NERVOUS SYSTEM Ⅲ
The sensory function of brain
Senses
Five basic types of sensory receptors
Mechanoreceptors
Thermoreceptors
Nociceptors(pain receptors): physical orchemical damage
Electromagnetic receptors:light on the retinaof the eye
chemoreceptors
Sensory receptor
A: Free nerve endings(pain, temperature)
B: Pacinian corpuscle (pressure)
C: Meissner’s corpuscle (touch)
D: Muscle spindle (stretch)
A
B
C
D
sensation
Somatic senses
Mechanoreceptive somatic senses
Stimulated by mechanical compression orstretching of some tissue of the body
Tactile sense
Touch , pressure, vibration , tickle senses
position sense
Static position and rate of movement senses
Thermoreceptive senses
Detect heat and cold
Pain senses
sensation
•Sensory pathway:
–1st : enters spinal cord from periphery
–2nd : crosses over (decussates), ascends inspinal cord to thalamus
–3rd : projects to somatosensory cortex
sensation
Sensory pathway
Spinothalamic pathway(anterolateral system)
Dorsal column pathway (dorsal column–medial lemniscal system)
Spinocerebellar pathway
Spinothalamic pathway
Function
Carries pain, temperature, crudetouch and pressure signals(superficial sensations)
Three-order neuron
1st order neuron enters spinalcord through dorsal root
2nd order neuron crosses over inspinal cord; ascends to thalamus
3rd order neuron projects fromthalamus to somatosensorycortex
spinothalamic
pathway
Pain , temperature, crudetouch and pressure signals
Spinothalamic Pathway
Small sensoryfibres:
Pain, temperature,some touch
Primary somatosensorycortex (S1)
Thalamus
Medulla
Spinal cord
Spinothalamictract
spinothalamic pathway
spinal cord injury
Loss of sense of (superficial sensations):
•crude Touch
•Pain
•Warmth/cold
in right leg
Spinothalamic damage
Dorsal column pathway
•Function
–Carries fine touch, vibration andconscious proprioception signals
(deep sensations)
•Three-order neuron
–1st order neuron enters spinalcord through dorsal root;ascends to medulla (brain stem)
–2nd order neuron crosses over inmedulla; ascends to thalamus
–3rd order neuron projects tosomatosensory cortex
dorsal
cloumn
pathway
fine touch, vibration and consciousproprioception signals
Dorsal column pathwayDorsal column pathway
Large sensory nerves:
Fine Touch, vibration, two-point discrimination,proprioception
Primary somatosensorycortex (S1) in parietallobe
Thalamus
Medulla
Medial
lemniscus
Spinal cord
Dorsal column
Dorsal column
nuclei
Dorsal column pathway
•Function
–Sensory nuclei of the trigenimal nervewhich subserve the same sensoryfunctions for the head
Dorsalcolumndamage
dorsal column
pathway
spinal cord injury
Loss of sense of(deep sensations):
•Fine touch
•proprioception
•vibration
in left leg
CentralPathways
Differences between the two system
Velocities
The dorsal column–medial lemniscal system: large,myelinated nerve fibers
30 to 110 m/sec,
The anterolateral system :smaller myelinatedfibers
a few meters per second up to 40 m/sec.
Differences between the two system
spatial orientation :in spinal cord
the dorsal column–mediallemniscal system :highdegree of with respect totheir origin
the anterolateral system :much less spatialorientation
![C:\Users\Administrator\AppData\Roaming\Tencent\Users\478838058\QQ\WinTemp\RichOle\%G4NEZ[8KF_{@BB{(]5)7DT.jpg](data/images/img19.jpg)
lower parts of the body---center ofthe cord
higher parts---lateral layers
Spinocerebellar pathway
Function :
receives inputs from golgitendon organs and musclestretch receptors.proprioception signals
Receptors : muscles &joints
Three-order neuron
1st order neuron: enters spinalcord through dorsal root
2nd order neuron: ascends tocerebellum
3rd order neuron to cortex
Spinocerebellar pathway
Division
Peripheral Processof First Order theNeuron
Region ofInnervation
Dorsal column damage
•Sensory ataxia (loss ofcoordination)
•Patient staggers; cannotperceive position ormovement of legs
•partially compensated byvisual surveillance
Spinocerebellar tract damage
•Cerebellar ataxia
–a failure of the fine coordination ofmuscle movements
•Clumsy movements
•Incoordination of the limbs (intentiontremor)
•Wide-based, reeling gait (ataxia)
•Alcoholic intoxication producessimilar effects
anterolateral view
"inner chamber” in Greek
Compositions of thalamus
Lateral-lower part of body
Medial –upper part
thalamus
2 Associated nuclei
Receive their driving inputs from
Other cortical areas
ventral-lateral nucleus
cerebullum ,globus pallidus—motor
Pulvinar nucleus
Medial ,lateral geniculate--sensors
thalamus
3 nonspecific projection nucleus
“nonspecific nuclei”connect to association areasof cortex and/or limbic structure.
Anterior nuclei
Medial nuclei
Intralaminar and reticular nuclei
Projection system of thalamus
Projection system of thalamus
Projection system of thalamus
Function
Specific projection system of thalamus
Specific senses: visual or auditory cortex (exceptolfaction)
Non-specific projection system of thalamus
Maintain and alter the excitatory situation ofcortex
Somatosensory cortex
Located in the post-central gyrus of thehuman cerebral cortex Ⅰ
Sagittal section
coronal section
From side
Somatotopic map ofthe somato-sensorycortex
Somatosensory cortex
Cross projection
Each side of the cortex receives sensoryinformation exclusively from the opposite side ofthe body (the exception: the sensor informationfrom face is bilateral projection).
Somatosensory cortex
The finer the sense, the larger thesomato-sensory cortex area
The lips, face and thumb are represented by largeareas in the somatic cortex, whereas the trunk andlower part of the body, relatively small area.
Somatosensory cortex
Inversely projection
“Up is down and down is up ”
The head in the most lateral portion, and the lowerbody is presented medially.
Visual cortex
Primary visual cortex
Secondary visualareas
bitamporal
nasal side
Pain
: Easily localized, occur first
: occur second
nociceptor
nociceptor
Aδ nerve
C nerve
spinothalamic
pathway
to reticular
formation
Impulses transmitted to spinal cord by
–Myelinated Aδ nerves: fast pain (80 m/s)
–Unmyelinated C nerves: slow pain (0.4 m/s)
Pain
reticular
formation
spinothalamic
pathway
thalamus
somato-sensory
cortex
Impulses ascend to somatosensory cortexvia:
–Spinothalamic pathway (fast pain)
–Reticular formation (slow pain)---cingulategyrus
Viseral sensation:
Pain ?
without proprioceptor
few thermoceptor
Visceral pain
Poorly localized; may be “referred”
Slow pain
Mostly caused by distension of holloworgans or ischemia (localized mechanicaltrauma may be painless)
Visceral pain
Agina:
due to ischemia of the heart muscle, generally due toobstruction or spasm of the coronary arteries.
Refered pain
Site of pain may be distant fromorgan
Visceral pain
(heart attack), where pain isoften felt in the neck,shoulders, and back ratherthan in the chest, the site ofthe injury.
Mechanism of refered pain
Convergence theory
The primary afferent axons of skin and visceraconverged on the same interneurons in the painpathways.
Mechanism of refered pain
Convergence theory
This theory explains why referred pain isbelieved to be segmented in much the same wayas the spinal cord.
Fail to explain why there is a delay between theonset of referred pain after local painstimulation.
Threshold for the local pain stimulation andthe referred pain stimulation are different, butaccording to this model they should both be thesame.
Mechanism of referred pain
Facilitated theory
The primary afferent axons of skin and visceraclosed to each other
Mechanism of referred pain
Facilitated theory
to explain why there is a delay between theonset of referred pain after local painstimulation.
Summary
Spinothalamic pathway
Dorsal column pathway
Specific projection system
Non-specific projection system
Sensory area of cerebral cortex
Referred pain