Hypothalamic and Limbic Systems Flashcards
Which nuclei does the anterior hypothalamic area harbor?
- Paraventricular nucleus
- Preoptic nucleus
- Anterior nucleus
- Supraoptic nuclei (medial and lateral)
- Suprachiasmatic nucleus
Which nuclei does the middle hypothalamic area harbor?
- Arcuate nucleus
- Ventromedial nucleus
- Dorsomedial nucleus
- Tuber cinereum
Which nuclei does the posterior hypothalamic area harbor?
- Posterior nucleus
- Mammillary bodies
Damage to the lateral zone/nucleus of the hypothalamus causes
- decrease in feeding behavior w/ resultant weight loss
- Contains the median forebrain bundle
Function of the supraoptic/paraventricular nuclei
- Contain oxytocin (PVN) and vasopressin/antidiuretic hormone (SON) w/in axons of the posterior pituitary gland
- Lesions can result in diabetes insipidus (DI), increased H2O intake and increased urination
Function of the suprachiasmatic nucleus
- Receives direct input from retina to mediate circadian rhythms (hormonal fluctuations secondary to light-dark cycles)
- Activity opposes drive for sleep and essential for timing of rest vs activity
- Cells maintain 24 hr periodicity via transcription/translational control of circadian genes and these gene products indirectly control melatonin secretion
- Damage may modify, or abolish, these rhythms
- Secretes releasing/inhibiting hormones
Function of anterior and preoptic nuclei
- Visceral/somatic functions
- Temperature regulation
- Parasympathetic activity
- Sleep
Function of hypothalamic ventromedial nucleus
- satiety center (inhibits eating and drinking by giving us sense of ‘fullness’)
- Lesions cause excessive eating and abnormal weight gain
Function of the hypothalamic dorsomedial nucleus
- Subserves emotional behavior
- Stimulation causes sham rage in animals
- Lesions result in decreased aggression and feeding
- Role in circadian rhythms
Function of the arcuate nucleus
-Secretes releasing/inhibiting hormones
Function of the medial mammillary nucleus
- Receives afferents from hippocampus via fornix
- Sends efferents to the thalamus and brainstem
- Lesions result in inability to convert short-term events into long-term memory
Function of the hypothalamic posterior nucleus
- Heat gain/conservation
- Cold temperature response
- Sympathetic activity
- Arousal/wakefulness
Blood supply of Hypothalamus: anteromedial group
- Branches from anterior communicating and A1 segments
- Supplies the preoptic area and supraoptic region, septal nuclei, rostral portions of lateral hypothalamic area
Blood supply of Hypothalamus: posteromedial group
- Perforating arteries from posterior communicating artery and P1 segment
- Rostral portion of posterior communicating supplies the tuberal region
- Caudal parts of posterior communicating artery supplies the mammillary region
Lesions in anterolateral medulla
-Disrupt hypothalamomedullary fibers causing disruption of the sympathetic outflow to face and head (Horner’s syndrome) or body
Afferent pathway of the hippocampal formation
Dentate gyrus –> cornus ammonis (CA)3 –> CA1 –> subiculum
Efferent pathway of the hippocampal formation
Fibers from cell bodies in subiculum (CA2) and hippocampus proper (CA1) bundle into fimbria and form the fornix –> terminates in medial mammillary nucleus, ventromedial nucleus and anterior nucleus of dorsal thalamus
-Other projections include the septal nuclei, frontal cortex, preoptic and anterior nuclei of the hypothalamus, and the nucleus accumbens
Korsakoff’s Syndrome
- Progressive degeneration of mammillary bodies, hippocampal complex and dorsomedial thalamic nucleus –> impedes retention of newly acquired memories b/c cannot convert short term into long-term memories
- Pt typically have severe difficulty learning new tasks and difficulty in understanding written material, as well as, conducting meaningful conversations
- Pt may confabulate - combine fragmented memories into a synthesized memory of an ‘event’ that never occurred
- Caused by thiamine deficiency, typically associated w/ chronic alcoholism
Hippocampal Amnesia
- B/l lesions of hippocampi resulting in deficient anterograde episodic memory (cannot learn new material) BUT spared procedural and working memory
- Pt IQ and formal reasoning ~ normal
Anosmia
- Loss of smell due to viral infection of olfactory mucosa, obstruction of nasal passages or congenital
- Lesions due to shearing of CN1 (e.g. MVA or head injury) or anterior cranial fossa floor tumors can also cause this
- Pts typically do not recover sense of smell b/c axons typically cannot regrow through small openings
Phantosmia (olfactory hallucination)
- Distortion in smell experience or perception of smell when no odor present (phantom smell)
- Due to abnormal sequence of neuronal activity caused by lesion of anterior/medial temporal lobe (hippocampus, amygdala, or dorsal thalamic nuclei)
Amygdala function
- Attaches emotional significance to stimulus
- Regulates visceral responses to emotional stimuli, including pain
- Emotional responses to food (e.g. pleasant smells stimulate appetite)
- Fear and fear conditioning
Afferents to amygdala
- Sensory info from raphe nuclei, periaqueductal grey, dorsal motor nucleus of X, nucleus solitarius and locus ceruleus
- Dorsomedial nucleus of thalamus and from other cortical areas
Efferents from amygdala
- Stria terminalis and ventral amygdalofugal pathways:
1. Target hypothalamus, ventral striatum and septal nuclei (ST,VAF)
2. Cerebral cortex (frontal, prefrontal, cingulate and inferior temporal cortical areas)
Kluver-Bucy Syndrome
- B/l temporal lobe lesions that abolish amygdaloid complex
- Behavioral changes include (but not always ALL of them):
1. Visual agnosia - inability to recognize an object by sight
2. Hyperorality - tendency to examine objects by mouth
3. Hypermetamorphosis - compulsion to intensively explore immediate environment or overreact to visual stimuli
4. Placidity - may not show fear/anger when rxn appropriate
5. Hyperphagia - excessive eating when not hungry or when objects not food
6. Hypersexuality
Ventral tegmental area (VTA)
- Medial to substantia nigra and houses dopaminergic neurons
- Connections w/ ventral striatum, amygdala and other limbic structures
- Reward and motivation and possibly addiction
Septal nuclei
- Small area rostral to anterior commissure
- Reciprocal connections w/ olfactory bulb, hippocampus (via fornix) and amygdala
- Role in reward/pleasure and control of rage behavior
Nucleus Accumbens
- Located in forebrain near continuation of caudate and putamen
- Important in addiction and chronic pain behaviors
Which areas of the hypothalamus regulate the autonomic nervous system?
- Anterior area activates parasympathetic activity (CNIII, VII, IX, X and S2-4)
- Posterior area activates sympathetic activity (lateral horn of T1-L2)
