Sensory systems-The visual system

The eye

1. The ananomy of the eye:注：1.Cornea：涵盖了眼睛80%的折光能力 2.Lens:涵盖了眼睛20%的折光能力 3.Posterior chamber产生Aqueous humor，后存在anterior chamber的地方注：关于对焦（accommodation），其依靠于晶状体的矫正（没有对焦的时候，是平坦的，其是Far vision；对焦时，晶状体更丰满些，For near vison），矫正又依赖于Ciliary muscle(通过Zonule fibers依附于lens)
2. The retina is diencephalic: 图示 The retina 源于发育中的forebrain(diencephalon)注：Phototransduction发生在Pigmented layer of retina
3. Photorecepters and phototransduction:注：1.photopigment存在于Outer segments里的disks上；Photo receptors的cell bodys存在于Outer nuclear layer；Outer plexiform layer是receptor的突触末端于retina中的五种细胞类型的连接处，该突出末端释放神经递质于bipolar cell上。 2.Horizontal cell于Photoreceptors的关系是bireactional relationship 3.Graded potentials（细胞与细胞之间的信号交流）由photorecepters和bipolar cells产生，action potential（传递电信号到大脑） 由 ganglion cells产生。 4.胶质细胞也存在于retina，其叫做mullar cell，其可支持retina中的neuron进行代谢以及信号传递。
   1. Photoreceptors:视锥细胞
      1. Dark:Photo-pigments:
      2. Light:注：The resting potential of the photoreceptors is -40mV注:此图示为光来时，Photoreceptors的构象产生了改变注：光来时会激活PDE（磷酸二酯酶），其会切断cGMP，导致channel的关闭。
      3. Specialization of rods and cones:注：适应光快的是cone注：Rods作用于Scotopic vision；Cones作用于Photopic vision中；Mesopic(月光下)注：Avascular zone是光抵达photoreceptor的通道，提高了光抵达受体的效率注：macula是retina的中心，foveola是macula的中心，若macula出现问题，则会看不清视野的中央（有一个黑点）
   2. Ganglion cell receptive fields:
      1. Two categroies of the ganglion cell:注:On-center ganglion cell对光反应迅速（当光来到recptive field中央时），反之，当光来到RF 周围时，off-center反应迅速
      2. Receptive fields:注：Center cone cell释放Glutamate，On-center是GLU的代谢性受体；Off-center是AMPA。GLU在Dark持续释放，其会导致On超极化（不会释放神经递质给On），off去极化注：当光来时，less GLU注：GLU作用于 Horizontal cell时，其会释放GABA反作用于光受体的末端，属于拮抗作用注：Ganglion cell可适应不同的environmental conditions

Central visual processing

1. The distribution of the axons of retinal ganglion cells:注：鼻侧视网膜（nasal）的ganglion cell发出的轴突投射到间脑的对侧，来自The temporal retina的GC发出的轴突投射到间脑的同侧。
2. V1 “Striate” cortex(The primary visual cortex):图示为髓鞘染色注：The primary visual cortex (V1) performs a number of important functions in visual encoding and visual perception. However, which of the following functions is best attributable to higher-­order visual cortical areas beyond V1?————the recognition and identification of complex visual stimuli, such as human faces
3. Hubel and wiesel’s experiment:注：随着electrode的深度加深，该cortex不同层数对视觉物体方向的选择性基本一致。注：当electrode在水平位置移动时，Cortex对视觉物体中的方向选择性改变（发生相位改变，是一个smooth progression change）。
4. Ocular dominance(眼优势)：注：LGN是一个layer 结构,（1,2是inner layer）layer1接收来自cotralateral eye的信号，layer2接收来自ipsilateral eye的信号。layer3 and 5接收来自ipsilateral eye的信号；4 and 6接收来自cotralateral eye的信号，然后这些信号投射到visual cortex，这些信号保持着单眼传递，即这些来自LGN的信号是一种相互交错的信号，并投射到附近区域以及visual cortex。
5. Stereopsis:结合了双眼的vision
6. Parallel pathways:The lateral geniculate nucleus:注：K cells投射到K layers；不同Layer投射到大脑皮层所在位置如右；大脑皮层2/3富含氧化代谢（oxidative metabolism）
7. Extrastriate visual cortex（纹外视觉皮层）：注：来自初级视觉皮层的信号会发送到inferior temporal lobe，即MT（What），MT位于 middle temporal visual area，其富含motion sensitive cells；这些motional signals 会投射到顶叶皮层来对视觉世界的事物进行空间分析（Where）
8. Central Visual pathways:注：1. LGN（位于the ventral part of the thalamus），这是thalamus的一部分传递视觉信号到visual cortex(cortical recipient zone 叫the primary visual cortex) 2.HROCR:接收来自retina的投射，投射到该区的Suprachiasmatic nuclears，其对于circadian rhythm（生理节律）有着重要的调控作用（通过visual inputs来调控） 3.Midbrain：Superior colliculus(参与了眼睛于头的运动方向) 4.Between midbrain and thalamus: Pretectum(这里的神经核调控眼球的对焦—改变瞳孔的直径，且调控cilliary muscle)
9. Visuotopy:注：1. The Fixation point: 通过每个retina的中心所见（fovea）,The right visual field 在右眼的nasal portion(55%)，左眼的temporal protion（45%）可见注：紫色部分是LGN run posterior in the （parietal）white matter投射到occipital lobe，且终止在绿色部分通过temporal lobe进行投射,终止在The lower back of the calcarine sulcus注：the upper part of the retina—the lower part of the vision问：There is a female patient who happens to enjoy a hot cup of tea most days at about 4:00 PM. Her problem is that she frequently spills her tea. The reason she spills her tea is that she does not appreciate the movement of tea filling her tea cup as she pours it out. She also has great difficulty judging the movement of traffic when she crosses a street at a crosswalk. Which of the following best explains her visual impairment?——She has a lesion in her lateral parieto-­occipital associational cortex in her dominant hemisphere.

The visual field deficits:

1. Types:
2. The deficits:注：A：R Anopsia； B：Bitemporal heteronymous hemianopsia；C：Left homonymous hemianopsia；E：Macular sparing；D：Left homonymous superior quandrantanopsia
3. 问：
   1. A patient complains of bumping into objects on the right, especially objects such as chairs and tables that are at waist height or below. You suspect a visual field deficit involving which structure(s)?—— lesion in the left parietal white matter、lesion in the left cuneus gyrus.
   2. A patient undergoes neurosurgery to remove an operable tumor (an early stage glioblastoma, which arises in white matter) from the right temporal lobe. Upon recovery in the acute care setting, the patient’s caregivers discover that when resting in bed she doesn’t readily notice visitors approaching from her left. What visual structure may have been injured in this surgical procedure?—— lesion in the right Meyer’s loop

Pupillary Light Reflex

1. Reflex circuitry:
2. 问
   1. During a physical exam, you shine a light into a patient’s left eye and you note that both pupils react only sluggishly to light. You stimulate the right eye and you find a brisk constriction of both pupils. From this information alone, what sort of neurological problem might you suspect?——lesion in the left eye or left optic nerve
   2. A patient has come to you complaining of double vision. His left eye fails to adduct when he makes eye movements to the right. His left eyelid droops (ptosis) and the pupil in his left eye is larger than the pupil in the right. The pupil in the left eye does not react to light nor does it respond when light is shown in the right eye. How would you explain this deficit in the pupillary light reflex?——lesion in the left Edinger-­Westphal nucleus or left oculomotor nerve
   3. A third patient comes to see you with ptosis of his left eye. You examine his eye movements and these seem normal. Then you notice that the pupil in his left eye is measurably smaller than that of his right eye. How do you account for the symptoms in this case?—— insufficient sympathetic tone to the left iris.