Lec 9 - Diencephalon

• The diencephalon is the caudal part of the forebrain ; primary relay and processing center for sensory information and autonomic control
• The diencephalon forms from the prosencephalon
• The diencephalon is made up of the epithalamus, hypothalamus, thalamus, and subthalamus
• The cavity of the diencephalon is the third ventricle
• The median eminence does not have a blood-brain barrier
• The infundibulum, also known as the pituitary stalk is the connection between the hypothalamus and the pituitary gland
• Mamillary bodies is a bilateral structure in front of the pons that is part of the limbic system
• The structures that "hug" the thalamus

  • optic nerve
  • optic chiasm
  • optic tract
• Label this inferior view of the forebrain

  A) median eminence

  B) infundibulum

  C) mamillary bodies

  D) optic nerve

  E) optic chiasm

  F) optic tract

  
• Label parts of the diencephalon

  A) thalamus

  B) hypothalamus

  C) subthalamus

  D) epithalamus

  
• The epithalamus is made up of the pineal gland and the habenular nucleus
• The hypothalamic sulcus is a groove that separates the thalamus from the hypothalamus
• The interthalamic adhesion is the point where the thalamus touch each other. No connection between them. Made up of glia and its a developmental remnant
• The walls of the thalamus make up the lateral walls of the 3rd ventricle
• The thalamus do not communicate with each other
• Label the landmarks of the diencephalon

  A) cerebrum

  B) hypothalamus

  C) pituitary

  D) mamillary bodies

  E) hypothalamic sulcus

  F) interthalamic adhesion

  
• The fornix is a c-shaped white matter tract connecting hippocampus. It is medial to the cerebral hemispheres and below the corpus callosum. Involved in the limbic system - cognition, memory consolidation, emotions
• The pineal gland secretes melatonin and is a part of the epithalamus. It is controlled by the SCN
• The suprachiasmatic nucleus (SCN) is above the optic chiasm and sets the pace for circadian rhythm
• Label these diencephalon landmarks

  A) fornix

  B) pineal gland

  C) suprachiasmatic nucleus

  
• The thalamus is a relay station - it relays information faithfully without alterations. No change to the information. It is the "gateway" to the cerebral cortex; processed sensory and motor information get relayed in thalamus before reaching cerebral cortex. All sensory info except for olfactory
• The thalamus is the largest mass of grey matter of the diencephalon
• The RNT are GABA neurons in the thalamus whereas all other neurons of the thalamus use glutamate. The RNT acts as the gate keeper - it approves signals to send to the cortex. It is a part of the thalamus but separated by external medullary lamina (white matter sheath)
• The thalamus contain an internal and external medullary sheath. The internal medullary sheath is a white matter fiber sheath where myelinated axons enter and leave the thalamic nuclei. It divides the thalamus into medial, anterior, and lateral sections
• Label the areas of the thalamus

  A) medial

  B) anterior

  C) lateral

  D) RNT

  E) external medullary lamina

  F) internal medullary lamina

  G) medial geniculate

  H) lateral geniculate

  I) interthalamic adhesion

  
• The limbic (emotion and memory function) nuclei of the thalamus

  • medial dorsal nuclei
  • anterior thalamic nuclei
  • lateral dorsal nuclei
• The nuclei of the thalamus responsible for higher order functions

  • lateral posterior nuclei
  • pulvinar (visual and higher order functioning)
• The motor nuclei receive info from the basal nuclei - they are:

  • ventral anterior nuclei
  • ventral lateral nuclei
• The sensory nuclei of the thalamus are

  • ventral posterolateral nuclei (general sensory)
  • lateral geniculate nuclei (vision)
  • medial geniculate nuclei (auditory)
• Label the nuclei of the thalamus

  A) medial dorsal

  B) anterior thalamic

  C) lateral dorsal

  D) ventral anterior

  E) ventral lateral

  F) RNT

  G) lateral posterior

  H) ventral posterolateral

  I) lateral geniculate

  J) medial geniculate

  K) pulvinar

  
• The hypothalamus is involved in homeostasis, endocrine, limbic, sleep, arousal, regulation of eating and drinking, autonomic activity, circadian rhythm. It comprises several subdivisions and nuclei
• The hypothalamus is exposed medially to the 3rd ventricle and related dorsally to the subarachnoid space. The hypothalamus is below the thalamus
• Neurons of the supraoptic (SO) and paraventricular nucleus (PV) send projections to the posterior lobe of the pituitary

  • SO neurons produce vasopressin (ADH), whereas PV neurons produce oxytocin and vasopressin
  • these hormones are released at nerve terminals in the posterior lobe of the pituitary gland (into capillary beds)
  • hormones will travel in systemic blood to target sites
• The supraoptic and paraventricular nucleus are nuclei of the hypothalamus
• Posterior pituitary hormones

  • oxytocin (acts on breasts and uterus)
  • vasopressin/ADH (act on blood vessels, kidneys to decrease water excretion/ increase water reabsorption)
• A group of neurons from the paraventricular nucleus (PV) sends axons to the median eminence. They have to travel through the pituitary stalk to get to the anterior pituitary. They will produce peptides and release them at the median eminence. Peptides picked up by capillaries at median eminence because no blood-brain barrier and carried by veins to the anterior lobe of the pituitary gland (hypothalamo-hypophysial portal system)

  
• Chemical signals from the median eminence to the anterior pituitary are carried by blood not by axons unlike communication to the posterior pituitary
• Peptides carried by capillaries to anterior lobe of the pituitary gland act on endocrine cells of the anterior pituitary gland. The endocrine cells secrete hormones that are picked up by capillaries of the systemic circulation and carried to target cells. This is the HPA axis (hypothalamus -> anterior pituitary -> adrenal cortex. Important control system of stress response (glucocorticoids)
• Anterior pituitary hormones (FLAT PG)

  • follicle stimulating hormone
  • luteinizing hormone
  • adrenocorticotropic hormone
  • thyroid stimulating hormone (TSH)
  • prolactin
  • Growth hormone (GH)
• Follicle stimulating hormone stimulates growth of ovarian follicles and induces secretion of estrogen in females. Needed for sperm production in males