6 The Muscular System Flashcards
What are the primary functions of muscles?
- Voluntary movement of the body (e.g., walking, jumping)
- Involuntary actions (e.g., reflexes, pupil adjustment, hair standing on end)
- Posture maintenance
- Heat production
- Internal organ movement (e.g., food through the digestive tract, bladder control)
Properties of muscles (4)
- excitability
- contractility
- extensibility
- elasticity
the capacity of a muscle to respond to a stimulus.
excitability
the ability of a muscle to shorten and generate a pulling force.
contractility
the property that allows a muscle to be stretched back to its original length.
extensibility
ability of a muscle to recoil to its original resting length after being stretched.
elasticity
muscle tissue:
- Under voluntary control
- Provides body movement
- Controlled by the nervous system
skeletal muscle tissue
muscle tissue:
- Involuntary (not under conscious control)
- Found in the walls of various internal organs
- Moves food and controls internal organs
smooth muscle tissue
muscle tissue:
- Involuntary (not under conscious control)
- Found in the heart (Works to pump blood)
cardiac muscle tissue
muscle fibers that contain more mitochondria and myoglobin, react slowly, resist fatigue, and are used in postural muscles that support the body’s stance.
red (slow) muscle fibers
muscle fibers that have lower myoglobin and mitochondria, react quickly, operate anaerobically, and provide quick bursts of power, useful in muscles that control fingers and eye movements.
white (fast) muscle fibers
blend traits of red and white fibers. They’re found in postural muscles like the calf, supporting both steady posture and rapid movements like running or jumping.
Intermediate muscle fibers
stimulate muscle fibers to contract, with each muscle fiber innervated by a branch of a neuron axon, forming a neuromuscular junction.
motor neurons
Muscles need high amounts of energy, so a __ supplies oxygen and nutrients and removes metabolic waste from muscle fibers.
dense capillary network
are the structural units in muscle fibers, containing actin and myosin protein filaments essential for contraction.
myofibrils
the functional unit of a myofibril, located between Z discs, where actin is anchored, and contraction occurs.
sarcomere
thick and consist of roughly 300 molecules, with each molecule resembling a “golf club” structure that enables it to bind to actin during muscle contraction.
myosin filament
bind to actin’s active sites, forming cross-bridges, and have ATPase activity, which releases energy to bend the hinge region during muscle contraction.
myosin head
Actin (thin) myofilaments consist of three major proteins: (3)
- fibrous (F) actin
- tropomyosin
- troponin
forms a double helix with myosin-binding sites on G actin monomers, allowing myosin to bind during contraction.
F actin
an elongated protein that winds along the groove of the F actin double helix, helping regulate muscle contraction by covering binding sites on actin.
Tropomyosin
What are the subunits of troponin and their functions? (3)
- Tn-A - binds to actin
- Tn-T - binds to tropomyosin
- Tn-C binds to calcium ions
crucial for muscle contraction control.
__ motor units control fine movements (e.g., fingers, eyes), while __ motor units control large weight-bearing muscles (e.g., thighs, hips).
- Small
- large
surrounds each myofibril, stores calcium (Ca++) when the muscle is relaxed, and releases it into the sarcoplasm when stimulated for contraction.
Sarcoplasmic reticulum (SR)
consists of one T-tubule and two terminal cisternae of the SR, crucial for transmitting the signal for muscle contraction.
triad
Ca++ pumps in the SR membrane return __ to the __, helping the muscle relax after contraction.
- calcium
- sarcoplasmic reticulum (SR)
Where does muscle stimulation occur?
neuromuscular junction
How do motor neurons communicate with muscle cells?
neurotransmitters, typically acetylcholine, which carry the impulse signal across the gap.
What happens in the muscle cell when it is stimulated?
Calcium ions are released into the muscle cell.
They trigger the interaction between actin and myosin.
calcium ions
How do actin and myosin interact during muscle contraction?
Actin filaments slide over the myosin filaments.
What model explains the interaction between actin and myosin?
Sliding Filament Model.
The myosin heads attach to actin and pivot, pulling the actin filaments __.
inward
What is the connection between myosin heads and actin called?
Cross-bridge
They bind to and release actin filaments asynchronously, allowing continuous contraction.
myosin heads
binds to troponin, which moves tropomyosin away from the binding sites on actin, allowing myosin to attach.
calcium
Calcium binds to __, which moves __ away from the binding sites on actin, allowing myosin to attach.
- troponin
- tropomyosin
Where are calcium ions stored in the muscle fiber?
sarcoplasmic reticulum (SR)
What provides energy for the myosin heads to pivot?
ATP
What theory? Actin filaments are pulled inward along myosin filaments, shortening the sarcomere, myofibrils, muscle fibers, and ultimately the whole muscle.
Sliding Filament Theory
depolarization in a muscle contraction: __ moves inside, causing the membrane to become positively charged.
Na+
What occurs during repolarization in muscle contraction?
membrane returns to a negative charge.
A period during depolarization when a second stimulus cannot cause a response.
absolute refractory period
During repolarization, a stronger stimulus can trigger a response.
relative refractory period
What mechanical change occurs in myofibrils during contraction?
Tension
Muscle shortens while tension remains the same; filaments slide, moving through a distance.
Examples: Walking, lifting, bending knee.
isotonic contraction
Muscle contracts without shortening; tension increases, but filaments do not slide.
Examples: Posture, holding an object, standing still.
isometric contraction
Recording motion or pressure changes over time to track muscle contractions, blood pressure, or physiological events.
kymograph
A single, brief, jerky contraction in response to a threshold stimulus.
muscle twitch
Successive stimuli are applied, not allowing muscle cells to relax, leading to a cumulative effect.
summation
A graphical recording of muscle activity.
myogram
Sustained, prolonged contraction due to rapid successive stimuli, developing high tension.
tetanus
When stimuli are applied slower than in tetanus, resulting in gradually stronger individual contractions.
treppe effect (staircase effect)
The state of partial contraction that gives muscles a certain firmness.
muscle tone
The ability to stretch without developing lasting tension. Initially, resistance to stretching occurs, but tension decreases as the muscle adjusts to the new length. Found in hollow visceral organs like the urinary bladder, stomach, and small intestines.
plasticity
An injury to a muscle or tendon, often caused by overuse, force, or stretching. Symptoms include pain, swelling, warmth, bruising, or difficulty moving the injured area.
strain
What is the R.I.C.E. method for treating muscle injuries?
- Rest: Stop all activities that cause pain.
- Ice: Reduce swelling (10-15 minutes at a time).
- Compression: Wrap the strained area to reduce swelling.
- Elevation: Keep the injured area elevated to prevent blood pooling.
Stiffness in skeletal muscles after death, caused by myosin-actin crossbridges remaining intact due to depletion of ATP. The bonds remain attached, causing rigid muscles.
Rigor mortis
When does rigor mortis disappear?
It disappears as the body decomposes.
