Chapter 49 Sensory and Motor Mechanisms Power Point

Chapter 49 Sensory and Motor Mechanisms Power. Point Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Overview: Sensing and Acting • Bats use sonar to detect their prey • Moths, a common prey for bats – Can detect the bat’s sonar and attempt to flee Figure 49. 1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Both of these organisms – Have complex sensory systems that facilitate their survival • The structures that make up these systems – Have been transformed by evolution into diverse mechanisms that sense various stimuli and generate the appropriate physical movement Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Concept 49. 1: Sensory receptors transduce stimulus energy and transmit signals to the central nervous system • Sensations are action potentials – That reach the brain via sensory neurons • Once the brain is aware of sensations – It interprets them, giving the perception of stimuli Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Sensations and perceptions – Begin with sensory reception, the detection of stimuli by sensory receptors • Exteroreceptors – Detect stimuli coming from the outside of the body • Interoreceptors – Detect internal stimuli Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Functions Performed by Sensory Receptors • All stimuli represent forms of energy • Sensation involves converting this energy – Into a change in the membrane potential of sensory receptors Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Sensory receptors perform four functions in this process – Sensory transduction, amplification, transmission, and integration Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Two types of sensory receptors exhibit these functions – A stretch receptor in a crayfish Weak muscle stretch Muscle Stretch receptor Axon Membrane potential (m. V) Dendrites Strong muscle stretch – 50 Receptor potential – 50 – 70 Action potentials 0 0 – 70 0 1 2 3 4 5 6 7 Time (sec) (a) Crayfish stretch receptors have dendrites stretch, producing a receptor potential in the embedded in abdominal muscles. When the stretch receptor. The receptor potential triggers action potentials in the axon of the stretch abdomen bends, muscles and dendrites Figure 49. 2 a Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 01 2 3 4 5 67 Time (sec) receptor. A stronger stretch produces a larger receptor potential and higher requency of action potentials.

– A hair cell found in vertebrates Fluid moving in one direction No fluid movement “Hairs” of hair cell Neurotransmitter at synapse More neurotransmitter Less neurotransmitter – 50 – 70 Action potentials 0 – 70 Membrane potential (m. V) – 50 Receptor potential Membrane potential (m. V) Axon Fluid moving in other direction – 70 0 (b) Vertebrate hair cells have specialized cilia or microvilli (“hairs”) that bend when surrounding fluid moves. Each hair cell releases an excitatory neurotransmitter at a synapse 0 1 2 3 4 5 6 7 Time (sec) with a sensory neuron, which conducts action potentials to the CNS. Bending in one direction depolarizes the hair cell, causing it to release more neurotransmitter and increasing frequency Figure 49. 2 b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 0 – 70 01 2 3 4 5 6 7 Time (sec) of action potentials in the sensory neuron. Bending in the other direction has the opposite effects. Thus, hair cells respond to the direction of motion as well as to its strength and speed. s

Sensory Transduction • Sensory transduction is the conversion of stimulus energy – Into a change in the membrane potential of a sensory receptor • This change in the membrane potential – Is known as a receptor potential Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Many sensory receptors are extremely sensitive – With the ability to detect the smallest physical unit of stimulus possible Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Amplification • Amplification is the strengthening of stimulus energy – By cells in sensory pathways Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Transmission • After energy in a stimulus has been transduced into a receptor potential – Some sensory cells generate action potentials, which are transmitted to the CNS Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Sensory cells without axons – Release neurotransmitters at synapses with sensory neurons Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Integration • The integration of sensory information – 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

• Some receptor potentials – Are integrated through summation • Another type of integration is sensory adaptation – A decrease in responsiveness during continued stimulation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Types of Sensory Receptors • Based on the energy they transduce, sensory receptors fall into five categories – Mechanoreceptors – Chemoreceptors – Electromagnetic receptors – Thermoreceptors – Pain receptors Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Mechanoreceptors • Mechanoreceptors sense physical deformation – Caused by stimuli such as pressure, stretch, motion, and sound Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• The mammalian sense of touch – Relies on mechanoreceptors that are the dendrites of sensory neurons Cold Light touch Pain Hair Heat Epidermis Dermis Figure 49. 3 Nerve Connective tissue Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hair movement Strong pressure

Chemoreceptors • Chemoreceptors include – General receptors that transmit information about the total solute concentration of a solution – Specific receptors that respond to individual kinds of molecules Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Two of the most sensitive and specific chemoreceptors known Figure 49. 4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 0. 1 mm – Are present in the antennae of the male silkworm moth

Electromagnetic Receptors • Electromagnetic receptors detect various forms of electromagnetic energy – Such as visible light, electricity, and magnetism Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Some snakes have very sensitive infrared receptors – That detect body heat of prey against a colder background Figure 49. 5 a (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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Many mammals appear to use the Earth’s magnetic field lines – To orient themselves as they migrate Figure 49. 5 b (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 • Thermoreceptors, which respond to heat or cold – Help regulate body temperature by signaling both surface and body core temperature Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Pain Receptors • In humans, pain receptors, also called nociceptors – Are a class of naked dendrites in the epidermis – Respond to excess heat, pressure, or specific classes of chemicals released from damaged or inflamed tissues Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Concept 49. 2: The mechanoreceptors involved with hearing and equilibrium detect settling particles or moving fluid • Hearing and the perception of body equilibrium – Are related in most animals Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Sensing Gravity and Sound in Invertebrates • Most invertebrates have sensory organs called statocysts – That contain mechanoreceptors and function in their sense of equilibrium Ciliated receptor cells Statolith Figure 49. 6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cilia Sensory nerve fibers

• Many arthropods sense sounds with body hairs that vibrate – Or with localized “ears” consisting of a tympanic membrane and receptor cells Tympanic membrane Figure 49. 7 1 mm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Hearing and Equilibrium in Mammals • In most terrestrial vertebrates – The sensory organs for hearing and equilibrium are closely associated in the ear Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Exploring the structure of the human ear 1 2 The middle ear and inner ear Overview of ear structure Incus Middle ear Inner ear Outer ear Stapes Skull bones Semicircular canals Malleus Auditory nerve, to brain Pinna Tympanic membrane Auditory canal Hair cells Cochlea Eustachian tube Tectorial membrane Tympanic membrane Oval window Eustachian tube Round window Cochlear duct Bone Vestibular canal Auditory nerve Basilar membrane Figure 49. 8 Axons of sensory neurons To auditory nerve 4 The organ of Corti Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tympanic canal 3 The cochlea Organ of Corti

Hearing • Vibrating objects create percussion waves in the air – That cause the tympanic membrane to vibrate • The three bones of the middle ear – Transmit the vibrations to the oval window on the cochlea Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• These vibrations create pressure waves in the fluid in the cochlea – That travel through the vestibular canal and ultimately strike the round window Cochlea Stapes Oval window Axons of sensory neurons Vestibular canal Perilymph Base Figure 49. 9 Round window Tympanic Basilar canal membrane Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Apex

• The pressure waves in the vestibular canal – Cause the basilar membrane to vibrate up and down causing its hair cells to bend • The bending of the hair cells depolarizes their membranes – Sending action potentials that travel via the auditory nerve to the brain Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• The cochlea can distinguish pitch – Because the basilar membrane is not uniform along its length Cochlea (uncoiled) Apex (wide and flexible) Basilar membrane 1 k. Hz 500 Hz (low pitch) 2 k. Hz 4 k. Hz 8 k. Hz 16 k. Hz (high pitch) Figure 49. 10 Base (narrow and stiff) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Frequency producing maximum vibration

• Each region of the basilar membrane vibrates most vigorously – At a particular frequency and leads to excitation of a specific auditory area of the cerebral cortex Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Equilibrium • Several of the organs of the inner ear – Detect body position and balance Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• The utricle, saccule, and semicircular canals in the inner ear – Function in balance and equilibrium 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 Vestibular nerve Cupula Hairs Hair cell Nerve fibers Vestibule Utricle Body movement Saccule Figure 49. 11 The utricle and saccule tell the brain which way is up and inform it of the body’s position or linear acceleration. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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.

Hearing and Equilibrium in Other Vertebrates • Like other vertebrates, fishes and amphibians – Also have inner ears located near the brain Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Most fishes and aquatic amphibians – Also have a lateral line system along both sides of their body Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• The lateral line system contains mechanoreceptors – With hair cells that respond to water movement Lateral line canal Scale Epidermis Neuromast Segmental muscles of body wall Opening of lateral line canal Lateral nerve Cupula Sensory hairs Supporting cell Figure 49. 12 Nerve fiber Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hair cell

• Concept 49. 3: The senses of taste and smell are closely related in most animals • The perceptions of gustation (taste) and olfaction (smell) – Are both dependent on chemoreceptors that detect specific chemicals in the environment Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• The taste receptors of insects are located within sensory hairs called sensilla – Which are located on the feet and in mouthparts Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

EXPERIMENT Insects taste using gustatory sensilla (hairs) on their feet and mouthparts. Each sensillum contains four chemoreceptors with dendrites that extend to a pore at the tip of the sensillum. To study the sensitivity of each chemoreceptor, researchers immobilized a blowfly (Phormia regina) by attaching it to a rod with wax. They then inserted the tip of a microelectrode into one sensillum to record action potentials in the chemoreceptors, while they used a pipette to touch the pore with various test substances. To brain Chemoreceptors Sensillum Microelectrode To voltage recorder CONCLUSION Any natural food probably stimulates multiple chemoreceptors. By integrating sensations, the insect’s brain can apparently distinguish a very large number of tastes. Figure 49. 13 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pore at tip Pipette containing test substance Number of action potentials in first second of response RESULTS Each chemoreceptor is especially sensitive to a particular class of substance, but this specificity is relative; each cell can respond to some extent to a broad range of different chemical stimuli. Chemoreceptors 50 30 10 0 0. 5 M Na. Cl 0. 5 M Sucrose Stimulus Meat Honey

Taste in Humans • The receptor cells for taste in humans – Are modified epithelial cells organized into taste buds • Five taste perceptions involve several signal transduction mechanisms – Sweet, sour, salty, bitter, and umami (elicited by glutamate) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Transduction in taste receptors – Occurs by several mechanisms Taste pore Sugar molecule Taste bud Sensory receptor cells Sensory neuron Tongue 1 Sugar A sugar molecule binds to a receptor protein on the sensory receptor cell. G protein Sugar receptor Adenylyl cyclase 2 Binding initiates a signal transduction pathway involving cyclic AMP and protein kinase A. ATP c. AMP Protein kinase A 3 Activated protein kinase A closes K+ channels in the membrane. SENSORY K+ RECEPTOR CELL Synaptic 4 The decrease in the membrane’s permeability to K+ depolarizes the membrane. vesicle —Ca 2+ 5 Depolarization opens voltage-gated calcium ion (Ca 2+) channels, and Ca 2+ diffuses into the receptor cell. Neurotransmitter Figure 49. 14 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 6 The increased Ca 2+ concentration causes synaptic vesicles to release neurotransmitter. Sensory neuron

Smell in Humans • Olfactory receptor cells – Are neurons that line the upper portion of the nasal cavity Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• When odorant molecules bind to specific receptors – A signal transduction pathway is triggered, sending action potentials to the brain Brain Action potentials Odorant Olfactory bulb Nasal cavity Bone Epithelial cell Odorant receptors Chemoreceptor Plasma membrane Figure 49. 15 Odorant Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cilia Mucus

• Concept 49. 4: Similar mechanisms underlie vision throughout the animal kingdom • Many types of light detectors – Have evolved in the animal kingdom and may be homologous Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Vision in Invertebrates • Most invertebrates – Have some sort of light-detecting organ Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• One of the simplest is the eye cup of planarians – Which provides information about light intensity and direction but does not form images Light shining from the front is detected Photoreceptor Visual pigment Ocellus Figure 49. 16 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nerve to brain Screening pigment Light shining from behind is blocked by the screening pigment

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

• Compound eyes are found in insects and crustaceans – And consist of up to several thousand light detectors called ommatidia 2 mm (a) The faceted eyes on the head of a fly, photographed with a stereomicroscope. (b) The cornea and crystalline cone of each ommatidium function as a lens that focuses light on the rhabdom, a stack of pigmented plates inside a circle of photoreceptors. The rhabdom traps light and guides it to photoreceptors. The image formed by a compound eye is a mosaic of dots produced by different intensities of light entering the many ommatidia from different angles. Figure 49. 17 a–b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cornea Crystalline cone Rhabdom Axons Photoreceptor Ommatidium Lens

• Single-lens eyes – Are found in some jellies, polychaetes, spiders, and many molluscs – Work on a camera-like principle Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The Vertebrate Visual System • The eyes of vertebrates are camera-like – But they evolved independently and differ from the single-lens eyes of invertebrates Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Structure of the Eye • The main parts of the vertebrate eye are – The sclera, which includes the cornea – The choroid, a pigmented layer – The conjunctiva, that covers the outer surface of the sclera Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

– The iris, which regulates the pupil – The retina, which contains photoreceptors – The lens, which focuses light on the retina Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• The 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 Figure 49. 18 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Optic disk (blind spot)

• Humans and other mammals – Focus light by changing the shape of the lens Front view of lens and ciliary muscle Ciliary muscles contract, pulling border of choroid toward lens Choroid Suspensory ligaments relax Lens (rounder) Retina Ciliary muscle Lens becomes thicker and rounder, focusing on near objects Suspensory ligaments (a) Near vision (accommodation) Ciliary muscles relax, and border of choroid moves away from lens Suspensory ligaments pull against lens Lens becomes flatter, focusing on distant objects Figure 49. 19 a–b (b) Distance vision Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lens (flatter)

• The human retina contains two types of photoreceptors – Rods are 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

Sensory Transduction in the Eye • Each rod or cone in the vertebrate retina – Contains visual pigments that consist of a lightabsorbing molecule called retinal bonded to a protein called opsin Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Rods contain the pigment rhodopsin – Which changes shape when it absorbs light Rod Outer segment H H 2 C Disks H CH 3 C H C CH 3 H C C H 3 C H C C C H O C H H H CH 3 cis isomer Inside of disk Cell body Enzymes Light Synaptic terminal H H H 2 C CH 3 C H H 2 C C C Cytosol Rhodopsin Figure 49. 20 a, b C C Retinal Opsin (a) Rods contain the visual pigment rhodopsin, which is embedded in a stack of membranous disks in the rod’s outer segment. Rhodopsin consists of the light-absorbing molecule retinal bonded to opsin, a protein. Opsin has seven helices that span the disk membrane. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings C C CH 3 H C C CH 3 C O H trans isomer (b) Retinal exists as two isomers. Absorption of light converts the cis isomer to the trans isomer, which causes opsin to change its conformation (shape). After a few minutes, retinal detaches from opsin. In the dark, enzymes convert retinal back to its cis form, which recombines with opsin to form rhodopsin.

Processing Visual Information • The processing of visual information – Begins in the retina itself Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Absorption of light by retinal – Triggers a signal transduction pathway Light EXTRACELLULAR FLUID INSIDE OF DISK Active rhodopsin PDE CYTOSOL Inactive rhodopsin Transducin Plasma membrane Disk membrane 3 Transducin activates the enzyme phos phodiesterae (PDE). Figure 49. 21 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Dark Light – 40 Na+ 2 Active rhodopsin in turn activates a G protein called transducin. 0 c. GMP 1 Light isomerizes retinal, which activates rhodopsin. Membrane potential (m. V) 4 Activated PDE detaches cyclic guanosine monophosphate (c. GMP) from Na+ channels in the plasma membrane by hydrolyzing c. GMP to GMP. �– 70 – Hyper polarization Time Na+ 5 The Na+ channels close when c. GMP detaches. The membrane’s permeability to Na+ decreases, and the rod hyperpolarizes.

• In the dark, both rods and cones – Release the neurotransmitter glutamate into the synapses with neurons called bipolar cells, which are either hyperpolarized or depolarized Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• In the light, rods and cones hyperpolarize – Shutting off their release of glutamate • The bipolar cells – Are then either depolarized or hyperpolarized Dark Responses Rhodopsin inactive Rhodopsin active Na+ channels open Na+ channels closed Rod depolarized Rod hyperpolarized Glutamate released Figure 49. 22 Light Responses Bipolar cell either depolarized or hyperpolarized, depending on glutamate receptors Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings No glutamate released Bipolar cell either hyperpolarized or depolarized, depending on glutamate receptors

• Three other types of neurons contribute to information processing in the retina – Ganglion cells, horizontal cells, and amacrine cells Retina Optic nerve To brain Retina Photoreceptors Neurons Cone Rod Amacrine cell Figure 49. 23 Optic nerve fibers Ganglion cell Horizontal cell Bipolar cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pigmented epithelium

• Signals from rods and cones – Travel from bipolar cells to ganglion cells • The axons of ganglion cells are part of the optic nerve – That transmit information to the brain Optic nerve Left visual field Right visual field Left eye Right eye Optic chiasm Lateral geniculate nucleus Figure 49. 24 Primary visual cortex Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Most ganglion cell axons lead to the lateral geniculate nuclei of the thalamus – Which relays information to the primary visual cortex • Several integrating centers in the cerebral cortex – Are active in creating visual perceptions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Concept 49. 5: Animal skeletons function in support, protection, and movement • The various types of animal movements – All result from muscles working against some type of skeleton Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Types of Skeletons • The three main functions of a skeleton are – Support, protection, and movement • The three main types of skeletons are – Hydrostatic skeletons, exoskeletons, and endoskeletons Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Hydrostatic Skeletons • A hydrostatic skeleton – Consists of fluid held under pressure in a closed body compartment • This is the main type of skeleton – In most cnidarians, flatworms, nematodes, and annelids Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Annelids use their hydrostatic skeleton for peristalsis – A type of movement on land produced by rhythmic waves of muscle contractions (a) Body segments at the head and just in front of the rear are short and thick (longitudinal muscles contracted; circular muscles relaxed) and anchored to the ground by bristles. The other segments are thin and elongated (circular muscles contracted; longitudinal muscles relaxed. ) Longitudinal muscle relaxed (extended) Bristles (b) The head has moved forward because circular muscles in the head segments have contracted. Segments behind the head and at the rear are now thick and anchored, thus preventing the worm from slipping backward. Figure 49. 25 a–c (c) The head segments are thick again and anchored in their new positions. The rear segments have released their hold on the ground and have been pulled forward. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Circular muscle contracted Circular muscle relaxed Longitudinal muscle contracted Head

Exoskeletons • An exoskeleton is a hard encasement – Deposited on the surface of an animal • Exoskeletons – Are found in most molluscs and arthropods Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Endoskeletons • An endoskeleton consists of hard supporting elements – Such as bones, buried within the soft tissue of an animal • Endoskeletons – Are found in sponges, echinoderms, and chordates Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• The mammalian skeleton is built from more than 200 bones – Some fused together and others connected at joints by ligaments that allow freedom of movement Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• 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 Figure 49. 26 Tarsals Metatarsals Phalanges Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Radius 3 Pivot joints allow us to rotate our forearm at the elbow and to move our head from side to side.

Physical Support on Land • In addition to the skeleton – Muscles and tendons help support large land vertebrates Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Concept 49. 6: Muscles move skeletal parts by contracting • The action of a muscle – Is always to contract Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Skeletal muscles are attached to the skeleton in antagonistic pairs – With each member of the pair working against each other Human Grasshopper Extensor muscle relaxes Biceps contracts Triceps relaxes Flexor muscle contracts Forearm flexes Extensor muscle contracts Biceps relaxes Forearm extends Figure 49. 27 Triceps contracts Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tibia flexes Tibia extends Flexor muscle relaxes

Vertebrate Skeletal Muscle • Vertebrate skeletal muscle – Is characterized by a hierarchy of smaller and smaller units Muscle Bundle of muscle fibers Nuclei Single muscle fiber (cell) Plasma membrane Myofibril Z line Light band Dark band Sarcomere TEM I band 0. 5 m A band I band M line Thick filaments (myosin) Figure 49. 28 Thin filaments (actin) Z line Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings H zone Sarcomere Z line

• A skeletal muscle consists of a bundle of long fibers – Running parallel to the length of the muscle • A muscle fiber – Is itself a bundle of smaller myofibrils arranged longitudinally Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• The myofibrils are composed to two kinds of myofilaments – Thin filaments, consisting of two strands of actin and one strand of regulatory protein – Thick filaments, staggered arrays of myosin molecules Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Skeletal muscle is also called striated muscle – Because the regular arrangement of the myofilaments creates a pattern of light and dark bands Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Each repeating unit is a sarcomere – Bordered by Z lines • The areas that contain the myofilments – Are the I band, A band, and H zone Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The Sliding-Filament Model of Muscle Contraction • According to the sliding-filament model of muscle contraction – The filaments slide past each other longitudinally, producing more overlap between the thin and thick filaments Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• As a result of this sliding – The I band the H zone shrink 0. 5 m (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. Figure 49. 29 a–c (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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Z H A Sarcomere

• The sliding of filaments is based on – The interaction between the actin and myosin molecules of the thick and thin filaments • The “head” of a myosin molecule binds to an actin filament – Forming a cross-bridge and pulling the thin filament toward the center of the sarcomere Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Myosin-actin interactions underlying muscle fiber contraction Thick filament 1 Starting here, the myosin head is bound to ATP and is in its lowenergy confinguration. Thin filaments 5 Binding of a new molecule of ATP releases the myosin head from actin, and a new cycle begins. Thin filament Myosin head (lowenergy configuration) ATP Thick filament Thin filament moves toward center of sarcomere. Figure 49. 30 + P i Cross-bridge binding site Actin ADP Myosin head (lowenergy configuration) ADP 2 The myosin head hydrolyzes ATP to ADP and inorganic phosphate ( P I ) and is in its high-energy configuration. P i ADP 4 Releasing ADP and ( P i), myosin relaxes to its low-energy configuration, sliding the thin filament. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings P i Cross-bridge Myosin head (highenergy configuration) 13 The myosin head binds to actin, forming a crossbridge.

The Role of Calcium and Regulatory Proteins • A skeletal muscle fiber contracts – Only when stimulated by a motor neuron Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• When a muscle is at rest – The myosin-binding sites on the thin filament are blocked by the regulatory protein tropomyosin Tropomyosin Actin Figure 49. 31 a Ca 2+-binding sites (a) Myosin-binding sites blocked Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Troponin complex

• 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 Ca 2+ Myosinbinding site Figure 49. 31 b (b) Myosin-binding sites exposed Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• The stimulus leading to the contraction of a skeletal muscle fiber – Is an action potential in a motor neuron that makes a synapse with the muscle fiber Motor neuron axon Mitochondrion Synaptic terminal T tubule Sarcoplasmic reticulum Ca 2+ released from sarcoplasmic reticulum Myofibril Figure 49. 32 Plasma membrane of muscle fiber Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sarcomere

• The synaptic terminal of the motor neuron – Releases the neurotransmitter acetylcholine, depolarizing the muscle and causing it to produce an action potential Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Action potentials travel to the interior of the muscle fiber – Along infoldings of the plasma membrane called transverse (T) tubules • The action potential along the T tubules – Causes the sarcoplasmic reticulum to release Ca 2+ • The Ca 2+ binds to the troponin-tropomyosin complex on the thin filaments – Exposing the myosin-binding sites and allowing the cross-bridge cycle to proceed Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• 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 ACh 2 Action potential is propagated along plasma membrane and down T tubules. SR 3 Action potential triggers Ca 2+ release from sarcoplasmic reticulum (SR). Ca 2 7 Tropomyosin blockage of myosinbinding sites is restored; contraction ends, and muscle fiber relaxes. Ca 2 CYTOSOL ADP P 2 PLASMA MEMBRANE T TUBULE 4 Calcium ions bind to troponin; troponin changes shape, removing blocking action of tropomyosin; myosin-binding sites exposed. 2+ 6 Cytosolic Ca is removed by active transport into SR after action potential ends. Figure 49. 33 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5 Myosin cross-bridges alternately attach to actin and detach, pulling actin filaments toward center of sarcomere; ATP powers sliding of filaments.

Neural Control of Muscle Tension • Contraction of a whole muscle is graded – Which means that we can voluntarily alter the extent and strength of its contraction Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• There are two basic mechanisms by which the nervous system produces graded contractions of whole muscles – By varying the number of fibers that contract – By varying the rate at which muscle fibers are stimulated Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• In a vertebrate skeletal muscle – Each branched muscle fiber is innervated by only one motor neuron • Each motor neuron – May synapse with multiple muscle fibers Motor unit 1 Spinal cord Motor unit 2 Synaptic terminals Nerve Motor neuron cell body Motor neuron axon Muscle fibers Figure 49. 34 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tendon

• A motor unit – Consists of a single motor neuron and all the muscle fibers it controls • Recruitment of multiple motor neurons – Results in stronger contractions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• A twitch – Results from a single action potential in a motor neuron • More rapidly delivered action potentials – Produce a graded contraction by summation Tension Tetanus Summation of two twitches Single twitch Action potential Time Pair of action potentials Figure 49. 35 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Series of action potentials at high frequency

• Tetanus is a state of smooth and sustained contraction – Produced when motor neurons deliver a volley of action potentials Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Types of Muscle Fibers • Skeletal muscle fibers are classified as slow oxidative, fast oxidative, and fast glycolytic – Based on their contraction speed and major pathway for producing ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Types of skeletal muscles Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Other Types of Muscle • Cardiac muscle, found only in the heart – Consists of striated cells that are electrically connected by intercalated discs – Can generate action potentials without neural input Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• In smooth muscle, found mainly in the walls of hollow organs – The contractions are relatively slow and may be initiated by the muscles themselves • In addition, contractions may be caused by – Stimulation from neurons in the autonomic nervous system Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Concept 49. 7: Locomotion requires energy to overcome friction and gravity • Movement is a hallmark of all animals – And usually necessary for finding food or evading predators • Locomotion – Is active travel from place to place Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Swimming • Overcoming friction – Is a major problem for swimmers • Overcoming gravity is less of a problem for swimmers – Than for animals that move on land or fly Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Locomotion on Land • Walking, running, hopping, or crawling on land – Requires an animal to support itself and move against gravity Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Diverse adaptations for traveling on land – Have evolved in various vertebrates Figure 49. 36 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Flying • Flight requires that wings develop enough lift – To overcome the downward force of gravity Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Comparing Costs of Locomotion • The energy cost of locomotion –Depends on the mode of locomotion and the environment EXPERIMENT Physiologists typically determine an animal’s rate of energy use during locomotion by measuring its oxygen consumption or carbon dioxide production while it swims in a water flume, runs on a treadmill, or flies in a wind tunnel. For example, the trained parakeet shown below is wearing a plastic face mask connected to a tube that collects the air the bird exhales as it flies. RESULTS This graph compares the energy cost, in joules per kilogram of body mass per meter traveled, for animals specialized for running, flying, and swimming (1 J = 0. 24 cal). Notice that both axes are plotted on logarithmic scales. CONCLUSION Flying Energy cost (J/Kg/m) For animals of a given body mass, swimming is the most energy. CONCLUSION efficient and running the least energyefficient mode of locomotion. In any mode, a small animal expends more energy per kilogram of body mass than a large animal. 102 Running 10 1 Swimming 10– 1 10– 3 Figure 49. 37 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1 103 Body mass(g) 106

• Animals that are specialized for swimming – Expend less energy per meter traveled than equivalently sized animals specialized for flying or running Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings