Neurophysiology and Pathophysiology Quiz

Pathophysiology of Seizures

• Seizures are characterized by abnormal hyperexcitability in the brain, potentially causing loss of consciousness, and or motor or non-motor symptoms
• The brain's primary excitatory neurotransmitter is glutamate, which promotes neuronal depolarization
• Inhibitory neurotransmitter GABA opposes excitation by promoting neuronal hyperpolarization

Nerve Action Potential

• A nerve action potential is a phenomenon characterized by the entry of sodium ions, leading to depolarization, and the efflux of potassium ions, leading to repolarization
• This movement allows for the transmission of electrochemical current down the axon
• Voltage-gated calcium channels are essential for releasing neurotransmitters at the synapse

Neurophysiology of Neuronal Excitation in the CNS

• Glutamate is the primary excitatory neurotransmitter in the central nervous system (CNS)
• NMDA receptors allow calcium influx when stimulated by glutamate
• AMPA receptors rapidly promote sodium influx when stimulated by glutamate
• GABA is the primary inhibitory neurotransmitter , promoting chloride influx and hyperpolarization

Regulation/Inhibition of Excitatory Activity in the CNS

• GABA is the primary inhibitory neurotransmitter in the CNS, primarily via GABA (A) and GABA (B) receptors.
• GABA(A) receptors allow chloride influx, causing hyperpolarization.
• GABA(B) receptors impact presynaptic and postsynaptic functions indirectly by influencing cAMP and protein kinase A

Biochemical Etiology of Seizures

• Excessive excitation, decreased inhibition, and synchronization of neuronal firing contribute to seizures
• Cellular energy failure from Hypoxia and oxidative damage and electrolyte abnormalities (like hyponatremia) can increase neuronal excitability and trigger seizures
• Autoimmune diseases such as SLE can result in inflammation and altered neuronal function, thereby increasing seizure risk

Important Neuroanatomical Locations

• Seizures can originate and spread through various brain regions affecting sensory/motor systems and causing different symptoms
• The frontal lobe encompasses sensory, motor and higher cognitive functions such as problem solving.
• The parietal lobe deals with sensory reception and spatial awareness.
• The occipital lobe deals with visual processing.
• The temporal lobe encompasses auditory, memory, and speech processing
• Sub-cortical areas like the thalamus and hippocampus, as well as the brainstem are related to autonomic and generalized seizures.

Subtypes of Seizures

• Focal seizures are restricted to one area of the brain; they can remain localized or spread
• Generalized seizures involve both brain hemispheres.

Status Epilepticus

• Status epilepticus (SE) is a medical emergency entailing continuous seizure activity
• SE presents as continuous seizure episodes without breaks, and can lead to serious consequences, including permanent neurologic damage.
• Three subtypes of SE include generalized convulsive, nonconvulsive, and focal status epilepticus
• Management of SE includes IV benzodiazepines (e.g., diazepam, lorazapam) to stop the acute seizure activity, along with anticonvulsant medication, to prevent future seizures.

Pathophysiologic Etiologies of Seizures (Additional Information Included)

• Various factors such as vascular, infectious, traumatic, autoimmune, metabolic, neoplastic, or drug-induced conditions can cause seizures
• Specific examples are ischemic/hemorrhagic strokes, infections like meningitis or encephalitis, trauma, autoimmune conditions like SLE, metabolic disturbances, and tumors or masses (neoplasms)
• The specific drugs that affect the seizure threshold include illicit drugs such as amphetamines, cocaine, and ketamine and, some prescribed medications such as antidepressants (like bupropion), and antipsychotics (like clozapine).
• Several additional factors can contribute to the occurrence of seizures
• For instance, sudden alcohol withdrawal, hypoglycemia, hyponatremia can trigger seizures.