Download Hypothalamus15

The Hypothalamus
A crucial part of the CNS that takes some part
in regulating most organs
• 3 major functions (we will review 2 today).
1.Regulating release of hormones from
pituitary gland.
2.Regulating the ANS; i.e., general visceral
motor functions we reviewed last time.
3.Regulating the “appetitive behaviours”
(eating, drinking, mating).
I.
II.
III.
IV.
V.
The 3 functional zones of the hypothalamus and
the nuclei contained therein.
Regulation of Pituitary: Parvocellular (anterior)
ad magnocellular (posterior) neurosecretory
systems.
Overview of ANS functional anatomy
(sympathetic, parasympathetic systems).
Regulation of autonomic functions by
descending projections from the hypothalamus.
Regional anatomy.
A. Anterior-posterior sections of hypothalamus and
review key nuclei.
B. Descending pathway and sc nuclei.
C. Clinical Note: Horner’s Syndrome.
I. 3 Functional Zones
• General location of hypothalamus:
- ventral to thalamus
- just over optic chiasm and pituitary
stalk (infundibulum).
- divided in half by 3rd ventricle
Hypothalamic Nuclei
Hypothalamus (Fig. 15-1, 2)
A. Periventricular zone
- a thin nuclei bordering the 3rd ventricle.
- regulates release of endocrine hormones from anterior
pituitary gland (See Table 15-1).
-uses neurosecretion as a portal vein system, rather than a
neurotransmitter across a synapse.
B. Middle zone
- regulates hormone release from posterior pituitary.
- regulates ANS.
C. Lateral zone
- integration and transmission of info from limbic system
structures (important in emotional regulation – will view
next lecture (limbic system).
3 Functional hypothalamic zones
(Fig. 15-14) – Mediolateral zones
Hypothalamic peptides for anterior pituitary
(Table 15-1)
II. Regulation of Pituitary: Parvocellular and
Magnocellular Neurosecretory Systems
A. Parvocellular system and the anterior pit.
- Small-diameter neurons in several
hypothalamic nuclei (of periventricular
zone) – most medial – regulate anterior
pituitary hormone release by neurovascular
rather than synaptic transmission.
Parvocellular System (Fig. 15-4A)
Note the various nuclei
Neurosecretion and Portal Vein System
(Fig. 15-5):
Note the path:
Parvocellular
neurosecretory
cells  anterior lobe
via portal vein.
Chemicals released
are peptides, which
either promote or
inhibit the release of
hormones from
anterior lobe
secretory cells
(Table 15-1).
B. Magnocellular system and the posterior
pituitary.
- Here, peptide hormones are produced by
large-diameter hypothalamic neurons from
same nuclei of the middle zone.
- Axons deliver these hormones down the
infundibular stalk and terminate on
fenestral capillaries (“leaky”) of the
posterior pit - this is 1 place lacking a
BBB.
Magnocellular System (Fig. 15-4B)
Hormones:
Vasopressin (ADH) –
peptide which incr bp by its
effects on vascular
smooth muscle as well as by
promoting H2O reabsorption
from DCTs of kidneys to
decr urine vol.
Oxytocin – incr uterine
contraction and milk ejection
from mammary glands.
Note the paraventricular
and supraoptic nuclei
III. Overview of Autonomic Nervous
System
Sympathetic and Parasympathetic systems –
Fig. 15-7.
Clearly distinct anatomical locations of
preganglionic (central) neurons.
Sympathetic: T1  L3
Parasympathetic: brainstem nuclei (reviewed
last time): S2  S4 (sacral spinal cord).
Also different locations of post-ganglionic
neurons.
Fig. 15-7 – The ANS
• Sympathetic: peripheral ganglia located
relatively close to the spinal cord
(sympathetic trunk).
• Parasympathetic: peripheral ganglia located
close to target organs (i.e., terminal ganglia
of X).
• Note: organs distal to splenic flexure of
colon served by sacral parasympathetic
nuclei.
• For both systems, anatomical location of
central neurons is analogous.
• Sympathetic: intermediate zone of spinal
cord (intermediolateral cell column) – Fig.
15-9.
• Parasympathetic: the 4 spinal cord nuclei
reviewed last time (general visceral motor
column): III, VII, IX, X and in sacral sc
intermediate zone.
IV. Descending Projections from the
Hypothalamus Regulate Autonomic Functions
• See Fig. 15-9
Descending pathways
controlling autonomic
nervous system
(Fig. 15-9):
From middle functional
Zone: parasympathetic
n. (using ADH and oxytocin)
+ several other areas  bs
parasym n. (dorsal motor n.
of X) + preganglionic neurons
(both sym and parasym) of sc.
Fig. 15-8.
Note: Mechanism of regulation
Is very analogous to the way the
Cortex regulates descending
Motor pathways and motor
Neurons.
1 Difference: Visceromotor
Regulation involves the 2-neuron
Circuit (pre- and postganglionic)
Some bs n. also contribute to
autonomic system regulation:
-Solitary n  intermediolateral n.
(also known for chemosensory
mechs) - a tie between viscerosensory and visceromotor.
• Ventral lateral medulla - adrenergic
descending projections regulating bp.
• Postmedullary reticular formation - complex
“reflex” response involving both visceral
and somatic changes; e.g., startle  incr bp.
• Raphe nuclei – projections from
hypothalamus uses serotonin to  spinal
autonomous nuclei.
V. Regional Anatomy
A. Sections through the hypothalamus –
Schematic of major nuclei – Fig. 15-3.
Anterior hypothalamic section, showing
preoptic region – Fig. 15-10.
Fig. 15-3 – Major nuclei
Anterior hypothalamus – Fig. 15-10
Note the preoptic region
Paraventricular Nucleus – Fig. 15-11
This nucleus contributes to all 3 functions we have discussed:
1. Parvocellular division  anterior pituitary
2. Magnocellular division  posterior pituitary
3. Autonomic division  descending paths
Posterior Hypothalamus
Fig. 15-17. Section reveals mammillary bodies. These, along with
Lateral zone noted earlier, play important role in behavioural
Regulation and the limbic system.
B. Descending Pathways and Spinal Cord Nuclei
Mid-medullary Section
Descending fibres
In dorsolateral
tegmentum.
DLF also contains
ascending and
descending fibres
to hypothalamus.
Adrenergic cell group
in VL medulla –
analogous to intermediolateral location in sc.
1. Intermediolateral sympathetic
(preganglionic) nucleus in thoracic sc.
2. Parasympathetic preganglionic nucleus in
intermediate zone of sacral sc.
Spinal cord nuclei and paths:
Fig. 15-21
C. Clinical Note: Horner’s Syndrome –
damage to dorsaolateral pons/medulla or
any part of descending autonomic control
system  disturbance of sympathetic
functions: e.g., PICA occlusion.
- Pupillary constriction on same side.
- Partial drooping of eyelid.
- Decr secretory, incr warmth and redness on
same side of face.
- Decr sympathetic function and unopposed
parasympathetic function.