Lecture 11 – 13: Nervous System and Motor Dysfunction

frontal lobe

primary motor cortex (precentral gyrus)

• apraxia

apraxia

unable to perform learned tasks

parietal lobe

primary somatosensory cortex (postcentral gyrus)= feeling/sensation

• agnosia

agnosia

unable to recognize meaningfulness of an object

• can feel but doesn’t know what it is

occipital lobe

visual cortex

Upper Motor Neuron (UMN) lesions

• Affect extensors in upper extremities and flexors in lower extremities

• Spinal reflexes remain intact but cannot be controlled by brain

• Hypertonia(tight), spasticity(stiff), clonus(repetitive jerking)

• Hyperreflexia (Reflexes are increased/exaggerated)

Lower Motor Neuron (LMN) lesions

• Weakness in distal limb(hands/feet)

• Muscle atrophy, fasciculations(twitch)

• Hypotonia(loose), flaccid paralysis(floppy)

• Hyporeflexia/areflexia (reflex are decreased/absent)

Myasthenia Gravis (MG)

• Autoimmune disease

• Gradual destruction of ACh receptors

antibodies destroy ACh receptors → weak muscle signals → weakness

Myasthenia Gravis (MG)- Etiology

• Antibody-mediated loss of ACh receptors in NMJ

• Due to sensitized helper T cells and an antibody-directed attack on ACh receptor in NMJ

• Antibody attack leads to shedding of ACh receptor-rich terminal portions in end plate of muscle fiber

• Fewer receptors and a widened synaptic space that impairs signal transmission

Myasthenia Gravis (MG) – Clinical Manifestations

• Least evident in morning

• Worsen with effort and as day proceeds

• Muscle weakness

• Most commonly affects eye and periorbital muscles (initial symptoms):

  • Ptosis – due to eyelid weakness (drooping eyelid)

  • Diplopia – due to extraocular muscle weakness (double vision)

• Progresses to generalized weakness including:

  • Respiratory weakness

  • Difficulty chewing and swallowing

• Weakness in limb movement more pronounced in proximal parts of extremity → difficulty climbing stairs and lifting objects

Guillain-Barré Syndrome (GBS)

• MCC of acute, flaccid nontraumatic paralysis

• Most patients had an acute, influenza-like illness before onset of symptoms

Guillain-Barré Syndrome (GBS)- Clinical manifestations

• Progressive ascending muscle weakness of limbs

• Symmetric flaccid paralysis and loss of tendon reflexes

• Paralysis may progress rapidly to involve respiratory muscles → may require ventilator

Guillain-Barré Syndrome (GBS)- ANS involvement

• Postural hypotension (drop in BP when standing)

• Arrhythmias (abnormal heart rhythm)

• Facial flushing (redness of face)

• Abnormalities of sweating and urinary retention

Disorders of Cerebellum

• Difficulty or inability to maintain a steady posture of trunk (unsteadiness of trunk) = truncal ataxia

• Inability to fix eyes on a target – constant conjugate readjustment of eye position = nystagmus

• Rapidly alternating movements are jerky and performed slowly

• Dysmetria – finger to nose test (Inability to judge distance properly)

• Rhythmic back-and-forth movement of a finger or toe that worsens as target is approached = intention tremor

Parkinson Disease

• Degenerative disorder of basal ganglia function

• Results in variable combinations of tremor, rigidity, bradykinesia and postural changes

• Characteristics:

  • Dopamine depletion results from degeneration of nigrostriatal pathway

  • Substantia nigra → striatum

• On microscopic exam:

  • Loss of pigmented substantia nigra neurons

  • Atrophic nerve cells

Parkinson Disease – Clinical Manifestations

• Resting tremor

  • Resemble motion of rolling a pill between thumb and forefinger = pill-rolling tremor

  • Occurs when limb is supported and at rest

  • Disappears with movement and sleep

• Rigidity

  • Involves jerky, ratchet-like movements = cogwheel rigidity

• Bradykinesia

  • Slowness in initiating and performing movements

  • Difficulty with sudden, unexpected stopping of voluntary movements

• Shuffling gait without swinging arms

• Loss of postural reflexes leads to frequent falls

Amyotrophic Lateral Sclerosis (ALS)

• Progressive neurodegenerative disorder that affects motor function

• Affects motor neurons in 3 locations:

  • UMNs in cerebral cortex

  • LMNs in ventral horn cells of spinal cord

  • Motor nuclei of brainstem, particularly hypoglossal nuclei

damage to brain + spinal cord + brainstem motor neurons → progressive weakness

ALS – Clinical Manifestations

• Slowly progressive weakness and atrophy in distal muscles of 1 upper extremity

• UMN lesions:

  • Spastic paresis or stiffness consists of a weakness of movement patterns and impaired fine motor control

• LMN lesions:

  • Fasciculations (muscle twitch)

  • Flaccid paresis consists of weakness of individual muscles

  • Muscle atrophy and hyporeflexia (reflexes decrease)

• Dysphagia (difficulty swallowing)

• Dysarthria (impaired articulation of speech)

• Dysphonia (difficulty making sounds of speech)

Multiple Sclerosis (MS)

Demyelinating disease characterized by inflammation and destruction of white matter of CNS myelin

Multiple Sclerosis (MS) - Pathogenesis

• Inflammatory autoimmune disorder

• Development of plaques

  • Hard, sharp-edged, demyelinated patches visible throughout white matter

• Result of acute myelin breakdown

• Decreased/absent oligodendrocytes → demyelination

• Conduction blocks and axonal degeneration

• Gliosis (scar tissue in CNS)

Complete Spinal Cord Injuries (SCI)

• Result in complete destruction of neural tissue

• UMN or LMN paralysis

• No motor or sensory function in sacral segments

total loss of movement + sensation below injury

Areas Affected by Spinal Cord Injury (SCI)

• Spinal reflexes

• Ventilation (breathing)

• Autonomic nervous system

  • Temperature regulation

• Sensorimotor function

• Bladder, bowel and sexual functions

Contusion

• Result from direct impact (head strikes hard surface), a depressed skull fracture, or a rapidly moving object strikes head

• Manifestations:

  • Loss of consciousness (< 5 min)

  • Hematoma (epidural, subdural, intracerebral)

    • Results from vascular injury and bleeding

Concussion

• Transient neurogenic dysfunction caused by mechanical force to brain

• Manifestations (depends on severity):

  • Loss of consciousness (> 30 min – 24 hrs) with anterograde amnesia lasting > 24 hrs

  • Headache, anxiety, insomnia, depression, irritability, fatigability

Epidural Hematoma (emergency)

• Rupture of meningeal arteries

• Unconsciousness → brief lucid period → rapid progression to:

  • unconsciousness

  • severe headaches

  • vomiting

  • seizure

  • hemiparesis

Subdural Hematoma (slow)

• Result of a tear in bridging veins

• Begins with:

  • headaches

  • drowsiness

  • restlessness or agitation

  • slowed cognition

  • confusion

Intracerebral Hematoma (inside brain)

• Occur due to head injury or contusion

• Hematoma acts as an expanding mass

• ↑ ICP

• Compression of brain tissues with resultant edema and ischemia

• Manifestations: decreasing level of consciousness

Ischemic Stroke

• Caused by arterial occlusion

  • Thrombi formed in a cerebral artery or intracranial vessels

  • Emboli formed outside the brain

• Attributed to atherosclerosis and inflammatory disease processes

Transient Ischemic Attack (TIA)

• Temporary episode of neurologic dysfunction

• Temporary disturbance in cerebral blood flow → reverses before infarction occurs

• Caused by focal brain, spinal cord or retinal ischemia without acute infarction

• Clinical manifestations:

  • Facial drooping

  • Arm or leg weakness on one side of body

  • Speech difficulty

Aneurysmal Subarachnoid Hemorrhage

Bleeding into subarachnoid space caused by a ruptured cerebral aneurysm

Aneurysmal Subarachnoid Hemorrhage- clinical manifestations

• “Worst headache of my life” – sudden, severe throbbing, explosive headache

-Vomiting, Visual disturbances, Motor deficits, Loss of consciousness

• Meningeal irritation → nuchal rigidity (neck stiffness) and photophobia

-Positive Brudzinski sign- When neck is flexed → legs automatically bend

-Positive Kernig sign- Pain when trying to extend the leg

dementia

• Cognitive decline caused by any disorder that permanently damages large association areas of cerebral hemispheres

• Disabling disorder in elderly

• Causes:

  • Neurodegenerative disorders

    • Alzheimer disease (MCC)

    • Dementia associated with Lewy bodies (Parkinson disease)

    • Huntington disease

  • Vascular dementia

  • Alcohol

Delirium

• Acute confusional state

• Transient disorder of awareness with a sudden or gradual onset

• Causes:

  • Postoperative (most commonly in critical care units following surgery)

  • Withdrawal from CNS depressants (alcohol or narcotic agents)

  • Metabolic disorders (hypoglycemia, thyroid storm)

  • Brain trauma/surgery

  • Febrile illness or heat stroke

  • Electrolyte imbalance, dehydration