L6 - Disorders of Neural Transmission Flashcards
1. Pathophysiology of seizures, epilepsy 2. Types of epilepsy 3. Underlying causes of epilepsy 4. Structural, genetic, autoimmune causes of epilepsy 5. Disorders of ion channels, central, peripheral, congenital, autoimmune (primary, paraneoplastic) 6. Disorder of neuromuscular junction: Myasthinia Gravis and effect of clostridial toxins
Define seizure?
Temporary disruption of brain function due to excessive discharge of cortical neurons.
What is Epilepsy?
Brain disorder characterized by a enduring predisposition to generate epileptic seizures.
State some different types of primary generalised seizures?
Absent seizures, tonic seizures, atonic seizures, clonic seizures, myoclonic seizures, tonic-clonic seizures
Absence seizures
Often occur in kids.
Characterised by staring into space or by subtle body movements
- eye blinking
- lip smacking
Tonic seizures
- Cause stiffening of muscles,
- Affect muscles in back, arms and legs.
- May cause you to fall to the ground.
Atonic seizures
Drop seizures, loss of muscle control
Clonic seizures
Repeated or rhythmic jerking muscle movements.
- neck, face and arms usually affected
Myoclonic seizures
Sudden brief jerks or twitches of arms and legs
Tonic-clonic seizures
Can cause abrupt loss of consciousness, body stiffening, shaking, loss of bladder control, biting tongue
Briefly describe the pathophysiology of seizures?
Excessive excitation or loss of inhibition of neurons.
Key unit of neurotransmission is the synpase.
- seizures involve malfunction of ion channels.
Main causes of epilepsy include:
Low oxygen during birth. Head injuries. Brain tumours. Infections e.g. meningitis or encephalitis Stroke Abnormal levels of sodium or BG
What are focal seizures?
- Abnormal discharge appears to start in one part of the brain
- may become generalised.
- With or without loss of awareness.
Describe structural causes of epilepsy?
Epilepsy may occur if brain cells are damaged. Some causes are: - damage to brain during development - bleeding in brain - infection in brain - head injury - stroke
Describe some genetic causes of epilepsy?
Certain types of epilepsy are known to have a genetic cause:
- Benign rolandic epilepsy
- Temporal lobe epilepsy
- Juvenile myoclonic epilepsy
Benign Rolandic Epilepsy
Common form of childhood epilepsy
- reffered to as benign as most children grow out of it
Give examples of autoimmune diseases which cause epilepsy?
- Systemic lupus ertyhematosus (immune system mistakenly attacks healthy tissue)
- stiff man syndrome (progressive rigidity and stiffness)
- Hashimoto’s encephalopathy (associated with hashimoto’s thyroiditis) (HT common cause of hypothyroidism, affects brain and contributes to seizures, confusion or dementia)
Describe how faulty ion channels contribute to epilepsy?
Genetic mutations, dysfunction in voltage and ligand gated ion channels.
- defective Na+ channels of inhibitory neurons
- defective GABAa receptors affecting pre/post synaptic GABAergic inhibition
Describe briefly how anti-epileptic drugs work?
Targets of AEDs
- Sodium ion channels
- Calcium ion channels
- the GABA system and receptor agonists
- Glutamate receptors antagonist
Describe examples of AEDs which target Sodium channels?
Phenytoin, Lamotrigine and carbamazepine
- AED binds/ attaches to Na+ channel
- Sodium channels responsbile for depolarisation of nerve cell membrane and conduction of AP.
Hence prevents signals from being passed on.
Describe the role of voltage gated calcium channels in neurones?
Control neurotransmitter release at pre-synaptic nerve terminal.
What is an important role of dopamine?
Neurons of the substantia nigra communicate with neurons of the basal ganglia by liberating the neurotransmitter dopamine.
- important for the fine tuning of an organisms movements.
What is Parkinson’s disease?
Neurological disorder that affects movement control.
- substantia nigra neurones progressively degenerate.
- amount of dopamine available for neurotransmission in the corpus striatum is lowered.
- biochemical imbalance results in symptoms like - resting tremor, bradykinesia, rigidity. loss of postural reflexes etc.
Where is dopamine produced?
Substantia nigra. ventral tegmental regions of brain, dopamine alterations are related to schizophreia.
Dopaminergic projections are divided into…
Nigrostriatal
- substantia nigra
- control of voluntary movement
Mesolimbic
- ventral tegmental area
- interactive and reactive behaviours
Mesocortical systems.
Excess dopamine may result in?
Schizophrenia
Symptoms: hallucinations and delusions as a result of increased subcortical release of dopamine.
Describe Lambert Eaton syndrome?
Condition where immune system attacks neuromuscular junctions.
Describe the mechanism of Lambert Eaton syndrome?
- antibodies against pre-synaptic calcium channels of the neuromuscular junction.
- decreased ACH release with neuronal transmission
What is Botulism?
Caused by clostridium botulinum.
Paralysis, starting in face to limbs. If it reaches breathing muscles, resp can fail.
