Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 50 Sensory and Motor Mechanisms

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 49.1

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sensory receptors Transmit signals to CNS Sensations are action potentials The brain interprets (integration)  perception of stimuli

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Integration Begins as soon as the information is received Occurs at all levels of the nervous system

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Information Processing 3 stages – Sensory input, integration, and motor output Figure 48.3 Sensor Effector Motor output Integration Sensory input Peripheral nervous system ( PNS ) Central nervous system ( CNS)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Neuron Structure Figure 48.5 Dendrites Cell body Nucleus Axon hillock Axon Signal direction Synapse Myelin sheath Synaptic terminals Presynaptic cell Postsynaptic cell

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure – + – – + – – + – – + – – + – – –– – + – + – – –– – – – – – –– – – –– –– – – – – – –– – – – – – –– – – Na + Action potential K+K+ K+K+ K+K+ Axon An action potential is generated as Na + flows inward across the membrane at one location. 1 2 The depolarization of the action potential spreads to the neighboring region of the membrane, re-initiating the action potential there. To the left of this region, the membrane is repolarizing as K + flows outward. 3 The depolarization-repolarization process is repeated in the next region of the membrane. In this way, local currents of ions across the plasma membrane cause the action potential to be propagated along the length of the axon. K+K+ Action Potentials At the site where the action potential is generated an electrical current depolarizes the neighboring region of the axon membrane

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Conduction Speed Increases with the diameter of an axon Myelinated axons also faster

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings When action potential reaches a terminal  release of neurotransmitters into the synaptic cleft Figure Presynaptic cell Postsynaptic cell Synaptic vesicles containing neurotransmitter Presynaptic membrane Postsynaptic membrane Voltage-gated Ca 2+ channel Synaptic cleft Ligand-gated ion channels Na + K+K+ Ligand- gated ion channel Postsynaptic membrane Neuro- transmitter 1 Ca

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mechanoreceptors sense physical deformation – e.g. pressure, stretch, motion, and sound Heat Light touch Pain Cold Hair Nerve Connective tissue Hair movement Strong pressure Dermis Epidermis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemoreceptors Transmit information about solute concentration 0.1 mm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Electromagnetic Receptors Detect light, electricity, EM radiation, and magnetism

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Many mammals use the Earth’s magnetic field lines to orient themselves as they migrate Figure 49.5b (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.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Thermoreceptors Help regulate body temperature by signaling both surface and body core temperature

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hearing and Equilibrium in Mammals  human ear Figure 49.8 Pinna Auditory canal Eustachian tube Tympanic membrane Stapes Incus Malleus Skull bones Semicircular canals Auditory nerve, to brain Cochlea Tympanic membrane Oval window Eustachian tube 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Equilibrium semicircular canals in the inner ear Figure 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Taste Modified epithelial cells organized into taste buds Five taste perceptions; sweet, sour, salty, bitter, and umami (elicited by glutamate)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Smell Olfactory receptor cells line the upper portion of the nasal cavity Brain Nasal cavity Odorant Odorant receptors Plasma membrane Odorant Cilia Chemoreceptor Epithelial cell Bone Olfactory bulb Action potentials Mucus Figure 49.15

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vision Most invertebrates have some sort of light- detecting organ Light Light shining from the front is detected Photoreceptor Visual pigment Ocellus Nerve to brain Screening pigment Light shining from behind is blocked by the screening pigment

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 types of image-forming eyes have evolved in invertebrates – compound eye and the single-lens eye

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vertebrate eye Figure 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Retina contains two types of photoreceptors – Rods,sensitive to light but do not distinguish colors – Cones, distinguish colors but are not as sensitive

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animal skeletons Support, protection, and movement Movement results from muscles working against some type of skeleton

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exoskeletons e.g. Molluscs and arthropods

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Endoskeletons Sponges, echinoderms, and chordates

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Muscles move skeletal parts by contracting

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vertebrate Skeletal Muscle hierarchy of smaller and smaller units Figure 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 I band M line Thick filaments (myosin) Thin filaments (actin) H zone Sarcomere Z line Nuclei

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Myofibrils are composed to 2 kinds of myofilaments – Thin filaments, consisting of actin – Thick filaments, arrays of myosin molecules

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Skeletal muscle is striated

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Sliding-Filament Model of Muscle Contraction Figure 49.29a–c (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. 0.5  m Z H A Sarcomere

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Myosin-actin interactions underlying muscle fiber contraction Figure Thick filament Thin filaments Thin filament ATP ADP P i Cross-bridge Myosin head (low- energy configuration) Myosin head (high- energy configuration) + Myosin head (low- energy configuration) Thin filament moves toward center of sarcomere. Thick filament Actin Cross-bridge binding site 1Starting here, the myosin head is bound to ATP and is in its low- energy confinguration. 2 The myosin head hydrolyzes ATP to ADP and inorganic phosphate ( I ) and is in its high-energy configuration. P 1The myosin head binds to actin, forming a cross- bridge. 3 4 Releasing ADP and ( i ), myosin relaxes to its low-energy configuration, sliding the thin filament. P 5 Binding of a new mole- cule of ATP releases the myosin head from actin, and a new cycle begins.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Role of Calcium and Regulatory Proteins When a muscle is at rest – The myosin-binding sites on the thin filament are blocked by the regulatory protein tropomyosin Figure 49.31a Actin Tropomyosin Ca 2+ -binding sites Troponin complex (a) Myosin-binding sites blocked

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings For a muscle fiber to contract – The myosin-binding sites must be uncovered This occurs when calcium ions (Ca 2+ ) – Bind to another set of regulatory proteins, the troponin complex Figure 49.31b Ca 2+ Myosin- binding site (b) Myosin-binding sites exposed

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Motor neuron axon Mitochondrion Synaptic terminal T tubule Sarcoplasmic reticulum Myofibril Plasma membrane of muscle fiber Sarcomere Ca 2+ released from sarcoplasmic reticulum Stimulus leading to the contraction of muscle fiber is an action potential in a motor neuron Figure 49.32

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ACh Synaptic terminal of motor neuron Synaptic cleft T TUBULE PLASMA MEMBRANE SR ADP CYTOSOL Ca 2  P2P2 Cytosolic Ca 2+ is removed by active transport into SR after action potential ends. 6 Review Figure Acetylcholine ( 1 Action potential 2 triggers Ca 2+ release from sarco- plasmic reticulum (SR). 3 Myosin cross-bridges 5 Calcium ions bind 4 Tropomyosin blockage 7

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other Types of Muscle Cardiac muscle, striated cells electrically connected by intercalated discs – Can generate action potentials without neural input Smooth muscle, contractions slow and may be caused by stimulation from autonomic nervous system