Lecture 11 Musculoskeletal 1

Question 1

Tissues

Answer 1

Groups of cells w/similar structure and special function

4 main types:

Muscle tissue
Nervous tissue (PC)
Epithelial tissue (IK)
Connective tissue

Question 2

Connective tissue

Answer 2

Connects and supports and anchors various body parts

Has few cells dispersed in abundant ECM e.g. tendons, bones, blood

Question 3

Tendons

Answer 3

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

Question 4

Bone

Answer 4

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

Question 5

Function of bone

Answer 5

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

Question 6

Classification of bone by shape

Answer 6

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

Question 7

Blood cell formation in some bone marroe

Answer 7

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

Question 8

The bone cycle

Answer 8

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

Question 9

Types of muscle

Answer 9

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

Question 10

Muscle categories

Answer 10

Skeletal - striated voluntary
Cardiac - striated involuntary
Smooth - unstriated involuntary

Some vol impact possible on cardiac e.g. fear increases heart rate

Question 11

Muscle contraction allows

Answer 11

Movement
Manipulation of external objects
Propulsion of contents through tubes
Emptying of contents of certain organs to external environment

Question 12

Skeletal muscle

Answer 12

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

Question 13

Skeletal muscle: myofibrils

Answer 13

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

Question 14

Muscle structure

Answer 14

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

Question 15

Composition of fibres : titin

Answer 15

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

Question 16

Myosin thick filaments

Answer 16

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

Question 17

Actin thin filaments

Answer 17

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

Question 18

Regulatory proteins tropomyosin and tropin

Answer 18

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

Question 19

Calcium and cross bridge formation

Answer 19

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

Question 20

Molecular basis of muscle contractions

Answer 20

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

Question 21

Contraction

Answer 21

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

Question 22

Nerve muscle interface

Answer 22

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