(3) The pathway for the conscious sensation of these stretches uses the
same structures as the deep touch general sense.
Section VIII. MOTOR PATHWAYS IN THE HUMAN NERVOUS SYSTEM
The CNS receives information through the sensory pathways and collates this
information against information stored in memory. This results in a decision. If the
decision is to do something, then the CNS sends out commands through the motor
pathways to the effector organs (muscles, glands, etc.).
a. The motor pathways descend in the neuraxis and transmit the commands to
the motor neurons. The processes of motor neurons leave the CNS by way of the
peripheral nerves. The somatic motor neurons activate striated muscle fibers. The
visceral motor neurons activate smooth muscle tissue, cardiac muscle tissue, and
b. We usually consider two general motor pathways--the pyramidal motor
pathways and the extrapyramidal motor pathways.
12-29. PYRAMIDAL MOTOR PATHWAYS
A pyramidal motor pathway is primarily concerned with volitional (voluntary)
control of the body parts, particularly with the fine movements of the hands. Since such
a pathway is concerned with volitional actions, it is suitable for neurological screening
a. Cerebral Motor Cortex. The pyramidal motor pathway begins in the
precentral gyrus of the cerebral hemisphere. As we have already seen with the sensory
pathways, the neurons making up the cerebral cortex of the precentral and postcentral
gyri are arranged in a pattern (motor homunculus) corresponding to the various parts of
the body to which they are connected.
b. Motor Neurons. From the precentral gyrus, the axons of these upper motor
neurons (UMN) pass into the neuraxis of the CNS and descend. At the level of the
appropriate segmental nerve, the UMN synapses either directly or indirectly with a lower
motor neuron of the segmental nerve. Direct synapses (monosynaptic) provide the
most rapid reactions. Such direct synapses are used in particular for the fine
movements of the hands.
c. Corticospinal Pathways. The medulla is the lowest part of the brainstem.
On the underside of the medulla, the axons of the UMNs form a pair of structures known
as the pyramids. Immediately below the pyramids, at the beginning of the spinal cord,