EPILEPSY Physiology Lecture Slideshow

• Epilepsy (also called “seizures”) is characterized by uncontrolled excessive activity of either part or all of the central nervous system.

• A person who is predisposed to epilepsy has attacks when the basal level of excitability of the nervous system rises above a certain critical threshold.

Why seizures???

Types Of Epilepsy:

• Epilepsy can be classified into three major types:

1. Grand Mal Epilepsy,
2. Petit Mal Epilepsy, And
3. Focal Epilepsy.

1.Grand Mal Epilepsy

Causes Of Grand Mal Epilepsy:

• Hereditary predisposition to epilepsy (about 1 of every 50 to 100 persons).
• In such people, factors that can precipitate attacks include
  (1) Strong emotional stimuli,
  (2) alkalosis caused by over breathing,
  (3) drugs,
  (4) fever, and
  (5) loud noises or flashing lights.
• Even in people who are not genetically predisposed, certain types of traumatic lesions in almost any part of the brain can cause excess excitability of local brain areas.

What initiates Grand Mal epilepsy:

• Extreme neuronal over activity is presumed to be massive simultaneous activation of many reverberating neuronal pathways throughout the brain.

Areas involved:

• During attack, extreme neuronal discharges in all areas of the brain—
  in the cerebral cortex, thalamus and sub-thalamic brain stem
  portions.

What happens during a Grand Mal Attack?

Sign And Symptoms

Phases Of Grand Mal Epilepsy:

1. Aura: A warning sign perceived by patient.
2. Tonic phase: Patient become unresponsive and exhibit muscle rigidity.
3. Clonic phase: Patient experience alternating episodes of muscle spasm and relaxation.
4. Postical phase/Recovery phase: The postictal state is an abnormal condition that lasts for a period that begins when a seizure subsides and ends when the patient returns to baseline.

EEG During Grand Mal Epilepsy:

• A typical EEG from almost any region of the cortex,
• during the tonic phase of a grand mal attack,
• demonstrates high- voltage, high-frequency discharges,
• occur over the entire cortex.

What Stops the Grand Mal Attack?

1. The major factor that stops the attack after a few minutes is neuronal fatigue.
2. A second factor is probably active inhibition by inhibitory neurons that have been activated by the attack.

2.Petit Mal Epilepsy:

Area involved:

• Petit mal epilepsy almost certainly involves the thalamo-cortical
  brain activating system.

Sign And Symptoms:

• It is usually characterized by 3 to 30 seconds of unconsciousness (or diminished consciousness) during which time the person has twitch-like contractions of muscles usually in the head region, especially blinking of the eyes;
• This is followed by return of consciousness and resumption of previous activities. This total sequence is called the absence syndrome or absence epilepsy.

Brain Wave Pattern In Petit Mal Epilepsy

• Spike and dome pattern.
• In fact, it results from oscillation of

(1) inhibitory thalamic reticular neurons (which are inhibitory gamma- aminobutyric acid [GABA]-producing neurons) and

(2) excitatory thalamocortical and corticothalamic neurons.

3:Focal Epilepsy:

Area involved:

• Focal epilepsy can involve almost any local part of the brain, either localized regions of the cerebral cortex or deeper structures of both the cerebrum and brain stem.

Focal Epilepsy:

Causes:
Most often, focal epilepsy results from some localized organic lesion or
functional abnormality, such as
(1) scar tissue in the brain that pulls on the adjacent neuronal tissue,
(2) a tumor that compresses an area of the brain,
(3) a destroyed area of brain tissue, or
(4) congenitally deranged local circuitry.

Focal Epilepsy:

• What initiate focal epilepsy?
• Lesions ——promote extremely rapid discharges —————–
  localized reverberating circuits ————-seizure.

When such a wave of excitation spreads over the motor cortex, it causes progressive “march” of
muscle contractions beginning most characteristically in the mouth region and marching progressively downward to the legs but at other times marching in the opposite direction. This is called jacksonian epilepsy.

Psychomotor Seizure:

• Another type of focal epilepsy is the so-called psychomotor seizure.
• Attacks of this type frequently involve part of the limbic portion of the brain, such as the hippocampus, the amygdala, the septum, and/or portions of the temporal cortex.
• Duration of 1 to 2 minute.

Psychomotor Seizure cont;

• Psychomotor Seizure cause
  (1) a short period of amnesia;
  (2) an attack of abnormal rage;
  (3) sudden anxiety, discomfort, or fear; and/or
  (4) a moment of incoherent speech or mumbling.
  (5) Sometimes the person cannot remember his or her activities during
  the attack, but at other times he or she is conscious of everything that
  he or she is doing but unable to control it.

Brain Wave Pattern In Focal Epilepsy

Low frequency rectangular wave