Neurophysiology Functional Anatomy PDF

Neurophysiology FUNCTIONAL ANATOMY GOOD LUCK!  1 Index Learning Objectives...............................................................................

Neurophysiology FUNCTIONAL ANATOMY GOOD LUCK!  1 Index Learning Objectives................................................................................................................ 2 Impairment caused by Right Dorsal Column Lesion........................................................... 2 Impairment caused by Right Fasciculus Cuneatus Lesion................................................ 3 Impairment caused by Right Lateral Corticospinal Tract Lesion...................................... 4 Impairment caused by Right Lateral Spinothalamic Tract Lesion..................................... 5 Impairment caused by Central Cord Syndrome................................................................... 6 Impairment caused by Hemicord Lesion (Brown-Séquard Syndrome)............................ 7 A hemicord lesion, also known as Brown-Séquard Syndrome, occurs when one side (hemisection) of the spinal cord is damaged. This leads to a characteristic pattern of motor and sensory impairments due to the specific pathways affected. 7 Key Impairments:............................................................................................................. 7 Impairment caused by Transverse Cord Lesion.................................................................. 8 Impairment caused by Posterior Cord Syndrome............................................................... 9 Impairment caused by Anterior Cord Syndrome............................................................... 10 Key Impairments:........................................................................................................... 10 Common Causes:........................................................................................................... 10 Clinical Presentation:..................................................................................................... 10  2 Learning Objectives After completing this module you should be able to: 1. Describe the signs and symptoms caused by a lesion of the spinal cord (fasciculus gracilis and fasciculus cuneatus, lateral corticospinal tract, and lateral spinothalamic tract). 2. Given a patient case (examination results and chief complaint), identify the functional systems causing the sensory and motor impairments. 3. Correlate neurology information between the behavioral and neuroanatomical levels Impairment caused by Right Dorsal Column Lesion Definition A lesion affecting the right dorsal column of the spinal cord, which consists of the fasciculus gracilis and fasciculus cuneatus. These structures carry light touch, vibration, and proprioception (position sense) from the body to the brain. Key Impairments  Ipsilateral loss of light touch, vibration, and proprioception below the level of the lesion. Common Causes  Trauma (e.g., spinal cord injury)  Multiple sclerosis  Vitamin B12 deficiency (subacute combined degeneration)  Tabes dorsalis (late-stage syphilis) Clinical Presentation  Loss of proprioception results in poor balance, especially in the dark or with eyes closed (Romberg’s sign positive).  Difficulty recognizing objects by touch (astereognosis).  No loss of pain, temperature, or motor function.  3 Impairment caused by Right Fasciculus Cuneatus Lesion Definition A lesion in the right fasciculus cuneatus, which is part of the dorsal column-medial lemniscus (DCML) pathway, disrupts the transmission of light touch, vibration, and proprioception from the upper limb and upper trunk (above T6) to the brain. Key Impairments  Ipsilateral loss of light touch, vibration, and proprioception in the upper limb and upper trunk (above T6). Common Causes  Multiple sclerosis  Spinal cord trauma  Vitamin B12 deficiency (subacute combined degeneration)  Tabes dorsalis (late-stage syphilis) Clinical Presentation  Loss of proprioception leads to clumsiness and difficulty coordinating hand movements.  Poor balance in the dark or with eyes closed (Romberg’s sign positive).  Astereognosis (inability to recognize objects by touch in the affected hand).  No loss of pain, temperature, or motor function.  4 Impairment caused by Right Lateral Corticospinal Tract Lesion Definition The lateral corticospinal tract (LCST) is responsible for voluntary motor control of the limbs. A lesion in the right LCST disrupts motor signals descending from the brain to the spinal cord, leading to motor weakness or paralysis on the ipsilateral (right) side of the body below the lesion. Key Impairments  Ipsilateral (right-sided) motor weakness or paralysis below the lesion.  Spasticity due to loss of upper motor neuron (UMN) control.  Hyperreflexia (exaggerated deep tendon reflexes).  Positive Babinski sign (toes extend instead of curling when the sole is stroked). Common Causes  Spinal cord trauma  Multiple sclerosis  Cervical or thoracic spinal cord compression  Amyotrophic lateral sclerosis (ALS) affecting UMNs Clinical Presentation  Weakness or paralysis in the right limbs below the lesion level.  Increased muscle tone (spasticity) and stiffness in affected muscles.  Exaggerated reflexes (e.g., knee jerk, ankle jerk).  Clumsiness, difficulty with fine motor tasks (e.g., buttoning a shirt).  No loss of sensation, as the corticospinal tract only controls movement.  5 Impairment caused by Right Lateral Spinothalamic Tract Lesion Definition The lateral spinothalamic tract (LSTT) is responsible for transmitting pain and temperature sensations from the body to the brain. Unlike motor pathways, the spinothalamic tract decussates (crosses over) in the spinal cord near the level of entry. This means that a lesion in the right lateral spinothalamic tract results in sensory loss on the left (contralateral) side of the body, below the lesion level. Key Impairments  Contralateral (left-sided) loss of pain and temperature sensation below the lesion.  No effect on touch, vibration, or proprioception (which are carried by the dorsal column).  No motor deficits, as the lesion affects a sensory tract. Common Causes  Spinal cord trauma  Syringomyelia (fluid-filled cavity in the spinal cord)  Multiple sclerosis  Tumors compressing the spinothalamic tract  Brown-Séquard Syndrome (hemisection of the spinal cord) Clinical Presentation  Left-sided pain and temperature loss below the lesion.  No motor weakness or paralysis (corticospinal tract is unaffected).  No loss of fine touch, vibration, or proprioception (dorsal column remains intact).  Burns, cuts, or injuries on the left side may go unnoticed due to sensory impairment.  6 Impairment caused by Central Cord Syndrome Definition Central Cord Syndrome (CCS) is an incomplete spinal cord injury that primarily affects the cervical spinal cord, leading to greater impairment in the upper limbs than the lower limbs. This occurs because the corticospinal tract is organized in a somatotopic manner, where fibers controlling the arms are more medial than those controlling the legs. The syndrome often results from compression, hyperextension injuries, or ischemia affecting the center of the spinal cord. Key Impairments  Greater motor weakness in the upper limbs than lower limbs (due to corticospinal tract involvement).  Variable sensory loss, especially pain and temperature in a "cape- like" distribution (due to damage to the decussating spinothalamic fibers in the anterior commissure).  Urinary dysfunction (in some cases).  No loss of proprioception, vibration, or fine touch (dorsal columns are usually spared). Common Causes  Hyperextension injuries (e.g., whiplash trauma, falls in elderly).  Cervical spinal cord compression (e.g., from osteoarthritis or spinal stenosis).  Syringomyelia (fluid-filled cyst in the central canal).  Tumors or ischemic injury affecting the central cord. Clinical Presentation  Weakness predominantly in the arms, sparing or with mild involvement of the legs.  Bilateral pain and temperature loss in the cape-like distribution (over shoulders, upper arms, and back).  Hands may be functionally impaired, making fine motor tasks difficult.  Leg function may remain largely intact, but some cases have mild weakness.  Possible bladder dysfunction (varies based on severity).  7 Impairment caused by Hemicord Lesion (Brown-Séquard Syndrome) Definition A hemicord lesion, also known as Brown-Séquard Syndrome, occurs when one side (hemisection) of the spinal cord is damaged. This leads to a characteristic pattern of motor and sensory impairments due to the specific pathways affected. Key Impairments: 1. Ipsilateral (Same-Side) Impairments – Occurs on the same side as the lesion:  Loss of light touch, vibration, and position sense (proprioception) o Affected Pathway: Dorsal column-medial lemniscus (DCML) o The DCML carries sensory information about fine touch, vibration, and proprioception. Since it ascends on the same side before crossing at the medulla, damage causes loss of these sensations on the same side as the lesion.  Muscle weakness or paralysis (Monoplegia) with upper motor neuron (UMN) signs o Affected Pathway: Lateral corticospinal tract o The corticospinal tract controls voluntary movement. Since it crosses at the medullary pyramids, a lesion in the spinal cord before the crossing affects the same-side muscles. o UMN signs include:  Spasticity (increased muscle tone)  Hyperreflexia (exaggerated reflexes)  Positive Babinski sign (toes extend instead of curling when the sole is stroked) 2. Contralateral (Opposite-Side) Impairments – Occurs on the opposite side of the lesion:  Loss of pain and temperature sensation o Affected Pathway: Lateral spinothalamic tract o The spinothalamic tract carries pain and temperature sensations and crosses immediately at the spinal level before ascending to the brain. o Since the fibers cross below the lesion, damage causes loss of pain and temperature on the opposite side.  8 Impairment caused by Transverse Cord Lesion Definition A Transverse Cord Lesion refers to a complete injury that affects the entire width of the spinal cord at a specific level. This results in bilateral (both sides) impairment of motor and sensory functions below the level of the lesion. Key Impairments: 1. Dorsal Column Lesion (Sensory Loss) o The dorsal columns carry information about light touch, vibration, and proprioception (position sense). o A complete transverse cord lesion causes bilateral loss of these sensations below the level of the lesion. 2. Lateral Corticospinal Tract Lesion (Motor Loss) o The lateral corticospinal tract controls voluntary movements. o Damage leads to bilateral upper motor neuron signs below the lesion, including:  Paraplegia (paralysis of both legs)  Spasticity (increased muscle tone and reflexes)  Hyperreflexia (exaggerated reflexes)  Babinski sign (toes extend upward when the sole of the foot is stroked) 3. Lateral Spinothalamic Tract Lesion (Pain & Temperature Loss) o The spinothalamic tract carries pain and temperature sensation. o A complete lesion causes bilateral loss of pain and temperature sensation below the level of injury. Common Causes:  Trauma (e.g., spinal cord injuries from accidents)  Tumors compressing the spinal cord  Multiple Sclerosis (MS)  Transverse Myelitis (inflammation of the spinal cord) This condition leads to complete loss of motor and sensory function below the lesion, making it one of the most severe spinal cord injuries.  9 Impairment caused by Posterior Cord Syndrome Posterior Cord Syndrome is a condition in which the dorsal columns of the spinal cord are damaged, while other major tracts remain intact. This results in significant sensory deficits but preserves motor function. Key Impairments: 1. Loss of Light Touch, Vibration, and Position Sense o The dorsal columns (fasciculus gracilis and fasciculus cuneatus) are responsible for transmitting fine touch, vibration, and proprioception (position sense). o Damage to these columns causes bilateral loss of these sensations below the level of the lesion. o Patients may struggle with coordinated movement, especially in the dark (where vision cannot compensate for the loss of proprioception). 2. Preserved Motor Function o Since the lateral corticospinal tracts (motor control) are unaffected, muscle strength remains intact. o However, patients may appear clumsy due to sensory ataxia (inability to coordinate movements due to a lack of position sense). 3. Intact Pain and Temperature Sensation o The spinothalamic tract (which carries pain and temperature sensation) remains unaffected. o Patients can still feel pain and temperature normally. Common Causes:  Multiple Sclerosis (MS)  Posteriorly located tumors compressing the spinal cord  Trauma affecting the dorsal side of the spinal cord  Vitamin B12 Deficiency (Subacute Combined Degeneration)  Syphilis (Tabes Dorsalis) Clinical Presentation:  Difficulty walking in the dark due to sensory ataxia.  Positive Romberg’s sign (patient sways when asked to stand still with their eyes closed).  May experience tingling or numbness, but no paralysis. Unlike other spinal cord syndromes, Posterior Cord Syndrome does not cause weakness or loss of pain perception, making it distinct in its clinical presentation.  10 Impairment caused by Anterior Cord Syndrome Definition Anterior Cord Syndrome occurs when the anterior (front) portion of the spinal cord is damaged. This affects both the corticospinal tract (motor function) and the spinothalamic tract (pain and temperature sensation) while sparing the dorsal columns (light touch, vibration, and position sense). Key Impairments: 1. Loss of Voluntary Movement (Paralysis or Weakness) o The lateral corticospinal tracts are responsible for voluntary muscle movements. o Damage leads to bilateral paralysis or weakness (paresis) below the level of the lesion. o The severity depends on how much of the corticospinal tract is affected:  Complete lesion: Total paralysis below the level of injury.  Partial lesion: Weakness with some preserved movement. o Upper Motor Neuron (UMN) signs like spasticity, hyperreflexia, and Babinski sign develop over time. 2. Loss of Pain and Temperature Sensation o The spinothalamic tract carries pain and temperature signals. o Damage causes bilateral loss of these sensations below the lesion level. o Patients cannot feel burns, cuts, or injuries in affected areas. 3. Preserved Light Touch, Vibration, and Position Sense o The dorsal columns (which carry fine touch, vibration, and proprioception) are not affected. o Patients can still feel pressure, vibrations, and know where their limbs are positioned. Common Causes:  Anterior Spinal Artery Occlusion (most common) o The anterior spinal artery supplies the anterior two-thirds of the spinal cord. o A stroke in this artery can cause ischemia (oxygen deprivation), leading to this syndrome.  Trauma (e.g., car accidents, falls, or penetrating injuries)  Multiple Sclerosis (MS)  Herniated Disc pressing on the anterior spinal cord  Tumors compressing the anterior spinal cord Clinical Presentation:  Paralysis/weakness in both legs and/or arms (depending on the lesion level).  Loss of pain and temperature sensation, increasing risk of burns or injuries.  Can still feel pressure, vibrations, and limb position.  Severe difficulty walking or complete loss of motor function.  Possible bladder and bowel dysfunction if the lesion is high enough.