94. Das somatosensorische Nervensystem: Rezeptoren
Charakterisieren Sie die somatosensorischen Rezeptoren anhand ihrer 1.
Modalitat (Mechano-,Thermo-,Nozizeptoren), 2. Quelle des Stimulus
(Extero-,Proprio-,Interozeptoren) und 3. histologischen Struktur
(korpuskulare Nervenendigungen, freie Nervenendigungen). Beschreiben
Sie die Mechanorezeptoren der Haut und ihre Funktionen: Vater-Pacini-
Korperchen, Meissner-Korperchen, Ruffini-Korperchen, Merkel-
Korperchen, freie Nervenendigungen.
Was ist ein Dermatom? Erklaren Sie wie diese am Kopf und Korper
verteilt sind.
Erlautern Sie die Grundlage der somatosensorischen rezeptiven Felder.
Inwiefern steht das Konzept des Dermatomes mit diesen rezeptiven
Feldern in Zusammenhang?
Definieren Sie die Termini Rezeptorsensitivitat, Rezeptorspezifizitat und
rezeptives Feld. Erklaren Sie inwiefern die Dichte der peripheren
Innervation mit der Große des rezeptiven Feldes korreliert.
Definieren Sie schnelle und langsame Adaptation der sensorischen
Rezeption.
95. Das somatosensorische Nervensystem: die Hinterstrangbahn
Beschreiben Sie die Untergruppen der somatischen Sensibilitat, welche durch das
lemniskale System bedient werden.
Listen Sie die Anteile des lemniskalen Systems und ihre trigeminalen Analoga auf.
Erklaren Sie die funktionellen Bestandteile des lemniskalen Systems.
Erlautern Sie die topographische Representation des Korpers in Hohe der Kerne im
Hinterstrang, im ventrobasalen Thalamus und im somatosensorischen Kortex.
Was ist die Zwei-Punkt-Diskrimination? Erlautern Sie wie diese mit der peripheren
Innervationsdichte und der Große des rezeptiven Feldes zusammenhangt.
Nennen Sie die Faktoren, welche fur die sehr hohe Tastscharfe der Hande und des
Gesichtes verantwortlich sind.
Was sind die Anzeichen und Symptome einer Dysfunktion des lemniskalen Systems?
Wie wird durch die laterale Hemmung die Zwei-Punkt-Diskrimination verbessert?
Erklaren Sie wie sich die Dichte der peripheren Innervation, in der Große des
respektiven reprasentierenden Feldes im Gyrus postcentralis widerspiegelt.
Was ist mit feinem Tastsinn gemeint? Nennen Sie die einzelnen Nerven und
Verbindungen, von der Peripherie bis zur Hirnrinde.
Das somatosensorische Nervensystem
Sehen
Gehor
Gefuhl
(Tastsinn)
Geschmack
Riechen
Aristoteles:
Die funf Sinne
:
THEORIEN ÜBER DIE FUNKTION
DES SOMATOSENSORISCHEN SYSTEMS
SPEZIFICITĀTSTHEORIE
THEORIE VON HENRY HEAD
”PATTERN” THEORIE
Gesetz der spezifischen Sinnesenergien
PHOSPHENE
Punktförmige Repräsentation der Rezeptoren/sensorisches Mosaik
Sir Henry Head (1861 to 1940)
Sir Henry Head's experiments increased our understanding of
the sensory system and enhanced our ability to examine
it.[5,37-41] Frustrated with the inconsistent reports of
patients with sensory loss, he performed his most famous
experiment in which he severed his own radial nerve and
documented the return of sensory modalities.[5,42] This
experiment, however, was not his major contribution to our
understanding of the sensory examination. After years of
experiments on sensory nerves, Head began to piece together
a possible organization for the sensory afferent system. He
divided the peripheral nervous system into three distinct
sensibilities: deep, protopathic, and epicritic. He described
deep sensibility as being served by fibers that ran mainly with
muscular nerves. They were concerned with pressure stimuli
as well as with joints, tendons, and muscle movement.
Protopathic sensibility was described as that which was
"capable of responding to painful cutaneous stimuli and
extremes of heat and cold."[5] Protopathic pain was
generated in the posterior nerve root and exhibited the highest
threshold for a pain response with poor localization, failure to
adapt, and intense response to stimulation. Epicritic
sensibility was the ability to discriminate between two
points and to recognize fine grades in temperature change.
Head believed it was more precisely tuned than protopathic
sensation. Head correctly surmised that epicritic pain fibers
were distributed throughout the peripheral nervous system and
had slower regeneration times.[5,43-45] Henry HEAD
1861-1940
HENRY HEAD:
PROTOPATHISCHE,
EPIKRITISCHE und
TIEFSENSIBILITÄT
In einem Selbstversuch untersuchte Head
die Ruckkehr der Sensibilitat der Haut
nach Durschneiden des n. cutaneus
antebrachii lateralis.
ÜBERTRAGENER
SCHMERZ REFERRED PAIN
A
[Head zones]
(Invest Opbthahnol Vis
Sd. 1999;4O:513-519)
Corneal sensations result from the activation of sensory
nerve afferents, which are the peripheral branches of various
types of trigeminal nociceptive neurons. In the cat's eye, some
of the corneal sensory nerve fibers (approximately 20%) are
activated only by mechanical forces and are called mechanosensory.
The majority of corneal nerve fibers (approximately
70%) also respond to chemical irritants and to noxious heat
and thus are classified as polymodal nociceptive fibers. Finally,
a small group (approximately 10%) respond preferentially to
cooling of the corneal surface and are called "cold" fibers (for
review see Ref. 6).
Innervation der Cornea:
nur C-Fasern
Humán cornea szenzitivitás
(Invest Ophthalmol Vis Sci. 2001;42:2063–2067)
METHYLÉNKÉK
VITÁLFESTÉS Hasonló morfológiájú, de funkcionálisan különböző receptorok.
identified in more than 70% of the cases. The incidence ofcorrect identification was slightly lower for heat stimuli.Mechanical stimuli were confounded with other types ofstimuli in about half of the trials.
Correlation between sensation parameters and single-fibre activity
Table 2 compares the stimulus intensities necessary toexcite primary corneal sensory units in the cat (firing
M. C. Acosta, C. Belmonte and J. Gallar520 J. Physiol. 534.2
Table 1. Percentage of correct identification of the stimulus modality applied to the humancornea
Stimulus reported
Stimulus No stimulusapplied Mechanical Chemical Heat Cold or undefined
Mechanical 47 ± 7% 17± 7% 17± 8% 19± 9% 0%Chemical 8± 4% 75 ± 7% 17± 7% 0% 0%Heat 3± 3% 31± 9% 64 ± 9% 0% 3± 3%Cold 11± 7% 17± 7% 0% 72 ± 10% 0%Sham 0% 6± 6% 6± 6% 0% 88 ± 7%
Data are means± S.E.M. of the percentage of correct identifications determined in 9 subjects.
Table 2. Sensation threshold in human and firing threshold of corneal units in the cat
Human Cat
Stimulus Sensation Polymodal Cold-sensitiveapplied threshold Mechanosensory units units
Mechanical (ml min_1) 79± 5 109± 24(23%) 79± 9(60%) 62± 8(25%)Chemical (%CO2) 21± 3 (3%)† 34± 3 (54%) 21± 4 (80%)Heat (°C) +1.2± 0.2 (4%)† +2± 0 (36%) (_60%)*Cold (°C) _2.4± 0.4 (4%)† _2.7± 0.8 (9%) _1± 0 (100%)
Data are means± S.E.M. Percentage of corneal sensory units recruited by each type of stimulation is alsoshown in parentheses. Data correspond to units that changed their basal firing frequency by more than30% in response to at least one-third of the pulses of each modality.* Percentage of units that reducedtheir firing discharge during application of heat stimuli. †For values below 5% thresholds were notcalculated.
Figure8. Correlation between VAS ratings in humansand impulse response of corneal units in cats
A, mechanical stimulation. B, cold stimulation. Data wereobtained using an identical stimulation protocol for thepsychophysical and the electrophysiological experiments.Pearson’s correlation and linear regression (continuouslines) were statistically significant.
(Journal of Physiology (2001), 534.2, pp.511–525)
NAFE (1934): “PATTERN” THEORIE”
Lele, Weddel: Untersuchungen an der corneale Sensibilitat:
identische Morphologie – unterschiedliche Funktion
ARANYKLORID
IMPREGNATIO
Sensations evoked in the cornea by selective mechanical, chemical, heat
and cold stimulation always presented an irritation component
MECHANOREZEPTION (TASTSINN)
[Asphyxie, Kaltblock, Kokain]
Tastsinn
Schwelle: 5-10 mg/10m
Rezeptivfelder: mm2-cm2
Zweipunktschwelle 0,9 - 40 mm
Innervationsdichte
Orientierung
Applikation der Reize:
simultan < nacheinander
Rezeptive Felder: mm2-cm2
Zwei-Punkt-Schwelle:
Rucken: 40 cm, Hand 20 cm,
Fingerspitze, Zunge: 1-3 mm
˃
Pacini
Ruffini
Meissner
Merkel
Räumliches Auflösungsvermögen und Innervationsdichte
Braille : 600/min (100 Worter)
Ereignis-korrelierte Potenziale
NEUROLOGY 2000;54:2230–2236
Superior tactile spatial acuity in blind Braille readers
Propriozeption
Tiefsensibilität, kinaesthetische Sensibilität
Stellungssinn - Bewegungssinn - Kraftsinn
- Muskelafferenzen - Muskelspindeln
McCloskey - Dehnung durchgeschnittener Sehnen erzeugt
Illusionen von Gelenkbewegungen
- Mechanosensoren in den Gelenkkapseln (Ruffini)
- Hautrezeptoren
- Mechanosensoren der Sehnen
- Visuelle u. vestibulaere Informationen
Syphilis
Tabes dorsalis
Haptische Wahrnehmung
Wahrnehmung durch aktive Exploration im Unterschied zur taktilen
Wahrnehmung, bei der das wahrnehmende Subjekt passiv beruhrt wird.
Überstreichen der Oberflache
Konturen nachfahren
Umfassen
Gewicht-
Schatzung
tasten
Temperatur
Explorationsstrategien zur
Objekterkennung:
Hinterstrangsystem (Lemniscus medialis)
Dermatom
Somatotopie
Modalitaetsspezifizitaet einzelner Neuronen ist erhalten
(Hinterstrangkernen, Thalamus, Kortex)
Laterale Hemmung - Kontrastverschaerfung
Kleine rezeptive Felder (distal kleiner)
Laterale Hemmung - Kontrastverschaerfung
Eigenschaften der lemniscalen VB Neurone:
Somatotopie
Kleine, kontralateral gelegene (gekreuzter Eingang)
rezeptive Felder mit Zentrum-Umfeld Organisation
Modalitats-spezifisch, Eingang nur von einem Rezeptortyp
(Druck, Beruhrung, Glenkstellung)
Eingange von Hinterstrang Kernen
Projektion nur zu SI und SII
François Magendie
(1783-1855)
Sir Charles Bell Bell-Magendie Gesetz
Syphilis
Tabes dorsalis
KAHLER-
REGEL
LEMNISCUS
MEDIALIS
LEMNISCUS
TRIGEMINALIS
Die Verarbeitung mechanorezeptiver Information im ZNS
LEMNISCUS MEDIALIS und LEMNISCUS TRIGEMINALIS
Dermatom (griech. derma „Haut“, tomus „Schnitt“):
das von einem Ruckenmarksnerven (Spinalnerven)
innervierte segmentale Hautgebiet.
Methode zur Bestimmung des Dermatoms:
* antidrome Vasodilatation
* Herpes Zoster (Gurtelrose)
* Denervation/Schadigung einzelner Hinterwurzel (”spared root”)
("ersparte Wurzel")
DERMATOM
segmentale Hautgebiet innerviert
von einer Hinterwurzel
peripheres
Nerv
Hinterwurzel
HERPES ZOSTER BEGRENZT AUF EINEM
DERMATOM
UNEMPFINDLICHE HAUTGEBIETE NACH
DORSALER RHIZOTOMIE
Dermatom: klinische Bedeutung : topographische Diagnose
C2
“Diskushernie”
Dermatom: klinische Bedeutung : topographische Diagnose
herpes zoster
übertragener
Schmerz
LATERALE HEMMUNG
Kontrastverscharfung
LATERALE HEMMUNG
Zwei-Punkt-
Diskrimination
exakte
Lokalisation
Kante
KORTIKALE LOKALISATION
FRENOLOGIE, [1825]
Franz Joseph GALL, (1758–1828)
J. C. Spurzheim (1776–1832)
Korbinian Brodmann
1868-1918
Paul Broca
1824-1880
Wilder Penfield
1891-1976
Carl Wernicke
1848-1904
Pierre Paul BROCA
Motorische Sprachregion, 1861:
„Nous parlons avec l’hemisphere gauche”
Broca-Areal: Area 44, 45
(motorische Aphasie)
Karl WERNICKE, 1867
Sensorische Sprachregion
Wernicke-regió: Areal 22
(sensorische Aphasie)
Korbinian BRODMANN, 1909
Zytoarchitektonischer Aufbau der Grosshirnrinde: 52 Areale
PET-AUDIO PET-VISUAL
First functional map of the human
cerebral cortex, outlining the areas of
the brain which produce movements
and auras. (Foerster & Penfield, 1930)
Sketch of a patient's brain, annotated throughout the
operation, to show the areas of motor and
somatosensory cortices which elicit movements of, or
sensations in, the mouth and lips. (Penfield &
Boldrey, 1937).
PENFIELD IN SHERRINGTON’S
LABORATÓRIUM IN LONDON
(operiert von
Herbert Olivecrona,
1936)
Wilder Penfield:
Kortikale Lokalisation
Reise um meinem Schadel
The first patient’s-eye-view
account of a brain operation in
medical history…remarkable.
— Time
[Karinthy] possesses the sharp
and biting satire of Voltaire; the
provocative doubt of Shaw; the
poetic fantasy of Maeterlinck.
Karinthy is a universal literary
genius: playwright, humorist,
poet, novelist, critic, essayist,
literary caricaturist, etc…He has
that rare ability of our own
Charlie Chaplin, in that whatever
he attempts to do, he can make
us feel that he is a genius.
— Los Angeles Times
The distinguished Hungarian author Frigyes Karinthy
was sitting in a Budapest café, wondering whether to
write a long-planned monograph on modern man or a
new play, when he was disturbed by the roaring—so
loud as to drown out all other noises—of a passing
train. Soon it was gone, only to be succeeded by
another. And another. Strange, Karinthy thought, it
had been years since Budapest had streetcars. Only
then did he realize he was suffering from an auditory
hallucination of extraordinary intensity.
What in fact Karinthy was suffering from was a brain
tumor, not cancerous but hardly benign, though it
was only much later—after spells of giddiness,
fainting fits, friends remarking that his handwriting
had altered, and books going blank before his eyes—
that he consulted a doctor and embarked on a series
of examinations that would lead to brain surgery.
Karinthy’s description of his descent into illness and
his observations of his symptoms, thoughts, and
feelings, as well as of his friends’ and doctors’ varied
responses to his predicament, are exact and
engrossing and entirely free of self-pity. A Journey
Round My Skull is not only an extraordinary piece of
medical testimony, but a powerful work of
literature—one that dances brilliantly on the edge of
extinction.
DIE GRÖSSE DER KORTIKALEN REPRESENTATION IST
DER REZEPTORENDICHTE ABHĀNGIG
Kortikale Representation
SENSORISCHER
HOMUNCULUS
Homonculus vs Hermunculus
Models of sensory and
motor homunculi at the
Natural History Museum
in London.
Somatotopie
medio-lateral
Modalität
antero-posterior
S I - kontralateral
S II - kontralateral u. ipsilateral
Area 3a - Muskelspindelrezeptoren
Area 3b - SA Mechanorezeptor
Area 1 - RA Mechanorezeptor
Area 2 - Gelenke, Periosteum, Fasciae
DER KOLUMNARE AUFBAU DES
SOMATOSENSORISCHEN CORTEX
Area 3a, 3b:
receptorspecifsche Neurone
Area 1, 2:
komplex Neurone
(ergreifen eines Objektes,
Bewegung auf der Hautoberflaeche)
Mountcastle, Brain (1997), 120, 701–722
ENTDECKUNG DES KOLUMNAREN AUFBAUS DES
SOMATOSENSORISCHEN CORTEX (1955)
Vernon B. Mountcastle (1918-)
The Brain Voyager , "the Jacques Cousteau of the cortex."
More than a half-century has passed, but revered neuroscientist Vernon Mountcastle
recalls his most celebrated moment of discovery with perfect precision. It was when he
determined that the brain, unlike any other part of the human body, is divided into
magnificent little subunits—or columns—each with its own specific role.
On that day in 1955, Mountcastle—who received his M.D. from the School of
Medicine in 1942 and went on to direct physiology from 1964 to 1980—was studying
the results of tests on the brains of cats, recording the character of each cell from
successive penetration layers. “I was writing them down vertically on a yellow piece
of paper,” he recalls. Suddenly the vertical notetaking helped him see the stunning
pattern in the brain: Skin cells lay atop skin cells, joint cells atop joint cells and so
on, extending in columns from the brain’s surface all the way down through six
layers of cortex. “That was my ‘aha’ experience,” he says.
Mountcastle’s revelations forever changed his field: Before his breakthrough,
researchers had believed that brain cells were organized randomly, with each layer of
the cortex having a specific function.
David Hubel in his Nobel Prize acceptance speech said
Mountcastle's "discovery of columns in the somatosensory
cortex was surely the single most important contribution to
the understanding of cerebral cortex since Ramón y Cajal.”
Jeff Hawkins in his book On Intelligence describes
Mountcastle's 1978 article, An organizing principle..., as "the
rosetta stone of neuroscience”.
[Mountcastle, V. B. (1978), "An Organizing Principle for
Cerebral Function: The Unit Model and the Distributed
System”]
Somatotopie: Hinterstrangskerne
und Thalamus
Plastizitaet im somatosensorischen Cortex nach
der Amputation des dritten Fingers
Mikrostimulation kutaner rezeptiver Felder mit vibro-tactilen Reizen
Kortikale Aktivation durch Mikrostimulation kutaner rezeptiver Felder mit vibro-tactilen Reizen:
fMRI-Untersuchungen (Funktionelle Magnetresonanztomographie)
Kortikale Aktivation infolge der Stimulation kutaner rezeptiver Felder
mit vibro-tactilen Reizen: fMRI-Untersuchungen
Journal of Neurophysiology 80, 1998, 1533-1546
Karen D. Davis1, 3, Chun L. Kwan1, 3, Adrian P. Crawley2, and David J. Mikulis2, 3
THALAMUS S II
SII
VPL S2
VPL
Kortexlaesionen SI: Erkenntniss von Form und Gestalt gestört
Kugel: Differenzlimen: intakt: 1.1 mm
laediert: 12 mm
Kugel vs Ellipsoid: intakt: 28 mm vs 27.5 x 30
laediert: 21 x 50 mm!
Schaedigung des Zwei-Punkt-Diskriminationsvermögens
Astereognosie (Tastblindheit)
Störungen der Vibrationssensibilitaet
verminderter Tastsinn
Schmerz- u. Temperatursinn bleiben intakt
Brodmann Area 5: Parietaler Assoziationscortex:
Störungen der Stereognosie