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Chapter 49

Sensory and Motor Mechanisms. Chapter 49. Muscles. Skeletal Muscle – attached to bones and is responsible for movement Cardiac Muscle – heart Do not need motor neurons to produce action potentials Ion channels cause rhythmic depolarizations Cannot reach tetanus Smooth Muscle

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Chapter 49

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  1. Sensory and Motor Mechanisms Chapter 49

  2. Muscles • Skeletal Muscle – attached to bones and is responsible for movement • Cardiac Muscle – heart • Do not need motor neurons to produce action potentials • Ion channels cause rhythmic depolarizations • Cannot reach tetanus • Smooth Muscle • Contract only when stimulated by neurons of ANS

  3. Muscle Hierarchy • Muscle • Bundle of muscle fibers • Single muscle fiber • Myofibril • Myofilament • Thin filament • Thick filament

  4. Sarcomere • The basic contractile unit of the muscle • Thin filament – 2 strands of actin (passive, attached to Z line) & 1 strand of regulatory protein coiled around one another • Thick filament – staggered arrays of myosin (active, does the work) molecules • Z Line – border of sarcomere – thin filaments run between Z line

  5. Motor Unit • Consists of a single motor neuron and all the muscle fibers it controls • When a motor neuron produces an action potential, all the muscle fibers in its motor unit contract as a group • The strength of the contraction depends on how many muscle fibers the motor neuron controls. • Nervous system regulates strength of contraction in whole muscle by determining how many motor units are activated • The force developed by a muscle progressively increases as more and more of the motor units are activated – this is called Recruitment

  6. The same motor neuron will control numerous muscle fibers

  7. Neuromuscular Junction • Chemical synapse is the same as ch. 48 using Acetylcholine as neurotransmitter. • Action potential triggers Ca++ release from sarcoplasmic reticulum • Ca++ bind to troponin; troponin changes shape, removing blocking action of tropomyosin; myosin binding sites are exposed

  8. Sliding Filament Theory • The neuron stimulate the sarcolemma • An Action Potential travels down the sarcolemma and T-tubules • Sarcoplasmic Reticulum releases calcium ions into the cytoplasm • Calcium uncovers myosin-binding sites on actin • Myosin heads attach to actin, bend and release, pulling the actin. ATP is used.

  9. http://www.youtube.com/watch?v=0kFmbrRJq4w&safety_mode=true&persist_safety_mode=1http://www.youtube.com/watch?v=0kFmbrRJq4w&safety_mode=true&persist_safety_mode=1

  10. The Senses • Sense organs are the windows to the brain. • Sense receptors • Interoceptors – respond to internal stimuli -bodyposition, chemicals, blood pressure • Exteroreceptors – respond to external stimuli -light, pressure, chemicals, heat • Integration – processing information • Some of this is often done at the receptor • Sensory adaptation – decrease in response due to continued stimulation

  11. Types of sensory receptors • Mechanoreceptors – pulled or stretched • Touch receptors in the skin • Arteries detect blood pressure change • Lungs respond to degree of lung inflation • Proprioceptors – posture and balance • Inner ear – sensitive to waves of fluid which establishes equilibrium

  12. Types of sensory receptors • Pain Receptors – respond to excess heat, pressure, or chemicals • Histamines, prostaglandins • Prostaglandins lower threshold of pain receptors • Aspirin & ibuprofen inhibit prostaglandins • Thermoreceptors – respond to heat or cold • Regulate body temperature • Chemoreceptors – monitor osmotic concentration, pH, specific chemicals • Taste & smell

  13. Types of sensory receptors • Electromagnetic receptors – light, electricity, magnetism, photoreceptors (sight) • Photoreceptors – respond to light energy • Types of eyes • Simple eye cup – light intensity & direction • Compound eye – 1000 or more ommatidia, each with its own lens • Gives mosaic image able to detect very slight movement • Insects, some arthropods • Single lens eye – focuses image on retina • Spider, mollusk, polychaete, vertebrates

  14. Compound Eye image

  15. Eye parts & functions

  16. Contralateral Processing • Nerve fibers bringing info from right half of visual field converge at optic chiasma & pass to left side of brain. Vice versa for left half of vision. • Image is inverted & reversed, brain corrects image for us to correctly perceive what is in whole visual field • Stimuli of color, form, & motion sent to other parts of the brain • Cerebral cortex rebuilds all parts to give us complete understanding of what we are seeing.

  17. Types of skeletons • Hydrostatic skeleton – fluid held under pressure in a closed body compartment • Cnidarians, flatworms, nematodes, annelids • Adv – aquatic environment; cushion internal organs • Disadv – cannot support terrestrial activities • Exoskeletons – hard encasement deposited on the surface of an animal • Molluscs, arthropods, insects • Adv – protection, strength, flexibility • Disadv – cannot grow, has to be shed, heavy • Endoskeleton – hard supporting elements • Chordates (mammals) • Adv – internal structure, support, shape • Disadv – offers no external protection

  18. Joints • Ball & socket – rotation of arms & legs • Humerus & shoulder • Femur & hip • Hinge joint – single plane movement • Elbow • Knee • Pivot joint – rotation • Forearm • Head on neck

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