Joints
 Joints = articulation or arthrosis
 Joints allow the movement of our body and hold it
together.
 Joints include bones, ligaments, muscles, tendons, and
nerves.
Types of Joints
B.1.1 – The role of bones in
human movement
 Bones are organs made up of different types of tissues.
 Functions:
Hard “framework” for body support
Protection of organs and soft tissue
Form blood cells in bone marrow
Store minerals, especially Calcium
and Phosphorus
 Act as levers for movement
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B.1.1 – The role of muscles
in human movement
 Muscles provide the force
necessary for movement.
 This happens by shortening their
cells (muscle fibers) when the
nerve signals.
 They must exist as antagonistic
pairs, so that the body part can
return to normal after one muscle
contracts.
B.1.1 – The role of tendons
in human movement
 Tendons attach
muscles to bones –
this is essential for
movement.
 Tendons are cords of
dense connective
tissue.
 By acting as levers,
bones magnify the
force provided by
muscles.
B.1.1 – The role of ligaments
in human movement
 Ligaments are tough, band-like
structures that strengthen and
stabilize the joint.
 Ligaments connect bone to bone.
B.1.1 – The role of nerves
in human movement
 Nerves send the signal to muscles
of when to contract.
 Special nerves in ligaments allow
proprioception (your body’s
ability to sense it’s own position
& movement).
 This helps prevent over-extension
of the joint.
B.1.2 – Hinge Joint:
Human Elbow Joint
 B.1.2 – label a diagram of the human elbow joint,
including:
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cartilage,
synovial fluid,
joint capsule,
named bones (radius, ulna ,humerus)
antagonistic muscles (biceps and triceps).
Pictures
 Quick Video:
http://www.youtube.com/watch?v=o2DpznoBqNY
Joint Part
Function
Humerus
Acts as a lever that allows the origin of the elbow muscles.
Radius
Acts as a lever where the biceps muscle inserts.
Ulna
Acts as a lever where the triceps muscle inserts.
Biceps muscle
Contracts to cause flexion (bending) of the arm.
Triceps muscle
Contracts to cause extension (straightening) of the arm.
Tendons
Attach muscle to bone.
Ligaments
Connect bone to bone.
Cartilage
Reduces friction & absorbs compression
Synovial fluid
Lubricates to reduce friction and provide nutrients to the
cells of the cartilage.
Joint capsule
Surrounds the joint, encloses the synovial cavity, and
unites the connecting bones.
B.1.4 – Hinge Joint: Knee
 The knee is a freely movable (diarthrotic) joint
B.1.4 – Ball and socket joint:
Hip
 The hip joint is also diarthrotic, but has many different
types of movement possibilities.
Hip vs. Knee Joints
Hip Joint
Knee Joint
Freely movable
Freely movable
Ball-like structure of femur fits Convex surface fits into a
into a cup-like depression in hip concave surface.
(the acetabulum)
Movements = flexion,
extension, abduction,
adduction, circumduction and
rotation.
Movements = flexion &
extension in one direction
Muscle Contraction –
“sliding filament hypothesis”
 http://www.youtube.com/watch?v=0kFmbrRJq4w
 http://www.youtube.com/watch?v=InIha7bCTjM
•Process of Contraction
1. Nerve signal (action potential) travels to the end of a motor
neuron (nerve that controls a muscle). End portion is called a
synaptic end-bulb.
Motor Neuron
Synaptic end bulb
Membrane
Inside of muscle cell
Point of connection = neuromuscular junction
2. Synaptic vesicles within neuron dump Acetylcholine (ACh) into
synapse (gap between the neuron and muscle) ACh diffuses across to
muscle and lands on ACh receptor proteins.
AcetylCholine
Membrane
ACh receptor proteins
3. ACh receptors start a new action potential (A.P.) that spreads
out across the sarcolemma. They will continue to send out A.P.
until the Ach is broken down.
4. A.P. spreads out across the sarcolemma and deep
within muscle fiber via transverse tubules
5. As the action potential passes by sarcoplasmic reticulum (SR)
the SR release Ca +2 which diffuse to the thin (actin) filaments.
6. Thin filaments are made of actin (to which myosin heads can
attach).
Ca +2 binds to actin , making it change shape so that it can accept
myosin heads
7. Myosin heads (with an attached ADP + P) binds to actin,
forming a cross-bridge. This triggers the heads to bend, pulling
on the thin filaments towards the H Zone using energy of the
now released ADP + P to shorten the sarcomere.
8. ATP will attach to myosin causing it to release the actin.
Thus, the cross-bridges are broken.
The crossbridges will reattach further down on actin and keep
pulling as long as there is Ca+2 and ATP is available.
9. Once the action potential stops, SR pump Ca+2 back in (using ATP).
Muscle contraction ends.
Muscle fibers
 Stages: fully relaxed, slightly contracted, moderately
contracted, fully contracted