Muscular System Flashcards
What are the three types of muscle tissue? Do they do voluntary or involuntary movement? What moves?
- Skeletal muscle- voluntary, move skeletal bones
- Cardiac muscle- involuntary, heart muslce
- Smooth muscle- involuntary, walls of blood vessels, air passages, digestive tract, and urinary tracts
What four basic properties do muscle tissues share?
- Excitability- respond to stimulus (neural impulse, hormonal action)
- Contractility- ability to shorten, muscles need to pull
- Extensibility- ability to stretch away from an original position
- Elasticity- recoil back to an original position
What is excitability?
Muscle’s ability to respond to stimulus (neural impulse, hormonal action)
What is contractility?
Ability to shorten, muscles need to pull
What is extensibility?
Ability to stretch away from an original position
What is elasticity?
Recoil back to an original position
What are the functions of skeletal muscles?
- Produce skeletal movement
- Maintain posture and body position
- Support soft tissue- reinforce adipose tissue and periostea layers, transmit force to tendons, etc
- Regulate entering and exiting of material- take in food during swallowing, voiding through urination or defecation
- Maintain body temperature- heat
What is myasthenia gravis?
A disorder where certain antibodies block or destroy the receptors at the neuromuscular junction.
What is the sarcomere and what are the components?
Where the action takes place.
- Myosin (thick filament)
- Actin (thin filament)
Both are arranged in repeating units called sarcomeres, which are the fundamental unit of myofibrils.
All the myofilaments are arranged parallel to the long axis of the cell.
What are the Z-lines?
Boundary points for a sarcomere. This is where one sarcomere ends and another begins.
Describe the process of muscle contraction.
- A contracting muscle shortens in length by exerting a pull (tension)
- Caused by interactions between thick and thin filaments within the sarcomere
- Triggered by the presence of calcium ions
- Requires the presence of ATP
- When a muscle contracts, actin filaments slide toward each other
This sliding action is called the sliding filament theory
What is the sliding filament theory?
When a muscle contracts, actin filaments slide toward each other.
What are the key components needed for muscle contraction?
- Acetylcholine (ACh)
- ATP
- Calcium ions Ca2+
- Contact between/with thick and thin filaments
Do the thick and thin filaments change length during contraction?
No, only the zone of overlap changes. In the contracted state, there is much more overlap.
The neural impulse which causes the release of ________, and its subsequent binding to its receptor, is kind of like the green light that signals the muscle that it now needs to contract.
Acetylcholine
Muscle Contraction Summary
The nerve impulse ultimately causes the release of a neurotransmitter (ACh), which comes in contact with the sarcoplasmic reticulum. This causes a change in the membrane potential. The action potential spreads across the surface along the T tubules. The sarcoplasmic reticulum releases its stored calcium ions. Calcium ions bind to troponin. The bound calcium ions cause the tropomyosin molecule to roll so that it exposes the active sites on actin. The myosin heads now extend and bind to the exposed active sites on actin. This cycle is repeated. Cross-bridge binding.
Steps That Initiate a Muscle Contraction
- ACh released, binding to receptors.
- Action potential reaches T tubules.
- Sarcoplasmic reticulum releases Ca2+.
- Active site exposure and cross-bridge formation.
- Contraction begins.
Muscle Relaxation Steps (After Contraction)
Acetylcholine is broken down by acetylcholinesterase. Action potential stops. Sarcoplasmic reticulum reabsorbs calcium ions. Troponin/tropomyosin complex returns to its normal position. Active sites are blocked. Cross-bridges cannot bind to the active sites. Muscle relaxes.
Steps That End a Muscle Contraction
ACh removed by AChE.
Sarcoplasmic reticulum recaptures Ca2+.
Active sites covered, no cross-bridge interaction.
Contraction ends.
Relaxation occurs, passive return to resting length.
Motor Unit
A particular neuron and all the muscle fibers it is responsible for innervating, the size of the motor unit is variable depending on the muscle(s) being considered (think about the contrast between large and fine motor movements).
Muscle Tone
Tension when muscle is in a resting/relaxed state, always some tension to keep muscles ready to contract and move.
Muscle Spindles
Sensory fibers that monitor tone, help the body to respond to needed changes in load or posture.
Muscle Atrophy
Discontinued use of a muscle. Physical therapy and exercise help to reduce the effects of atrophy.
What are the three major types of muscle fibers?
Fast fibers, slow fibers, and intermediate fibers
