Anatomy and Physiology I - Lesson 10

Joints (Pt.1)

Joint (articulation)

Any point where 2 bones meet, whether or not the bones are movable at that interface

• Some joints are NOT movable

Arthrology

The science of joint structure, function, and dysfunction

What determines the direction and distance of movement in a joint? AKA its range of motion

The joint STRUCTURE

Kinesiology

The study of musculoskeletal movement

How are joints classified?

Classified by the manner in which bones are bound to each other (how they are connected to one another)

• Structural + functional classifications

What are the 4 structural classifications of joints?

1. Bony

2. Fibrous

3. Cartilaginous

4. Synovial

What are the 3 functional classifications of joints?

1. Synarthrosis - immovable

2. Amphiarthrosis - slightly movable

3. Diarthrosis - freely movable

Bony Joint (Synostosis)

An immobile joint formed when the gap between 2 bones ossified, and the bone becomes a single bone

• IMMOVABLE (synarthrosis)

What are examples of bony joints?

• Left + right frontal and mandibular bones in infants fuse together

• Coxal hip bones

• 1st rib and sternum

• Parietal bones along sagittal suture

Fibrous Joint (Synarthrosis)

Adjacent bones are bound by collagen fibers that emerge from one bone and penetrate into the other

• IMMOVABLE

Fibrous joint: suture

Immobile or slightly mobile fibrous joints in which SHORT collagen fibers bind the bones of the skull to each other

Serrate Suture

Interlocking wavy lines

• Coronal, sagittal, lambdoid sutures

Lap (squamous) Suture

Overlapping beveled edges

• Temporal, parietal bones

Plane (butt) Suture

Straight, non-overlapping edges

• Palatine processes of maxillae

Fibrous joint: gomphosis

Attachment of a tooth to its socket on maxilla or mandible

How are teeth attached to their sockets in the jawbone? What does this allow for?

Teeth held in place by fibrous PERIODONTAL LIGAMENTS (collagen fibers)

• Allows tooth to move a little under the stress of chewing - only slight movement under a lot of pressure

Fibrous joint: syndesmosis

Joint at which 2 bones are bound by LONG collagen fibers

• Longer collagen fibers makes joint slightly more movable

Why are syndesmoses more movable than other fibrous joints?

• Separation of bones

• Length of the fibers

Provide example of a mobile and less mobile syndesmosis joint

• Mobile: interosseus membrane (joins radius to ulna)

• Less mobile: joint between tibia to fibula

Cartilaginous Joint (Ampiarthrosis)

Two bones are linked together by cartilage, with slight movement

Cartilaginous joint: SYNCHONDROSIS

Bones are joined by hyaline cartilage

• Ex. Epiphyseal plate, rib attachment to sternum

Cartilaginous joint: SYMPHYSIS

Bones are joined by fibrocartilage

• Ex. Pubic symphysis/interpubic disc, intervertebral discs

Synovial Joints (Diarthrosis)

Joint in which two bones are separated by a joint cavity (fluid between bones)

What is the most familiar type of joint?

Synovial joints

Are synovial joints more or less mobile? Why?

Most are freely MOBILE

• Joint cavity, weaker joint, and multiaxial range of motion make it less stable ——→ prone to dislocation

• Mobility is important for quality of life

Synovial joints are the MOST….:

1. Structurally complex joint

2. Likely to develop painful dysfunction (arthritis)

3. Important for physical and occupational therapists, coaches, nurses… trying to recover movement

Synovial Joint Structure: articular cartilage

Layer of HYALINE cartilage covering the facing surfaces of 2 bones

Synovial Joint Structure: joint cavity

Separates the articular surfaces of 2 bones, creating a GAP

Synovial Joint Structure: synovial fluid (describe composition, function)

Slippery lubricant in joint cavity rich in albumin and hyaluronic acid

• Nourishes articular cartilage and removes waste

How does synovial fluid work?

Compression of joint squeezes articular cartilage, releasing synovial fluid

• Fluid allows movement of synovial joints to be mostly friction free

What happens with a lot or a little force on a synovial joint?

• Great force: makes synovial fluid more solid for protection

• Lesser force: spongy bone sucks synovial fluid until it is activated and squeezed out

Synovial Joint Structure: joint capsule

Connective tissue that encloses the cavity and retains the fluid

• Prevents leakage of fluid and entry of pathogens

Outer fibrous capsule

Continuous with periosteum of adjoining bones

Inner synovial membrane

Composed of synoviocytes (secrete synovial fluid and macrophages to remove debris from joint cavity)

What are joint capsules and ligaments well supplied with? Why?

Supplied with lamellar corpuscles + sensory receptors

• Allows brain to monitor limb movements (proprioception)

Synovial Joint Structure: articular disc

Pad between articulating bones in some synovial joints that crosses the ENTIRE joint capsule

• Fibrocartilage grows inward to form pad

• Ex. Jaw/TMJ, clavicle joints, ulna/carpal bones

Synovial Joint Structure: meniscus

Crescent-moon pas that does NOT cross joint entirely

Where are meniscus found? What do they do?

Found in the knee (knee pads = meniscus)

• Absorb shock and pressure

• Stabilize joint and guide bones across each other to improve their fit together

Tendon

Collagenous tissue strip that attaches MUSCLE to bone

Ligament

Collagenous tissue strip that attaches BONE to bone

Bursa (bursae) - description, location, function

Fibrous sac filled with synovial fluid between the muscles

• Found where tendons pass over bone or between bone and skin

• Cushions muscles, helps tendons slide over joints, modifies direction of tendon pull

Bursitis

Inflamed bursa causing pain

• Due to repetitive motion, irritation, trauma, infection….

  • Ex. Bunion

Tendon/synovial sheath

Elongated cylindrical bursa wrapped around a tendon

• Abundant in hand and foot

What does exercise do to articular cartilage? (Hint: warming up)

Exercise WARMS synovial fluid, making is less viscous and easily absorbed by cartilage

• Cartilage SWELLS to provide effective cushion against impact

What does repetitive compression of nonvascular cartilage during exercise do?

Repetitive compression of nonvascular cartilage squeezes fluid + metabolic waste OUT of cartilage

What happens to cartilage when removing weight while exercising?

Cartilage absorbs synovial fluid, taking in oxygen and nutrients to the chondrocytes

Range of Motion (ROM)

The degrees through which a joint can move (how much movement you have in a joint)

What is the range of motion determined by?

1. Structure of articular surfaces

2. Strength and stiffness of ligaments + joint capsules (more stretching + long/slack ligaments = more ROM)

3. Action of muscles and tendons by nervous system

Muscle Tone

State of tension maintained in resting muscles

• Affects stress on bones

Dislocation (Luxation)

Caused by extreme stress on a joint, causing it to not hold bones together in proper alignment

• Articulating surfaces out of position

• Damaged articular cartilage, ligaments, joint capsule

What joint is the most prone to dislocation due to its high ROM?

Shoulder joint

Subluxation

Partial dislocation

Multiaxial Joint

Joint has 3 degrees of freedom/axes of rotation

• Ex. Shoulder, coxal/hip joints

What are the 6 major types of synovial joints? What distinguishes them from one another?

1. Ball and socket

2. Condylar

3. Saddle

4. Plane

5. Hinge

6. Pivot

**Differ by SHAPES of articular surfaces and degrees of freedom (structure and movement)

Ball and socket joints

Smooth, hemispherical head fits within cup-like socket

• Multiaxial joints

• Ex. Shoulder, coxal/hip bones

Condylar (ellipsoid) joints

Oval convex surface of one bone fits into a complementary shaped depression on the other

• Biaxial joints (movement in 2 planes)

• Ex. Radiocarpal joint, metacarpophalangeal joints

Saddle joints

Both bones have an articular surface that is shaped like a saddle, one concave and the other convex

• Biaxial joints

• Ex. Opposable thumb, sternoclavicular joint

Plane (gliding) joints

Flat articular surfaces, bones slide over each other

• Biaxial joints

• Ex. Between carpals of wrist and tarsals of ankle, between vertebrae

Hinge joints

One bone with convex surface fits into a concave depression of another bone

• Monoaxial joints (move in 1 plane)

• Ex. Elbow, knee, joints within fingers and toes

Pivot joints

A bone spins on its longitudinal axis

• Monoaxial joints

• Ex. C1, C2, Radioulnar joint at elbow