Chapter 50

1. Chapter 50 • Sensory and Motor Mechanisms

2. Figure 49.1

3. Sensory receptors • Transmit signals to CNS • Sensations are action potentials • The brain interprets (integration) perception of stimuli

4. Integration • Begins as soon as the information is received • Occurs at all levels of the nervous system

5. Sensory input Integration Sensor Motor output Effector Central nervoussystem (CNS) Peripheral nervoussystem (PNS) Figure 48.3 Information Processing • 3 stages • Sensory input, integration, and motor output

6. Dendrites Cell body Nucleus Synapse Signal direction Axon Axon hillock Presynaptic cell Postsynaptic cell Myelin sheath Synapticterminals Figure 48.5 Neuron Structure

7. – – + + + + + + – – + + + + + + Axon Actionpotential An action potential is generated as Na+ flows inward across the membrane at one location. 1 + + – – – – – – Na+ – – – – – – + + – – + + + + + + Actionpotential 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. K+ – – – + – – + – Na+ – – – – – – + + – – + + + + + + K+ Actionpotential The depolarization-repolarization process isrepeated 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. 3 K+ – – – – + + + + – + + + + – – – Na+ – – – + + – + + – + + – – Figure 48.14 – + + K+ Action Potentials • At the site where the action potential is generated an electrical current depolarizes the neighboring region of the axon membrane

8. Conduction Speed • Increases with the diameter of an axon • Myelinated axons also faster

9. Postsynaptic cell Presynapticcell Na+ Neuro-transmitter Synaptic vesiclescontainingneurotransmitter K+ Presynapticmembrane Postsynaptic membrane Ligand-gatedion channel Voltage-gatedCa2+ channel Ca2+ Postsynaptic membrane 3 Synaptic cleft Ligand-gatedion channels 6 5 4 1 2 Figure 48.17 • When action potential reaches a terminal release of neurotransmitters into the synaptic cleft

10. Cold Light touch Pain Hair Heat Epidermis Dermis Hair movement Nerve Strong pressure Connective tissue Mechanoreceptors • sense physical deformation • e.g. pressure, stretch, motion, and sound

11. 0.1 mm Chemoreceptors • Transmit information about solute concentration

12. Electromagnetic Receptors • Detect light, electricity, EM radiation, and magnetism

13. 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, apparentlysense Earth’s magnetic field and use the information, along with other cues, for orientation.

14. Thermoreceptors • Help regulate body temperature by signaling both surface and body core temperature

15. 1 2 Overview of ear structure The middle ear and inner ear Incus Semicircularcanals Skullbones Stapes Middleear Outer ear Inner ear Malleus Auditory nerve,to brain Pinna Tympanicmembrane Cochlea Eustachian tube Auditory canal Ovalwindow Eustachian tube Tympanicmembrane Tectorialmembrane Hair cells Roundwindow Cochlear duct Bone Vestibular canal Auditory nerve Axons of sensory neurons Basilarmembrane To auditorynerve Tympanic canal Organ of Corti 4 3 The organ of Corti The cochlea Hearing and Equilibrium in Mammals human ear Figure 49.8

16. 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 rateof rotation, inertia prevents endolymph in the semicircular canals from moving with the head, so the endolymph presses against the cupula, bending the hairs. Flowof endolymph Flowof endolymph Vestibular nerve Cupula Hairs Haircell Nervefibers 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. Equilibrium • semicircular canals in the inner ear Figure 49.11

17. Taste • Modified epithelial cells organized into taste buds • Five taste perceptions; sweet, sour, salty, bitter, and umami (elicited by glutamate)

18. Brain Action potentials Odorant Olfactory bulb Nasal cavity Bone Epithelial cell Odorantreceptors Chemoreceptor Plasmamembrane Cilia Figure 49.15 Odorant Mucus Smell • Olfactory receptor cells line the upper portion of the nasal cavity

19. Light Light shining from the front is detected Photoreceptor Nerve to brain Visual pigment Screening pigment Ocellus Light shining from behind is blockedby the screening pigment Vision • Most invertebrates have some sort of light-detecting organ

20. 2 types of image-forming eyes have evolved in invertebrates • compound eye and the single-lens eye

21. Sclera Choroid Retina Ciliary body Fovea (centerof visual field) Suspensoryligament Cornea Iris Opticnerve Pupil Aqueoushumor Lens Vitreous humor Central artery and vein of the retina Optic disk(blind spot) • Vertebrate eye Figure 49.18

22. Retina contains two types of photoreceptors • Rods,sensitive to light but do not distinguish colors • Cones, distinguish colors but are not as sensitive

23. Animal skeletons • Support, protection, and movement • Movement results from muscles working against some type of skeleton

24. Exoskeletons • e.g. Molluscs and arthropods

25. Endoskeletons • Sponges, echinoderms, and chordates

26. Muscles move skeletal parts by contracting

27. Muscle Bundle ofmuscle fibers Nuclei Single muscle fiber (cell) Plasma membrane Myofibril Z line Lightband Dark band Sarcomere TEM 0.5 m A band I band I band M line Thickfilaments(myosin) Thinfilaments(actin) H zone Z line Z line Sarcomere Vertebrate Skeletal Muscle • hierarchy of smaller and smaller units Figure 49.28

28. Myofibrils are composed to 2 kinds of myofilaments • Thin filaments, consisting of actin • Thick filaments, arrays of myosin molecules

29. Skeletal muscle is striated

30. 0.5 m Z (a) Relaxed muscle fiber. In a relaxed muscle fiber, the I bandsand H zone are relatively wide. H A Sarcomere (b) Contracting muscle fiber. During contraction, the thick andthin filaments slide past each other, reducing the width of theI bands and H zone and shortening the sarcomere. (c) Fully contracted muscle fiber. In a fully contracted musclefiber, the sarcomere is shorter still. The thin filaments overlap,eliminating the H zone. The I bands disappear as the ends ofthe thick filaments contact the Z lines. • The Sliding-Filament Model of Muscle Contraction Figure 49.29a–c

31. Thick filament Thin filaments 1 Starting here, the myosin head is bound to ATP and is in its low-energy confinguration. 5 Binding of a new mole- cule of ATP releases the myosin head from actin, and a new cycle begins. Thin filament Myosin head (low-energy configuration) ATP The myosin head hydrolyzes ATP to ADP and inorganic phosphate ( I ) and is in its high-energy configuration. 2 ATP Cross-bridge binding site Thick filament P Actin Thin filament moves toward center of sarcomere. ADP Myosin head (high-energy configuration) Myosin head (low-energy configuration) P i 1 The myosin head binds toactin, forming a cross-bridge. 3 ADP + Cross-bridge ADP P i P i Releasing ADP and ( i), myosinrelaxes to its low-energy configuration, sliding the thin filament. 4 P • Myosin-actin interactions underlying muscle fiber contraction Figure 49.30

32. Tropomyosin Ca2+-binding sites Actin Troponin complex (a) Myosin-binding sites blocked 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

33. Ca2+ Myosin-binding site (b) Myosin-binding sites exposed • For a muscle fiber to contract • The myosin-binding sites must be uncovered • This occurs when calcium ions (Ca2+) • Bind to another set of regulatory proteins, the troponin complex Figure 49.31b

34. Motorneuron axon Mitochondrion Synapticterminal T tubule Sarcoplasmicreticulum Ca2+ releasedfrom sarcoplasmicreticulum Myofibril Sarcomere Plasma membraneof muscle fiber • Stimulus leading to the contraction of muscle fiber is an action potential in a motor neuron Figure 49.32

35. Synapticterminalof motorneuron 1 Acetylcholine ( PLASMA MEMBRANE T TUBULE Synaptic cleft 2 ACh Action potential SR 4 Action potential triggers Ca2+ release from sarco- plasmic reticulum (SR). 3 Ca2 7 Tropomyosin blockage Calcium ions bind Ca2 CYTOSOL Cytosolic Ca2+ is removed by active transport into SR after action potential ends. 6 ADP P2 5 Myosin cross-bridges Review Figure 49.33

36. 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