Chapter 10: Muscles Flashcards
1
Q
muscle fiber
A
a sketeletal muscle cell
2
Q
endomysium
A
delicate connective tissue that covers each muscle fiber
3
Q
fascicles
A
bundles of grouped muscle fibers
4
Q
perimysium
A
sheath of tougher connective tissue that encases the fascicles
5
Q
epimysium
A
layer of connective tissue that surrounds the muscle as a whole and binds all the muscle fibers together
6
Q
facia
A
connective tissue that surrounds the muscle outside the epimysium
- deep facia lies between muscles
- superficial facia (hypodermis) resides just under the skin
7
Q
direct attachment
A
muscle fibers merge with the periosteum of a bone, forming a strong attachment
8
Q
indirect attachment
A
the epimysium extends past the muscle as a tendon. the tendon then merges with the periosteum
9
Q
aponeurosis
A
flat, broad tendon that attaches muscle to another muscle (or occasionally a bone)
10
Q
muscle cells
A
- long, thread-like
- multiple nuclei pressed against the side of the plasma membrane
11
Q
sarcolemma
A
the plasma membrane surrounding each muscle fiber
12
Q
sarcoplasm
A
the cytoplasm of a muscle cell
13
Q
myofibrils
A
- long protein bundles that fill the sarcoplasm
- store glycogen and oxygen
- thin and thick myofilaments stacked together
14
Q
sarcoplasmic reticulum (SR)
A
- the smooth ER of a muscle fiber
- surrounds each myofibril
- where calcium ions are stored
15
Q
myofilaments
A
- fine fibers that make up myofibrils
- 2 types:
- thick (myosin)
- thin (actin)
- arrangement if myosin and actin gives skeletal muscle its striated appearance
16
Q
transverse (T) tubules
A
- system of tubules extending across the sarcoplasm
- formed from inward projections of the sarcolemma
- allow electrical impulses to travel deep into the cell
17
Q
thick filaments
A
- consists of hundreds of myosin molecules stacked together
- myosin heads face outward
- myosin molecules are shaped like golf clubs
18
Q
thin filaments
A
- consists of 2 chains of actin
- look like a string of beads
- tropomyosin and troponin are intertwined with the actin
19
Q
sarcomeres
A
- units of myofibrils
- the section between the Z-discs
- where muscle contraction occurs
20
Q
Z-disc
A
serves as an anchor point for thin myofilaments
21
Q
relaxed muscle
A
- the myosin and actin lie side by side, partially overlapping
- myosis and actin are completely detached from one another
22
Q
contraction
A
- occurs when myosin heads latch onto actin myofilaments, forming a cross bridge
- this happens repeatedly, creating “power strokes”
- the actin myofilaments are propelled forward, pulling the Z-discs together and shortening the sarcomere
- as the sarcomere shortens, so does the myofibril and the entire muscle
- this is known as the sliding-filament model of contraction
23
Q
the body at work
A
- ATP allows myosin heads to release their grip on the actin filament
- the myosin splits the ATP, giving it fuel to form a cross bridge
- the SR releases calcium
- calcium binds with the troponin, unblocking attachment sites on the actin filaments
24
Q
motor neuron
A
- nerves that stimulate skeletal muscle
- cell bodies of motor neurons reside in the brainstem and spinal cord
25
axon
- extensions from the cell bodies
- carry impulses to skeletal muscles
- branches multiple times
- each branch stimulates a different muscle fiber
26
neuromuscular junction
the connection between a motor neuron and muscle fiber
27
synaptic cleft
a narrow space between the end of the motor nerve and the muscle fiber
28
how muscle fibers contract
1. when an impulse reaches the end of a motor neuron, it causes small vesicles to fuse with the cell membrane and release a neurotransmitter called acetylcholine (ACh) into the synaptic cleft
2. the ACh diffuses across the synaptic cleft, where it stimulates receptors in the sarcolemma
3. this sends an electrical impulse over the sarcolemma and inward along the T tubules. the impulse in the T tubules causes the sacs in the SR to release calcium
4. the calcium binds with the troponin on the actin filament to expose attachment points. this allows the myosin heads to grab onto the thin filaments and create muscle contraction
28
how muscle fibers contract
1. when an impulse reaches the end of a motor neuron, it causes small vesicles to fuse with the cell membrane and release a neurotransmitter called acetylcholine (ACh) into the synaptic cleft
2. the ACh diffuses across the synaptic cleft, where it stimulates receptors in the sarcolemma
3. this sends an electrical impulse over the sarcolemma and inward along the T tubules. the impulse in the T tubules causes the sacs in the SR to release calcium
4. the calcium binds with the troponin on the actin filament to expose attachment points. this allows the myosin heads to grab onto the thin filaments and create muscle contraction
29
how muscle fibers relax
- impulses stop arriving at the neuromuscular junction
- ACh is no longer released
- acetylcholinesterase (enzyme) breaks down any remaining ACh
- calcium ions are pumped back into the SR
- with calcium gone, the troponin again prevents myosin heads from attaching
- muscle fiber relaxes
30
botulism
- form of food poisoning
- bacteria "Clostridium botulinum" blocks release of ACh
- death results from paralysis of respiratory muscles
31
myasthenia gravis
- body produces antibodies against receptors for ACh
- not all ACh can find a receptor
- nerve transmission is poor
- results in profound muscular weakness
32
tetanus ("lockjaw")
- results from bacterium Clostridium tetani
- causes motor neurons to fire excessively
- leads to overstimulation of muscles
- results in severe muscle spasms and sustained contractions
- jaw muscles are typically affected first
33
curare
- used in anesthesia to relax skeletal muscles
- binds to ACh receptor sites, stopping nerve transmission and causing paralysis
- patients receiving curare must be mechanically ventilated
34
length-tension relationship
the strength of a contraction depends upon the length of the fibers before the contraction begins
1. contraction is weak in overly contracted fibers
2. contraction is weak in overly stretched fibers
3. strongest contraction occurs when thin and thick filaments are partially overlapped; Z-discs are far enough apart to allow movement but close enough together to allow the myosin heads to get a firm grip
35
muscle tone
- continuous state of partial contraction
- nervous system constantly stimulates muscle fibers just enough to achieve their optimal resting length
- allows you to stand, hold up your head, and maintain posture
- allows you to react quickly to a dangerous situation
36
motor unit
- a neuron and all the muscle fibers it stimulates
- can include a few fibers or a few hundred
- fibers are scattered throughout the muscle, allowing the contraction to be spread over a wide area
