CNS Flashcards
1
Q
Central Nervous System
A
- PNS comprises of somatic and autonomic nervous system
- Gray matter: Nerve cell bodies, unmyelinated axons, in clusters called nuclei. White matter: Consists of myelinated axons running in bundles called tracts. PNS: Clusters of neurons called ganglia and bundles of axons called nerves
- Dorsal root carriers afferent(incoming) signals, ventral root carries efferent(outgoing) signals from CNS to body
- Ascending tracts carry signal to the brain(dorsal), descending tracts carry signal from the brain(ventral)
- Brain stem is control center for autonomic functions
2
Q
Introduction to Senses
A
- Labeled lines: indicate stimulus modality
- Phasic: Respond briefly then stop firing, Tonic: maintain activity when stimulus not changing, Phasic-tonic: react to change but don’t return all the way to zero firing
- Lateral inhibition: Cells inhibit their neighbor -> accentuate edges
- Sensory pathways run via thalamus to cortex, except olfactory, equilibrium pathway project to cerebellum
3
Q
Optics of the Eye
A
- Lens is transparent disk that focuses light -> light passes from cornea to lens through the pupil
- Parasympathetic contract constrictor muscle to shrink pupil in bright light -> lens round for near vision
- Sympathetic signals contract dilator muscles to dilate pupil in dark light -> lens flatter for far vision
- When pupil constrict -> full depth of field(everything in focus). When dilate -> shallow depth of field(objects near specific distance are in focus)
- Near point of accommodation: closest point a person can focus -> old people have farther near point of accommodation
- Hyperopia: focal point falls behind retina -> convex lens helps out
- Myopia: Focal point fall in front of retina(light bend too much) -> concave lens helps
4
Q
Visual Processing
A
- When light hits a photoreceptor, they hyperpolarize to reduce release of glutamate(more active in darkness)
- Cones for bright light, rods for dim light. Fovea mostly contains cones, peripheral contains rods
- Photoreceptors synapse onto bipolar cells which synapse onto ganglion cells
- On center cell: excited by light in center and inhibited by light in surround. Off center: inhibited by light in center and excited by light in surround. Bipolar cells react when light is contrasted(not uniform)
- Fovea good at spatial detail, peripheral is not
- Magnocellular: movement of objects, Parvocellular: fine details, Melanopsin: Project to SCN for circadian rhythm
- LGN has 2million neurons
5
Q
Color Vision
A
- Wavelength we normally see are from 400nm - 700nm
- Trichromats: Have red(63%), green(31%), and blue(6%) cones. Red and green cones see yellow/yellow-green light, Blue cones see blue light, rhodopsin sees blue-green, Melanopsin sees blue
- Spectral colors: Evoked by single wavelength, Extraspectral: Evoked by mix of wavelengths
- Yellow channel(R + G cells): excited by red and green light, Red-green opponent channel(R - G or G - R): Excited by red/green, inhibited by red/green
- Blue-yellow opponent channel(B - R - G): Excited by blue light and inhibit by red and green
- Color constancy: Brains can infer reflectance, see ripe banana even in green light
6
Q
Hearing and Equilibrium
A
- External ear: pinna and ear canal, sealed at its end by tympanic membrane(eardrum). Middle ear: Connected to pharynx by Eustachian tube. Inner ear: Contains sensor, cochlea for hearing and vestibular apparatus for equilibrium
- At peaks, pressure is high, at troughs, pressure is low. Frequency is perceive as pitch(range: 16-20,000 Hz, acuity highest 1000-3000 Hz). Amplitude determines perception of loudness
- Eardrum vibrates ossicles(malleus to incus to stapes -> pushes against oval window)
- Cochlea: Vestibular and tympanic duct contain perilymph(communicate at helicotrema). Cochlear duct contains endolymph. Wave energy enter through oval window and exit back into middle ear through round window
- Organ of corti contains auditory receptor cells(around 20k per cochlea). Each hair cell has 50-100 stiff hairs called stereocilia
- When cilia bend towards longest cilium, hair cell depolarizes and release transmitter. Axons form auditory nerve, branch of cranial nerve VIII
- High frequency displace at oval window end, low frequency displace at helicotrema
- Primary auditory cortex in temporal lobe
- Conductive hearing loss: sound cant be transmitted through external/middle ear, Sensorineural: Damage to hair cells. Presbycusis is sensorineural. Central: Damage to cortex or pathway from cochlea t cortex.
- Vestibular apparatus sense head position and motion -> project to cerebellum
7
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8
Q
Smell and Taste
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- Olfactory epithelium contains olfactory receptors -> has 10 million receptors
- 400 kinds of receptor cells: Golf increases cAMP -> cation channel open to depolarize receptor neurons and trigger an action potential that travels to olfactory bulb
- Sends axon through cribriform plate -> projection to olfactory nerve(cranial nerve 1)
- Olfactory cortex in frontal and temporal lobes)
- Limbic system: old brain region concerned with motivation and emotion -> odors can call up emotional memories
- Pheromones: chemicals released by animal that affect behavior or physiology. Rodents have vomeronasal organ involved in responses to sex pheromones
- 5000 taste buds, babies have 10000 taste buds -> each contain 100 receptor cells
- 5 kinds of receptor cells: Sweet(detect sugar), umami(detect glutamate), Bitter(detect poison), Salty(detect Na+), Sour(detect H+)
- Type 2: include sweet, bitter, and umami -> release ATP, Type 3: sense sour -> form synapses with sensory neurons activating by serotonin, Type 1: sense salt
- Nerve endings in wall of mouth have TRP channels sensitive to temperature and chemicals.
- Receptor cells in taste buds excite fibers of cranial nerves VIII, IX, and X(facial, glossopharyngeal, and vagus nerves) -> synapse in medulla and thalamus en route to cortex
- TRP receptors excite cranial nerve V
9
Q
Hypothalamic Control
A
- Hypothalamus contains control centers for feeding, plasma osolality, blood temperature and sexual/stress response.
- Lesions in ventromedial hypothalamus -> obese, Lesions in lateral hypothalamus -> thin. Controlled by arcNPY and arcPOMC
- ArcNPY: inhibit PVN -> inhibit sympathetic nervous system, stimulate LH -> release orexin to inhibit PVN -> LH stimulates feeding
- ArcPOMC: cleave POMC to make alpha-MSH -> excite neurons in PVN and VMH and inhibits DMH -> PVN and VMH excite sympathetic nervous system to inhibit feeding
- Leptin inhibits ArcNPY and stimulates PVN -> or excite ArcPOMC and VMH -> inhibit DMH -> inhibit feeding
- Rising blood glucose excited ArcPOMC to inhibit feeding
- CCK, PYY, and GLP-1 excite vagus nerve to excite VMH via the nucleus tractus solitarius(NTS)
- Ghrelin stimulates ArcNPY and LH to stimulate feeding
10
Q
Circadian Rhythm
A
- In fruit flies: per transcribed at night -> mRNA abundant at 10pm -> PER most abundant 6 hours later. PER represses transcription of per, drives transcription-translation feedback loop. tim and TIM oscillate like per and PER. TIM binds PER to form PER/TIM dimer -> repress transcription of tim and per. high levels of PER/TIM at 4am shut off per/tim -> PER/TIM gradually falls -> per/tim rise to peak in late evening
- clk codes for CLK, cyc codes for CYC. CLK-CYC dimer stimulates transcription of per and tim in morning. PER/TIM block CLK-CYC binding to DNA at night to repress per/tim transcription.
- DBT breaks down PER, levels of PER rise slowly than normal, result in cycle length of 24 hours
- Mammals use cry/CRY instead of TIM. clk, cyc, and dbt are called clk, bmal1 and ck1e. CLK/BMAL1 dimer stimulates transcription of per and cry
- Internal clocks kept in sync by zeitgeber: light, temperature, feeding cues. Zeitgeber is light sensed by melanopsin retinal ganglion cells that project to suprachiasmatic nucleus(SCN) of hypothalamus
- Retinal signals lead to breakdown of PER/CRY. If drop occurs after 4am, set clock forward a little, if in evening, set clock back
- Nudging a clock into synchrony with another rhythm is called entrainment. Other clocks entrained to SCN
- Pineal body secretes melatonin in darkness -> peaks at 2am then fall back down at 8am. Melatonin acts on SCN to reset clock to night
- In day: SCN excite LH to secrete orexin -> cause arousal. In dark: release MCH to induce sleep
- Breakdown of ATP cause adenosine buildup to make us sleepy. Caffeine blocks adenosine receptors -> when caffeine wears off we crash. Half life of 6 hours
- In REM sleep -> erratic 30-40 Hz brain waves. In NREM -> dreamless with slower brain wave. Stage 3 has regular 2-4Hz brain waves
- First REM stage occurs after 90 min -> as night progress -> sleep shallower and REM stages longer
