps femoris, semitendinosus & semimembranosus)

• Gastrocnemius: responsible for plantar flexion of the foot (“toe dancer’s muscle”)