musculoskeletal system definitions Flashcards
skeletal muscle
- The muscles that move bones and enable us to walk, run and carry out a wide range of voluntary physical activities
- Voluntary: under conscious control
- Attached to the bones of the skeleton.
- Striated
- Contractions of the skeletal muscles bring about movement at the joints.
- They also give the body its form and contours, and allow it to maintain posture.
smooth muscle
- Involuntary: not under conscious control, involuntary muscles.
- Non-striated
- When the smooth muscles that wrap around the alimentary canal contract, the diameter of the canal narrows, pushing the contents along. (Peristalsis).
- Stomach, small intestine
cardiac muscle
When cardiac muscle contracts, it reduces the space in the chambers of the heart and pushes the blood from the heart into the blood vessels.
contractibility
The ability to shorten
Extensibility
The ability to be stretched.
elasticity
The ability to return to the original length after being stretched.
perimysium
A sheath of connective tissue called the perimysium surrounds each bundle so that it can function as an individual unit.
epimysium
Sheaths of connective tissue that hold the bundles together. Towards the end of the muscle they taper and blend to form the tendon.
sarcolemma
A thin, transparent plasma membrane around the cell containing cytoplasm, called the sarcoplasm.
myofibrils
Bundles of thread-like protein filaments
sarcoplasmic reticulum
A tubular network that surrounds the myofibrils.
A storage site for calcium ions, which are released during muscle contractions.
myofilaments
Each myofibril is composed of many smaller myofilaments, made of protein, which are the actual units involved in the contraction of the muscle.
thick myofilaments
Composed mainly of the protein myosin
thin myofilaments
Composed mainly of the protein actin
sarcomere
The distance between successive Z-lines
sliding filament theory: contraction
When a muscle fibre is supplied with sufficient energy, in the form of adenosine triphosphate (ATP), and is activated by a nerve impulse, these thick and thin protein filaments slide past each other. As the thin actin filaments slide over the thick myosin filaments, the Z lines are drawn closer together and the sarcomere is shortened. This results in a shortening of the muscle fibres and, hence, a shortening of the whole muscle.
excitability
Ability to be stimulated by a nerve impulse
Z lines
Protein discs in the middle of the thin filaments.
A band
The length of a thick filament (myosin). At the ends of the A band, the thin and thick filaments overlap.
H zone
The middle of the A band, containing the thick filaments only (so it is lighter).
I band
The distance between successive thick filaments, containing only thin filaments.
sliding filament theory: relaxation
When the muscle relaxes, the actin and myosin filaments can be pulled past one another in the opposite direction and the muscle fibre returns to its original, uncontracted state.
tendons
Fibrous, inelastic connective tissue that connects muscle to bone. They bridge the joints, so when a muscle contraction occurs, the bones move.
antagonistic muscles
If muscles contract pulling a bone in one direction, another set of muscles must contract to pull the bone in the opposite direction. Thus, the muscles that move parts of the skeleton are always grouped in pairs.
Example: biceps and triceps, hamstring and quadriceps.
When the biceps muscle contracts to bend the arm, the triceps must relax, and vice versa to straighten the arm.
biceps
One end is fixed to the scapula (shoulder blade), and the other end is attached to the radius.
triceps
Fixed to the scapula and to the humerus at one end, and to the ulna at the other.
origin
The end of the muscle fixed to the stationary bone.
insertion
The attachment to the movable bone of the other end of the muscle.
belly
The fleshy portion of the muscle between the tendons of the origin and the insertion.
agonist/prime mover
A muscle that causes a desired action.
antagonist
A muscle that has an effect that is opposite to that of the agonists (i.e. it yields to the movement of the agonist)
synergists
Muscles that help the prime mover/agonist. May produce the same movement as the prime mover, or they may steady a joint during a particular movement so that unwanted movement is prevented and the agonist can function more efficiently.
Example: without synergistic muscles, the wrist would flex every time the fist was clenched, because the muscles that curl the fingers also pass across the wrist. Synergistic muscles immobilise the wrist, stopping it from flexing.
fixer
A synergist that works by immobilising a joint, acting as a stabiliser of one part of the body during movement of another part.
muscle tone
Maintaining partial contraction of skeletal muscles. This tightens a muscle, but not enough fibres are contracting at a time to produce movement.
Muscle tone is caused by many different fibres taking turns to contract, rather than the constant contraction of the same fibres.
Muscle tone holds many of our body parts in position.
Example: the head is held up by the partial contraction of the neck muscles.
posture
The characteristic way in which someone holds their body when standing or sitting.
Posture depends on muscle tone.
*!!!!!!! functions of the skeleton
- provides a scaffold to support the weight of the rest of the body.
- facilitates movement by being points of attachment for muscles.
- protects vital internal organs.
- produces red blood cells.
- act as storage organs for mineral salts and fat. (yellow)
define
axial skeleton
- bones that lie around the central axis of the body.
- provides support for erect posture
- protection of the central nervous system and the organs within the thorax
components of the axial skeleton
- (bones forming) skull
- vertebral column
- ribs
- sternum (breastbone)
define
appendicular skeleton