Muscular System
Movement: bones or fluids/blood
Balance: maintaining posture and body position
Stabilizing joints
Heat generation (skeletal)
Excitability (responsiveness/irritability): receive and respond to stimuli
Contractility: shorten when stimulated
Extensibility: ability to be stretched
Elasticity: recoil to resting length
Skeletal muscle: attached to bones and skin; striated; voluntary
Cardiac muscle: only in the heart; striated; involuntary; insulated discs
Smooth muscle: walls of hollow organs; not striated; involuntary
“myo”/ “mys” = muscle
“Sarco” = flesh
A single muscle fiber is enclosed by the endomysium
A muscle fiber is the same thing as a muscle cell
The perimysium wraps around a bundle of muscle fibers(fascicle)
The entire muscle is covered by the epimysium which blends into muscle attachment
Sarcolemma: specialized plasma membrane
Myofibrils: long organelles
Sarcoplasm: cytoplasm
Sarcoplasmic reticulum: specialized smooth ER; stores and releases calcium
T-tubules: allow electrical nerve transmissions to reach deep interior of muscle fiber
Sarcomere: contractile unit of a muscle fiber
Myofibrils align to give distinct banding
I band = light; thin filaments
A band = dark; thick filaments
H zone = bare sone, not thin filaments at rest
Sarcomere = contractile unit of a muscle fiber
Myosin: thick filaments, ATPase enzymes, myosin heads & tails
Actin: thin filaments, anchored to z discs
Myofibrils thick & thin filaments
Myosin - thick filaments
During contraction, the heads link thick and thin filaments together, forming cross bridges
Offset from each other -> staggered array of heads at different points along thick filament
Actin - thin filaments
G actin subunits bear sites for myosin head
G actin subunits link together to form long, fibrous F (filamentous) actin -> two F actin strands twist together to form a thin filament
Nerve stimulus --> action potential
Skeletal muscles stimulated by motor neuron(nerve associated with motor cells)
Motor unit = one motor neuron and all he skeletal muscle cells stimulated by that neuron
Neuromuscular junction = association site of axon terminal of motor neuron and muscle
Synaptic cleft = gap between nerve and muscle
Activation by nerve causes myosin heads to attach to binding site on the actin(cross-bridge)
Action potential reaches axon terminal of motor neuron (phone ringing)
Calcium (Ca+2) channels open and Ca2+ enters the axon terminal (someone picks up the phone)
Ca2+ entry causes some synaptic vesicles to to release their contents(acetylcholine, a neurotransmitter) by exocytosis (calcium coming in, forces acetylcholine out)
Acetylcholine diffuses across the synaptic cleft and binds to the receptors in the sarcolemma
When ACh binds to the receptors and the channel opens which allows sodium to comes in and potassium leaves; more sodium comes in than potassium leaving(more positive coming in then leaving) making the inside the of the cell positive; the change in charge between the outside and inside of the cell
ACh effects are ended by its breakdown in the synaptic cleft by the enzyme acetylcholinesterase
Muscle fiber contraction id “all or none”
Not all muscle fibers/cells may be stimulated at the same interval
Different combinations of muscle fibers contracting may give differing responses (graded responses; as in a scale)
Graded responses depend on: the frequency of muscle stimulation(how often are we getting simulation); and number of stimulated muscle cells at one time(how many are being stimulated)
Type | Definition |
|---|---|
Twitch | Single contractionBrief contractionNot a normal muscle function |
Summing | One contraction immediately after anotherDoes not return to resting stateEffects are additive |
Unfused Tetanus | Incomplete, not smoothSome relaxation between contractionsNerve stimuli arrive faster than summing |
Fused Tetanus | Complete, smoothNo relaxation in between contractionsSustained muscle contractionHeld contraction: sitting up |
Isotonic contractions:
Myofilaments slide past each other
Muscle shortens and movement occurs
Ex: you pick up, put down; includes reps;
Isometric contractions:
Increased tension in muscles
Muscle is unable to shorten or produce movement
Ex: wall sit; pushing
Fibers contract at different times to provide muscle tone and be constantly ready (some fibers are contracted even in a relaxed muscle)
Common challenges for low muscle tone:
Poor posture
Limited muscle strength
Poor core stability
Increased joint flexibility
Gross motor delays
Easily fatigued
Stronger, more flexible, resistance to fatigue
Makes body metabolism more efficient
Improves digestion and coordination
Increases size, increase strength
Strengthen and stabilizes
Helps posture
Muscle cells store CP (high energy molecule)
After ATP is depleted, ADP is left
CP transfers a phosphate group to ADP, to regenerate ATP
CP supplies are exhausted in less than 15 seconds
About 1 ATP is created per CP
Reaction that breaks down glucose without oxygen
Glucose broken down to pyruvic acid to produce about 2 ATP
Pyruvic acid is converted to lactic acid
Reaction is fast but not efficient, requires huge amounts of glucose, and leads to muscle fatigue
Slower reaction
Requires continuous oxygen
Glucose is broken down
A series of metabolic pathways occur in the mitochondria
Releases lots of energy (about 32 ATP)
CO2 and H2O are produced
Common cause for muscle fatigue is oxygen debt
Oxygen is required to get rid of accumulated lactic acid
Increasing acidity(from lactic acid + lack of ATP = less muscle contraction
Fatigued muscles cannot contract even with a stimulus
Muscles cross at least one joint
Bulk of muscle proximal to joint crossed
At least 2 attachments (origin & insertion)
Muscles can only pull
Insertion moves toward origin
Prime mover: major responsible for movement
Antagonist: opposes or reverses prime mover
Synergist: aids/in sync with prime mover and prevents rotation
Fixator: stabilizes origin of prime mover
Recruitment - is the ability to activate more motor units as more force (tension) needs to be generated
Atrophy - muscles will not get or stay big if stress is not apple(if you don’t workout)
Hypertrophy - occurs when a muscle is “stressed”(strong demand on the muscle)
Causes more myofilaments/myofibrils to be produced within muscle fibers
Allows for more “cross bridges” resulting in more force (strength) as well as larger size
Muscle tear: tear a muscle cell from the tendon
Literal translation: rigor = intense/hard; mortis = mortal/intense: = hard death
3 - 12 hours after death
Body stiffens
Dying cells let Ca2+ levels rise → muscles contract
ATP production stops at death → actin & myosin are locked; muscles stay contracted
48-60 hours after death
Muscle proteins breakdown
Rigor mortis ends
Arrowhead poison used by South American Indians
Binds to ACH receptors on motor end plate (muscles cannot contract): the nerve knows we have to move, the nerve sends the action potential but it doesn't allow the action potential to reach the sarcomere so muscles don’t contract
Causes cardiac and respiratory arrest
Similar chemicals are used in medicine for procedures like intubation
Many nerve gasses have a similar effect by inhibiting acetylcholinesterase
Acute(small) muscle pain
Immediate pain (during or directly after use)
Longer contraction
Due to deficient blood supply
Delayed muscle pain
Delayed 24-48 hours
Do activity that hasn’t been done in a while
Tear muscle cells and fibers
Tissue swells
Sex-linked recessive disorder
Usually diagnosed around 2 years old
Lack dystrophin (protein that helps stabilize the sarcomere)
Initially muscles enlarge due to fat and connective tissue deposit
Muscle fibers degenerate
Movement: bones or fluids/blood
Balance: maintaining posture and body position
Stabilizing joints
Heat generation (skeletal)
Excitability (responsiveness/irritability): receive and respond to stimuli
Contractility: shorten when stimulated
Extensibility: ability to be stretched
Elasticity: recoil to resting length
Skeletal muscle: attached to bones and skin; striated; voluntary
Cardiac muscle: only in the heart; striated; involuntary; insulated discs
Smooth muscle: walls of hollow organs; not striated; involuntary
“myo”/ “mys” = muscle
“Sarco” = flesh
A single muscle fiber is enclosed by the endomysium
A muscle fiber is the same thing as a muscle cell
The perimysium wraps around a bundle of muscle fibers(fascicle)
The entire muscle is covered by the epimysium which blends into muscle attachment
Sarcolemma: specialized plasma membrane
Myofibrils: long organelles
Sarcoplasm: cytoplasm
Sarcoplasmic reticulum: specialized smooth ER; stores and releases calcium
T-tubules: allow electrical nerve transmissions to reach deep interior of muscle fiber
Sarcomere: contractile unit of a muscle fiber
Myofibrils align to give distinct banding
I band = light; thin filaments
A band = dark; thick filaments
H zone = bare sone, not thin filaments at rest
Sarcomere = contractile unit of a muscle fiber
Myosin: thick filaments, ATPase enzymes, myosin heads & tails
Actin: thin filaments, anchored to z discs
Myofibrils thick & thin filaments
Myosin - thick filaments
During contraction, the heads link thick and thin filaments together, forming cross bridges
Offset from each other -> staggered array of heads at different points along thick filament
Actin - thin filaments
G actin subunits bear sites for myosin head
G actin subunits link together to form long, fibrous F (filamentous) actin -> two F actin strands twist together to form a thin filament
Nerve stimulus --> action potential
Skeletal muscles stimulated by motor neuron(nerve associated with motor cells)
Motor unit = one motor neuron and all he skeletal muscle cells stimulated by that neuron
Neuromuscular junction = association site of axon terminal of motor neuron and muscle
Synaptic cleft = gap between nerve and muscle
Activation by nerve causes myosin heads to attach to binding site on the actin(cross-bridge)
Action potential reaches axon terminal of motor neuron (phone ringing)
Calcium (Ca+2) channels open and Ca2+ enters the axon terminal (someone picks up the phone)
Ca2+ entry causes some synaptic vesicles to to release their contents(acetylcholine, a neurotransmitter) by exocytosis (calcium coming in, forces acetylcholine out)
Acetylcholine diffuses across the synaptic cleft and binds to the receptors in the sarcolemma
When ACh binds to the receptors and the channel opens which allows sodium to comes in and potassium leaves; more sodium comes in than potassium leaving(more positive coming in then leaving) making the inside the of the cell positive; the change in charge between the outside and inside of the cell
ACh effects are ended by its breakdown in the synaptic cleft by the enzyme acetylcholinesterase
Muscle fiber contraction id “all or none”
Not all muscle fibers/cells may be stimulated at the same interval
Different combinations of muscle fibers contracting may give differing responses (graded responses; as in a scale)
Graded responses depend on: the frequency of muscle stimulation(how often are we getting simulation); and number of stimulated muscle cells at one time(how many are being stimulated)
Type | Definition |
|---|---|
Twitch | Single contractionBrief contractionNot a normal muscle function |
Summing | One contraction immediately after anotherDoes not return to resting stateEffects are additive |
Unfused Tetanus | Incomplete, not smoothSome relaxation between contractionsNerve stimuli arrive faster than summing |
Fused Tetanus | Complete, smoothNo relaxation in between contractionsSustained muscle contractionHeld contraction: sitting up |
Isotonic contractions:
Myofilaments slide past each other
Muscle shortens and movement occurs
Ex: you pick up, put down; includes reps;
Isometric contractions:
Increased tension in muscles
Muscle is unable to shorten or produce movement
Ex: wall sit; pushing
Fibers contract at different times to provide muscle tone and be constantly ready (some fibers are contracted even in a relaxed muscle)
Common challenges for low muscle tone:
Poor posture
Limited muscle strength
Poor core stability
Increased joint flexibility
Gross motor delays
Easily fatigued
Stronger, more flexible, resistance to fatigue
Makes body metabolism more efficient
Improves digestion and coordination
Increases size, increase strength
Strengthen and stabilizes
Helps posture
Muscle cells store CP (high energy molecule)
After ATP is depleted, ADP is left
CP transfers a phosphate group to ADP, to regenerate ATP
CP supplies are exhausted in less than 15 seconds
About 1 ATP is created per CP
Reaction that breaks down glucose without oxygen
Glucose broken down to pyruvic acid to produce about 2 ATP
Pyruvic acid is converted to lactic acid
Reaction is fast but not efficient, requires huge amounts of glucose, and leads to muscle fatigue
Slower reaction
Requires continuous oxygen
Glucose is broken down
A series of metabolic pathways occur in the mitochondria
Releases lots of energy (about 32 ATP)
CO2 and H2O are produced
Common cause for muscle fatigue is oxygen debt
Oxygen is required to get rid of accumulated lactic acid
Increasing acidity(from lactic acid + lack of ATP = less muscle contraction
Fatigued muscles cannot contract even with a stimulus
Muscles cross at least one joint
Bulk of muscle proximal to joint crossed
At least 2 attachments (origin & insertion)
Muscles can only pull
Insertion moves toward origin
Prime mover: major responsible for movement
Antagonist: opposes or reverses prime mover
Synergist: aids/in sync with prime mover and prevents rotation
Fixator: stabilizes origin of prime mover
Recruitment - is the ability to activate more motor units as more force (tension) needs to be generated
Atrophy - muscles will not get or stay big if stress is not apple(if you don’t workout)
Hypertrophy - occurs when a muscle is “stressed”(strong demand on the muscle)
Causes more myofilaments/myofibrils to be produced within muscle fibers
Allows for more “cross bridges” resulting in more force (strength) as well as larger size
Muscle tear: tear a muscle cell from the tendon
Literal translation: rigor = intense/hard; mortis = mortal/intense: = hard death
3 - 12 hours after death
Body stiffens
Dying cells let Ca2+ levels rise → muscles contract
ATP production stops at death → actin & myosin are locked; muscles stay contracted
48-60 hours after death
Muscle proteins breakdown
Rigor mortis ends
Arrowhead poison used by South American Indians
Binds to ACH receptors on motor end plate (muscles cannot contract): the nerve knows we have to move, the nerve sends the action potential but it doesn't allow the action potential to reach the sarcomere so muscles don’t contract
Causes cardiac and respiratory arrest
Similar chemicals are used in medicine for procedures like intubation
Many nerve gasses have a similar effect by inhibiting acetylcholinesterase
Acute(small) muscle pain
Immediate pain (during or directly after use)
Longer contraction
Due to deficient blood supply
Delayed muscle pain
Delayed 24-48 hours
Do activity that hasn’t been done in a while
Tear muscle cells and fibers
Tissue swells
Sex-linked recessive disorder
Usually diagnosed around 2 years old
Lack dystrophin (protein that helps stabilize the sarcomere)
Initially muscles enlarge due to fat and connective tissue deposit
Muscle fibers degenerate
