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How do muscles generate force?
By contracting their cells
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What has these roles?
1. Movement
2. Stabilization
3. Moving substances throughout the body
4. Heat generation for thermoregulation
Muscles
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Skeletal muscle
- Voluntary & Multinucleated
- LOTS of mitochondria
- Controlled by the somatic NS
- Squeeze blood & lymph
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Agonist, Antogonist, and synergistic muscles + physics beind contraction
- 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
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Tendons v ligaments
Tendons : muscle-bone
Ligaments: bone-bone
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What is shivering?
A thermoregulatory process by the contraction of the skeletal muscles to warm the body
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Slow Twitch Fibers
Skeletal muscle fibers
- Red
- LOTS of myoglobin (only 1 O2 molecule)
- LOTS of mitochondria
- Slow to tire
- Postural
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Fast Twitch A Fibers
Skeletal Muscle fibers
- Red
- Rapid Contraction
- Myoglobin
- Less resistant to fatigue as slow twitch
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Fast Twitch B Fibers
Skeletal muscle fibers
- White
- Low myoglobin
- LOTS of glycogen because employ lots of glycogenolysis for energy
- Very rapid contraction
- Very fast to tire
- Biceps
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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
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Organization of muscle
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
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Muscle cell AP genesis
- 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
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Which muscle tissue structure ensures contraction of skeletal muscle is uniform and fast? What about for Cardiac muscle?
T-tubules
Gap jxns
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Steps of contraction:
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
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Rigor mortis
ATP needed to dislodge myosin from actin but after death no ATP so muscles initially remain contracted
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Role of ATP in contraction
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
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Recruitment of motor units
The more units that fire, the stronger the contraction
Smaller motor units for intricate contractions
Allows adjustments between picking up dumbell and pencil
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Do myocytes undergo mitosis?
No. Hypertrophy because too specialized to mitose.
Grow in diameter, number of sarcomeres & mitochondria, grow in sarcomere length also
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Cardiac muscle
- 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)
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Smooth muscle
- 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
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What do smooth muscles respond to?
- Neural stimulus
- pH
- O2
- CO2
- Temperature
- [ions]
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Glands of the skin
Sebacious = oil
Sudiferous = sweat
Cereminous = wax
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Types of joints
Fibruous - no movement
Cartilaginous - little movement, ribs
Synovial - most ROM, synovial fluid contains lymphocytes
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Hardness of bone given by? Tensile strength given by?
Hardness: Hydroxyapatite crystals Ca10(PO4)6(OH)2
Tensile strength: Collagen
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What has these roles?
1. Protection
2. Support
3. Movement
4. Energy storage
5. Blood cell production
6. Mineral storage
Bone
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What has these roles?
1. Thermoregulation
2. Protection
3. Sensory information
4. Blood reservoir
5. Immunity
6. Vit D
Skin
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When skin is burned, what is one of the biggest first aid concerns?
Water loss
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Role of muscle and fat?
Muscle generates heat, fat insulates
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Skin comes from which germ layer?
Epidermis = ectoderm
Dermis = Mesoderm!!!
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Is epidermis vasculated? Innervated? Alive?
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
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Dermis d glands
- Vascularized
- Contain hair follicles
- Innervated by both nerves an
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SubQ
- Fat layer of skin
- For thermoregulation
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Vit D and skin
- Skin contains melanocytes
- UV radiation promotes Vit D synthesis
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Types of thermoregulatory actions of skin
- 1. Radiation
- 2. Piloerection - goverened by smooth muscles
- 3. Vasoconstriction/dilation of blood vessels feeding skin in smooth muscles of arterioles
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Cartilage
- Know for: Flexibility and Resiliance
- Type of connective tissue
- Made of collagen
- Avascular and un-innervated
- Hyaline in joints
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Osteoblasts
- Secrete collagen and matrix
- CANNOT mitose
- Differentiate into Osteocytes
- Actions upregulated by calcitonin
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Osteocytes
- Bone cells
- CANNOT mitose
- Exchange nutrients & waste with blood
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Osteoclasts
- Resorb bone matrix
- Release minerals back into blood
- Thought to develop from monocytes
- Actions upregulated by PTH
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Effect on osteoclasts and osteoblasts on bone diameter and tips
 bones are hollow...osteoclasts make more hollow
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Types of bones
1. Long - compact & spongy
2. Short - cuboidal, ankle & wrist
3. Flat - skull, sternum, ribs
4. Irregular - vertebrae
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In long bone, where is spongy bone? Where is compact bone? Where are the different marrows?
Spongy bone - at either end, contains red marrow(site of RBC synthesis)
Compact bone - in diaphysis, surrounds yellow marrow(adipocytes)
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Mineral homeostasis in bones
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
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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
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Osmoregulation of skin
sweat excretes salts and nitrogenous wastes!
Also insulated bady against water loss
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Heat homeostasis skin
Too cold: piloerection + vasoconstriction
Too hot: vasodilation, sweat (evaporative cooling)
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Protection against abrasions, chemicals, bacteria
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
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Different types of heat exchange mechanisms
- 1. Radiation
- 2. Conduction
- 3. Evaporative cooling
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