Sensory and Motor Mechanisms 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

Figure 49.4 Chemoreceptors in an insect 0.1 mm

Figure 49.5 Specialized electromagnetic receptors (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. Eye Infrared receptor

Figure 49.14 Sensory transduction by a sweetness receptor Taste pore Sugar molecule Sensory receptor cells Sensory neuron Taste bud Tongue G protein Adenylyl cyclase 4 The decrease in the membrane’s permeability to K+ depolarizes the membrane. 5 Depolarization opens voltage-gated calcium ion (Ca2+) channels, and Ca2+ diffuses into the receptor cell. 6 The increased Ca2+ concentration causes synaptic vesicles to release neurotransmitter. 3 Activated protein kinase A closes K+ channels in the membrane. 2 Binding initiates a signal transduction pathway involving cyclic AMP and protein kinase A. —Ca2+ ATP cAMP Protein kinase A Sugar Sugar receptor SENSORY RECEPTOR CELL Synaptic vesicle K+ Neurotransmitter 1 A sugar molecule binds to a receptor protein on the sensory receptor cell.

Figure 49.15 Smell in humans Brain Odorant Nasal cavity Odorant receptors Plasma membrane Cilia Chemoreceptor Epithelial cell Bone Olfactory bulb Action potentials Mucus

Figure 49.8 The Structure of the Human Ear Pinna Auditory canal Eustachian tube Tympanic membrane Stapes Incus Malleus Skull bones Semicircular canals Auditory nerve, to brain Cochlea Oval window Round window Vestibular canal Tympanic canal Auditory nerve Bone Cochlear duct Hair cells Tectorial membrane Basilar membrane To auditory nerve Axons of sensory neurons 1 Overview of ear structure 2 The middle ear and inner ear 4 The organ of Corti 3 The cochlea Organ of Corti Outer ear Middle ear Inner ear

Figure 49.9 Transduction in the cochlea Stapes Oval window Apex Axons of sensory neurons Round window Basilar membrane Tympanic canal Base Vestibular canal Perilymph

Figure 49.11 Organs of equilibrium in the inner ear The semicircular canals, arranged in three spatial planes, detect angular movements of the head. Body movement Nerve fibers 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. 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. Vestibule Utricle Saccule Vestibular nerve Flow of endolymph Cupula Hairs Hair cell

Figure 49.18 Structure of the vertebrate eye Ciliary body Iris Suspensory ligament Cornea Pupil Aqueous humor Lens Vitreous humor Optic disk (blind spot) Central artery and vein of the retina Optic nerve Fovea (center of visual field) Retina Choroid Sclera

Figure 49.23 Cellular organization of the vertebrate retina Optic nerve fibers Ganglion cell Bipolar cell Horizontal cell Amacrine cell Pigmented epithelium Neurons Cone Rod Photoreceptors Retina Optic nerve To brain

Figure 49.21 Production of a receptor potential in a rod EXTRACELLULAR FLUID Membrane potential (mV) – 40 – 70 Dark Light – Hyper- polarization Time Na+ cGMP CYTOSOL GMP Plasma membrane INSIDE OF DISK PDE Active rhodopsin Light Inactive rhodopsin Transducin Disk membrane 2 Active rhodopsin in turn activates a G protein called transducin. 3 Transducin activates the enzyme phos-phodiesterase(PDE). 4 Activated PDE detaches cyclic guanosine monophosphate (cGMP) from Na+ channels in the plasma membrane by hydrolyzing cGMP to GMP. 5 The Na+ channels close when cGMP detaches. The membrane’s permeability to Na+ decreases, and the rod hyperpolarizes. 1 Light isomerizes retinal, which activates rhodopsin.

Figure 49.26 Bones and joints of the human skeleton 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. 2 Hinge joints, such as between the humerus and the head of the ulna, restrict movement to a single plane. 3 Pivot joints allow us to rotate our forearm at the elbow and to move our head from side to side. Key Axial skeleton Appendicular skeleton Skull Shoulder girdle Clavicle Scapula Sternum Rib Humerus Vertebra Radius Ulna Pelvic girdle Carpals Phalanges Metacarpals Femur Patella Tibia Fibula Tarsals Metatarsals 1 Examples of joints 2 3 Head of humerus

Figure 49.27 The interaction of muscles and skeletons in movement Human Grasshopper Biceps contracts Triceps relaxes Forearm flexes Biceps relaxes Triceps contracts Forearm extends Extensor muscle relaxes Flexor muscle contracts Tibia flexes Extensor muscle contracts Flexor muscle relaxes Tibia extends

Figure 49.28 The structure of skeletal muscle Bundle of muscle fibers Single muscle fiber (cell) Plasma membrane Myofibril Light band Dark band Z line Sarcomere TEM 0.5 m I band A band M line Thick filaments (myosin) Thin filaments (actin) H zone Nuclei

Figure 49.29 The sliding-filament model of muscle contraction Z H A I Sarcomere (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.

Figure 49.30 Myosin-actin interactions underlying muscle fiber contraction (layer 1) Thick filament Thin filaments Thin filament ATP Myosin head (low- energy configuration) Thick filament

Figure 49.30 Myosin-actin interactions underlying muscle fiber contraction (layer 2) Thick filament Thin filaments Thin filament ATP ADP P i Myosin head (low- energy configuration) Thick filament Actin Cross-bridge binding site

Figure 49.30 Myosin-actin interactions underlying muscle fiber contraction (layer 3) Thick filament Thin filaments Thin filament ATP ADP P i Cross-bridge Myosin head (low- energy configuration) Thick filament Actin Cross-bridge binding site

Figure 49.30 Myosin-actin interactions underlying muscle fiber contraction (layer 4) Thick filament Thin filaments Thin filament ATP ADP P i Cross-bridge Myosin head (low- energy configuration) + Thin filament moves toward center of sarcomere. Thick filament Actin Cross-bridge binding site

(a) Myosin-binding sites blocked (b) Myosin-binding sites exposed Figure 49.31 The role of regulatory proteins and calcium in muscle fiber contraction Actin Tropomyosin Ca2+-binding sites Troponin complex (a) Myosin-binding sites blocked Myosin- binding site Ca2+ (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 Myofibril Plasma membrane of muscle fiber Sarcomere Ca2+ released from sarcoplasmic reticulum

Figure 49.33 Review of contraction in a skeletal muscle fiber ACh Synaptic terminal of motor neuron Synaptic cleft T TUBULE PLASMA MEMBRANE SR ADP CYTOSOL Action potential is propa- gated along plasma membrane and down T tubules. Action potential triggers Ca2+ release from sarco- plasmic reticulum (SR). 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. 1 2 3 Tropomyosin blockage of myosin- binding sites is restored; contraction ends, and muscle fiber relaxes. 7 Cytosolic Ca2+ is removed by active transport into SR after action potential ends. 6 Myosin cross-bridges alternately attach to actin and detach, pulling actin filaments toward center of sarcomere; ATP powers sliding of filaments. 5 Calcium ions bind to troponin; troponin changes shape, removing blocking action of tropomyosin; myosin-binding sites exposed. 4 Ca2 P2