Muscles, Bones, and Skin

By contracting their cells

Muscles 

• Voluntary & Multinucleated 
• LOTS of mitochondria 
• Controlled by the somatic NS
• Squeeze blood & lymph  

• Agonist - contracts 
• Synergists - help agonist by stabilizing bones involved in movement
• Antagonist - Stretches

Muscles apply force at insertion point of bone -- The bone is then rotated about an axis of rotation i.e. joint

• Muscles DECREASE the body's bulk by INCREASING the force and DECREASING the lever arm --- this allows us to maintain our ROM
•  

Tendons : muscle-bone 

Ligaments: bone-bone  

A thermoregulatory process by the contraction of the skeletal muscles to warm the body 

Skeletal muscle fibers 

• Red
• LOTS of myoglobin (only 1 O2 molecule)
• LOTS of mitochondria
• Slow to tire
• Postural  

Skeletal Muscle fibers 

• Red
• Rapid Contraction
• Myoglobin
• Less resistant to fatigue as slow twitch  

Skeletal muscle fibers 

• White
• Low myoglobin
• LOTS of glycogen because employ lots of glycogenolysis for energy
• Very rapid  contraction 
• Very fast to tire
• Biceps  

H zone - Thick filaments, gets smaller 

I band - Actin only, gets smaller, light 

A band - both thick and thin filaments, doesn't change length, dark

Sarcomere = smallest fxnal unit of muscle 

2+sarcomeres = myofibril

Myofibril covered by sarcoplasmic reticulum (filled with Ca2+)

2+myofibrils = Muscle cell

Muscle cells wrapped by Sarcolemma

• 1. Efferent neuron releases ACh at neuromuscular synapse 
• 2. ACh generates AP in Sarcolemma
• 3. AP moves into T-tubules
• 4. AP reaches SR
• 5. SR becomes permeable to Ca2+
• 6. At end of contraction, Ca2+ is pumped back into SR  

T-tubules 

Gap jxns 

1. Tropomyosin covers active site of actin, myosin head is bound to ADP and cocked 

2. Ca2+ ions cause troponin to pull tropomyosin back, revealing actin's active site

3. Myosin binds actin

4. Myosin loses ADP and tugs on actin, contraction and shortening of sarcomere

5. ATP attached to myosin to release myosin from actin


6. ATP --> ADP and myosin cocks itself once again  

ATP needed to dislodge myosin from actin but after death no ATP so muscles initially remain contracted 

ATP BINDING causes myosin to release from active site

ATP SPLITTING causes myosin head to cock to readiness (this is what requires energy)

Myosin is like an ATPase because it hydrolyzes ATP to ADP 

The more units that fire, the stronger the contraction 

Smaller motor units for intricate contractions

Allows adjustments between picking up dumbell and pencil  

No. Hypertrophy because too specialized to mitose. 

Grow in diameter, number of sarcomeres & mitochondria, grow in sarcomere length also  

• Striated (having sarcomere) 
• Connected via intercalated discs and gap jxns
• Mono-nucleate
• Involuntary
• Grows by hypertrophy 

AP plateau due to slow v-gated Ca2+ channels (serves to lengthen time of contraction)  

• Involuntary & mono-nucleate 
• Unstriated 

Innervated by autonomic NS  

• Contains intermediate filaments, which are attached to dense bodies
• When actin and myosin pull together, they pull intermediate filaments and dense bodies together also

Can be connected via gap jxns for smooth contraction  

• Neural stimulus 
• pH
• O2
• CO2
• Temperature
• [ions] 

Sebacious = oil 

Sudiferous = sweat

Cereminous = wax 

Fibruous - no movement

Cartilaginous - little movement, ribs

Synovial - most ROM, synovial fluid contains lymphocytes  

Hardness: Hydroxyapatite crystals Ca10(PO4)6(OH)2

Tensile strength: Collagen  

Bone 

Skin 

Water loss

Muscle generates heat, fat insulates 

Epidermis = ectoderm 

Dermis = Mesoderm!!! 

Non-vascular 

Innervated by smooth muscle - for thermoregulation & by merkle cells for sensation 

The outermost part is dead - as keratinocytes move outwards, they die off

Callous - thickened epidermis 

• Vascularized 
• Contain hair follicles
• Innervated by both nerves an 

• Fat layer of skin 
• For thermoregulation  

• Skin contains melanocytes 
• UV radiation promotes Vit D synthesis  

• 1. Radiation 
• 2. Piloerection - goverened by smooth muscles
• 3. Vasoconstriction/dilation  of blood vessels feeding skin in smooth muscles of arterioles  

• Know for: Flexibility and Resiliance 
• Type of connective tissue 
• Made of collagen
• Avascular and un-innervated
• Hyaline in joints  

• Secrete collagen and matrix 
• CANNOT mitose
• Differentiate into Osteocytes
• Actions upregulated by calcitonin  

• Bone cells 
• CANNOT mitose
• Exchange nutrients & waste with blood

• Resorb bone matrix 
• Release minerals back into blood
• Thought to develop from monocytes
• Actions upregulated by PTH 

• 
• bones are hollow...osteoclasts make more hollow 

1. Long - compact & spongy 

2. Short - cuboidal, ankle & wrist

3. Flat - skull, sternum, ribs

4. Irregular - vertebrae  

Spongy bone - at either end, contains red marrow(site of RBC synthesis) 

Compact bone - in diaphysis, surrounds yellow marrow(adipocytes)

Ca2+ in blood - bound to proteins or as salt/phosphates 

• Too much Ca2+ = fatigue & lethargy
• Too little = cramps

Most Ca2+ stored as hydroxyapatite in bone  - this makes bone a storage site for both Ca2+ and phosphates

Haveresian canals - tunneled by osteoclasts and contain blood + lymph vessels

Volkmann canals: interconnect H canals

Lamellae - matrical rings within H canals laid by osteoblasts

Canaliculi - pores that allows osteocytes to exhange nutrients with blood, within H canals  

sweat excretes salts and nitrogenous wastes! 

Also insulated bady against water loss  

Too cold: piloerection + vasoconstriction 

Too hot: vasodilation, sweat (evaporative cooling)  

1. Keratin makes tight seal to form barrier against pathogens and protect from abrasion 

2. Sweat is ACIDIC, contains Abs

3. Sebum kills bacteria

4. Natural flora

• 1. Radiation 
• 2. Conduction
• 3. Evaporative cooling