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2025 SEM 2 HUMAN HISTOLOGY (LEC) > muscle tissue > Flashcards

muscle tissue Flashcards

1
Q

it is responsible for the creation and movement of the body and its parts and for changes in the size and shape of internal organs

A

muscle tissue
- characterized by specialized, elongated cells (muscle fibers) arranged in parallel arrays that have the pri role of contraction

[Muscle tissue helps the body move and change shape. It is made up of long, special cells called muscle fibers that are lined up in rows. Their main job is to contract (tighten and shorten), which allows movement of the body and its internal organs.]

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2
Q

how are the muscle cells classified according to the appearance of the contractile cells

A

STRIATED MUSCLES (has cross striations)
- skeletal muscle
muscles attached to the bone
- visceral striated muscle
same w bone but in limited part of the viscera
(tongue, pharynx, lumbar part of the diaphragm & upper part of esophagus)
- cardiac muscle
found in the walls of heart and base of large veins

SMOOTH MUSCLES (no striations, cross striations)

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3
Q

what are the characteristics of skeletal muscle fiber

A

multinucleated syncytium
nuclei are located at the sarcolemma (the plasma membrane of the muscle fiber)
held tgt by CT to form bundles and muscles (fascicles)
- endomysium: single muscle fiber
- perimysium: a bundle of muscle fiber
- epimysium: a collection of fascicles

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4
Q

A single muscle fiber is formed by the fusion of multiple cells, making it have more than one nucleus.

A

muscle syncytium

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5
Q

classification of skeletal muscle fiber

A

CONTRACTILE SPEED
determine how fast fiber can relax/ contract
based on EV & MP
[determines if fiber is slow or fast twitch]

ENZYMATIC VELOCITY
indicates rate/ speed whr enzyme (myosin ATPase) can break down ATP during contraction cycle
[faster ATP production = faster muscle contractions]

METABOLIC PROFILE
the capacity for ATP production by either oxidative phosphorylation or glycolysis
[decides if use O2 (aerobic) or sugar (anaerobic) ]

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6
Q

oxidative phosphorylation vs glycolysis

A

oxidative phosphorylation:
- requires O2
- in mitochondria
* muscles that tends to have a higher oxidative phosphorylation = higher no. of mitochondria
- high conc. of myoglobin

glycolysis:
- does not require O2
- use glycogen as an alternative source

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6
Q

transports/ delivers oxygen from bloodstream to the muscle cells in order for the mitochondria to process it into ATP

A

myoglobin
- a protein that stores and transports oxygen in muscle tissue

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6
Q

composed mainly by myosin II mol.

A

thick filaments of myofilaments

  • the globular head
    (top - actin binding site
    bottom - atp binding site)
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7
Q

what are the 3 types of enzymatic activity

A

(index card)
type I (slow oxidative fiber)
type IIa (fast oxidative glycolytic fibers)
type IIb (fast glycolytic fibers)

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7
Q

Order of Organization

A

myofilaments > myofibrils > muscle fibers > muscle fibers > muscle fascicles > skeletal muscle

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8
Q

composed primarily of actin molecules

A

thin filaments
* indiv actin molecules is aka G-actin, a collection is called F-actin
= these contain binding site for myosin II

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9
Q

circulates or covers the myosin II binding site of the actin molecules during the resting muscle stage

A

tropomyosin

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10
Q

troponin complex

A

TnC (calcium)
TnT (tropomyosin and anchors the troponin complex to trpomyosin)
TnI (actin and inhibits actin-myosin interactions)

  • Each tropomyosin molecule is characterized by 1 troponin complex
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11
Q

can be found in the negative end and covers ends of filament for protection

A

tropomodulin

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12
Q

its orderly organization of the myofilaments in the sarcolemma gives its characteristics cross striations

A

myofibrils
*skeletal and cardiac muscles (which have an orderly structure) are striated, while smooth muscle (which has a random arrangement) is not striated

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13
Q

characterized by darker staining to the cross-striation of the thick and thin filaments

A

A-band (anisotropic)
- as it is birefringent which gives the myofibrils its cross striation property
- alternating thick and thin filament results to a non-uniformed distribution of light, giving a darker stain

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14
Q

represent te bare zone for the thick filaments, free from globin heads which can be found in the two polar sides of the thick filaments

A

H-band

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15
Q

this anchors thin filaments to the z line

A

a-actin

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16
Q

stabilizes thick filaments along the m-line

A

protein C (myosin-binding protein C)

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17
Q

M line proteins

A

Myomesin
M-protein
Obscurin
Creatine Kinase

  • stabilize thick filaments to m-line
  • stabilize titin molecules
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18
Q

the portion from the z-line to another z-line

A

sarcomere
- functional unit of myofibrils
- involved in muscle contraction/ relaxation
- bound to other sarcomeres to sarcolemma through accessory proteins (desmin and dystropin)

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19
Q

how does sarcomere bound to other sarcomeres into the sarcolemma

A

through accessory proteins:
desmin - anchors sarcomere to sarcolemma and other sarcomeres
dystropin - bind f-actin to thin filaments to the dystroglycans

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20
Q

sugar/ carbohydrate units that can be found in the sarcolemma

A

dystroglycans

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21
Q

the binding of the dystropin to dystroglycan

A

Dystropin Glycoprotein Complex
- binds to the ECM proteins (laminin and agrin)
- binds the whole muscle fiber to the whole ECM

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22
maintains or prevents the excessive stretching of sarcomere by developing a restoring force
titin molecules - serves as a molecular spring - during contraction = globin heads bind to thin filaments and pulled towards the end lines - during relaxation = release, result in restoring thin filaments to original position
23
bound near the α-actinin in z-line and the Protein C and M-line proteins in the M-line
titin molecules
24
The interaction between thick and thin filaments
actomyosin cross bridge cycle
25
How Calcium (Ca²⁺) Triggers Muscle Contraction
it releases when muscle gets a signal to contract binds to troponin TnT = makes tropomyosin move out of the way, uncovering the myosin-binding site on actin myosin can now attach to actin & start contraction cycle 💡 Without calcium, the binding sites stay covered, and muscles remain relaxed.
26
5 steps of the actomyosin cross-bridge cycle
ATTACHMENT myosin head attach to actin called the rigor state RELEASE ATP binds to myosin = release actin myosin let go of the actin molecule BENDING myosin break down ATP into ADP + P = gives myosin energy to bend into a ready position FORCE GENERATION (I to III) myosin grabs a new actin site and pulls the thin filament forward = moves sarcomere closer, contraction occurs REATTACHMENT myosin attaches to another actin site
27
The rapid delivery and removal of calcium ions is accomplished by the sarcoplasmic reticulum and transverse tubular system (T tubules)
regulation
28
What are the two main structures responsible for calcium regulation in muscle contraction?
Sarcoplasmic Reticulum (SR) ○ Ryanodine receptors (RyR1) ○ Calsequestrin ○ Ca2+- activated ATPase pump T-Tubules (Transverse Tubules). Dihydropyridine-sensitive receptors (DHSRs)
29
what triggers the release of Ca ions
by the actions/ events happening in the neuromuscular junction 1️⃣ A nerve signal reaches the muscle at the neuromuscular junction. 2️⃣ This signal travels down the T-tubules and activates special proteins (DHSRs). 3️⃣ These proteins trigger the Ryanodine receptors (RyR1) in the sarcoplasmic reticulum, which then release calcium. 4️⃣ The released calcium binds to troponin (TnT), uncovering the myosin binding sites on actin. 5️⃣ Myosin binds to actin → Muscle contracts!
30
how calcium is removed
1️⃣ Once the nerve signal stops, the RyR1 channels close to stop calcium release. 2️⃣ Proteins like Calsequestrin help store calcium back in the sarcoplasmic reticulum. 3️⃣ A Ca²⁺-activated ATPase pump actively removes calcium from the muscle cell to stop contraction. 4️⃣ Without calcium, the myosin-binding sites get covered again, and the muscle relaxes.
31
What protein detects the nerve impulse and triggers calcium release?
Dihydropyridine-sensitive receptors (DHSRs) in the T-tubules.
32
What receptor in the sarcoplasmic reticulum releases calcium into the muscle cell?
Ryanodine Receptor (RyR1).
33
What does calcium bind to in order to start muscle contraction?
Troponin (TnT), which moves tropomyosin and exposes myosin-binding sites on actin.
34
What stops muscle contraction and helps the muscle relax?
removed by the Ca²⁺-ATPase pump, and proteins like Calsequestrin help store it back in the sarcoplasmic reticulum.
35
what controls the skeletal muscles that send signals from the brain or spinal cord
motor neurons
36
it is where the nerve and muscle connect
Neuromuscular Junction
37
How does a nerve signal cause muscle contraction?
nerve signal travels down to the neuromuscular junction. This causes the release of acetylcholine (ACh), a neurotransmitter, into the synaptic cleft Acetylcholine binds to receptors on the muscle fiber = allow sodium ions (Na⁺) to enter. Sodium entry causes depolarization, triggering muscle contraction. To stop continuous contraction, an enzyme called acetylcholinesterase (AChE) breaks down acetylcholine.
38
Why is nerve supply important?
Muscles need nerve signals to maintain their structure and function.
39
occurs when there is no movement of muscles
muscle athropy
40
What triggers muscle contraction?
action potential from the nerve travels down the axon to the axon terminal, releasing acetylcholine (ACh). ACh binds to nicotinic ACh receptors on the sarcolemma, opening sodium (Na⁺) channels and causing depolarization.
41
a specialized stretch receptor consisting of nuclear bag fibers, nuclear chain fibers
muscle spindle ■ Nuclear Bag fibers: collection of different type of fibers within the muscle ■ Usually just a specialized muscle type wherein the nerve fibers or sensory nerve fibers attach to
42
2 types of fibers
● Afferent II and Ia (sensory) nerve fibers Sense the information from the muscle to CNS ● Efferent y-S and y-D (motor) nerve fibers Provides, gives, delivers the message from the CNS to muscle tissue
43
Sensory nerve endings that detect posture and movement changes in the body.
proprioceptors
44
How do muscles detect changes in position and movement?
Through encapsulated sensory receptors found in muscles and tendons.
45
they are derived from myogenic stem cells from unsegmented paraxial mesoderm or segmented mesodern of somites
myoblast two areas in the developing embryo: Unsegmented paraxial mesoderm – helps form muscles in the head. Segmented mesoderm (somites) – helps form muscles in the body and limbs. [basically, myoblasts are the building blocks of muscles, starting from stem cells and eventually growing into muscle fibers.]
46
What gene helps regulate muscle growth?
Myostatin regulates muscle development to prevent excessive growth.
47
they are responsible for the skeletal muscle's ability to regenerate but their regenerative capacity is limited
satellite cells - why is it limited as they are few in number compared to other connective tissue cells - protein used to identify Pax7 transcription factor
48
it represents highly specialized attachment sites between adjacent cells
intercalated disks
49
what does cardiac muscle contain
fascia adherens + macula adherens = high order of binding to cardiac tissues anchoring junctions gap junctions
50
Generate and rapidly transmit the contractile impulse to various parts of the myocardium in a precise sequence
purkinje fibers - Special heart fibers that quickly send electrical signals through the heart. - Help make sure the heart contracts in the right sequence and at the right speed.
51
These act as calcium-release channels, helping with muscle contraction in cardiac.
RyR2 receptors
52
Can the heart muscle repair itself easily?
No, cardiac muscle has a very limited ability to repair itself because most of its cells do not divide after birth. they cannot replace damaged ones like skin or liver cells can.
53
How many heart muscle cells can divide and regenerate?
less than 0.1% of cardiac muscle cells can divide which is not enough for significant repair.
53
also known as a heart attack, it occurs when the heart muscle doesn’t get enough oxygen, often due to blocked blood flow.
myocardial infarction - one of the most common reasons for death of hert muscles - symptoms are usually late and happen at peak
54
How do doctors confirm a heart attack?
check for specific markers in the blood, which indicate heart muscle damage. [MyoTropICAL] 1. Myo = myoglobin First to increase (1-3 hours after MI) Found in many muscles, but still used for early heart attack detection 2. TropI = Troponin I/T Most sensitive marker for heart attacks Unique to heart muscle (unlike myoglobin) 3. C = Creatine Kinase (CK-MB) usually has isoform called CK-MB 4. Aspartate Aminotransferase (AST) usually increase in other disease but are very first makers fr MI 5. : Lactate Dehydrogenase (LDH) usually increase in other disease but are very first makers fr MI
55
generally occurs as a bundles or sheets of elongated fusiform cells with finely tapered ends
smooth muscle
56
Contractile Machinery of smooth muscles
🔹 Thin Filaments (Help with contraction) Actin (main component) Tropomyosin (special smooth muscle version) Caldesmon & Calponin (help regulate contraction) 🔹 Thick Filaments (Made of Myosin) No bare zone, making smooth muscle non-striated
57
proteins associated with contractie apparatus in smooth muscle
Myosin light-chain kinase Calmodulin a-Actinin
58
It provide an attachment site for thin filaments and intermediate filaments. Contains a variety of attachment plaque proteins, including the a-actinin
dense bodies
59
What are the two major intermediate filaments in smooth muscle?
Desmin & Vimentin – They link muscle fibers to the cell skeleton and membrane.
60
here is smooth muscle commonly found?
In hollow organs such as the stomach, intestines, blood vessels, and uterus.
61
What is the main function of smooth muscle?
To contract slowly and for long periods without fatigue.
62
A state where smooth muscle stays contracted for a long time with minimal energy use.
latch state
63
what controls smooth muscle contraction?
autonomic nervous system (ANS), which works automatically without conscious control.
64
Where are nerve terminals found in smooth muscle?
Only in the connective tissue near the muscle cells, not directly inside the muscle.
65
What substances do smooth muscle cells secrete?
Collagen (Type III & IV) – Provides strength Elastin – Adds flexibility Proteoglycans & Glycoproteins – Help with structure and function
66
Why does smooth muscle secrete connective tissue
o help support organs (viscera) and maintain their structure.
67
Can smooth muscle cells divide and regenerate?
Yes, they can divide to replace or increase their numbers.
68
What type of stem cells can form new smooth muscle cells?
Undifferentiated mesenchymal stem cells in blood vessels.
69
Cells found around capillaries and venules that can become smooth muscle cells when needed.
vascular pericytes
70
Cells that have properties of both fibroblasts and smooth muscle, helping with wound healing and tissue repair.
myofibroblasts
71
what are the different type of signals when smooth muscle contraction happens
Mechanical signals – Voluntary movement or stretching of the muscle. Electrical signals – Causes voltage-dependent channels to open. Hormonal/Chemical signals – Hormones or chemicals activate receptors that lead to calcium release.

2025 SEM 2 HUMAN HISTOLOGY (LEC) (11 decks)

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