PSY106 Fall 2024 Lecture 8: Rods & Cones PDF

Mean: 85 Median: 88 23 Perfect Scores!  WEEK 5, OCT 28TH – NOV 3RD Two in-person lectures (Mon & Wed) Read Week 5 Readings on Canvas Complete Quiz 4 on Canvas by Sunday at 11:59pm Available at 5pm on Wednesday Optional: Attend a ULA session Optional: Participate in Week 5 D...

Mean: 85 Median: 88 23 Perfect Scores!  WEEK 5, OCT 28TH – NOV 3RD Two in-person lectures (Mon & Wed) Read Week 5 Readings on Canvas Complete Quiz 4 on Canvas by Sunday at 11:59pm Available at 5pm on Wednesday Optional: Attend a ULA session Optional: Participate in Week 5 Discussion by Sunday at 11:59pm If you wish to access your exam and see what you got wrong, please go to TA office hours – ULAs can go through exam questions, but can’t access your exam & grade  WEEK 5 & 6 TUTORING SESSIONS Structured sessions: sheep brain neuroanatomy! Thurs 10/31 2-3pm with Leia & Xi (Psych East 3834) Fri 11/1 2-3pm with Uma & Sukari (Psych East 3834) Tues 11/5 5-6pm with Joey & Grace (Psych East 3834) Thurs 11/7 4-5pm with Leia & Xi (Psych East 3834) Fri 11/7 1-2pm with Uma & Sukari (Psych East 3834) Fri 11/7 2-3pm with Joey & Grace (Psych East 3834) Drop-in sessions Wed 10/30 5-6pm with Grace & Sukari (Library 4574) Thurs 10/31 12-1pm with Joey & Leia (Transfer Student Center) Fri 11/1 11-12pm with Xi and Joey (ONDAS Student Center) ULAs can go through exam questions, but can’t access your exam Today’s Topics: 8A: Everything but the Cortex (cont.) 8B: Visual System Basics 8C: Overview of the Eye 8D: Rods & Cones DR. SCUDDER PSY106 INTRODUCTION TO BIOPSYCHOLOGY FALL 2024 LECTURE 8A: EVERYTHING BUT THE CORTEX (CONTINUED) DR. SCUDDER PSY106 GOALS OF THIS SECTION Describe the three components of the brainstem Explore the sources of modulatory neurotransmitters in the brain Describe the organization and role of the cerebellum BRAINSTEM Composed of midbrain, pons, and medulla Responsible for control of many automatic but essential functions and behaviors (like breathing, heartbeat, sleep) The various nuclei in this part of the brain are responsible for making many modulatory neurotransmitters that regulate transmission throughout the brain (dopamine, serotonin, norepinephrine) Exploring the Brain (Bear, Connors & Paradiso) BRAINSTEM: MIDBRAIN Tectum (“roof”): dorsal part of the midbrain; has two sets of “bumps” Inferior colliculi: auditory system Superior colliculi: visual system (visual reflexes) Tegmentum (“floor”) Exploring the Brain (Bear, Connors & Paradiso) BRAINSTEM: MIDBRAIN Tegmentum: ventral part of midbrain beneath the tectum Substantia nigra (SN): movement Connected to basal ganglia Produces dopamine for movement initiation areas Ventral tegmental area (VTA): motivational/reward Connected to prefrontal cortex & nucleus accumbens Produces dopamine for reward/motivation areas Reticular formation (rostral end) Collection of nuclei producing other modulatory neurotransmitters Raphe nuclei: produce serotonin Involved in sleep, arousal, attention, movement, reflexes BRAINSTEM: PONS Pons: Large bulge in brainstem between the midbrain and the medulla, ventral to the cerebellum Reticular formation continues Sleep and arousal regulation More raphe nuclei (serotonin-producing neurons) Locus coeruleus (norepinephrine-releasing neurons) Relay nuclei Pontine nuclei Information from cortex to the cerebellum (motor cortex) Some types of motor commands are routed through these nuclei BRAINSTEM: MEDULLA Medulla oblongata (or just medulla) Most caudal portion of the brain Lower border connects to the spinal cord Reticular formation continues here (more raphe nuclei) Regulates cardiovascular system, breathing, & skeletal muscle tone Some sensory systems make a stop here before information goes to other brain regions  NEUROTRANSMITTERS Dopamine projections Dopamine is synthesized and released by neurons in the ventral tegmental area and substantia nigra (both in midbrain) Norepinephrine is synthesized and released by neurons in the locus coeruleus, in the pons Serotonin is synthesized and released by neurons in the raphe nuclei, located Goodman & Gilman throughout brainstem Serotonin projections Norepinephrine projections Matchett et al., 2021 Tarland et al., 2019 CEREBELLUM “Little cerebrum” Composed of two cerebellar hemispheres Very densely packed with neurons – about half of the neurons in your brain are in the cerebellum! Important component of the motor system Involved in any movement that needs timing information Involved in complex movement patterns Ex. Walking, shooting a layup, playing the piano THE CEREBELLUM IS GORGEOUS! Baizer et al., 2014 UToronto  Cerebellum connects to the rest of the brain via the pons INTRODUCTION TO BIOPSYCHOLOGY FALL 2024 LECTURE 8B: VISUAL SYSTEM BASICS DR. SCUDDER PSY106 GOALS OF THIS SECTION Learn the basic principles of visual sensation and perception Describe the overall organization of the visual system WHY FOCUS ON VISION? About a third of the human brain is specialized for vision! Brains are always specialized for the relevant behaviors of the organism – rodents have far less of their brain devoted to vision, but far more devoted to their sense of smell Provides a nice example of how stimuli in our environment are represented and used by neurons We know more about the visual system than the other sensory systems LOTS OF VISION RESEARCH IN PBS! PRINCIPLES OF VISION Sensation = signals from the outside world being detected by our nervous system Perception = awareness of a sensation, but heavily influenced by context, expectation, etc. You can have sensation in the absence of perception, and perception in the absence of sensation! Mystery #2 from the first week of class: a blind man who can avoid a ball thrown at him – more on that next week Illusions can demonstrate both of these possibilities VISUAL ILLUSIONS This is an example of a pretty “low-level” illusion – some basic circuitry in the eye can allow for these “color opponency” illusions You’re perceiving color signals in the black and white picture Here’s a more “high-level” visual illusion, which relies on your assumptions about the context of an image you are looking at  Do you see a dress that is white and gold or blue and black? THE DRESS Some of you will (accurately) perceive this as a blue and black dress, but some of you will instead see a white and gold dress (I usually do) While your eyes are sensing the correct colors (blue and black), your perception can be very different from that due to all of the processing your brain does on incoming images THE DRESS BASIC ORGANIZATION Eye Primary Secondary Thalamus (retina) Visual Cortex Visual Areas INTRODUCTION TO BIOPSYCHOLOGY FALL 2024 LECTURE 8C: OVERVIEW OF THE EYE DR. SCUDDER PSY106 GOALS OF THIS SECTION Define the basic properties of light Explore the overall anatomy of the retina and the cell types it contains LIGHT: WHAT IS IT? When we “see” something, we are experiencing the result of certain kinds of electromagnetic radiation affecting the neurons in our retina, and all of the downstream effects of this Light is just a wave of energy within a particular range of wavelengths – different wavelengths are what we perceive as different colors Our eyes can detect wavelengths between 400 and 700 nm (other organisms have different ranges and sensitivities) EFFECTS OF EVOLUTION Nervous systems are specialized to handle the particular types of signals that are most relevant to it The organization and location of light- sensing organs (such as eyes) can tell you what aspects of the environment an organism needs to be aware of Different species are capable of detecting different ranges of light wavelengths - some animals can see UV light (shorter wavelengths) Some migratory birds have additional proteins in their eye neurons that allow them to “see” the Earth’s magnetic field! As humans, we use two front-facing eyes to detect light wavelengths in the 400 – 700 nm range THE EYE The eye is an organ specialized for the detection, localization, and analysis of light Cornea and lens work together to focus the various waves of light striking the eye, “projecting” this onto the retina at the back of the eye Don’t worry about the parts of the eye: we’ll just focus on the retina  THE EYE: EVERYTHING IS FLIPPED The visual scene in front of us enters our eyes (in the form of electromagnetic waves) and affects the activity of neurons in the retina Everything gets flipped “When I see you, I really see you upside down. side to side and upside But my brain knows better – it picks you up and down when “projected” turns you around” onto the back of our eye -Death Cab for Cutie (the retina) Stimulus: physical object in environment THE RETINA The cells of the retina are arranged in a bizarre and backwards way – the neurons responsible for sensing incoming light (called photoreceptors) are buried under two layers of non-light-sensitive neurons: bipolar cells and retinal ganglion cells Light RETINAL ORGANIZATION The fovea is the part of the retina where the upper layers of cells have been pushed away to give the underlying photoreceptors better access to light Fine details of an object are easier to discriminate when you look right at it – you are putting that part of the visual scene onto your fovea RETINAL ORGANIZATION The blind spot (also called optic disc) is the part of the retina where the axons from ganglion cells leave the eye in a big bundle (called the optic nerve) No photoreceptors present at this spot in each eye (Axons from RGCs) Find your blind spot (cover your right eye, look at dots on the right until the red dot disappears) CELLS OF THE RETINA Let’s first explore the light-sensing neurons in the eye: neurons known as “photoreceptors”, which includes rods and cones INTRODUCTION TO BIOPSYCHOLOGY FALL 2024 LECTURE 8D: RODS & CONES DR. SCUDDER PSY106 GOALS OF THIS SECTION Compare and contrast rods and cones Describe the process of phototransduction PHOTORECEPTORS Convert electromagnetic radiation (light) into neural signals: a type of transduction called phototransduction Despite the misleading name, these are neurons, NOT individual proteins! Rods: Far more sensitive to light - responsible for vision at low light levels No color detection (don’t distinguish between different wavelengths) Low spatial acuity – not good at fine details Cones: Responsible for vision at high light levels Color detection High spatial acuity – good at fine details RETINAL ORGANIZATION Distribution of rods and cones varies across the retina – cones are concentrated at the fovea, while rods are prevalent in the periphery RETINAL ORGANIZATION This has some interesting consequences for vision: Stare up at a bright star on a clear night. In your peripheral vision, you’ll likely start to see many nearby stars appear. If you move your eyes to look directly at them, they disappear – why? The rods in your peripheral retina enable you to see them initially, but when you look directly at them, their image is now only on your fovea, which has no rods Walk around at night and try to distinguish the color of cars that you see parked on the street. Unless the street is brightly lit, colors are very hard to discern – why? Your rods are doing most of the work when you’re exploring a dark scene, and they are not sensitive to color PROPERTIES OF RODS & CONES Rods & cones are neurons, but they break all of the rules that I taught you! Synaptic vesicles full Weird shape – no dendrites, and one very of glutamate stubby axon terminal These neurons rest at -30 mV when no light is present, due to a steady inward leak of sodium via sodium channels Don’t use action potentials to communicate – instead, their volume of neurotransmitter release is just Resting membrane correlated to their membrane potential potential is around -30 mV These neurons release the neurotransmitter glutamate Less negative = more glutamate More negative = less glutamate RODS & CONES Light is transduced into neural signals by proteins called photopigments, which are located on disks inside of rods and cones Photopigment: a protein that changes conformation (shape) when waves of light strike it, causing a G-protein-mediated response Photopigment in rods is called rhodopsin, and cones have one of 3 different conopsins Sound familiar? This arrangement is very similar to that of G-protein-coupled receptors! PHOTOTRANSDUCTION: RODS A molecule called cGMP acts as a doorstop, keeping those sodium channels open when there is no light present – allows for continual inward Na+ flow When light strikes photopigments, the resulting cascade of events from G- protein activation causes those sodium channels to close (cGMP is removed, so the “door” closes) As a result, the detection of light by photopigments hyperpolarizes the rod, causing it to stop releasing glutamate (or release less) In the light: In the dark: Na+ channels close, Na+ channels open, cell is cell is depolarized hyperpolarized Lots of glutamate Little to no released glutamate released PHOTOTRANSDUCTION IN CONES Nearly identical to process described in rods, but rather than rhodopsin, the photopigment (light-sensing protein) is one of three types of conopsins Each opsin is sensitive to a particular range of wavelengths (colors) A single cone will have a single type of opsin, meaning there are three types of cone cells The pattern of activation of these three types of neurons results in the perception of a particular color ABNORMAL CONES It is relatively common for an individual to have one dysfunctional type of cone, leading to various types of color blindness (more common in men) A very small percentage of individuals (more commonly women) have an additional functional type of cone – this enables them to distinguish more subtle color differences than the rest of us Called “tetrachromacy”  PHOTORECEPTORS Let’s say that you’re in a completely dark room, getting ready to fall asleep, and your roommate rudely barges in and flips on all of the lights. Which statement best describes what happens in your photoreceptor cells (rods and cones)? A) Sodium channels close, the cells become hyperpolarized, and glutamate release is reduced B) Sodium channels close, the cells become depolarized, and glutamate release is increased C) Sodium channels open, the cells become depolarized, and glutamate release is increased https://forms.office.com/r/9XQxrL9w20 D) Sodium channels open, the cells become hyperpolarized, and glutamate release is reduced  PHOTORECEPTORS Let’s say that you’re in a completely dark room, getting ready to fall asleep, and you’re roommate rudely barges in Loss of inward sodium and flips on all of the lights. Which statement best flow (positive ions) describes what happens in your photoreceptor cells (rods makes cells more and cones)? negative (hyperpolarizes A) Sodium channels close, the cells become them) hyperpolarized, and glutamate release is reduced B) Sodium channels close, the cells become depolarized, and glutamate release is increased More negative = less C) Sodium channels open, the cells become depolarized, glutamate release and glutamate release is increased D) Sodium channels open, the cells become hyperpolarized, and glutamate release is reduced PHOTORECEPTORS Loss of inward sodium flow (positive ions) makes cells more negative (hyperpolarizes them) More negative = less glutamate release Klapper et al., 2016 THE NEXT CELL LAYER When photoreceptors are in their depolarized state (in the absence of light) they are continually releasing glutamate onto neurons called bipolar cells Next lecture: the rest of the circuitry in the retina  Cerebral cortex can be KEY CONCEPTS divided up into 4 lobes with different functions Locations in the nervous system can The modulatory be described using a neurotransmitters dopamine, specific set of terms serotonin, and norepinephrine are produced by brainstem nuclei Photoreceptors (rods & cones) are depolarized & release glutamate in the dark, but are hyperpolarized The retina is a layer of neurons at the back by light of the eye composed of light-sensitive cells called photoreceptors and several other cell types in a structured circuit  WEEK 5 TAKEAWAYS By the end of this week, you should be able to: Use anatomical terms to describe the locations of brain regions Label key regions of the brain, including cortical lobes and subcortical areas Lecture 7 Explain some of the methods used to gain information about what different brain regions contribute to Describe the components of the brainstem and what role they play in brain function and behavior Identify the regions responsible for creating and releasing the modulatory neurotransmitters dopamine, serotonin, and norepinephrine List the major components of the visual system Lecture 8 Describe the overall anatomy of the retina, including cell layers and important features Compare and contrast rods and cones Describe the transduction mechanism for light  WEEK 5, OCT 28TH – NOV 3RD Two in-person lectures (Mon & Wed) Read Week 5 Readings on Canvas Complete Quiz 4 on Canvas by Sunday at 11:59pm Available at 5pm on Wednesday Optional: Attend a ULA session Optional: Participate in Week 5 Discussion by Sunday at 11:59pm If you wish to access your exam and see what you got wrong, please go to TA office hours – ULAs can go through exam questions, but can’t access your exam & grade