Lambert-Eaton myasthenic syndrome

With Lambert-Eaton myasthenic syndrome, or LEMS for short, “myasthenia” refers to muscle weakness, and Lambert-Eaton refers to Edward Lambert and Lealdes Eaton, the two physicians who first described the condition. So, Lambert-Eaton myasthenic syndrome is a rare autoimmune condition that attacks the peripheral nervous system, causing muscle weakness, weak or absent reflexes, and autonomic dysfunction.

First, let's focus on physiology and how muscles normally work. Whether you’re reaching for a slice of pizza or sinking that perfect shot in basketball, it all starts in the brain. The upper motor neuron of the cerebral cortex fires an action potential down the spinal cord to activate lower motor neurons. Next, lower motor neurons pick up these signals and pass them along their axons toward terminal branches and axon terminals, all the way to skeletal muscle fibers.

This communication site between the lower motor neuron and the skeletal muscle fiber is known as the neuromuscular junction, which consists of three main parts. First, there’s the presynaptic membrane, which is the axon terminal of the lower motor neuron packed with acetylcholine vesicles. Acetylcholine is actually the neurotransmitter that enables muscle contraction. Next, there’s the postsynaptic membrane, which is the membrane of the skeletal muscle fiber, rich in nicotinic acetylcholine receptors.

Finally, this tiny space between two membranes is called the synaptic cleft and contains the enzyme acetylcholine esterase.

Now, when the action potential reaches the axon terminal, it opens voltage-gated calcium channels called P/Q type channels. Next, calcium rushes in through these channels, triggering the acetylcholine vesicles to fuse with the presynaptic membrane and release acetylcholine into the synaptic cleft. Once inside the cleft, acetylcholine moves across to bind nicotinic acetylcholine receptors on the postsynaptic membrane. Eventually, this binding triggers the muscle cell to depolarize, setting off a chain of intracellular events that lead to contraction. Once the contraction is over, acetylcholine is broken down by acetylcholine esterase, allowing the muscle to relax and prepare for the next signal.

This subdivision of the peripheral nervous system that controls voluntary movements is known as the somatic nervous system. There is also the autonomic nervous system, which controls involuntary actions like heart rate, breathing, and digestion. Thanks to the autonomic nervous system, you don’t have to worry about your digestion or heart rate while you’re shooting basketballs with your friends.