Sensory Systems Chapter 45

Overview of Sensory Receptors Axon nerve endings respond to stimuli...Axon nerve endings are not dendrites!!! And they can be afferent or efferent -Exteroceptors -Interoceptors 1. Mechanoreceptors are stimulated by mechanical forces such as pressure 2. Chemoreceptors detect chemicals or chemical changes 3. Energy-detecting receptors react to electromagnetic and thermal energy

Overview of Sensory Receptors Sensory information is conveyed to the CNS and perceived in a four-step process 1. Stimulation 2. Transduction 3. Transmission 4. Interpretation

Afferent Nerve undergoing depolarization & “local current flow” Mechanoreceptors Afferent Nerve undergoing depolarization & “local current flow” Nociceptors = pain receptors -Free nerve endings, are located where damage is most likely to occur Temperature extremes affect the transient receptor potential (TRP) ion channel -Produces depolarization by an inward flow of Na+ and Ca2+, which in turn causes the sensory neuron to fire -Leads to a release of glutamate and an EPSP in neurons in spinal cord, which ultimately produces the pain response

Mechanoreceptors Receptors in the skin contain sensory Cells with ion channels that open in Response to mechanical distortion... Touch detectors -Phasic = Intermittently activated -Tonic = Continuously activated

Mechanoreceptors Proprioceptors become activated when muscle is stretched -Provide information about the relative position or movement of animal’s body parts -Examples: -Muscle spindles sensory neuron innervates thin group of muscle fibers -Golgi tendon organs Monitors tension in tendons

Mechanoreceptors Baroreceptors monitor blood pressure -A highly branched network of afferent neurons located in the carotid sinus (blood to the brain) aortic arch (near the heart) -Detect tension or stretch in the walls of these blood vessels -When blood pressure decreases, the frequency of impulses produced by baroreceptors decreases...Sympathetic Division of Autonomic Nervous system Creates Vasoconstriction

Hearing Hearing is the detection of sound waves -Sound is the result of vibration, or waves, traveling through a medium Auditory stimuli travel farther and more quickly than chemical ones Auditory receptors provide better directional information than chemoreceptors

Lateral Line System in Fish “Distant Touch” Canals running the length of the fish’s body -Contain hair cells with cilia that project into a gelatinous cupula(moves around)...Detect pressure waves. Allows fish to swim in schools, hunt... Bend cilia toward kinocilium = stimulate

Ear Structure of Land Vertebrates Air vibrations are channeled through the auditory canal of the outer ear -Vibrations reach the tympanic membrane causing movement of three small bones (ossicles) in the middle ear... -Malleus (hammer), incus (anvil) and stapes (stirrup) -The stapes vibrates against the oval window, which leads into the inner ear... The inner ear consists of the cochlea, a bony structure

Ear Structure of Land Vertebrates Pressure vibrations enter into the oval window... which opens into vestibular canal crosses through the cochlear duct into the tympanic canal...All three chambers are filled with fluid -Pressure waves travel down the tympanic canal to the round window, which is another flexible membrane -Transmits pressure back to middle ear (So no echo!!!)

But How do We Get Sound to the Brain?? The organ of Corti, which transduces sound in the cochlea, consists of: -Basilar membrane: Bottom of cochlear duct -Hair cells with associated sensory neurons & stereocilia -Tectorial membrane: Overhanging, gelatinous membrane (holds top of stereocilia in place) Stereocilia of hair cells bend in response to vibrations of the basilar membrane -Hair cells are depolarized or hyperpolarized and signals are sent to brain via afferent auditory nerve... You hear a sound

Navigation by Sound A few mammals have the ability to perceive presence and distance of objects by sound -Bats, shrews, whales, dolphins -They emit sounds and then determine the time it takes these sounds to return -This process is called echolocation The invention of sonar (sound navigation and ranging) relied on echolocation principles

Detection of Body Position Most invertebrates can orient themselves with respect to gravity due to a sensory structure called a statocyst -Consists of ciliated hair cells embedded in a gelatin with calcium carbonate stones called statoliths (the stones are called statoliths) In vertebrates, the gravity receptors consist of two chambers in the membranous labyrinth -Utricle and saccule

Detection of Body Position Within the utricle and saccule are hair cells with stereocilia and a kinocilium -Embedded in the calcium carbonate-rich otolith membrane Utricle more sensitive to horizontal acceleration Saccule more sensitive to vertical acceleration -Both types of accelerations cause cilia to bend, thus producing an action potential in an associated sensory neuron

Detection of Body Position The utricle and saccule are continuous with three semicircular canals that detect angular acceleration in any direction -At the ends of the canals are swollen chambers called ampullae -Groups of cilia protrude into them -Tips of cilia are embedded within a gelatinous cupula, that protrudes into the endolymph fluid of each canal

Detection of Body Position When the head rotates, the semicircular canal fluid pushes against the cupula, causing the cilia to bend -Bending in the direction of the kinocilium causes a receptor potential -Stimulates an action potential in the associated sensory neuron Saccule, utricle and semicircular canals are collectively called the vestibular apparatus

Chemoreception Used in Taste & Smell Chemoreceptors -Membrane of sensory neuron becomes depolarized and produces action potentials Taste (gustation) -Broken down into five categories: -Sweet, bitter, and umami sensations are transmitted via G-protein coupled receptors on receptor cells...Salty tastes are detected via ion channels that take in Na+...Sour tastes are detected through H+ ion channels

Taste Flies taste with hairs in their feet and fish can taste from all over their body surface In land vertebrates, taste buds are located in the epithelium of the tongue and oral cavity within raised areas called papillae... That contain taste buds that are a epithelial cells associated with afferent neurons.

Smell In land vertebrates, the sense of smell (olfaction) involves neurons located in the upper portion of the nasal passages.... Chemoreceptor neurons have dendrites, with G-protein coupled receptors & cilia Projecting into nasal mucosa. Axons synapse with Olfactory bulb that project into cerebral cortex Humans can discern thousands of different smells

pH Peripheral chemoreceptors -Found in the aortic and carotid bodies -Sensitive primarily to the pH of plasma Central chemoreceptors -Found in the medulla oblongata of the brain -Sensitive to the pH of cerebrospinal fluid

Vision Vision begins with the capture of light energy by photoreceptors -Visual information is used to determine both the direction and distance of an object Invertebrates have simple visual systems with photoreceptors clustered in an eyespot -Flatworms can perceive the direction of light but cannot construct a visual image

Vision The members of four phyla have evolved well-developed, image-forming eyes that use the same light-capturing molecule -Annelids, mollusks, arthropods, and chordates Although these eyes are similar in structure, they have evolved independently -An example of convergent evolution. -

Structure of the Vertebrate Eye Retina Optic nerve Fovea Vein Artery Iris Cornea Lens Suspensory ligament Suspensory ligament Sclera Ciliary muscle Pupil Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sclera = White portion of the eye, formed of tough connective tissue Cornea = Transparent portion through which light enters; begins to focus light Iris = Colored portion of the eye -Contraction of iris muscles in bright light decreases the size of its opening, the pupil Lens = A transparent structure that completes focusing of light onto the retina Ciliary Muscle bends lens

The Vertebrate Retina contains two types of Photoreceptors: Outer segment Inner segment Synaptic terminal Nucleus Mitochondria Pigment discs Rod Cone Connecting cilium Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The Vertebrate Retina contains two types of Photoreceptors: black-and-white vision color vision Rhodopsin Photopsin

Humans have three kinds of cones Each cone possesses a photopsin consisting of a cis-retinal bound to a protein with slightly different amino acid sequences 100 80 60 40 Light absorption (percent of maximum) Blue cones 420 nm Green 530 nm Red 560 nm Rods 500 nm 400 500 600 700 Wavelength (nm) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Humans have three kinds of cones

Sensory Transduction in the Eye When rhodopsin absorbs light, 11 cis-retinal is isomerized into all-trans-retinal -Activates a G protein that stimulates the enzyme phosphodiesterase, which converts cGMP to GMP -Na+ channels close, leading to a hyperpolarization of the membrane -Prevents the release of the inhibitory neurotransmitter onto bipolar cells

...Bipolar cells fire and then ganglion cells send signal to optic nerve and brain Axons to optic nerve Bipolar cell Choroid Horizontal Amacrine Rod Cone Ganglion Light Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

AND THEN YOU SEE THE LIGHT