2014 Pearson Education, Inc. 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. 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 long- term 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 (a) Receptor is afferent neuron. Afferent neuron (b) Receptor regulates afferent neuron. Sensory receptor To CNS Stimulus Afferent neuron Receptor protein To CNS Sensory receptor cell Stimulus Neurotransmitter Stimulus leads to neuro- transmitter release. 2014 Pearson Education, Inc. 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 Gentle pressure Sensory receptor More pressure Low frequency of action potentials High frequency of action potentials 2014 Pearson Education, Inc. Perception Perception is the brains 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 Earths magnetic field to orient themselves 2014 Pearson Education, Inc. Figure (b) Beluga whales (a) Rattlesnake Infrared receptor Eye 2014 Pearson Education, Inc. Thermoreceptors detect heat and cold In humans, thermoreceptors in the skin and anterior hypothalamus send information to the bodys thermostat in the posterior hypothalamus Thermoreceptors 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 Tongue Taste buds Sensory receptor cells Key Sensory neuron Taste pore Food molecules Taste bud Papillae Papilla Umami Bitter Sour Salty Sweet 2014 Pearson Education, Inc. 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 Statolith Ciliated receptor cells Sensory nerve fibers (axons) Cilia 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 Outer ear Inner ear Middle ear Malleus Skull bone Incus Stapes Semicircular canals Auditory nerve to brain Auditory canal Tympanic membrane Oval window Round window Eustachian tube Cochlea Pinna Auditory nerve Cochlear duct Organ of Corti Vestibular canal Tympanic canal Bone To auditory nerve Tectorial membrane Basilar membrane Axons of sensory neurons Hair cells Bundled hairs projecting from a hair cell (SEM) 1 m 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 Receptor potential More neuro- trans- mitter Time (sec) Membrane potential (mV) Signal (a) Bending of hairs in one direction 50 70 0 70 Receptor potential Less neuro- trans- mitter Time (sec) Membrane potential (mV) Signal (b) Bending of hairs in other direction 50 70 0 70 2014 Pearson Education, Inc. 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 Semicircular canals Vestibular nerve Vestibule Saccule Utricle Fluid flow Nerve fibers Hair cell Hairs Cupula Body movement PERILYMPH 2014 Pearson Education, Inc. 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 LIGHT DARK Ocellus Visual pigment Photoreceptor Nerve to brain Screening pigment 2014 Pearson Education, Inc. 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 Compound Eyes 2014 Pearson Education, Inc. Figure mm 2014 Pearson Education, Inc. 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 Single-Lens Eyes 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 Right click slide / Select play 2014 Pearson Education, Inc. Figure 38.25a Sclera Choroid Retina Fovea Cornea Suspensory ligament Iris Optic nerve Pupil Aqueous humor Lens Optic disk Vitreous humor Central artery and vein of the retina Retina Optic nerve fibers Rod Cone Neurons Photoreceptors Ganglion cell Amacrine cell Bipolar cell Horizontal cell Pigmented epithelium 2014 Pearson Education, Inc. Figure 38.25bd Cone Rod 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 Active rhodopsin Transducin Light Inactive rhodopsin Phospho- diesterase Disk membrane Membrane potential (mV) Plasma membrane Hyper- polarization EXTRA- CELLULAR FLUID INSIDE OF DISK CYTOSOL DarkLight Time GMP cGMP Na 40 70 0 2014 Pearson Education, Inc. 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. 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 Processing of Visual Information in the Brain 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 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 The Visual Field 2014 Pearson Education, Inc. Figure 38.UN03 Cerebral cortex Forebrain Hindbrain Midbrain Thalamus Pituitary gland Hypothalamus Spinal cord Cerebellum Pons Cerebrum Medulla oblongata