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IMS: Neuroanatomy > Hypothalamus > Flashcards

Hypothalamus Flashcards

1
Q

Neurohypophysis

A

Hypothalamus + Pituitary

  • Tuber cinereum ⟾ inferior surface of hypothalamus
    • connects with median eminence and infundibular stalk
    • serves to connect hypothalamus to pituitary
  • Infundibular stalk continuous with posterior pituitary
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2
Q

Hypothalamus

Functions

A
  1. Homeostatic regulation
    • temperature
    • water balance
    • blood pressure
    • feeding
    • sleep-wake cycle
  2. Endocrine control
  3. Autonomic control
  4. Limbic mechanisms
    • memory
    • emotion
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3
Q

Hypothalamus

Location

A

Nuclei bounded by:

Red nucleus posteriorly

Thalamus dorsally

Internal capsule laterally

Lamina terminalis rostrally

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4
Q

Hypothalamus Regions

Rostral-Caudal

A

Divided into 3 regions:

  1. Anterior region
    • preoptic
    • supraoptic
  2. Tuberal region
  3. Posterior region
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5
Q

Hypothalamus Regions

Mediolateral

A

Divided into 2 regions:

  1. Medial region
  2. Lateral region
    • called lateral hypothalamus area caudally
    • called lateral preoptic area rostrally

Fornix seperates medial from lateral.

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6
Q

Hypothalamus

Posterior Region

Nuclei

A
  1. Posterior nucleus (po)
  2. Tuberomammillary nucleus
  3. Mammillary body (mb)
  4. Lateral hypothalamus
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7
Q

Hypothalamus

Tuberal Region

Nuclei

A
  1. Dorsomedial nucleus (dm)
  2. Ventromedial nucleus (vm)
  3. Arcuate nucleus (ar)
  4. Lateral hypothalamus
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8
Q

Hypothalamus

Anterior Supraoptic Region

Nuclei

A
  1. Paraventricular nucleus (pv)
  2. Anterior nucleus (an)
  3. Supraoptic nucleus (so)
  4. Suprachiasmatic nucleus (sc)
  5. Lateral hypothalamus

Fornix divides this level into lateral region and medial region (anterior nucleus and paraventricular nucleus).

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9
Q

Hypothalamus

Anterior Preoptic Region

Nuclei

A

Characterized by 2 main nuclei:

  1. Medial preoptic nucleus (mpr)
  2. Lateral preoptic nucleus

Generally classified as telencephalic origin but functionally associated with hypothalamus.

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10
Q

Hypothalamus

Nuclear Subdivision Summary

A
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11
Q

Hypothalamus

Blood Supply

A

Supplied by terminal branches of the circle of Willis:

Anterior region → anterior cerebral (ACA) and anterior communicating arteries (Acom)

Tuberal region → posterior communicating artery (Pcom)

Posterior region → posterior communicating (Pcom), posterior cerebral (PCA), and basilar arteries (BA)

Lateral hypothalamus → middle cerebral (MCA) and anterior choroidal arteries

Venous drainage via cerebral veins.

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12
Q

Posterior Nucleus

A
  1. Controls sympathetic nervous system:
  • contributes to descending hypothalamic fibers → preganglionic sympathetic neurons in IML cell column (T1-L2)
  • stimulation ⟾ sympathetic & fight-or-flight responses
  • lesion ⟾ Horner’s syndrome
    • myosis, anhidrosis, ptosis
  1. Controls thermoregulation:
  • conservation of heat (thermogenesis) in response to ↓ body temp
    • vasoconstriction
    • shivering
  • lesion ⟾ poikilothermia
    • ​inability to regulate body temperature
    • destroys both heat conservation mechanisms & descending pathways for heat dissipation from anterior nucleus
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13
Q

Tuberomammillary Nucleus

A

Promotes wakefulness via histaminergic neurons.

Wide projections to cerebral cortex, thalamus, basal forebrain, and brainstem regions.

Lesion = hypersomnia.

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14
Q

Mammillary Body

A

Involved in consolidation of memory.

  • Part of Papez’s circuit for memory consolidation
  • Associated with limbic system
  • Input from hippocampus via fornix
  • Relays to anterior nucleus of thalamus via mammillothalamic tract
  • Lesion or thiamine (B1) deficiency
    • Wernicke’s encephalopathy in acute phase
      • ocular palsies
      • ataxic gait
      • mental confusion
    • Karsakoff’s syndrome in chronic phase
      • anterograde amnesia
      • confabulation
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15
Q

Posterior Region

Summary

A
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16
Q

Tuberal Region

Characteristics

A

Characterized by projections to anterior pituitary.

Hypophyseal portal systems travels through median eminence.

Lateral hypothalamus & ventromedial hypothalamus located here.

Both involved in feeding behavior.

MFB travels through lateral hypothalamus.

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17
Q

Median Eminence

A

Site of release of many peptides controlling the function of the anterior pituitary.

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18
Q

Medial Forebrain Bundle

(MFB)

A

Major fiber system running in lateral hypothalamus.

Part of the reward circuit.

Stimulation causes pleasure due to dopamine release.

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19
Q

Lateral Hypothalamus

A
  1. Feeding center
    • Promotes hunger and feeding behavior
    • Lesion ⟾ anorexia and weight loss
  2. Regulates sleep/wake state
    • Orexin/Hypocretin neurons
      • neuropeptide
      • regulates sleep/wake state, feeding behavior, reward processes
    • Orexin deficiency ⟾ narcolepsy
    • Supplementation ⟾ appetite stimulation, wakefulness
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20
Q

Ventromedial Nucleus

A

Satiety Center

  • contains leptin-sensitive neurons
  • promotes cessation of eating
  • lesion = hyperphagia and obesity
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21
Q

Dorsomedial Nucleus

A

Control center for feeding and body weight regulation.

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22
Q

Arcuate Nucleus

A
  1. Controls secretion of hypophyseal hormones
    • Contains tuberoinfundibular dopamine neurons (TIDA)
      • dopamine (DA) → median eminence → ⨂ prolactin by anterior pituitary
    • Contains growth hormone-releasing hormone neurons (GHRH)
      • GHRH → median eminence → ⊕ GH by anterior pituitary
  2. Controls feeding behavior
    • Contains neurons sensitive to leptin, ghrelin, and orexin
    • Project to other feeding centers
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23
Q

Feeding Behavior

Network

A

Neural network for regulating feeding behavior.

Includes:

Lateral hypothalamus

Ventromedial nucleus

Dorsomedial nucleus

Paraventricular, suprachiasmatic, and arcuate nuclei

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24
Q

Leptin

A
  • Secreted by adipocytes
  • Reflects body fat stores
  • Acts on hypothalamus to promote behavioral and metabolic adaptations to nutrient availability

Nutrient abundance ⇨ ↑ leptin ⇨ ↓ appetite & ↑ energy expenditure

Nutrient insufficiency ⇨ ↓ leptin ⇨ ↑ appetite & ↑ energy conservation

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25
Q

Ghrelin

A
  • Released by stomach​ in blood
    • Highest just prior to a meal
    • Falls after eating
  • Stimulates food intake
  • May have role in meal initiation
    • signaling involves gastric vagal afferent
    • action on ghrelin-sensitive arcuate neurons
  • ↑ [Ghrelin] during diet/weight-loss episode ⟾ harder to maintain diet
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26
Q

Hypothalamic-Hypophyseal Portal System

A

Factors controlling hormonal secretion of anterior pituitary gland → HPA axis portal system → target.

Influences activity of acidophils and basophils in anterior pituitary.

27
Q

Tuberal Region

Summary

A
28
Q

Anterior Nucleus

A
  1. Control of parasympathetic system
    • Descending hypothalamic fibers → preganglionic PNS neurons in cranial nerve nuclei (CN III, VII, IX, X) and IML cell column (S2-S4)
    • Produces parasympathetic and rest-and-digest responses
    • Lesion ⟾ deficit in PNS function
  2. Control of thermoregulation
    • Mediates dissipation of heat (thermolysis)
      • vasodilation and sweating
    • Lesion ⟾ hyperthermia
29
Q

Suprachiasmatic Nucleus

A
  1. Controls circadian rhythms
    • pacemaker or biological clock (25 hr cycle)
    • receives light info from retinal ganglion cells via retinohypothalamic tract
      • adjusts rhythm to 24-hr cycle
  2. Modulates pineal gland function
    • inhibits production of melatonin during the day
    • light info from hypothalamus via descending SNS fibers → IML nucleus → superior cervical gnaglia → pineal gland
    • lesion → disruption of cyclic variations of bodily functions
      • BP, hormone levels, body temp, sleep/wake
30
Q

Supraoptic and Paraventricular Nuclei

A

Contains magnocellular neurosecretory neurons

⟾ projects directly to posterior pituitary

⟾ releases oxytocin or vasopressin (ADH) into general circulation

  1. Vasopressin-secreting neurons
    • promotes water retention
    • causes urine concentration by kidneys
    • lesion = diabetes insipidus
  2. Oxytocin-secreting neurons
    • promotes milk letdown
    • promotes contraction of uterine muscles
31
Q

Paraventricular Nucleus

Only

A

Contains parvocellular neurosecretory neurons

⟾ projects to median eminence/portal system

⟾ controls anterior pituitary function

  1. Corticotropin-releasing-hormone neurons (CRH-neurons)
    • ⊕ adrenocorticotropic hormone (ACTH) secretion
    • involved in stress/HPA-axis response
  2. Thyrotropin-releasing-hormone neurons (TRH-neurons)
    • ⊕ thyroid-stimulating hormone (TSH) secretion
  3. Somatostatin-releasing neurons
    • ⊖ growth hormone secretion
    • lesion = endocrine deficits
32
Q

Anterior Supraoptic Region

Summary

A
33
Q

Anterior Preoptic Region

Characteristics

A

Involved in temperature regulation, behavioral courting, and mating displays.

Contains medial and lateral preoptic nuclei.

Substantia innominata and anterior commisure present at this level.

34
Q

Ventral Lateral Preoptic Nucleus

(VLPO)

A

Found within ventrolateral (anterior) preoptic hypothalamus.

  • Contains GABAergic neurons which inhibit:
    • wake-promoting orexinergic neurons in lateral hypothalamus
    • histaminergic neurons in posterior hypothalamus
    • cholinergic, serotonergic, and noradrenergic neurons in brainstem
  • Functions:
    • inhibits wakefulness
    • promotes non-rapid eye movement sleep (non-REM)
    • control global brain activity
35
Q

Medial Preoptic Nucleus

A

Found in anterior preoptic region of hypothalamus.

Functions:

  1. Thermoregulation set-point:
    • contains set-point temperature-sensitive neurons
    • regluates body temp
      • controls activity of heat conservation/dissipation hypothalamic centers
    • fever triggered by pyrogens
      • prostaglandins (PGE2) act on medial preoptic neurons
        • resets set-point to higher temp
      • cytokines
      • NSAIDS ↓ fever by ⨂ COX
    • lesion ⟾ hyperthermia
  2. Regulates release of gonadotrophic hormones & sexual behavior:
    • contains gonadotropin-releasing neurons (GnRH-neurons)
      • ⊕ LH and FSH from anterior pituitary
    • sexually dimorphic
      • larger in males ⟾ continual release of GnRH
      • small in females ⟾ cyclical release of GnRH
    • lesion ⟾ amenorrhea and impotence
36
Q

Anterior Commissure

A

Present above the preoptic region of hypothalamus.

Contains commissural fibers innterconnecting anterior temporal lobes.

37
Q

Nucleus Basalis of Meynert

A

Found within substantia innominata @ level of anterior preoptic region of hypothalamus.

  • basal forebrain nucleus
  • rich in cholinergic neurons
  • wide projection to neocortex
  • compromised in Alzheimer’s disease
38
Q

Hypothalamic Inputs

A

Inputs arise from 2 major regions:

  1. Forebrain projections
    • associated with limbic areas
  2. Brainstem and spinal cord projections
    • resonsible for conveying visceral and somatosensory information
39
Q

Hypothalamic Outputs

A

3 major pathways involved in hypothalamic control of ANS:

  1. Dorsal longitudinal fasciculus (DLF)
  2. Mammillotegmental and mammilothalamic tracts
  3. Medial forebrain bundle (MLF)

Hypothalamo-hypophyseal tract is unidirectional.

40
Q

Fornix

A

Hippocampal pyramidal neurons → mammillary bodies and septum

Part of Papez’s circuit for memory consolidation.

41
Q

Mammillothalamic Tract

A

Mammillary bodies → anterior thalamic nucleus

Associated with Papez’s circuit for memory consolidation.

42
Q

Stria Terminalis

A

Hypothalamus ↔ Amygdala

43
Q

Medial Forebrain Bundle

(MFB)

A

Hypothalamus ↔ Brainstem & Forebrain

  • Mix of afferent and efferent projections
  • Part of the mesolimbic pathway
    • contains serotonergic, noradrenergic, dopaminergic projections from brainstem
    • projects to ventral striatum and accumbens nucleus
  • Part of reward system
    • electrical stimulation of MFB produces intense pleasurable sensations
44
Q

Supraoptico-Hypophyseal Tract

A

Contains axons from paraventricular and supraoptic nuclei → posterior pituitary gland.

45
Q

Retinohypothalamic Tract

A

Carries light information from retinal ganglion cells → suprachiasmic nucleus of hypothalamus.

46
Q

Dorsal Longitudinal Fasciculus

A
  1. Contains afferent hypothalamic fibers
    • carries visceral and taste sensation
    • inputs relayed to hypothalamus via solitary and parabrachial nuclei
  2. Contains efferent hypothalamic fibers innervating:
    1. preganglionic parasympathetic neurons in brainstem and spinal cord (S2-S4)
      • dorsal motor nucleus of X
      • inferior and superior salivatory nuclei
      • Edinger-Westphal nucleus
    2. preganglionic sympathetic neurons in spinal cord
      • intermediolateral nucleus (T1-L2)
      • lesion of descending fibers in lateral medulla ⟾ Horner’s syndrome
    3. autonomic regulatory centers in medulla
      • respiration, HR, BP
    4. periaqueductal gray (PAG)
      • pain modulation
47
Q

Other Hypothalamic Pathways

A

There are various reciprocal connections between hypothalamus ↔ cortical regions including:

ventromedial prefrontal cortex

cingulate cortex

insula

48
Q

Pituitary Gland

Blood Supply

A

Hypophyseal portal system

Hypothalamus ↔ pituitary gland

Allows endocrine signaling between structures.

Pituitary gland supplied by 2 arteries:

  1. Superior hypophyseal artery
    • forms primary portal plexus
    • penetrates median eminence and infundibulum
  2. Inferior hypophyseal artery
    • forms capillary network within posterior pituitary

Venous drainage via hypophyseal veins.

49
Q

Camel Thermoregulation

Adaptation to Desert Life

A

Diurnal fluctuation of body temp from 93.2 → 107 °F.

  • Daytime
    • hypothalamic thermostat set point high
    • stores heat in body tissues
    • reduces need for cooling by evaporative water loss
  • Nightime
    • thermostat set point low
    • releases excess heat absorbed during the day
    • body temp cools by several degrees
    • reduces energy needed to maintain body temp
    • prepares camel for following day by starting at abnormally low temp
  • Carotid rete system
    • protects brain from large ↑ in body temp
    • arterial blood precooled by passing through rete of thin-walled arteries
      • embedded in cavernous sinus
      • cooled by venous blood returning from nose
  • Mechanisms to maintain fluid balance
    • ability to excrete highly concentrated urine
50
Q

Kangaroo Rat Fluid Balance

Adaptation to Desert Life

A
  • Don’t drink water
  • Live on seeds and dry plant material
  • Depends mostly on metabolic water from cellular respiration
  • Use behavioral habits & physiological features that conserve water
    • nocturnal life
    • efficient kidney function
      • extremely hypoerosmotic urine
      • related to length of LoH and high [ADH]
    • low fecal water content
    • lower evaporative water loss
      • nasal passage as countercurrent heat exchanger
    • dry food stored in burrows absorps moisture lost in breathing
51
Q

Arctic Ground Squirrel

Adaptation to Arctic Life

A
  • Hibernates for 7-8 months
    • Rewarms body to normal temp every 2-3 weeks
      • uses 85-95% of fat stores
  • Hyperphagy for 4 months before hibernation
    • increase adipose stores
    • doubles body weight
    • hypothalamic circuits regulating body weight become uncoupled or insensitive to signals from adipose tissue
  • Hibernation starts → temp set point from 98.6 to 30 °F
    • temp continuously regulated with ± metabolic rate to ∆ body temp to ambient temp
    • ⨂ SNS → ↓ shivering and vasoconstriction
  • Hibernation ends → rewarming
    • ⊕ SNS → brown adipose tissue → non-shivering thermogenesis
    • shivering is not started until body temp > 60 °F
52
Q

Anterior Preoptic Region

Summary

A
53
Q

Circumventricular Organs

A

Functional interface between nervious and endocrine systems.

BBB weak or non-existent.

Can have specialized receptors or secretory propterties.

  • Receptor CVO’s
    • area postrema
    • subfornical organ
    • organum vasculosum in hypothalamus
  • Secretory CVO’s
    • median eminence
    • neurohypophysis
    • subcomissural organ
    • pineal gland
54
Q

Neuroendocrine Control

A

Paraventricular, supraoptic, arcuate, and medial preoptic nuclei.

  1. Neurosecretory control ⟾ neurohypophysis
    • vasopressin and oxytocin from magnocellular neurons
      • supraoptic and paraventricular nuclei
    • travels to posterior pituitary
    • released into bloodstream
  2. Humoral control ⟾ adenohypophysis
    • peptide hormones from parvocellular neurons
      • paraventricular, arcuate, medial preoptic nuclei
    • travels via portal system to anterior pituitary
    • stimulates/inhibits hormone release
      • ACTH
      • TSH
      • GH
      • Prolactin
      • LH & FSH
55
Q

Weight Control

&

Feeding Behavior

A

Major nuclei involved:

  1. Ventromedial nuclei (VMN) ⟾ satiety or fullness center
    • lesion = extreme obesity
    • stimulation = stop eating
  2. Lateral hypothalamic area (LHA) ⟾ feeding center
    • stimulation = eat even when not hungry
  3. Arcuate and Dorsomedial nuclei

Lesion of LHA and VMN ⟾ animal stops eating completely.

56
Q

Heat Regulation

A

Medial preoptic, anterior hypothalamic, and posterior hypothalamic nuclei.

Involves descending hypothalamic fibers in dorsal longitudinal fasciulus (DLF) → autonomic centers of brainstem and spinal cord.

  • “set point” established
    • feedback loop restores temp when actual ≠ desired
  • ↑ body temp:
    • anterior hypothalamic nucleus → thermolysis
      • vasodilation
      • sweating
      • increased respiratory rate
      • decreased metabolic rate
  • ↓ body temp:
    • posterior hypothalamus → thermogenesis
      • vasoconstriction
      • increased metabolic rate
      • shivering
      • decreased respiratory rate
57
Q

Fever

A

Medial preoptic, anterior hypothalamic, and posterior hypothalamic nuclei.

  • Temp set-point in medial preoptic nucleus elevated
  • Normal, adaptive, nearly universal trait in vertebrates
  • acute phase response ⟾ coordinated response
    • autonomic
    • neuroendocrine
    • behavioral
58
Q

ADH Regulation

A

Subfornical organ detects plasma osmolality.

Organum vasculosum detects angiotensin concentration.

Both CVOs facilitate ADH release from supraoptic and paraventricular nuclei.

Nuclei further regulated by ascending signals from carotid bodies and aortic arch receptors.

Magnocellular neurons influenced by feedback systems that ∆ ADH secretion.

59
Q

Osmoregulation

A

Osmosensitive CVOs in 3rd ventricle, lateral and anterior hypothalamus monitor water balance.

Stimulates thirst and secretion of ADH.

ADH released from magnocellular neurons of supraoptic and paraventricular nuclei.

↑ renal water reabsorption

60
Q

Blood

Pressure/Volume

Regulation

A

Baroreceptor reflex regulates BP.

Extrinsic baroreceptors in aortic arch and carotid sinus.

Sends info to solitary nucleus of medulla ⟾ dorsal vagal nucleus ⟾ ∆ HR.

Solitary nucleus also sends direct info to hypothalamus.

Hypothalamus ∆ baroreceptor reflex via dorsal vagal nucleus.

61
Q

Oxytocin

A

Released by magnocellular neurons of supraoptic and paraventricular nuclei.

2 major effects:

  1. Initates milk letdown via lactation reflex
    • Afferent limb → tactile, visual, or auditory stimuli
    • Efferent limb → contraction of myoepithelial cells of mammary glands
    • Reflex can be inhibited by anxiety
  2. Uterine contraction during parturition
    • Afferent limb → pressure on cervix to hypothalamus
    • Efferent limb → oxytocin increases uterine contractions
62
Q

Gonadotrophins

A

Parvocellular neurons of medial preoptic nucleus release GnRH.

GnRH stimulates FSH and LH secretion by anterior pituitary.

FSH promotes ovarian follicular growth.

LH & FSH surge induces ovulation.

63
Q

Sleep-Wake Cycle

Nuclei

A
  1. Suprachiasmatic nucleus (SCN)
    • controls circadian rhythm
    • receives input from retina
  2. Tuberomammillary nucleus
    • histaminergic neurons
    • projects to cortex
    • important for alert state
  3. Ventrolateral preoptic area
    • GABAergic neurons
    • projects to posterior hypothalamus
    • inhibits histaminergic neurons

IMS: Neuroanatomy (23 decks)

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