Lecture 11 Musculoskeletal 1 Flashcards
Tissues
Groups of cells w/similar structure and special function
4 main types:
Muscle tissue
Nervous tissue (PC)
Epithelial tissue (IK)
Connective tissue
Connective tissue
Connects and supports and anchors various body parts
Has few cells dispersed in abundant ECM e.g. tendons, bones, blood
Tendons
Connective tissue
Transmit the mechanical force of muscle contractions to bones
Connected to muscle fibres one end and bone at the other
Very strong w/ one of the highest tensile strengths of soft tissue
Bone
A compromise between strength and weight
Dynamic tissue continuously remodelled
Comprises of mineralised collagen fibres embedded in amorphous ground substance
Calcium (hydroxyapatite) gives strength and collagen gives flexibility
Bones/tendons/ligaments/muscle allow movement
Composition:
Organic 30% - cells (2%) type l collagen (93%) ground substance (5%)
Inorganic 70% - Ca2+, PO4³- crystals
Function of bone
Support
- support soft tissues, attachment sites for tendons
Protection
- cranium protects brain, ribs protect heart and lungs, pelvic girdle protects reproductive organs
Movement
- sites for muscle attachment, work to produce movement
Storage
-minerals Ca and phosphorus
Blood cell formation
- in marrow of some bones
Classification of bone by shape
Long bone e.g. humerus of arm
Short bone e.g. carpals of wrist
Flat bone e.g. parietal bone of skull
Irregular bone e.g. vertebra
Blood cell formation in some bone marroe
Hematopoietic stem cells differentiate to
Myeloid progenitor cells to become
-monocytes
-erythrocytes
For clotting:
- neutrophils
- basophils
- basophils
Or lymphoid progenitor cells
Becoming T or B cells
The bone cycle
Osteoblasts are resorptive cells
Preosteoclasts arrive at resting bone surface and become active osteoclasts. Resorption occurs and mononuclear cells arrive. Reversal occurs and preosteoblasts arrive causing bone formation and osteocytes cause mineralisation
Types of muscle
3 types:
Skeletal: makes up muscular system
Cardiac: found only in heart
Smooth: throughout body in hollow organs and tubes
Two classifications:
Striated/unstriated
Voluntary/involuntary
Muscle categories
Skeletal - striated voluntary
Cardiac - striated involuntary
Smooth - unstriated involuntary
Some vol impact possible on cardiac e.g. fear increases heart rate
Muscle contraction allows
Movement
Manipulation of external objects
Propulsion of contents through tubes
Emptying of contents of certain organs to external environment
Skeletal muscle
Made up of a no. Of muscle fibres lying in parallel held together by connective tissue.
Single skeletal muscle cell is known as a muscle fibre
- multinucleated
-large, elongated, cylindrical shape
- fibres usually extend entire length of muscle
Skeletal muscle: myofibrils
Contractile element of fibre
Regular arrangement of thick (myosin) and thin (actin) filaments
Viewed microscopically myofibrils display alternating dark (A bands) and light (I bands) giving striation appearance
Muscle structure
Sarcomere - functional unit of skeletal muscle - found between 2 z lines
Regions of sarcomere:
A band - thick filaments w/portions of thin filaments that overlap both ends of the thick filaments
H zone - region within middle of A band where filaments do not reach
M line - extends vertically down centre of A band within mid part of H zone
I band - made of remaining bit of thin filaments that does not project into A band
Composition of fibres : titin
Titin
- large, very elastic protein
-extends in both directions from M line along lengths of thick filament to Z lines at opposite ends of the sarcomere
2 roles:
- stabilises site of thick filaments in relation to thin filaments
- increases muscle elasticity by acting like a spring
Myosin thick filaments
Made up of 2 identical tail ends wrapped around each other with globular heads that project out of one end
Tails orient towards centre of filaments and globular heads point outwards at regular intervals
Heads form cross bridges between thick and thin filaments
Cross bridges have 2 important sites for contraction:
1) actin binding site
2) myosin ATPase site
Actin thin filaments
Spherical molecules
2 other proteins involved - tropomyosin and tropin
Each actin molecule has specialised binding site for attachment with myosin cross bridge - binding results in contraction of muscle fibre
Regulatory proteins tropomyosin and tropin
Tropomyosin
Threadlike molecules that lie end to end alongside the groove of the actin spiral covering actin sites blocking interactions that lead to muscle contractions
Troponin
Made of 3 polypeptide units:
Troponin C, I and T
Calcium and cross bridge formation
Troponin
Stabilises tropomyosin in blocking position over actins cross bridge binding sites
When Ca2+ binds to troponin tropomyosin moves away from blocking position
With tropomyosin out of the way actin and myosin bind - interact at cross bridge
Muscle contracts
Molecular basis of muscle contractions
Sliding filament mechanism
Ca2+ increases and filaments start to slide
Thin filaments slide inwards over stationary thick filaments towards middle of A band during contraction
As they slide inward they pull z lines closer together
All sarcomeres throughout muscle fibres length shorten simultaneously
Contraction is accomplished by thin filaments from opposite sides of each sarcomere sliding closer between thick filaments
Contraction
Ca2+ released into sarcoplasm from sarcoplasmic reticulum
Myosin head binds to actin
Myosin heads swivel towards centre of sarcomere (power stroke)
ATP binds to myosin head and detaches it from actin
Hydrolysis of ATP transfers energy to myosin head and reorients it
Contraction continues if ATP is available and Ca2+ level in sarcoplasm remains high
Relaxation depends on reuptake of Ca2+ in SR
Nerve muscle interface
Neuromuscular junction
Synapse
Presynaptic (motor neurone)
Postsynaptic (muscle fibres)
Release of ACh is stimulus for muscle to contract
Two membranous structures in fibre important to link excitation to contraction
- sarcoplasmic reticulum
- transverse tubules
