Skeletal muscle
Striated and voluntary
Attached to bone
Functions of muscle
Generate force
Produce movement
Produce heat
Smooth muscle
No striated and involuntary
Ex. Peristalsis, vasodilation
Cardiac muscle
Striated and involuntary
Muscle consists of a number of muscle fibers lying parallel to one another held together by _________
Connective tissue
Muscle fiber
Single muscle cell
Multinucleated
May have >100
Formed from my oblasts (embryonic cells)
Sarcoplasmic
Cytoplasm within muscle cell
Sarcoplasmic reticulum
- Modified Endoplasmic reticulum
- Ends of segments expand to form saclike regions - terminal CISTERNAE
- System of tunnels
Transverse tubules
Penetrate into muscle fiber from sarcolemma
- action potential on surface membrane spreads down into t-tubule
Transverse tubules - spread of AP down a t tubule triggers ________________
Release of calcium from SR into Sarcoplasm
Myofibrils
Contractile elements of muscle fiber
Contains the myofilaments
Thick filaments
Myosin
Thin filaments
Actin
Sarcomere
Functional unit of skeletal muscle
- found between two z-lines (connects thin filaments of two adjoining sarcomeres)
A band
Made up of thick filaments along with portions of thin filaments that overlap on both ends of thick filaments
H zone
Lighter area within middle of A band where thin filaments do not reach
Myosin only
M line
Extends vertically down middle of A band within center of H zone (middle)
I band
Consists of remaining portion of thin filaments that do not project into A band (actin only )
Proteins in muscle (list 3)
Contractile
Regulatory
Structural
Myosin
- golf club
- component of the thick filament
- tails oriented toward center of filament and globular heads protrude outward at regular intervals
- heads form cross bridges between thick and thin filaments
- has two important sites critical to contractile process
Two critical sites for contractile process of myosin
- actin binding site
- myosin ATPase site
ATPase of myosin
- splits ATP into ADp and Pi
- energy released is transferred to the myosin head
- this causes the myosin head to be cocked
- analogy - pulling back a rubber band
Actin
- spherical in shape
- contains two other regulatory proteins
- each actin molecule has special binding site for attachment with myosin cross bridge (actin active site)
regulatory proteins - found on _______
thin filament
tropomyosin
- thread-like molecules that lie end to end alongside groove of actin spiral
- regulatory protein
- covers actin active sites blocking interaction that leads to muscle contraction
troponin
- thumb tack
- regulatory protein
- made of three polypeptide units:
- binds to tropomyosin, actin, and calcium
troponin - when not bound to _____, troponin stabilizes tropomyosin in blocking position over actin’s cross-bridge binding sites
calcium
when calcium binds to _____, ________ moves away from blocking position
troponin
tropomyosin
with tropomyosin out of the way, _____ and ______ are free to interact
actin
myosin
structural protein - ______
titin
extends in both directions from M line along length of thick filament to Z lines at opposite ends of sarcomere
two important roles of titan
- stabilize myosin
2. acts like a spring to provide elasticity
excitation - contraction coupling
how APs cause contraction
sliding filament mechanism
how the sarcomere shortens
- how do myosin and actin interact to have this happen
muscle contraction steps
- AP travels down motor neuron to NMJ where synaptic transmission occurs
- AP travels down T tubules
- Ca+ released from SR
- Ca+ binds with troponin and tropomyosin moves away from actin
- Actin active sites binding sites are exposed
- myosin crossbridges bind with actin
- ADP and Pi are released from myosin to change myosin’s shape
- myosin head bends toward center of sarcomere = power stroke
- actin slides over myosin
- new ATP binds to myosin to detach it from actin
- cycle is repeated
contraction continues if ____ is available and ____ level in sarcoplasm is high
ATP
Ca+
during shortening: Z lines ________
get closer
during shortening: H zone ______
shortens
during shortening: A _____
same
shortening: I band _____
shortens (only actin)
muscle relaxation steps
- motor neuron AP stops
- AChE breaks down ACh at NMJ
- muscle fiber AP stops
- reuptake of Ca+ into SR
- TT complex cover actin active sites
rigor mortis
state of muscle rigidity post death
- there is no ATP being produced
- Ca+ leaks out of SR
- sliding filament mechanism begins
- no ATP to break crossbridges
length tension relationship
sarcomeres can generate the most tension when the overlap of filaments is optimal
tension generated is determined by _______
the number of crossbridges that can be formed
finely controlled movement
contain fewer fibers per motor unit
coarsely controlled movement
have larger number of fibers per motor unit
twitch
- brief, weak contraction
- produced from single AP
- too short and too weak to be useful
- normally does not take place in body
- ex. gastrocnemius in frogs
twitch summation
if the muscle fiber is stimulated before it has completely relaxed
- results from sustained elevation of cytostolic calcium
tetanus
sustained contraction
- occurs if muscle fiber is stimulated so rapidly that it does not have a chance to relax between stimuli
- contraction is usually 3 to 4 times stronger than a single twitch
- caused by greater crossbridge cycling
- maximum calcium release and prolonged removal
what causes power stroke?
when ADP and Pi leave
isotonic muscle contraction
muscle tension remains constant as muscle changes length
ex. angle changes
isometric contraction
muscle length remains constant to generate force
ex. when you plant your foot
steps requiring ATP
splitting of ATP by myosin
binding of ATP to myosin
active transport of Ca+
steps requiring ATP: splitting of ATP by myosin
provides energy that leads to power stroke (cock the head)
steps requiring ATP: binding of ATP to myosin
to detach from actin
steps requiring ATP: active transport of Ca+
back into SR during relaxation depends on energy derived from breakdown of ATP
3 biochemical pathways: transfer of high-energy phosphate from ______ to ADP
PC
- < 1 minute (amount of ATP that lasts)
- first energy at onset of x - used for short-burst, high-intensity x
creatine
molecule capable of storing ATP energy
- creatine + ATP –> PC + ADP
creatine phosphate
molecule with stored ATP energy
3 biochemical pathways: oxidative phosphorylation
(CAC and ETC)
- takes place within muscle mitochondria IF sufficient O2 is present
- fuel from glucose/glycogen or fatty acids
- relatively slow to generate ATP
- aerobic exercise - sustainable, non-fatiguing, system working most to produce ATP
3 Biochemical pathways - Glycolysis
- supports high-intensity exercise, burst of power, quick to fatigue (anaerobic exercise)
- much faster than oxidative phosphorylation
muscle fatigue
when exercising muscle can no longer respond to stimulation
- defense mechanism that protects muscle from reaching point at which it can no longer produce ATP
- underlying causes of muscle fatigue are unclear
slow oxidative fibers (type 1)
dark (red meat)
- low myosin ATPase activity
- slow
- high to fatigue
- high oxidative phosphorylation
- many mitochondria
- many capillaries
- high myoglobin content
fast oxidative fibers (type IIa)
- high myosin ATPase activity
- fast
- high oxidative phosphorylation capacity
- many mitochondria
fast glycolytic fibers (type II x)
- high myosin ATPase activity
- fast
- low to fatigue
- few mitochondria
- few capallaries
produce ATP by ________
oxidation phosphorylation
smooth muscle: found in ______
walls of hollow organs and tubes
smooth muscle characteristics
- spindle shaped cells
- no sarcomeres
- circular and longitudinal fibers to allow for peristalsis
- thin filaments contain tropomyosin, but lack troponin
smooth muscle: Ca+ binds to _______
calmodulin
smooth muscle: muscle contractions are _______
slow and sustained
2 types of smooth muscle: multiunit
- in large blood vessels
- in large airways to lungs
- function independantly
- must be stimulated by nerves
- in order to get contraction, a nerve has to talk to it
2 types of smooth muscle: single unit
- visceral smooth muscle (in guts)
- contract as a single unit
- exhibit pacemaker activity
- arranged in sheets
- will still contract if no nerves stimulate it
steps in smooth muscle contraction
- AP causes voltage gated Ca+ channels to open
- Ca+ in the cell interacts with calmodulin
- Ca+ calmodulin complex activates enzymes
- causes myosin head to be phosphorylated
- myosin interacts with actin
- contractions are slow and sustained
