Download 7-4_DescendingPathways_HubaT

1.
Welcome everybody, my name is Huba Tamás, and I am going to hold a short lecture
about the function and organization of descending pathways in the spinal cord.
Our nervous system is divided into the central nervous system and the peripheral nervous
system. The main components of the central nervous system are the brain and the spinal cord.
The descending pathways often originate in the brain and go through the whole spinal cord.
2.
In this picture you can see the 31 pairs of spinal nerves. Spinal nerves are grouped
according to the place where they emerge from the spinal cord. Spinal nerves are responsible
for carrying information between the central nervous system and other parts of the body. The
spinal cord is the center of many reflexes, such as the patellar reflex, and contains nerve fibers
ascending to and descending from the brain.
3. The spinal cord consists of an external white substance and a gray, butterflyshaped central region made up of nerve cell bodies. Nerve fibers make up pathways in the
white matter. Ascending pathways contain sensory fibers that originate in the body, while
descending pathways contain motor fibers that originate in the brain.
3.b We can separate three types of descending pathways, the pyramid tract,
extrapyramidal tract and vegetative tract. The pyramid tracts emerge from the cerebral cortex,
and most of them crossing-over in the medulla, and continue it’s way to the anterior horn of
the spinal cord, where they make synapses with motor neurons. The main function of the
pyramid tracts is to bring signal to muscles to make a decisived, voluntary movement.
The extrapyramidal tracts originate from the gray brainstem nuclei, and also controlling
movements. It is responsible for unconscious automatic movement of the body and
extremities. And organise a full move from little parts. For example walking, or swimming.
The vegetative tracts start from higher vegetative centres, and they are controlling mainly the
smooth muscles of our organs.
4. The organization of the descending pathways:
The muscle function information from the cerebral cortex and other higher centers,
goes through a chain of neurons in the nervous system, these are the descending pathways.
The cerebral cortex or usually other higher centres are the starting points, and the whole
landing route consists of three neurons. The primary order neuron cell bodies are in the
cortex. It’s axon will join, and make synapse to the second order neuron, which is set in
spinal cord gray matter in the anterior horn. The second order neuron’s axon is usually short,
and it joins, and make synapse to the third order neurons. It is called the lower motor neurons
in the anterior horn of the gray matter. The third neuron’s axon innervating smooth and
skeletal muscle through the front roots of the spinal cord. This is the system, how they look
like. The greatest example for the muscle answer is the patella reflex. (when you hit your
knee, and it send the information from the injury to your nervous system, which gives the
muscle answer, pulls up the knee)
5.
The function of descending pathways:
These pathways are mainly responsible for reflexes, and handle the motor neurons, so
movements! Lower motor neurons, and upper motor neurons are responsible for, controlling
voluntary motor activities, and controlling muscle tone and reflex activities.
Thank you for your attention. Now I try to answer your questions.