2-Anterolateral system updated.pptx

Physiology

1. Dr Saboohi Saeed

2. Learning Objectives 1-Sensations carried by antrolateral pathway 2- Physiological anatomy of anterolateral pathway 3-Disease related to anterolateral pathway 4-Comparison of dorsal column and anterolateral pathway

3. PATHWAYS Ascending tracts Descending tracts Fasciculus cuneatus Fasciculus gracilis Ventral spinothalamic Lateral spinothalamic Ventral spinocerebellar Dorsal spinocerebellar Spinotectal , spino-olivary Ventral corticospinal Lateral corticospinal Rubrospinal Reticulospinal Vestibulospinal Tectospinal Olivospinal

4. Ascending Tracts Four groups: 1) Dorsal column, medial leminiscal system includes Fasciculus Gracilis , Fasciculus cuneatus 2) Antero-lateral system includes 1) Ventral spinothalamic tract. 2) Lateral spinothalamic tract. 3 ) Spino-cerebellar tracts 4) Miscellaneous group/tracts:Spinotectal,spino-olivary,Spino-cortical,spinovestibular,spinoreticular, Postrolat . Tract of Lissauer .

5. Tracts of spinal cord medial leminiscal system

6. Anterolateral System

7. Anterolateral System Anterolateral System-Transmission of following Sensory Signals 1. Pain 2. Thermal sensations, including both warmth and cold sensations 3. Crude touch and pressure sensations capable only of crude localizing ability on the surface of the body 4. Tickle and itch sensations 5. Sexual sensations

8. SPINOTHALAMIC TRACTS Anterior and lateral tracts Anterior spinothalamic tract – 1- crude touch, 2- pressure, 3-itch , tickle Lateral spinothalamic tract – 1- pain 2- temperature These tracts consists of small myelinated fibers of 40 meter/sec.

9. Anatomy of the Anterolateral Pathway The sensory fibers from pain, thermal and crude touch receptors –> dorsal root ganglion - dorsal nerve root  spinal cord --  laminae I, IV, V, and VI of dorsal horn . These laminae are where many of the dorsal root sensory nerve fibers terminate after entering the cord. The anterolateral fibers cross immediately in the anterior commissure of the cord to the opposite anterior and lateral white columns, where they turn upward toward the brain by way of the anterior spinothalamic and lateral spinothalamic tracts.

10. Cross section of the spinal cord, showing the anatomy of the cord gray matter and of ascending sensory tracts in the white columns of the spinal cord .

11. Anterior spinothalamic tract Receptor ( crude touch & pressure )  1 st order neuron (dorsal root ganglion) lamina V,VI  2 nd order neuron cross over to opposite sidemedulla spinal lemniscus  pons  midbrain thalamus Ventropostrolateral VPL nucleus3 rd order neuron sometosensory area (3,1,2).

12. Lateral spinothalamic tract Receptor (pain & temperature)  1 st order neuron (dorsal root ganglion) lamina 1,11,111  2 nd order neuron cross over to opposite side (lateral)medulla spinal lemniscus  pons  midbrain thalamus VPL nucleus3 rd order neuron sometosensory area (3,1,2).

13. The upper termination of the two spinothalamic tracts The upper termination of the two spinothalamic tracts is mainly twofold: (1) throughout the reticular nuclei of the brain stem (2) in two different nuclear complexes of the thalamus, the ventrobasal complex the intralaminar nuclei. Anterior spinothalamic tract  the tactile signals are transmitted mainly into the ventrobasal complex of thalamus. Lateral spinothalamic tract  pain signals - --> only a small fraction of the pain signals project directly to the ventrobasal complex of the thalamus. Instead, most pain signals terminate in the reticular nuclei of the brain stem and from there are relayed to the intralaminar nuclei of the thalamus where the pain signals are further processed

14. Spatial arrangement of tracts both of these ascending systems are laminated, with cervical , thoracic, lumbar, and sacral segments represented from medial to lateral in the anterolateral pathways and lateral to medial in the dorsal columns . Because of this lamination, tumors arising outside the spinal cord first compress the spinothalamic fibers from sacral and lumbar areas, causing the early symptom of loss of pain and temperature sensation in the sacral region . Intraspinal tumors cause loss of sensation first in higher segments.

15. Thus right sided pain ,temperature, crude touch and crude pressure sensations are carried by the opposite sided spinothalamic tract .

16. Characteristics of Transmission in the Anterolateral Pathway (1) the velocities of transmission are only one third to one half those in the dorsal column–medial lemniscal system, ranging between 8 and 40 m/sec; (2) the degree of spatial localization of signals is poor; (3) the gradations of intensities are also far less accurate, most of the sensations being recognized in 10 to 20 gradations of strength, rather than as many as 100 gradations for the dorsal column system

17. Comparison of dorsal column and anterolateral systems 1-Type of sensations carried DORSAL COLUMN 1. Touch sensations requiring a high degree of localization of the stimulus 2. Touch sensations requiring transmission of fine gradations of intensity and tactile discrimination 3. Phasic sensations, such as vibratory sensations 4. Sensations that signal movement against the skin 5. Position sensations from the joints 6. Pressure sensations related to fine degrees of judgment of pressure intensity ANTEROLATRAL 1. Pain 2. Thermal sensations, including both warmth and cold sensations 3. Crude touch and pressure sensations capable only of crude localizing ability on the surface of the body 4. Tickle and itch sensations 5. Sexual sensations

18. 2-Cossing over of fibers- Decussation DORSAL COLUMN carries signals upward to the medulla of the brain mainly in the dorsal columns of the cord. Then, after crossing to opposite side synapse opposite side in the medulla , they continue upward through the brain stem to the thalamus by way of the medial lemniscus . 2 nd order axons end in thalamus VPL nucleus. ANTEROLATRAL signals in the anterolateral system, immediately after entering the spinal cord from the dorsal spinal nerve roots, synapse in the dorsal horns of the spinal gray matter, then cross to the opposite side of the cord and ascend through the anterior and lateral white columns of the cord. They terminate at all levels of the lower brain stem and in the thalamus VPL and intralaminar nuclie .

19. 3-Type of fibers and conduction velocities DORSAL COLUMN The dorsal column–medial lemniscal system is composed of large, myelinated nerve fibers that transmit signals to the brain at velocities of 30 to 110 m/sec, ANTEROLATRAL the anterolateral system is composed of smaller myelinated fibers that transmit signals at velocities ranging from a few meters per second up to 40 m/sec the velocities of transmission are only one third to one half those in the dorsal column–medial lemniscal system, ranging between 8 and 40 m/sec

20. 4-Spatial Orientation of the Nerve Fibers in the Dorsal Column-Medial Lemniscal System and anterolateral system

21. DORSAL COLUMN Spatial Orientation of the Nerve Fibers in the Dorsal Column–Medial Lemniscal System very well developed fibers from the lower parts of the body lie toward the center of the cord, whereas those that enter the cord at progressively higher segmental levels form successive layers laterally. cervical to sacral segments from lateral to medial in the dorsal columns.Sacral is medial. the thalamus, distinct spatial orientation is still maintained, with the tail end of the body represented by the most lateral portions of the ventrobasal complex and the head and face represented by the medial areas of the complex the left side of the body is represented in the right side of the thalamus, and the right side of the body is represented in the left side of the thalamus. Anterolateral system Cervical to sacral segments represented from medial to lateral in the anterolateral pathways,Sacral is lateral. Spatial orientation less developed .

22. 5-Degree of spatial and temporal fidelity DORSAL COLUMN dorsal column–medial lemniscal system has a high degree of spatial orientation of the nerve fibers with respect to their origin, sensory information that must be transmitted rapidly with temporal and spatial fidelity is transmitted mainly in the dorsal column– medial lemniscal system;(from where and when). Anterolateral system the anterolateral system has much less spatial orientation. the degree of spatial localization of signals is poor ; .

23. The dorsal system is limited to discrete types of mechanoreceptive sensations mainly fine touch . The anterolateral system has a special capability —that is, the ability to transmit a broad spectrum of sensory modalities, such as pain, warmth, cold, and crude tactile sensations DORSAL COLUMN–MEDIAL LEMNISCAL SYSTEM Anterolateral system 6-Sensations from mechanoreceptors

24. 7-CHARACTERISTICS OF SIGNAL TRANSMISSION AND ANALYSIS IN THE DORSAL COLUMN–MEDIAL LEMNISCAL SYSTEM transmits sensory signals that do not have highly discrete localization of the signal source and do not have discrimination of fine gradations of intensity. Anterolateral system

25. Divergance in the pathway at each synapse. The upper curves of the figure show that the cortical neurons that discharge to the greatest extent are those in a central part of the cortical“field ” for each respective receptor. Thus, a weak stimulus causes only the most central neurons to fire. A stronger stimulus causes still more neurons to fire, but those in the center discharge at a considerably more rapid rate. Fine Changes in stimulus intensity are discriminated precisely. as many as 100 gradations of intensity of the sensations can be identified by the dorsal column system; do not have discrimination of fine gradations of intensity. the gradations of intensities are also far less accurate, with most being recognized in 10 to 20 gradations of strength, DORSAL COLUMN–MEDIAL LEMNISCAL SYSTEM Anterolateral system

26. 8-DORSAL COLUMN–MEDIAL LEMNISCAL SYSTEM Two-Point Discrimination very well developed due to mechanism of lateral inhibition Lateral inhibition not well developed Anterolateral system

27. Lateral inhibition, it blocks lateral spread of the excitatory signals and increases the degree of contrast in the sensory pattern perceived in the cerebral cortex. in the following: (1) the dorsal column nuclei of the medulla; (2) the ventrobasal nuclei of the thalamus; (3) the cortex itself. At each of these levels, the lateral inhibition helps to block lateral spread of the excitatory signal. As a result, the peaks of excitation stand out, and much of the surrounding diffuse stimulation is blocked. This effect is demonstrated by the two red curves showing complete separation of the peaks when the intensity of lateral inhibition is great. Lateral inhibition not well developed only crude touch. Two point Tactile discrimination not well developed

28. 9-Transmission of Rapidly Changing and Repetitive Sensations DORSAL COLUMN–MEDIAL LEMNISCAL SYSTEM apprising the sensorium of rapidly changing peripheral conditions. this system can recognize changing stimuli that occur in as little as 1⁄400 of a second . Vibratory signals are rapidly repetitive and can be detected as vibration up to 700 cycles per second from pacinian corpuscles and 200cps from meisseners corpuscle travel only in this tract. the ability to transmit rapidly changing or rapidly repetitive signals is poor Anterolateral system

29. Diseases of ascending tracts

30. Effects produced by lesion of posterior white column 1-The person can still feel contact and pressure when these stimuli are applied but tactile localization and tactile discrimination is poor or lost. 2-Vibration sense dec or lost 3-Astreognosis 4-Position and movement sense is severely affected esp in distal extermities . Loss of position sense impairs the performance of voluntary motor function. This sensory loss causes the movements to become clumsy,uncertain and poorly coordinated (post col ataxia).If the pat. Is asked to stand upright with his eyes closed he staggers or falls termed as Romberg’s sign—not specific for post column lesions.

31. Sensory ataxia-Romberg’s sign + ve in cerebellar disease and negative in dorsal column damage Eyes Eye closed

32. Tabes dorsalis Tabes dorsalis is a late manifestation of syphilis (Tertiary stage) presents as signs and symptoms associated with impaired sensations as a result of demyelination of the dorsal columns. Signs include an ataxic wide-based gait as a result of loss of touch and proprioception , paresthesias (altered sensations), bladder dysfunction (e.g., urinary retention), Romberg sign is positive. a positive Romberg sign -unable to maintain a steady posture while standing with feet together and eyes closed ; the inability to maintain a steady posture while standing with feet together and eyes open indicates cerebellar dysfunction, (not a DCML impairment).Romberg sign negative. Ataxia with both eyes open and closed is Romberg negative.

33. Myopathic Gait (Waddling Gait)

34. Syringomyelia is a term referring to a disorder in which a  cyst  or cavity forms within the  spinal cord . This cyst, called a  syrinx , can expand and elongate over time, destroying the spinal cord. The damage may result in pain,  paralysis , weakness,and stiffness in the back, shoulders, and extremities.  Syringomyelia  may also cause a loss of the ability to feel extremes of hot or cold, especially in the hands. The disorder generally leads to a cape-like loss of pain and temperature sensation along the back and arms .

35. Syringomyelia

36. Syringomyelia is a term referring to a disorder in which a  cyst  or cavity forms within the  spinal cord . This cyst, called a  syrinx , can expand and elongate over time, destroying the spinal cord. The damage may result in pain,  paralysis , weakness,and stiffness in the back, shoulders, and extremities.  Syringomyelia  may also cause a loss of the ability to feel extremes of hot or cold, especially in the hands. The disorder generally leads to a cape-like loss of pain and temperature sensation along the back and arms.

37. A  syrinx  is a fluid-filled cavity within the  spinal cord  ( syringomyelia ) or brain stem ( syringobulbia ). Predisposing factors include craniocervical junction abnormalities, previous  spinal cord  trauma, and   spinal cord  tumors.

38. Most cases of syringomyelia are caused by a  malformation  of the brain known as Chiari  type 1  malformation  (CM1). A CM1 occurs where the brain joins the spinal cord. In this  malformation , the brainstem lies lower than normal.

39. . Causes  of  Chiari Malformations .  Chiari malformations  are usually caused by structural defects in the brain and spinal cord. These defects develop during fetal development. Due to genetic mutations or a maternal diet that lacked certain nutrients, the indented bony space at the base of the skull is abnormally small.

40. Complications Myelopathy is the most serious consequence of syringomyelia .

41. Complications due to myelopathy include the following : Recurrent pneumonia Paraplegia or quadriplegia Decubitus ulcers Bowel and urinary dysfunction

42. Signs and symptoms Syringomyelia causes a wide variety of neuropathic symptoms due to damage of the spinal cord and the nerves inside. Patients may experience severe chronic pain,  abnormal sensations  and loss of sensation particularly in the hands.

43. A syrinx may also cause disruptions in the  parasympathetic  and  sympathetic nervous systems , leading to abnormal body temperature or sweating, bowel control issues. If the syrinx is higher up in the spinal cord or affecting the brainstem as in syringobulbia ,  vocal cord paralysis , ipsilateral tongue wasting ,  trigeminal nerve  sensory loss, and other signs may occur.

44. Classically, syringomyelia spares the  dorsal column / medial lemniscus  of the spinal cord, leaving pressure, vibration, touch and  proprioception  intact in the upper extremities.  Neuropathic arthropathy , also known as a Charcot joint, can occur, particularly in the shoulders, in patients with syringomyelia . The loss of sensory fibers to the joint is theorized to lead to damage of the joint over time .

45. Horner syndrome results in a decreased pupil size, a drooping eyelid and decreased sweating on the affected side of your face

46. Horners ’ Syndrome Interruption of sympathetic pathways leads to several implications. It inactivates the  dilator muscle  and thereby produces miosis . It inactivates the  superior tarsal muscle  which produces ptosis. It inactivates the  orbitalis muscle  which produces the effect of enophthalmos . It also reduces sweat secretion in the face.

47. Thankyou