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Human Skeleton and Muscles: Anatomy and Physiology

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  • SABRINA PACE-HUMPHREYS

UNIT TITLE: ANATOMY & PHYSIOLOGY OF THE HUMAN SKELETON AND MUSCLES

In a short account explain skeletal and bone features which aid them to carry out their roles, Remember to link structure and function for both.

Adult skeletons consist of 206 individual bones arranged in two divisions – axial and appendicular skeleton. The former runs along the body’s midline and includes skull, rib and vertebral column regions. The latter consists of bones in upper limbs such as the radius and ulna, lower limbs and pelvic girdle regions.

Skeletal key functions:

  • Support – Structural framework for the body, supporting soft tissues and providing attachment points for skeletal muscle tendons.
  • Protection of internal organs from injury. E.g. rib cage protects lungs and heart.
  • Movement – Most skeletal muscles attach to bones and, on contraction, pull to produce movement. E.g. thigh muscles attach to the femur and pull on it during hip/knee joint movement.
  • Mineral storage/release – Bone tissue stores minerals like calcium and phosphorus which aid bone strength. Minerals are released on demand into blood to maintain mineral balances/travel to other body parts.
  • Blood cell production – Bones like pelvic and rib bones (adults) contain red bone marrow producing red blood cells.
  • Triglyceride storage – Yellow marrow consists of adipose cells storing triglyceride chemical energy reserve.

Bones are living organs made of cells, protein fibres and minerals. They include:

  • Diaphysis/Epiphyses – Bone shaft/End
  • Mataphyses – Region between above structures. In growing bone it contains a growth plate/layer of hyaline cartilage that allows the bone to lengthen.
  • Articular cartilage - Thin layer of hyaline cartilage covering part of the epiphyses where the bone forms a joint with another bone. Reduces friction/absorbs shock at freely moveable joints.
  • Periosteum - Tough connective tissue sheath. Protects bone, assists in fracture repair, nourishes bone tissue, serves as an attachment point for ligaments and tendons. Associated blood supply surrounds bone surface when articular cartilage not present. The inner osteogenic layer, consisting of cells, allows bone to grow in thickness.
  • Medullary cavity - Hollow space within diaphysis containing fatty bone marrow and blood vessels. Minimizes weight of the bone by reducing dense bone material where not needed. Tubular design of provides maximum strength with minimum weight.

 

Joint

Joint Type

Movement range

Hip

Ball and socket – Ball-like surface of bone fits into cup-like depression of another bone.

Permits movement around 3 axes – flexion-extension, adduction-abduction and rotation. E.g. The round ball head of the femur rests into the cup like acetabulum (socket) of the pelvis.

Elbow

Hinge - convex structure of bone fits into concave structure of another.

Produces angular open and close movement. One bone remains fixed while other moves on its axis. Permit only flexion and extension.

Wrist

Gliding

Relatively flat bone surface moves back-and-forth and from side-to-side. Limited in range but can be combined with rotation.

Ankle

Condyloid – convex, oval shaped projection of one bone fits into oval-shaped depression of another bone.

Permits movement across two axes – flexion/extension and abduction/adduction plus limited circumduction.

Thumb

Saddle – articular surface of bone is saddle shaped, while surface of other bone fits into saddle (like a rider).

Same as condyloid joint.

Cervical vertebrae (atlas-axis)

Pivot – rounded/pointed surface of bone articulates with a ring formed by another bone & ligament.

Allows movement around its own longitudinal axis. Allows for turning motion without sideway displacement or bending. E.g. CV allows for the heads range of motion while maintaining stability of head/neck.

Wrist

Plane – Surface is flat or slightly curved.

Back-and-forth, side-to-side movements. Some rotation.

Suture

Fibrous (Fused) – Lack synovial cavity.

Composed of a thin layer of dense tissue. Allows little/no movement. Sutures occur between skull bones. E.g. coronal suture between parietal and frontal bones. Irregular interlocking edges give them added strength/decrease chance of fracture.

Symphisis

Cartilaginous

No joint cavity. Bones held in place by cartilage. Limited movement. Only occur in body midline. E.g. pubic synthesis between anterior surfaces of hip bones.

 

Part 1 – Explain what joint and muscle movements are involved in running and how are they involved.

The legs move forward using the quadriceps at the front of the thigh. Quadriceps bend (flex) the hip joint and straighten (extend) and stabilise the knee. As the body moves forward the hamstrings are recruited to straighten (extend) the hip and bend (flex) the knee. They also help to bend the knee behind a runner. At the same time the muscles of the lower leg (inner and outer calf) extend and flex each ankle/foot during landing and take off e.g. plantar and dorsi flexion of the ankle joint. Impact is also absorbed by these muscles. The gluteal muscles not only help to extend the hip but also stabilize the trunk, keeping a runner upright. Hip flexors and extenders work with quads and hamstrings to move legs forward and back as well as stabilizing the hip joint which contributes to good running form.

The arms and shoulders are another key driving force for running power. The arms, which when running are held in a partially flexed position at the elbow joint due to the triceps flexing, are continuously moving at the shoulder joint in a backwards-forwards direction when running. This movement is also strengthened, and held, by recruitment of the Trapezius muscles.

Part 2 – Explain what joint and muscle movements are involved in working at a computer in an office and how are they involved.

When working at a computer the following joint and muscle movements, starting from the tip of the head, are:

The cervical vertebrae pivot joint enables our head to turn side-to-side/up and down which assists us when looking for information on a computer screens. Elbow joints, when resting or hovering over a desk, are in a constant 90 degree flexed state with the bicep muscles being flexed to bring the elbow joint to this position. The wrist joints, when working on a keyboard, are moving left, right and up and down closely followed by the finger and thumb joints which are flexing, extending and hovering to enable typing. Midline joints, such as vertebrae, hips, pelvis etc are in a neutral position in order to alleviate back pain associated with sitting for long periods of time. Well developed core muscles in the abdomen, back (latissimus dorsi) and shoulders help to keep us sitting upright in a neutral spinal position by continually contracting. When sitting our hips may often be pushed slightly out of line/forward, the joint is flexed. Gluteus muscles are in a constant state of flexion when a person is sitting as are the knee joints (if a person is sitting with the soles of their feet on the floor).

 

Skeletal muscles have complicated structures that allow them to move, what are these structures and how do they allow muscles to carry out their roles.

Skeletal muscle consists of numerous elongated muscle fibre cells arranged in fasciculi bundles. These bundles are separated by endomysium connective tissue with each of these surrounded by a stronger perimysium sheath. Blood vessels transport nutrients/oxygen in and move metabolic waste away. Hundreds of muscle fibres are enclosed within the epimysium connective tissue envelope and extend the muscles full length.

Fibres consist of cell membrane, myofibril, sarcoplasm (containing organelles such as mitochondria) and myofilaments actin and myosin.

Myosin is surrounded by 6 actin (each consisting of two heads wrapped around each other). At the myosin binding site on the actin (the twist) the myosin head attaches and both filaments overlap creating cross-bridges. When overlapping the myosin head - containing ATPase enzyme - releases ATP, powering muscle contraction.

Muscle contraction triggers when an impulse from the central nervous system is sent to a muscle via a motor neuron nerve. When it reaches the fibre the Sliding Filament Mechanism - a series of chemical events causing the above actin/myosin to overlap described above - is triggered. Myosin pulls on actin shortening the sarcomere. This signal is synchronized across all fibres so all myofibrils contract simultaneously.

Muscular functions are to produce body movements such as locomotion e.g. running; stabilize body positions; store and move substances around the body (oxygen to the muscle and metabolic waste from it); generate heat through contraction - vital for maintaining body temperature.

Antagonistic muscle pairs work in opposition with one moving a joint in one direction and another moving it back. E.g. the bicep contracts to bend the arm while the tricep muscle releases.

Three types of voluntary muscle fibre: Type 1 – Slow twitch fibres using aerobic respiration for sustained muscular contractions, such as maintaining posture. Type 2a – Fast Oxidative Fibres: mix of type 1 and 2b fibres using aerobic and anaerobic respiration to produce fast, strong muscle contractions - used in resistance training. Type 2b – Fast Twitch Glycolictic Fibres using anaerobic respiration for short, fast bursts of power.

 

‘Movement requires muscle and all muscles have antagonistic pairs’. Using this as the title write a short account of how muscle contraction and antagonism is vital for the co-ordinated movement of an organism. 200 words

Muscles are attached to bones by tendons so that when a muscle contracts (shortens) it pulls on the bone and, if part of a joint, said bone moves.

Muscles can only pull, they can’t push. So, if a joint was only controlled by one muscle, it would cause a problem as the bone would move in one direction and stay there.

Voluntary antagonistic muscles work in opposition so that when one group contracts the other relaxes. It’s impossible to fully stimulate the contraction of two antagonistic muscles at the same time. Muscles allow us to stand and sit by contracting/releasing constantly to stabilise the skeleton and to walk and run by contracting/releasing to move lower body limbs.

Antagonistic pairs normally consist of a flexor and extensor. E.g. to flex the elbow, the bicep flexor muscle works across three joints while the tricep (extensor) muscle is primarily concerned with extension of the elbow joint.

To move our legs we need to use the lower limbs and it is here that antagonistic muscles such as the quadriceps and hamstring work together to move the upper leg limbs while the tibalis anterior works in opposition to the calf muscle to move the lower leg.

Bibliography

Bbc.co.uk, (2014). BBC - GCSE Bitesize: Functions of the skeleton. [online] Available at: http://www.bbc.co.uk/schools/gcsebitesize/pe/appliedanatomy/2_anatomy_skeleton_rev1.shtml [Accessed 31 Dec. 2014].

Bbc.co.uk, (2015). BBC - GCSE Bitesize: Muscle tone and posture. [online] Available at: http://www.bbc.co.uk/schools/gcsebitesize/pe/appliedanatomy/3_anatomy_muscles_rev5.shtml [Accessed 6 Jan. 2015].

Bbc.co.uk, (2015). BBC Science & Nature - Human Body and Mind - Muscles Layer. [online] Available at: http://www.bbc.co.uk/science/humanbody/body/factfiles/skeletalsmoothandcardiac/quadriceps_animation.shtml [Accessed 6 Jan. 2015].

Kelly, J. (2014). Leg Muscles Used in Running - HowStuffWorks. [online] HowStuffWorks. Available at: http://adventure.howstuffworks.com/outdoor-activities/running/training/leg-workouts-for-runners1.htm [Accessed 31 Dec. 2014].

Mackenzie, B. (2014). Movement Analysis. [online] Brianmac.co.uk. Available at: http://www.brianmac.co.uk/moveanal.htm [Accessed 31 Dec. 2014].

Marieb, E. (1995). Human anatomy and physiology. Redwood City, Calif. [etc.]: Benjamin/Cummings, pp.293, 295.

S-cool.co.uk, (2014). GCSE PE How the Body Moves Revision - Joints | S-cool, the revision website. [online] Available at: http://www.s-cool.co.uk/gcse/pe/how-the-body-moves/revise-it/joints [Accessed 31 Dec. 2014].

Tortora, G. and Grabowski, S. (2003). Principles of anatomy and physiology. New York: Wiley, pp.290 - 304.


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