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PSL300H1 Study Guide - Midterm Guide: Pretectal Area, Pupillary Light Reflex, Reticular Formation


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Doug Mac Kay
Study Guide

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retinal ganglion cells contain absorbing pigment called melanopsin
(light absorbing pigment, depolarizes with light detecting general light levels)
also important for sychronizing circadian rhythms w/ day-night cycle. pupillary light reflex
does NOT begin in same area as parasympathetic. organized in the pretectal area of midbrain
uses ON and OFF afferents to detect luminance and darkness, in olivary pretectal nucleus :
melanopsin detects light sends signals to pretectoral area in midbrain retinal ganglion cells detect light or dark info
prcessed in pretectual nucleus in the brain.
when too bright parasympathetic activated: reflex via 3rd cranial nerve to ciliary ganglion and circular iris muscles.
uses ACh for pupillary constriction.
when too dark sympathetic activated: reflex via thoracic cord, sympathetic chain to radial muscles. (uses NA for
pupillary dilation). cocaine can inhibit NA reuptake, causing eyes to stay dilated.
Central control of the ANS:
reticular formation: most direct influence over autonomic function sends signal to spinal cord.
hypothalamus: main integration center integrates diff signals. processes many types of things.
amygdala: main limbic region for emotions stimulates sympathetic activity, especially previously learned fear-relating
behaviour. can be voluntary when decide to recall a frightful experience, cerebral cortex acts through amygdala. some ppl
can regulate autonomic activities by gaining extraordinary control over their emotions.
brainstem autonomic centers:
sympathetic modulatory tracts from raphé nuclei and locus coeruleus.
cardiovascular center, and respiratory pattern generator in lateral medulla/pons
periaqueductal gray: midbrain promoter center, for autonomic behavioural programs.
Reticular activating systems: diffuse collection of nuclei in brainstem. modulatory (cause global shift in CNS activity,
mainly metabotropic):
cholinergic: determines levels of attn. sleep-wake cycle, mainly ascending (pontine reticular formation and BNM nuclei)
serotonergic: stress situations, influences mood, sleep-wake cycle. too much serotonin aggression. 
adrenergic: for stressful situations and vigilance
serotonergic and adrenergic produce strong motor effects.
Histaminergic system: origins = posterior hypothalamus, TBN (tuberomamillary nucleus) specifically. projects
through forebrain and to other activating systems in brainstem.-> ascending and descending. important for sleep/wake
cycle. systems turns off when you fall asleep. histamine lvl decreases.
Autonomic Pattern Generators: CPGs controlling autonomic behaviors located in brainstem.
PAG in midbrain = major organizing center. most of these functions related to homeostatis.
Hypothalamic control centers:
NTS - info abt bloos pressure and gut distention (homeostatis)
Reticular formation - from CN X, info abt skin temperature, relayed to hypothalamus.
Retina - some fibers from optic nerve go directly to smallnucleus within hypothalamus called superchiasmatic nucleus,
which relates circadian rhythms, and couples them to light/dark cycles. (through melanopsin)
limbic and olfactory systems - regulates behaviour such as eating and reproduction.
temperature regulation: if skin temprature diff from body temp, info relayed from skin detecting changes in enviro.
thermoreceptors at base of hypothalamus, also detect enviro changes. warm-sensitive neurons outnumber cold-sensitive
neurons in brain, ultimately control thermogenesis.
when too cold skin vasoconstricts, piloerection, decreased circadian output, shift of fluid out of plasma , shivering -- a
somatomotor effect) posterior hypothalamus. need NA adrenergic input.
when too hot skin vasodilates, sweats, increased cardiac output, shift of fluid into plasma from extra-cellular space, ADH
released to prevent loss of fluid through urination. anterior hypothalamus. need serotonin serotenergic input
Cardiovascular center:
mainly in ventrolateral medulla, beside respiratory center.
NTS receives input from baroreceptors and cends this info to caudal VLM. rostral half excites sympathetic efferents
raises blood pressure and heart rate (pressure function). 
caudal half INHIBITS rostral hald blood pressure drops.
baroreflex: baroreceptors n. solitary tract ventro. lateral medulla sympathetic output (activate/inactivate)
Hypothalamic control of homeostatis:
hypothalamus = major regulator of core parameters (glucose in plasma, osmolality, temp regulation)
sensors located in hypothalamus to detect changes. corrective actions take place when detected, via autonomic endocrine
and somatomotor mechanisms. 
interacts with brainstem motor and autonomic centers via axonal projections.
interacts with endocrine system via pituitary
in hypothalamus:
arcuate nucleus control: NPY neurons drive feeding via paraventricular nucleus., other neurons (melanocortin) are
antagonistic (suppress feeding).
ventromedial nucleus: glucoreceptors, discharge in relation to ambient glucose lvls, inhibit NPY-mediated drive to feeding
behaviours. glucose = NPY inhibition. 
leptin, secreted by white adipose tissue (fat), long term suppression of feeding, inhibiting NPY-containing neurons in
arcuate nucleus.
G.I tract to control feeding ghrelin from empty stomach promotes feeding (orexigenic hormone)
PPY release in intestine in response to food and insulin from pancreas, inhibiting feeding. borborygmus (release of ghrelin,
stomach growls)
Amygdala part of B.G., controls autonomic behav. input from limbic cortex, output generally inhibitory on PAG-
hypothalaumus (shutting down a lot of programs). lesions = uncontrolled autonomic behav. (sham rage, hypersexuality,
Emotion related behaviour memories related to emotional experiences (especially fearful, rely on amygdala for
amygdala is not a site of memory storage. 
Limbic cortex: border region of cerebral cortex. made up of cingulate gyrus, hippocampal region (consolidates memories)
subserves emotional experience, motivation and memory consolidation.
neurons from this region project to hypothalamus, PAG and amygdala.
retinal ganglion cells
pupillary light reflex
olivary pretectal
pretectal area of
circular muscles
radial muscles
periaqueductal gray
reticular activating
autonomic pattern
cadiovascualr center
arcuate nucleus
ventromedial nucleus
orexigenic hormone
June-04-132:01 PM
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