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?

GSSFLSPEHQRVQQRKESKKPPAKLQPR

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