Hypothalamus

Hypothalamus

Homeostasis
1. Regulation of internal environment in response to a constantly changing external environment
2. Modulates body temp, appetite, fluid balance and behaviour
  1. Communication with the body and the CNS
Location
1. Collection of nuclei surrounding the third ventricle
2. Ventral to the thalamus
3. Two sides, one on each side of the brain
4. Column organisation along the medial-lateral plane
  1. From the inside out: periventricular zone, medial zone and lateral zone
    1. Medial and lateral zones regulate behaviour
    2. Periventricular zone regulates circadian rhythms and nerve innervation and controls the ANS
5. Anterior-posterior plane organisation
  1. Relative to landmarks
    1. Posterior (back) - mammillary section by the mammillary body
    2. Middle - Tuberal section by the tuber cinereum
    3. Anterior (front) - Chiasmatic section by the optic chiasm
Input
1. Inputs from parts of the brain and spinal cord, motor and sensory systems from the internal organs
  1. Processed by periventricular and lateral nuclei. Send information via preganglionic neurons
    1. Nucleus of the Solitary Tract (NTS)
    2. Parabrachial Nucleus (PBN)
    3. Rostroventrolateral Medulla (RVLM)
  2. Olfactory inputs to the medial nuclei. Some are involved in appetitive behaviours as well as defensive
Output
1. Brain stem, spinal cord and pituitary gland
Tract Tracing Anatomical Connections
1. Retrograde
  1. Tracer taken up at the synapse and transported along the axon to the soma
  2. Tracing inputs
  3. e.g HRP
2. Anterograde
  1. Tracer taken up in the soma and transported down the axon to the synapse
  2. Tracing outputs
  3. e.g. PHA-L
3. Chemical tracer infused into a region of interest and nearby neurons take it up, where it is transported along axons to the input/output areas
Body Clock
1. Natural light programs the suprachiasmatic nucleus (SCN) directly, via the retina
  1. Chiasmatic section
  2. Lesions disrupt normal rhythm, electrical stimulation shifts it
  3. SCN neurons have a 24 hour rhythm of electrical activity
    1. Maintained by active 'clock' genes which are transcribed into mRNA and translated into proteins, which reduce transcription (negative feedback)
    2. Regulate the secretion of melatonin from the pineal gland
2. Sleep
  1. Regulated by hypothalamic communication
    1. Direct output to the cerebral cortex
    2. Indirect output via the brain stem as noradrenaline and serotonin
  2. Sleep promotion
    1. Preoptic nucleus in the chiasmatic section releases GABA/galanin to the tuberomammillary nucleus
      1. Lesions cause insomnia
  3. Wakefulness promotion
    1. Lateral nucleus secretes hypocretin/orexin to the tuberomammillary nucleus
      1. Lesions promote sleep
  4. Projections from the preoptic and lateral nuclei help control the release of histamine, indirectly regulating sleep

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	Created by Lydia Buckmaster almost 11 years ago