B1: Limbic Structures

Question 1

Describe the anatomical sections of the Hypothalamus:

Note also the deliniations between these

Answer 1

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

Question 2

Describe anatomical relations of hypothalamus

Answer 2

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

Question 3

Overarching Functions of Hypothalamus

Answer 3

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**

Question 4

Functions of the Ventromedial Nucleus (VMN) (& location)

Answer 4

Tuberal (middle) Region, Medial Zone.

Satiety Centre.

Related to lateral hypothalamic zones - feeding centre

Question 5

Functions and location of Suprachiasmic Nucleus

Answer 5

“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

Question 6

General functions of other hypothalamic nuclei

Answer 6

Sympathetic (posterior regions) and Parasympathetic (anterior regions) functions.

Other areas also contribute to sleep/wake cycles and body temperature conservation

Question 7

Describe the regulation of autonomic functions by the hypothalamus (basics) & the CNs/Spinal levels it is active through

Answer 7

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)

Question 8

Describe the Hypothalamic Control of Neurohypophysis

Answer 8

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

Question 9

Describe hypothalamic control of adenohypophysis

Answer 9

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)

Question 10

What are Circumventricular Organs, and which are directly relevant to the Hypothalamus?

Basic functions of these

Answer 10

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)

Question 11

Describe the sensory component of the Hypothalamic Involvement in regulation of water balance

Answer 11

Sensory circumventricular organs:
Organ of Lamina Terminalis - detects changes in blood osmolarity

Subfornical Organ - detects changes in Angiotensin II

Question 12

What are the major inputs to hypothalamus (afferents)

Answer 12

-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

Question 13

Major Tracts of Aferents to Hypothalamus:

Answer 13

From brainstem:
Dorsal Longitudinal Fasiculus
Medial Forebrain Bundle

From Amygdala:
Solitary Tract*
VAP (more direct -> Ventral Amygdalofugal Pathway)

Question 14

Major Outputs from Hypothalamus

Answer 14

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

2. Input to Thalamus via Mammillothalamic tract

Question 15

Blood supply of hypothalamus?

Answer 15

Perforating branches from circle of willis

Question 16

Major Function of the Limbic System. How do the parts integrate (in theory)

Answer 16

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

Question 17

What are the principal components of the limbic system

Answer 17

Amygdala (anterior and superior to the…)
Hippocampus (which extends into the…)
Fornix
Cingulate Cortex (around the top of fornix)

Question 18

What is the Papez Circuit? (functionally)

Answer 18

The route through which the neocortexinfluences the hypothalamic and limbic activity

I.e. cortical control of emotional activity

Question 19

Describe basic route of Papez Circuit

Answer 19

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)

Question 20

Function, composition and Location of Amygdala

Answer 20

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

Question 21

What afferents does amygdala recieve from sensory association areas?

Answer 21

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

Question 22

Efferents from the Amygdala

Answer 22

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...

1. To the Periaqueductal Grey (PAG) in midbrain -> triggers antinociception
2. Parabrachial Nucleus (junction of midbrain/pons): Triggers hyperventilation
3. PSNS output to Dorsal Motor Neurons of X -> triggers bradycardia, fainting
4. 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)

Question 23

Describe the anatomy & location of the hippocampus

Answer 23

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

Question 24

What are the parts of the fornix?

Answer 24

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

Question 25

Route of Efferents of Hypothalamus

Answer 25

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

Question 26

Why do chronic alcoholics suffer memory loss?

Answer 26

Due to mammillary and some hippocampal degeneration

Question 27

Effects of Alzheimer’s disease on the brain structure:

Answer 27

Most common type of dementia
Memory and cognition impairments
Shrinkage of brain size -> widened sulci
Enlarged ventricles
Shrinkage of hippocampus and language areas

Question 28

Memory: bilateral hippocampal damage results in

Answer 28

Permanent anterograde amnesia of explicit (declarative) memory
No conscious recall of newly acquired information beyond a few minutes

Question 29

Memory: Damage to cerebellum results in

Answer 29

Issues with implicit (procedural) memory -> e.g. improving your tennis game
(cerebellum appears to be primary store)

Question 30

Memory: Damage to prefronal cortex?

Answer 30

Affects working memory (i.e. attention)