U1iv / 23A16 / 18A20: Outline the structure (20 marks) & function (80 marks) of the hypothalamus

23A16: Exam Report

Outline the role of the hypothalamus.

29% of candidates passed this question.

This question required candidates to integrate parts of the syllabus that are often not presented together in the reference texts.

Many candidates provided only an incomplete list of the roles of the hypothalamus as their answer which did not score enough marks to pass. Additionally, presenting information succinctly and in a format that demonstrated an understanding of priority of function with respect to the CICM syllabus, was critical for time management and ensuring that more the important/major roles were presented in more detail.

This question required candidates to cover roles including autonomic control, thermoregulation, hormonal regulation, body rhythms and regulation of drives with feedback control mechanisms where appropriate.

Those who scored well demonstrated a comprehensive breadth of knowledge of these areas as well as giving the pertinent points around areas of positive and negative feedback and the sensor areas and effector responses required to answer an outline question.

18A20: Exam Report

Outline the structure (20% of marks) and function (80% of marks) of the hypothalamus.

21% of candidates passed this question.

Most candidates understood the endocrine functions of the hypothalamus, and to some degree its interactions with the pituitary. Fewer candidates mentioned the importance of the hypothalamus as an integrator for the autonomic nervous system, or its roles in arousal/emotions.

Many candidates had only a vague idea of the structure of the hypothalamus, while the best candidates were able to relate function to structure quite accurately.

U1iv / 23A16 / 18A20: Outline the structure (20 marks) & function (80 marks) of the hypothalamus

Definition

The hypothalamus is a functionally diverse region of the forebrain

Structure

  • Very small, almond shaped, 4g
  • Lies below thalamus & above pituitary gland
  • One of the 4 major components of the Diencephalon
    • Thalamus
    • Hypothalamus
    • Subthalamus
    • Epithalamus
  • Organised ANT → POST & MEDIAL → LATERAL

Anterior –> Posterior

Hypothalamic Nuclei
  • Preoptic region: medial & lateral preoptic nuclei
  • Supraoptic region
    • Suprachiasmatic nuclei
    • Paraventricular nuclei
    • Anterior hypothalamic nucleus
    • Supraoptic nucleus
  • Tuberal region
Nucleus
  • Mammillary region: posterior hypothalamic nucleus & mamillary body

Function

Hypothalamus is centre for neural & endocrine control of internal organs

1) Direct Control of ANS

  • Parasympathetic effects → anterior region
  • Sympathetic effects → posterior region
    • Controls vasomotor centre
    • VC response to cold
    • CV centre in PONTINE & MEDULLARY RETICULAR FORMATION
  • Thermoregulation → preoptic region
    • Controls body temp
    • Senses ∆ temp of blood to regulate thermostat

2) Hormonal Control Of Pituitary System

  • Direct connection → sends hormones to PPG for storage & release; ADH & Oxytocin
  • Indirect → sends hormones to the APG to regulate the production & release of LH, FSH, ACTH, TSH
  • OSMORECEPTORS in Supraoptic Nucleus → control ADH release
  • Paraventricular Nucleus → releases Oxytocin to Mammary gland

3) Communicates with Limbic System & Midbrain

  • Circadian rhythms
    • Mamillary body regulates wakefulness & arousal
    • Stimulation of anterior hypothalamus can induce sleep
    • Normal circadian rhythm reset by retinal input (normally 24hrs)
  • Hunger & satiety
    • Ventromedial nuclei inhibit appetite by sensing BGL
    • Lateral hypothalamus → seeks food
  • Thirst
    • Lateral hypothalamus → seeks food + H2O
  • Emotions
    • Fear, rage, aversion, pleasure, reward

III. Pathways and Nuclei

Function

Autonomic Nervous System

Pathway

Dorsal Longitudinal fasciculus

Afferents

Nucleus of tractus solitarius→parabrachial nucleus (taste, pain, general visceral sensation)

Nuclei

Periventricular Posterior

Efferents

Midbrain central gray

Ventral tegmental area (DA)

Medulla, autonomic centers

Braintem

Sympathetic and paras of spinal cord=hypothalamo-spinal tract

Function

Pertuitary Endocrine Function

Pathway

Supraoptico-hypophyseal tract

Tuberoinfundibular tract

Afferents

Receptors responsive to physiological state – feedback

Nuclei

Praventricular Supraoptic (magnocellular)

Arcuate (Parvocellular)

Efferents

Supraoptico-hypophyseal tract → post, pituitrary capillaries (rel ADH, OXT)

Tuberoinfundibular tract → Median eminence → hypophys portal vein (release / rel-inhib factors to anterior pituatary)

Function

Circadian Rhythms

Pathway

Retinohypothalamic fibers

Afferents

Retinal ganglion cells (melanopsin-respons to light → Optic tract fibers

Nuclei

Suprachiasmatic

Efferents

Endogenous oscillator in SCN → normal circadian rhythms, reset by retinal input (normal 24.5 hrs)

Function

Species-preserving behaviors

*hypothal motivates, limbic system selects among them

Pathway

Medical forebrain bundle (MFB)

Mammilliary peduncle (MP)

Afferents

LMA incl VTA (info on species-preserving behaviors, rewarding properties of behav)

Periaqueductal gray of LMA (info abt pain, aversive stimuli)

Nuclei

LHA 

Ventromedial

Mammillary bodies

Efferents

Basal forebrain area, picks up fibers from LHA → limbic midbrain areas

Midbrain reticular formation

Function

Connections with higher cortex – limbic systen and prefrontal cortex

Pathway

  1. Fornix
  2. ventral amygdalofug
  3. Stria terminalis
  4. diffuse fibers
  5. mammilithal tract 
  6. MFB

Afferents

Hippocampus

Amygdala → basal forebrain

Amygdala

Basal forebrain

Nuclei

MMB and LHA

LHA

Periventricular

Periventricular

Mammillary bodies 

Entire hypothal

Efferents

Significance of events

Amygdala – signif of visc-sens

Amygdala

MD, intralam nuc (thal) → ant cing cx, prefrontal

Ant thal nuc →  entire cing cx

Telencephalic, midbrain limbic