A nerve root (Latin: ''radix nervi'') is the initial segment of a

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the ...

leaving the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...

. Nerve roots can be classified as: *

Cranial nerve Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and ...

roots: the initial or proximal segment of one of the twelve pairs of cranial nerves leaving the central nervous system from the

brain stem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is co ...

or the highest levels of the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...

. *

Spinal nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...

roots: the initial or proximal segment of one of the thirty-one pairs of spinal nerves leaving the central nervous system from the

. Each spinal nerve is formed by the union of a sensory

dorsal root The dorsal root of spinal nerve (or posterior root of spinal nerve or sensory root) is one of two "roots" which emerge from the spinal cord. It emerges directly from the spinal cord, and travels to the dorsal root ganglion. Nerve fibres with the ve ...

and a motor ventral root, meaning that there are sixty-two dorsal/ventral root pairs, and therefore one hundred and twenty-four nerve roots in total, each of which stems from a bundle of nerve rootlets (or root filaments).

Cranial nerve roots

Cranial nerves originate directly from the brain's surface: two from the

cerebrum The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. ...

and the ten others from the

. Cranial roots differ from spinal roots: some of these roots do not separate into individual sensory (

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal c ...

) and motor (

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

) roots, but can emerge from one fusion root instead; of the eleven cranial nerves, four express this concept of fusion. The remaining eight nerve roots only express one of the two types of connections. Five of these are exclusive motor roots, and the remaining three are all sensory.Biga, L., Dawson, S., Harwell, A., Hopkins, R., Kaufmann, J., LeMaster, M., . . . Runyeon, J. (unk). 13.3 Spinal and Cranial Nerves. Retrieved November 20, 2020, from https://open.oregonstate.education/aandp/chapter/13-3-spinal-and-cranial-nerves/

Spinal nerve roots

Spinal nerve roots are much more uniform than

cranial nerves Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and f ...

, one emerging from each level of the

spinal column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordates ...

. These roots look extremely similar to one another, and form separate sensory and

motor An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power g ...

root connections to the central nervous system. Sensory nerves all enter the column as dorsal nerve roots, while motor nerves enter as ventral roots. They are expressed uniformly on both sides of each

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

along the spinal column. The specific vertebrae classify spinal nerve roots they originate from. These are separated into three sections: cervical, thoracic, lumbar, and sacral. The cervical is separated into eight vertebrae named C1-C8. The thoracic segment consists of T1-T12; the lumbar is L1-L5; and sacral S1-S5.

Pain and pathologies

Damage to nerve roots can cause

paresis In medicine, paresis () is a condition typified by a weakness of voluntary movement, or by partial loss of voluntary movement or by impaired movement. When used without qualifiers, it usually refers to the limbs, but it can also be used to desc ...

and

paralysis Paralysis (also known as plegia) is a loss of motor function in one or more muscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory damage. In the United States, roughly 1 in 5 ...

of the muscle innervated by the affected

spinal nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...

. It may also cause pain and numbness in the corresponding dermatome. A common cause of damage to the

nerve roots A nerve root (Latin: ''radix nervi'') is the initial segment of a nerve leaving the central nervous system. Nerve roots can be classified as: *Cranial nerve roots: the initial or proximal segment of one of the twelve pairs of cranial nerves leaving ...

is spine

lesions A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals. Types There is no designated classifi ...

, such as prolapse of the

nucleus pulposus An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, to act as a ligament to hold t ...

, spinal tuberculosis,

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molec ...

, spinal tabs. Root pain syndromes, known colloquially as radiculitis and

sciatica Sciatica is pain going down the leg from the lower back. This pain may go down the back, outside, or front of the leg. Onset is often sudden following activities like heavy lifting, though gradual onset may also occur. The pain is often described ...

, are among the most common symptoms caused by damage to the nerve root.

Radiculopathy Radiculopathy, also commonly referred to as pinched nerve, refers to a set of conditions in which one or more nerves are affected and do not work properly (a neuropathy). Radiculopathy can result in pain ( radicular pain), weakness, altered sen ...

is commonly called the "root". In addition to pain, nerve damage may lead to impaired muscle control. Typically, mechanical dysfunction is caused by pressure on the nerve root or shock, affecting both the lower limbs and arms' roots. The first sign of disease (sometimes preceding the occurrence of the radicular syndrome by up to a few years) is a sensation of

pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, ...

in the neck and shoulder area. This pain often manifests due to

hypothermia Hypothermia is defined as a body core temperature below in humans. Symptoms depend on the temperature. In mild hypothermia, there is shivering and mental confusion. In moderate hypothermia, shivering stops and confusion increases. In severe ...

, poor posture or

ergonomics Human factors and ergonomics (commonly referred to as human factors) is the application of psychological and physiological principles to the engineering and design of products, processes, and systems. Four primary goals of human factors learnin ...

during work or sleep, or sudden head movement. Team roots are localized mostly within the three lower cervical roots, namely C5, C6, and C7.

Symptoms

*Forced reflexive position of the spine *Paraspinal muscle contracture *Reduction of cervical lordosis *Numerous painful points on the edges of the blade *Pain at the back of the head slope *Pain radiating to the upper chest and shoulder area *The positive sign of nerve root tension in the upper limbs *Weakness, especially with certain activities

C5 radiculopathy

*Sensation of pain along the lateral brachium of the affected side of the arm *C5 innervated muscle weakness may be found (e.g., rhomboids and deltoids)

C6 radiculopathy

*Sensation of pain along the lateral antebrachium of the affected arm *C6 innervated muscles are weak (e.g., forearm pronator and supinator and wrist extensors)

C7 radiculopathy

*Sensation of pain along with the middle finger of the affected arm *C7 innervated muscles are weak (e.g., wrist flexors and finger extensors)

Treatment

Treatment should be initiated as early as possible, before any muscle tone increases, which further intensifies the pain. Traction is recommended to decompress compressed roots. Radiculopathy can be caused by herniated nucleus pulposus. Surgery is the last resort when conservative therapy is unsuccessful.

Lower limb radiculopathies

The cause is a herniated

intervertebral disc An intervertebral disc (or intervertebral fibrocartilage) lies between adjacent vertebrae in the vertebral column. Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae, to act as a ligament to h ...

, often on a single nerve root. The first sign of the nerve root sickness is usually

lumbago Low back pain (LBP) or wiktionary:lumbago#Etymology, lumbago is a common musculoskeletal disorders, disorder involving the muscles, nerves, and bones of the back, in between the lower edge of the ribs and the lower fold of the buttocks. Pain can ...

, which usually occurs with periods of remission. The time to develop a full radicular syndrome may take several months or several years. Pain generally increases gradually, but it can also be sudden. Cold causes muscle contraction, which leads to increased previously hidden symptoms.

Symptoms

Scoliosis Scoliosis is a condition in which a person's spine has a sideways curve. The curve is usually "S"- or "C"-shaped over three dimensions. In some, the degree of curve is stable, while in others, it increases over time. Mild scoliosis does not ty ...

*Paraspinal muscle contracture *The reduction of lumbar

lordosis Lordosis is historically defined as an ''abnormal'' inward curvature of the lumbar spine. However, the terms ''lordosis'' and ''lordotic'' are also used to refer to the normal inward curvature of the lumbar and cervical regions of the human spin ...

Tingling Paresthesia is an abnormal sensation of the skin (tingling, pricking, chilling, burning, numbness) with no apparent physical cause. Paresthesia may be transient or chronic, and may have any of dozens of possible underlying causes. Paresthesias a ...

numbness Hypoesthesia or numbness is a common side effect of various medical conditions that manifests as a reduced sense of touch or sensation, or a partial loss of sensitivity to sensory stimuli. In everyday speech this is generally referred to as num ...

* Increased sensitivity * Other inflammatory diseases

L4 radiculopathy

*Pain located on the front of the thigh and shin further radiates towards the inner ankle, sometimes the medial toe *Occasionally, failure of the quadriceps muscle and reflex weakness

L5 radiculopathy

*Pain radiates to the side of the thigh and lower leg towards the back of the foot and toes 1–3 *All reflexes are preserved

S1 radiculopathy

*Pain radiates to the posterior side of the thigh and lower leg to the ankle side, sometimes up to the fourth toe *Gluteal muscles are weakened *Difficulty standing on toes

Treatment

Treatment can vary based on the nature and severity of the disease. A compressed nerve root can cause radicular pain with or without radiculopathy. Most of the time, symptoms from a compressed nerve will start to feel better within 6 to 12 weeks of nonsurgical treatment. To unlock the nerve root in the acute phase, it is recommended to apply traction and isometric muscle relaxation, and should be the first procedure to be performed in cases of severe pain. In cases where manipulation is undesirable or impossible to carry out, the infiltration may be root. Anti-inflammatory medications may be used to alleviate symptoms. In the acute setting, the main goal is to restore proper mobility by reducing pain. Surgery is used when other methods do not produce results, except when paralysis is observed; in those cases, surgery should be performed as soon as possible to avoid irreversible

of muscles.

References

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