SRE 5

Roles & Structure of the Human

Skeletal System

Support

Lower extremity bones support the upper skeleton

Support for muscles - provides origin and insertion points

Protection

Spinal column houses the spinal cord

Ribcage encases heart and lungs

Skull protects the brain

Levers

Movable joints work alongside the muscular system

Electrolyte Balance

Maintain mineral stores: Ca & Phosphates

Detoxification

Removes heavy metals from the blood (stored for later excretion)

Bone Marrow

RBC production: 2.6m per second

Lymphocyte (WBC) production

Bone Formation & Remodeling

Ossification of Bones

Bone disease, the effects of aging on the skeletal system

Osteoporosis

When osteopenia compromises normal function, the condition is known as OSTEOPOROSIS

Typically no symptoms until a bone breaks. May weaken to such a degree that a break may occur with minor stress or spontaneously

Osteoarthritis

Degenerative joint diseases affect 85% of people over 75 years

Synovial fluid declines & cartilage becomes thinner or absent

Exposed bone surfaces abrade each other, causing friction, pain, & reduced mobility

Bone Fractures

Room for Growth

Types of Muscle

Skeletal Muscle

Smooth Muscle

Cardiac Muscle

Functions of Skeletal Muscle

Muscular contraction for the purpose of:

• Movement (locomotion)
• Breathing
• Circulation

Posture - maintains posture by holding joints in place

Support of internal organs, supports and stabilises the spinal column

Protection - guards entrances & exits with circular muscles called "sphincters". Abdominals protect organs of the abdominal cavity

Heat production - 85% of body heat is produced by contraction of muscles

How the Nervous System Enables Muscle Contraction

NEUROMUSCULAR JUNCTION

Meeting point between neuron and the muscle fiber

Muscle fibers never fire in isolation. Instead a group of fibers in innervated by a single motor neuron

A motor unit is defined as one motor neuron and all the muscle fibers it innervates

Parts of a Motor Unit:

One motor neuron

Muscle fibers

Neuromuscular junction

Components of Muscles

Sarcolemma

A muscle fibre is surrounded by plasma membrane called SARCOLEMMA

Inside the sarcolemma, there are MYOFIBRILS, which are rod-like structures running the length of the muscle fibre.

A gelatine-like substance fill the spaces between the myofibrils. This is the SARCOPLASM.  This is where fuels are stored, e.g. glycogen, amino acids and triglycerides.

The SARCOPLASMIC RETICULUM is a longitudinal network of tubules (blue in the picture). These lie parallel to the myofibrils and loop around them.

The sarcoplasmic reticulum is a storage site for CALCIUM, which is essential for muscle contraction.

Myofibrils & Sarcomere

Each muscle fibre consists of several hundred to several thousand myofibrils.

Myofibrils are the contractile elements of skeletal muscle.

Myofibrils appear as long strands of even smaller sub units called SARCOMERES

Myofibrils are broken up along their lengths into sarcomeres.  It is the interaction between the two myofilaments found within these repeating sub-units that we need to understand in order to fully appreciate how a muscle contracts. 

Myofilaments

Myofibrils are composed of two types of myofilament called ACTIN and MYOSIN.

ACTIN is a thin protein filament.

MYOSIN is a thick protein filament.

It is these myofilaments that interact to cause contraction of a sarcomere, which translates to contraction of a myofibril, muscle fibre and in the end the muscle itself.

Injury to Muscle or Connective Tissue

Damage to the muscle or connective tissue around a joint will lead to decreased force production of the muscles surrounding the joint. The brain is less likely to recruit musculature that causes pain. Trying to continue movement will most likely lead to movement compensation (e.g. limping).

Fibrous Joints

Bones held together by Collagenous fibres - emerge from matrix of one bone into the matrix of the next; no joint cavity

Fibrous Joints

Examples:

• Skull sutures
• Teeth in sockets - gomphosis
• Tibiofibular joints - two bones held by a ligament only (syndesmoses)

Cartilagenous Joints

Two bones bound by cartilage

There are two types of cartilage that can joint bones:

Hyaline Cartilage

Cartilagenous Joints

Fibro Cartilage

Softer and with more give. Often has a bluish hue.

Think gristle in the end of a chicken drumstick bone

• Ribs to sternum (hyaline costal cartilage
• Articulating joints of the spine

Tougher, denser, more rigid cartilage.

• Pubic symphysis
• Intervertebral discs

Synostosis Joints

Fibrous and cartilagenous joints ossify with age

Synostosis Joints

Two bones become one

• Bones of the Skull
• Shafts and heads of long bones
• First rib to sternum

Synovial Joints

Bones separated by joint cavity:

All synovial joints contain:

• Synovial fluid
• Articular cartilage
• Fibrous joint capsule
• Synovial membrane

Synovial Joints

Shoulder - Ball & socket Hip - Ball & socket

Elbow - Hinge Atlas (neck) - Hinge

Knee - Hinge/Condyloid Ankle - Hinge/Gliding

Intercarpal joints - Gliding Axis (neck) - Pivot

Thumb - Saddle

The Spine

The spine (along with connecting axial bones) is the structure to which many other bones attach

Protects the spinal cord

Vital for body structure, movement, balance, stability, and posture

Consists of 33 vertebrae in five regions:

Cervical 7, Thoracic 12, Lumbar 5, Sacrum 5, Coccyx 4

Mobility vs Flexibility

Lower Cross Syndrome

Upper Cross Syndrome

Tight Muscles:

Pectoralis

Upper Trapezius

levator Scapula

Sternocleidomastoid

Subscapularis

Latissimus Dorsi

Weak Muscles:

Rhomboids

Lower Trapezius

Arms Extensors

Patellofemoral Pain Syndrome