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Midterm 2 material

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Bruce Mc Kay

The visual system The cells work constantly in the dark, when you turn on the light they TURN OFF The dark current: keep sensors in the polarized state Opto-genetics: optically activated genes and put them into animals, and maybe one day humans The retinal Geniculate Striate Pathway  The left hemiretina of each eye (r. visual field) connects to the left lateral geniculate nucleus; the right hemiretina connects to the right LGN  Partial Decussation: fibres from each retina cross over in the middle, but not all of them. Each retina picks up on info on both sides of the world o Why does the Rs go to the left side of the brain, why does the left go to the right? NO IDEA. Retinotopic Organization of the Brain  Only about 10% of the information to the visual cortex is actually primary visual information. The other 90% comes form the brain, especially memory centres. What you see is only 10% of the actual visual world. …THE REMEMBERED PRESENT: when you see something in the present, you are remembering the present  Information received at adjacent portions of the retina remains adjacent in the striate cortex  More cortex is devited to areas of high acuity- like the disproportionate representation of sensitive body parts in somatosensory cortex  About 25% of primary visual cortex is dedicated to input from the fovea. Receptive Fields of Visual Neurons  The area of the isual field within which it is possible for a visual stimulus to influence the firing of a given neuron  Hubel and wielsel looked at receptive fields in cat retinal ganglion, LGN, and lower layer IV of striate cortex  Hubel and wiesel; nobel proze in 1982 for their discoveries concerning information processing in the visual system  Chances favours the prepared mind o Did the experiment by hand, accidentally put a slide in sideways Receptive Fields  Retinal ganglion neurons and LGN neurons have receptive fields with a centre surround organization: excitatory and inhibitory regions separated by a circulatory boundary  Some cells are “on-centre” an some are “off-centre” Receptive Felds in the Visual Cortex  In lower layers IV of the striate cortex, neurons with circular receptive fields(as in retinal ganglion cells and LGN) are rare o Simple cells:  Rectangular th February 6 2013 Blood Supply To the Brain  Blood reaches the brain through o Internal carotid arteries: 2 on each side, start off your neck supplies, front half of the brain o Vertebral arteries: back half of the brain  Circle of Willis o The circle of willis distributes blood into the brain:  Middle cerebral arteries  Anterior cerebral arteries  Anterior communicationg arteries  Posterior cerebral arteries  Posterior communicating arteries  BASILAR artery: on the base of the brain, courses around the pons which splits off onto a bunch of other arteries into a circle. It forms a series of arteries called the posterior arteries. These join to the middle arteries, and eventually the anterior arteries.  **2 major pairs that come together to create a blood supply which goes around the base and around to eventually supply the entire brain. ** o why would you have a structure which connects everything into a circle?  if there was a plug somewhere, it can just take another route around the circle  Cortical areas supplied by ACA MCA and PCA o Bottom one is the back right side of the brain.  The posterior cerebral artery: going to innervate the back side of the visual motors.  On the medial side the anterior cerebral artery which covers most of the middle of the brain  carotid do the front of the brain  As long as everything is working that’s great, but if there is a problem with blood flow you have a condition called a STROKE  Stroke Definition o STROKE: any interruption of blood flow to the brain; sudden in onset; behavioural deficits correlate with site of event o Stroke is the most common cause of adult disability  Behavioural deficits reflect the specific part of the brain, and thus arterial system, that has been compromised. o General warning signs that a stroke has occurred  Confusion, trouble speaking, sudden weakness on one side of the body, blurred vision, dizziness/loss of coordination.  Symptoms of disruption to the blood supply o Middle cerebral artery: (eg. Left side)  Talking problems bc the broca’s area is on the left side.  Right sided motor problems, bc the primary motor cortex is on the left side  Facial problems o Anterior Cerebral Artery: (eg. Left side)  Right sided loss of leg control, leg feeling  Motivation o PCA  Difficulty seeing  Dizziness bc of blurry vision. The fovea…some vision in the middle, but none in the edges, what you end up with is like dark in the edges and a brightly lit tube to look through basically, and you have floating sensation, and extensive memory recall, and the amygdala tells you everything is so important bc emotions are racing. Youre in a tunnel racing toward a bright light and everything is important which sounds like youre dying bc “life is flashing before your eyes, and youre reaching the light”  Stroke-ischemia o Cerebral ischemia- disruption of blood supply  Arteriosclerosis: hardening of blood vessels..  you cant regulate the flow of blood, so your vessels can burst in the face of pressure.  Atherosclerosis: wall of blood vessels thicken, usually due to fat deposits,  Little plaques form in the vessels, as the plaques grow up they can dislodge which leads to the last 2 problems. If the plaque gets stuck and lodges its thrombosis, if a plaque forms somewhere else is an embolism.  Thrombosis: a plug forms in the brain  Embolism: a plug forms elsewhere and moves to the brain. OR a bubble can get into your system, and air is a problem because you cant pump it b/c it is infinitely flexible…it never goes anywhere it just keeps flattening and puffing back up.  Stroke- Hemorrhage o Aneurysm: a weakened point in a blood vessel that makes a stroke more likely; may be congenital or due to trauma or infection  Symptoms of aneurysm(there is no symptoms, but if you have it in the family you should get it checked o Hemorrhage: blood vessel ruptures and bleeds out into the brain  Blood is TOXIC to the brain  Symptoms of a hemorrhage (totally depends on where it is)  Closed head injuries often cause bleeding o Brain injurires due to blows that do not penetrate the skull- the brain collides with the skull  Contrecoup injuries: contusions are often on the side of the brain opposite to the blow as well  Often found in alcoholics bc when you hit one side of your head it is often damaged 180 degrees around  Contusions: closed-head injuries that involve damage to the cerebral circulatory system  Hematoma: the bruise that forms  Symptoms vary with site of brain damage  If you have a gematoma over brocas area: you cant talk anymore  Damage due to cerebral ischema o Does not develop immediately o Most damage is a consequence of excess neurotransmitter release- especially glutamite o Blood deprived neurons become overactive and release glutamate o Glutamate overactivates its receptors, especially NMDA receptors leading to an influx of sodium and calcium o Structures like the hippocampus are vulnerable  The cells all cascade and kill eachother  Other problems: migraines o Symptoms  Headache  Flashing lights  Pulsating sensations  Nausea  Photophobia  Phonophobia o Many theories, here’s one  Stress increases then decreases serotonin levels  This causes blood vessels to constrict then to dilate  Inflammatory molecules are released  Dilation of cerebral vessels + inflammation is painful o Cause? Triggers (food weather emotion) o Treatments:  analgesics,  anti-emetics,  serotonin agonist like drugs,  caffeine  where did the stroke occur? o Medical imaging of blood flow (or accumulation) is based on adaptions of X-Ray technology  There is no exploratory brain surgery, they need to know whre to look  Xray: doesn’t usually show much, except If theres something lodged in the brain like a nail…can sometimes be manipulated to show better information  Angiography  Contrast xrays: inject something that absorbs xrays less  Computed tomography (CT)  2D images combined to create a 3D image  protecting the brain o physical protection  skull: outside protects the brain, on the inside of the skull theres sharp objects… if you get hit too hard your brain gets pushed against these hard objects.  Meninges: CNS encased in bone and covered by 3 meninges.  Dura mater: tough outer membrane  Arachnoid membrane: web-like  Pia mater: adhered to the CNS surface  The meninges act as baffles between the hemispheres, and the cerebellum  Meningitis: inflammation of the meninges o Severe headache o Nuchal rigidity o Sudden high fever o Altered mental status o Caused by bacteria or viruses o Can be fatal o No pain receptors in the skull etc., all in the meninges  Cerebrospinal Fluid:  Fluid serves as cushion  Neutral buoyancy, your brain sits buoyant in the skull  Flow of the fluid: o CSF synthesized in choroid plexusleteral ventricles3 ventricle4 ventriclevarious cisterns and sinusesabsorbed by arachnoid vili and into cerebral veins  Hydrocephalus o Non communicating: obstruction in the ventricles o Communicating: blockage in subarachnoidal space o Ex vacuo: secondary to neuronal loss(huntingtons) o Headache, nausea, vomiting, seizures, coma, sudden in adultsgradual in infants o Treated with a shunt  Ephedrine vs. amphetamine  Ephedrine cannot cross the barrier, amphetamines can  Peripheral effects: o Strong activation o
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