2019B13 Briefly outline the roles of the hypothalamus.

List:

· Intro

· Autonomic function

· Endocrine function

· Other specific homeostatic functions

Intro:

· Subcortical component of the limbic system

· Control centre for endocrine and involuntary neural functions

· Dense connections with higher and lower centres

Autonomic function:

Anterior stimulation	· Depressor area -> PSNS response
Posterior stimulation	· SNS response o Effect via hindbrain (e.g. RVLM) and spinal cord (intermediolateral horn) o Organ-specific projections: e.g. skeletal muscle vs skin vs splanchnic o Stimulation by ARAS maintains wakefulness

· Anterior stimulation (depressor area) -> PSNS response

· Posterior stimulation -> SNS response

o Effect via hindbrain (e.g. RVLM) and spinal cord (intermediolateral horn)

o Organ-specific projections: e.g. skeletal muscle vs skin vs splanchnic

o Stimulation by ARAS maintains wakefulness

Endocrine function:

Via posterior pituitary	· Releases into infundibulum from the SON and PVN: o ADH -> water retention, vasoconstriction o Oxytocin -> myometrial contraction in labour, behavioural effects
Via anterior pituitary	· Secretes into hypophyseal portal system o CRH -> ↑ACTH -> ↑cortisol -> stress response o TRH -> ↑TSH -> thyroid hormones -> metabolic homeostasis o GHRH -> ↑GH -> ↑IGF -> tissue growth, metabolic effects o GnRH -> ↑FSH, LH -> reproductive function o ↓Dopamine -> ↑PRL -> lactation (note negative feedback from pituitary hormones and target organ-derived hormones)

Other specific homeostatic functions:

Temperature	· Senses temperature (anterior); controls set point (posterior); responds outside inter-threshold range · Anterior stimulation (pre-optic nuclei): triggers autonomic and behavioural heat loss responses (e.g. sweating, cutaneous vasodilatation) · Posterior stimulation (tuberal nuclei): triggers autonomic and behavioral heat gain and conservation responses (e.g. shivering, cutaneous vasoconstriction)
Water	· Paraventricular region: contains a thirst centre activated by hypertonicity, hypovolaemia, dry mouth, other o ↑ADH synthesis o ↑Thirst -> water-seeking · Contains internal osmoreceptors: supraoptic (and paraventricular) nuclei · Receives input from external osmoreceptors: SFO, OVLT
Food	· Ventromedial: senses [glucose], induces satiety · Lateral: induces hunger and food-seeking
Sleep-wake	· Suprachiasmatic nucleus: generates circadian rhythm (input from photosensitive cells) VLPO nuclei vs brainstem ARAS: the awake-NREM flip-flop
Emotion	· Well connected to other limbic structures (e.g. limbic lobe, amygdala, hippocampus) · Mediates emotional expression via autonomic and somatic nervous systems · Defence area: anterior perifornical region o Activated by the limbic system o Stimulation -> ↑HR, ↑BP, vasodilatation of skeletal muscle arterioles, splanchnic and renal vasoconstriction o i.e. fight-or-flight response · Depressor area: anterior region o Stimulation -> ↓HR, ↓BP o ?Accompanies the ‘playing dead’ response in some young animals
Sexual function	· By control of pituitary hormones: onset of puberty; menstrual cycle · Medial region control sexual behaviour