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Bones, Joints, Action! – 40 Informal Points & 3 Points for the Joint Dissection
The human body can carry out an incredible variety of movements, from typing a letter or playing a video
game to riding a bike or flipping on a trampoline. Body movements, large or small, require the coordinated
action of our muscles and our bones. With only one exception (the hyoid bone in the throat), every bone in the
human body meets up with at least one other bone at junctions called joints. Our skeletons are rigid and offer
great protection and support, but thanks to joints, they are also flexible and allow for a great range of motion.
Without joints, we would be unable to bend and flex.
Joints can be classified by either their structure or their function. Functionally, joints are classified by how
much motion they allow. Some joints permit very little movement, but are very strong and durable. Immovable
joints and slightly movable joints are restricted mainly to the axial skeleton where protection and stability are
key. Other joints provide a greater degree of motion, but do not provide as much strength. Freely movable
joints are found on the appendicular skeleton and permit flexibility in the limbs.
Structurally, joints are classified as fibrous, cartilaginous, or synovial. Most fibrous joints are also called
"fixed" or "immovable", because they do not move; these joints have no joint cavity and are connected via
fibrous connective tissue. Cartilaginous joints are connected entirely by cartilage. Cartilaginous joints allow
more movement between bones than a fibrous joint but less than the highly mobile synovial joint. Synovial
means relating to a type of joint that is surrounded by a thick flexible membrane forming a sac into which is
secreted a viscous fluid that lubricates the joint for easy, painless movement. These classifications are based
on whether there is fibrous tissue, cartilage or a fluid filled cavity separating the bony ends of the joint. The
skull bones are connected by fibrous joints called sutures. In fetal skulls the sutures are wide to allow slight
movement during birth at the same time shielding your brain. The pubic symphysis, the piece of cartilage at
the bottom of the pelvic bone, is actually a slightly moveable cartilaginous joint. While all of the types of joints
play a role in movement and protection of the human frame, this activity will focus on synovial joints, freely
moveable joints. It is these joints and the oily fluid-filled cavity that separates the bones that allow us to swing
our arms or jump up and down.
In this activity, you will investigate the main types of synovial joints that are found in the human body. Each
joint involves a unique interaction between bones and permits a different set of movements. By looking at an
elbow joint of a cow, you will have a chance to see a joint in action and analyze important structure. In the
next activity, you will explore the flexibility of joints found in your body as you measure the range of motion of
your own joints.
Part I: Background Research
1. Use the Internet to research the structure and function of synovial joints, the main type of joints that assist
with movement. Describe at least three distinguishing features of these joints in the space below.
Feature #1: Articular Cartilage – the smooth, white tissue that covers the ends of bones where
they come together to form joints; may be damaged by injury or normal wear and tear
Feature #2: Joint Cavity – Part of the joint that is filled with synovial fluid
Feature #3: Articular (fibrous) capsule – An envelope surrounding the synovial joint. Each joint
capsule has two parts: an outer fibrous layer and an inner synovial layer.
Feature #4: Synovial Membrane – Also known as synovium or stratum synoviale. Specialized
connective tissue that lines the inner surface of capsules of synovial joints. It makes direct
contact with the synovial fluid lubricant which it is primarily responsible for maintaining.
Feature #5: Synovial Fluid – Also called synovia. A viscous fluid that reduces friction between the
articular cartilage of the synovial joints during movement.
2. Research the six main types of synovial joints and fill in the table below.
Abduction: movement that moves a limb laterally away from the body (Ex. spreading of the fingers)
Adduction: movement that moves a limb medially toward or across the midline of the body (Ex. bringing
fingers together)
Circumduction: circular motion of the arm, thigh, hand, thumb, or finger
Depression: downward (inferior) motion (Ex. Opening of the jaw)
Dorsiflexion: movement at the ankle that brings the top of the foot toward the anterior leg
Elevation: upward (superior) motion (Ex. Closing of the jaw)
Eversion: foot movement in which the bottom of the foot is turned laterally, away from the midline
Extension: movement in the sagittal plane that increases the angle of a joint (straightens the joint);
(Ex. motion involving returning to the upright position from a bent over position (ie, like coming up
from touching your toes))
Flexion: movement in the sagittal plane that decreases the angle of a joint (bends the joint); (Ex.
motion involving anterior bending of the vertebral column (ie, like touching your toes.)
Hyperextension: excessive, unnatural extension of joint, beyond the normal range of movement; this
increases risk of injury
Hyperflexion: excessive flexion of joint, beyond the normal range of movement
Inversion: foot movement which the bottom of the foot is turned toward the midline
Lateral excursion: side-to-side movement (Ex.) movement of the mandible away from the midline,
toward either the right or left side)
Lateral Flexion: bending of the neck or body toward the right or left side
Lateral (external) Rotation: movement of the arm at the shoulder joint or the thigh at the hip joint
that moves the anterior surface of the limb away from the midline of the body (Ex. Lifting arm up to
the side)
Medial Excursion: side-to-side movement that returns the mandible to the midline
Medial (internal) Rotation: movement of the arm at the shoulder joint or the thigh at the hip joint
that brings the anterior surface of the limb toward the midline of the body (Ex. Brining arm that had
been lifted up to the side, back to the body)
Opposition: thumb movement that brings the tip of the thumb in contact with the tip of a finger (Ex.
Touch tip of thumb to tip of pinky)
Plantar Flexion: foot movement at the ankle in which the heel is lifted off of the ground
Pronated Position: forearm position in which the palm faces backward
Pronation: forearm motion that moves the palm of the hand from the palm forward to the palm
backward position
Protraction: anterior motion of the scapula or mandible (Ex. Jutting out the jaw or moving shoulder
Reposition: movement of the thumb from opposition back to the anatomical position (next to index
Retraction: posterior motion of the scapula or mandible (Ex. pulling jaw back in from being jutted)
Rotation: movement of a bone around a central axis or around its long axis; twisting of the vertebral
column resulting from the summation of small motions between adjacent vertebrae
Superior Rotation: movement of the scapula in an upward direction as the medial end of the
scapular spine moves in a downward direction (Ex. Lifting arms out)
Supinated Position: forearm position in which the palm faces anteriorly (anatomical position)
Supination: forearm motion that moves the palm of the hand from the palm backward to the palm
forward position
3. Compare your findings with another student in the class and add any missing details.
Part II: Cow Elbow Dissection
4. Form a team of two or three and obtain a cow elbow joint from your teacher. Place this joint in a
dissecting tray or on a covered lab bench.
5. Refer to the diagram of the cow elbow. Use the diagram to help you orient your specimen so that the
joint is in the position it would be in if the cow were standing.
6. Locate the humerus, ulna and radius. Observe that the humerus meets up with both the ulna and the
radius, but the distal portion of the ulna fuses with the radius. The ulna and radius are visible, but do not
appear as two distinct bones. How does this arrangement compare to the arm bones of a human?
Answer in the space below.
The ulna and radius fuse together seeming to become one bone, whereas in a human they are two very
distinct bones with a space in between.
7. Lift the humerus and watch the joint move. Do not be afraid to push on the joint so the humerus begins to
point upward.
8. Extend the joint until you feel it lock into an extended position. This position allows a cow to stand for long
periods of time while expending little energy.
9. Release the joint and feel how the joint moves back into its relaxed state. Allow each group member to
feel this movement.
10. Extend the joint again so you can see the joint cavity, the space between the bones. If part of the joint
capsule is still covering the opening to the joint, use your scissors to cut into the membrane and expose
the interaction between the bones.
11. As a group, decide what type of synovial joint you are seeing in action. Compare your cow elbow to the
pencil sketches in your laboratory journal. Describe your ideas in the space below and be prepared to
defend your decision.
It is a hinge joint due to the motion being similar to opening and closing a door.
12. Rub the surfaces of the condyles of the humerus with your fingers and note the texture of the articular
(hyaline) cartilage. Describe the texture in the space below/
Hyaline cartilage is very smooth, almost rubbery. This makes it resistant to pressure, protecting the bone
from being injured.
13. In a fresh specimen, this joint cavity would be filled with synovial fluid. In the space below, describe the
function of this fluid.
Lubrication and friction reduction.
14. Find the fat pads that cushion the joint.
15. Based on what you see in the diagram and on the cow elbow, describe the function of ligaments and
tendons in the table below. If necessary, complete additional research to help complete the table.
Connects two bones or cartilages; holds a joint together
ACL (Anterior
Cruciate Ligament)
Prevents movement that might damage a joint
PCL (Posterior Cruciate
Connects muscle to bone to allow for movement; give flexibility
16. Find a remnant of a ligament on your cow joint. In the space below, describe the appearance of the ligament.
Stringy, fibrous, connective tissue
17. Note that hyaline cartilage, tendons and ligaments are all types of connective tissue. Describe the
structure and function of hyaline tissue in the space below.
Coats the bone to provide cushioning. You may have peeled this thin, almost translucent layer off of the
bones surface.
18. Turn the joint so you can view a cross-section of bone. In the space below, sketch what you see and
describe the appearance of this bone in words.
Description in words:
The bone is hollow because that is where the bone marrow would be. Remember from last year that the
bone marrow makes the red blood cells.
Conclusion Questions
1. How do you think bones, muscles and joints work together to move the body?
Our bones provide support and give our bodies shape, but cannot move on their own. The muscles provide
the movement. The joints help attach bones to one another to provide flexibility & allow the muscles to
help give the bones a way to move
2. Your friend Andre comes to school and tells you that he has a dislocated shoulder. Based on what you
now know about joints, what do you think this means?
The shoulder is a ball and socket joint. When you have a dislocated shoulder, it means the entire ball is
out of the socket. When you have a partly dislocated shoulder, it means only part of the ball is out of
the socket. This is called a shoulder subluxation.
3. How are tendons and ligaments similar and how are they different?
Ligaments connect bone to bone. Tendons connect muscle to bone. They work together to allow movement.
4. Explain why the elbow joint of a cow and the elbow joint of a human have similar, but not identical
structure. Think about the actions each organism completes with this limb.
They are homologous structures. They have the same structure but different function. The connecting bones
are the same – ulna, radius, humerus. The difference in the bones is that in a cow the ulna and radius
become fused whereas in a human they are two distinct bones with a space in between. Functionally,
they are different because humans use their arm/elbow to lift, carry, etc… Cows use their arm/elbow to
stand or walk. They are both hinge joints.
5. What type of joint is the hip joint? Describe the type(s) of movements this joint can perform.
Ball and socket synovial joint. Allows for movement in three planes; permitting flexion, extension,
abduction, adduction and rotation.