Joints and Muscle Action Flashcards
What cells cause muscle cells to contract?
Motor neurons
A muscle is composed of:
- multiple muscle cells
- muscles function by contracting
Muscle cell contraction is:
- all or none
- every muscle cell innervated by a single motor neuron will contract fully and simultaneously when that motor neuron is depolarized
A motor unit is:
- a motor neuron and all the muscle cells that are innervated by it
- all or none; every muscle cell innervated by a single motor neuron will contract fully and simultaneously when that motor neuron is depolarized
How is gradation of function in muscle achieved (i.e. how is the amount of contraction force determined)?
- recruitment of additional motor units (motor neuron + innervated muscle cells)
- the more motor units recruited, the greater the force
What determines the amount of force a muscle exerts?
- the amount of motor units recruited and simultaneously contracting
What types of muscles have a large number of muscle cells per motor unit (> 500)?
- Muscles designed for large gross movements
- large gradations in function
- e.g. shoulder girdle and hip girdle
What types of muscles have a small number of muscle cells per motor unit (<20)?
- Muscles designed for small fine movements
- small gradations of function
- e.g. intrinsic hand muscles, extraocular muscles
Do muscles that perform fine movements (i.e. eye and hands) have a large or a small number of muscle cells per motor unit?
- small
- allows for smaller gradations in function (changes in force)
The three potential outcomes of muscle contraction:
- Cause Movement (e.g. lift arm)
- Prevent Movement (e.g. hold arm elevated)
- Control Movement (e.g. slowly lower arm)
The type of muscle contraction that causes movement:
- Concentric Contraction
- muscle shortens
The type of muscle contraction that prevents movement:
- Isometric Contraction
- muscle length remains constant
The type of muscle contraction that controls movement:
- Eccentric Contraction
- muscle lengthens
- often resisting effect of gravity
The three tyes of joints:
- fibrous
- cartilaginous
- synovial
Structure of fibrous Joints:
- Connected via fibrous connective tissue.
- Generally immovable.
- e.g. sutures of skull
Structure of cartilaginous joints:
- Connected with cartilage and fibrous tissue.
- Slightly mobile.
- e.g. intervertebral disks
Structure of synovial joints:
- Articular cartilage lines the end of each bone.
- Fibrous capsule spans joint holding bones together.
- Synovial membrane lines the joint.
- Synovial fluid fills the synovial cavity.
Synovial fluid in synovial joints is produced by:
- Synovial membrane.
Osteoarthritis:
- Degeneration of the articular cartilage that lines the bones in synovial joints.
- Can lead to complete bone-on-bone contact and bone spurs (osteophytes).
Action of the ascending and descending fibers of the trapezius:
- Collectively, cause upward rotation of the scapula around a center axis.
- “see-saw” motion
Action of the transverse fibers of the trapezius:
- Medial retraction (adduction) of the scapula.
Skeletal muscles always cross joints. Which muscle end moves toward the other?
- The movable end (insertion) always moves toward the fixed end (origin).
INSERTION MOVES TOWARD ORIGIN.
Origin:
- fixed end of a muscle
- does not move
Insertion:
- movable end of muscle
- moves toward the origin
Equation to determine the amount of force a muscle has on a joint:
- torque
- t = (F)(d)(sinØ)
- maximum at 90° (sin = 1)
- minimum at 0° (sin = 0)
