Can a moth evade a bat in the dark? Figure 50.1 Can a moth evade a bat in the dark?

Sensory receptors in human skin Heat Gentle touch Pain Cold Hair Epidermis Dermis Figure 50.3 Sensory receptors in human skin Hypodermis Nerve Connective tissue Hair movement Strong pressure

Chemoreceptors in an insect Figure 50.4 0.1 mm

Specialized electromagnetic receptors Eye Infrared receptor (a) Rattlesnake – infrared receptors detect body heat of prey Figure 50.5 (b) Beluga whales sense Earth’s magnetic field – as they navigate migrations.

Ciliated receptor cells The statocyst of an invertebrate Ciliated receptor cells Cilia Statolith Figure 50.6 Sensory axons

Many arthropods sense sounds with body hairs that vibrate or with localized “ears” consisting of a tympanic membrane and receptor cells Figure 50.7 An insect “ear”—on its leg Tympanic membrane 1 mm

Human Ear Figure 50.8 The structure of the Middle ear Outer ear Inner ear Skull bone Stapes Semicircular canals Incus Malleus Auditory nerve to brain Cochlear duct Bone Auditory nerve Vestibular canal Tympanic canal Cochlea Oval window Eustachian tube Pinna Auditory canal Tympanic membrane Round window Organ of Corti Tectorial membrane Hair cells Figure 50.8 The structure of the Hair cell bundle from a bullfrog; the longest cilia shown are about 8 µm (SEM). Basilar membrane Axons of sensory neurons To auditory nerve

Sensory reception by hair cells. “Hairs” of hair cell Neuro- trans- mitter at synapse More neuro- trans- mitter Less neuro- trans- mitter Sensory neuron –50 –50 Receptor potential –50 –70 –70 –70 Membrane potential (mV) Membrane potential (mV) Membrane potential (mV) Action potentials Signal Signal Signal –70 –70 –70 Figure 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 Time (sec) Time (sec) Time (sec) (a) No bending of hairs (b) Bending of hairs in one direction (c) Bending of hairs in other direction

Organs of equilibrium in the inner ear Semicircular canals Flow of fluid Vestibular nerve Cupula Hairs Hair cells Vestibule Figure 50.11 Axons Utricle Body movement Saccule

The lateral line system in a fish has mechanorecptors that sense water movement Surrounding water Scale Lateral line canal Opening of lateral line canal Cupula Epidermis Sensory hairs Figure Hair cell Supporting cell Segmental muscles Lateral nerve Axon Fish body wall

Smell in humans Brain Olfactory bulb Odorants Nasal cavity Bone Action potentials Olfactory bulb Odorants Nasal cavity Bone Epithelial cell Odorant receptors Chemo- receptor Figure 50.15 Plasma membrane Cilia Odorants Mucus

Eye cup of planarians provides information about light intensity and direction but does not form images. Ocellus Light Figure 50.16 Ocelli and orientation behavior of a planarian Photoreceptor Nerve to brain Visual pigment Screening pigment Ocellus

Compound eyes (a) Fly eyes Cornea Lens Crystalline cone Rhabdom 2 mm (a) Fly eyes Cornea Lens Crystalline cone Rhabdom Figure 50.17 Photoreceptor Axons Ommatidium (b) Ommatidia

Fovea = center of visual field Vertebrate Eye Sclera Choroid Retina Ciliary body Fovea = center of visual field Suspensory ligament Cornea Optic nerve Iris Pupil Aqueous humor Figure 50.18 Lens Central artery and vein of the retina Vitreous humor Optic disk (blind spot)

Humans and other mammals focus light by changing the shape of the lens. Ciliary muscles relax. Ciliary muscles contract. Choroid Suspensory ligaments pull against lens. Suspensory ligaments relax. Retina Lens becomes thicker and rounder. Lens becomes flatter. Figure 50.19 Focusing in the mammalian eye (a) Near vision (accommodation) (b) Distance vision

Membrane potential (mV) Receptor potential production in a rod cell INSIDE OF DISK EXTRACELLULAR FLUID Light Disk membrane Active rhodopsin Phosphodiesterase Plasma membrane CYTOSOL Sodium channel cGMP Inactive rhodopsin Transducin GMP Na+ Dark Figure 50.21 Receptor potential production in a rod cell Light Membrane potential (mV) –40 Hyper- polarization Na+ –70 Time

Neural pathways for vision Right visual field Optic chiasm Right eye Left eye Figure 50.24 Left visual field Optic nerve Primary visual cortex Lateral geniculate nucleus

Skeletal Muscle Thick filaments myosin Thin filaments actin Bundle of muscle fibers Nuclei Single muscle fiber (cell) Plasma membrane Myofibril Z lines Sarcomere Figure 50.25 The structure of TEM 0.5 µm M line Thick filaments myosin Thin filaments actin Z line Z line Sarcomere

The sliding-filament model of muscle contraction Sarcomere 0.5 µm Z M Z Relaxed muscle Contracting muscle Fully contracted muscle Figure 50.26 For the Cell Biology Video Conformational Changes in Calmodulin, go to Animation and Video Files. For the Cell Biology Video Cardiac Muscle Contraction, go to Animation and Video Files. Contracted Sarcomere

Myosin-actin interactions underlying muscle fiber contraction Thick filament Myosin-actin interactions underlying muscle fiber contraction Thin filaments Thin filament Myosin head (low- energy configuration ATP ATP Thick filament Myosin binding sites Thin filament moves toward center of sarcomere. Actin Myosin head (low- energy configuration ADP Myosin head (high- energy configuration P i Figure 50.27 Myosin-actin interactions underlying muscle fiber contraction ADP ADP + P i P i Cross-bridge

(a) Myosin-binding sites blocked Tropomyosin Ca2+-binding sites Actin Troponin complex (a) Myosin-binding sites blocked Ca2+ Figure 50.28 The role of regulatory proteins and calcium in muscle fiber contraction Myosin- binding site (b) Myosin-binding sites exposed when Ca2+ released.

Ca2+ Regulation of skeletal muscle contraction Synaptic terminal of motor neuron Synaptic cleft T Tubule Plasma membrane ACh SR Ca2+ ATPase pump Ca2+ ATP CYTOSOL Figure 50.29b The Ca2+ ADP P i

Spinal cord Motor unit 1 Motor unit 2 Synaptic terminals Nerve Motor units in a vertebrate skeletal muscle Spinal cord Motor unit 1 Motor unit 2 Synaptic terminals Nerve Motor neuron cell body Motor neuron axon Figure 50.30 Muscle Muscle fibers Tendon

Summation of twitches Tetanus Summation of two twitches Tension Single twitch Figure 50.31 Time Action potential Pair of action potentials Series of action potentials at high frequency

The interaction of antagonistic muscles and skeletons in movement Human Grasshopper Extensor muscle relaxes Biceps contracts Tibia flexes Flexor muscle contracts Forearm flexes Triceps relaxes Biceps relaxes Extensor muscle contracts Tibia extends Figure 50.32 For the Discovery Video Muscles and Bones, go to Animation and Video Files. Forearm extends Flexor muscle relaxes Triceps contracts

Crawling by peristalsis Longitudinal muscle relaxed (extended) Circular muscle contracted Circular muscle relaxed Longitudinal muscle contracted Bristles Head end Head end Figure 50.33 Head end

Bones and joints of the human skeleton Head of humerus Examples of joints Skull Scapula 1 Clavicle Shoulder girdle Scapula Sternum 1 Ball-and-socket joint Rib 2 Humerus 3 Vertebra Radius Ulna Humerus Pelvic girdle Carpals Ulna Phalanges Metacarpals Figure 50.34 2 Hinge joint Femur Patella Tibia Fibula Ulna Radius Tarsals Metatarsals Phalanges 3 Pivot joint

Energy-efficient locomotion on land Figure 50.35

You should now be able to: Distinguish between the following pairs of terms: sensation and perception; sensory transduction and receptor potential; tastants and odorants; rod and cone cells; oxidative and glycolytic muscle fibers; slow-twitch and fast-twitch muscle fibers; endoskeleton and exoskeleton. List the five categories of sensory receptors and explain the energy transduced by each type.

Explain the role of mechanoreceptors in hearing and balance. Give the function of each structure using a diagram of the human ear. Explain the sliding-filament model of muscle contraction. Explain how a skeleton combines with an antagonistic muscle arrangement to provide a mechanism for movement.