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Ascending Sensory Pathways Dorsal Column-Medial Lemniscus system fine touch position sense Anterolateral system temperature coarse touch pain James Bisley.

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Presentation on theme: "Ascending Sensory Pathways Dorsal Column-Medial Lemniscus system fine touch position sense Anterolateral system temperature coarse touch pain James Bisley."— Presentation transcript:

1 Ascending Sensory Pathways Dorsal Column-Medial Lemniscus system fine touch position sense Anterolateral system temperature coarse touch pain James Bisley

2 Dorsal Column-Medial Lemniscus system Conveys mechanosensory information from the periphery to the cortex Cutaneous Mechanoreceptors (fine touch) Proprioception & Kinesthesia (position)

3 Fine touch receptor afferent Pain Temperature Coarse touch

4 Kinesthesia is the “awareness” of body position and movement Proprioception is the “sub-concious” information used in the feed-back control of posture and precise movements. Position sense

5 Position sense information comes from: Muscle spindles Golgi tendon organs Joint receptors Cutaneous mechanoreceptive afferents Efference copy Position sense

6 Proprioceptors Motor unit (controlled by efferent) Muscle spindle Golgi tendon organ Joint receptor

7 Afferent fiber information Fiber typeClassDiameter (μm) Conduction Vel. (m/s) Types of receptors AαAαIa Ib Primary muscle spindle Golgi tendon organ AβAβII Skin mechanoreceptors Secondary muscle spindle AδAδIII Coarse touch, temperature, and pain C (no myelin) IV Coarse touch, temperature, and pain

8 Dorsal Column-Medial Lemniscus system Some terminology We use the terms first, second and third order neurons to describe the steps of the pathway to cortex. receptor First order neuron Second order neuron Third order neuron

9 Dorsal Column-Medial Lemniscus system Afferents have their cell bodies in the DORSAL ROOT GANGLIA. Called pseudo-unipolar neurons.

10 Dorsal Column-Medial Lemniscus system The DRG axons enter through the dorsal horn of the spinal cord Spinal reflexes, Clarke’s Nucleus, etc

11 Dorsal Column-Medial Lemniscus system Fibers that convey information from lower limbs and body (below spinal segment T6) travel ipsilaterally along the GRACILE TRACT.

12 Dorsal Column-Medial Lemniscus system Fibers that convey information from upper limbs and body (above spinal segment T6) travel ipsilaterally along the CUNEATE TRACT. GRACILE TRACT There is a topographic representation of the body in the dorsal columns

13 Dorsal Column-Medial Lemniscus system Fibers in the Gracile Tract have their first synapse in the GRACILE NUCLEUS. Fibers in the Cuneate Tract have their first synapse in the CUNEATE NUCLEUS. Caudal medulla There is a topographic representation of the body in the dorsal column nuclei

14 Dorsal Column-Medial Lemniscus system Axons from the second order neurons form the INTERNAL ARCUATE FIBERS in the caudal medulla, which decussates becoming the contralateral MEDIAL LEMNISCUS. Caudal medulla There is a topographic representation of the body in the medial lemniscus

15 Dorsal Column-Medial Lemniscus system The representation of the body shifts as the medial lemniscus runs rostrally.

16 Dorsal Column-Medial Lemniscus system The axons of the second order neurons terminate in the VENTRAL POSTERIOR LATERAL NUCLEUS of the thalamus (VPL). There is a topographic representation of the body in the VPL (lower extremities are lateral)

17 Dorsal Column-Medial Lemniscus system Gracile Cuneate What about the face?

18 Dorsal Column-Medial Lemniscus system Pseudo-unipolar neurons have their cell bodies in the TRIGEMINAL GANGLION. What about the face? Mid-pons Except for Proprioception Pseudo-unipolar neurons have their cell bodies in the MESENCEPHALIC NUCLEUS inside the CNS.

19 Dorsal Column-Medial Lemniscus system Pseudo-unipolar neurons have their cell bodies in the TRIGEMINAL GANGLION. What about the face? Except for Proprioception Pseudo-unipolar neurons have their cell bodies in the MESENCEPHALIC NUCLEUS inside the CNS.

20 Dorsal Column-Medial Lemniscus system Axons project to second order neurons in the PRINCIPAL (SENSORY) NUCLEUS OF THE TRIGEMINAL COMPLEX in mid-pons. What about the face? Mid-pons There is a topographic representation of the face in the principal (sensory) nucleus

21 Dorsal Column-Medial Lemniscus system Axons of the second order neurons decussate and join the TRIGEMINOTHALAMIC TRACT (which runs adjacent to the medial lemniscus). What about the face? Mid-pons

22 Dorsal Column-Medial Lemniscus system The axons of the second order neurons terminate in the VENTRAL POSTERIOR MEDIAL NUCLEUS of the thalamus (VPM). What about the face? There is a topographic representation of the face in the VPM Mid-pons

23 Dorsal Column-Medial Lemniscus system Neurons in the VP complex project to PRIMARY SOMATIC- SENSORY CORTEX via the POSTERIOR LIMB of the INTERNAL CAPSULE. The whole body is represented in the ventral posterior complex.

24 Dorsal Column-Medial Lemniscus system Neurons in the VP complex project to PRIMARY SOMATIC- SENSORY CORTEX via the POSTERIOR LIMB of the INTERNAL CAPSULE.

25 Dorsal Column-Medial Lemniscus system Area 3a Primarily proprioception input Area 3b Primarily tactile input Area 1 Primarily tactile input, but receptive fields usually cover several digits Area 2 Combination of tactile and proprioception. Hand configuration & stimulus shape are both important

26 Dorsal Column-Medial Lemniscus system The whole body is represented in each area of SI Owl Monkey

27 Dorsal Column-Medial Lemniscus system The somatosensory homunculus

28 Anterolateral system Conveys pain, temperature and coarse touch information from the periphery to the cortex Fiber typeClassDiameter (μm) Conduction Vel. (m/s) Types of receptors AαAαIa Ib Primary muscle spindle Golgi tendon organ AβAβII Skin mechanoreceptors Secondary muscle spindle AδAδIII Coarse touch, temperature, and pain C (no myelin) IV Coarse touch, temperature, and pain

29 Central Pain Pathways: Sensory discriminative component As with the tactile system, the cell bodies are located in the DORSAL ROOT GANGLIA. Pseudo-unipolar neurons.

30 Central Pain Pathways: Sensory discriminative component The DRG axons enter through the dorsal horn of the spinal cord Upon entering, the axons branch into ascending and decending collaterals forming the DORSOLATERAL TRACT of LISSAUER.

31 Central Pain Pathways: Sensory discriminative component The axons run up or down several spinal cord segments in Lassauer’s tract before synapsing in the gray matter of the dorsal horn.

32 Central Pain Pathways: Sensory discriminative component The second order neurons decussate immediately and form the SPINOTHALAMIC TRACT (aka the anterolateral tract). anterior white commissure

33 Central Pain Pathways: Sensory discriminative component The second order neurons decussate immediately and form the SPINOTHALAMIC TRACT (aka the anterolateral tract). There is a topographic representation of the body in the spinothalamic tract anterior white commissure

34 Central Pain Pathways: Sensory discriminative component The second order neurons decussate immediately and form the SPINOTHALAMIC TRACT (aka the anterolateral tract).

35 Central Pain Pathways: Sensory discriminative component The second order neurons decussate immediately and form the SPINOTHALAMIC TRACT (aka the anterolateral tract).

36 Central Pain Pathways: Sensory discriminative component The second order neurons decussate immediately and form the SPINOTHALAMIC TRACT (aka the anterolateral tract).

37 Central Pain Pathways: Sensory discriminative component The second order neurons decussate immediately and form the SPINOTHALAMIC TRACT (aka the anterolateral tract).

38 Central Pain Pathways: Sensory discriminative component Neurons in the spinothalamic tract terminate in the VENTRAL POSTERIOR LATERAL NUCLEUS (VPL) of the Thalamus. Just like the tactile system There is a topographic representation of the body in the VPL (lower extremities are lateral)

39 Some simple differences between the pathways Test the pathway Light touch Vibration 2-point discrimination Sense of position Dorsal columnAnterolateral X X Test the pathway Pain Temperature Coarse touch

40 Central Pain Pathways: Sensory discriminative component What about the face? Pseudo-unipolar neurons have their cell bodies in the TRIGEMINAL GANGLION and ganglia associated with nerves VII (Facial), IX (Glosso- pharyngeal) & X (Vagus). Anterolateral tract

41 Central Pain Pathways: Sensory discriminative component After entering the brain stem, the fibers descend in the SPINAL TRIGEMINAL TRACT to the medulla, where they synapse onto neurons in the SPINAL NUCLEUS of the TRIGEMINAL COMPLEX (primarily the pars caudalis). There is a topographic representation of the head in the pars caudalis Anterolateral tract

42 Central Pain Pathways: Sensory discriminative component Axons from the second order neurons decussate immediately and then join the ascending anterolateral tract in the brain stem.

43 Central Pain Pathways: Sensory discriminative component Axons from the second order neurons terminate in the VENTRAL POSTERIOR MEDIAL NUCLEUS (VPM) of the Thalamus. There is a topographic representation of the face in the VPM Anterolateral tract

44 The whole body & all somatic senses are represented in the ventral posterior complex. Neurons in the VP complex carrying pain information project to PRIMARY and SECONDARY SOMATIC- SENSORY CORTEX. Central Pain Pathways: Sensory discriminative component

45 Central Pain Pathways: Sensory discriminative component Cortex localization of pain Sub-cortical perception of pain Paleospinothalamic pathways suffering component of pain (reduced by benzodiazepines)

46 Central Pain Pathways: Descending Control of Pain Stimulation of PAG results in analgesia. The same holds true for the pars caudalis of the spinal nucleus of the trigeminal complex

47 Central Pain Pathways: Descending Control of Pain Endogenous opioid Opioids play a role in the descending control of pain In the dorsal horn or the pars caudalis

48 Central Pain Pathways: Local Control of Pain Interaction between dorsal column and anterolateral systems regulates pain perception. This is why rubbing a wound after sharp pain helps a bit. Cutaneous mechanoreceptor Cutaneous nociceptor Stimulation of dorsal columns can antidromically induce analgesia

49 Central Pain Pathways: Local & Descending Control of Pain What you should know Aα and Aβ fibers excite interneurons that reduce the transmission of pain information Descending fibers excite interneurons that reduce the transmission of pain information

50 Dorsal Column-Medial Lemniscus system Information content Fine touch, vibration and sense of position The path to cortex Locations & projections of 1 st, 2 nd & 3 rd order neurons Where decussation occurs Differences between DRG inputs & V th nerve inputs Basic arrangement of topography throughout the system The organization of somatosensory cortex 4 areas Basic arrangement of topography

51 Anterolateral system Information content Coarse touch, temperature & pain The path to cortex Locations & projections of 1 st, 2 nd & 3 rd order neurons Where decussation occurs Differences between DRG inputs & V th nerve inputs Basic arrangement of topography throughout the system The path from cortex Main areas involved in descending control of pain 2 ways that pain can be modulated in dorsal horn


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