Nervous Tissue & the Spinal Cord - Term Paper Example

The spinal cord begins at the base of the brain in the medulla and goes down to the second lumbar level. Inside the spinal cord is a central butterfly-like pattern of grey matter. Inside the spinal cord there are two main branches of the spinal nerve that are connected to the spinal cord. These are called the ventral and the dorsal root. Ventral root is located on the front and contains high density of motor nerve axons. This area is mainly responsible for sending impulses from the spinal cord to the skeletal muscles.

The dorsal root is the posterior branch of the spinal cord that contains sensory nerve fibers which carry nerve impulses from the sensory organs to the spinal cord. The cluster of cell bodies from the sensory nerve forms the dorsal root ganglion on the dorsal root. The outer lighter part or the white matter of the spinal cord is composed of a mixture of axons of motor neurons and sensory neurons (Paxinos et al). They grey matter consists mainly of interneurons, motor neurons, axons without a myelin sheath and a cluster of neuroglia cells.

The white matter is composed of axons of the cell bodies that have been insulated by a fatty sheath called myelin. This insulation prevents any cross interaction between different neurons and also considerably slows the speed of the electrical impulses that are transmitted. In the exterior of the spinal cord, two enlarged regions are present to allow for the larger number of nerve cells that are needed to coordinate responses with the upper and lower limbs. The cervical enlargement contains nerve cells linked with the arms while the lumbar enlargement connects with the feet.

The spinal cord is divided into 31 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal and out of each of these segments emerge the spinal nerves (Todd). Spinal nerves are a pair of nerves that originate inside the spinal cord. The nerve roots branch out from the spinal cord and travelling through the spaces in the vertebrae known as the foramina, they create of network of nerves around the whole body. Each spinal nerve branches out but ends at a particular area of the body known as a dermatome.

The spinal nerve consists of two roots, one entering the dorsal region while the other emerging from the ventral. The cell bodies of one root are concentrated in the dorsal root ganglion and it enters the spinal cord via dorsal root. As it consists of many sensory fibers, its function is to carry impulses of the stimuli to the spinal cord. The other root emerges from the ventral part and contains multitude of motor fibers which in collaboration with the brain are responsible to produce an effect in response to the stimuli detected by sensory fibers (Craven 150-151).

All of these impulses are channeled through the spinal cord to the brain. The reflex actions are an exception as these are directed by the spinal cord rather than the brain. The pathway of a reflex action is known as the reflex arc. A reflex arc allows for a rapid protective action which protects an organism from harm. In a reflex arc, the stimulus is detected by the receptor cells which are connected to the sensory neurons via synapses. The sensory neurons are responsible for carrying the impulse to the central nervous system.

An interneuron connects the motor neuron and a sensory neuron via synapse and the impulse is transferred form a sensory neuron to motor neuron through it. The spinal cord serves as a mediator between