Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
CAMPBELL BIOLOGY IN FOCUS Urry • Cain • Wasserman • Minorsky • Jackson • Reece 38 Nervous and Sensory Systems Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge © 2014 Pearson Education, Inc. Overview: Sense and Sensibility Gathering, processing, and organizing information are essential functions of all nervous systems © 2014 Pearson Education, Inc. Figure 38.1 © 2014 Pearson Education, Inc. Concept 38.1: Nervous systems consist of circuits of neurons and supporting cells The ability to sense and react originated billions of years ago in prokaryotes Hydras, jellies, and cnidarians are the simplest animals with nervous systems In most cnidarians, interconnected nerve cells form a nerve net, which controls contraction and expansion of the gastrovascular cavity © 2014 Pearson Education, Inc. Figure 38.2 Eyespot Brain Nerve cords Nerve net Transverse nerve (a) Hydra (cnidarian) (b) Planarian (flatworm) Brain Brain Ventral nerve cord Spinal cord (dorsal nerve cord) Sensory ganglia Segmental ganglia (c) Insect (arthropod) © 2014 Pearson Education, Inc. (d) Salamander (vertebrate) In more complex animals, the axons of multiple nerve cells are often bundled together to form nerves These fibrous structures channel and organize information flow through the nervous system Animals with elongated, bilaterally symmetrical bodies have even more specialized systems © 2014 Pearson Education, Inc. Cephalization is an evolutionary trend toward a clustering of sensory neurons and interneurons at the anterior Nonsegmented worms have the simplest clearly defined central nervous system (CNS), consisting of a small brain and longitudinal nerve cords © 2014 Pearson Education, Inc. Annelids and arthropods have segmentally arranged clusters of neurons called ganglia In vertebrates The CNS is composed of the brain and spinal cord The peripheral nervous system (PNS) is composed of nerves and ganglia © 2014 Pearson Education, Inc. Glia Glia have numerous functions to nourish, support, and regulate neurons Embryonic radial glia form tracks along which newly formed neurons migrate Astrocytes (star-shaped glial cells) induce cells lining capillaries in the CNS to form tight junctions, resulting in a blood-brain barrier © 2014 Pearson Education, Inc. Figure 38.3 CNS PNS Neuron VENTRICLE Cilia Oligodendrocyte Schwann cell Microglial cell Capillary Ependymal cell Astrocytes 50 m Intermingling of astrocytes with neurons (blue) © 2014 Pearson Education, Inc. LM Figure 38.3a Astrocytes 50 m Intermingling of astrocytes with neurons (blue) © 2014 Pearson Education, Inc. LM Organization of the Vertebrate Nervous System The spinal cord runs lengthwise inside the vertebral column (the spine) The spinal cord conveys information to and from the brain It can also act independently of the brain as part of simple nerve circuits that produce reflexes, the body’s automatic responses to certain stimuli © 2014 Pearson Education, Inc. Figure 38.4 Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) Cranial nerves Ganglia outside CNS Spinal nerves © 2014 Pearson Education, Inc. The brain and spinal cord contain Gray matter, which consists mainly of neuron cell bodies and glia White matter, which consists of bundles of myelinated axons © 2014 Pearson Education, Inc. The CNS contains fluid-filled spaces called ventricles in the brain and the central canal in the spinal cord Cerebrospinal fluid is formed in the brain and circulates through the ventricles and central canal and drains into the veins It supplies the CNS with nutrients and hormones and carries away wastes © 2014 Pearson Education, Inc. The Peripheral Nervous System The PNS transmits information to and from the CNS and regulates movement and the internal environment In the PNS, afferent neurons transmit information to the CNS and efferent neurons transmit information away from the CNS © 2014 Pearson Education, Inc. Figure 38.5 Central Nervous System (information processing) Peripheral Nervous System Afferent neurons Efferent neurons Sensory receptors Autonomic nervous system Motor system Control of skeletal muscle Internal and external stimuli Sympathetic Parasympathetic division division Enteric division Control of smooth muscles, cardiac muscles, glands © 2014 Pearson Education, Inc. The PNS has two efferent components: the motor system and the autonomic nervous system The motor system carries signals to skeletal muscles and can be voluntary or involuntary The autonomic nervous system regulates smooth and cardiac muscles and is generally involuntary © 2014 Pearson Education, Inc. The autonomic nervous system has sympathetic, parasympathetic, and enteric divisions The enteric division controls activity of the digestive tract, pancreas, and gallbladder © 2014 Pearson Education, Inc. The sympathetic division regulates the “fight-orflight” response The parasympathetic division generates opposite responses in target organs and promotes calming and a return to “rest and digest” functions © 2014 Pearson Education, Inc. Concept 38.2: The vertebrate brain is regionally specialized The human brain contains 100 billion neurons These cells are organized into circuits that can perform highly sophisticated information processing, storage, and retrieval © 2014 Pearson Education, Inc. Figure 38.6a © 2014 Pearson Education, Inc. Figure 38.6b Brain structures in child and adult Embryonic brain regions Telencephalon Cerebrum (includes cerebral cortex, white matter, basal nuclei) Diencephalon Diencephalon (thalamus, hypothalamus, epithalamus) Mesencephalon Midbrain (part of brainstem) Metencephalon Pons (part of brainstem), cerebellum Myelencephalon Medulla oblongata (part of brainstem) Forebrain Midbrain Hindbrain Midbrain Hindbrain Mesencephalon Metencephalon Diencephalon Cerebrum Diencephalon Myelencephalon Midbrain Pons Forebrain Embryo at 1 month © 2014 Pearson Education, Inc. Telencephalon Medulla oblongata Cerebellum Spinal cord Spinal cord Embryo at 5 weeks Child Figure 38.6ba Embryonic brain regions Telencephalon Forebrain Diencephalon Midbrain Mesencephalon Metencephalon Hindbrain Myelencephalon Brain structures in child and adult Cerebrum (includes cerebral cortex, white matter, basal nuclei) Diencephalon (thalamus, hypothalamus, epithalamus) Midbrain (part of brainstem) Pons (part of brainstem), cerebellum Medulla oblongata (part of brainstem) © 2014 Pearson Education, Inc. Figure 38.6bb Mesencephalon Midbrain Hindbrain Metencephalon Diencephalon Forebrain Embryo at 1 month © 2014 Pearson Education, Inc. Telencephalon Myelencephalon Spinal cord Embryo at 5 weeks Figure 38.6bc Cerebrum Diencephalon Midbrain Pons Medulla oblongata Cerebellum Spinal cord Child © 2014 Pearson Education, Inc. Figure 38.6c Left cerebral hemisphere Right cerebral hemisphere Cerebral cortex Corpus callosum Cerebrum Basal nuclei Cerebellum Adult brain viewed from the rear © 2014 Pearson Education, Inc. Figure 38.6d Diencephalon Thalamus Pineal gland Hypothalamus Pituitary gland Brainstem Midbrain Pons Medulla oblongata Spinal cord © 2014 Pearson Education, Inc. Arousal and Sleep Arousal is a state of awareness of the external world Sleep is a state in which external stimuli are received but not consciously perceived Arousal and sleep are controlled in part by clusters of neurons in the midbrain and pons © 2014 Pearson Education, Inc. Sleep is an active state for the brain and is regulated by the biological clock and regions of the forebrain, which regulate the intensity and duration of sleep Some animals have evolutionary adaptations that allow for substantial activity during sleep For example, in dolphins, only one side of the brain is asleep at a time © 2014 Pearson Education, Inc. Figure 38.7 Key Low-frequency waves characteristic of sleep High-frequency waves characteristic of wakefulness Location Left hemisphere Right hemisphere © 2014 Pearson Education, Inc. Time: 0 hours Time: 1 hour Biological Clock Regulation Cycles of sleep and wakefulness are examples of circadian rhythms, daily cycles of biological activity Mammalian circadian rhythms rely on a biological clock, a molecular mechanism that directs periodic gene expression Biological clocks are typically synchronized to light and dark cycles and maintain a roughly 24-hour cycle © 2014 Pearson Education, Inc. In mammals, circadian rhythms are coordinated by a group of neurons in the hypothalamus called the suprachiasmatic nucleus (SCN) The SCN acts as a pacemaker, synchronizing the biological clock © 2014 Pearson Education, Inc. Emotions Generation and experience of emotions involve many brain structures including the amygdala, hippocampus, and parts of the thalamus These structures are grouped as the limbic system © 2014 Pearson Education, Inc. Generation and experience of emotion also require interaction between the limbic system and sensory areas of the cerebrum The brain structure that is most important for emotional memory is the amygdala © 2014 Pearson Education, Inc. Figure 38.8 Thalamus Hypothalamus Olfactory bulb Amygdala © 2014 Pearson Education, Inc. Hippocampus The Brain’s Reward System and Drug Addiction The brain’s reward system provides motivation for activities that enhance survival and reproduction The brain’s reward system is dramatically affected by drug addiction Drug addiction is characterized by compulsive consumption and an inability to control intake © 2014 Pearson Education, Inc. Addictive drugs such as cocaine, amphetamine, heroin, alcohol, and tobacco enhance the activity of the dopamine pathway Drug addiction leads to long-lasting changes in the reward circuitry that cause craving for the drug © 2014 Pearson Education, Inc. Figure 38.9 Nicotine stimulates dopaminereleasing VTA neuron. Inhibitory neuron Dopaminereleasing VTA neuron Opium and heroin decrease activity of inhibitory neuron. Cocaine and amphetamines block removal of dopamine from synaptic cleft. Cerebral neuron of reward pathway © 2014 Pearson Education, Inc. Reward system response Functional Imaging of the Brain Functional imaging methods are transforming our understanding of normal and diseased brains In positron-emission tomography (PET) an injection of radioactive glucose enables a display of metabolic activity © 2014 Pearson Education, Inc. In functional magnetic resonance imaging, fMRI, the subject lies with his or her head in the center of a large, doughnut-shaped magnet Brain activity is detected by changes in local oxygen concentration Applications of fMRI include monitoring recovery from stroke, mapping abnormalities in migraine headaches, and increasing the effectiveness of brain surgery © 2014 Pearson Education, Inc. Figure 38.10 Nucleus accumbens Happy music © 2014 Pearson Education, Inc. Amygdala Sad music Figure 38.10a Nucleus accumbens Happy music © 2014 Pearson Education, Inc. Figure 38.10b Amygdala Sad music © 2014 Pearson Education, Inc. Concept 38.3: The cerebral cortex controls voluntary movement and cognitive functions The cerebrum is essential for language, cognition, memory, consciousness, and awareness of our surroundings The cognitive functions reside mainly in the cortex, the outer layer Four regions, or lobes (frontal, temporal, occipital, and parietal), are landmarks for particular functions © 2014 Pearson Education, Inc. Figure 38.11 Motor cortex (control of skeletal muscles) Frontal lobe Somatosensory cortex (sense of touch) Parietal lobe Prefrontal cortex (decision making, planning) Broca’s area (forming speech) Temporal lobe Auditory cortex (hearing) Cerebellum Wernicke’s area (comprehending language) © 2014 Pearson Education, Inc. Sensory association cortex (integration of sensory information) Visual association cortex (combining images and object recognition) Occipital lobe Visual cortex (processing visual stimuli and pattern recognition) Language and Speech The mapping of cognitive functions within the cortex began in the 1800s Broca’s area, in the left frontal lobe, is active when speech is generated Wernicke’s area, in the posterior of the left frontal lobe, is active when speech is heard © 2014 Pearson Education, Inc. Figure 38.12 Max Hearing words Seeing words Min Speaking words © 2014 Pearson Education, Inc. Generating words Lateralization of Cortical Function The left side of the cerebrum is dominant regarding language, math, and logical operations The right hemisphere is dominant in recognition of faces and patterns, spatial relations, and nonverbal thinking The establishment of differences in hemisphere function is called lateralization © 2014 Pearson Education, Inc. The two hemispheres exchange information through the fibers of the corpus callosum Severing this connection results in a “split brain” effect, in which the two hemispheres operate independently © 2014 Pearson Education, Inc. Information Processing The cerebral cortex receives input from sensory organs and somatosensory receptors Somatosensory receptors provide information about touch, pain, pressure, temperature, and the position of muscles and limbs The thalamus directs different types of input to distinct locations © 2014 Pearson Education, Inc. Frontal Lobe Function Frontal lobe damage may impair decision making and emotional responses but leave intellect and memory intact The frontal lobes have a substantial effect on “executive functions” © 2014 Pearson Education, Inc. Figure 38.UN02 © 2014 Pearson Education, Inc. Evolution of Cognition in Vertebrates In nearly all vertebrates, the brain has the same number of divisions The hypothesis that higher order reasoning requires a highly convoluted cerebral cortex has been experimentally refuted The anatomical basis for sophisticated information processing in birds (without a highly convoluted neocortex) appears to be a cluster of nuclei in the top or outer portion of the brain (pallium) © 2014 Pearson Education, Inc. Figure 38.13 Cerebrum (including pallium) Cerebellum Hindbrain Thalamus Midbrain (a) Songbird brain Cerebrum (including cerebral cortex) Thalamus Midbrain Hindbrain (b) Human brain © 2014 Pearson Education, Inc. Cerebellum Neural Plasticity Neural plasticity is the capacity of the nervous system to be modified after birth Changes can strengthen or weaken signaling at a synapse Autism, a developmental disorder, involves a disruption of activity-dependent remodeling at synapses Children with autism display impaired communication and social interaction, as well as stereotyped and repetitive behaviors © 2014 Pearson Education, Inc. Figure 38.14 N1 N1 N2 N2 (a) Synapses are strengthened or weakened in response to activity. (b) If two synapses are often active at the same time, the strength of the postsynaptic response may increase at both synapses. © 2014 Pearson Education, Inc. Memory and Learning Neural plasticity is essential to formation of memories Short-term memory is accessed via the hippocampus The hippocampus also plays a role in forming longterm memory, which is stored in the cerebral cortex Some consolidation of memory is thought to occur during sleep © 2014 Pearson Education, Inc. Concept 38.4: Sensory receptors transduce stimulus energy and transmit signals to the central nervous system Much brain activity begins with sensory input A sensory receptor detects a stimulus, which alters the transmission of action potentials to the CNS The information is decoded in the CNS, resulting in a sensation © 2014 Pearson Education, Inc. Sensory Reception and Transduction A sensory pathway begins with sensory reception, detection of stimuli by sensory receptors Sensory receptors, which detect stimuli, interact directly with stimuli, both inside and outside the body © 2014 Pearson Education, Inc. Sensory transduction is the conversion of stimulus energy into a change in the membrane potential of a sensory receptor This change in membrane potential is called a receptor potential Receptor potentials are graded; their magnitude varies with the strength of the stimulus © 2014 Pearson Education, Inc. Figure 38.15 (a) Receptor is afferent neuron. (b) Receptor regulates afferent neuron. To CNS To CNS Afferent neuron Afferent neuron Receptor protein Neurotransmitter Sensory receptor Stimulus © 2014 Pearson Education, Inc. Sensory receptor cell Stimulus leads to neurotransmitter release. Stimulus Transmission Sensory information is transmitted as nerve impulses or action potentials Neurons that act directly as sensory receptors produce action potentials and have an axon that extends into the CNS Non-neuronal sensory receptors form chemical synapses with sensory neurons They typically respond to stimuli by increasing the rate at which the sensory neurons produce action potentials © 2014 Pearson Education, Inc. The response of a sensory receptor varies with intensity of stimuli If the receptor is a neuron, a larger receptor potential results in more frequent action potentials If the receptor is not a neuron, a larger receptor potential causes more neurotransmitter to be released © 2014 Pearson Education, Inc. Figure 38.16 Gentle pressure Sensory receptor Low frequency of action potentials More pressure High frequency of action potentials © 2014 Pearson Education, Inc. Perception Perception is the brain’s construction of stimuli Action potentials from sensory receptors travel along neurons that are dedicated to a particular stimulus The brain thus distinguishes stimuli, such as light or sound, solely by the path along which the action potentials have arrived © 2014 Pearson Education, Inc. Amplification and Adaptation Amplification is the strengthening of stimulus energy by cells in sensory pathways Sensory adaptation is a decrease in responsiveness to continued stimulation © 2014 Pearson Education, Inc. Types of Sensory Receptors Based on energy transduced, sensory receptors fall into five categories Mechanoreceptors Electromagnetic receptors Thermoreceptors Pain receptors Chemoreceptors © 2014 Pearson Education, Inc. Mechanoreceptors Mechanoreceptors sense physical deformation caused by stimuli such as pressure, touch, stretch, motion, and sound Some animals use mechanoreceptors to get a feel for their environment For example, cats and many rodents have sensitive whiskers that provide detailed information about nearby objects © 2014 Pearson Education, Inc. Electromagnetic Receptors Electromagnetic receptors detect electromagnetic energy such as light, electricity, and magnetism Some snakes have very sensitive infrared receptors that detect body heat of prey against a colder background Many animals apparently migrate using Earth’s magnetic field to orient themselves © 2014 Pearson Education, Inc. Figure 38.17 Eye Infrared receptor (a) Rattlesnake (b) Beluga whales © 2014 Pearson Education, Inc. Figure 38.17a Eye Infrared receptor (a) Rattlesnake © 2014 Pearson Education, Inc. Figure 38.17b (b) Beluga whales © 2014 Pearson Education, Inc. Thermoreceptors Thermoreceptors detect heat and cold In humans, thermoreceptors in the skin and anterior hypothalamus send information to the body’s thermostat in the posterior hypothalamus © 2014 Pearson Education, Inc. Pain Receptors In humans, pain receptors, or nociceptors, detect stimuli that reflect conditions that could damage animal tissues By triggering defensive reactions, such as withdrawal from danger, pain perception serves an important function Chemicals such as prostaglandins worsen pain by increasing receptor sensitivity to noxious stimuli; aspirin and ibuprofen reduce pain by inhibiting synthesis of prostaglandins © 2014 Pearson Education, Inc. Chemoreceptors General chemoreceptors transmit information about the total solute concentration of a solution Specific chemoreceptors respond to individual kinds of molecules Olfaction (smell) and gustation (taste) both depend on chemoreceptors Smell is the detection of odorants carried in the air, and taste is detection of tastants present in solution © 2014 Pearson Education, Inc. Humans can distinguish thousands of different odors Humans and other mammals recognize just five types of tastants: sweet, sour, salty, bitter, and umami Taste receptors are organized into taste buds, mostly found in projections called papillae Any region of the tongue can detect any of the five types of taste © 2014 Pearson Education, Inc. Figure 38.18 Papilla Tongue Papillae Taste buds Taste bud Key Sweet Salty Sour Bitter Umami Taste pore Sensory neuron © 2014 Pearson Education, Inc. Food molecules Sensory receptor cells Concept 38.5: The mechanoreceptors responsible for hearing and equilibrium detect moving fluid or settling particles Hearing and perception of body equilibrium are related in most animals For both senses, settling particles or moving fluid is detected by mechanoreceptors © 2014 Pearson Education, Inc. Sensing of Gravity and Sound in Invertebrates Most invertebrates maintain equilibrium using mechanoreceptors located in organs called statocysts Statocysts contain mechanoreceptors that detect the movement of granules called statoliths Most insects sense sounds with body hairs that vibrate or with localized vibration-sensitive organs consisting of a tympanic membrane stretched over an internal chamber © 2014 Pearson Education, Inc. Figure 38.19 Ciliated receptor cells Cilia Statolith Sensory nerve fibers (axons) © 2014 Pearson Education, Inc. Hearing and Equilibrium in Mammals In most terrestrial vertebrates, sensory organs for hearing and equilibrium are closely associated in the ear © 2014 Pearson Education, Inc. Figure 38.20 Middle ear Outer ear Skull bone Inner ear Stapes Incus Malleus Semicircular canals Cochlear duct Auditory nerve to brain Bone Auditory nerve Vestibular canal Tympanic canal Cochlea Pinna Oval Auditory window canal Tympanic Round membrane window Eustachian tube Organ of Corti 1 m Tectorial membrane Bundled hairs projecting from a hair cell (SEM) © 2014 Pearson Education, Inc. Basilar Hair membrane cells Axons of sensory neurons To auditory nerve Figure 38.20a Middle ear Outer ear Skull bone Inner ear Stapes Incus Malleus Semicircular canals Auditory nerve to brain Cochlea Pinna © 2014 Pearson Education, Inc. Oval Auditory window canal Round Tympanic window membrane Eustachian tube Figure 38.20b Cochlear duct Bone Auditory nerve Vestibular canal Tympanic canal Organ of Corti © 2014 Pearson Education, Inc. Figure 38.20c Tectorial membrane Basilar membrane © 2014 Pearson Education, Inc. Hair cells Axons of sensory neurons To auditory nerve 1 m Figure 38.20d Bundled hairs projecting from a hair cell (SEM) © 2014 Pearson Education, Inc. Hearing Vibrating objects create pressure waves in the air, which are transduced by the ear into nerve impulses, perceived as sound in the brain The tympanic membrane vibrates in response to vibrations in air The three bones of the middle ear transmit the vibrations of moving air to the oval window on the cochlea © 2014 Pearson Education, Inc. The vibrations of the bones in the middle ear create pressure waves in the fluid in the cochlea that travel through the vestibular canal Pressure waves in the canal cause the basilar membrane to vibrate and attached hair cells to vibrate Bending of hair cells causes ion channels in the hair cells to open or close, resulting in a change in auditory nerve sensations that the brain interprets as sound © 2014 Pearson Education, Inc. Figure 38.21 More neurotransmitter Less neurotransmitter 0 −70 Time (sec) (a) Bending of hairs in one direction Membrane potential (mV) −70 0 1 2 3 4 5 6 7 © 2014 Pearson Education, Inc. −50 Signal Membrane potential (mV) Signal Receptor −50 potential Receptor potential −70 0 −70 0 1 2 3 4 5 6 7 Time (sec) (b) Bending of hairs in other direction The fluid waves dissipate when they strike the round window at the end of the vestibular canal © 2014 Pearson Education, Inc. The ear conveys information about Volume, the amplitude of the sound wave Pitch, the frequency of the sound wave The cochlea can distinguish pitch because the basilar membrane is not uniform along its length Each region of the basilar membrane is tuned to a particular vibration frequency © 2014 Pearson Education, Inc. Equilibrium Several organs of the inner ear detect body movement, position, and balance The utricle and saccule contain granules called otoliths that allow us to perceive position relative to gravity or linear movement Three semicircular canals contain fluid and can detect angular movement in any direction © 2014 Pearson Education, Inc. Figure 38.22 Semicircular canals PERILYMPH Cupula Vestibular nerve Fluid flow Hairs Hair cell Vestibule Utricle Saccule © 2014 Pearson Education, Inc. Nerve fibers Body movement Concept 38.6: The diverse visual receptors of animals depend on light-absorbing pigments The organs used for vision vary considerably among animals, but the underlying mechanism for capturing light is the same © 2014 Pearson Education, Inc. Evolution of Visual Perception Light detectors in animals range from simple clusters of cells that detect direction and intensity of light to complex organs that form images Light detectors all contain photoreceptors, cells that contain light-absorbing pigment molecules © 2014 Pearson Education, Inc. Light-Detecting Organs Most invertebrates have a light-detecting organ One of the simplest light-detecting organs is that of planarians A pair of ocelli called eyespots are located near the head These allow planarians to move away from light and seek shaded locations © 2014 Pearson Education, Inc. Figure 38.23 LIGHT DARK Photoreceptor Ocellus Visual pigment Ocellus © 2014 Pearson Education, Inc. Nerve to brain Screening pigment Compound Eyes Insects and crustaceans have compound eyes, which consist of up to several thousand light detectors called ommatidia Compound eyes are very effective at detecting movement © 2014 Pearson Education, Inc. Figure 38.24 2 mm © 2014 Pearson Education, Inc. Single-Lens Eyes Single-lens eyes are found in some jellies, polychaetes, spiders, and many molluscs They work on a camera-like principle: the iris changes the diameter of the pupil to control how much light enters The eyes of all vertebrates have a single lens © 2014 Pearson Education, Inc. The Vertebrate Visual System Vision begins when photons of light enter the eye and strike the rods and cones However, it is the brain that “sees” Animation: Near and Distance Vision © 2014 Pearson Education, Inc. Figure 38.25a Sclera Retina Choroid Retina Suspensory ligament Photoreceptors Fovea Neurons Rod Cone Cornea Iris Optic nerve Pupil Aqueous humor Lens Vitreous humor Optic disk Central artery and vein of the retina Optic nerve fibers © 2014 Pearson Education, Inc. Ganglion Bipolar Horizontal cell cell cell Amacrine cell Pigmented epithelium Figure 38.25aa Sclera Suspensory ligament Choroid Retina Fovea Cornea Iris Optic nerve Pupil Aqueous humor Lens Vitreous humor © 2014 Pearson Education, Inc. Optic disk Central artery and vein of the retina Figure 38.25ab Retina Photoreceptors Neurons Optic nerve fibers © 2014 Pearson Education, Inc. Rod Ganglion Bipolar Horizontal cell cell cell Amacrine cell Cone Pigmented epithelium Figure 38.25b CYTOSOL Rod Synaptic terminal Cell body Retinal: cis isomer Outer Disks segment Light Enzymes Cone Rod Retinal: trans isomer Cone Retinal INSIDE OF DISK © 2014 Pearson Education, Inc. Opsin Rhodopsin Figure 38.25ba Rod Synaptic terminal Cone Rod Cone © 2014 Pearson Education, Inc. Cell body Outer Disks segment Figure 38.25bb CYTOSOL Retinal: cis isomer Light Enzymes Retinal: trans isomer Retinal INSIDE OF DISK © 2014 Pearson Education, Inc. Opsin Rhodopsin Figure 38.25bc Retinal: cis isomer Light Enzymes Retinal: trans isomer © 2014 Pearson Education, Inc. Figure 38.25bd Rod Cone © 2014 Pearson Education, Inc. Sensory Transduction in the Eye Transduction of visual information to the nervous system begins when light induces the conversion of cis-retinal to trans-retinal Trans-retinal activates rhodopsin, which activates a G protein, eventually leading to hydrolysis of cyclic GMP © 2014 Pearson Education, Inc. When cyclic GMP breaks down, Na channels close This hyperpolarizes the cell The signal transduction pathway usually shuts off again as enzymes convert retinal back to the cis form © 2014 Pearson Education, Inc. Figure 38.26 Light Active rhodopsin EXTRACELLULAR FLUID INSIDE OF DISK Phospho- Disk diesterase membrane Plasma membrane Inactive rhodopsin CYTOSOL Transducin GMP Membrane potential (mV) 0 Dark cGMP Na Light −40 −70 Hyperpolarization Time © 2014 Pearson Education, Inc. Na Processing of Visual Information in the Retina Processing of visual information begins in the retina In the dark, rods and cones release the neurotransmitter glutamate into synapses with neurons called bipolar cells Bipolar cells are either hyperpolarized or depolarized in response to glutamate © 2014 Pearson Education, Inc. In the light, rods and cones hyperpolarize, shutting off release of glutamate The bipolar cells are then either depolarized or hyperpolarized © 2014 Pearson Education, Inc. Signals from rods and cones can follow several pathways in the retina A single ganglion cell receives information from an array of rods and cones, each of which responds to light coming from a particular location The rods and cones that feed information to one ganglion cell define a receptive field, the part of the visual field to which the ganglion cell can respond A smaller receptive field typically results in a sharper image © 2014 Pearson Education, Inc. Processing of Visual Information in the Brain The optic nerves meet at the optic chiasm near the cerebral cortex Sensations from the left visual field of both eyes are transmitted to the right side of the brain Sensations from the right visual field are transmitted to the left side of the brain It is estimated that at least 30% of the cerebral cortex takes part in formulating what we actually “see” © 2014 Pearson Education, Inc. Color Vision Among vertebrates, most fish, amphibians, and reptiles, including birds, have very good color vision Humans and other primates are among the minority of mammals with the ability to see color well Mammals that are nocturnal usually have a high proportion of rods in the retina © 2014 Pearson Education, Inc. In humans, perception of color is based on three types of cones, each with a different visual pigment: red, green, or blue These pigments are called photopsins and are formed when retinal binds to three distinct opsin proteins © 2014 Pearson Education, Inc. Abnormal color vision results from alterations in the genes for one or more photopsin proteins The genes for the red and green pigments are located on the X chromosome A mutation in one copy of either gene can disrupt color vision in males © 2014 Pearson Education, Inc. The Visual Field The brain processes visual information and controls what information is captured Focusing occurs by changing the shape of the lens The fovea is the center of the visual field and contains no rods but a high density of cones © 2014 Pearson Education, Inc. Figure 38.UN01 Circadian period (hours) 24 Wild-type hamster Wild-type hamster with SCN from hamster 23 22 21 hamster hamster with SCN from wild-type hamster 20 19 Before procedures © 2014 Pearson Education, Inc. After surgery and transplant Figure 38.UN03 Cerebral cortex Cerebrum Forebrain Thalamus Hypothalamus Pituitary gland Midbrain Hindbrain © 2014 Pearson Education, Inc. Pons Medulla oblongata Cerebellum Spinal cord