The diencephalon includes the thalamus and hypothalamus. The thalamus relays sensory information, except smell, to the cortex and is involved in arousal, motor integration, pain modulation, and memory/behavior. The hypothalamus regulates homeostasis through the endocrine, autonomic, and motivational systems. It contains peptidergic neurons that secrete hormones through the pituitary to control endocrine functions. The thalamus and hypothalamus are critical for sensory/motor processing, arousal, homeostasis, and motivated behavior.

1. Diencephalon:
Thalamus and Hypothalamus
MM Obimbo

4. The diencephalon
• “between brain”
• Posterior part of embryonic forebrain
• Lies between brainstem and cerebral
hemispheres
• Includes: thalamus, hypothalamus,
subthalamus, epithalamus

6. Diencephalon
• Relay between the brainstem & cerebral cortex
• Dorsal-posterior structures
– Epithalamus
• Habenular nuclei – integrate smell & emotions
• Pineal gland – monitors diurnal / nocturnal rhythm
– Thalamus
– Metathalamus
• Medial geniculate body – auditory relay
• Lateral geniculate body – visual relay
• Ventral-anterior structure
– Hypothalamus

7. Function of the Thalamus
• Sensory relay
– ALL sensory information (except
smell)
• Motor integration
– Input from cortex, cerebellum
and basal ganglia
• Arousal
– Part of reticular activating
system
• Pain modulation
– All nociceptive information
• Memory & behavior
– Lesions are disruptive

8. Input to the Thalamus

9. Input to the Thalamus
Metathalamus
Vision and Hearing

10. Input to the Thalamus
Sensory relay - Ventral posterior group
all sensation from body and head, including pain

11. Input to the Thalamus
Motor control and integration

12. Input to the Thalamus
Behavior and emotion
connection with hypothalamus

13. Projections from the Thalamus
Metathalamus
Vision and Hearing

14. Projections from the Thalamus
Sensory relay
Ventral posterior group
all sensation from body and head,
including pain

15. Projections from the Thalamus
Motor control
and integration

16. Projections from the Thalamus
Behavior and emotion
connection with hypothalamus

17. Thalamus: axial view
Descending upper motor neurons
Cerebral peduncles Internal capsule

18. Thalamus: axial view

19. Thalamus: sagittal view
Pons

20. Thalamus: sagittal view

21. Thalamus: coronal view

22. Thalamus: coronal view
3rd ventricle

23. Thalamus: coronal view
Internal capsule

24. Thalamus: coronal view
Internal capsule
Cerebral
peduncles

25. Thalamus: coronal view
Mediodorsal nucleus Internal capsule
Dorsomedial nucleus has
reciprocal connections to
prefrontal cortex.
Concerned with judgment,
decision making, memory
and behavior.

26. Thalamus
Mediodorsal nucleus Internal capsule
Ventral
lateral
nucleus
VL nucleus has reciprocal
connections with primary motor
cortex. It receives input from
cerebellar nuclei.
With VA nucleus (which receives
input from basal ganglia)
contributes to planning and
control of movement.

27. Thalamus: blood supply

28. Hypothalamus
Located ventral-anterior to
thalamus.
(Subthalamus, located
ventral to thalamus, will be
discussed with basal
ganglia.)

29. General description
• Master regulator!!
• Vital regulatory functions include: temperature, heart
rate, blood pressure, blood osmolarity, goal seeking
behavior, emotional behavior, visceral nervous system,
sexual activity, food & water intake
• homeostasis
• Below rostral thalamus (hypo =“under”/”beneath)
• Forms floor and lower walls of third ventricle
• Contains various classes of peptidergic neuroendocrine
cells which control endocrine function
• Communicates with cortex via limbic system and also
via direct projections

30. Involvement with 3 major systems
• Endocrine system (HPA: hypothalamo-
pituitary-adrenal axis)
• Autonomic nervous system
• Motivation system
….Also adaptive emotional behavior

31. Anatomy of Hypothalamus
science.tjc.edu/ images/brain/Index.htm

32. Anterior: preoptic, superchiasmatic,
supraoptic, paraventricular
Middle: dorsomedial, ventral medial nuclei,
arcuate nucleus
Posterior: mamllary body, posterior
hypothalamic area, tubermammillary
nucleus
Medial-Lateral Zones
Periventricular
Medial
Lateral

33. Main Inputs to Hypothalamus
• receives info on external and internal
conditions:
– specific sensory info (e.g., direct retinal projection
to suprachiastmatic nucleus)
– input from visceral senses (NTS: nucleus of the
solitary tract-taste)
– contains many neurons that are sensitive to local
temperature, osmolarity, glucose, sodium
– circulating hormones influence it via the
circumventricular organs

34. Circumventricular organs
•Brain regions near ventricles
that lack a blood-brain barrier,
e.g., subfornical organ, OVLT,
median eminence, area
postrema
•Highly vascularized
•Influenced by circulating
hormones, osmotic changes,
substances in CSF, afferent
fibers from other parts of the
nervous system

35. Hypothalamic pathways
PATHWAY FROM TO
Fornix Hippocampus Mammillary bodies
Mammillothalamic tract Mammillary bodies Anterior thalamic nucleus
Stria medullaris Lateral preoptic area Habenular complex
Stria terminalis (reciprocal) Amygdala, BNST Medial hypothalamus
Dorsal longitudinal fasciculus
(reciprocal)
Hypothalamus Periaqueductal gray, medulla, pons
Medial forebrain bundle* Hypothalamus Preganglionic sympathetic and
parasympathetic nuclei
Hypothalamohypophyseal
pathways
Hypothalamus Pituitary
Histamine, orexin Lateral hypothalamus Cerebral cortex

36. Medial forebrain bundle
• “…one of the most famous hypothalamic bundles but also
one of the most incomprehensible”-Lennart Heimer

37. Peptidergic neuroendocrine cells:
Magnocellular neurons
• “Large” neurons
• Located in paraventricular and supraoptic nuclei
• Secrete oxytocin and vasopressin into general
circulation via posterior pituitary
• Oxytocin uterine contraction & milk ejection
• Vasopressin vasoconstriction, water
resorption by the kidney

38. Brainmaps.org

39. Magnocellular Secretory System
clem.mscd.edu/~raoa/ bio2320/endo1/sld003.htm

40. • “small” neurons
• Located in medial basal region, arcuate and
tuberal nuclei, periventricular region, preoptic
and paraventricular nuclei
• Secrete releasing and inhibiting hormones into
portal vasculature via anterior pituitary
• Nobel prize awarded to Guillemin (Salk), Schally
and Yalow in 1977 for their (independent) work
in proving the hypothesis that the hypothalamus
releases hormones that regulate the pituitary
Peptidergic neuroendocrine cells:
Parvocellular neurons

41. Hypothalamic Portal System
clem.mscd.edu/~raoa/ bio2320/endo1/sld003.htm

42. Hypothalamic inhibitors
Hypothalamic hormone Anterior pituitary hormone
Prolactin release-inhibiting hormone
(PIH), dopamine
Prolactin
Growth hormone release-inhibiting
hormone (GIH; somatostatin)
GH, thyrotropin
Melanocyte-stimulating hormone release
inhibiting factor (MIF)
MSH

43. Hypothalamic releasers
Hypothalamic hormone Anterior pituitary hormone
Thyrotropin-releasing hormone
(TRH)
Thyrotropin, prolactin
Corticotropin-releasing hormone
(CRH)
Adrenocorticotropin, b-lipotropin
gonadotropin-releasing hormone
(GnRH)
LH, FSH
Growth-hormone releasing
hormone (GHRH)
GH
Prolactin-releasing factor (PRF) Prolactin
Melanocyte-stimulating hormone-
releasing factor (MRF)
MSH, b-endorphin

44. Peripheral Influence of Hypothalamus
clem.mscd.edu/~raoa/ bio2320/endo1/sld003.htm

45. Hypocretin
From Thannickal et al., Neuron 27: 469,
2000
•Also known as “orexin”
•Peptide involved in arousal
and feeding behavior
•Project to thalamus, cortex
and brainstem regions
associated with arousal,
cardiovascular control, and
autonomic functions
•Few thousand neurons
•Loss of hypocretin neurons
implicated in human
narcolepsy

46. Don’t lie!
Thank you