visceral reflexes and “drive states”: autonomic nervous system · nervus vagus n. vagus (x....
TRANSCRIPT
1. PNS and the autonomic nervous system
- differences between the somatic
and the autonomic nervous system
- differences between the Sympathicus
and the Parasympathicus
2. Integration and control of the autonomic nervous system:
Hypothalamus
3. Drive states
Visceral reflexes and “drive states”: Autonomic
nervous system
Regulation of energy consumption and homeostasis,
largely involuntary „visceral reflexes“
- Sympathicus: often increasing energy consumption,
preparation for action, „fight and flight“
- Parasympathicus: often decreasing energy consumption,
regeneration, „rest and digest“
Sometimes antagonistic action in the same organ (heart,
lung), sometimes only one system (bladder)
Differences between the
autonomic and the somatic
system
I. Different anatomy of the
autonomic nervous system:
Production of a fine network in the
target organs („Plexus“)
II. Different target innervation:
No specialized pre- or
postsynaptic region but
swellings (varicosities) where
neurotransmitters are
released and diffuse over
some distances
No point-to-point contacts
but more diffuse control
Differences between the autonomic and the somatic
system
III. Presence of axo-axonic synapses between sympathic,
parasympathic and sympathic-parasympathic fibers
Differences between the autonomic and the somatic
system
IV. Different position of the neurons:
Cell bodies of the motoneurons are located outside of the spinal
cord in the autonomous ganglia
Differences between the autonomic and the somatic
system
Preganglionic neuron in
the spinal cord (lateral
horn of the thoracic and
lumbar region),
postganglionic neuron in
the autonomous ganglia
Anatomical distinction
according to the origin of the
neurons
- Sympathicus: Mostly middle
portion of the spinal cord
(thoracic and lumbar region)
- Parasympathicus: Medulla
(brain stem) and sacral spinal
cord
Differences between the
Sympathicus and the
Parasympathicus
Main nerve of the parasympathicus:
Nervus Vagus
N. vagus (X. brain nerve) is the only
brain nerve of the 12 cranial
nerves that does not only
innervate parts of the head
region
Distinction according to the neurotransmitter of the
neurons; in both systems usually chain of 2 neurons
- Sympathicus: 1st synapse acetylcholin, 2nd synapse
norepinephrin
- Parasympathicus: 1st and 2nd synapses acetylcholin
Preganglionic fibers of the
sympathicus: B-fibers
(myelinated) – speed of
conductance between the
C- and the A fibers
Differences between the Sympathicus and the
Parasympathicus
Integration and coordination of the autonomic nervous
system
Hypothalamus:
Part of the diencephalon (red)
Very small (4 g)
Contains many nuclei
Heavily connected with other brain regions
Brain region where peptidergic neurons are
most abundant
By hypothalamus and formatio reticularis (brain stem)
Input:
Several brain regions, i.e.,
- liquor-contact-neurons (sense
composition of the CSF)
- sensoric centers of the telencephalon
(information about environment)
- body hormones
Infundibulum
pituitary
gland
Hypothalamus
Hypothalamus controls endocrine system via the pituitary gland
(„Hypophyse“, „Hirnanhangdrüse“).
Pituitary gland consists of
- posterior pituitary gland („Neurohypophyse“
part of the brain) and
- anterior pituitary gland („Adenohypophyse“ gland)
Direct and indirect control
- Direct control: Neuroendocrine motoneurons from nuclei of the
hypothalamus project to posterior pituitary gland
Anterior pituitary
gland
Posterior pituitary
gland
Hypothalamus
Nucleus supraopticus
Nucleus paraventricularis
Indirect control:
Neurohormons from hypothalamus regulate secretion of hormones
from the anterior pituitary gland
No direct blood supply for the anterior pituitary gland by arteries
Local portal circulation ( „Portalgefäße“)
anterior pituitary gland
posterior pituitary gland
hypthalamus
Example how the system works: „Drive states“
Drive states: characterized by tension and discomfort due to a
physiological need followed by a relief when the need is
satisfied
Examples: hunger, thirst, sexual desire etc.
Important role of the hypothalamus: wide spectrum of
transmitters have strong effects on feeding behavior when
injected into the hypothalamus.
Norepinephrin: stimulates feeding, more carbohydrate than fat
Galanin: selectively increases ingestion of fat
Opiates: enhance consumption of protein
(D.E. Cummings and M.W. Schwartz (2003) Genetics and
Pathophysiology of Human Obesity. Annu. Rev. Med. 54:453-471)
Leptin in the regulation of anabolic and catabolic processes
(D.E. Cummings and M.W. Schwartz
(2003) Genetics and Pathophysiology of
Human Obesity. Annu. Rev. Med.
54:453-471)
Complex regulation of second order neurons
How does leptin work?
adipocytes
leptin
NPY Hypothalamic
neuron
Pituitary gland
- Increasing appetite
- Reducing metabolic rate
Arcuate nucleus
blood stream
Hypothalamic
neuron
leptin
db
blood brain barrier
First order neuron
(anabolic)
adipocytes
leptin
Hypothalamic
neuron
Pituitary gland
- Decreasing appetite
- Increasing metabolic rate
blood stream
Hypothalamic
neuron
leptin
db
blood brain barrier
First order neuron
(katabolic)
aMSH
How does leptin work – Part II ?
Ghrelin:
- synthesized by X/A-like cells in the stomach
- infusion of ghrelin stimulates feeding and obesity in rodents
- ghrelin leads to upregulation of NPY
The whole story?
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adipocytes
leptin
NPY Hypothalamic
neuron
- Increasing appetite
- Reducing metabolic rate
Arcuate
nucleus
blood stream
Hypothalamic
neuron
leptin
db
blood brain barrier
GHS-R
ghrelin stomach