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Sensory and Motor Mechanisms
Chapter 50 Campbell Biology – 9th Edition
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You must know The location and function of several types of sensory receptors How skeletal muscles contract Cellular events that lead to muscle contraction
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Sensory Receptors ____________________________: physical stimuli – pressure, touch, stretch, motion, sound ____________________________: detect heat/cold ____________________________: transmit solute conc. info – taste (gustatory), smell (olfactory) ____________________________ receptors: detect EM energy – light (photoreceptors), electricity, magnetism _____________ receptors: respond to excess heat, pressure, chemicals
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Sensation = action potentials reach brain via sensory neurons
_________________________: receptor detects a stimulus Sensation = action potentials reach brain via sensory neurons _________________________: information processed in brain
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Retina Optic nerve To brain Cone Photoreceptors Rod Neurons Pigmented epithelium Bipolar cell Amacrine Horizontal Optic nerve fibers Ganglion Vision Compound eyes: several thousand ommatidia (light detectors) with its own lens; insects & crustaceans Vertebrates: Rods: sense ___________ Cones: ________________ vision Rhodopsin: light-absorbing ________________ that triggers signal transduction pathway that leads to sight
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Muscles always contract
Muscles work in antagonistic pairs to move parts of body Biceps contracts Human Triceps relaxes Forearm flexes extends Extensor muscle Flexor Grasshopper Tibia
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Skeletal Muscle Structure
Bundle of muscle fibers Single muscle fiber (cell) Plasma membrane Nuclei Muscle Myofibril Dark band Sarcomere Z line Light band I band TEM A band 0.5 µm M line Thick filaments (myosin) H zone Thin filaments (actin) Attached to bones by __________ Types of muscle: _____________ (internal organs) _____________ (heart) _____________ (striated) 1 long fiber = single muscle cell Each muscle fiber = bundle of myofibrils, composed of: _________: thin filaments _________: thick filaments
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______________: basic contractile unit of the _____________
Sarcomere 0.5 µm Z H A Relaxed muscle fiber I Contracting muscle fiber Fully contracted muscle fiber Z lines – border I band – _______ actin filaments A band – _______ myosin filaments
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(Note: Filaments do ________________)
Muscle Contraction: Sarcomere 0.5 µm Z H A Relaxed muscle fiber I Contracting muscle fiber Fully contracted muscle fiber Sarcomere relaxed: actin & myosin _____________________ Contracting: Muscle fiber stimulated by ________ ________________ Length of sarcomere is reduced ___________ slides over __________ Fully contracted: actin & myosin completely overlap ________________________________: thick & thin filaments slide past each other to increase overlap (Note: Filaments do ________________)
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Muscle fibers only contract when stimulated by a motor neuron
Ca2+ released from sarcoplasmic reticulum Mitochondrion Motor neuron axon Synaptic terminal T tubule Sarcoplasmic Myofibril Plasma membrane of muscle fiber Sarcomere ______ is released from the sarcoplasmic reticulum
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Synaptic terminal of _________ neuron releases ____________
Muscle fiber _________ ______ released Initiate _____________ of _____________ Ca2+ CYTOSOL SR PLASMA MEMBRANE T TUBULE Synaptic cleft Synaptic terminal of motor neuron ACh
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Depolarization of muscle cell releases _________ binds to _________ _______________________
Myosin-binding sites blocked. Myosin-binding sites exposed. Tropomyosin Ca2+-binding sites Actin Troponin complex Myosin- binding site Ca2+
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Hydrolysis of ATP by myosin cross-bridge formed thin filament pulled toward center of sarcomere
Thin filaments Thick filament Thin filament Thick filament Myosin head (low-energy configuration) Cross-bridge binding site Myosin head (high- energy configuration) Actin Myosin head (low- Thin filament moves toward center of sacomere.
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Speed of muscle contraction:
Fast fibers – brief, rapid, powerful contractions Slow fibers – sustain long contractions (posture)
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Problems ALS (Lou Gehrig’s disease): degeneration of motor neurons, muscle fibers atrophy Botulism: block release of acetylcholine, paralyzes muscles Myasthenia gravis: autoimmune disorder, produce antibodies to acetylcholine Calcium deficiency: muscle spasms and cramps Rigor mortis (after death): no ATP to break actin/myosin bonds; sustained muscle contraction until breakdown (decomposition)
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