Somatic Sensation Notes PDF

Sample Footer Text Sensory system Somatic sensation L2-3 Dr. Faris Almasabi MBBS, PhD 9/14/2024...

Sample Footer Text Sensory system Somatic sensation L2-3 Dr. Faris Almasabi MBBS, PhD 9/14/2024 1 Dermatomes Dermatomes are areas of the skin whose sensory distribution is innervated by the afferent nerve fibres. In total there are 30 dermatomes - 8 cervical nerves (note C1 has no corresponding dermatomal area), 12 thoracic nerves, 5 lumbar nerves and 5 sacral nerves. Dysfunction or damage to a spinal nerve root from infection, compression, or traumatic injury can trigger symptoms in the corresponding dermatome. dermatomes Dermatomes are useful to help localize neurologic levels, particularly in radiculopathy and Shingles. Key Dermatomes for Clinical Examination: – T4: Nipple line; used as a reference point for thoracic spinal injuries. – T10: Umbilical region; relevant for abdominal referred pain. – L4, L5, S1: Commonly involved in lumbar radiculopathy due to disc herniation (Sciatica). Radiculopathy ‫ سواء يكون عليه ضغط او اصابه تسمى امراضها‬spinal cord ‫اي اصابه تكون ف‬ Radiculopathy is a condition caused by the compression, irritation, or damage of a spinal nerve root as it exits the spinal column.  ‫تكلم عن الفرق بي ‪.‬ا تكون ا‪2‬صابه ف ‪ nerve‬ا‪6‬اص‬ ‫ب‪ dermatome‬وبي ‪.‬ا تكون ا‪2‬صابه ف ‪ spinal cord‬نفسه‬ ‫مثال‪% :‬ا تكون ا‪+‬صابه ف ‪spinal cord at T4‬‬ ‫مثال‪. :‬ا تكون ا‪2‬صابه ف ‪dermatome T4‬‬ ‫راح يصير ‪ loss of sensation‬ف‬ ‫راح يصير ‪ loss of sensation‬ف‬ ‫منطقة ‪ T4‬فقط وما ‪G‬تها ما يتاثر‬ ‫منطقة ‪ T4‬وما ‪G‬تها‬ Shingles (herpes zoster ) It is a viral infection that causes a painful skin rash with blisters in a localized area. Although shingles can occur anywhere on your body, it most often appears as a single stripe of blisters that wraps around either the left or the right side of your torso. Shingles is caused by the varicella-zoster virus — the same virus that causes chickenpox. Once the chickenpox has resolved, the virus can remain inactive (dormant) in human nerve cells for years or decades, after which it may reactivate. Sciatica (Lumbar radiculopathy) Sciatica refers to pain that travels along the path of the sciatic nerve (from the lower back to the leg). Could cause sever pain, numbness, tingling and muscle weakness in the affected leg. Usually unilateral, and its suddenly onset. Most common cause of sciatica is a spinal disc herniation. Could resolved spontaneously in less than 6 weeks. Red flags: pain after injury, severe pain, loss of controlling bowel or bladder function. Sciatica Carpal tunnel syndrome It is the collection of symptoms and signs associated with compression of the median nerve as it travels through the wrist at the carpal tunnel. The characteristic symptom of CTS is numbness, tingling, or burning sensations in the thumb, index, middle, and radial half of the ring finger. Numbness or tingling is usually worse with sleep. ‫يب‬# ‫ا‬% ‫حساس وليس النظر مثل‬3‫القدره على =ديد عدد النقاط عن طريق ا‬ ‫ق العي وتعرف انها ثنتي‬K‫دبوسي و=طها على اصبعك اثناء اغ‬ Diminished two-point discrimination … pathway Ascending pathways Dorsal column - medial lemniscus pathway – Fast pathway – Well localized Spinothalamic pathway – Slow pathway – Broad spectrum of modalities  note: second-order neuron in dorsal column start at Medulla and cross to other side also note: second-order neuron in Spinothalamic tract start at same level in spinal cord and cross to other side also … Ascending pathways (Differences) Dorsal column - medial lemniscus pathway Spinothalamic pathway Decussate in Medulla oblongata Decussate immediately in the spinal cord Large myelinated Smaller myelinated Velocity 30-110 m/sec Velocity up to 40 m/sec Better temporal and spatial orientation Less temporal and spatial orientation Well localized Transmit broad spectrum modalities … Ascending pathways (Modalities) Dorsal column - medial lemniscus pathway Spinothalamic pathway Position sense Pain Fine touch Thermal sensations – Highly localized touch Crude touch & pressure – Fine gradation of intensity Crude localizing sensations Pressure: fine degree Tickle & itch Vibratory sensations Sexual sensations Spinal cord lesions Complete transaction if there is cut in spinal cord from where it start – Result in sensory loss below the level. Hemi-section spinal cord lesion (Brown Squared Syndrome). Central cord lesion – Syringomyelia Brown Sequard Syndrome At the level of lesion Same side – Loss all sensation Opposite side – Almost normal Below the level of lesion Same side – Loss of fine touch and proprioceptive sensations while pain and temperature are not (dorsal column) Opposite side – Loss of pain and temperature sensation while fine and proprioception are not lost (spinothalamic) Syringomyelia It is a central lesion of the spinal cord where a cyst or cavity forms within the spinal cord. This cyst, called a syrinx, can expand over time, destroying the spinal cord. Classically, syringomyelia spares the dorsal column/medial lemniscus while affect pain and temperature sensation. Why? The combination of symptoms varies from one patient to another depending on the location of the syrinx within the spinal cord, as well as its extent. Syringomyelia Thalamus All sensory sensations (except olfactory) synapse on thalamus. General perception (without details) will take place on thalamus. Role of thalamus in sensation: – Relay station: Directs sensory signals to the appropriate cortical areas. – Processing hub: Modulates, amplifies, or dampens sensory inputs. – Selective filter: Focuses attention on important stimuli. – Integrative center: Combines and integrates different types of sensory information. Important regions in thalamus: – Ventral Posterolateral (VPL) Nucleus: for somatosensory – Lateral Geniculate Nucleus (LGN): for vision – Medial Geniculate Nucleus (MGN): for hearing Somatosensory cortex This area of the brain is located in the postcentral gyrus of the parietal lobe, specifically in the primary somatosensory cortex (S1), which is organized in a very specific and topographical manner. The somatosensory cortex is arranged in a map-like representation called the sensory homunculus (little man). Each side of the cortex receives information from the opposite side of the body (except face bilaterally) The somatosensory cortex is capable of reorganization [plasticity]. If a part of the body is injured or no longer provides sensory input, the corresponding area in the cortex may shrink, and neighboring areas may take over the cortical space. Similarly, increased use of a body part can lead to an expansion of its cortical representation. ‫ الشخص ا&عمى ما يستمعل منطقة ا&بصار ف‬9‫مث‬ ‫يا الي ف منطقة السمع تهاجر لها‬9A‫ ا‬9‫الدماغ فمث‬ ‫بصر‬F‫وبالتالي يصبح السمع عند ا&عمى افضل من ا‬ Somatosensory cortex role Gradation, spatial and temporal characteristics are appreciated at somatosensory cortex Spatial recognition: Localization of the site of stimulus Two-point discrimination: The ability to recognize two touch points stimuli while eyes close. Recognition of intensity of stimuli. Stereognosis: The ability to recognize objects by touching them without looking at them. sensory homunculus Unequal representation of the body Lips have greatest area of representation followed by the face and the thumb Trunk and lower body have the least area The legs are represented on the top of the gyrus and the head at the bottom of the gyrus. The degree of representation of a certain part of the body is directly proportional to the density of receptors in that part.