sensory pathway-感觉通路-神经解剖学-华西医大课件

1、Sensory pathwayDr. Wang fan Ascending pathwayAscending (somatosensory) pathway carry impulses from pain, thermal, tactile, muscle and joint receptors to the brain. Some of this information finally reaches a conscious level (the cerebral cortex) while some is destined for subconscious centres (e.g. t

2、he cerebellum)Spinocerebellar pathway is destined for subconscious (unconscious) centres .The somatosensory system includes multiple types of sensation from the body - light touch, pain, pressure, temperature, fine touch and joint and muscle position sense (also called proprioception). Generally, th

3、ere are three types of sensation.The first sensation is called discriminative touch (fine touch ), which includes touch, pressure, and vibration perception, and enables us to read raised letters with our fingertips, or describe the shape and texture of an object without seeing it. The second sensati

4、on is pain and temperature, which is just what it sounds like, and also includes the sensations of itch and tickle. The third sensation is called proprioception, and includes receptors for what happens below the body surface: muscle stretch, joint position, tendon tension, and so on. Ascending pathw

5、ay that carry information to a conscious level share certain common characteristics: 1.there is a sequence of three neurones between the peripheral receptor and the cerebral cortex. fasciculus gracilis and fasciculus cuneatusMedial lemmiscusspinothalamic tracts. Trigeminothalamic lemmiscusSpinothala

6、mic lemmiscus4.The third-order neurones has its cell body in thalamus. Its axon passes to the somatosensory cortex of the parietal lobe of the cerebral hemisphere.5. Any sensory system going to the cerebral cortex will have to cross over at some point, because the cerebral cortex operates on a contr

7、alateral (opposite side) basis. The discriminative touch system crosses high level- in the medulla. The pain system crosses low level- in the spinal cord. Two main Ascending pathways in the spinal cord : the dorsal (posterior) column ( the fasciculus gracilis and fasciculus cuneatus) and the spinaot

8、halamic tracts.The central visual pathwayThere are five important ascending tracts (key point) 1. The dorsal (posterior) column Pathwaysmedial lemmiscus2. spinaothalamic lemmiscus3. trigeminal lemmiscus4.visual pathway5.auditory pathway1. The dorsal (posterior) column Pathways or the deep sensory (o

9、r the proprioceptive) and discriminative (fine) touch pathways 1).This pathway convey information of deep sensory and fine touch of trunk and limbsThe first neurons are located spinal gangliaThe second neurons: gracile and cuneate nuclei Decussation of medial lemniscus The third neurons: ventral pos

10、terolateral nucleusReceptors muscles tendon periosteum and jointSpinal nerve（peripheral processes）Spinal gangliaThe first neuronsDorsal roots(Central processes : fasciculus cuneatus and gracilis)Gracile and cuneate nuclei The second neuronsthalamocortical tractRunning through the posterior limb of t

11、he internal capsule toCortex of the cerebrumDecussation of medial lemniscusThe third neuronsVentral posterior lateral nucleusMedial lemniscus, through the medulla oblongata pons and midbrainSummary of dorsal (posterior) column Pathways The thalamocortical tract run through the posterior limb of the

12、internal capsule to somatic sensory cortex.2. The superficial sensory pathways1.The superficial sensory pathway of trunk and limbs-spinothalamic pathway2. The superficial sensory pathway of head and face- trigeminal lemmiscus Spinothalamic pathwayhas two parts1).The Lateral Spinothalamic Pathway con

13、vey pain and thermal sensations.2)The Anterior Spinothalamic pathway convey rude touch and pressure sensation. Notices:(The route is almost same as the pain and thermal pathway except for a little difference. We discuss the lateral and anterior spinothalamic pathway together. )Spinothalamic pathwayT

14、he first neurons: spinal ganglionThe second neurons: nucleus proprius The third neurons: ventral posteriolateral nucleusCross through the anterior white commissure Cross through the anterior white commissure Receptors Cutaneous exteroceptor of the trunk and limbsSpinal nerve（peripheral processes）Spi

15、nal gangliaThe first neuronsDorsal roots(lateral bundle)(Central processes : dorsolateral fasciculus)Nucleus proprius The second neuronsthalamocortical tractRunning through the posterior limb of the internal capsuleCortex of the cerebrumCross through the anterior white commissure and form the spinot

16、halamicThe third neuronsVentral posterio-lateral nucleusRun upward within one or two segmentsSummary of Spinothalamic pathwayDorsomedial nucleus Ant. nuclear group internal medullary lamina and nucleiVentral anterior Ventral lateral(VL)or Ventral intermediate Ventral posterolateral (VPL)medial and s

17、pinothalamic lemniscus Ventral posteromedial (VPM ) Pulvinar Medial geniculate body (MGN) Lateral geniculate body (LGN) Latral posterior nucleus (LP)Interthalamic connectionLateral dorsalMidline nucleus group3.The superficial sensory pathway of head and faceThe first-order neurons are located in the

18、 trigeminal ganglion, whose peripheral processes join the sensory branches of the trigeminal nerve and terminate in the superficial receptors in the skin and mucosa of head and face.The central process enter the pons via the sensory root of the trigeminal nerve to joint the spinal tract of trigemina

19、l nerve.Descending fibers in this tract conducts the impulses associated with pain and thermal sensations, and terminate in the spinal nucleus of trigeminal nerve. Ascending fibers in this tract are concerned with tactile and pressure sensation and terminate in the pontine nucleus of trigeminal nerv

20、e. Dorsomedial nucleus Ant. nuclear group internal medullary lamina and nucleiVentral anterior Ventral lateral(VL)or Ventral intermediate Ventral posterolateral (VPL) Ventral posteromedial (VPM ) third-order neurones of trigeminal lenmniscus Pulvinar Medial geniculate body (MGN) Lateral geniculate b

21、ody (LGN) Latral posterior nucleus (LP)Interthalamic connectionLateral dorsalMidline nucleus groupThe third-order neurones give rise to axons to form the thalamocortical tract (medial , spinothalamic and trigeminal lemniscus ) ascending through the posterior limb of the internal capsule to the infer

22、ior part of the postcentral gyrus3.The superficial sensory pathway of head and faceReceptor skinmucosaPeripheral processesTrigeminal ganglionThe first neuronsCentral processes enter the ponsSpinal nucleus of trigeminal nerve（pain and thermal）、pontine nucleus of trigeminal nerve（tactile and pressure）

23、The second neurons trigeminal lemniscusVentroposterior medial nucleusThe third neuronsThalamocortical tractPosterior limb of the internal capsule Inferior part of the postcentral gyrusDeep sensory pathway of head and face is still not know.4. The Visual Pathways and Pupillary ReflexVision is generat

24、ed by photoreceptors in the retina, a layer of cells at the back of the eye. The information leaves the eye by way of the optic nerve, and there is a partial crossing of axons at the optic chiasm. After the chiasm, the axons are called the optic tract. The first-order: bipolar cell in retina.The gan

25、glionic cells in the innermost layer of the retina are the second-order neurones.The optic tract wraps around the midbrain to get to the lateral geniculate nucleus (LGN, third-order neurones ), where all the axons must synapse. from there, the LGN axons fan out through the deep white matter of the b

26、rain as the optic radiations (or geniculocarine tract), which pass through the posterior limb of internal capsule and ultimately travel to primary visual cortex (or striate cortex)the LGN axons fan out through the deep white matter of the brain as the optic radiations (or geniculocarine tract)1.Visu

27、al pathwaysReceptor Rod and cone cellsBipolar cells The first neuronsGanglionic cellsThe second neuronsOptic nerve, optic chiasma ,optic tractPartial decussatuion of the fibers from the nasal halves of the retinaLateral geniculate bodyThe third neuronsOptic radiationPosterior limb of the internal ca

28、psuleBoth back of the calcarine sulcuswraps around the midbrainNoticesVisual fields: Information about the world enters both eyes with a great deal of overlap. you have two halves of the retina, a left half and a right half. Generally, the halves are referred to as a temporal half (next to your temp

29、le) and a nasal half (next to your nose). Visual images are inverted as they pass through the lens. Therefore, in your right eye, the nasal retina sees the right visual field of the world, while the temporal retina sees the left visual field of the world. Notice:A small portion of the optic tract co

30、ntinues through brachium of superior colliculus to the pretectal area and the superior colliculi, the fibers of the suprerior colliculi descend to form the tectospinal tract which is concerned with optic reflex.What Is optic reflex? Discuss laterLateral geniculate body (LGN)Medial geniculate body (M

31、GN)brachium of superior colliculusConnect the superior colliculus with Lateral geniculate body superior colliculusLoss of vision for one half of the field is known as hemiaopia. Lesion A: One eye is completely blacked out. Complete blindness in on eye is caused by an interruption of the optic nerve

32、on the same side. Lesion B: Bitemporal hemiaopia. Blindness in the temporal halves of the fields of both eyes , results form interruption of the field crossing in the optic chiasma and is sometimes caused by pituitary tumors.Lesion C: lesions in the left side of the optic tract, optic radiation or o

33、ptic center produce blindness in right halves of both visual fields.Pupillary reflexLight shone the retina of one eye causes both pupils to constrict normally. The response in the eye stimulated is called the direct pupillary light reflex, while that in the opposite eye is known as the indirect pupi

34、llary light reflex. Pathways involved in the pupillary light reflex are not entirely known, but invlole:Pupillary reflex(1) axons of retinal ganglion cells which pass via the optic nerve, optic tract and branchium of superior colliculus to the pretectal area, (2) axons of pretectal neurones which pa

35、rtially cross in the posterior commissure and presumably terminate bilaterally in Edinger-Westphal neucleus,(3) preganglionic fibers from the E-W neucleus course with fibers of the oculomotor nerve and synapse in the ciliary ganglion, and (4) postganlionic fibers from the ciliary ganglion innervate

36、to the sphincter of the iris to regulate the contraction of the pupil.Pupillary reflexlight shone on the retina of one eye whose optic nerve is injured, could not cause both pupils to constrict, but light shone on the healthy one cause both pupils to constrict. The pupil on the side of which the ocu

37、lomotor nerve is damaged, does not constrict when light is shone on either pupil.2. Pupillary reflexes(the direct pupillary light reflex and indirect pupillary light reflex)Retina Optic nerveOptic chiasmaBilateral optic tractBrachium of superior colliculus Pretectal areaAccessory (E-W) nucleus of oc

38、ulomotor nerveOculomotor nerveCliary ganglionPostganglionic fibersSphincter of the iris Auditory pathwayThe first-order neurones are bipolar cells in the cochlear. Their peripheral processes run to the spiral organ (of Corti) in the internal ear, whose central processes join the cochlear nerve and p

39、ass through the internal acoustic meatus to the cochlear nuclei, which are the second-order neurons. Some axons of the second-order neurons course medially along the ventral border of the pontine tegmentumt form the trapezoid body, which passes through or ventrally to the medial leminiscus. They nex

40、t cross the midline to opposite to form a longitudinal ascending bundle known as the lateral lemniscus.lateral lemniscus.Auditory PathwayThe trapezoid body is made up of fibers derives from the cochlear nuclei and the nuclei of the trapezoid body. They run transversely in the anterior part of the te

41、gmentum.The fibers of the lateral lemniscus terminate directly or indirectly the medial geniculate body, whose cells are the third-order neurones. The axons join the acoustic radiation. The fibers of the acoustic radiation course via the posterior limb of the internal capsule (the inferior thalamic

42、radiation) to the Auditory area ( transverse temporal gyri). Because the acoustic center on one side receives fibers from the bilateral cochlear nuclei, damage to ipsilateral paths does not cause a hearing defect. The fibers of the acoustic radiation course via the posterior limb of the internal cap

43、sule (the inferior thalamic radiation) to the Auditory area ( transverse temporal gyri).) Acoustic pathwayReceptorCorti organ Cochlear ganglionThe first neuronCochlear nerve through the iternal acoustic meatusCochlear nucleiThe second neuronsTrapezoid bodyLateral lemniscusMedial geniculate bodyThe t

44、hird neuronsAcoustic radiation Transverse temporal gyriLateral geniculate body (LGN)Medial geniculate body (MGN)The third neurons of Acoustic pathwaybrachium of superior colliculusConnect the superior colliculus with Lateral geniculate body If the someones brain stem was damaged in area by labeled b

45、ias, what structures are damaged? And what symptom appear in the patient? HomeworkAnswer of homework Damaged structures are : Right hypoglossal nerve Right Medial Lemniscus Right pyramidal tract Right Tectospinal tract THE SYMPTOMS：1. The hypoglossal nerve (lower motor neurones) controls all the int

46、rinsic and intrinsic muscles of the tongue, Lesion of Right hypoglossal nerve ,result in paralyzed of the left tongue.-soft paralysis2.The medial lemniscus carries information from deep and fine touch impulses to the cerebral cortex. lesions of the medial lemniscus, in the brain stem, result in CONT

47、RALATERAL deficits (since its constituent axons have crossed).Lesions of the medial lemniscus results in loss of 2 pt. discrimination, vibration and conscious proprioception from the contralateral side of the body. 3. Lesion of pyramidal tract (upper motor neurones, hard paralysis )Lesion above the decussation of the pyramid results in impairment of contralateral muscles , below the decussation of the pyramid results in impairment of ipsilateral hard paralysis of