Lecture 6: Disorders of Neural Transmission

How do nerve’s communicated and send signals?

• Action potential 

• Electrochemical gradient across axon membrane (at rest = -70mV)

• More Na+ outside and more K+ inside axon 

• Na2+/K+ pump

• synapses

• myelin sheath helps conduction speed

Define the term seizure;

• a sudden, excessive, synchronised electrical discharge of neurones in the brain

What does the clinical effects of a seizure depend on?

• the location in the brain where these neurones are firing

Why do seizures occur?

• due to the hyper-excitability of nerve cells

• reduced inhibitory control

• ion channelopathies

• hypersynchromy (neurons fire as a group in synchrony)

What is a focal seizure?

• seizures that arise from a specific focus within the brain e.g. in cortical and lobe areas of the brain

What is a generalised seizure?

• seizures that affect all of the cortex from the onset

can focal seizures become generalised?

• yes

What is the definition of epilepsy?

• the syndrome where more than one seizure occurs and they are normally unprovoked

List 5 causes of provoked seizures:

1. traumatic brain injury

2. alcohol-related

3. central nervous system infections

4. metabolic disturbances

5. drug toxicity or withdrawal

List 4 causes of epilepsy:

1. genetic

2. structural

3. immune mediated

4. unknown

What is the genetic cause of epilepsy?

1. ion channels in the brain have genetic mutations

What is the structural cause of epilepsy?

• injury or defect in part of brain from birth

What is the immune-mediated cause of epilepsy?

• immune system mistakenly attacks healthy brain cells, leading to brain inflammation and seizures

What are ionchannelopathies?

• group of disorders caused by dysfunction of ion channels → disregulated flow of ions like sodium, potassium, calcium and chloride in/out of cells.

• genetic mutations (hereditary)

• autoimmune, toxic, metabolic causes

these disorders primarily affect excitable tissue, like nerves, muscles and the heart.

List 2 conditions which affect the function of the neuromuscular junction:

1, Myasthenia Gravis - chronic autoimmune disease that causes weakness and rapid fatigue in skeletal muscle.

2. Botulism - toxin

How does myasthenia gravis affect the NMJ?

1.  The body produces harmful antibodies which block Ach from binding to its receptors in the muscle cells.

How does botulism affect the NMJ?

•  toxin which prevents the binding of Ach-containing vesicles with the presynaptic membrane. = causes paralysis of skeletal muscle. Prevents the nerve from releasing Ach.