CHAPTER 3 SENSORY SYSTEMS. Disorders of sensory systems. Deficits Sensory organ Sensory nerves Central nervous system Hyperactivity Central neuropathic pain Tinnitus Tingling Normal response that is redirected Pain from touch Dizziness and vertigo from head movements. - PowerPoint PPT Presentation
CHAPTER 3SENSORY SYSTEMS
Disorders of sensory systems• Deficits
– Sensory organ– Sensory nerves– Central nervous system
• Hyperactivity– Central neuropathic pain– Tinnitus– Tingling
• Normal response that is redirected– Pain from touch – Dizziness and vertigo from head movements
Disorders of sensory systems
• Reduced sensitivity– Hearing loss– Visual impairment
• Incorrect response– Hyperacusis– Distorted sounds– Allodynia– Hyperpathia
Disorders of sensory systems
• Impaired conduction of the physical stimulus to the receptors
• Impaired function of receptors
• Impaired function of sensory nerves
• Impaired or changed function of the central nervous system
Reduced sensitivity
• Often caused by disorders of the sense organs
• Injury to afferent nerves
Hyperactive sensory disorders
• Increased sensation of physical stimuli
• Altered sensation of physical stimuli
• Sensation without any physical stimulation
General organization of sensory systems
• Conduction of the physical
stimulus to the receptors
• Sensory receptors
• Sensory nerves
• Central nervous system
Sensory transduction
• A physical stimulus generates a receptor potential
• The receptor potential is a graded potential
• The receptor potential is conducted electrotonically to the spike generation site
Bipolar receptor cells (taste)
Initiation of nerve impulses
• Occurs at the first node of Ranvier
Two different types of receptors, with bipolar nerve fibers
Sensory transduction (mechanoreceptor in a muscle)
Central nervous system
HUMAN
Mouse
Chick
Cochlea
Reticularformation
Cochlearnucleus
MGB
Primary auditory cortex
Midline
Inferiorcolliculus
Ventralthalamus
AN LL
Auditory nervous systemAscending auditory pathways
From: Møller, 2005
Two different ascending sensory pathways have been identified:
• The classical systems
• The non-classical systems
From: Møller: Sensory Systems, 2003
Classical auditorypathways
Non-classical auditory pathways
Non-classical auditory pathways
Receive input from the somatosensory system
Use the dorsal part of the MGB
From: Møller, 2005
The classical ascending pathways
• The number of nuclei is different in different sensory systems
• Use ventral thalamic nuclei that project to primary sensory cortices
• Neurons processes only input from of one sensory modality
Midline
LGN
Primary visual cortex
LGN
Primary visual cortex
Thalamus
Retinalganglion cells
Retinalganglion cells
SCN andhypothalamus
Pretectalnucleus
Superiorcolliculus
Externaleye muscles
Thalamus
Thalamus
Pulvinar
Lightreflexes
Other regionsof the CNS
Extrastriatecortex
A B
From: Møller, 2005
Visual systemClassical ascending pathways Non-classical ascending pathways
The nonclassical pathways
• Use dorsal and medial thalamic nuclei that project to secondary cortices and to other parts of the CNS
• Receive input from more than one sense
Fig 3.3
Reticular formation
Thalamusventral
Limbic system Association cortex
Anteriorlateral tract
Mediallemniscus
Thalamusdorsal
SII
AROUSAL
"WHERE""WHAT"
Pain pathways
cortex SI
Somatosensory pathways
Classical pathways Non-classical pathways
From: Møller, 2005
Trigeminalganglion
Thalamus
Cerebralcortex
Motornuclei
RF
Brainstem
Midbrain
Spinalcord
Processing after primary sensory cortices
• Integration of input from different sensory systems occurs in association cortices
• Parallel processing• Stream segregation
The neocortex has six layers
Simplified diagram of the connections to and from the different layers of the cerebral cortex
From: Møller: Sensory Systems, 2002
Maps
Tonotopic
Somatotopic
SURFACE VIEW
LOWER BODY IS REPRE-SENTED NEAR THE MIDLINE
Tonotopic organization in the CN of a cat, as an example of tonotopic organization in the auditory system
Tonotopic organization in the CN of a cat, as an example of tonotopic organization in the auditory system
Parallel processingStream segregation
Parallel processing:Cochlear nucleus
Function of sensory nervous systems
• Processing of sensory input at the peripheral level– Convergence (spatial integration)– Interplay between inhibition and excitation
Spatial integration: Receptive field of a dorsal column nucleus cell
Convergence of input to a secondary neuron
Lateral inhibition
Central processing of sensory information
• Each stage enhances or suppress specific Information
Parallel processing:The same information is
processed in different structures
Stream segregation:Different kinds of information is processed in different structures
(“What” and “Where”)
Processing after primary sensory cortices
• Integration of input from different sensory systems occurs in association cortices
From: Møller: Sensory Systems, 2003
Stream segregation Cortical circuitry
Dorsal stream“where”
Ventral stream“what”
Sensory information can reach other regions than sensory
regions
Motor systems
Memory
Emotional brain (limbic system)
Fig 3.7
DorsalmedialMGB
AII
VentralMGB
Thalamus
AAF
Endocrine
Behavioral
Autonomic
AI
ICXDC
ICC
Amygdala
Associationcortices
AL ABL ACE
Nucleusbasalis
Arousaland
plasticity
Cortex
"High Route"
"Low Route"
Polymodalassociation
cortex
Other corticalareas
From: Møller, 2005
Two different routes to the Amygdala from a sensory system
From: Møller: Sensory Systems, 2003
Connections from a sensory system to the amygdala “the high route”
Connections from a sensory system to the amygdala “the low route”
From: Møller: Sensory Systems, 2003
From: Møller: Sensory Systems, 2003
Connections from the amygdala
Hypoactive sensory disorders
• Loss of sensitivity– Hearing loss– Poor vision– Numbness– Loss of vestibular (balance) function
Frequency in kHz
0.250.125 0.50.75 1 1.5 3 4 6 82
10
-10
20
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HE
AR
ING
LE
VE
L A
T 4
kH
z
NOISE IMMISSION LEVEL
Courtesy of M. Charles Liberman
Genetic, epigenetic and environmentalCauses (and a stochastic component ?)
Age-related hearing loss
10
Left Ear
4000 Hz. Women
Right Ear
20
30
40
50
60
70
80
90
100
0-9 20-29 40-49 60-69 80-8910-19 30-39 50-59 70-79 90-99dB
Number
10
Left Ear
4000 Hz. Men
Right Ear
20
30
40
50
60
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80
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100
0-9 20-29 40-49 60-69 80-8910-19 30-39 50-59 70-79 90-99dB
Number
Normal variations in hearing loss of 70 year old individuals
N=179
Men 70 years old
25
50
75
100
≥92%76-88%<76%<48% deaf
%
N=197
Women 70 years old
25
50
75
100
≥92%76-88%<76%<48% deaf
%
Left EarRight Ear
Left EarRight Ear
Variations in speech discrimination in 70 year old individuals
10
-10
20
30
40
50
60
70
80
90
100
110
Frequency in kHz
0.250.125 0.5 0.75 1 1.5 3 4 6 82
Hearing loss in Ménière's disease
I: Pre-op Discr.=96% ASII: 5 days post-op Discr.=0% AS
II
I
Frequency in kHz
0.250.125 0.50.75 1 1.5 3 4 6 82
10
-10
20
30
40
50
60
70
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I: Pre-op Discr.=80% ASII: 7 days post-op Discr.=30% AS
II
I
B
A
Frequency in kHz
0.250.125 0.5 0.75 1 1.5 3 4 6 82
10
-10
20
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Effect of surgical injuries to the auditory nerve:
Large decrease in speech discrimination
Hyperactive sensory disorders
• Tinnitus
• Paresthesia
• Phosphenes
• Phantom sensations
• Central neuropathic pain
Subjective and objective tinnitus
• Different forms of tinnitus have very different effects on an individual’s life
Similarities between chronic pain and severe tinnitus
There are many forms of tinnitus
• Mild tinnitus:
Does not interfere noticeably with everyday life• Moderate tinnitus:
May cause some annoyance and may be perceived as unpleasant • Severe tinnitus:
Affects a person’s entire life in major ways
Patients’ own perception varies between mild, moderate and severe (disabling)
Important to have words for disorders
• We cannot think about matters that do not
have names
• The same words is used to describe very different forms of tinnitus and pain
• Using the same names for fundamentally different disorders is a disadvantage in treating these disorders
How prevalent is severe tinnitus?
Some statistics show 50 million people
have tinnitus in the USA
The prevalence of severe (bothersome) tinnitus is infrequent at young age; it reaches 12-14% for people at age 65 according to one study
How prevalent is severe pain?
Some pain was reported by 86% of
individuals above the age of 65(Iowa study, 1994)
The prevalence of severe pain was 33% for people at age 77 and above (Swedish study, 1996)
Severe tinnitus affects a person’s entire life in major
ways
• Prevents or disturbs sleep
• Interferes with or prevents
Intellectual work
• Often accompanied by altered perception of sound
Severe pain affects a person’s entire life in major ways
• Prevent or disturb sleep• Interfere with or prevents intellectual work• May cause suicideMay involve limbic structures causing affective
reactionsOften accompanied by abnormal sensations
from touch
Severe tinnitus is often accompanied by altered
perception of sound
• Sounds are distorted
• Sounds have exaggerated loudness (hyperacusis)
• Sounds are unpleasant
• Sounds are painful and arouse fear (phonophobia)
Little is known about the cause of subjective tinnitus
• Noise exposure
• Ototoxic antibiotic
• Acoustic tumors
The sympathetic nervous system is involved in some
forms of severe tinnitus
Some forms of tinnitus
can be cured by sympathectomy
Deprivation of sound can cause changes in neural processing such as change in temporal integration
• Expression of neural plasticity
The anatomical location of the abnormality that cause chronic pain and tinnitus may be different from
that to which the pain or the tinnitus is referred
The abnormal neural activity that causes symptoms are not
generated at the location where the symptoms are felt
Examples:
• Phantom pain
• Tinnitus with severed auditory nerve
The tinnitus in some patients can be modulated by stimulation of
the somatosensory systems (such as by electrical stimulation
of the median nerve)“cross-modal” interaction
Non-classical auditory pathways
Receive input from the somatosensory system
Use the dorsal part of the MGB
From: Møller, 2005
Other signs of involvement of the somatosensory system
•Gaze related tinnitus
•Neck muscles and tinnitus
•TMJ and tinnitus
•Sensation of sound from touching the skin
Connections between spinal C2 segment and the dorsal
cochlear nucleus
Can explain why electrical stimulation of the skin behind the
ears can modulate tinnitus
Symptoms and signs of neuropathic pain
and severe tinnitus
• Strong emotional components
• Depression
• High risk of suicide
Severe tinnitus is often associated with affective (mood) disorders
• Depression
• Phonophobia
The amygdala is involved in fear and other mood disorders
Connections from the auditory system to the amygdala
• Cortical-cortical connections (the “high route”)
• Subcortical connections
(the “low route”)
Fig 3.7
DorsalmedialMGB
AII
VentralMGB
Thalamus
AAF
Endocrine
Behavioral
Autonomic
AI
ICXDC
ICC
Amygdala
Associationcortices
AL ABL ACE
Nucleusbasalis
Arousaland
plasticity
Cortex
"High Route"
"Low Route"
Polymodalassociation
cortex
Other corticalareas
From: Møller, 2005
CONCLUSION
ACTIVATION OF NON-CLASSICAL ASCENDING SENSORY PATHWAYS CAN CAUSE SYMPTOMS AND SIGNS OF SEVERAL DISEASES
Neural plasticity play greater role in generating symptoms and
signs than previously assumed
• Plastic changes are reversible
• Treatments without medicine and surgery may alleviate pain and tinnitus
Therapy
There is no treatment for tinnitus that is comparative to common pharmacological treatment of pain. Treatment of tinnitus has been mainly benzodiazepines (GABAA agonists)
Reversal of neural plasticity
• “TENS” (transderm electric nerve stimulation) has been used for many years in treatment of chronic pain
• Recently sound stimulation in various forms have been introduced in treatment of severe tinnitus
Stimulation of somatosensory system can relieve tinnitus
• Electrical stimulation – of the ear and– of the skin behind the ears have been used
to treat tinnitus
• Electrical stimulation of the auditory cortex is in a stage of development
• Few systematic studies of efficacy have been published
