The spinal ganglion is a collection of nerve cell bodies at the roots of the spinal nerves. Sensory information from the peripheral nervous system reaches the central nervous system through the spinal ganglia. in diseases such as Friedreich’s ataxia, the spinal ganglia degenerate and cause movement disorders.
What is the dorsal root ganglion?
Ganglion is the medical term for collections of individual nerve cell bodies that thicken a nerve cord. The spinal ganglion is composed of somatic nerve fibers. In the associated, somatic nervous system, the motor function of the skeletal muscles is controlled. Thus, somatic nerve fibers play a major role in all voluntary and reflex movements of the body. It is through the somatic nervous system that the human being first has an active relationship with the outside world. The spinal nerves of the spinal cord in particular perform important tasks in the somatic nervous system. The spinal ganglia are located at each dorsal spinal nerve end and conduct sensitive signals to the posterior horn of the spinal cord. These sensitive signals play a role primarily in reflex movements. Each reflex is preceded by a specific stimulus that reaches the spinal cord via afferent sensory nerves, where it is switched to motor nerves that innervate muscles, realizing the ultimate muscle contraction as a movement response to the stimulus. Spinal ganglia are sometimes referred to as spinal ganglion, dorsal ganglion, or spinal sensorium nervi ganglion, and ultimately transmit stimuli from the peripheral nervous system to the spinal nerves and thus to the central nervous system. In some places, the nerve ganglia are also referred to as dorsal, intervertebral, and posterior root ganglia.
Anatomy and structure
Ganglia are autonomous neuronal structures. The spinal ganglia of the body are composed of neurons of the somatic nervous system that contain afferent sensory fibers. The nerve cell assemblies thickened nerve cords in the spinal cord and sit the dorsal root of all spinal nerves. One spinal ganglion is located on each side of each spinal cord segment, where it imprints as a distention of the dorsal nerve root. The ganglia pass through the foramina intervertebralia of adjacent vertebrae of the spinal column. The foramina intervertebralia are paired openings in the vertebral canal that form the adjacent vertebrae. Dorsal ganglia contain pseudounipolar neurons and use their dendrites to collect sensitive information about stimuli from a particular spinal cord segment. The axons of the neurons conduct over the posterior nerve root of the spinal nerves. Their neuronal bodies consist of epineurium, perineurium and endoneural connective tissue. Their perikarya range in size from 15 to 110 µm and have large nucleoli. The cell bodies are sheathed by spinal ganglion cells. These are specialized glial cells, also known as mantle cells or satellite cells. The individual ganglion neurons carry fenestrated capillaries in their interstices. Each spinal ganglion is composed of perikaries of afferent nerve fibers. Because spinal ganglia are pseudounipolar nerve fibers, sensory ganglia do not contain any synapses.
Function and Tasks
The central nervous system provides commands for all bodily processes in the form of excitation. The spinal cord mediates between information from the body and commands from the central nervous system. Thus, it transmits information from the peripheral nervous system to the central nervous system and also transmits central nervous system commands to target organs in the periphery. The most important switching point of the spinal cord is the spinal canal. This canal is composed of individual openings in the vertebrae, with each vertebra carrying about 31 branches on the left and right sides, known as spinal nerves, which extend from the spinal cord to all parts of the body for the purpose of transmitting stimuli. Sensory, or sensitive, nerves reach the spinal cord from the individual sensory organs via the posterior root. Motor fibers for movements draw from the spinal cord to the muscles. Their exit point corresponds to the anterior root of each spinal cord. The cell bodies of all sensory nerves are located in the dorsal root ganglion, while the cell bodies of motor nerves are located in the gray matter. Via long dendrites, the sensory fibers send information about touch, temperatures, body positions and pain from the body to the central nervous system.Many sensory fibers from the spinal ganglion are connected to the gray matter of the spinal cord via interneurons. Here, the motor fibers emerge via the anterior root and extend to the skeletal muscles. Nerves interconnected in this way are responsible for voluntary movements. Sensory fibers may also be directly interconnected with a motor pathway. Such interconnections correspond to reflexes. A reflex arc is composed of each of the elements receptor, sensory afferent nerve fiber, spinal cord, motor efferent nerve fiber, and effector such as muscle or gland. Reflexes are stereotyped stimulus responses that are triggered after a certain stimulus threshold is exceeded. The dendrites of the pseudounipolar nerve cells in the spinal ganglion collect sensory information from the body related to the particular spinal segment and transmit these stimuli either to the brain or, in the case of reflexes, directly to the effectors.
Diseases
One disease involving the spinal ganglia is Guillain-Barré syndrome. It is an acute inflammation of peripheral nerves and associated spinal ganglia with an as yet unexplained cause. In addition to symptoms such as back pain and sensory disturbances, symptomatic symptoms may include paralysis, muscle weakness, muscle pain, coordination disorders, or gait disturbances. Herpes viruses can also affect the spinal ganglia and infect neurons in addition to ganglion cells. Some herpes viruses remain in the nucleus of neurons and can flare up the herpes infection at any time. Friedreich’s ataxia is also associated with diseases of the dorsal root ganglia. In this genetic neurogenic disease, cardiac insufficiency and diabetes often occur in addition to paralysis. The cause of the individual symptoms is a degeneration of the spinal ganglia and brain cells. Apart from this, post-zoster neuralgia after infections with chickenpox, for example, is related to the spinal ganglia. This disease is triggered by the varicella-zoster virus, which permanently settles in the spinal ganglia of the body after infection. When the immune system loses efficiency due to stress or similar contexts, the original chickenpox infection becomes shingles. In post-zoster neuralgia, impaired transmission of stimuli in the spinal ganglia is considered causative. The viruses often leave permanent damage to the affected nerve roots, causing chronic neurogenic pain.
