Chapter 14, Problem 14.1.1AYLO

Four functions of the spinal cord and their relationship to spinal tracts, central patern generators, and reflex arcs in the cord

Summary Introduction

To write:

The four roles of spinal cord and their relationship to central pattern generators, spinal tracts and reflex arcs.

Introduction:

Motor control can be defined as the systematic control of movement in organisms which contain a nervous system. The primary motor cortex (M1) is the main area of the brain that is involved in the motor function. M1 is present in the frontal lobe of the brain.

Explanation of Solution

The spinal cord can be defined as the cylindrical bundle of the nerve fibers and connected tissue. It is surrounded in the spinal region and joins approximately all the body parts to the brain. It forms the central nervous system with the brain.

1) Spinal cord obtains and initiates to mix the primary sensory input-somatosensory fibers from the receptors of skin, skeletal muscle. The tendons-viscero sensory fibers or viscerosensory afferents from the receptors present in abdominal, thoracic, and pelvic viscera. This evidence is used to facilitate the reflexes is spread to the higher centers through ascending fibers or both.

2) It has motor neurons which innervate the target structures

i). Somatic motor neurons or somatic efferents that innervates the skeletal muscle.

ii). Visceral motor neurons or visceral efferents that these preganglionic neurons would synapse in a peripheral ganglion to affect the smooth muscle, cardiac muscle, or glandular epithelium

3) It contains the descending fibers from the brainstem or cortex that control the action of spinal motor and sensory neurons.

4) It also mediates the spinal reflexes.

1. A spinal nerve:

It can be defined as a mixed nerve that carries sensory, motor and autonomic signals or information between the spinal cord and the remaining body. In the human body, there are present 31 pairs of spinal nerves. These are located one on each side of the vertebral column.

2. The ascending tracts:

These are the neural pathways by which the sensory message from the peripheral nerves is transferred to the cerebral cortex. These are also known as somatosensory systems or pathways.

3. Descending tracts:

These are those pathways by which the motor signals are directed from the brain to the lower motor neurons. These neurons then directly stimulate the muscles to produce movement.

4. A reflex arc:

It can be defined as a neural pathway which regulates a reflex. In the vertebrates, most of the sensory neurons cannot pass straight into the brain, but they usually synapse in the spinal cord. The reflex arc has the following five components:

a. Receptor: It is present in sense organs such as skin, muscle, or the other organ.

b. Sensory neuron: It brings the impulse towards CNS.

c. Interneuron: This component brings the impulse within CNS.

d. Motor neuron: This component of the reflex arc carries impulse away from the CNS.

e. Effector: The motor neuron transfers the efferent impulses to the effector. It then produces the response.

5. The gray matter:

In the transverse sections, the gray matter is divided into dorsal and ventral horns.

Dorsal horn:

The posterior grey column or dorsal horn of the spinal cord is one of the three grey columns of the spinal cord. It receives numerous types of sensory data from the body, together with proprioception, fine touch, and vibration. It receives and processes the incoming somatosensory information.

Ventral horn:

The anterior grey column or ventral horn of the spinal cord is the front column of grey matter in the spinal cord. It is the column where the alpha motor neurons cell bodies are present. It transmits the message or neural signals to the skeletal muscles. In the transverse sections, the gray matter is divided into dorsal and ventral horns.

6. Central pattern generators or CPGs:

These are usually recognized as the special systems that can yield oscillatory motor output in the lack of any oscillatory input.

Conclusion

The spinal cord can be defined as the cylindrical bundle of the nerve fibers and connected tissue. The spinal nerves are known as mixed nerves because their posterior roots bear the sensory axons, while their anterior roots bear the motor axons.