CHAPTER 19 Musculoskeletal System

1. THE SKELETAL SYSTEM •  A skeleton has many functions:

– Supports body – Protects soft body parts – Produces blood cells – Stores mineral and fat – Along with muscles, permits flexible body

movement

•  The human endoskeleton is composed of cartilage and bones

– The axial skeleton • Supports the axis of the body and

includes the skull, vertebral column, and rib cage.

– The appendicular skeleton • Is made up of the bones of the limbs,

shoulders, and pelvis.

Skull:

mandible

ribs

phalanges

humerus

ulna

phalanges

tibia

clavicle scapula Thoracic cage:

sternum

Costal cartilages Vertebral column

Pelvic girdle sacrum coccyx

femur

patella fibula

carpals radius

tarsals metatarsals

metacarpals

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cranium Axial skeleton Appendicular skeleton

Coccyx: usually 3–5 fused vertebrae "tailbone". Sacrum: 5 fused vertebrae

5 lumbar vertebrae in small of back

12 thoracic vertebrae Ribs attach here.

7 cervical vertebrae in Neck region

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The Vertebral Column

1.  FIBROUS– immovable – Sutures between bones of skull

2.  CARTILOGENOUS– slightly movable – Connected by hyaline cartilage – Ribs / sternum – Connected by fibrocartilage –  Intervertebral discs

3.  SYNOVIAL – freely movable

JOINTS There are 3 types of joints:

TYPES OF SYNOVIAL JOINTS Synovial which means they are freely movable

– Bones are separated by a cavity – Tendons help to stabilize the joint – Synovial membrane produces synovial fluid

3 types:

permit movement in all planes Ex: shoulder joint

permit movement in one direction only Ex: elbow

permit only rotational movement

Bone Structure

Bones are complex organs consisting of several kinds of tissues. Bones

– Are covered with a connective tissue membrane.

– Have cartilage at the ends that cushions the joints.

– Are served by blood vessels and nerves.

compact bone

cartilage

spongy bone (contains red bone marrow)

Central cavity (contains yellow bone marrow)

blood vessel

diaphysis

epiphysis

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epiphysis

Fibrous connective tissue

– The central cavity of a long bone (or diaphysis) • Contains yellow bone marrow, which

is mostly stored fat.

– The end of a long bone (or epiphysis) • Contains red bone marrow, a

specialized tissue that produces blood cells.

osteon

spongy bone Blood vessels

central canal Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

compact bone

Compact Vs Spongy Bones

•  COMPACT BONE – HARD MATERIAL of the bone – Highly organized

•  SPONGY BONE – Unorganized appearance (but plates follow

lines of stress so spongy bone is strong) – Spaces filled with red bone marrow

Skeletal Diseases and Injuries The human skeleton is quite strong and provides reliable support, but it is susceptible to disease and injury, such as:

A. Fracture B. Osteoporosis C. Arthritis

A. Fracture

•  If a force applied to a bone exceeds its capacity to bend, the result is a broken bone or fracture.

•  The treatment of a fracture involves 2 steps: 1.  Putting the bone back into its natural shape 2.  Immobilizing it until the body can repair the fracture

–  In severe cases, a fracture can be repaired surgically by inserting plates, rods, and/or screws to hold the broken pieces together.

COMMINUTED The bone has fractured into a number of pieces

SOME TYPICAL BONE FRACTURES

SPIRAL At least one part of the bone is twisted

TRANSVERSE The fractured is at a right angle with the bone axis

COMPOUND or OPEN

The skin is broken, the bone sticks out

LINEAR The fracture is parallel to the bone long axis

B. Osteoporosis

• Bones lose mass and mineral content •  Leads to an increase risk of fractures

•  Osteoarthritis – Degenerative joint disease

(cartilage)

•  Rheumatoid arthritis – Autoimmune disease –  Joints and other tissues

are attacked

C. Arthritis

2. THE MUSCULAR SYSTEM

2. THE MUSCULAR SYSTEM

•  Pull on bones to produce movements

•  Skeletal muscles = voluntary movements

•  Attached to the bone by tendons

•  650 human skeletal muscles

Antagonistic pairs of muscles bring about movement in opposite directions

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deltoid

a. Anterior view

extensor digitorum longus tibialis anterior

peroneus longus

quadriceps femoris group adductor longus

external oblique rectus abdominis

biceps brachii

pectoralis major

trapezius

frontalis

gastrocnemius

sartorius

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deltoid

gastrocnemius

Gluteus maximus

External oblique

Latissimus dorsi

b. Posterior view

Peroneus longus

Hamstring group

Extensor digitorum

Gluteus medius

triceps brachii

trapezius

occipitalis

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bundle of muscle fibers

myofibrils

One muscle fiber/cell

Muscle structure • The skeletal muscle consists of bundles of parallel muscle fibers • One muscle fiber is a muscle cell

MUSCLE FIBER

•  One muscle fiber has many myofibrils •  Is called striated, because the myofibrils

exhibit alternating light and dark bands when viewed with a light microscope.

•  A sarcomere is the region between two dark, narrow lines called Z lines. It is the unit of contraction

How does a muscle contract? •  A myofibril is composed of 2 kinds of filaments:

– Thin filaments, made mostly of the protein actin – Thick filaments, made mostly of the protein myosin

•  A sarcomere contracts – When its thin filaments slide across its thick

filaments.

Figure 27.33

The sliding-filament model Myosin heads in the thick filaments binds to specific sites on actin molecules in the thin filaments.

Muscle contractrion videos

•  http://www.youtube.com/watch?v=CepeYFvqmk4

•  http://www.youtube.com/watch?v=v71ZP8_RoOU&feature=related

•  http://www.youtube.com/watch?v=0kFmbrRJq4w&NR=1

Control of muscle contraction Motor neurons

•  Stimulate muscles to contract.

•  Can branch to a number of muscle fibers.

A motor unit consists of a neuron and all the muscle fibers it controls.

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Skeletal muscle fiber Axon branch Axon terminal

myofibril

neuromuscular junction

a. One motor axon causes several muscle fibers to contract.

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© Victor B. Eichler, Ph.D.

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Na+

The release of a neurotransmitter (ACh) causes receptors to open and Na+ to enter a muscle fiber.

folded sarcolemma ACh receptor

acetyl choline (ACh)

synaptic cleft

synaptic vesicle

Whole Muscle Contraction •  In the Body

– A motor unit is a nerve fiber together with all the muscle fibers it innervates

– As the intensity of nervous stimulation increases, more motor units are activated

– Some muscle fibers are contracting while others are relaxing

– Even when muscles appear to be at rest, some fibers are always contracting (muscle tone)

Athletics and Muscle Contraction •  Exercise and Size of Muscles

– Muscles that are not used decrease in size (atrophy)

–  If stimulation is not restored, muscle fibers are gradually replaced by fat and fibrous tissue

– Forceful activity over prolonged period causes muscle to increase in size

•  Hypertrophy occurs only if muscle contracts to at least 75% of maximum tension

•  Increase in number of myofibrils within fibers causes hypertrophy

Are all your muscle fibers the same? •  What types of exercises can you do?

•  Aerobic such as running •  Anaerobic such as lifting weight

•  Are their requirements in oxygen the same? •  Aerobic such as running needs lots of oxygen •  Anaerobic doesn’t

•  They will need different amount of : – mitochondria (remember turns oxygen into

energy) – myoglobin (protein that binds oxygen and iron)

NO

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slow-twitch fibers fast-twitch

fibers

© G.W. Willis/Visuals Unlimited

Different fibers for different types of exercises:

Slow-Twitch and Fast-Twitch Muscle Fibers

Slow-twitch muscle fiber: • Is dark in appearance (Contains lots of mitochondria and myoglobin) •  is aerobic

has steady power • has endurance

Fast-twitch muscle fiber: • Is light in appearance • is anaerobic has explosive power

• Fatigues easily