Psychology 224: Neuroscience Lecture PDF

Psychology 224: Neuroscience Sensory Systems: Vision and Audition Reading: Carlson, Chapters 6 &7  Announcement Exam #3 Exam 3 will be on 11/7, not 11/4. The Visual System  LIGHT *Depolarized in darkness* INFORMATION FLOW ...

Psychology 224: Neuroscience Sensory Systems: Vision and Audition Reading: Carlson, Chapters 6 &7  Announcement Exam #3 Exam 3 will be on 11/7, not 11/4. The Visual System  LIGHT *Depolarized in darkness* INFORMATION FLOW The retinal ganglion cells encode how much light falls on the center and surround of their receptive fields and they carry information about the wavelength of that light (color). What does the cortex do?  Primary Visual Cortex The primary visual cortex is often called the “striate cortex”, because it contains dark staining layer The primary visual cortex is Striate cortex of a rhesus also referred to macaque monkey  Primary Visual Cortex Approximately 25% of V1 is devoted to processing information from the fovea, which represents a small part of the visual field. Cells in V1 respond to specific features of the visual world – each individual cell in V1 collects information from several different retinal ganglion cells Orientation & Movement Mostneurons in V1 are sensitive to orientation Stimulus ON This cell is maximally responsive to the vertical line! Visual Association Cortex V1 cannot “see” a whole object, only features Output of V1 is sent to the adjacent extrastriate cortex, or V2 – V2 cells receive input from several V1 cells – here, information begins to be reassembled to “rebuild” visual scene From V2, the visual information then takes one of 2 paths: – The Ventral Stream – Projects to the inferior temporal lobe  Processes “what” an object is – The Dorsal Stream – Projects to the posterior parietal lobe  Processes “where” an object is “Where?” “What?” The Auditory System  Sound as a Stimulus Sounds are produced by objects that vibrate A vibrating object causes the molecules of air to alternately condense together and pull apart, creating a sound wave Structure of the Human Ear  The Outer Ear Sound is first collected from the environment by the pinnae Sound waves are funneled by the pinnae into the ear canal The length and shape of the ear canal enhances certain sound frequencies  The Tympanic Membrane The tympanic membrane is the ear drum It is a thin membrane at the end of the outer ear canal Vibrates in response to sound Border between outer and middle ear  Middle Ear The ossicles are three tiny bones that amplify and transmit sounds to the inner ear They are the smallest bones in the body Vibrations from the tympanic membrane first reach the malleus (hammer)  Middle Ear The malleus (hammer) connects with the incus (anvil). The incus connects to the stapes The stapes is attached to the oval window of the cochlea The stapes is the smallest bone in the body Anatomy of the Ear 3. 4. 1. 2. https://www.britannica.com/video/193415/humans-mammals-sound  Inner Ear The inner ear is where fine changes in sound pressure are translated into neural signals The function is analogous to that of the retina Consists of the cochlea – spiral structure – contains the Organ of Corti – filled with fluid in three parallel canals  Three Canals of the Cochlea Three canals of the cochlea: - Vestibular canal - Tympanic canal - Middle canal Three canals are separated by membranes: - Reissner’s membrane - Basilar membrane  The Organ of Corti The Organ of Corti has 3 major parts: – 1) Hair Cells – receptive cells of the auditory system – 2) Basilar Membrane – anchors the hair cells – 3) Tectorial Membrane – lies over the hair cells  Hair Cells Hair cells in the Organ of Corti are embedded in the basilar membrane Each hair cell contains a soma and a number of cilia that protrude from the top Two major types of hair cells: – 1) Inner Hair Cells – less numerous; do not touch overlying tectorial membrane but moves when fluid moves – 2) Outer Hair Cells – more numerous; directly attached to the tectorial membrane The hair cells make synapses with bipolar cells whose axons bring the information from the inner ear to the brain The Organ of Corti  Transduction of Sound Sound waves that enter the ear cause the tympanic membrane to vibrate at the same frequency The tympanic membrane translates the vibrations to the ossicles, which transfer them to the oval window of the cochlea Vibrations at the oval window cause the basilar membrane and the tectorial membrane to flex up and down These movements bend the cilia of the hair cells in one direction or another, which initiates release of neurotransmitters  *The portion of the basilar membrane that bends the most is When the stapes pushes against the oval determined by the window, the round window bulges frequency of the sound. The Organization of Cilia Adjacent cilia are linked up to each other by an elastic filament called a tip link The points of attachment for each tip link are called insertional plaques – here, ion channels are located and receptor potentials are created Because cilia are linked together, a movement in one direction will make them all move together in that direction Organization of Hair Cell Cilia  Hair Cell Displacement Displacement of hair cells causes changes in membrane potential When there is movement toward the tallest cilium, ion channels near the insertional plaques open fully – This allows Ca2+ and K+ ions to flow in, strongly depolarizing the membrane – the hair cell releases glutamate onto the auditory nerve dendrites When there is movement toward the shortest cilium, the ion channels close completely, preventing ion entry and hyperpolarizing the membrane  Perception of Pitch Eachposition along the basilar membrane encodes a different frequency of sound wave – Neurons near the oval window side respond to higher frequencies (10-20 kHz) – Neurons near the end of the basilar membrane respond to lower frequencies (