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Foundations 2 > Muscle Histology > Flashcards

Muscle Histology Flashcards

1
Q

Name the three muscle types.

A

skeletal muscle, cardiac muscle, smooth muscle

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2
Q

skeletal muscle

A

attaches to bone, ligaments, the dermis of facial, skin, and the eyeballs

also called striated muscle because of actin and myosin filaments

muscle cells are a very long syncytium with peripheral nuclei

10-100 microns in diameter with

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3
Q

motor unit

A

number of muscle cells innervated by one neuron

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4
Q

cardiac muslce

A

striated and restricted to the heart

differs from skeletal muscle in that cells branch, have central nuclei, and are attached to each other with intercalated discs

contraction is initiated within the conduction system but regulated by the autonomic nervous system

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5
Q

smooth muscle

A

lines the walls of blood vessels and hollow organs

controls blood pressure, contractions of the stomach, peristalsis in the GI tract, and childbirth

smaller than skeletal and cardiac muscle

spindle shaped, central nuclei

contraction is slower, requires less energy, and can result form nerve impulses, hormones, and response to stretch

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6
Q

molecular mechanism of muscle contraction

A

the rachetlike sliding of actin and myosin myofilaments alongside each other

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7
Q

role of calcium in muscle contraction

A

required for binding of actin and myosin filaments in all three muscle types

mechanism is different for smooth muscle

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8
Q

fascicles

A

groups of muscle fibers, which are the individual cells

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9
Q

endomysium

A

thin connective tissue layer surrounding the fibers

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10
Q

perimysium

A

surrounds fascicles and forms larger septa within muscles

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11
Q

epimysium

A

connective tissue surrounding the whole muscle

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12
Q

myofibrils

A

filamnets of thick and thin myofilaments that pack muscle fibers

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13
Q

three components of thin filaments

A

actin, tropomyosin, and a troponin complex

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14
Q

f-actin

A

a long double-stranded helix formed from the polymerization of g-actin

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15
Q

tropomyosin

A

a double helix that runs in the groove between F-actin molecules

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16
Q

troponin complex and its three components

A

plays an important role in the attachment of the myosin thick filaments

made up of troponin-C, tropnon-T, and troponin-I

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17
Q

Troponin-C

A

binds calcium and allows myosin to bind with actin

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18
Q

troponin-T

A

anchors the complex to tropomyosin

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19
Q

troponin-I

A

binds actin to inhibit myosin-actin interactions

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20
Q

Describe the structure of the sarcomere.

A

I band = actin myofilaments

H band = isolated myosin in A band

M line = myosin cross-linked

A band = kength of myosin molecules, here overlapping with actin

Z line = boundaries of a sarcomere

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21
Q

I band

A

actin filaments by itself

Z line bisects the I band

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22
Q

H band

A

isolated myosin in the A band

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23
Q

M line

A

myosin-cross linked with each other by myomesin and C protein

stabilizes the myosin and keeps them in register

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24
Q

A band

A

length of myosin molecules, overlapping with actin

length remains constant during contraction of the sarcomere

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25
Q

Z line

A

boundaries of sarcomere

composed of alpha-actinin

thin filaments are anchored to the Z line and thick filaments are attached indirectly by titin

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26
Q

titin

A

a molecules that connects myosin to the Z-line

coiled appearance, has elastic properties

27
Q

excitation-contraction coupling

A

the linking of the external neural signal to the internal mobilization of calcium to initiate a contraction cycle

28
Q

dystrophin protein/glycoprotein complex

A

links f-actin/cell interior with extracellular proteins laminin and agrin

just under the cell membrane, transmembrane glycoproteins connect it with the extracellular proteins

29
Q

sarcoplasm

A

cytoplasm that surrounds myofibrils

contains mitochondria, glycogen, myoglobin, and and extensive network of ER

30
Q

transverse T tubules

A

invaginations of muscle cell membranes that are flanked two cysterns of ER

brings the depolarization into the interior of the cell at the level of the A-I junction

31
Q

triad

A

the combination of a T-tubule and two adjacent terminal cisternae of sarcoplasmic reticulum that responds to depolarization of the membrane and releases calcium into the sarcoplasm

32
Q

How is calcium released in response to membrane depolarization?

A

L-type Ca2+ channels open in response to membrane depolarization

done through mechanical coupling

33
Q

major steps of the contraction cycle

A

depolarization of the sarcolemma, mobilization of intracellular calcium, and the hydrolysis of ATP

34
Q

Describe the contraction cycle.

A

two important effects of P released form myosin head:

head binds more tightly to actin

head unbends to its original conformation, which is the power stroke

35
Q

rigor configuration

A

the orientation of the myosin heads without the presence of ATP or ADP

bound tightly to actin

36
Q

power stroke

A

the process of ADP and phosphate detaching from the myosin head, which moves the head to its original conformation

37
Q

motor unit

A

the number of muscle fibers supplied by one neuron

force of contraction is determined in part by how many motor units are recruited by the central nervous system

38
Q

neuromuscular junction

A

characterized by a motor end plate, the terminal portion of an axon branch that sits in a recess of the sarcolemma called the synaptic cleft

myelin sheath ends, and only a thin layer of Schwann cell cytoplasm overlies the end plate

39
Q

What is the neurotransmitter used in motor innervation?

A

acetylcholine

40
Q

Describe the process of depolarization of the muscle cell.

A

acetylcholine is released from the neurons

ACh-gated Na+ channels open

Volatage-gated Na+ channels open

Na+ enters the cell and depolarization spreads across the plasma membrane

41
Q

myasthenia gravis

A

an autoimmune disease where antibodies block the acetylcholine receptor sites on the sarcolemma

42
Q

sensory innervation in skeletal muscle

A

consists of general sensation including pain, but also encapsulated sensory receptors that sense stretch and tension in muscle

43
Q

proprioception

A

sensory input that helps the brain determine movement and positions int he body

44
Q

components of the muscle spinder

A

nuclear bag fiber

nuclear chain fiber

afferent nerve endings

internal capsule

45
Q

nuclear bag fiber

A

specialized muscle cell with an expanded section containing many nuclei

46
Q

nuclear chain fiber

A

specialized muscle cell with a section containing a series of aligned nuclei

47
Q

golgi tendon organs

A

encapsulated receptors similar in function that are found in tendons

48
Q

organization of heart muscle

A

similar to skeletal muscle but the nucleus is central, myofibrils are not discrete, mitochondria are large, T-tubules are lare at the Z line, and there are diads instead of triads

49
Q

interalatred disks

A

dense-staining junctions that have step-like interdigitations with fascia adherens junctions, macula adherens junctions, and gap junjunctions

also serve as anchors for the thin actin filaments

50
Q

How does the depolarization of the heart differ from that of skeletal muscle?

A

T-tubules penetrate group sof myofibrils at the level of the Z line

myofibrils and sarcoplasmic reticulum are less organized

calcium-triggered calcium release

51
Q

calcium-triggered calcium release mechanism

A

calcium passing from the lumen of the T-tubule into sarcoplasm is an absolute requirement for contraction

depolarization of the cell and T-tubule membranes open voltage-sensitive calcium channels that open the SR calcium channels nearby

the amount of calcium released in cardiac muscle is dependent on the amount of calcium that enters the cell, whereas in skeletal muscle, it depends on the frequency of membrane polarizations

52
Q

purkinje fibers

A

specialized cells in the heart that can carry an impulse faster than heart muscle cells

53
Q

Where does a heartbeat start?

A

in pacemaker cells in the sinuatrial node in the right atrium

54
Q

two hormones secreted by heart muscle cells and their functions

A

atrial natriuretic factor (ANF) and brain natriuretic factor (BNF) - both are diuretics that affect sodium excretion, act on kidney, adrenal gland, and vascular smooth muscle to lower blood pressure

55
Q

dense bodies

A

the equivalent of Z-lines in smooth muscle cells

they are the attachment sites for thin filaments and contain alpha-actinin within a reticulum of intermediate filaments (desmin and viementin)

56
Q

caveolae

A

numerous invaginationso f the cell membranes that replace T-tubules in smooth muscle cells along with vesicles that provide a route of entry of calcium into the cell

57
Q

initiation of actin-myosin interactions in smooth muscle

A

result from the phosphorylation of myosin heads rather than calcium acting on the troponin complex, which is absent in smooth muscle

58
Q

three mechanisms that initiate contraction in smooth muscle cells

A

voltage-sensitive calcium channels in the cell membrane that open from autonomic impulses, no neuromuscular junctions so neurotransmitters diffuse to initiate depolarization

stretching of smooth muscle opens mechanosensitive calcium channels

hormone receptors and other signals trigger the formation of second messengers that act on gated channels in the ER to release calcium

59
Q

Ca++-calmodulin-myosin light chain kinase

A

in the presence of calcium, regulates contraction by phosphorylating regulatory light chains on the myosin heads to expose actin-binding sites

60
Q

latch state

A

where smooth muscles remains contracted for long periods of time with minimal ATP expenditure

after myosin attaches to actin, the heads are dephosphorylated, which results in a decrease in aATPase activity, and the myosin head is unable to detach from actin

61
Q

smooth muscle relaxation

A

results from the synergistic action of calcium efflux from the cell, membrane hyperpolarization, and reduced sensitivity to calcium

can be triggered through specific receptors with their own G protein and second messenger pathways that results in the phosphorylation of many proteins

62
Q

epinephrine

A

activates a beta2-receptor cAMP pathway in skeletal muscle arterioles

relaxes smooth muscles in blodo vessels of the GI tract to contract and skeletal muscle vasculature to relax

63
Q

nitric oxide

A

an important vasodilator

diffuses into vascular smooth muscle cells to act via a cGMP pathway

Foundations 2 (33 decks)

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