Chapter 10 - Muscular System Flashcards
Muscular tissue is made up of _______ cells that are specialized to ____ and _____ force
Elongated, contact, exert
What are the functions of muscular tissue?
Movement
Digestion/waste elimination
Breathing, speech, and expression
Blood/circulatory system
What are the three types of muscular tissue?
- skeletal
- cardiac
- smooth
When you say muscular system, what types of muscular tissue are you referring to?
Skeletal
Where are skeletal muscles found and describe them
- Bone or skin attachment
- Long, parallel unbranched muscle fibers
- Striated
- Voluntary control
- Each muscle fiber has multiple nuclei near edges of cell
What types of cells make up skeletal muscles?
Muscle fiber (or myofibers)
Where is cardiac muscle found and describe it
- Found only in heart
- Short, branded cells
- Striated
- Involuntary control
- Central nuclei within each cell
What types of cells make up cardiac muscles?
Cardiomyocytes
Where are smooth muscles found and describe them
- Blood vessels and hollow organ (ex: stomach, uterus)
- Fusiform shape
- NO striations
- Involuntary control
- Single nucleus per cell
What types of cells make up smooth muscles?
Myocytes
About how many human skeletal muscles are there? What percentage of our body weight is that?
~600 muscles
~50% of body weight
What is the major purpose of skeletal muscles?
Take chemical energy (ATP) and convert it into mechanical energy
What is myology?
The study of the muscle system (molecular, cellular, and tissue level)
How do muscles function to aid in movement?
- externally visible movements
- internal movement (keeping the digestive tract going, helping you pee)
- communication (writing, talking, etc)
How do muscles function to aid in stability?
- prevent unwanted movement
- help with posture and holding bones/joints in place
How do muscles function to aid in the control of body openings and passages?
- sphincter muscles
- control how much light we get in our eyeballs
- control where blood goes, waste, etc
How do muscles function to aid in heat generation?
- 20-30% of body heat
How do muscles function to aid in glycemic control?
- aids in regulation of blood glucose
- absorbs, stores, and uses glucose
Why are older individuals more prone to type 2 diabetes?
Because they have decreased muscle mass and function, which means their muscles don’t do as well of job at absorbing, storing, and using glucose properly
What type of muscle is voluntary and striated?
Skeletal
What type of muscle is involuntary and not striated?
Smooth
What type of muscle is involuntary and striated?
Cardiac
Muscle cells have some universal properties. What does it mean for a muscle to be excitable?
- Respond when stimulated
- Can be stimulated via electrical changes across the plasma membrane
Muscle cells have some universal properties. What does it mean for a muscle to exhibit conductivity?
- Local electrical excitation imitates a wave of excitation that travels along the muscle fiber
- Which is how it contracts
- (The muscle fiber is the conductor of the excitation)
Muscle cells have some universal properties. What does it mean for a muscle to be contractable?
- Shortens when stimulated (resulting in movement)
Muscle cells have some universal properties. What does it mean for a muscle to exhibit extensibility?
- Capable of being stretched between contractions
Muscle cells have some universal properties. What does it mean for a muscle to exhibit elasticity?
- Returns to its original rest length after being stretched
What is the thick myofilament?
Myosin
What is the thin myofilament?
Actin
A bunch of myofilaments together make a ___?
Myofibril
A bunch of myofibrils together make a ____?
Muscle Fiber
A muscle fiber is surrounded by?
Endomysium
Muscle fibers are bundled into ________
Muscle fascicles
Muscle fascicles are surrounded by ______
Perimysium
Muscle fascicles all together make up the ______
Muscle
The muscle is surrounded by ________
Epimysium
What are -myosiums made up of?
[primarily] areolar connective tissue
What are the 3 myosiums and what do they surround?
- epimysium (fibrous sheath, surrounds whole muscle)
- Perimysium (thickish CT, surrounds muscle fascicles)
- Endomysium (loose CT, surrounds muscle fiber)
What are some features of the epimysium?
Fibrous sheath
Fascia - sheet of CT that separates muscles/groups
What are some features of the perimysium?
Thickish CT
Nerves, blood vessels, and stretch receptors
What are some features of the endomysium?
Loose CT
Allows room for capillaries and nerves
Extracellular chemical environment for contraction
Describe skeletal muscle cells? What are they called
Long, slender shape
Multiple nuclei - pressed against the inside of the sarcolemma
Name: muscle fibers
What is the sarcolemma?
Plasma membrane of muscle fiber (muscle cell)
What is the sarcoplasm?
Cytoplasm of a muscle fiber (muscle cell)
What are myofibrils?
Thick bundles of contractile proteins
Myofilaments = actin and myosin
What can you find packed between myofibrils?
Mitochondria, smooth endoplasm reticulum
Glycogen (carbohydrate)
Myoglobin (oxygen-storing pigment)
What are Transverse (T) tubules and what do they do?
Infoldings of the sarcolemma
Penetrate muscle fiber
Carry electrical current
What is the sarcoplasmic reticulum and what does it store?
Smooth endoplasmic reticulum of muscle fiber
Forms web around myofibrils
Stores calcium
What are terminal cisternae?
Dilated sacs around T tubules
Aid in calcium storage by binding to calsequestrin
What is a Triad?
T tubule + 2 terminal cisterns
What does the sarcoplasmic reticulum need to released into the cytosol for a muscle contraction?
Calcium
Describe thick filaments/myosin
2 chains: shaft-like tail and double globular head (golf club)
Heads directed outward in a helical array (head on one half angle to left, angle to right on other half, bare zone in the middle with no heads)
What are elastic filaments called and what do they do?
Titin (aka connectin) Huge, springy protein Runs through core of thick filament (anchors myosin to Z disc and M line) Stabilizes and positions Prevents overstitching Provides recoil
What do contractile proteins do in a myofilament?
shorten the muscle fiber
What regulatory proteins are found in a myofilament and what do they do?
Tropomyosin and troponin
Act like a switch that determines when fiber can (and cannot) contract
Calcium can flip the switch
Where types of cells are myosin and actin found?
Nearly all cells
Most abundant in skeletal and cardiac muscle
Organization accounts for striations in muscles
What do other proteins associated with myofilaments do?
Anchor, align, and regulate
What is dystrophin and what does it do?
It’s a clinically important protein
Links actin in outermost myofilaments to membrane proteins and then to the endomysium
transfers forces of muscle contraction to CT and ultimately leads to tendon
What protein is muscular dystrophy related to?
Dystrophin (genetic defects in it)
How do striations occur?
Precise organization of actin and myosin
What is the different in A bands and I bands?
A bands:
- dark bands
- thick and thin filaments overlap
- Middle part (H-band) has myosin only (so not as dark)
I bands:
- light bands
- only thin filaments
- bisected by thin dark line (Z disc)
What is a sarcomere and what does it do?
The segment from one Z disc to the next
Functional contractile unit
Muscle shortening - due to sarcomeres shortening/sliding, pull z discs closer together
What is the functional contractile unit in a muscle cell?
Sarcomere
What changes during shortening of a sarcomere?
The amount of overlap
Do thick filaments change length during shortening of a sarcomere? What about thin filaments?
Neither change length, only the amount of overlap changes
How does dystrophin play into shortening of a sarcomere?
Dystrophin and linking proteins pull on extracellular proteins
This transfers pull to the extracellular tissues
What must happen for skeletal muscle to contract?
It must be stimulated by a nerve (or artificially)
What happens if nerve connections are lost?
The muscle is paralyzen
What is denervation atrophy?
Shrinkage of paralyzed muscle when nerve remains disconnected
What are the two types of cells in nervous tissue?
- Neurons (nerve cells, initiate and conduct electrical activity)
- Glial cells (cells that support and protect neurons)
What do somatic motor neurons do?
Stimulate skeletal muscles
Soma located in brainstem/spinal cord
What are somatic nerve fibers and what do they do?
Axons of motor neurons leading to muscles
Branch to muscle muscle fibers
One fiber : one motor neuron
Can 1 neuron innervate multiple fibers?
Yes
Can 1 fiber have multiple neurons innervating it? Why/how?
No
Because you don’t want conflicting signals, so just one neuron so only one signal
What is a motor unit? How big are they?
One motor neuron and all the muscle fibers supplied (all contract at once)
Some are very large for power (1 neuron = ~1000 fibers)
Some are very small for fine motor control (1 neuron = 3-5 fibers)
What does it mean for motor units to “work in shifts”
Don’t always all need to work at once
We are always using muscles (ex: just to hold our head up in class)
Working in shifts prevents fatigue
Helps with long-term contraction of muscle
What is the place called where a nerve meets a muscle fiber?
Synapse
What is an axon terminal? What’s another name for it?
Aka synaptic knob
Swelling / depression in muscle fiber
What is the synaptic cleft?
Gap between terminal and sarcolemma
What insulates the neuromuscular junction (NMJ)?
Schwann Cells Basal lamina (layer of collagen and glycoprotein)
What are synaptic vesicles?
Membrane-bound sacs in axon terminal Contain acetylcholine (ACh), a neurotransmitter
What is ACh and what does it do?
Acetylcholine (a neurotransmitter)
Released by nerve fiber (via exocytosis)
Binds to receptors on sarcolemma (motor end plate)
What is the purpose of junctional folds?
Increase the surface area
What is acetylcholinesterase?
An enzyme that breaks down acetylcholine (stops muscle stimulation)
What are the steps of muscle contraction (4)?
- Excitation
- Excitation-Contraction Coupling
- Contraction
- Relaxation
What happens in the first step of muscle contraction (excitation)?
Process in which nerve action potentials lead to muscle action potentials
Electrical nerve signal –> electrical signal (action potential) in muscle fiber
Describe the steps of muscle excitation (4)
- Nerve signal arrives at terminal
- Stimulates synaptic vesicles to release ACh into cleft (diffuses across cleft)
- Binds ACh receptors on sarcolemma
- Initiates wave of voltage changes (action potential) spread in all directions away from neuromuscular junction and down t-tubules
Describe the steps of excitation-contraction coupling (5)
- Action potentials pass into/down t-tubules (sarcoplasmic reticulum triggers calcium release from terminal cisterns)
- Cytosol floods
- Calcium binds to troponin
- Calcium binding leads to change in shape of troponin-tropomyosin complex, which reveals active sites on actin
- During all this, ATP binds to myosin heads, spits into ADP and phosphate, and the myosin head becomes cocked into postion
Action potentials on sarcolemma lead to activation of myofilaments
Describe the steps of muscle contraction (like break down step 3 of the entire contraction process) (3 steps)
- Myosin head binds to active site on actin, forms cross-bridge
- Myosin releases phosphate and ADP, flexes into OG position, power stroke
- ATP binds to m myosin AGAIN, actin released by myosin head, breaks the cross-bridge
the head is now prepared to repeat the whole process
Describe what happens to the following when a muscle contracts and a sarcomere shortens:
- Z discs
- A bands
- I bands
- Thin filaments
- H band
- Z discs: move closer together
- A bands: do NOT shorten
- I bands: narrow
- Thin filaments: do not shorten, slide toward the M-line
- H band: shortens/disappears
Describe the relationship between thick and thin filaments during contraction
Thin filaments slide past thick filaments
Do the length of filaments change when the muscle is contracted or relaxed?
They never change, only their relative positions change
Describe the steps of muscle relaxation (4)
- Nerve signal ceases, no more ACh released
- ACh already in synapse is released from receptors, broken down by acetylcholinesterase, stops muscle fiber stimulation
- Calcium is actively pumped out of the cytoplasm and reabsorbed by the sarcoplasmic reticulum (requires ATP)
- In the troponin-tropomyosin complex, calcium dissociates, everything returns to resting positions, myosin is blocked from binding to actin, muscle is relaxed
