Exam 3: Muscle Tissue Flashcards
How does the muscular system produce motion?
Contraction and relaxation of muscles
Functions of muscle tissue
Produce skeletal movement Stabilize posture and body position Support soft tissues Guard entrances and exits Maintain body temperature Store nutrient reserves
Properties of muscle tissue
Electrical excitability
Contractility
Extensibility
Elasticity
The ability to respond to internal or external stimuli by producing action potentials
Electrical excitability
The ability to contract when stimulated by an action potential
Contractility
The ability to stretch without being damaged
Extensibility
The ability to return to original shape and size after contraction or extension
Elasticity
Types of muscle tissue
Skeletal muscle
Cardiac muscle
Smooth muscle
Skeletal muscle
Associated with skeleton and skin
Striated
Mainly voluntary control
Cardiac muscle
Located in heart
Striated
Involuntary control
Smooth muscle
Located in walls of hollow internal structures (respiratory, circulatory, digestive systems, etc. ) and in skin
Non-striated
Involuntary control
Also called muscle fibers because of their elongated shape
Muscle cells
What are the connective tissue components of skeletal muscle?
Fascia
Tendons
Deep fascia
Sheet of connective tissue surrounding a muscle
Fascia
Connects muscle to skin
Superficial fascia
Connects muscle to muscle or muscle to bone
Deep fascia
Extensions of connective tissue (fascia) that attach a skeletal muscle to the periosteum of a bone
Tendons
Deep fascia is underlaid by 3 other layers of connective tissue which are:
Epimysium
Perimysium
Endomysium
Connective tissue that surrounds the entire muscle
Epimysium
Connective tissue that surrounds groups of 10-100 muscle fibers and separates them into bundles, or fascicles
Perimysium
Connective tissue that surrounds and separate individual muscle fibers within a fascicle
Endomysium
How does the muscle tissue get nerve and blood supply?
- Somatic motor neurons stimulate muscles. Each neuron has branches that extend to individual muscle fibers.
- Each muscle supplied by one artery and one or two veins. Associated with a capillary bed that extends to all muscle fibers
What is the embryonic origin of muscle fibers?
Arise from fusion of myoblasts in embryo
Plasma membrane of muscle fibers
Sarcolemma
Invaginations of the sarcolemma extending from surface of muscle fiber inward; Open to outside of cell and Filled with interstitial fluid
Transverse tubules
Cytoplasm of muscle fibers
Richly supplied with glycogen
Richly supplied with myoglobin
Sarcoplasm
Extends length for muscle fiber
Contractile organelles of skeletal muscle fibers
Striated
Myofibril
Surrounds myofibril and is a system of fluid filled membranous sacs, similar to smooth ER; stores Ca2+
Sarcoplasmic reticulum
2 types of protein filaments that compose myofibrils
Thick and thin filaments
Functional unit of myofibril, and compartments where filaments are arranged
Sarcomeres
Each thick filament is surrounded by ____ thin filaments.
Two
Regions of the sarcomere
A band I band Zone of overlap Z disc H zone M line
Extends length of thick filaments
A line
Region with thin filaments only
I line
Region of overlap between thick and thin filaments
Zone of overlap
Region found through center of each I band
Z disc
Region with thick filaments only
H zone
Region that support proteins linking thick filaments
M line
Myofibrils include which proteins?
Contractile protein - generates force during contraction
Regulatory protein - switch contraction process on and off
Structural protein - keep thick and thin filaments in alignment
Two contractile proteins
Myosin and actin
Main component of thick filaments
Functions as motor protein
Includes tail and two “heads”
Converts chemical energy of ATP into mechanical energy of motion (production of force)
Myosin
Main component of thin filaments
Functions as anchor point for myosin
Actin
Two regulatory proteins
Troponin and tropomysin
Where do regulatory proteins occur?
Thin filament
Overview of sliding filament mechanism
- Muscles get shorter (during contraction) or longer (during relaxation) because thick and thin filaments side past one another
- Myosin heads bind to actin in thin filaments and “walk” along thin filaments, pulling thin filaments toward M line
- Sarcomeres contract
Contraction cycle (just be familiar with it)
- ) Contraction cycles begins
- Myosin head is already energized
- Ca2+ ions enter myofibril - ) Active-site exposure
- Ca2+ binds to troponin
- Troponin pulls troponin myosin away from active sites of actin - ) Cross-bridge formation
- Energized myosin heads bind to active sites of actin
- Forming cross-bridges between thick and thin filaments - ) Myosin head pivoting
- Myosin head pivoted toward M line during power stroke
- ADP and phosphate group are released - ) Cross-bridge detachment
- Another ATP binds to myosin head
- Myosin head detaches from active site of actin
- Cross-bridge is broken - ) Myosin reactivation
- Free myosin head cleaves phosphate group from ATP
- Myosin head becomes energized
Describe the excitation-contraction coupling.
Increase of Ca2+ conc. in cytosol triggers muscle contraction
Sarcoplasmic reticulum releases Ca2+ into cytosol via Ca2+ release channels
Ca2+ release channels open in response to a muscle action potential (electrical excitation)
Nerve action potential propagating triggers a muscle action potential via a ____________.
Neurotransmitter
Synapse between neuron and muscle fiber
Neuromuscular junction (NMJ)
Neurotransmitter responsible for communication across NMJ
Acetylcholine
Describe the events at the NMJ
- ) ACh packaged in vesicles at synaptic end bulb of neuron
- ) Action potential reaches synaptic end bulb of neuron
- ) Action potential triggers release of ACh into synaptic cleft via exocytosis
- ) ACh diffuses across synaptic cleft and binds to receptors in sarcolemma of muscle fiber
- Na+ channels in sarcolemma open, and Na+ enters sarcoplasm - ) Acetylcholinesterase (AChE) breaks down ACh
What breaks down ACh?
Acetylcholinesterase (AChE)
Force of contraction of a muscle varies due to:
Nutrient and oxygen availability
Frequency of stimulation (rate at which action potentials arrive at NMJ)
Amount of stretch before contraction
Number of muscle fibers contracting
Contraction of all muscle fiber in response to one nerve action potential
Twitch contraction
Three phases of the twitch contraction
Latent period
Contraction period
Relaxation period
What happens when there are 20-30 action potentials per second?
Incomplete (unfused) tetanus
Sustained but wavering contraction
Muscle fibers can’t completely relax between stimuli
What happens when there are 80-100 action potentials per second?
Complete (fused) tetanus
Sustained, unwavering contraction
Muscle fibers can’t relax at all between stimuli
