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A & P - The Muscular System
Skeletal/smooth/cardiac muscle tissue, skeletal muscle activity, contraction cycle, stimulation of muscle
44
Anatomy
Undergraduate 1
08/14/2012

Additional Anatomy Flashcards

 


 

Cards

Term
Name the four tissue types
Definition

Epithelial tissue

 

Connective tissue

 

Muscle tissue

 

Neural tissue

Term
Describe the distinctive organelles of muscle cells
Definition

Sarcolemma = plasma membrane of muscle fibre

 

Sarcoplasm = cytoplasm of muscle fibre

Term
Name 3 types of muscle tissue
Definition

Skeletal

 

Cardiac

 

Smooth

Term
Name 5 characteristics of Skeletal muscle tissue
Definition
  • Large (long and cylindrical) muscle cells
  • Called muscle fibres
  • Multinucleated (just inside the plasma membrane)
  • Striated
  • Cells do not divide (microsatellite cells make new fibres)

 

Term
Give 4 functions of skeletal muscle tissue
Definition
  • Moves or stabilizes the position of the skeleton
  • Guards entrances and exits to the digestive, respiratory and urinary tracts
  • Generates heat
  • Protects internal organs
Term
How do muscle fibres develop?
Definition
Through the fusion of mesodermal cells called myoblasts
Term
What type of muscle tissue is skeletal muscle tissue?
Definition
Striated voluntary muscle
Term
What enables muscle fibre cells to contract simultaneously?
Definition
Transverse tubules that extend into the sarcoplasm and enable contraction
Term
Describe myofibrils
Definition
  • Bundles of protein filaments called myofilaments
  • Thin filaments (actin)
  • Thick filaments (myosin)
  • Myofibrils are attached to the inner surface of sarcolemma
  • When it shortens it enables muscle contraction
Term
Describe the Scarcoplasmic Reticulum
Definition
  • Where transverse tubules encircle a myofibril it is tightly bound to the membrane of the scarcoplasmic reticulum
  • Scarcoplasmic reticulum is like the smooth endoplasmic reticulum of muscle cells
  • Forms a tubular network around each myofibril
Term
What is a terminal citernae?
Definition
On either side of a transverse tubule the scarcoplasmic reticulum enlarges to form terminal citernae
Term
What is a triad?
Definition
A transverse tubule in combination with two terminal cisternae
Term
When does muscle contraction begin?
Definition
When stored calcium is released into the sarcoplasm
Term
What are sarcomeres?
Definition

Myofibrils are bundles of myofilaments (thick and thin)

 

Myofilaments are organised into repeating functional units called Sarcomeres

 

Myofibril has about 10,000 sarcomeres

Term
What do sarcomeres contain?
Definition
  • Thick filaments (myosin)
  • Thin filaments (actin)
  • Proteins that stabilise the position of thin and thick filaments
  • Proteins that regulate interactions between thin and thick filaments
  • Each sarcomere has dark bands (A bands) and light bands (I bands)
Term
What do A bands contain?
Definition

Thick filaments (myosin) at the centre of the sarcomere

 

3 subdivisions

  • M Line = proteins that connect neighbouring thick filaments
  • H band = region either side of M line, thick but not thin filaments
  • Zone of overlap = thin and thick filaments overlap
Term
I bands contain:
Definition

Thin filaments (actin) but not thick filaments extends from the A band of one sarcomere to the A band of the next sarcomere

 

Term
What is the Z line?
Definition
Boundary between adjacent sarcomeres. Interconnect filaments in adjacent sarcomeres. Thin filaments extend from here towards the zone of overlap
Term
Summarise muscle tissue in 5 layers
Definition
  • Skeletal muscle - surrounded by Epimysium, contains muscle fascicles
  • Muscle fascicles - surrounded by Perimysium, contains muscle fibres
  • Muscle fibre - surrounded by Endomysium, contains myofibrils
  • Myofibrils - surrounded by sarcoplasmic reticulum, consists of sarcomeres (z line to z line)
  • Sarcomere - contains thick filaments and thin filaments
Term
Describe Cardiac Muscle Tissue
Definition
  • Only found in heart
  • Cardiocyte - cell is smaller than skeletal muscle
  • Typically one central nucleus
  • Striations - actin and myosin (same as skeletal muscle)
  • Branched network of interconnected muscle cells (join at intercalated discs)
Term
Give two functions of cardiac muscle tissue
Definition

Circulates blood

 

Maintains blood pressure

Term
What type of muscle is cardiac muscle?
Definition
Striated involuntary muscle
Term
Describe smooth muscle tissue
Definition

Found in walls of blood vessels, respiratory, digestive systems


Cells = small, spindle shaped with a single nucleus often referred to as fusiform in shape


Can divide and regenerate


Actin and myosin are present but organised differently (no striations)


Not voluntarily controlled

 

Term
Give three functions of smooth muscle tissue
Definition
  • Moves food, urine and reproductive tract secretions
  • Controls diameter of respiratory passageways
  • Regulates diameter of blood vessels
Term
What type of muscle is smooth muscle
Definition
Non-striated involuntary muscle
Term
Describe how smooth muscle tissue contracts
Definition
  • No myofibrils and sarcomeres (therefore no striations)
  • Thick filaments scattered throughout sarcoplasm
  • Thin filaments attach to dense bodies
  • Dense bodies transmit the contracile forces between
Term
What occurs with the sarcomere of skeletal muscle fibre when it contracts?
Definition
  • The H and I bands get smaller
  • The zones of overlap get larger
  • The Z lines move closer together
  • The width of the A band remains constant
Term
What happens when the skeletal muscle fibre contracts?
Definition
  • Sliding occurs in all sarcomeres in the myofibril
  • Myofibril gets shorter
  • Muscle fibre gets shorter
  • Muscle gets shorter
  • Produces TENSION
Term
Describe the 5 steps through which neurons stimulate muscle fibres
Definition

1. Action potential arrives at the synaptic terminal

2. Acetylcholine is released. Permeability of the membrane changes and triggers the release of ACh

3. ACh molecules cross synaptic cleft and bind to ACh receptors on sarcolemma

4. The sodium ions rushing into the sarcolemma generate an action potential which spreads across each T tubule

5. Acetylcholine is broken down by Acetylcholinesterase. Now it is ready for next action potential to arrive at the synaptic terminal

Term
What is Myasthenia Gravis?
Definition
  • General muscle weakness
  • Chronic muscle fatigue from the slightest exertion
  • Begins with muscles of the head
  • Weakness results from a reduction in the number of ACh receptors
  • These are receptors on the motor end plate
Term
How does the arrival of an action potential lead to muscle contraction?
Definition
Excitation-Contraction Coupling
Term
Describe step 1 (resting state) of muscle contraction in excitation-contraction coupling
Definition
Tropomyosin strands cover the active sites on the thin filaments stopping cross-bridge formation
Term
Describe step 2 (active site exposure) of excitation-contraction coupling
Definition
  • Action potential (reaches triad)
  • Calcium ions released from cisternae of SR
  • Calcium binds to and changes shape of troponin molecule
  • Troponin molecule roles the tropomyosin from the active sites
Term
Describe step 3 (cross bridge formation) of excitation-contraction coupling
Definition
  • Myosin heads bind to active sites of F-actin
  • Contraction cycle begins
Term
What are the 3 steps of excitation-contraction coupling?
Definition

1. Resting state


2. Active site exposure


3. Cross-bridge formation

Term
Describe the 5 steps of the cross-bridge cycle in muscle contraction
Definition

1. Exposure of active sites (calcium ions released from cisternae of SR, calcium binds to and changes shape of troponin molecule, troponin molecule roles the tropomyosin from the active sites)

2. Formation of cross bridges (active sites are exposed, energized myosin heads bind with them forming cross-bridges)

3. Pivoting of myosin heads (myosin head pivots towards M line, requires energy, reffered to as power stroke)

4. Detachment of cross-bridges (ATP binds to myosin head and breaks the link to actin, the active site is now exposed again ready to form a new cross bridge)

5. Reaction of myosin (Free myosin head splits ATP into ADP and a phosphate group, energy released 'cocks' the myosin head, cycle can now be repeated)

Term
Describe the 5 steps of muscle relaxation
Definition

1. ACh broken down by AChE


2. Sarcoplasmic reticulum recaptures Ca2


3. Active sites covered, no cross-bridge interaction


4. Contraction ends


5. Relaxation occurs, passive return to resting length

 

Term
A single twitch can be divided into 3 phases
Definition

1. Latent period
Begins at stimulation
Action potential sweeps across sarcolemma
Causes SR to release calcium
Before contraction


2. Contraction phase

Tension rises to a peak


3. Relaxation phase

Calcium levels are falling, active sites are being covered, active cross-bridges decreasing, tension falls to resting

Term
What is 'treppe'?
Definition

Peak tension can increase with successive stimulation

 

(If the stimulation occurs straight after the relaxation phase of the last twitch tension increases)

 

Most skeletal muscles do not show treppe

Term
What is 'wave summation'?
Definition
If a second stimulus arrives before the relaxation phase has ended a second stronger contraction occurs.
Term
What is 'incomplete tetanus'?
Definition
If a muscle fibre is never allowed to relax, tension will rise almost to peak tension
Term
What is complete tetanus?
Definition

If a higher stimulation frequency eliminates the relaxation phase complete tetanus occurs

 

Stimuli arrive so rapidly the sarcoplasmic reticulum cannot reclaim the calcium

 

As the calcium concentration in the sarcoplasm increases contraction is prolonged making it continuous

Term
What is a 'motor unit'
Definition

All of the muscle fibres controlled by a single motor neuron is referred to as a motor unit

 

Motor unit size depends on the precision of movement required

Term
What does 'recruitment' refer to?
Definition
Increased muscular tension produced by increasing the number of active motor units
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