• SPONGY BONE - Less dense than compact bone – Contains red marrow: stem cellsblood cell components – Yellow marrow: fat storage centers
Types of Joints• The type of joints that are particularly important for physical activity and sport are: – BALL AND SOCKET JOINT - allows a full range of movement. E.g. the hip and shoulder joints – HINGE JOINT - movement in one plane: flexion and extension.
– GLIDING JOINT - these occur in the many small bones of the hand and feet. They allow a slight sliding motion forwards and backwards and from side to side.– PIVOT JOINT - allows rotation. E.g. atlas and axis in the neck.
• TASK:• the picture shows:• 1: Shoulder joint -ball and socket• 2: Elbow joint - hinge joint• can you name another ball and socket and hinge joint?
FOUR MAJOR TYPES OF BONES1. LONG BONES2. SHORT BONES3. FLAT BONES4. IRREGULAR BONES
LONG BONES• Greater in length than width• Absorb stress from body weight• Upper/lower appendages
Long bone structure1. Diaphysis- shaft with compact bone & medullary cavity2. Epiphysis- ends, articular cartilage & compact bone covering cancellous bone3. Epiphyseal line- between epiphysis & diaphysis- region of bone growth (epiphyseal plate)4. Medullary cavity- central cavity within diaphysis
SHORT BONES• ~ equal length/width• Wrists, ankles
FLAT BONES• Thin, flat in structure• Skull, ribs, sternum
IRREGULAR BONES• Variety of shapes• Vertebral column / bones of face
Skeletal Muscle Connections• Direct connection to Bone• Indirect connection via TENDON• ORIGIN: bone that does NOT move when muscle contracts• INSERTION: bone that MOVES when muscle contracts
Microscopic Structure of Muscle Fiber• Cell membrane = Sarcolemma• Cytoplasm = Sarcoplasm• Multiple Mitochondria = High E output• Fiber is filled with long myofibrils• Myofibrils filled with filaments arranged in contractile units called SARCOMERES. – Myosin (thick filament) – Actin (thin filament)
Sarcoplasmic Reticulum• Specialized ER connected to cell surface by T- tubules• Surrounds each myofibril• At rest, filled with Ca++ maintained by a calcium “pump”, uses ATP• When activated, pores open and release calcium, initiating contraction
Actin (thin) filament Composition• Long chains of actin globules in double spiral arrangement• Each actin contains binding site for myosin• Tropomyosin spiral around chain – blocks active site on actin• Troponin clustered along spiral – Binding site for calcium!
Myosin (thick) filament Composition• Contains 2 tails each with globular heads• Heads have ATP binding sites and ATPase for splitting ATP• Heads attracted to active sites on actin molecules• Heads form cross-bridges with actin
Sarcomere structure• Alternating dark and light bands• Central H-zone contains MYOSIN only• Lateral A-bands contain both ACTIN and MYOSIN filaments• End in I-bands contain ACTIN only (with Z-line in center) Z LINE TO Z LINE = 1 SARCOMERE
Nerve supply to Muscle Fiber• Each muscle fiber served by a motor neuron• Motor neuron ends in a pad filled with vacuoles packed with neurotransmitter• Pad sits above specialized piece of sarcolemma called motor end plate
Neuron pad + motor end plate = Neuromuscular junction(Space between called synaptic cleft )
Sliding Filament Theory of Muscle ContractionSequence of Steps:1. Neuron releases neurotransmitter, acetylcholine (ACh) into synaptic cleft2. ACh diffuses to motor end plate3. ACh binds to receptor on motor end plate4. Gated channel protein opens, Na+ rushes into cell interior, upsets RMP!
Generation of Action Potential• RMP = -70 Mv• Sudden influx of Na+ generates Action Potential• RMP later restored to normal by sodium-potassium pump
5. Action potential carried along the sarcolemma to transverse (“T”) tubules connected to Sarcoplasmic Reticulum6. SR membrane becomes permeable to calcium7. Sarcoplasm is flooded with calcium ions
8. Ca++ binds to troponin9. Ca/Troponin pulls tropomyosin out of the way, unmasks active site on actin molecules10. Myosin heads attach to actin11. Heads rotate, pull actin in to H-zone12. Z lines get closer…
13. Myosin splits ATP to recharge14. Continues until Action Potential is restored and Ca++ is pumped back into SR15.All sarcomeres shorten, shortening muscle cell
16. Shortening cell pulls on tendons attached to bones, moving bone at articulation17. Contraction of opposite muscle required to fully elongate shortened muscle
Reminders:• Refractory Period• All or None Effect• Breakdown of ACh by ACh-esterase
Disorders/Conditions of the Muscular System• Duchenne’s Muscular Dystrophy – Sex linked inheritance – Dystrophin protein deficiency – Tearing of sarcolemma – Accumulation of CT/fat – Muscular ATROPHY