Flashcards in Physiology 3.8 + 3.10 Deck (35):
How many neurons are activated in a seizure?
What is epilepsy?
recurrent unprovoked seizures; 1% of population
What is a seizure?
episode of abnormally synchronized and high-frequency firing of neurons in the brain; 10-15% of population
What are the most common causes of seizures in infancy and childhood?
What are the most common causes of seizures in patients over 60?
How are simple and complex seizures differentiated?
How are partial and generalized seizures differentiated?
localized versus whole brain
How are Petit Mal and Grand Mal seizures differentiated?
generalized; less dramatic versus whole body shaking
-sudden, rapid, muscular jerk
-fastest of all mvmt disorders (after tremor)
-can be focal unilateral or bilateral
alternating pattern of sustained contraction and rhythmic jerking
seizure of along duration; grater than 5 minutes
What is a seizure aura?
-brief, simple partial seizure without outward behavioral menifestaiton
-feeling of extreme fear or anxiety
What is the most prevalent seizure seen in children?
absence seizure (genetic)
-seizure with a staring spell
compared to other staring spell seizures:
period of time in between seizures; fire multiple action potentials as long as membrane potential is above the threshold
What is the main idea of how seizures occur?
imbalance between excitatory and inhibitory synapses
Flow of which ions causes ESPS?
Flow of which ions causes ISPS?
out of cell:
How can neurons become hyperexcitable in a partial seizure?
-toxins (glutamate analog)
-calcium waves in glia (absorb and release glutamate)
Repetitive discharge of neurons during a seizure lead to what?
-increased K+ outside the cell
-accumulate Ca2+ in presynaptic neuron; leads to further synaptic release
-Ca2+ entry through NMDA glutamate channels of postsynaptic neuron
What is the paroxysmal depolarization shift?
-20-40 mV positive shift in membrane potential
-shift triggers a train of action potentials at the peak of the shift
What allows for the activation of the paroxysmal depolarizing shift within a seizure?
What is the afterhyperpolarization?
-PDS; limits the duration of the depolarizing shift
-mediated by Ca2+ and K+ channels, GABAa (Cl-) and GABAb (K+)
What are the three things which must be considered when understanding the loss of control of neural circuits in a seizure?
1) loss of local inhibition**
2) increased excitability of neurons
3) spread of excitation
Why are inhibitory neuron effects strongest in the cerebral cortex?
"inhibitory surround" restricts the center excitability and its spread
How does penicillin affect the local spread of excitability?
-weak GABAa natagonist and can be convulsant
-"generalized penicillin epilepsy"
Which brain structure could facilitate the spread of neuronal activity across long distances, such as in the Jacksonian march of a seizure?
Which cells become entrained in a generalized seizure?
cortical and thalamic cells
What is the difference between a generalized seizure and an absence seizure?
-inhibition is preserved
-depolarizing and hyperpolarizing phases become stronger
What are thalamocortical oscillations?
T-type Ca2+ channels in thalamic relay cells are activated by hyperpolarization
**K+ conductances affect the relay cells in the thalamus**
What is status epilepticus?
repeated generalized seizures without a return to full consciousness; 5-10 minute standard