Chapter 12 Muscles Flashcards
What are the 3 types of muscle cell
Skeletal - attached to bones
Smooth - organs and skin
Cardiac - heart
What characteristics in skeletal
Striated
Voluntary
Somatic
What characteristics in smooth
Non-striated
involuntary
Autonomic
What characteristics in cardiac
Striated
Involuntary
Autonomic
What is a skeletal muscle cell known as
Muscle fiber
Characteristics of muscle fiber
Multiple nuclei in fiber due to fusion of multiple cells (myoblasts)
Can be up to 20cm long
Fibers usually shorter than entire muscle
What is a muscle
multiple skeletal muscle fibers bound together with connective tissue
What is muscle attached to the bone by
tendons = bundles of connective tissue consisting of collagen fibers
What do each muscle fibers contain
myofibrils which contain myofilaments
What gives the striated appearance
Alternating dark [A BANDS] and light [I BANDS]
“A” bands are
Dark
Thick filaments
Myosin
“I” bands are
Light
Thin filament
Actin
What is a neuromuscular junction
Location where muscle fiber and neuron meet
List the pathway of a AP in a muscle
Stimulation of a neuron inititates AP in muscle
- AP causes acetylcholine release into neuronmuscular junction
- ACh binds to Nicotinic Ach receptor in muscle fiber and initiates AP in muscle fiber
- Contraction of fiber
What is a motor unit
1 motor neuron + many muscle fibers
What do smaller motor units allow
finer muscle control
What is recruitment
Process of increasing the number of motor units that are active in a muscle at any given time in order to increase the strength of contraction
What are the two ways of recruitment
- Activation of more motor neurons
2. Summation
What is contained within skeletal muscle fibers
Myofibrils
What is contained within myofibrils
Myofilaments
Actin
Myosin
Myofibrils are…
bundle of myofilaments
What are the different sections of a myofibril called
sacromeres
The think dark filament has…
It forms…
Myosin
Forms cross bridges which contact thin filaments during muscle contraction
The thin light filament has…
and…
Actin
Regulatory proteins:
Troponin
Tropomyosin
What are the different Troponin proteins and what do they bind
C = binds calcium T = binds tropomyosin I = binds actin
What does tropomyosin do
blocks myosin binding site on actin
What is a sacromere
basic contractile unit in striated muscle structure
What characteristics are there for sacromere
Section of myofibril Pattern of thick and thin filaments Z lines at each end Actin is anchored to Z lines Myosin is anchored in place by titin fibers
What is the definition of contraction
Activation of the force generating sites in muscle fibers
What happens to the Z lines when actin is pulled by the myosin
Come closer together
What bands reduces in width when actin is pulled by the myosin
I bands
What must occur first in order for a contraction to occur
Corss-bridge in myosin must bind to actin
When a muscle is relaxed, what is blocked and by what
Actin is blocked
By tropomyosin
What does troponin do
holds tropomyosin in blocking position
Explain the stages of a muscle contraction
- Muscle fiber depolarised
- Signal travels down transverse tubules
- Causes release of Ca from sarcoplasmic reticulum
- Ca binds to Troponin C
- Troponin T changes shape
- Tropomyosin moves out the way
- Myosin cross-bridge with actin
Explain how myosin “cocks”
- ATP binds to myosin head
- Hydrolysis of ATP
- Myosin changes shape to become cocked
- Myosin head binds to actin via cross-bridge
- Power stroke
Explain the process of a power stroke
- ATP hydrolysis = myosin cocked
- Binding of myosin to actin releases energy
- Release in energy causes power stroke
- Actin pulled towards center of sarcomere
- A new ATP must then attach to the myosin in order to break bond between myosin and actin
What is excitation
Coupling of AP with muscle contraction
What does the transverse tubule do
Surrounds myofibrils
Brings AP into fiber
What does the sacroplasmic reticulum do
Releases Ca into fiber’s sarcoplasm
What does Ca bind to in order to stimulate a muscle contraction
Troponin C
What is a latent period
Period in between AP and contraction
List the pathway of excitation contraction coupling in a muscle (11)
- ACh released in somatic motor neuron
- Binds to nicotinic ACh in Sarcolemma
- Opens channels, Na diffuses in
- AP produced
- AP travels along T tubules
- T tubules bring AP into skeletal muscle fiber
- Depolarise membrane close to sarcoplasmic reticulum
- AP opens voltage-gated Ca channels
- Stimulates release of calcium ions
- Calcium readily diffuses into sarcoplasm to all of the troponin C binding sites
- Calcium troponin complex pulls tropomyosin out of the way in myofibril
What 4 steps follow a muscle contraction
- Muscle cell membrane repolarises
- Calcium transported back into sacroplasmic reticulum
- Tropomyosin covers binding site
- Therefore muscle relaxes
What is tension
Force exerted on an object by a contracting muscle
What is load
Force exerted on a muscle by an object
What is special between tension and load
They are opposing forces
What is Summation
Increase in muscle tension from successive APs occurring during contraction
What is recruitment
Activation of more muscle fibers due to increased stimulation
e.g. increased voltage
What is Tetanus
Maintained contraction due to repetitive stimulation
What is a twitch
Single stimulus to a muscle to generate a muscle twitch
What is unfused tetanus
Partial dissipation of elastic tension between subsequent stimuli
What is fused tetanus
no time for dissipation of elastic tension between rapidly recurring stimuli
What are the 2 types of contraction
Isometric = same size contraction Isotonic = same tension contraction
What is an isometric contraction
- Same size contraction
- Muscle develops tension but doesnt change length
- Tension = load
What is an isotonic contraction
- Same tension contraction
- Tension remains constant and muscle changes length
- Occurs when tension exceeds load
What happens when the sarcomere is short
Actin filaments lack room to slide = little tension can be developed
What happens when the sarcomere is optimal length
Lots of actin-myosin overlap = plenty of room to slide = maximum tension
What happens when the sarcomere is long
Actin and myosin do not overlap much = little tension can be developed
What are the two main ways skeletal muscles can be differentiated
Contraction speed
Pathway used to form ATP
Fast twitch fibers have
high ATPase activity
Slow twitch fibers have
Low ATPase activity
Oxidative fibers have
High capacity for aerobic respiration
Are red due to many blood vessels to provide oxygen
Glycolytic fiber have
Few mitochondria and blood vessels
Anaerobic respiration
White due to few blood vessels
Larger diameter = more filaments producing force = more tension
What are the 3 skeletal muscle fiber types
Type 1 = Slow oxidative fiber
Type 2A = Fast Oxidative fiber
Type 2X = Fast Glycolytic fiber
What is special about Type 1
What does it respond to
Fatigue resistant Small diameter Red Many mitochondria Oxidative Low glycoltic
Responds well to repetitive stimulation without becoming fatigued
What is special about Type 2A
What does it respond to
Fatigue resistant Large diameter** Red Many mitochondria Oxidative Intermediate glycoltic**
Responds quickly and to repetitive stimulation without becoming fatigue
What is special about Type 2X
What does it respond to
Fatigable Large diameter White Few mitochondria High Glycolytic
Responds to quick bursts of strong activation
Where is maximum tension generated the quickest
Fast twitch
The percentage of muscle types depends on what two factors
Genetics
Physical training
What is muscle fatigue
Decrease in muscle tension due to previous contractile activity
What contributes to muscle fatigue (4)
- Increased extracellular K+ after many APs
- Lactic acid build up = denatures proteins
- Reduced ability for SR to release Ca prevents excitation-contraction coupling
- Depletion of fuel
What is a “muscle cramp”
What causes it
Involuntary tetanic contraction
Due to electrolyte imbalance or dehydration
What is hypocalcemic tetany
What causes it
Involuntary tetanic contraction
Due to low extracellular Ca
What is muscular dystrophy
Deterioration of muscle mass
What is myasthenia gravis and what causes it
Paralysis due to decreased number of ACh receptors
What is special about cardiac muscle (8)
- Found in heart only
- Involuntary
- Contracts spontaneously - pacemaker cells
- Striated - sarcomeres
- Similar functions with troponin and tropomyosin
- Sliding filament mechanism
- Single nucleus
- Cardiac muscle cells join end to end at intercalated disks
What is special about smooth muscle (8)
- Not striated
- Single nucleus
- Arranged in layers
- Surrounds hollow structures
- Involuntary
- Uses cross bridge movements to generate force
- Calcium ions control cross bridge activity
- Different organisation of filaments and excitation-contraction coupling
How do the thick filaments in smooth muscle stack
Vertically
What is the key difference between smooth muscle and skeletal muscle
Ca mediated changes in thick filaments activate cross bridges
There is no troponin C = tropomyosin doesnt block actin
What is the process of cross bridge formation in smooth muscle starting from the SR
- Ca binds to Calmodulin
- Ca regulated enzyme phosphorylates myosin
- Phosphorylated myosin binds to actin
- Cross bridge activation
- Cross bridge generates force as long as myosin is phosphorylated
Gap junctions are located in which muscle(s)
Caridac
Smooth
Striation occurs in which muscle(s)
Skeletal
Cardiac
What is the order of most developed SR to least
Skeletal
Cardiac
Smooth
Which muscle(s) have troponin C
Skeletal
Cardiac
What muscles(s) have Ca enter the cytoplasm from the SR AND extracellular fluid
Cardiac
Smooth
Which muscle(s) can contract without stimulation
Cardiac
Smooth
