lecturetest_04_muscle

Muscle plasma membrane

• 1. Excitability
• 2. Contractility
• 3. Extensibility
• 4. Elasticity 

• 1. Movement
• 2. Posture
• 3. Stabilize Joints
• 4. Generate Heat 

Surrounding each individual muscle fiber.

Fine sheath of CTT composed of reticular fibers & loose CT.

Surrounds groups of muscle fibers (fasicles)

Fibruous CT 

Surrounds the entire muscle

dense irregular CT (mostly collagen bundles)

Each Skeletal muscle is covered with this tough fibrous layer of CT. May extend past the length of the muscle and attach that muscle to a bone.

Less moveable site on bone at which tendons attach

helps to stabilize the muscle 

site on bone which tendons attach to allow muscle contraction and to move bone around a joint

• - tough collagen fibers
• - found at end of muscle
• - epimysium comes together to form a tendon
• - CT of muscle wrappings continuous with tendons
• - no muscle fibers 

myoblasts that do not fuse, but can aid in repair and some regeneration in adults.

Satellite cells can divide and fuse to fibers for repair but cannot generate new fibers 

Cytoplasm of muscle cells

granules that store glycogen (which can be converted to glucose and then ATP)

contained in the sarcoplasm 

oxygen binding protein

red pigment (stores Oxygen) 

Smooth ER of muscle cell

surrounds each myofibril 

Plasma member of muscle fiber

forms a membrane connection between each sarcomere by means of T tubules 

membranous channels that extend into the sarcoplasm as invaginations continuous with muscle cell sarcolemma

filled with extracellular fluid from cell's exterior

penetrate into cell's interior at A band - I band junction

T-tubule with Sarcoplasmic Reticulum on each side

Contains integral membrane proteins act as voltage sensors

Foot proteins are gated channels that regulate Ca release from Sarcoplasmic Reticulum

Smallest contractile unit of a muscle

Region between two succesize Z-discs.

• Ca ions are pumped into the sarcomere from the SR terminal cisternae to begin muscle contraction.
•  

Thin Filament

• Thick Filament
• Has Heads and Tails 

• Dark Band
• Actin and Myosin fibers overlapping

• Light band
• actin filaments only 

• Darker midline in the I-band
• Formed by coin shaped sheet of proteins of a-actinin 
• helps keep the actin fibers in place

elastic filaments that attach thing & thick filments to the Z-disc

• lighter region in the middle of A band
• Thing filaments do not overlap thick filaments
• No myosin heads, only tails 

• darker region in middle of H-zone
• Composed of myomesin - helps hold adjacent filmanents together 

• Two sites:
• a. Actin binding site
• b. ATP binding site 

• Thread like strands of protein that spiral around the actin
• covers actin binding site when muscle is at rest
• blocks myosin cross bridge from binding to actin molecule.

• Polypeptide complex located on tropomyosin
• Binds Ca
• Inhibits myosin binding by binding to actin

• Thin filaments slide past the thick filaments
• in relaxed state thin and thick overlap only slightly 

Stimulate skeletal muscle

Where motor neuron meets muscle fiber. 

Part of the sarcolemma that is highly folded and contains acetylcholine (ACh) receptors and helps form the neuromuscular junction

small membrane sacs filled with the neurotransmitter Acetylcholine (ACh) within the axon terminals of the motor neuron.

tiny space that separates the axon terminal ends and muscle fibers.

Filled with a gel like extracellular fluid composed of collagen fibers and glycoproteins

• 1. Voltage-regulated Ca channels open allow Ca to enter the axon terminal
• 2. Ca inside the axon terminal causes synaptic vesicles to fuse the axon terminal plasma membrane
• 3. Fusion relases ACh into synaptic cleft via exocytosis
• 4. ACh diffuses across the synaptic cleft to ACh receptors on the sarcolemma (motor end plate)
• 5. Binding of ACh to its receptors initiates an ACTION POTENTIAL in the muscle
• 6. ACh is destroyed by Acetylcholinesterase
•  

• A local electrical event
• Interior of sarcolemma becomes less negative
• More Na diffuses in than K out.
• Depolarization

A transient depolarization event that includes polarity reversal of a sarcolemma and the propagation of an action potential along the entire membrane.

• End plate potentials spreads to adjancent sarcolemma
• Causes voltage gated Na channels to open
• Na leaves the cell which causes a decrease in membrane voltage
• Once critical threshold is reached an action potential is generated 

• Local depolarization wave contenues to spreads changing the permeability of the sarcolemma
• More voltage gated Na channels open in the adjacent patch causing it to depolarize
• Once initiated the action potential is unstoppable and results in muscle contraction 

• Occurs immediately after depolarization wave passes
• Na+ channels close
• Voltage gated  K+ channels open
• K+ diffuses out of the cell restoring the resting polarity
• must occur before muscle can be stimulated again (refractory period) 

Sequence of events by which an action potential occurs and depolarizes the sarcolemma which leads to the sliding of actin and myosin myofilaments

Between Action Potential and muscle shortening 

• ACh is released from axon terminal of motor neuron
• ACh diffuses across synaptic cleft
• ACh binds onto receptor sites on sarcolemma
• Na+ ions initiate and generate an Action Potential
• Action Potential is propogated along the sarcolemma
• Action Potential travels down the T-tubules
• Voltage sensitive t-tubule proteins change shape and cause SR foot proteins to change shape as well
• SR releases Ca+ ions in massive amounts
• Ca+ ions diffuse into sarcomeres and bind to troponin
• Troponin changes shape and removes blocking action of tropomyosin exposing the actin binding site
• myosin binds to actin (cross bridge forms) 

ATP binds to myosin to release, cock, and reposition the myosin head on the actin

• Following death...
• Ca leaks out of SR causes muscles to contract
• Ca binds to troponin, tropomyosin frees actin, cross bridge forms but cannot detach because no ATP
• Peak rigidity at 12 hours
• Dissipates over next 48-60 hours as proteins breakdown 

The force exerted by a contracting muscle on an object

Nerve and all the muscle cells it makes a neuromuscular junction with

Avg # of muscle fibers per motor unit is 150 muscle cells/neuron 

• Coarse movements
• found in large weight-bearing muscles (thighs, hips) 

• Fine movements
• example: fingers  

Response of a muscle to a single, brief threshold stimulus (AP) on it's motor neuron

• 1. Latent Period
• - Tension begins, no change in length

• 2. Period of Contraction
• - Tension increases and peaks, muscle shortens

• 3. Period of Relaxation
• - muscle relaxes, tension decreases, Ca reabsorbed

It is the variation of stimulation needed in skeletal muscle contraction in order to have controlled movement.

• Muscle can be graded in 2 ways
• 1) changing frequency of stimulation
• 2) changing strength of stimulation 

• Muscle contractions are summed
• muscle is already partially contracted when 2nd stimulus is delivered and ever more Ca is released into the cytoplasm from SR
• Muscle does not have time to completely relax
• Increases contractile force 

graphic recording of contractile activity

the muscle relaxes slightly before the next contraction

the muscle does not relax at all betweeen stimuli

maximal tension is reached 

muscle is unable to contract and its tension drops to zero

due to inability to produce enough ATP 

• Steplike increase in tension after repeated stimulation of a muscle even though muscle is allowed to complete each relaxation phase
• muscle enyzmes become more efficient because heat is increased as muscle contracts 
• Contractions increase because there is increased availability of Ca. 

• 1. Treppe - tension due to warming and increased enyzme efficiency
• 2. Incomplete Tetanus - Rapid cycles but some relaxation
• 3. Complete Tetanus - Smooth sustained contraction
• 4. Fatigue - tension decreases due to low ATP and buildup of lactic acid

• caused by increasing strength of stimulus
• more motor units contracting simultaneously
• smallest muscle fibers activated first followed larger fibers 

• State of partial contraction even when at rest which does not produce active movements
• helps stabilize joints and maintain posture 

• results in increases in muscle tension but no lengthening or shortening of the muscle occurs
• example: standing 

• Results in movement occuring at the joint
• example: walking

Type of Isotonic contraction in which Lengthening of the muscle occurs

Type of isotonic contraction in which Shortening of the muscle occurs

• 1. From energy of creatine phosphate (15 seconds worth)
• 2. From anaerobic glycolysis ( 30-40 sec. worth)
• 3. From aerobic cellular respiration

Point where muscle start to use the anaerobic glycolysis pathway

length of time a muscle can continue to contract using aerobic pathway

Extra oxygen needed for a muscle to return to a resting state

• contract slowly
• fatigue resistant 

• Contract quickly
• moderate resistance to fatigue
• Not found in humans 

• Contract quickly
• easily fatigued 

• Muscles get larger
• from resistance training
• increased mitochondria, increased myofilaments
• increase in glycogen stored in muscle 

• increase in slow oxidative fibers
• increase in capillary penetration, number of mitochondria, and increased synthesis of myoglobin 

Takes place place of troponin in Smooth muscle

• Smooth muscle responds to a stretch only briefly and then adapts to new length
• retains its ability to contract
• Allows stomach, bladder, etc, to temporarily store contents

• Single unit
• contract rhythmically as a unit
• electrically coupled to one another via gap junctions
• Multi-unit 
• gap junctions are rare

• Skeletal - can not divide
• Cardiac - can not divide
• Smooth - can divide and regenerate

• Alternating contractions and relaxations of smooth muscles that maix and squeeze substances through the lumen of hollow organs
• When the longitudinal layer contracts -> organ dilates and contracts
• When the circular layer contractions -> orgran constricts and elongates