Introduction
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The Control Center | The Messengers | How Muscles Move | ALS - No Messages
Before one can understand ALS, it is necessary to have some basic knowledge on how muscles work, since they are the parts affected when a person becomes afflicted with ALS. In order for muscles to exhibit movement, complex interactions between the brain, motor neurons, and the muscles themselves must happen.
The Control Center
Weighing only about three pounds, the brain is the control center of our body and has three major areas--the cerebrum, cerebellum, and the brainstem. The cerebrum is the biggest part of the brain, and controls activities such as the ability to see, smell, hear, taste, and touch; the ability to think, and the ability to feel emotions. Under the cerebrum lies the cerebellum, which is in charge of coordinating movements. The cerebrum and the cerebellum are then connected to the spinal cord through an extension called the brain stem, which regulates involuntary movement. Voluntary movement, on the other hand, begins in the cerebrum, in an area called the motor cortex.
The Messengers
Neurons are the cells that carry electrical impulses, or messages, to and from the brain. With over 100 billion neurons in the brain itself, we are constantly sending and receiving messages non-stop, 24 hours a day for as long as we live. There are two types of neurons, sensory neurons and motor neurons. Sensory neurons carry messages about our five senses, while motor neurons carry messages from the brain directing the voluntary movement of muscles. It is these motor neurons that are affected by ALS. Two types of motor neurons exist in the nervous system--upper motor neurons and lower motor neurons. Upper motor neurons run from the brain to the spinal cord while lower motor neurons run from the spinal cord to the muscles.
How Muscles Move
When motor neurons are healthy, messages begin from the motor cortex and end up at the muscle. A motor neuron is comprised of a cell body containing the nucleus with dendrites sprouting from the cell body, much like the branches on a tree. Also connected to the cell body is a long myelin-coated fiber, called an axon, which branches out at the base into the axon terminals, looking much like the roots of a tree. Messages travel down the dendrites, through the cell body, down the axon, and to the terminals, where a chemical agent called a neurotransmitter picks them up and carries them across the synapse, the space between two motor neurons. and carried across the synapse, the space between two motor neurons. The neurotransmitter in this case is glutamate. Once across the synapse, the message is received by ports on the dendrites of the next motor neuron, the process repeating until the muscle gets the message. Once the message is received, the muscle will move.
ALS - No Messages
- Amyotrophic: A - without, Myo - muscle, Trophic - nourishment
- Lateral - side of [the spinal cord]
- Sclerosis - hardening or scarring
In ALS, messages from the brain are stopped from reaching the muscle, leaving the motor neurons to shrivel up in die, pulling away from the muscle. Even though the neurons are dying, up to 80% could be dead before any signs of weakness show up, for as long as new neurons form, the muscle will function as normal. Eventually, the muscle will atrophy, or waste away, followed with paralysis as more motor neurons die. In the beginning, only one part of the body may be affected, but the disease soon progresses until the person can no longer move, even speak. Death of an ALS-afflicted person usually occurs within 3-5 years from the onset of symptoms. In most cases, the cause of death is accumulation of carbon dioxide, when the lungs are no longer able to provide a person with enough oxygen to survive.
Think of the brain as a general directing his army, the muscles, sending different orders through his soldiers, the motor neurons. The orders get passed along, from the highest-ranking officers to the lowest, until they reach their destination and get carried out. When the orders cease to reach their destination, nothing gets carried out, and the army weakens until it is basically no more--much like the muscles do in ALS.
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