Transcript Muscle
Chapter 49 Sensory and Motor Mechanisms Objective: You will be able to explain how an impulse begins at chemical receptors. Do Now: Take a packet Figure 49.3 Sensory receptors in human skin Cold Light touch Pain Hair Heat Epidermis Dermis Nerve Connective tissue Hair movement Strong pressure 0.1 mm Figure 49.4 Chemoreceptors in an insect Figure 49.5 Specialized electromagnetic receptors Eye Infrared receptor (a) This rattlesnake and other pit vipers have a pair of infrared receptors, one between each eye and nostril. The organs are sensitive enough to detect the infrared radiation emitted by a warm mouse a meter away. The snake moves its head from side to side until the radiation is detected equally by the two receptors, indicating that the mouse is straight ahead. (b) Some migrating animals, such as these beluga whales, apparently sense Earth’s magnetic field and use the information, along with other cues, for orientation. Figure 49.14 Sensory transduction by a sweetness receptor Taste pore Sugar molecule Taste bud Sensory receptor cells Sensory neuron Tongue 1 A sugar molecule binds to a receptor protein on the sensory receptor cell. Sugar G protein Sugar receptor Adenylyl cyclase 2 Binding initiates a signal transduction pathway involving cyclic AMP and protein kinase A. ATP cAMP Protein kinase A SENSORY RECEPTOR CELL 3 Activated protein kinase A closes K+ channels in the membrane. K+ 4 The decrease in the membrane’s permeability to K+ depolarizes the membrane. Synaptic vesicle —Ca2+ 5 Depolarization opens voltage-gated calcium ion (Ca2+) channels, and Ca2+ diffuses into the receptor cell. Neurotransmitter 6 The increased Ca2+ concentration causes synaptic vesicles to release neurotransmitter. Sensory neuron Figure 49.15 Smell in humans Brain Action potentials Odorant Olfactory bulb Nasal cavity Bone Epithelial cell Odorant receptors Chemoreceptor Plasma membrane Odorant Cilia Mucus Figure 49.8 The Structure of the Human Ear 1 Overview of ear structure 2 The middle ear and inner ear Incus Middle ear Inner ear Outer ear Stapes Skull bones Semicircular canals Malleus Auditory nerve, to brain Pinna Tympanic membrane Hair cells Cochlea Eustachian tube Auditory canal Tectorial membrane Tympanic membrane Oval window Eustachian tube Round window Cochlear duct Bone Vestibular canal Auditory nerve Basilar membrane Axons of sensory neurons 4 The organ of Corti To auditory nerve Tympanic canal 3 The cochlea Organ of Corti Figure 49.9 Transduction in the cochlea Cochlea Stapes Oval window Axons of sensory neurons Vestibular canal Perilymph Base Round window Tympanic Basilar canal membrane Apex Figure 49.11 Organs of equilibrium in the inner ear The semicircular canals, arranged in three spatial planes, detect angular movements of the head. Each canal has at its base a swelling called an ampulla, containing a cluster of hair cells. When the head changes its rate of rotation, inertia prevents endolymph in the semicircular canals from moving with the head, so the endolymph presses against the cupula, bending the hairs. Flow of endolymph Flow of endolymph Vestibular nerve Cupula Hairs Hair cell Nerve fibers Vestibule Utricle Body movement Saccule The utricle and saccule tell the brain which way is up and inform it of the body’s position or linear acceleration. The hairs of the hair cells project into a gelatinous cap called the cupula. Bending of the hairs increases the frequency of action potentials in sensory neurons in direct proportion to the amount of rotational acceleration. Figure 49.18 Structure of the vertebrate eye Sclera Choroid Retina Ciliary body Fovea (center of visual field) Suspensory ligament Cornea Iris Optic nerve Pupil Aqueous humor Lens Vitreous humor Central artery and vein of the retina Optic disk (blind spot) Figure 49.23 Cellular organization of the vertebrate retina Retina Optic nerve To brain Retina Photoreceptors Neurons Cone Rod Amacrine cell Optic nerve fibers Ganglion cell Horizontal cell Bipolar cell Pigmented epithelium Figure 49.21 Production of a receptor potential in a rod Light EXTRACELLULAR FLUID INSIDE OF DISK Active rhodopsin PDE CYTOSOL Plasma membrane Membrane potential (mV) 0 Dark Light Inactive rhodopsin Transducin cGMP Disk membrane – 40 GMP Na+ 1 Light isomerizes retinal, which activates rhodopsin. 2 Active rhodopsin in turn activates a G protein called transducin. 3 Transducin activates the enzyme phosphodiesterase (PDE). 4 Activated PDE detaches cyclic guanosine monophosphate (cGMP) from Na+ channels in the plasma membrane by hydrolyzing cGMP to GMP. – 70 – Hyperpolarization Time Na+ 5 The Na+ channels close when cGMP detaches. The membrane’s permeability to Na+ decreases, and the rod hyperpolarizes. Figure 49.26 Bones and joints of the human skeleton Key Axial skeleton Appendicular skeleton Skull Examples of joints Head of humerus Scapula 1 Shoulder girdle Clavicle Scapula Sternum Rib Humerus 2 Vertebra 3 Radius Ulna Pelvic girdle 1 Ball-and-socket joints, where the humerus contacts the shoulder girdle and where the femur contacts the pelvic girdle, enable us to rotate our arms and legs and move them in several planes. Humerus Carpals Phalanges Ulna Metacarpals Femur Patella 2 Hinge joints, such as between the humerus and the head of the ulna, restrict movement to a single plane. Tibia Fibula Ulna Tarsals Metatarsals Phalanges Radius 3 Pivot joints allow us to rotate our forearm at the elbow and to move our head from side to side. Figure 49.27 The interaction of muscles and skeletons in movement Human Grasshopper Extensor muscle relaxes Biceps contracts Triceps relaxes Tibia flexes Forearm flexes Extensor muscle contracts Biceps relaxes Forearm extends Triceps contracts Flexor muscle contracts Tibia extends Flexor muscle relaxes Figure 49.28 The structure of skeletal muscle Muscle Bundle of muscle fibers Nuclei Single muscle fiber (cell) Plasma membrane Myofibril Z line Light band Dark band Sarcomere TEM I band A band 0.5 m I band M line Thick filaments (myosin) Thin filaments (actin) Z line H zone Sarcomere Z line Figure 49.29 The sliding-filament model of muscle contraction 0.5 m Z (a) Relaxed muscle fiber. In a relaxed muscle fiber, the I bands and H zone are relatively wide. (b) Contracting muscle fiber. During contraction, the thick and thin filaments slide past each other, reducing the width of the I bands and H zone and shortening the sarcomere. (c) Fully contracted muscle fiber. In a fully contracted muscle fiber, the sarcomere is shorter still. The thin filaments overlap, eliminating the H zone. The I bands disappear as the ends of the thick filaments contact the Z lines. H A Sarcomere I Figure 49.30 Myosin-actin interactions underlying muscle fiber contraction (layer 1) Thick filament Thin filaments Thin filament ATP Myosin head (lowenergy configuration) Thick filament Figure 49.30 Myosin-actin interactions underlying muscle fiber contraction (layer 2) Thick filament Thin filaments Thin filament ATP Myosin head (lowenergy configuration) Thick filament Cross-bridge binding site Actin ADP Pi Myosin head (lowenergy configuration) Figure 49.30 Myosin-actin interactions underlying muscle fiber contraction (layer 3) Thick filament Thin filaments Thin filament Myosin head (lowenergy configuration) ATP Thick filament Cross-bridge binding site Actin ADP Pi ADP Pi Cross-bridge Myosin head (lowenergy configuration) Figure 49.30 Myosin-actin interactions underlying muscle fiber contraction (layer 4) Thick filament Thin filaments Thin filament Myosin head (lowenergy configuration) ATP ATP Thick filament Thin filament moves toward center of sarcomere. + Pi ADP Pi Actin ADP Myosin head (lowenergy configuration) ADP Cross-bridge binding site Pi Cross-bridge Myosin head (lowenergy configuration) Figure 49.31 The role of regulatory proteins and calcium in muscle fiber contraction Tropomyosin Actin Ca2+-binding sites Troponin complex (a) Myosin-binding sites blocked Ca2+ Myosinbinding site (b) Myosin-binding sites exposed Figure 49.32 The roles of the sarcoplasmic reticulum and T tubules in muscle fiber contraction Motor neuron axon Mitochondrion Synaptic terminal T tubule Sarcoplasmic reticulum Ca2+ released from sarcoplasmic reticulum Myofibril Plasma membrane of muscle fiber Sarcomere Figure 49.33 Review of contraction in a skeletal muscle fiber Synaptic terminal of motor neuron 1 Acetylcholine (ACh) released by synaptic terminal diffuses across synaptic cleft and binds to receptor proteins on muscle fiber’s plasma membrane, triggering an action potential in muscle fiber. Synaptic cleft 2 ACh PLASMA MEMBRANE T TUBULE Action potential is propagated along plasma membrane and down T tubules. SR 3 Action potential triggers Ca2+ release from sarcoplasmic reticulum (SR). Ca2 7 Tropomyosin blockage of myosinbinding sites is restored; contraction ends, and muscle fiber relaxes. Ca2 4 Calcium ions bind to troponin; troponin changes shape, removing blocking action of tropomyosin; myosin-binding sites exposed. CYTOSOL ADP P2 6 Cytosolic Ca2+ is removed by active transport into SR after action potential ends. 5 Myosin cross-bridges alternately attach to actin and detach, pulling actin filaments toward center of sarcomere; ATP powers sliding of filaments.