PHYSIOLOGY ofMUSCULOSKELETAL

DR. Dr. H. Busjra M Nur MSc

Dept. Physiology FKUI / FKUMJ

Sarcomeres

• Fundamental units of contraction

• Composed of thick (myosin) and thin (actin) myofilaments, joined by crossbridges.

• Contraction of individual sarcomeres results in shortening or force development of the whole muscle

Types of Contraction (duration)

• Twitch

• Tetanic

Types of Contraction (length)

• Isotonic

• Isometric

• Motor unit

• Motor unit recruitment

• Reflexes in movement

• Gamma motor neuron

• Alfa motor neuron

• Muscle spindle

• Upper motor neuron

• Lower motor neuron

Motor Unit

• for precision function

- eye muscles

- fingers muscles

• for strength

- legs muscles

Motor unit recruitment

• All or none one motor unit

• Degree of strength degree of recruitment of motor units

Reflexes in movement

Upper motor neuronLower motor neuron

• Spastic paralysis / paresis

• Flaccid paralysis / paresis

Crossbridge cycle (skeletal & cardiac)

• Membrane potential Ca ion release from sarcoplasmic reticulum

• Ca binds to Troponin C

• Energy from ATP cross bridge

• Ca taken away Cross bridge release (need ATP)

• No ATP rigor mortis

• Calcium antagonist in cardiac disease

Neuromuscular Junction

• Motor neuron

• Terminal button

• Neuromyal cleft

• Motor end-plate

• Acetylcholine

Neuromuscular Junction

• Acetylcholin

- neurotransmitter

- ligand gated depolarization

- in the neuromuscular junction,

preganglionic and parasympathetic

neurons

• Black widow spider venom

- deadly effect

- explosive release of ACh

- prolonged depolarixation

diaphragm fail to relax properly

respiratory failure

• Clostridium botulinum toxin

- food poisoning

- lethal blow

- blocks release of ACh

- prevents muscle contraction

respiratory failure

• Curare

- blocks ACh receptor sites

no mucle tone / contraction

respiratory failure

in surgery

• Myasthenia gravis

- autoimmune disease

- antibodies inactivate ACh receptor sites

• Organophosphates

- pesticides

- inhibit AChE (irreversible) ACh ↑

muscle failure to repolarize

respiratory failure

- antidote : atropine (ACh antagonist)

• Neostigmine

- inhibit AChE (temporary)

- ↑ ACh in neuromuscular junction

+

Fatigue

• Muscle fatigue

- lactic acid

- depletion of energy

• Central fatigue

- psychological fatigue

• Neuromuscular fatigue

- inability to synthesize ACh rapidly

Muscle fiber types

• Slow Oxidative Fiber (TYPE I)

• Fast Oxidative Fiber (TYPE IIa)

• Fast Glycolytic Fiber (TYPE IIb)

Smooth Muscle

• Highly Economical in Its Energy Usage

• Cross bridge much more slowly

• Can maintain high level of force

• Can adapt to physiological needs: uterus muscle in pregnancy

• Composed of small, unstriated cells, contained contractile proteins

Smooth Muscle

• Single-Unit

• Multi-Unit

Single-Unit Smooth Muscle

• Gastrointestinal tract

• Blood vessels

• Respiratory tract

• Uterus

Multi-Unit Smooth Muscle

• iris

• ciliary

Cardiac muscle

• Small, striated cells

• Sarcomeres are similar to skeletal muscle

Cardiac muscle

• Atrium

• Ventricle

Bone

• Is living tissue

• A form of connective tissue

• Osteoblasts (“bone formers”) produce the organic matrix (collagen fibers)

• Osteoclasts (“bone breakers”)

Physiology of Bone

• Matrix calcium deposit

• Osteoblast bone deposition

• Osteoklast bone resorption

• Continously undergous remodeling

Calcium Deposit

• Calcium Input

• Vitamine D

• Vitamine D activation in the kidney

• Vitamine D in the liver

• Calsium absorption in the intestine

• Calsium reabsoption in renal tubulus

Additional Factors

• Physical activity

• Hormone – estrogene

-- testosterone

-- growth hormone

PTH (parathyroid hormone)

• Is essential for life

• ↑ Ca ions in the plasma

• ↑ reabsorption Ca ion in the kidney

• ↓ reabsorption of phosphate in the kidney

• Via vit D ↑ Ca absorption in intestine

• Calcitonin : ↓ Ca level

• Vit D : ↑ Ca absorption in intestine

Decreasing factors Osteoporosis

• Inactivity

• Long term Corticosteroid

• Malnutrition

• Menopause

• Decrease calcium absorption in intestine