Muscular System Flashcards
3 types
Skeletal, Smooth, Cardiac
Striations are in _____ muscle
Skeletal and Cardiac
Intercalated disks are in the _______ muscle
Cardiac
Skeletal muscle fiber traits
Multinucleated, mitochondria, transverse(t) tubules
Sarcolemma
Plasma membrane in skeletal muscle
Sarcoplasm
Cytoplasm in skeletal muscle
Smooth e.r in skeletal muscle
Sarcoplasm reticulum
T tubules
Channels made up of membrane that send action potential from sarcolemma to Sarcoplasm reticulum
Traits of skeletal muscle
Sarcomeres, myofibrils, striations
Sarcomeres
Form myofibril, smallest contractile unit of muscle
Myofibrils
Contractile organelles, cause striations
Striations
Caused by myofibrils, thick and thin filaments
Contraction
Activation of force generating sites within muscle fibers (cross bridges)
Motor unit
Motor neuron and skeletal muscle fibers it innervates
Steps of muscle contraction
- ATP binds to myosin head
- ATP broken down into ATP+ phosphate
- Myosin head extends and binds to actin filament
- ADP and phosphate detach from myosin head
- M.H returns to compact formation and pulls actin filament as it does
- Myosin head detaches from actin filament when ATP binds again
Cardiac Muscle
Striated, use sliding filament method to contract
1-2 central nuclei
Branched w intercalated disks
Desmosomes and gap junctions
Absolute refractory period is 250 milli, prevent tetanic contractions
Nodal cells
Stimulate own action potentials in the heart (automaticity) for the heart
Single unit smooth muscle
Respond to stimuli as single unit bc cells are connected by gap junctions
Multi unit smooth muscle
Respond to stimuli independently, few gap junctions
Response (excitatory or inhibitory) depends on ________________
Receptors the chemical receptors bind to and what mechanism they activate
A single motor neuron connects to _______ muscle fiber
Many
Each muscle fiber is connected to more than one motor neuron.
False
When an action potential occurs in a _______ all the _________ contract
Motor neuron, muscle fibers (the muscle fibers are the h*es that copy)
There’s are many motor units within a muscle
True
Skeletal muscle are only activated by action potentials from neurons.
True
Alpha motor neurons
Neurons whose axons activate skeletal muscle fibers
Where are the cell bodies of (alpha) motor neurons located?
Brain stem and spinal cord
The axons of the motor neurons are ________ to allow ________
Myelinated, signals to travel fast
Neuromuscular junction
Junction between axon terminal and muscle cell, transport vesicles with acetylcholine
Events at N.M junction
Action potential flys down axon, voltage gated calcium channel open and calcium rushes into cell, The change in potential releases ACh from terminals into NMJ, ACh binds to receptors on muscle cells, Sodium channels open, sodium rushes into cell, change in potential causes muscle cell to depolarize, action potential started in muscle cell, down the m. Fiber, excess acetylcholine in NMJ is broken down to prevent over excitation
All neuromuscular junctions are ______
Excitatory
Acetylcholineesterase
Enzyme that breaks down ACh
Botulinum toxin (Cosmetic BOTOX)
Potent poison that blocks the release of ACh from axon terminals (disrupts proteins necessary for ACh vesicles to bind)
What makes up a Sarcomeres?
Skeletal muscle made up of actin and myosin filaments
Protein composition of thin filaments
Actin, troponin, tropomyosin that regulate contraction
Each actin molecule contains…
A binding site for myosin
Tropomyosin
Rod shaped
Two intertwined polypeptides
Held in position by troponin
Troponin
Holds tropomyosin down to actin
When calcium binds to troponin, it releases and allows tropomyosin to binds to actin
Sliding Filament Mechanism
Force causes shortening of muscle, overlapping thick and thin filaments in each Sarcomeres move past each other, propelled by movement of cross bridges
Shortening of Sarcomeres causes shortening of filaments
False; it changes the amount of overlap
Single Fiber Contraction
Muscle tension, load, twitch
Muscle tension
Forces exerted on object by contracting muscle
Load
Force exerted on muscle by object
Twitch
Mechanical response of muscle fiber to a single action potential
Isometric Twitch
Length of muscle stays the same of tension changes
Isotonic Twitch
Tension stays the same but muscle length changes
Summation
Increase in muscle tension from successive action
Tetanus
Maintained contraction in response to repetitive simulation
Titin
Protein responsible for passive elastic properties of relaxed muscle fibers (stetching increases passive tension)
Muscle fatigue
Decline in muscle tension as result of previous contractile activity, (slower rate of relaxation and ⬇️ shortening velocity)
Acute fatigue from excessive involves
⬇️ ATP concentration, ⬆️in ADP, Pi, Mg, H and O2 free radicals
Types of skeletal muscle fibers
Oxidative and glycolytic, slow and fast
Oxidation skeletal fibers
Numerous mitochondria for E, long term contraction
Glycolytic skeletal fibers
Few mitochondria but lots of glycolytic enzymes and stores, produce E quickly
Type 1 Skeletal Fibers
Slow oxidative, combine low myosin - ATPase activity w high oxidative capacity
Rate of fatigue: slow
Small fiber diameter
Type 2A Skeletal Fibers
Rate of fatigue: intermediate
Type 2X Skeletal Fibers
Rate of fatigue: Fast
Each muscle fiber only contains one of each fiber
False; it contains a mixture of all
Tension a muscle can develop depends on…
Amt of tension developed from each fiber, number of fibers contracting at once
Motor Unit Size Varies
Small motor units are in small intricate places
Shortening velocity…
M. Adaptation to Excersize
Increase size of muscle fibers (hypertrophy)
Changes capacity for ATP production
Changes myosin they express
USE IT OR LOSE IT
Disuse atrophy
Arm in a cast
Denervation Atrophu
Nerve damage = loss of function
Muscle cramps
Involuntary tetanic contraction of skeletal muscle
A.P fire are highhh rates
Caused by electrolyte imbalance in extra cellular fluid (persistent dehydration or over excersize
Smooth muscle fibers are ______ than skeletal muscles
Smaller
Smooth muscle cells
Single nucleus
Divide throughout life
DO NOT have troponin
DO NOT have Sarcomeres (no banding pattern, hence smooth)
Smooth muscle contraction occurs by…
Sliding filament mechanism
Pacemaker Potential
Varicosities
