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tissues Flashcards

1
Q

What is tissue, cellular and sub-cellular structure?

A
  • tissues = how cells combine with EC material and each other to form tissue
  • cellular = cell shape and organisation of components to support function
  • sub-cellular = organelles
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2
Q

What are the four main tissue types in the body?

A
  • connective
  • nervous
  • muscle
  • epithelial
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3
Q

What are the two main components of tissue?

A
  • cells

- ECM (highly-organised molecules formed by cells to influence complex structure)

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4
Q

What are the two functions of the ECM?

A
  • mechanical support

- nutrients and metabolite exchange

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5
Q

What are the five stages of preparing a specimen for microscopy?

(SPSSM)

A
  • specimen dissection
  • preparation
  • sectioning
  • staining
  • microscopy

(16-48 hrs)

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6
Q

What is the aim of tissue processing?

A

to embed tissue in medium firm enough to support and enable cutting of thin sections

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7
Q

Summarise the main stages of tissue processing and the purposes of each one.

FDCESC
(Hint - Frances Does Crazy Expeditions So Cleverly)

A
  • fixation: treated with chemical agent to prevent autolysis and shape changes i.e. aldehydes and ketones
  • Dehydration: fixative + water removed from specimen and replaced with dehydration fluid (graded series from 10-100% ethanol)
  • Clearing: dehydrating fluid replaced with miscible fluid (dehydrating fluid and embedding medium) using clearing agents i.e. zylene, tulouene, chloroform, benzene, petrol, histo-clear, histo-choice
  • Embedding: tissues embedded with medium to provide support during sectioning i.e. plastic resin, paraffin wax (3 μm), polymerising resin
  • Sectioning: cut using microtome, sectioned with cryostat (>6μm)
  • Cryo-embedding: tissue samples snap frozen in LN₂/CO₂ and slides stored
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8
Q

Why is paraffin wax used for embedding?

A
  • polycrystalline, elastic mixture with high MP

- increases hardness, improves ribboning and adhesion between specimen and wax

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9
Q

What are the three requirements for tissues after embedding stage?

A
  • no clearing agent
  • no dust particles
  • rapidly-cooled to reduce wax crystal size
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10
Q

What is staining?

A
  • permits examination of tissues by LM

- tissues and cells are translucent (>1 stain can be used)

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11
Q

What are most stains not compatible with?

A

paraffin wax

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12
Q

How are slides readied for examination?

CRSDCMC

A
  • cleared in xylene
  • rehydrated via (graded) alcohol series + washed
  • stained
  • dehydrated
  • cleared with xylene
  • mounted using xylene medium + coverslip
  • cryo-embedded and stored
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13
Q

For each stain state the structures and the colours they are stained:

a) H and E
b) alcian blue
c) oil red o
d) masson’s trichrome
e) reticulin
f) periodic acid solution (PAS)
g) DAPI (4′,6-diamidino-2-phenylindole)
h) millers sirius red

A

a)
- (H) nucleus and proteins → blue
- (E) cytoplasm → pink
b)
- acid mucins + proteoglycans → blue
- nuclei → red/black
c)
- fat → brilliant red
- nuclei → blue
d)
- nuclei and basophilic structures → blue
- cytoplasm, muscle, erythrocytes, keratin → bright red
- collagen → green/blue
e)
- reticulin fibers → black
- collagen fibers → brown
- nuclei → pink
f)
- glycoproteins → magenta
- nuclei → blue
g)
- DNA and nuclei → blue
h)
- elastin → dark purple/black
- collagen → red/pink
- phase contrast → changes brightness for clarity
- collagen fibers → befringent (shadowy)

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14
Q

What is IHC?

A
  • application of specific antibodies to tissue preparation

- for localization of specific antigens

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15
Q

What type of detection system is IHC and how is the antibody visualised?

A
  • highly-sensitive

- using marker (i.e. fluorescent dye, colloidal gold)

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16
Q

What is the direct method of IHC?

A
  • single-step

- use of directly-labelled primary antibody supplied to detect antigens within tissue

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17
Q

What is the indirect method of IHC?

A
  • utilizes unlabeled primary antibody and secondary labelled antibody
  • binds to it to detect tissue antigen
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18
Q

What is IHC antigen retreival?

A
  • tissue antigens can be masked by tissue fixation

- different methods can be used to reveal antigen: enzymatic digestion, citric acid, EDTA, heat

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19
Q

What can be used for inhibition of endogenous tissue components (reactions during staining) and for the blocking of non-specific sites?

(HInt - sounds like Alvin)

A
  • inhibition of endogenous tissue: 3% (v/v) H₂O₂ and 0.01 % (w/v) Avidin
  • blocking of non-specific sites: 10% (v/v) normal serum
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20
Q

State some controls which can be used in IHC.

A
  • positive control - tissue known to contain epitope
  • diluent control - buffer only (tissue section known not to express target antigen)
  • omission of primary antibody
  • omission of secondary antibody
  • isotype antibody - isotype of antibody used to bind to same antigen (see if it binds/not)
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21
Q

Give examples of IHC

A
  • collagen type IV: collagenfound in basal lamina
  • α-Gal; carbohydrate in mammalian cell membranes
  • fluorescent examples: SM cells, DAPI and actin, human skin, E-cadherin
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22
Q

State pros and cons of IHC.

A

pros:
- high specificity for molecular species
- can be used for light, confocal, or electron microscopy
cons:
- time-consuming and expensive
- fixation can interfere with Ab (Alcian Blue) binding particularly with small molecules
- reproducibility - false positives due to cross-reactivity
- qualitative

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23
Q

What are the five types of microscopy.

CDKPF

A
  1. bright field/kohler illumination
  2. phase contrast
  3. differential interference contrast (DIC) microscopy
  4. fluorescence
  5. confocal
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24
Q

State the pros and cons of confocal microscopy.

A 
pros:
- excellent resolution in thick samples
- greater number of flurophore as specific λs used to illuminate samples
- collects light from a single focal plane
cons:
- photo-bleaching and phototoxicity
- increased sensitivity to noise
- technical method - labour-intensive
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25
Q

What is an ELIZA (enzyme-linked immunosorbent assay)?

A
  • lab technique that uses antibodieslinkedtoenzymes
  • to detect and measure the amount of substance in solution (i.e. serum)
  • (can be sandwich, indirect or competitive)
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26
Q

Describe the ELIZA method and how it is used.

A
  • can be used to detect both antibody and antigen
  • relies on monoclonal antibodies
  • enzyme’s activity used as “reporter” where enzymatic reaction produces coloured species
  • unknown sample determined using standard curve
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27
Q

How is a indirect ELIZA or sandwich ELIZA carried out?

Hint - make a well, AB/A, 2 AB, S → colour and measure up

A
  1. antigen coated well
  2. wash - add specific antibody to be measured
  3. wash - add enzyme-conjugated secondary antibody
  4. wash - add substrate (S) and measure colour
  • sandwich ELIZA is identical except step specific “antigen” is added in step 2
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28
Q

How is a competitive ELIZA carried out?

A
  1. incubate antibody with antigen to be measured
  2. add Ag-Ab mixture to antigen-coated well
  3. wash - add enzyme-conjugated secondary antibody
  4. wash - add substrate (S) and measure colour
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29
Q

What is CT?

A
  • diverse, deep tissue never exposed to outside body derived from mesoderm
  • can contain bone, blood and fat
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30
Q

What are the four main functions of CT?

SPSR

A
  • support by binding tissues (e.g. cartilage)
  • store nutritional substances (e.g. fat)
  • produce protective and regulatory substances (ECM)
  • repair (by replication)
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31
Q

Describe the cells and vascularisation of CT.

A
  • sparsely cellular tissues
  • cell adhesion mechanism (to ECM)
  • highly vascularised and well-nourished – send nutrients to epithelium
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32
Q

What are the three types of fascia (framework of CT)?

A
  • superficial fascia (betwe/ skin and organs)
  • deep fascia (strong, fibrous internal membrane)
  • subserous membrane (between serous membranes and deep fascia)
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33
Q

Classify the cell types in CT.

HInt - three types which are least to most solid

A
  • CT proper → loose and dense CT
  • fluid CT → blood and lymph
  • supporting CT → cartilage and bone
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34
Q

What are the 3 basic components of any connective tissue?

A
  1. specialised cells (i.e. fibroblast, osteocyte)
  2. protein fibres (e.g. collagen)
  3. ground substance
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35
Q

Describe the ground substance found within CT.

A
  • fills spaces between cells and surrounds all CT fibres (most of the CT volume)
  • matrix (ECM) = fibres + ground substance
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36
Q

Name five examples of support cells found in CT.

(2x ‘-blast’- active, growing/secreting ECM)
(3x ‘-cyte’ quiescent (inactive/dormant)

(MACOF)

A
  • fibroblasts
  • chondrocytes
  • osteocytes
  • myofibroblasts
  • adipocytes
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37
Q

Describe the three main CT fibres.

A
  • collagen: long, straight, branched, strong, flexible
  • reticular fibre: a network thinner than collagen which forms a branching interwoven framework
  • elastic fibre: branched, wavy, recoils after being stretched
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38
Q

Classify CT into five groups.

A
  1. embryonic
  2. proper: loose, dense regular, dense irregular, elastic, reticular, adipose
  3. cartilage: hyaline, fibrocartilage, elastic
  4. bone
  5. vascular: blood
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39
Q

Describe embryonic CT.

A
  • undifferentiated (mesenchyme)
  • migrates interacts with other tissues during foetal development → forms organs
  • some persists past embryonic period i.e. fibroblasts around blood vessels, umbilical cord
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40
Q

Describe CT proper.

Hint - it is the spindle tissue

A
  • (spindle-shaped) fibroblast cells → produce collagen, elastic and reticular fibres
  • loose flexible matrix
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41
Q

What are the functions of loose and adipose CT? Give an example for each.

(Hint - loose = joining and adipose = when we have no food left)

A

• loose CT:
- functions: binding and packing, flexible, strength in all directions
- i.e. skin to underlying muscle, surrounds blood vessels/nerves
• adipose CT:
- cells store fat droplets which act as food reserve, protect organs and insulate
- i.e. skin hypodermis, cardiac surface, breast, surrounding joints

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42
Q

State the arrangement of fibres in dense regular CT, dense irregular CT, elastic CT and reticular CT. Give an example for each.

A

• dense regular CT:
- densely-packed collagen fibres parallel to direction of force
- i.e. tendons and ligaments
• dense irregular CT:
- densely-packed, interwoven collagen fibres, strength in all directions
- i.e. skin dermis, submucosa of GI tract
• elastic CT:
- elastic fibres, irregular arrangement, yellow, stretch and recoil
- i.e. wall of large arteries, larynx, trachea, bronchial tubes
• reticular CT
- jelly-like matrix, woven network of reticular fibres
- i.e. forms framework of liver, spleen

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43
Q

Describe cartilage.

Hint - not blood but not altogether bone either

A
  • supportive, protective CT with elastic properties
  • but associated with bone and avascular (difficult to heal)
  • contains chondrocyte cells
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44
Q

Describe the three types of cartilage and where they are found.

A
  1. hyaline cartilage: provides stiff, flexible support and reduces friction between bony surfaces
    - located: between tips of ribs, sternum, at synovial joints, larynx, trachea, part of nasal septum
  2. elastic cartilage: supports and tolerates distortion without damage
    - located: auricle of ext. ear, epiglottis, auditory canal, cuneiform cartilage of larynx
  3. fibrocartilage: resists compression limiting relative movement and prevents bone-to-bone contact
    - located: pads within knee joint, between pubic bones and intervertebral discs
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45
Q

Describe bone CT.

A
  • cells: osteoblasts, osteoclasts and osteocytes
  • rigid (calcium phosphate) and flexible (collagen fibres)
  • metabolically active with rich vascular supply
  • can be compact (dense, hard outer layer)or spongy/cancellous (porous, vascular inner layer, contains blood cells)
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46
Q

Describe vascular CT (blood).

A
  • contains: erythrocytes, leukocytes, thrombocytes (platelets)
  • highly-specialised → viscous with liquid plasma matrix
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47
Q

What is epithelia?

A
  • tissues that serve as protective and secretory layers

- formed into tightly-cohesive cellular sheets as components of bodily organs

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48
Q

What is the function of epithelia and what does it usually form the functional unit of?

A
  • to cover/line body surfaces (e.g. alimentary canal, exocrine ducts)
  • secretory glands i.e. salivary, mammary, sweat
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49
Q

What are the five common features of all epithelia?

A
  • limited intercellular space
  • single/multiple layers of cells
  • free apical surfaces
  • basement membrane
  • mitotic capability
50
Q

How is epithelia classified?

A

• layers:
- simple: 1-cell-thick e.g. alveoli and lung capillaries
- stratified: 1+ cells thick
• shape:
- squamous - flattened cells e.g. oesophagus, skin
- columnar - cells taller than wide i.e. small intestine, salivary gland duct
- cuboidal – cells of similar height, depth and width i.e. kidney tubules, sweat gland duct
- transitional - cells in layers which change shape when stretched i.e. urological tract

51
Q

What is the basal surface and basement membrane of a epithelial layer?

(BS = BR and BM = CE)

A
  • basal surface: basal lamina (sheet) + reticular fibre layer underlying it
  • basement membrane: separation from underlying CT used to support epithelia and selectively filter entering substances
52
Q

What can be found on the apical surface of a layer of epithelium?

A
  • microvilli (‘brush border’ in small intestine)

- cilia (e.g. trachea and resp. bronchus)

53
Q

What can be found on the lateral surface of a layer of epithelium?

A
  • cell junctions connecting cells
  • 3 types:
    1. desmosomes (adhesive spots with cadherins)
    2. tight junctions (fused PMs of cells - GI tract)
    3. gap junction (spot-like electrical propagation in cardiac tissues)
54
Q

What is glandular epithelium and which products can it secrete?

(SHEMOM)

A
  • aggregates of epithelial cells clustered together to perform specific excretory function
  • sweat
  • hormones
  • enzymes
  • milk
  • oil
  • mucous
55
Q

What are exocrine glands?

A
  • pour products into ducts that open into lumen of organ/onto skin
56
Q

What are endocrine glands?

A
  • ductless glands which secrete into empty tissues spaces → eventually bloodstream
57
Q

Describe the three main types of endocrine glands and provide examples of them.

(M for Minimal damage, ‘holo’ is Latin for ‘whole’ cell destruction and ‘apocrine’ gland for ‘apical’ end)

A
  • merocrine gland: secretion passes from cells without damage to PM – exocytosis i.e. salivary gland
  • holocrine gland: involves death of cell i.e. sebaceous gland – cellular debris part of secretion (sebum)
  • apocrine gland: apical end is pinched off e.g. mammary gland
58
Q

What are the four morphological classifications of exocrine glands?

(CS lewis used BT broadband)

A
  • simple – single tube i.e. simple tubular glands in colon
  • compound – branched duct system
  • branches
  • tubular acinar/alveolar (grape-like)
59
Q

What is an epithelial membrane and what does it contain?

A
  • thin sheets of flexible tissue that line parts or membranes of the body
  • contains: epithelia + (underlying) CT
60
Q

What is a serous membrane (serosa)?

A
  • simple squamous epithelium on a layer of loose CT which lines closed body cavities and internal organs
  • secretes serous fluid (lubrication)
  • two layers; parietal (body wall) and visceral (to organ)
  • i.e. pleura, pericardium, peritoneum
61
Q

What is a mucous membrane (mucousa)?

A
  • epithelial tissue which lines cavities open to outside and secretes mucus
  • i.e. mucus cells/glands, lumen of digestive system (microvilli), gut, reproductive, respiratory tract (cilia)
62
Q

What is a cutaneous membrane?

Hint - what it says on the tin

A
  • membrane covering outer surface of body

- skin

63
Q

What is a synovial membrane?

A

contains only CT and lines cavities of (freely-moveable) synovial joints

64
Q

Which epithelia is exposed to the environment?

A
  • skin
  • respiratory tract
  • digestive tract
  • reproductive system
  • circulatory system
  • endothelium
  • urinary system
  • glands e.g. liver
65
Q

What is pathology?

A
  • study of disease processes (diagnosis not treatment)
  • affect histological organisation of tissues and organs
    – biopsy needed for diagnosis
66
Q

What does inflammation occur in response to?

A

• tissue injury due to:

  • impact, abrasion, distortion
  • chemical irritation, extreme temp
  • infection, pathogenic organisms
  • if to a hyper-sensitive degree → kills cells, damages fibres and injures tissue
67
Q

What is necrosis?

A
  • tissue degeneration by lysosomal enzymes

- produces dead cells, debris, fluid and necrotic tissue compounds (pus)

68
Q

How does aging affect tissue repair?

A
  • decreases with age as structural + chemical composition of tissues affected e.g. epithelia get thinner
  • cancer rates increase w/ age
  • chemical exposure/environmental factors/smoking
69
Q

What are the stats for most common cancer in and which is the most common cause of death in males and females?

A 
F: 
- most common = breast 
- cause of cancer death = lung (white), breast (Hispanic)
M:
- most common = prostate 
- cause of cancer death = lung
70
Q

What is dysplasia?

A

loss of normal architecture of cells but not cancerous

71
Q

Describe signs of dysplasia, treatment, future risks and examples of this.

A

• signs:
- chronic irritation arises in epithelial tissue
- cells with a high nuclear: cytoplasmic ratio
- increase in mitotic divisions
• treatment: remove irritant/surgery
• future risks: leads to neoplasm - a malignancy if cells start to mutate and invade
• i.e. cervix, sun-epidermis, smoking and respiratory epithelium

72
Q

Describe possible causes of progression dysplasia (neoplasia) in the following epithelia:

a) squamous epithelium
b) epidermis
c) colonic mucosa
d) gastric mucosa
e) respiratory epithelium

A

a) cervix
b) sun-exposed skin
c) long-standing chronic colitis
d) long-standing chronic gastritis
e) smoking

73
Q

What is metaplasia and what can metaplasiac tissues do?

A
  • when tissues adapt to environmental stimuli by change in cell differentiation
  • differentiate into new, stable cell type better-equipped to withstand particular environmental stress

(most common in epithelial tissues: ciliated columnar/transitional epithelium → squamous epithelium)

74
Q

What is neoplasia?

A
  • permanent alteration of normal cellular growth pattern to transformed cells which proliferate excessively
  • to form a lump (neoplasm or ‘new growth’) which can be benign or malignant
75
Q

Describe malignant neoplasms.

A
  • cell growth so abnormal cells can grow into adjacent local tissues at expense of other tissues (damage + destruction)
  • move to another part of body (metastasis) and grow as separate secondary tumour
76
Q

What does the differentiation of benign tumours/neoplasms resemble?

A

closely resembles cells of origin

77
Q

What do malignant tumours/neoplasms in their variable degrees of differentiation resemble?

A
  • well-differentiated: closely resemble tissue of origin
  • poorly-differentiated: slightly resemble tissue of origin
  • anaplastic: no resemblance to tissue of origin
78
Q

How do we name tumours according to epithelial origin?

A
  • benign = for solid and surface epithelium -adenoma
  • malignant = prefix = cell type, suffix = carcinoma
    (classify further by adding tissue of origin)
79
Q

Describe histological changes in response to cigarette smoke (reversible dysplasia).

A
  • change in shape, size and organisation of tissue cells
  • trachea lined pseudostratified, ciliated, columnar Ep
  • normal function of cilia: move mucus, trap foreign particles, moisten incoming air
  • smoke : paralyses cilia therefore mucous builds up leading to ‘smokers cough’
80
Q

What are the four stages (→) by which normal cells can become cancerous?

A

normal → hyperplasia → dysplasia → cancer

81
Q

What is metaplasia (reversible)?

A
  • structural change
  • lose cilia cells
  • new stem cells no longer differentiate into ciliated columnar epithelium but into sq. epithelium which allows protection against drying and chemical irritation
  • protects underlying tissues but smoke can now reach more delicate epithelium
  • eliminates moisturising and cleaning properties (no cilia)
82
Q

What is irreversible metaplasia/anaplasia?

A
  • tissue organisation breaks down
  • cells change size and shape becoming very small/large
  • epithelial cell transformed into tumour cell (lung cancer)
83
Q

What is atherosclerosis, its pathogenesis and its associated risk factors?

A
  • thickening and inelasticity of artery walls
  • pathogenesis: damage to endothelium so LDL’s enter intima causing fatty streak, endothelium becomes fragile and platelet aggregation occurs by exposure to underlying collagen → possible thrombosis
  • risk factors: age, sex, hyperlipidaemia, hypertension, diabetes, smoking
84
Q

How does an atheroma decrease blood flow?

A

as fatty streak is enlarging makes lumen of artery smaller

85
Q

What is dermatopathology?

A
  • skin is exposed to more damaging agents than other tissues
  • wide range of disease patterns and tumours (30-40)
  • other epithelial surfaces e.g. respiratory – limited range of disease processes
86
Q

What is non-specific dermatitis (eczema)?

A
  • red, itchy, tender skin with tiny blisters → vesicles formed due to fluid accumulation between epidermal cells
  • vesicles erupt causes clear, yellow fluid to crust over
87
Q

What is chronic dermatitis?

Hint - brick guy from hulk

A
  • repeated trauma – thick, cracked, skin covered by thick opaque scale (thickened by keratin overlying epidermis)
  • epidermis thickened by increase of cells in various layers (stratum spinosum and granular layer)
  • elongation and accentuation of rete ridges in epidermis
88
Q

Describe smooth muscle.

A
  • SM cells connected by gap junctions
  • spindle-like cells w/ central nucleus
  • diagonally-arranged across cell
  • actin thin filaments anchored to dense bodies arranged w/in a network of intermediate (desmin) fibres
  • myosin fibres scattered throughout cell w/in network of intermediate fibres
  • lines tubular and hollow structures in body
89
Q

Describe cardiac muscle.

A
  • striated and each fibre (sarcomere) consists of a single branched cell
  • central nucleus and lots of mitochondria
  • fibres connected via thickenings of sarcolemma (s. membrane) called intercalated discs (composed of desmosomes and gap junctions for electrical signals to go cell-to-cell)
  • heart only
90
Q

Describe skeletal muscle.

A
  • major muscle type - 40% of BW
  • movement of bones
    surrounded by CT sheath (epimysium)
  • beneath epimysium are muscle fascicles (bundles of muscle fibres made lots of fused myoblasts)
  • each fascicle surrounded by perimysium (CT layer)
91
Q

What are satellite cells and when are they found?

A
  • unfused myoblasts found within muscle fibres

- can enlarge and divide after muscle injury

92
Q

What are the constituents of muscle fibers and what are they made of?

(Hint - fibrils and AM)

A
  • myofibrils (1-2 μm diameter, but extend whole length of the cell)
  • 2 forms of myofilaments:
    1. (thin) actin filaments
    2. (thick) myosin filaments
93
Q

What does the membrane potential of excitable cells depend on and what is RMP?

A
  • membrane potential is dependent on relative permeability of membrane to Na and K
  • resting MP = -95mv
94
Q

What effect do depolarisation and repolarisation have on excitable cells?

A
  • depolarisation; opening of ligand and voltage-gated Na channels → promote Ca2+ release from SR
  • repolarisation: changes K permeability and Na/K pump
95
Q

Why do all components in a muscle fibre contract simultaneously?

A
  • as signal distributed evenly by T-tubules
  • narrow tubes filled with EC fluid which extend from sarcolemma into sarcoplasm of muscle fibre
  • tightly-bound to membrane of SR
96
Q

What does sarcoplasmic reticulum enlarge and fuse to form?

A
  • large chambers (= terminal cisternae) either side of each T-tubule
  • a tubular network around each myofibril
97
Q

What is a triad is sarcoplasmic reticulum?

(1 + 2 = 3)

A

association betw/ an encircling T-tubule and a pair of terminal cisternae

98
Q

Describe sarcoplasmic reticulum and its actions in muscle.

A
  • sarcoplasm deficient in Ca2⁺
  • SR has stored Ca2⁺
  • when muscle cells fire AP, potential change conducted along T-tubule
  • allows release of Ca2⁺ from SR into sarcoplasm
99
Q

Which types of muscle both share the sliding filament model as a contraction mechanism? Describe this mechanism.

(Hint - I/A xZ)

A
  • skeletal + cardiac muscle
  • when muscle contracts:
    1. actin filaments of I-band slide over myosin filaments of A-band
    2. Z-discs move closer together
100
Q

What is myosin (A-band)?

A
  • formed from myosin-II
  • consists of two identical heavy chains, each bound to pair of light chains:
    • heavy chain (A-band):
  • NH₂ terminal forms motor head domain
  • COOH end forms elongated tail (forms α-helix with second heavy chain to form dimer)
  • heavy chain dimers polymerise into stable bipolar filaments with free head groups at either end
    • actin – I band
  • chain of globular actin molecules each of which has a binding site for myosin head
  • actin helix coupled every 7th molecule to two other proteins - tropomyosin and troponin
101
Q

Describe tropomyosin.

A
  • rod-shaped

- binds via troponin molecule to groove on actin helix to mask myosin binding site

102
Q

Troponin is made up of a complex of troponin I, T, C. Describe its structure and which molecule each form of troponin binds to.

A
  • complex of troponin I, T, C
  • binding to 4 Ca2⁺ ions causes a conformational change in its structure
  • moves tropomyosin from myosin binding side
    • troponin I → actin
    • troponin T → tropomyosin
    • troponin C → calcium
103
Q

State the four stages of the cycle of muscle contraction.

A
  1. contraction is result of muscle cell excitation
  2. stored Ca2⁺ released from SR
  3. Ca2⁺ binds to troponin C causing conformational change in troponin complex
  4. tropomyosin moves away from actin binding sites, so myosin head can bind

all driven by ATP → ADP + Pi

104
Q

What happens to bands during movement/contraction?

A
  • HI = H and I band shorten during muscle contraction
  • Z discs move closer together
  • A band stays the same + M line (central)
105
Q

How is skeletal muscle controlled?

A

NS control:
- single axon branches within perimysium of muscle fascicle and roots will extend at ends to synaptic terminals
- form apposing the sarcolemma
- NMJ is formed from this; occurs halfway down muscle fibre length
(synaptic terminal, synaptic cleft, sarcolemma)

106
Q

What occurs at the synaptic cleft duing depolarisation

A
  1. ACh travels across synaptic cleft
  2. ACh binds to ACh receptors in sarcolemma
  3. triggers opening of Na channels and myocyte action potential
  4. ACh broken down by AChE

(motor-end-plate or MEP = region of sarcolemma rich in ACh receptors folded to increase SA and number available)

107
Q

What is the length-tension relationship of a muscle?

A
  • linear positive relationship between degree of stretch and tension:
  • tension generated dependent on number of cross-bridges formed between actin and myosin
  • stretching muscle modifies tension - varied degree of overlap between filaments
108
Q

What does a single stimulation of a muscle induce and what are its three main phases?

A
  • a single contraction called a twitch
    1. latent period (2ms)
    2. contraction phase (ends 15ms after stimulation)
    3. relaxation phase (lasts 25ms after contraction phase)
109
Q

What is the stimulus frequency (treppe) theory of muscle contraction?

A
  • if second stimulation occurs immediately after end of relaxation phase, next contraction → slightly bigger
  • continues for first 30-50 stimulations
  • theory; due to steadily increasing Ca concentrations
110
Q

What is physiological tetanus?

A

if 2nd stimulation occurs before relaxation phase ends contractions will merge and become larger

111
Q

Compare incomplete (unfused) complete (fused) tetanus.

Hint - incomplete is the weird unemployed person but complete is the normal graduated person

A

• incomplete (unfused)
- summation of contractions just after relaxation phase started
- subsequent stimulations applied at same frequency induce tension to rise until max. value reached (approx. 4x Treppe) - sketchy
• complete (fused)
- achieved by increasing stimulating frequency, eliminating relaxation phase
- muscle contracts up to max tension - smooth

112
Q

What is a motor unit?

A
  • muscle fibres collectively called motor unit

- 1 motor neurone innovates hundreds/thousands of muscle fibres

113
Q

What does motor unit size determine?

A
  • degree of fine control
  • e.g. muscles of eye → 1 motor unit has 4-6 muscle fibres
  • muscles of leg → 1 motor unit has 1000-2000 fibres
114
Q

What is muscle tone and what two things does it enable?

A
  • resting tension in some muscle cells or fibres of smooth and skeletal muscle
  • even when the whole muscle is at rest
  • enables:
    • maintenance of posture
    • diameter of tubular structures (blood vessels etc.) and thus resistance to flow
115
Q

Summarise the types and subtypes of contractions.

A
  • isotonic → concentric and eccentric

- isometric

116
Q

What is an isotonic contraction?

A
  • tension rises and muscle exceeds resistance to force

- length changes

117
Q

What is a isometric contraction?

A
  • tension generated in muscle does not exceed resistance to force
  • length does not change
118
Q

What is a concentric contraction?

Hint - short people have to concentrate more in sport

A
  • cross bridges are shortened

- muscle length changes

119
Q

What is a eccentric contraction?

Hint - most eccentric people are quite lanky/tall

A
  • cross bridges are lengthened
  • muscle length changes

(tension generated less than resistance, contraction of muscle slows extension i.e. when sitting, walking etc…)

120
Q

State the type of contraction in each example:

a) maintaining posture
b) pushing against locked door
c) picking up very heavy weights
d) 2kg of tension (resistance) must be generated before weight can be moved; after tension generated, muscle remains at 2kg
e) maintaining posture
f) when muscles not being moved e.g. holding yoga positions
g) 2kg of tension (resistance) must be generated after which muscle will remain at 2kg

A

a) isometric
b) isometric
c) isometric
d) isotonic
e) isometric
f) isometric
g) isotonic (concentric)

IMS (11 decks)

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