B1: Limbic Structures Flashcards
Describe the anatomical sections of the Hypothalamus:
Note also the deliniations between these
From Rostral to Dorsal: Postoptic, Anterior (above optic chiasm), Tuberal (above and including the tuberal Cinerium) and Posterior Regions Above and including Mamillar Bodies)
From median to Lateral: Periventricular, Medial and Lateral Zones
Describe anatomical relations of hypothalamus
Anteriorly: Lamina Terminalis
Superiorly: Hypothalamic Sulcus
Inferiorly (ant-post): Optic chiasm->pituitary gland/infundibulum->mamillary bodyies
Posteriorly: Tegmentum of Midbrain
Midially: 3rd ventricle (i.e. against periventricular section of hypothalamus)
Lateral: Internal Capsule, Basal Forebrain
*Fornix runs through hypothalamus
Overarching Functions of Hypothalamus
Maintains Homeostasis
Various inputs from other limbic strucutres, the cortex (mainly optic/retinal), and brainstem. Outputs reflect these inputs, with addition of inputs to pituitary and thalamus.
Involved in autonomic (interaction with brainstem), endocrine (interaction with pituitary), emotional (interaction with limbic structures), and somatic (interaction with cerebral cortex) processes.
Physically part of the diencephalon, but functions as part of the limbic system**
Functions of the Ventromedial Nucleus (VMN) (& location)
Tuberal (middle) Region, Medial Zone.
Satiety Centre.
Related to lateral hypothalamic zones - feeding centre
Functions and location of Suprachiasmic Nucleus
“Master clock” -> control of circadian rhythms. Major inputs from retina (MELANOPSIN pathway -> melatonin receptors in SCN) -> light acting is zeitgeber for synchronise circ. rhyth. with environment.
Also control over body temperature and hormone secretions
General functions of other hypothalamic nuclei
Sympathetic (posterior regions) and Parasympathetic (anterior regions) functions.
Other areas also contribute to sleep/wake cycles and body temperature conservation
Describe the regulation of autonomic functions by the hypothalamus (basics) & the CNs/Spinal levels it is active through
Posterior regions of hypothalamus -> SNS output -> via Hypothalamospinal Tract -> T1-T2
Anterior regions -> PSNS output -> Hypothalamobulbar Tracts -> mainly to CNIII, VII, IX, X and pelvic parasympathetics (S2-4)
Describe the Hypothalamic Control of Neurohypophysis
Supraoptic Nucleus and Paraventricular Nuecleus -> send fibres (magnocellular neurons) to Posterior Pituitary (neurohypophysis) via the:
Supraopticohypophyseal Tract
(so named because most fibres coming from SON)
-> release of ADH (vasopressin) and oxytoxin
Describe hypothalamic control of adenohypophysis
Parvocellular neurons from the Arcuate Nucleus, and nearby regions of the walls of the 3rd ventricle -> secrete ‘Releasing Hormones’ and ‘Inhibiting Hormones’ into the Median Eminence (of infundibulum) -> these hormones gain access to the first capillary bed of the Hypophyseal Portal System (capillary arising from the Superior Hypophyseal Artery) -> are carried in Hypophyseal Vein to the Adenohypophysis (second capillary bed)
What are Circumventricular Organs, and which are directly relevant to the Hypothalamus?
Basic functions of these
COs = highly vascular areas of brain devoid of BBB
Subfornical Organ and Vascular Organ of Lamina Terminalis = Sensory Organs involved in fluid balance
Median Emminence, Pineal Gland = Secretory. Neuroendocrine function (ME) and Melatonin Secretion (PG)
Describe the sensory component of the Hypothalamic Involvement in regulation of water balance
Sensory circumventricular organs:
Organ of Lamina Terminalis - detects changes in blood osmolarity
Subfornical Organ - detects changes in Angiotensin II
What are the major inputs to hypothalamus (afferents)
-Other limbic structures: Hippocampus (to medullary body), Amygdala (mainly via Solitary Tract), Orbital Cortex
Sensory Input
- Inputs from brainstem (e.g. pain, temperature, taste, etc.) via Dorsal Longitudinal Fasiculus (DLF) and Medial Forebrain Bundle (MFB)
- Inputs from cortex: retina, olfactory cortex, septal nuclei
Major Tracts of Aferents to Hypothalamus:
From brainstem:
Dorsal Longitudinal Fasiculus
Medial Forebrain Bundle
From Amygdala:
Solitary Tract*
VAP (more direct -> Ventral Amygdalofugal Pathway)
Major Outputs from Hypothalamus
Largely the same as inputs, and following those same tracts.
Addition of:
1. Output to piuitary via Hypophyseal Portal System (parvocellular neurons -> from arcuate nucleus & nearby regions of 3rd ventricle walls to adenohypophysis)
AND Supraoptico-Hypophyseal Tract from supraoptic and paraventricular nuclei -> magnocellular neurons -> ADH and oxytocin to neurohypophysis
- Input to Thalamus via Mammillothalamic tract
Blood supply of hypothalamus?
Perforating branches from circle of willis
Major Function of the Limbic System. How do the parts integrate (in theory)
Portion of brain concerned with feelings, emotional responses, and behaviour
Interconnecting: A given function may be carries out by multiple parts, and one part can participate in multiple functions
Serves as interconnection between the thinking neocortex and the hypothalamus
What are the principal components of the limbic system
Amygdala (anterior and superior to the…)
Hippocampus (which extends into the…)
Fornix
Cingulate Cortex (around the top of fornix)
What is the Papez Circuit? (functionally)
The route through which the neocortexinfluences the hypothalamic and limbic activity
I.e. cortical control of emotional activity
Describe basic route of Papez Circuit
Hypothalamus -> Fibre budle emerges (fornix) -> swings over thalamus and converges behind anterior commissure of hypothalamus as the ‘columns of the fornix’
Columns of fornix project to mammillary body
Fibres then follow mammillothalamic tract to the Anterior and Dorsomedial Neclei of Thalamus
Then fibres are sent into Cingulate cortex to the Cingulate Gyrus
Which sends fibres down to the Entorhinal Cortex (major interface between neocortex and hypothalamus)
Function, composition and Location of Amygdala
Located anteriorly/superiorly to the Hippocampus, Deep to the Uncus
Composition = collection of several nuclei
Responses to physical and emotional stressors - i.e. co-ordinates behavioural, endocrine and autonomic responses to environmental stimuli
Receives stimuli from several sesory association areas
What afferents does amygdala recieve from sensory association areas?
Somatosensory (from postcentral gyrus)
Auditory (from auditory cortex in temporal lobe)
Visual: object and face recognition pathway (from vision area 4 on inferior surface) and movement detection pathway (vision area 5). Both V4 and 5 are commected to amygdala via the hippocampus thus fearful memories can be elicitied by current visual scene
Locus Ceruleus (nucleus in the pons) -> to do with attention and vigilance
Visceral Sensory Input via hypothalamus (from solitary tract?)
Direct input from Lateral (thalamic visual relay centre) Medial (thalamic auditory relay) Geniculate Nuclei
Efferents from the Amygdala
Efferents via two key pathways:
Stria Terminalis (curves around lateral ventricle, in groove between thalamus and caudate nucleus) Then to the Hypothalamus (leads to release of stress hormone) and various austonomic centres...
- To the Periaqueductal Grey (PAG) in midbrain -> triggers antinociception
- Parabrachial Nucleus (junction of midbrain/pons): Triggers hyperventilation
- PSNS output to Dorsal Motor Neurons of X -> triggers bradycardia, fainting
- SNS output to spinal cord lateral horn -> adrenalinergic projection
Ventral AmygdaloFugal Pathway to hypothalamus and ventral striatum (includes nucleus accumbens -> implicated in reward/addictive behavious)
Describe the anatomy & location of the hippocampus
Comprised of 3 components:
Subiculum
Hippocampus Proper
Dentate Gyrus
Is a 3-layered allocortex
Folded under the medial aspect of the temporal bone
Forms medial wall of the inferior horn of the lateral ventricle
What are the parts of the fornix?
Fimbria: mostly efferent fibres from hippocampus (these extend superiorly into the…)
Crus (which arch into the)
Body (joining of the crura, and some exchange of fibres between crura via the commissure of the fornix)
Pre-commissural areas of the fornix: send fibres mainly to the septal and supraoptic nuclei, and ventral striatum
Post-commissural areas of the fornix: Fibres to mammilary bodies and hypothalamus
Route of Efferents of Hypothalamus
Two major routes: fornix and entorhinal cortex
Fornix: to mammillary bodies, hypothalamus, septal nuclei, ventral striatum
Entorhinal Cortex: to the Amygdala, or or backwar along the cingulum to the cingulate gyrus
Why do chronic alcoholics suffer memory loss?
Due to mammillary and some hippocampal degeneration
Effects of Alzheimer’s disease on the brain structure:
Most common type of dementia Memory and cognition impairments Shrinkage of brain size -> widened sulci Enlarged ventricles Shrinkage of hippocampus and language areas
Memory: bilateral hippocampal damage results in
Permanent anterograde amnesia of explicit (declarative) memory
No conscious recall of newly acquired information beyond a few minutes
Memory: Damage to cerebellum results in
Issues with implicit (procedural) memory -> e.g. improving your tennis game
(cerebellum appears to be primary store)
Memory: Damage to prefronal cortex?
Affects working memory (i.e. attention)
