Vision and Chemoreception PDF

# Vision and Chemoreception ## Transduction & Converting outside Stimuli into neuron activity. - **Perception:** Subjective interpretation of what we sense. - **Receptors** release specific odorants into the air that affects receptors in the nose → ↓AP affect areas of the limbic system. - **Visi...

# Vision and Chemoreception ## Transduction & Converting outside Stimuli into neuron activity. - **Perception:** Subjective interpretation of what we sense. - **Receptors** release specific odorants into the air that affects receptors in the nose → ↓AP affect areas of the limbic system. - **Vision:** Most essential sense. ## The Eye - Info passed to the thalamus → decoded in the **Primary visual cortex** [occipital and temporal lobes]. ## Light - **Electromagnetic spectrum:** Energy produced by electrical charges radiated in waves. - **Light** consists of **photons** (acts chemical substance, Important for Photosynthesis). - **Blue and purple:** ~400nm length - **Orange and red:** ~700nm length - **Animals** transducing light to nerve signals ## The Eye - **Light rays** (70-80% of focusing) - **Cornea, pupil and lens** focus on the retina → converts the rays into **impulses** → **optic nerve** → brain where they are recognized as images. - **Cornea:** 70% - 80% of focusing occurs; Protects the eye - **Pupil:** Surrounded by **Iris** (controls diameter of pupil: larger in dim light and smaller in bright light). - Autonomic N.S. (Sympathetic N.S.) - **Lens:** Controls the 20% - 30% of focusing. - You get older the lens get stiffer. - **Optic nerve** leaves the retina. ## The Retina - Back of the eye = Retina. - Made of several cells. - **Ganglion cells:** Light first hits here; gets info. from Intermediate and photoreceptor cells. Axons make up optic nerve. - **Intermediate cells:** transmits info. from photoreceptor to ganglion. - **Connects ganglion cells to photoreceptors.** - Bipolar, amacrine and horizontal cells. - Can transduce light to A.P. - Receives input in photoreceptors. ## Phototransduction Of Rods - In the dark, Dosil Nat flow into rod cells through **ion channels** that are activated by **CGMP** [helps to keep depolarizing dark current flowing into the rods] - Influx of Na+ = cells are depolarized which leads to continuous release of **NT glutamate**. - **Rod rhodopsin** is inside the **rod cell**. - **Opsin + retinal** - **Capable of absorbing light**. - When retinal absorbs light, its configuration changes and prompts **Opsin to activate a molecule called transducin**. - Transducin activates an enzyme (**phosphodiesterase**) which breaks down **CGMP**. - As **CGMP** levels fall, ion channels that are opened by **CGMP** begin to close. - Sodium enters cell and it becomes more hyperpolarized due to **C-1**. - **Glutamate release** which acts as a signal that a light stimulus is present. - **Rod cells** return to normal state when activated **rhodopsin** is deactivated and a protein called **arrestin** binds to it. - **Blocks** the ability of **rhodopsin** to activate **transducin** (clenatures **CGMP)** - A complex process restore **retinal** to original configuration → ready to absorb light again. ## LGN of thalamus - **Retinotopic map**. - LGN is a map of the retina. - Types of ganglion cells that send signals to the LGN. - **P cells** - Gets info from fovea and send projections to layers 3, 4, 5 & 6 in **LGN** - **Parvocellular layer** gets info. from **P cells** and processes colour, shapes and details. - **M cells** - Large ganglion cells found in periphery of retina and projects to the magnocellular layer. - **Magnocellular layer** gets info. from **M cells** and process movement and low-intensity light. - **K cells** ## Visual Coney - **Cells of the primary Visual Cortex** - **Primary Visual Cortex** - Also called **V1** and **striate cortex**. - Is located in the occipital lobe and gets the first info. from **LGN**. - **Neuronal tuning** (neurons represent a specific stimulus). - Discovered by David Hubel and Torsten Wiesel. - **Types of neurons** described by Hubel and Wiesel - **Simple cells:** Rectangular receptive fields; gets info. directly from **LGN** and are sensitive to lines of specific orientation. - **Complex cells:** Gets info. from simple cells. Respond selectively to lines of specific orientation that move in specific directions. - **Hyper complex cells** and **end-stop cells**: Simple + complex and respond to lines with specific orientation, angles and length. ## Extrastriate pathways. - **Dorsal stream** - Starts @ magnocellus to the **V1, V2, V3** and **V5** and then the parietal lobe. - "Where" a "now" stream because it is to movement & location. - Akinetopsia (damage to dorsal stream where an individual is unable to see object moving). - **Ventral stream** - Parvocellular **V1, V2, V4 **→ inferior temporal. - "What" pathway because of **V4** processes info. - Cerebral achromatopsia (color blindness to **V4**) - **Inferior and medial Temporal lobes** (outside the **V1**) - **Inferior temporal (IT)** - Responds to complex shapes and faces. - **Medial temporal (MT)** - Perception and memory. ## Vision and cheomorecoption - **Memo recordings** - **Single celled organisms = chemical sensations.** - Olfactory - The reason why we smell things is because items are given off volatile chemicals and they go into the nose and attach to mucosa. - Visceral - Senses in gut - Vibration - Touch and auditory from a distance. - **Electromagnetic sensation** [energy produced by electrical charges radiated in waves] - Vision - Images are perceived that have form, movement, color, identity & location. - Done simultaneously. - Conscious perception. - Called parallel processing. - **The eye is responsible for capturing the light.** - Blue: sensitive to green → first - Red: sensitive to yellow - **Left visual field crosses to the right visual field and vice versa through the optic chasm**. Optic nerve = part between the eye and optic chasm. Part between the optic chasm and LGN is tract. Ipsilateral. - Ganglion cells form the medial retina are contralateral while lateral retina is ipsilateral. - Optic radiation: fan out. ## The Callosum - The brain is mostly used to process finger touch information move. - Main sulcus in the center of the medial occipital lobe. - Where the center of the visual field. - Primary visual cortex/V1/Rodman area #11 - **Parallel subcortical Pathways** - **Hypothalamus** - Superchiasmatic nucleus [keeps track of the day night cycle or circadian rhythm] - **Midbrain** - Superior Colliculus [helps detect what is going on] - **Rods are sensitive to the same photopigment** - **Rhodopsin** - In the dark, light turns them off. [Every active in the dark] - Dark current: depolarization occurs in the dark and light hyperpolarizes it. The brighter the light, the brighter the hyperpolarization - The more rhodopsin is struck, the less the dark current occurs. - In the dark, there is production of **Cmp** which opens **Nat** channels, producing **EPSPs** and causes transmitters to be released from the rods. No A.P here. - When more light, less **Cmp** and less transmitters - The brighter the light, the less activity, the darker the light the more activity. - **Rods influence horizontal cells.** - **Ganglion cells are A.P** - **Cell voltage** is depolarized until light hyperpolarizes it. **Bipolar cells depolarize** when rods hyperpolarize. - **(+) decreases neurotransmitter. - Less glutamate is released during hyper polarization. - What makes the cells change the response depends on the channel opened (depolarize or hyperpolize) - **Na+ desphere. rt brinemnal: ** ## 1. Define/describe the following terms: - **Transduction** - **Receptor cell** - **Distal/proximal stimulus** - **Sensation versus perception** - **Receptive field** - **Sensory organ** ## 2. For what reason have the various senses developed? Describe some of the physical energies they are capable of detecting. ## 3. Describe how the eye collects and manipulates light. What is the function of the cornea, lens, iris, and retina? What is the physical nature of light (as particles and electromagnetic radiation)? ## 4. Describe the function and structure of the retina. - **Photoreceptor cells: rods and cones** - **Bipolar cells** - **Ganglion cells** - **Horizontal and amacrine cells** - **Fovea** - **Blind spot/optic disk** ## 5. Describe the connections of the retina to the rest of the brain. - Where is the first synapse outside the retina? - What purpose does the optic chiasm serve? - What is the lateral geniculate nucleus **(LGN)**? How is it organized and how is this organization related to function? (hint: parvocellular & magnocellular) To where do **LGN** neuron axons extend? - What is striate cortex and where is it located? ## 6. Describe the various cortical visual areas in the occipital lobe and surrounding area (including extrastriate areas). Pay particular attention to **V1** (primary visual cortex), **V4**, **V5** and the inferior temporal ("ventral/inferior stream") and posterior parietal areas ("dorsal stream"). Be familiar with how these function were discovered (both human brain injury and animal experimental data). What does it mean that the visual cortex is modular (hint: parallel processing)? ## 7. How is it that cones provide both color vision and acute vision (hint: divergence v. convergence of ganglion cells)? A related question: how is it that the foveal area of the visual field is "blown up" or "zoomed" on the visual cortex? ## 8. What is the receptive field of a sensory neuron and how is it created? Compare and contrast the receptive fields of ganglion cells and neurons in the primary visual cortex. What is the purpose of these receptive fields? ## 9. Describe the functions of subcortical brain areas that are not responsible for perception yet receive "light" input: - **Optic tectum (superior colliculus)** - **Hypothalamus (suprachiasmatic nucleus)** - **Amygdala** ## 10. Why is it said that consciousness may be constructed by the brain (hint: blind spot)? Since the visual experience seems to broken down into its components, where is it all put back together?