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
What are fast fibers?
Fast fibers (white fibers)/FG/Type IIb(x)- less myoglobin, quick movements, tire quickly (eye muscles for rapid movement)
What are slow fibers?
Slow fibers (red fibers)/SO/Type I- more myoglobin, large postural muscles, tire slowly (leg muscles to hold you up when standing)
What are intermediate fibers?
Intermediate fibers (pink fibers)/FOG/Type IIa- endurance
What are origins?
Fixed point of the muscle. (to the bone that is stationary)
What are insertions?
Point that moves toward the origin (to bone that will move)
What are actions?
Movements the muscle creates.
What is innervation?
The nerve that allows the muscle to work (motor neuron innervating it)
What are the four types of muscle groupings in accordance with their primary actions?
Prime movers (agonists)
Antagonists
Synergists
Fixators
What are prime movers (agonists)?
Responsible for producing a particular movement.
What are antagonists?
Actions oppose the action of the agonist.
What are synergists?
Assist the prime mover in performing an action.
What are fixators?
Agonist and antagonist muscles contracting at the same time to stabilize a joint.
Example of prime movers (agonists)
Biceps brachii
Example of antagonists
Triceps
Example of synergists
Brachioradialis
Example of fixators
Holding something in hand (wrist is staying neutral)
Example of stabilizers
Pelvic girdle, hip girdle
Aging and the Muscular System
Changes occur in muscles as we age
- Skeletal muscle fibers become smaller in diameter
- Due to a decrease in the number of myofibrils
- Contain less glycogen reserves, less myoglobin
- Less elastic, develop fibrosis
- All of the above results in a decrease in strength and endurance
- Muscles fatigue rapidly
- Ability to recover from injury decreases
- But muscle can be built with resistance training
What are the two bones that form the bony nasal septum?
Ethmoid and vomer
The lambdoid suture of the skull is primarily formed by the union of which two bones?
Parietal and occipital
What muscle type is under conscious control?
Skeletal muscle only
With which bones does the hyoid bone articulate?
It does not join any other bone
During muscle contraction, calcium ions bind to what molecule?
Troponin
The thick muscle filament is called what?
Myosin
The sella turcica feature in the skull is found on which bone?
Sphenoid
Flexion and extension fall under which category of movement?
Angular motion
What are some examples of fibrous joints in the body?
IV discs, pubic symphysis
Blood and lymph fall under what category of connective tissue?
Fluid connective tissue
What plane divides the body into left and right portions?
Sagittal plane
Consider two muscles (muscle A and muscle B). If they did directly opposite actions, what term describes the functional relationship these muscles have to each other?
Antagonistic
True/False: Spongy bone in heavier in weight compared to compact bone.
False, it would be lighter. Compact bone is more dense and therefore has greater weight.
True/False: The humerus (arm), the femur (thigh), and the ribs are all part of the appendicular skeletal system.
False, remember that the ribs are part of the axial skeletal system.
The _________ suture is found between the frontal and the parietal bones.
Coronal suture.
