Skeletal and Muscular System

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Skeletal and Muscular System

• Movement -characteristic of animals. result of
  contraction of muscles
• skeleton helps transmit movement.
• Skeletons are either a fluid-filled body cavity,
  exoskeletons, or internal skeletons.

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Just because watch a cut through of the human
body

• http//www.nlm.nih.gov/research/visible/mpeg/umd_v
  ideo.mpg
• Page 102 study guide. Outline the great
  diversity of locomotion in fish earthworm, flying
  bird and walking arthropod.

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Hydrostatic systems

• Hydrostatic skeletons fluid-filled closed
  chambers.
• Internal pressures generated by muscle
  contractions cause movement as well as maintain
  the shape of the animals, such as the sea anemone
  and worms

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Exoskeleton

• Exoskeletons are characteristic of the Phylum
  Arthropoda. hard segments that cover the muscles
  and visceral organs. Muscles for movement attach
  to the inner surface of the exoskeleton.

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Endoskeleton

• Vertebrates -internal mineralized (in most cases)
  endoskeleton composed of bone and/or cartilage.
  Muscles are on the outside of the endoskeleton.
  Cartilage and bone are types of connective
  tissue.

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Functions of Muscles and Bones

• The skeleton and muscles function together as the
  musculoskeletal system.
• Plays an important homeostatic role allowing the
  animal to move to more favorable external
  conditions.
• Certain cells in the bones produce immune cells
  as well as important cellular components of the
  blood.

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• Bone also helps regulate blood calcium levels,
  serving as a calcium sink.
• Rapid muscular contraction is important in
  generating internal heat, another homeostatic
  function.
• Howstuffworks "Muscle Types Animation"

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Skeletal Muscle Systems/101 sg

• Vertebrates move by the actions of muscles on
  bones. Tendons attach skeletal muscles across
  joints, allowing muscle contraction to move the
  bones across the joint.

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• Muscles generally work in pairs to produce
  movement when one muscle flexes (or contracts)
  the other relaxes, a process known as antagonism.

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Ligaments

• Ligaments are tough, elastic, connective tissue
  joining bone to bone.
• Ligaments limit the range of motion at a joint
  while providing joint stability.

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Tendons

• Tendons are thick, dense connective tissues
  attaching muscle to bone. They are a continuation
  of the fascia.
• Tendons are relatively inelastic and transmit the
  energy of muscle action to bone.

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Put it all together in the elbow, page 102 sg
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Structure of skeletal muscle

• Look at page 101 sg. You will be asked to draw
  the structure of skeletal muscles fibers.
  Include actin filaments and thick myosin
  filaments, sarcoplasmic reticulum and
  mitochondria
• APC 100

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Muscles page 101 sg

• Muscles both electrical and chemical activity.
• There is an electrical gradient across the muscle
  cell membrane the outside is more positive than
  the inside.
• Stimulus causes an instantaneous reversal of this
  polarity, causing the muscle to contract (the
  mechanical characteristic) producing a twitch or
  movement.

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Organization of muscles
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Skeletal Muscle Structure

• Muscle fibers are multinucleated, with the nuclei
  located just under the plasma membrane. Most of
  the cell is occupied by striated, thread-like
  myofibrils. Within each myofibril there are dense
  Z lines.

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• A sarcomere (or muscle functional unit) extends
  from Z line to Z line. Each sarcomere has thick
  and thin filaments..

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• The thick filaments are made of myosin and occupy
  the center of each sarcomere. Thin filaments are
  made of actin and anchor to the Z line.

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• Muscles contract by shortening each sarcomere.
• The sliding filament model of muscle contraction
  has thin filaments on each side of the sarcomere
  sliding past each other until they meet in the
  middle.
• Myosin filaments have club-shaped heads that
  project toward the actin filaments.

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Myosin head

• Myosin heads attach to binding sites on the actin
  filaments.
• swivel toward the center of the sarcomere
• detach and then reattach to the nearest active
  site of the actin filament.
• http//www.sciencemag.org/feature/data/1049155s1.m
  ov

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• Each cycle of attachment, swiveling, and
  detachment shortens the sarcomere 1. Hundreds of
  such cycles occur each second during muscle
  contraction.

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The MYOSIN HEAD has several important
characteristics

• it has ATP-binding sites (ATP represents
  potential energy.)
• ACTIN-binding sites into which fit molecules of
  ACTIN.
• it has a "hinge"at the point where it leaves the
  core of the thick myofilament. This allows the
  head to swivel back and forth, and the
  "swivelling" is, as will be described shortly,
  what actually causes muscle contraction.

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Thin myofilaments are composed of 3 types of
protein

• ACTIN
• TROPONIN
• TROPOMYOSIN
• Animation Myofilament Contraction

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ACTIN

• when actin combines with MYOSIN HEAD the ATP
  associated with the head breaks down into ADP.
  This reaction released energy that causes the
  MYOSIN HEAD to SWIVEL.

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TROPOMYOSIN

• In a relaxed muscle, the MYOSIN HEADS of the
  thick myofilament lie against TROPOMYOSIN
  molecules of the thin myofilament. As long as the
  MYOSIN HEADS remain in contact with TROPOMYOSIN
  nothing happens (i.e., a muscle remains relaxed).

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TROPONIN

• Troponin molecules have binding sites for calcium
  ions. When a calcium ion fills this site it
  causes a change in the shape and position of
  TROPONIN.
• TROPONIN shifts, it pulls the TROPOMYOSIN to
  which it is attached.
• When TROPOMYOSIN is moved, the MYOSIN HEAD that
  was touching the tropomyosin now comes in contact
  with an underlying ACTIN molecule.
• Animation Action Potentials and Muscle
  Contraction

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Muscle contraction

• Because skeletal muscle is voluntary muscle,
  contraction requires a nervous impulse.
• 1 impulse is transferred from a neuron to the
  SARCOLEMMA of a muscle cell.
• 2 The impulse travels along the SARCOLEMMA and
  down the T-TUBULES. From the T-TUBULES, the
  impulse passes to the SARCOPLASMIC RETICULUM.

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• 3 - As the impulse travels along the Sarcoplasmic
  Reticulum (SR), the calcium gates in the membrane
  of the SR open. As a result, CALCIUM diffuses out
  of the SR and among the myofilaments.
• 4 - Calcium fills the binding sites in the
  TROPONIN molecules. As noted previously, this
  alters the shape and position of the TROPONIN
  which in turn causes movement of the attached
  TROPOMYOSIN molecule.

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• 5 - Movement of TROPOMYOSIN permits the MYOSIN
  HEAD to contact ACTIN.
• 6 - Contact with ACTIN causes the MYOSIN HEAD to
  swivel

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• 7 - During the swivel, the MYOSIN HEAD is firmly
  attached to ACTIN. So, when the HEAD swivels it
  pulls the ACTIN (and, therefore, the entire thin
  myofilament) forward. (Obviously, one MYOSIN HEAD
  cannot pull the entire thin myofilament. Many
  MYOSIN HEADS are swivelling simultaneously, or
  nearly so, and their collective efforts are
  enough to pull the entire thin my

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• Animation Quizzes crossbridge

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• 8 - At the end of the swivel, ATP fits into the
  binding site on the cross-bridge this breaks
  the bond between the cross-bridge (myosin) and
  actin. The MYOSIN HEAD then swivels back. As it
  swivels back, the ATP breaks down to ADP P and
  the cross-bridge again binds to an actin
  molecule.

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• 9 -  As a result, the HEAD is once again bound
  firmly to ACTIN. However, because the HEAD was
  not attached to actin when it swivelled back, the
  HEAD will bind to a different ACTIN molecule
  (i.e., one further back on the thin myofilament).
  Once the HEAD is attached to ACTIN, the
  cross-bridge again swivels, SO STEP 7 IS
  REPEATED.

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• Skeletal muscle relaxes when the nervous impulse
  stops. No impulse means that the membrane of the
  SARCOPLASMIC RETICULUM is no longer permeable to
  calcium (i.e., no impulse means that the CALCIUM
  GATES close

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• So, under most circumstances, calcium is the
  "switch" that turns muscle "on and off"
  (contracting and relaxing).

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Nerves, muscles and movements

• Nerve cells are called neurons.
• Nervous system divided into CNS ( brain and
  spinal cord) and PNS ( peripheral nerves).

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• dendrites provide a large surface area for
  connecting with other neurones, and carry nerve
  impulses towards the cell body.
• A single long axon carries the nerve impulse
  away from the cell body.
• Most neurones have many companion cells called
  Schwann cells, which wrap their cell membrane
  around the axon in a spiral to form a thick
  insulating lipid layer called the myelin sheath.

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• Nerve Impulses
• Neurones send messages electrochemically this
  means that chemicals cause an electrical impulse.
  
• Chemicals in the body are electrically charged
  when they have an electrical charge, they are
  called ions.

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• Resting Membrane Potential
• When a neurone is not sending a signal, it is at
  rest.
• The inside of the neurone is negative relative to
  the outside.
• K can cross through the membrane easily
• Cl- and Na have a more difficult time crossing
• Negatively charged protein molecules inside the
  neurone cannot cross the membrane.

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• Resting Membrane Potential
• The membranes contain sodium-potassium pumps
  (NaKATPase).
• Uses ATP to simultaneously pump 3 sodium ions out
  of the cell and 2 potassium ions in.
• Animations

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• There are also sodium and potassium ion channels
  in the membrane.
• These channels are normally closed, but even when
  closed, they leak, allowing sodium ions to leak
  in and potassium ions leak out down their
  concentration gradients.

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• This creates an action potential.
• Chapter 39 Introduction
• Tutorial 44.2 The Action Potential

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This creates an action potential.

• An action potential is initiated by a stimulus
  above a certain intensity or threshold.
• Not all stimuli initiate an action potential.
• The stimulus could be a pin prick, light, heat,
  sound or an electrical disturbance in another
  part of the neuron.

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Depolarization

• A stimulus causes a gate in the Na Channel to
  open.
• Since there is a high concentration of Na
  outside, Na diffuses into the neuron.
• The electrical potential changes to 40 mV.

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Repolarization

• Depolarization causes the K Channel gate to
  immediately open.
• K diffuses out of the neuron.
• This reestablishes the initial electrical
  potential of -60 mV.

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Refractory Period

• During this time ( 1 msec), the Na and K
  Channels cannot be opened by a stimulus.
• The Na/K Pump actively pumps Na out of the
  neuron and K into the neuron. This reestablishes
  the initial ion distribution of the resting
  neuron. Action Potential

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• Nerve impulse can be passed from the axon of one
  neuron to the dendrite of another at a synapse. A
  nerve is a discrete bundle of several thousand
  neuron axons.

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The message

• http//www.mind.ilstu.edu/flash/synapse_1.swf
• Animation Function of the Neuromuscular Junction
  (Quiz 1)

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These images illustrate the general process of
synaptic transmission

• Step 1. The neurotransmitter is manufactured by
  the neuron and stored in vesicles at the axon
  terminal.

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• Step 2. When the action potential reaches the
  axon terminal, it causes the vesicles to release
  the neurotransmitter molecules into the synaptic
  cleft.

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• Step 3. The neurotransmitter diffuses across the
  cleft and binds to receptors on the post-synaptic
  cell.
• Step 4. The activated receptors cause changes in
  the activity of the post-synaptic neuron.

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• Step 5. The neurotransmitter molecules are
  released from the receptors and diffuse back into
  the synaptic cleft

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• Diffusion back

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• Step 6. The Neurotransmitter is re-absorbed by
  the post synaptic neuron. This process is known
  as Reuptake

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• http//users.rcn.com/jkimball.ma.ultranet/BiologyP
  ages/A/autonomic.gif
• synaptic transmission

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Signal Transduction Across the Synapse ( once
again)

• When the wave of Action Potentials reach the end
  of the axon the electrical signal is converted
  into a chemical signal. 
• This chemical or neurotransmitter crosses the
  space (Synapse) between adjacent neurons and
  initiates an Action Potential on another neuron.

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• The action potential activates a calcium channel
  and Ca diffuses into the neuron.
• This Ca causes vesicles to fuse with the cell
  membrane. Through exocytosis, neurotransmitters
  (chemicals) are released into the synapse

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• These neurotransmitters diffuse across the
  synapse and bind to receptors on another neuron.
  This causes special Na channels to open and an
  action potential is initiated in the next neuron
• Once the message has been passed on to the next
  neuron, the neurotransmitter is reabsorbed into
  the axon, diffuses away or it is destroyed by an
  enzyme.
• Synapse

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vision

• McGraw-Hill Online Learning Center TestltBLURTgt
• We woll do the dissections from this on line
  site. http//www.exploratorium.edu/learning_studi
  o/cow_eye/coweye.pdf

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Anatomy of the eye

• Optic Nerve The fatty pad around the eye is
  pulled back, revealing parts of the skeletal
  muscles (in dark brown) that control the movement
  of the eye. The forceps are holding the optic
  nerve.

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Sectioned Eye

• The left section shows the vitreous humor still
  attached to the lens ciliary body. The right
  section shows retina in the back of the eye.
  Alani did this dissection.

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• The left upper piece is the semi-transparent
  cornea
• lower left darkly pigmented ciliary body iris
• The pupil is the hole in the center of the iris

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Lens - capsule peeled back

• Note the thin, fibrous looking epithelial cells
  that make up the lens. Hand is holding the lens.