Hypothalamus & Limbic System Flashcards
Hypothalamus is involved in the mediation of:
- Autonomics
- Neuroendocrine (Pituitary and Pineal Glands)
- Behavioral functions
Structures located near Hypothalamus:
- Epithalamus
- Mammillary body (posteroinferior)
- Anterior Commissure
- Optic Chiasm
- Infundibulum with Pituitary Gland
- Forms floor and inferior walls of third ventricle
Anteromedial Hypothalamus produces ____ activity
Parasympathetic
(ex. satiety, sleep, heat dissipation to decrease temperature)
Posterolateral Hypothalamus produces _____ activity
Sympathetic
(ex. hunger, wakefulness, heat conservation to increase body temperature)
What Nuclei are located in the Hypothalamus?
- Lateral
- Anterior
- One in the PreOptic area
- Suprachiasmatic
- Paraventricular
- Ventromedial
- Posterior
- Arcuate
- Supraoptic
Lateral Nucleus of Hypothalamus
- Sense a drop of glucose (hunger)
- Lesion makes you Lean
Anterior Nucleus of Hypothalamus
- Cooling via Parasympathetic
- Sense elevation of temperature
- Increases sweating and dilates superficial vessels
Nuclei in Preoptic Area of Hypothalamus
- Releases GnRH
- Influences reproduction and sexual behavior
Suprachiasmatic Nucleus of Hypothalamus
- Circadian rhythm
- Can function independently
- Can be regulated by the Ganglion Cells of CN II
Paraventricular Nucleus of Hypothalamus
Produces Oxytocin and ADH
Ventromedial Nucleus of Hypothalamus
- Sense elevated glucose (satiety)
- Lesion makes you Very Massive
Posterior Nucleus of Hypothalamus
- Senses temperature drop (heating)
- Has sympathetic center
Arcuate Nucleus of Hypothalamus
Secretes Dopamine directly to the Pituitary Gland where it inhibits prolactin secretion in adenohypophysis
Supraoptic Nucleus of Hypothalamus
- Secretes ADH and Oxytocin
- Senses drop in water concentration (thirst)
- Located in Posterior Pituitary Gland
The major efferents of Suprachiasmatic Nucleus project to the ___ ___
Pineal Gland
During the night, fibers from the SCN release ___ in the Pineal Gland which stimulate the pinealocytes, triggering the production of ____
- NE
- Melatonin
Supraopticohypophysial Tract
Axons carry ADH and Oxytocin into Posterior Pituitary where it is stored in Herrying Bodies and released if needed (i.e hypothalamus osmoreceptors sense lack of water in blood and CSF)
Two main pathways from the Hypothalamus that are the source of most of the central control of autonomic functions:
- Medial Forebrain Bundle
- Dorsal Longitudinal Fasciculus
The Medial Forebrain Bundle and the Dorsal Longitudinal Fasciculus connect the Hypothalamus with:
the major parasympathetic nuclei in the brain stem and the preganglionic (central) neurons of the thoracolumbar spinal cord
Medial Forebrain Bundle
- Anterior area for parasympathetic activity
- Goes to S2-S4
Dorsal Longitudinal Fasciculus
- Sympathetic
- Major output pathway of the hypothalamus that descends through the gray matter of the brain stem and into the spinal cord T1-L2
Lesion of hypothalamus is noticeable mostly in ____ lesion
Bilateral
- Typically results in autonomic and neuroendocrine dysfunction (ex. temperature, thirst, etc)
4 Main Limbic Structures
- Amygdala
- Hippocampus
- Cingulate Gyrus
- Parahippocampal Gyrus
Importance of Limbic Structures
- Emotional responses
- Drive-related behavior
- Memory
- Smell
Fornix
- White matter between lateral and 3rd ventricles
- Connects hippocampus to mammillary bodies
Hippocampus converges to form:
Fimbria of Fornix
Fimbria come together to form the:
Crus of Fornix
At Anterior Commissure, Body of Fornix splits into:
Columns of Fornix
Major role of Hippocampus
Formation of new memory (learning memory)
Papez Circuit
Hippocampus –> Mammillary Bodies –> Anterior Thalamic Nuclei –> Cingulate Cortex –> Entorhinal Cortex –> Hippocampus
*primary nuclei of circuit: mamillary bodies
Role of Papez Circuit
Assists with spatial and episodic memory consolidation and storage
What happens if there is damage to the Fornix or Mammillary Bodies?
Amnesia
Mammillary Bodies
- One of the primary nuclei of the Papez Circuit
- Assist with emotion and reward behaviors and goal-directed behaviors
- Primary function is recollective memory
- Memory consolidation occurs here – processing short-term memory into long-term memory
What happens if there is a lesion to the Mammillary Bodies?
Anterograde Amnesia – inability of retention of newly acquired memory; has no difficulty in remembering events occurring months or years before the lesion
Fornix is situated between what ventricles?
Between the Lateral and Third Ventricles
Fornix bifurcates at the level of the ___ ___ with the ___ fibers projecting to the ___ ___
- Anterior Commissure
- Postcommissural
- Mammillary Bodies
Korsakoff Psychosis (Syndrome)
- Caused by Thiamine (Vitamin B1) Deficiency (usually from chronic alcoholism
- Leads to degeneration of the Mammillary Bodies
- Lesion is bilateral
- Irreversible condition characterized by triad: anterograde amnesia, confabulation, personality changes (reckless behavior)
Anterograde Amnesia
- Inability to create new memory
- Function of the mammillary bodies with the hippocampus
Confabulation
Act of filling in gaps in memory with fabrications that are believed to be true
___ ____connect Amygdala with the ___
- Stria Terminalis
- Hypothalamus (Lateral Nucleus)
What are the main efferent fibers of the Amygdala?
Stria Terminalis
Role of Amygdala
- Form memories related to emotional events
- Facilitate long-term memory formation (together with hippocampus)
- Convert and retain learning from pleasure or fear responses
- Help us tell what other people express: aggression, love, indifference, etc
Causes of Kluver-Bucy Syndrome
- Result of trauma or surgery (for epilepsy) to temporal lobe
- Can also be caused by Herpes Encephalitis
Kluver-Bucy Syndrome
- Associated with damage to both amygdala resulting in abnormalities in memory, social and sexual functioning and idiosyncratic behavior
- Diminished ability to visually recognize object, loss of normal fear and anger responses
- Associated with Hyperphagia, Hypersexuality, and Hyperorality
Hyperphagia
Eating a lot even if person is not hungry; sometimes eats objects that are not actually food
Hypersexuality
Extremely urgent sexual desire
Hyperorality
Tendency to examine things by mouth; taste, chew, put everything in their mouth
Anosmia
- Loss of smell due to a viral infection of the olfactory mucosa, obstruction of the nasal passages or may be congenital
- Lesions occur due to shearing of CNI or tumors in the floor of the anterior cranial fossa
Phantosmia (Olfactory Hallucination)
Distortion in a smell experience or the perception of a smell when no odor is present
Causes of Phantosmia
- Abnormal sequence of neuronal activity
- Lesion of anterior/medial temporal lobe – hippocampus, amygdala, or medial dorsal thalamic nuclei
Two major dopaminergic areas of the brain:
- Substantia Nigra
- Ventral Tegmental Area
Vental Tegmental Area (VTA)
- Located medial to the Substantia Nigra
- Role in all behavioral and mental activities in which dopamine is released in our brain (reward, motivation, addiction)
Two of the most prominent efferents that project from the VTA:
- Mesolimbic
- Mesocortical
Mesolimbic Pathway
Travels from VTA to Ventral Striatum (Nucleus Accumbens)
Mesocortical Pathway
Travels from VTA to Cortical Areas
Schizophrenia
- Dopaminergic neurons in the VTA play a role in this disorder
- Associated with high levels of dopamine
ADHD
Linked to low dopamine activity in the VTA
Integrity of the ___ is crucial to proper brain function
VTA
Central Diabetes Insipidus
- Condition in which the kidneys are unable to concentrate urine because of a lack of circulating ADH
- Low levels of ADH are due to either decreased production within the hypothalamus or decreased release from the Posterior Pituitary Gland
- Present with Polyuria (too much urine), nocturia (increased urination at night), and polydipsia (thirst)
Hyperthermia
- May occur if there is a lesion (stroke or CNS damage) in the Anterior Nucleus of the Hypothalamus, which is involved in thermoregulation, specifically cooling the body down
- Damage to this region prevents the body from being able to cool itself
- Works via stimulation of the Parasympathetic NS
Functional Hypothalamic Amenorrhea
- Primary cause of secondary amenorrhea (cessation of menses)
- Results from decreased pulsation of GnRH from a nuclei of the PreOptic Area that occurs during times of severe physical or psychological stress
- Most commonly associated with eating disorders or overexercise
Effect of Lesion to the PreOptic Area
Reduction or abolition of sexual drive
Hyperprolactinemia
- Elevated levels of Prolactin (hormone of adenohypophysis) in the blood
- Most common cause is a prolactin-secreting pituitary adenoma, but also can be caused by loss of inhibitory dopamine secretion by the hypothalamus
- Can occur when dopaminergic neurons from the arcuate nuclei of the hypothalamus are damaged or if the infundibulum is transected during surgery
- Sxs: galactorrhea (milk discharge), oligoamenorrhea, erectile dysfunction
