Motor Spinal Pathways

Motor Pathways

Motor pathways can also be called efferent pathways.  These pathways are series of neuronsThe functional cells of the nervous system that transmit signals. that carry information from the central nervous systemComposed of the brain and spinal cord; integrates and processes information.  to the peripheral nervous systemPNS All nervous tissue outside the CNS; includes nerves and ganglia..  Most of the neurons in these pathways are the multipolar-type neurons that we have been using as the standard example of a neuron.  The green colored neurons in these pictures are all the upper motor neuronsNeurons that originate in the brain and control lower motor neurons., or the first neurons in the pathway.  They usually have their cell bodyThe central part of a neuron containing the nucleus and organelles. in the part of the brain called the primary motor cortex.  The upper neuron leaves the primary motor cortex and uses a motor pathway to descend the spinal cordThe central nervous system structure that relays signals between the brain and body..  In the gray matterThe inner portion of the spinal cord composed mostly of neuron cell bodies and synapses. of the spinal cord, this upper motor neuronA neuron that originates in the brain and synapses on a lower motor neuron. synapses with the cell body of a lower motor neuronA neuron that directly stimulates a muscle., all pictured here in red.  The lower motor neuron then leaves the spinal cord through the ventralRelating to the front or belly side of the body. root, the spinal nerve, then the ventral ramus and finally to one of the four nerve plexuses.

Specific Motor Pathways

There are many ways to classify motor pathways.  One such way is to designate them as carrying conscious or unconscious information.  This is a broad generalization, but it can work for us at this level.  The corticospinal pathway is named because of its origin in a cortex of the brain, mostly the primary motor cortex.  These tractsBundles of nerve fibers in the CNS that carry signals between brain regions. are located here on this transverse section A cut or slice of the body or an organ for study. of the spinal cord.  Remember that this side of the spinal cord is blue representing sensory pathways and the red represent motor pathways.  The spinal cord has symmetry so both sensory and motor pathways are on both sides.  I have a picture here of someone doing embroidery, which requires fine motor skills of the hands.  Because this is conscious information, I know that it is controlling skeletal muscle.  Therefore the red, lower motor neuronsNerve cells that directly stimulate muscles to contract. all connect to a skeletal muscle at the neuromuscular junctionThe connection between a motor neuron and a muscle fiber..

I also have a person here with their brachial plexusA network of nerves in the neck and shoulder that control the upper limbs..  Remember that there are 4 plexuses of motor neuronsNeurons that carry outgoing information from the CNS to effector organs.: cervical, brachial, lumbar, and sacral.  So, all these lower motor neurons are leaving the spinal cord and making these plexuses or nerve networks.

Specific Motor Pathways

The tectospinal pathway is really important in many sports, such as baseball.  This pathway houses motor neurons that originate in an area called the midbrainThe upper portion of the brainstem involved in visual and auditory processing..  The midbrain is the superiorAbove or toward the upper part of the body. most portion of the brain stem.  This area of the brain is involved in taking in visual and auditory information and producing headRounded proximal end that fits into the acetabulum of the hip bone. movements.  It’s kinda like how you just can’t resist turning your head in the direction of a loud noise.  This is the result of the midbrain controlling your neckNarrow region just below the head; common fracture site. muscles.  Your optic nerve is the only sensory nerve transmitting information TO your brain, but there are a few cranial nervesNerves that arise from the brain and control head and neck functions. that control the muscles around the eye when information comes FROM the brain.  The oculomotor and trochlear are only two that carry motor information for the eye.

Motor Pathways Examples

The reticulospinal pathways also have an origin in the brainstemThe lower part of the brain that connects to the spinal cord and controls vital functions.. As you can see here the upper motor neurons are coming from the ponds and the medulla oblongataThe lowest part of the brainstem controlling vital functions like breathing and heart rate.. You can also see how the motor neurons are extending to the lumbar plexusA network of nerves supplying the lower back and upper legs. and controlling large skeletal muscles of the leg. This accounts for how this motor pathway plays a part in controlling your balance and posture.

Motor Pathways Examples

The vestibulospinal pathway also carries unconscious information about balance and posture. However this pathway unlike the reticulospinal incorporates information gathered from the vestibulo cochlear cranial nerve to produce a pattern of output. I have someone dancing here because doing ballet not only requires manipulation of balance and posture it also requires manipulation of the head. This is the pathway that allows you to continue walking forward even though you might turn your head to one side to look at something. Also note that the upper motor neurons from these pathways originate in the medulla oblongata and as you can see this pathway right here extends almost all the way to the sacral plexusA network of nerves in the lower back that controls the pelvis and lower limbs. period