Forebrain and Limbic System Flashcards
divisions of forebrain
- diencephalon
- internal capsule
- limbic system
divisions of diencephalon
- epithalamus: pineal gland, habenula
- thalamus: all sensory (minus olfaction) paths relay here, composed of distinct nuclei
- hypothalamus
- subthalamus
divisions of limbic system
- hippocampus
- hypothalamus
- amygdala
subdivisions of thalamic nuclei (as defined by internal medullary lamina)
- ant: ant nucleus, important limbic relay, sits in split in IML
- med: dorsomedial
- lat: 1. dorsal tier- lateral dorsal, lat post, pulvinar 2. ventral tier- vent ant, VPL, VPM, med and lat geniulates
* largest subdivision* - intralaminar: centromedian, parafascicular
- reticular nuc: regulatory role
- midline nuc
theme of all thalamic nuclei (except reticular)
- projection neurons: provide output from thalamus
- interneurons: small, inhibitory
*proportions vary
3 categories of thalamic nuclei
- relay nuc: receive well defined specific input from subcortical source and project to well defined area of cortex
- association nuc: receive specific inputs and regulatory from association cortex and project abck
- intralaminar and midline nuc: receive distinct set of specific inputs, project to cortex, BG, and limbic structures
reticular nucleus
- imp source of regulatory input to thalamus
- no projections to cortex
- input: cortex and thalamus
- output: inhib axons to thalamus
sensory system relay nuclei
VPL and VPM
motor system relay nuc
VA and VL
limbic system relay nuc
anterior, LD
main association nuc
DM (prefrontal lobe)
pulvinar (parietal-occipital-temporal)
internal capsule
- thalamocortical and corticothalamic fibers pass thru
- collects and forms cerebral peduncle (corticopontine/bulbar/spinal fibers descend thru)
5 parts of internal capsule (based on relationship to lenticular nucleus)
- ant limb: lenticular nuc, caudate
- post limb: lenticular nuc, thalamus
- genu: btwn A and P limbs
- retrolenticular: behind lenticular nuc (inf visual field)
- sublenticular: not seen in horiz sections, sup visual field
hypothalamus
critical in autonomic, endocrine, emotional, and somatic fnctns, maintains homeostasis
3 types of hypothalamus connections
- interconnected w limbic system
- output to pituitary
- interconnects visceral/somatic nuc
hypothalamic control of pituitary
sup hypophyseal br: cap bed in infundibulum and 2nd cap bed around endocrine cells, caps drain into portal vessels in ant lobe
inf hypophysela br: neurohypophysis , caps drain into cavernous sinus, delivers ant and post pit hormones to systemic circ
what controls pituitary secretions
neuroendocrine cells
2 types of neuroendocrine cells
- parvocellular: end in median eminence (short axons)
2. magnocellular: end in post lobe (long axons)
what do parvocellular cells give rise to
tuberoinfundibular tract
2 hormones released by neurons in paravent and supraoptic nuclei
- ADH/vasopressin
2. oxytocin: contract labor mm
hypothalamic functions
- autonomics
- feeding
- fight or flight
- sleeping/waking, sexual arousal, memory
hypothalamus and autonomics
ant hypo: stim produces parasymp effects (dec HR, constrictpupils, peristalsis)
post hypo: stim produces symp effects (increase HR, BP, dilate pupils)
hypothalamus and feeding
-lat and VM nuc create appetite set point, can be altered by serotonin (anorexia = increased, bulemia = decreased)
stim lat nuc->feeding, lesion->refuse food
stim VM nuc->refuse food, lesion->feeding
*areas also key to fear and rage
hypothalamus and fight or flight
- corticotrophin RH released by paravent nuc->ACTH release pituitary->increased cortisol from adrenal gland
- activation in lat prefrontal cortex
other hypothalamic fnctns
- sleeping/waking
- sexular arousal
- memory
hypothalamic inputs
- forebrain (limbic structures):
2. BS/SC
forebrain as hypothalamic input
- info to mediate autonomic/somatic of some emotional states
- amygdala via stria terminalis, VAP
BS/SC as hypothalamic input
- visceral and sensory info (IX and X)
- mainly DLF
limbic system
- mainly cingulate and parahippocampal gyrus)
- feelings/emotions from sensory inputs, evolved to promote survival so activity varies depending on physiologic needs
- bridges autonomic/voluntary responses to environmental changes
2 parts of limbic system
- limbic cortex: 3 layeres allocortex of hippocampus and septal area and mesocortex in parahippocampal gyrus, cingulate, and insula
- subcortical nuclei: amygdala (emotional responses), hypothalamus, nucleus accumbens and reticular form
hippocampus
specialized area of cortex rolled up into medial temp lobe, critical to memory formation, esp declarative memory
parts of hippocampus
- dentate gyrus
- hippocampus proper
- subiculum
hippocampus afferents
input from septal nuc and entorhinal cortex
hippocampus afferent connections
- afferent fibers from sensory cortex
- entorhinal cortex projects to dentate gyrus
- dentate neuron projects to CA3
- CA3 neuron projects into fimbria and CA1
- CA1 neuron projects to subiculum
- subiculum projects to fimbria (alvear path)
- subicular neuron projects to entorhinal cortex
- entorhinal neuron projects to sensory cortex
hippocampus efferents
- fimbria is an imp efferent
- entorhinal neuron is largest efferent
- fornix is continuation of fimbria, does outputs from subiculum and entorhinal cortex
papez circuit
MEMORY
- neurons in cingulate gyrus project back
- projection into entorhinal cortex
- projection into hippocampus
- fornix
- mammilary tract
- projections from ant nucleus of thalamus to cingulate cortex
types of memory
- short term: hold info briefly (phone number)
- long term: stored, can be retrieved (explicit: facts/events, implicit: performing a learned motor fnctn)
- working: needed for task at hand
- consolidation: process of storing new info in long term
amygdala
-primary association with fear
nuclear groups of amygdala
- medial: olfaction
- central: hypothalamus, PAG, emotional responses
- basolateral (HUGE): cortex; cent nuclei; emotional responses
amygdala afferents
- all sensory assoc area have direct input to lat nuc
- all areas also linked to prefrontal cortex via assoc fibers so sensations can be cognitively evaluated
amygdala efferent paths
- stria terminalis (to hypothalamus and septal nuclei)
2. ventral amygdalofugal path: also synapses with nuc accumbens
kluver-bucy syndrome
- bilat temp lobe injury, iinvolves amygdala, parahippo gyrus
- fearless, placid, no emotion, males are hypersexual: amygdala damage
- inordinate attn to all sensory stim, pick up same object repeatedly: visual assoc cortex damage
nucleus accumbens
stim: sense of well being, feeling “high” due to dopamine release
AKA ventral striatum
limbic loop in BG
- pleasure increases ventral striatal dopamine release from ventral tegmental area in midbrain
- drive related info to influence movement/behavior
- assoc stim with reward
