W14 - Skeletal Muscle Anatomy And Physiology Flashcards
Differentiate between axial and appendicular skeleton
Axial: axis of skeleton (main body)
- skull, vertebrae, ribs and sternum
Appendicular: appendages (limbs)
- bones of upper limb (including clavicle and scapula)
- bones of lower limbs (including pelvic bones)
Describe the main features of a long bone
- Diaphysis (shaft)
- Medullary (marrow) cavity: empty space in shaft
- Filled with bone marrow (red: blood; yellow: fat)
- Metaphysis (area between epiphysis and diaphysis)
- Epiphysis (wider upper and lower region)
- Proximal: Upper region (closer to axial region)
- Distal: Lower region (further from axial region)
(Check Notion image)
Explain how compact bone is arranged
Compact bone: hard, outer layer of bone, surrounds marrow cavity
- Cancellous bone: loose, internal spongy (mesh work of thin, bony struts)
- Osteons & Haversian system
- 1 Osteon = concentric layers of bone (lamellae)
- lacunae = tiny spaces between lamellae
- each lacuna contains osteocyte (living bone cells)
- lacunae = tiny spaces between lamellae
- Has central Haversian canal
- contains blood vessels and nerves
- External environment: bone lined by periosteum
- Internal environment: marrow cavity
(Check Notion image)
- 1 Osteon = concentric layers of bone (lamellae)
Explain the role of osteocytes in bone
- surrounded by bone matrix
- have cytoplasmic processes
- extend from their cell bodies & are contained in tiny canals (canaliculi)
- the processes of multiple osteocytes are connected
- enables nutrients and oxygen to pass from central vessels in Haversian canal -> osteocytes in the outermost concentric lamella
(Check Notion image)
- enables nutrients and oxygen to pass from central vessels in Haversian canal -> osteocytes in the outermost concentric lamella
State the stages of fracture repair
Fracture -> haematoma (most pool of blood clot around fracture) -> cartilage (fibrovascular tissue) -> callus (matrix, thick and surrounds bone) -> bone remodelling
Explain the structure of the upper limb
Top to bottom (check Notion image)
- Pectoral Girdle (shoulder region): scapula (shoulder blade), clavicle (collar bone)
- Humerus (upper arm)
- Radius (outer) and Ulna (inner)
- Bones of hand
Explain the structure of the lower limb
Top to bottom (check Notion image)
- Pelvic girdle (hips region): pelvic bone
- Femur (thigh)
- Tibia (inner) and Fibula (outer)
- Bones of the foot
Classify the different types of muscles
- Skeletal muscle - “voluntary” muscle (has the ability to move)
- Cardiac muscle - “involuntary” muscle (can not move)
- makes up the muscular walls of the heart (myocardium)
- Smooth muscle - “involuntary muscle”
Explain the structure of muscles
(Check Notion image)
- muscles are aligned either parallel or oblique (slanting, not parallel nor fully 90°) in line of action
- Fusiform or Flat sheet (parallel)
- eg. Biceps brachii (tendon, belly, tendon)
- contraction = greater distance being moved (shortens) -> increased speed (broad sheet
- Multipennate (oblique)
- eg. Deltoid muscle (shoulder)
- has more muscle fibres/myofibrils/sarcomeres than parallel muscles, despite being the same size
- i.e. don’t shorten, produces greater force
Compare and contrast tendon and ligament
- Both are composed of dense connective tissue w/ high collagen content
- Very similar structural composition, w/ minor diff.
- tendons have more type 1 collagen, but lesser type 3 collagen and ground substance than ligaments
- Tendons
- Found b/w bone and muscle
- Help generate movement by transferring force between the 2 structures
- Ligaments
- Found b/w bone and bone
- Generally stiff, inelastic = stabilises joints by limiting movement in specific directions
Explain the structure of a tendon
Parallel collagen fibres, arranged in a wave-like pattern, and fibroblast nuclei between the collagen fibres
(Check Notion image)
Explain how tendons are inserted into bone (?)
- Enthesis
- parallel collagen fibres of the tendon
- transition from unmineralised to mineralised fibrocartilage
- cortical bone
Explain ligaments in the elbow joint
- Synovial hinge joint
- Ligaments on the medial (inner elbow) and lateral side (outer elbow)
- Lateral collateral ligament (connect more to radius)
- Medial collateral ligament
Explain ligaments in the knee joint
- inferior end of of femur doesn’t fit with superior end of tibia (low congruency) = not much stability
- Lateral Collateral Ligament (thin, outer of the leg)
- Medial Collateral Ligament (inner leg)
- Anterior and Posterior Cruciate ligament (from a cross between the bones, anterior goes from back to front, posterior goes from front to back)
Explain ligaments in the intervertebral joints
- Ligamentum Flavum has a higher content of elastin fibres (less stiff)
- connects the anterior parts of the laminae to next vertebrae
- Anterior longitudinal ligament (lines the front of vertebral bodies/column)
- Posterior longitudinal ligament (lines back of vertebral body/column, in between the gap of the laminae)
How is muscle contraction triggered?
Contraction for all three types (skeletal, cardiac, smooth) is triggered by an increase in Ca2+
How does skeletal muscle contract?
- in response to neuromuscular synaptic transmission
- 1 skeletal muscle cell (fibre) -> 1 NMJ w/ concentrated ACh receptors
- receptors: non-selective cation channels that open in response to ACh binding -> depolarisation -> epp -> if epp > threshold -> V-gated Na+ -> action potential generated -> ACh is inactivated by ACh-esterase (quickl) -> cycle begins again
Describe the structures of myofibrils in relation to the whole muscle
Muscle -> Multiple muscle fibres layered w/ connective tissue -> muscle fibre -> made of multiple myofibrils
- Myofibrils have dark A bands followed by light I bands
- Sarcomere: layers of thin (actin) and thick (myosin) filament (myosin and actin = protein molecules) (filaments = cytoskeletal elements)
- Cross bridges: arm like attachments that extend from the thick to thin filaments
- Z-line: separates sarcomeres
- M-line: mid-line of sarcomeres
- A band: main expanse of sarcomere body
- I band: ends of sarcomere (includes Z-line)
- Sarcomere: layers of thin (actin) and thick (myosin) filament (myosin and actin = protein molecules) (filaments = cytoskeletal elements)
Explain how skeletal muscle fibres are striated by a highly organised internal arrangement
- Single skeletal muscle cell (muscle fibres are striated by highly organised internal arrangement)
- 10-100 μm in diameter and up to ~75 cm in length
- multiple nuclei and lots of mitochondria
- have 100s-1000s of myofibrils
- myofibrils: specialised contractile elements that extend throughout muscle fibre
Explain the arrangement of cytoskeletal element actin in thin filaments
- Actin molecules come together to form a helix
- they contain binding sites for attached with myosin cross bridge
- (tropo)myosin with the help of binding molecules troponin in wraps around the helical structure
- Tropomyosin blocks binding site on actin
- This is the structure of thin filaments
Explain the function of troponin
- Heterotrimer
- 1x troponin interactions with 1x tropomyosin -> interacts directly with 7x actin monomers
- Three types:
- Troponin T: binds to 1x tropomyosin
- Troponin C: binds Ca2+
- Troponin I: binds to actin and inhibits contraction
Explain the structure of myosin in thick filaments
-100 nm helical tail made of titin, with heads
- head contain Actin binding sites (binds to actin molecules) and myosin ATPase sites (hydrolyses ATP)
- made of multiple myosin-II molecules
- double trimmer, containing 2x of each of the following:
- intertwined heavy chains, intertwined light chains, alkali/essential light chains
- the two heavy chains are made up of a tail, hinge and head region
- tails: α-helices that intertwine
- hinge joint opens up -> 2x globular heads
- head regions: S1 fragments (cross bridges) b/w thick and thin filaments
- made of 2 light chains, 1 alkali/essential and 1 regulatory (attached on hinge region)
- alkali light chain = stabilises myosin head
- reg. light chain = regulates ATPase activity
- via phosphorylation by kinases
- made of 2 light chains, 1 alkali/essential and 1 regulatory (attached on hinge region)
- the two heavy chains are made up of a tail, hinge and head region
- intertwined heavy chains, intertwined light chains, alkali/essential light chains
- double trimmer, containing 2x of each of the following:
Explain the process of muscle contraction
- myosin-II heads bind to action -> cross-bridges become distorted -> detach
- energy for this comes from hydrolysis of ATP
- increase in [Ca2+]i triggers contraction by removing the inhibition of cross-bridge cycling
- Upon stimulation, [Ca2+]i may rise from resting level of < 10^-7 to > 10^-5 M
- Subsequent decrease in [Ca2+] -> relaxation, cross-bridge cycling relaxes
Explain the role of Ca2+ in cross-bridge cycling
- modulates contraction via regulatory proteins rather than interacting directly with the contractile proteins
- In absence of Ca2+: regulatory proteins inhibit actin-myosin interactions -> contractile process inhibited
- Ca2+ binding to one of more proteins: conformation change in regulatory complex -> inhibition stopped
(Check Notion image)
Explain what each Troponin C molecule is composed of + its role
- 2x high affinity Ca2+ binding sites
- help bind Troponin C to thin filaments
- Ca2+ doesn’t affect muscle activation
- 2x low affinity Ca2+ binding sites
- binding of Ca2+ -> conformational change
- Troponin I shifts -> tropomyosin molecule can now move, and with the help of Troponin T, tropomyosin is moved away from the myosin-binding site on the actin and into the actin groove
- binding of Ca2+ -> conformational change
- myosin is able to interact with actin and engage in cross bridge cycling
Explain the cross-bridge cycle ???? (SLIDE 23)
Contractile proteins convert the ATP hydrolysis energy -> mechanical energy
1. ATP binding
2. ATP hydrolysis
3. Cross-bridge formation
4. Release of Pi from myosin
5. ADP release
Explain what is meant by the sliding filament hypothesis of muscle contraction
- cross-bridge interaction b/w in actin and myosin -> muscle contraction with the sliding filament mechanism
- thin filaments on each side of a sarcomere slide inwards over stationary thick filaments
- as they slide inwards, the thin filaments, which are attached to Z lines, pull them closer together (power stroke) -> sarcomere shorten -> detaches -> cycle repeats
- all sarcomeres shorten simultaneously -> entire fibre shortens (not the actual filaments)
- A band: determine by thick filaments: stays same
- I band: thin filaments doesn’t overlap thick: width decreases
- H zone : within A band, thick filaments don’t overlap thin, width decreases
- Distance between Z lines: decreases
- thin filaments on each side of a sarcomere slide inwards over stationary thick filaments
Understand how and when rigor mortis occurs
- begins 3-4 hours after death and finished in 12 hours
