SCI Primer/SCI Terms
Glossary OF terms in Spinal Cord Injury
Acute spinal cord injury. The early stage of spinal cord injury. Some people use to term to refer to a period when there is still continuing damage. This time period is controversial. Some investigators consider the period to be relatively short, i.e. several hours during which treatments can be given to prevent progressive or secondary tissue damage. Other investigators may consider the acute period to extend several weeks, during which there may be Wallerian degeneration of spinal tracts that have been cut off from the cell body. The acute period of spinal cord injury precedes a “subacute” period where presumably the spinal cord injury is undergoing both degeneration and repair.
agonist - a drug capable of combining with a receptor and initiating action.
. The act of walking.
antagonist - a drug that opposes the effects of another by physiological or chemical action or by a competitive mechanism.
Anterior Cord Syndrome-Incomplete spinal cord lesion with primary damage in anterior cord; loss of motor function, sense of pain and temperature; perseveration of proprioception, kinesthesia, and vibration below level of lesion.
. This is the muscle that flexes the ankles. Located at the front fo the leg between the knee and the ankle, this muscle is what lifts the foot up during the swing phase and prevents foot drop. Its antagonist muscle is the gastrocnemius.
apoptosis - also called programmed cell death. A form of cell death in which a programmed sequence of events leads to the elimination of old, unnecessary, and unhealthy cells.
arrhythmia - an abnormal heart rhythm. The heartbeats may be too slow, too rapid, too irregular, or too early.
astrocyte - a type of glial cell responsible for neurotransmission and neuronal metabolism.
autonomic dysreflexia - a potentially dangerous complication of spinal cord injury in which blood pressure rises to dangerous levels. If not treated, autonomic dysreflexia can lead to stroke and possibly death.
Avulsion-Pulling of tearing of a piece of bone away from the main bone.
axial traction - the application of a mechanical force to stretch the spine; used to relieve pressure by separating vertebral surfaces and stretching soft tissues.
axon - the long, thin extension of a nerve cell that conducts impulses away from the cell body.
axonal growth cone - dynamic structures present at the tip of developing and regenerating axons that respond to chemical cues for growth and direction.
. This is a complex reflexive movement of the toes when the bottom of the feet (near the toes) is scratched from the base of the little toe towards the base of the big toe. Normally, the toes tend to curl downward or not react to such scratching if the person can inhibit movements of the toes. However, in somebody who has had brain damage involving the motor cortex or the spinal cord involving the corticospinal tract, the toes show a “positive Babinsky response” which is a spreading and upward movement of the toes.
Brown-Sequard Syndrome-Incomplete spinal cord lesion caused by hemisection of the cord; loss of motor function, proprioception, and kinestheia on side of lesion; loss of sense of pain and temperature on opposite side.
Bulbocavernous Reflex (Positive)-Pressure on the glans penis or glans clitoris elicits a contraction of the external anal sphincter.
Burst (Explosion) Fracture-A comminuted vertebral fracture associated with pressure along the long axis of the vertebral column; also associated with flexion injuries; bone fragments are displaced centripetally.
Cauda Equina Lesion-Damage to the peripheral nerve roots below the first lumbar vertebra; some regeneration is possible.
Central Cord Syndrome-Incomplete spinal cord lesion producing greater neurologic involvement in upper extremities (cervical tracts more centrally located) than in the lower extremities (lumbar and sacral tracts more peripheral).
Contusion (SCI)-Damage to the spinal cord produced by pressure from displaced bone and/or soft tissues or swelling within the spinal canal.
Crede Maneuver-Technique for emptying urine from a flaccid bladder; pressure is placed between the umbilicus and sympysis pubis in an upward and downward direction.
. These are a family of neurotransmitters, including epinephrine, norepinephrine, serotonin, and others. These are sympathetic neurotransmitters that tend to increase the activity of smooth muscles.
Central Nervous System (CNS). The CNS refers primarily to the brain and the spinal cord. The boundaries of the CNS are the blood-brain-barrier.
central pattern generators (CPG) - neural circuits that produce self-sustaining patterns of behavior independent of their sensory input. Researchers have found evidence of a locomotor CPG in the spinal cord that synchronizes muscle activity during alternating stepping of the legs and feet.
cervical - the part of the spine in the neck region
Chronic spinal cord injury
. The stage of spinal cord injury where there is no longer continuing damage or recovery. Some people use the word to refer to people who have been injured for a long time. While there is no question that people have “chronic” spinal cord injury after several years, there is no clear consensus on what constitutes the time limit for chronic.
. This is an abnormal reflex pattern where a deep tendon reflex is hyperexcitable and repeats multiple times. For example, if the foot of somebody with spinal cord injury is grasped and then flexed firmly, the foot undergoes several “beats”, i.e. repeated extension and then flexion. Clonus can be seen on other muscles as well.
coccygeal - the part of the spine at the bottom of the spinal column, above the buttocks.
Complete Lesion (SCI)-No sensory or motor function below the level of lesion.
. Indentation of tissue, causing a deformation of the tissue. When the indentation is fast enough to cause cell breakage, it is usually called contusion. If the compression is slow (<0.5 m/sec), the main cause of damage is due to ischemia or loss of blood flow. The compression increases tissue pressure and the tissue pressure counters blood pressure, preventing blood flow.
Compression Fracture-A vertebral fracture resulting from pressure along the long axis of the vertebral column; closely associated with flexion injuries.
cytokine - a small protein released by immune cells that has a specific effect on the interactions between cells, or communications between cells, or on the behavior of cells. dendrite - a short arm-like protuberance from a neuron. Dendrite is from the Greek for "branched like a tree." disc - shortened terminology for an intervertebral disc, a disc-shaped piece of specialized tissue that separates the bones of the spinal column.
Deep Tendon Reflex
. This is a muscle reflex that is activated by sudden stretching of the tendon of a muscle. Muscles have stretch receptors that detect the tension of the muscle and these receptors send excitatory signals back to motoneurons that activate the muscle to contract. This forms a feedback loop so that the muscle contraction is held at a constant level. When the muscle is stretched, the motoneurons fire to contract the muscle so that it opposes the stretch. A deep tendon reflex is usually tested by using a rubber tipped hammer to tap the tendon. This produces a sudden stretch of the muscle and the muscle should respond with a contraction. This reflex is also called the monosynaptic reflex because only one synapse is interposed in the reflex circuit. The monosynaptic reflex can also be activated electrically by stimulating the nerve to the muscle and recorded electrically from the muscle. Nerve stimulation activates a contraction of the muscle (M-reflex) and this is followed by the monosynaptic reflex (H-reflex).
Dislocation-Displacement of a bone or vertebral body from its normal position.
. This refers to parts of the anatomy that are towards the back of the body. The word dorsal is usually applied to quadriped (four-legged) animals whereas the word “posterior” is usually used for human. Dorsal and posterior have the same meaning. Dorsal is opposite of ventral.
. The white matter of the spinal cord is organized into columns: two dorsal columns (left and right), lateral columns, and ventral columns. The dorsal columns (also called posterior columns) carry proprioceptive information.
. Spinal cord gray matter has four “horns”, two dorsal horns and two ventral horns. Thus, the dorsal horn refers to the gray matter in the spinal cord that is close to the back (posterior) side of the cord. The dorsal horn contains mostly sensory neurons that receive inputs for sensory afferents that come into the spinal cord through the dorsal roots.
. Each segment of the spinal cord has four roots, two dorsal roots and two ventral roots. The ventral roots contain the axons of motoneurons that go out to innervate muscle.
Dorsal Root Ganglia
. These are collections of neurons that are attached to spinal roots just outside the spinal canal. These ganglia contain the cell bodies of dorsal root sensory neurons that send one axon that splits into a peripheral and a central branch. The peripheral branch goes to receptor structures in skin, muscle, joints, and other tissues. The central branch enters the spinal cord through the dorsal root, branches to connect with neurons in the segment and send axons up and down the spinal cord in the dorsal columns. One branch of the axon ascends to the brainstem where it makes synapses with the neurons in the nucleus cuneatus or nucleus gracilis.
Dysesthesias (SCI)-Bizarre, painful sensations experienced below the level of lesion following spinal cord injury; often described as burning, numbness, pins and needles, or tingling sensations.
electroejaculation - a technique that uses an electric probe to stimulate ejaculation.
embryonic stem cells - undifferentiated cells from the embryo that have the potential to become a wide variety of specialized cell types.
excitotoxicity - a neurological process that is the result of the release of excessive amounts of the neurotransmitter glutamate.
extracellular matrix - the material found around cells composed of structural proteins, specialized proteins, and proteoglycans.
. These refer to muscles that extend the limbs, particularly the legs. Leg extensor muscles include the gluteus maximus, quadriceps, and gastrocnemius. They are responsible for supporting the weight of the body against gravity and oppose the action of flexor muscles.
fetal spinal cord cells - cells used by scientists to derive undifferentiated embryonic stem cells for transplant into the damaged spinal cord.
. These refer to muscles that flex the limbs. Leg flexor muscles include the psoas, the hamstrings, and the anterior tibialis.
free radicals - highly reactive chemicals that attack molecules and modify their chemical structure.
functional electrical stimulation (FES) - the therapeutic use of low-level electrical current to stimulate muscle movement and restore useful movements such as standing or stepping; also called functional neuromuscular stimulation.
. This is the muscle that extends the ankles. Located at the back of the leg between the knee and the ankle, this muscle is what allows people to stand on tip toes and provides the foot thrust for forward locomotion. Its antagonist muscle is the anterior tibialis.
glia -supportive cells in the brain and spinal cord. Glial cells are the most abundant cell types in the central nervous system. There are three types: astrocytes, oligodendrocytes, and microglia. glutamate - an excitatory neurotransmitter.
. This is a large muscle in the buttock that is responsible for extending the leg backward at the hip joint. It is used during locomotion for forward propulsion. It opposes the action of the psoas which brings the leg forward and flexes the hip joint.
. This refers to areas of the brain and spinal cord that contain mostly neuronal cell bodies. It is called gray matter because these areas appear dusky gray when examined in dead bodies. The name is used in conjunction with white matter which refers to areas of the brain and spinal cord that contain mostly myelinated axons. In the spinal cord, the gray matter is situated in the central part of the cord. When the spinal cord is viewed in cross-section, the gray matter appears to be butterfly-shaped area. The wings of the butterfly that are towards the back (dorsal or posterior) are called the dorsal horns. The wings that are towards the front (ventral or anterior) are called the ventral horns.
growth-inhibiting proteins: protein molecules that inhibit axon regeneration.
guidance molecules - molecules that guide axons to their target. Some guidance molecules attract certain axons while repelling others.
. This the the muscle that flexes the knee and opposes the quadriceps.
Heterotopic Bone Formation-Abnormal bone growth in soft tissues; a potential secondary complication following spinal cord injury; occurs below the level of the lesion. SYN: ectopic bone.
hypothermia - abnormally low body temperature.
Incomplete Lesion (SCI)-Some preservation of sensory or motor function below the level of lesion.
interneurons - neurons with axons that remain within the spinal cord.
Intrathecal Injection-Central (within the spinal canal) chemical injection that interrupts the reflex arc; used to decrease severe spasticity.
intubation - the process of putting a tube into a hollow organ or passageway, often into the airway.
. These are white matter columns in the spinal cord, situated on the two sides of the spinal cord. The lateral columns carry both sensory and motor information, including the spinothalamic tract, the spinocerebellar tract, the corticospinal tract, the rubrospinal tract, and others.
. Edward Taub first proposed this phenomenon from experiments involving the cutting of dorsal roots in monkeys and finding that the monkeys stopped using the arm that had lost sensation. These monkeys become virtually paralyzed even though the ventral motor roots remained intact. However, when these monkeys are forced to use their arms by constraining the movement of the good arm, they frequently recovered motor control in the denervated arm. He called this phenomenon “learned non-use”. More recently, Taub and colleagues have reported that constraint-induced movement therapy can restore function in people with hemiplegic strokes.
ligament - a tough band of connective tissue that connects various structures such as two bones.
lumbar - the part of the spine in the middle back, below the thoracic vertebrae and above the sacral vertebrae.
Maceration-Softening of a solid by exposure to water or other fluid; usually pertains to the skin.
macrophage - a type of white blood cell that engulfs foreign material. Macrophages are key players in the immune response to foreign invaders such as infectious microorganisms Macrophages also release substances that stimulate other cells of the immune system.
methylprednisolone - a steroid drug used to improve recovery from spinal cord injury.
Micturation-Voiding of urine. SYN: urination.
microglia - glial cells that function as part of the immune system in the brain and spinal cord.
monocyte - a white blood cell that has a single nucleus and can engulf foreign material. Monocytes emigrate from blood into the tissues of the body and evolve into macrophages.
Motoneuron. Sometimes also called motor neurons, these neurons send axons peripherally to innervate muscles. Located in the ventral horn of the spinal cord, spinal motoneurons release the neurotransmitter acetycholine to activate striated muscles. They receive afferent signals directly from sensory axons carrying information from muscle stretch receptors.
Motor Recovery. Recovery of voluntary movement. While there may not seem to be any ambiguity or difficulty with this definition, many people have asked whether spasms represent motor recovery.
. These are cells that can contract and relax. Muscle cells are unusual cells. While most cells contain a single nucleus, muscle cells contain hundreds or even thousands of nuclei. Muscle fibers or myofibers are single cells with multiple nuclei. There are two kinds of muscles: smooth muscles and striated muscles.
. Myelin is a membrane produced by Schwann cells or oligodendroglial cells. Myelin wraps many times around the axons. Schwann cells myelinate peripheral axons while oligodendroglial cells myelinate central axons. One Schwann cell myelinates only one axon while one oligodendroglial cell may myelinate as many as 21 axons. Each of these cells myelinate only a segment of the axon. Between the myelin segments, there are areas of no myelination called Nodes of Ranvier.
myelin - a structure of cell membranes that forms a sheath around axons, insulating them and speeding conduction of nerve impulses.
. Axons are often ensheathed by myelin. Myelinated axons are paradoxically more sensitive to stretching because the myelin prevents parts of the axon from stretching and therefore concentrates the stretch in axons between the myelin segments, i.e. the Nodes of Ranvier.
myelotomy - a surgical procedure that cuts into the spinal cord.
Neurectomy-Partial or total excision or resection of a nerve; used to reduce severe spasticity.
neural prostheses - prosthetic devices that can respond to signals from the brain.
neurogenic pain - generalized pain that results from nervous system malfunction.
neuromodulation - a series of techniques employing electrical stimulation or the administration of medication by means of devices implanted in the body. These techniques allow the treatment of a range of disorders including certain forms of pain, spasticity, tremor, and urinary problems.
neuron - also known as a nerve cell; the structural and functional unit of the nervous system. A neuron consists of a cell body and its processes: an axon and one or more dendrites.
neurostimulation - the act of stimulating neurons with electrical impulses delivered via electrodes attached to the brain.
neurotransmitter - a chemical released from neurons that transmits an impulse to another neuron, muscle, organ, or other tissue.
neurotrophic factors - proteins responsible for the growth and survival of neurons.
neutrophil - a type of white blood cell that engulfs, kills, and digests microorganisms.
. This adjective refers to sensations that are painful, as well as thermal (hot, cold), sensations. When a person loses nociception, this means that the person cannot sense pain (pinprick), heat, or cold. Nociceptive sensations differ from proprioceptive sensations that represent touch and position sense. In the spinal cord, axons in the spinothalamic tract in the lateral columns carry nociceptive information.
Nocturia-Excessive urination during the night.
. Mammalian cells contain nuclei that hold the DNA encoding the genetic information of the cell. Mammalian cells are eucharyotic cells. Unlike bacteria or other procaryote cells, eucharyote cells have nuclei. The membrane that surrounds the nucleus, or nuclear membrane, controls the movement of nuclear transcriptional factors that can get into the nucleus.
. These are specialized cells in the central nervous system that myelinate central axons. A typical oligodendroglial cells may myelinate as many as 21 axons surrounding it.
olfactory ensheathing glia - non-myelinating glial cells that ensheath olfactory axons within both the PNS and CNS portions of the primary olfactory pathway. They are being used in experiments to build bridges between damaged areas of the spinal cord.
oligodendrocyte - a type of nerve cell in the brain and spinal cord that surrounds and insulates axons
Osteoporosis-Decreased density or softening of bone.
paralysis - the inability to control movement of a part of the body.
paraplegia - a condition involving complete paralysis of the legs.
Peripheral Nerve Block-Local chemical injection (e.g., phenol) used to block transmission of a motor nerve selectively; used to decrease spasticity.
Posterior Cord Syndrome-A rare incomplete lesion with primary damage to the posterior cord; preservation of motor function, sense of pain and light touch with loss of proprioception and epicritic sensations below the level of lesion.
Postural Hypotension-A decrease in blood pressure that occurs when moving toward an upright posture. This occurs normally but may be severe following prolonged bedrest.
pressure sore (also known as a pressure ulcer or bed sore) - a reddened area or open sore caused by unrelieved pressure on the skin over bony areas such as the hip-bone or tailbone.
. This is the muscle that flexes the hip (forward), opposing the action of the gluteus maximus.
Primary Tissue Damage. Cellular damage that are directly attributable to the cause of the injury is called “primary tissue damage”. In the case of a contusion injury, the primary injury is due to mechanical stretching and shearing of cellular elements. In the case of compression injury, the primary injury is due to the loss of blood flow that causes cell damage. In the case of a cut or a penetrating wound, the primary injury is due to the severance or crushing of axons and cells. Primary tissue damage initiates secondary tissue damage.
. This adjective refers to sensations that indicate position. It also includes the ability to detect and localize touch sensation on the skin. When a person loses proprioception, this means that the person cannot tell light touch and joint position. Proprioceptive sensations differ from nociceptive sensations which are painful. In the spinal cord, axons in the dorsal (posterior) columns carry proprioceptive information.
. This is the large muscle in the front of the leg that is responsible for extending the knee joint. It opposes the action of the hamstrings which flex the knee.
quadriplegia - a condition involving complete paralysis of the legs and partial or complete paralysis of the arms.
receptor - a structure on the surface or interior of a cell that selectively receives and binds to a specific substance.
. This refers to activity of cells that are not necessarily under conscious control. For example, a deep tendon reflex is a movement of muscle that can be evoked by stretching the muscle, mediated by neurons that are situated in the spinal cord and the dorsal root ganglia. Although the brain can inhibit or suppress of deep tendon reflex, the reflex can occur in the absence of supraspinal influence. Sme reflexes are only under partial conscious control. For example, micturation (the act of passing urine) is a reflex that is mediated by neurons situated in the spinal cord and can occur in the absence of supraspinal influences. Once started, it may be difficult for a person control micturation. Some reflexes can be activated by supraspinal events. For example, sweating of the palms is produced by nervous activity but most people cannot readily control such sweating. Some reflexes are not under conscious control. For example, the contractile response of the pupil of the eye to light is a reflex that is mediated by neurons that are situated in the brainstem and superior cervical ganglia.
regeneration - repair, regrowth, or restoration of tissues; opposite of degeneration.
rhizotomy - an operation to disconnect specific nerve roots in order to stop severe spasticity.
sacral - refers to the part of the spine in the hip area.
Sacral Sparing-Incomplete lesion in which some sacral innervation remains intact; complete loss of motor function and sensation in other areas below the level of lesion.
. Action potentials conduct in myelinated axons by jumping from node to node of Ranvier. Large axons are myelinated while smaller axons are typically not myelinated by oligodendroglial cells. Saltatory conduction greatly increases the speed of signal conduction. In large sensory axons of the dorsal column, for example, saltatory conduction allows transmission of signals at speeds exceeding 100 meters/second.
Schwann cell - the cell of the peripheral nervous system that forms the myelin sheath.
Secondary Tissue Damage
. The injured spinal cord shows progressive tissue damage over several hours or days after injury, depending on the severity of the injury.
. The term afferent refers to input or incoming signals. Sensory afferent means incoming axons that carry sensory signals.
Shearing-Application of a horizontal or parallel force relative to adjacent structures; opposite to force which is normally present; associated with fracture dislocations of the thoracolumbar region.
Spasms. Involuntary organized movements, often involving multiple muscles. Spasms may be involuntary or voluntarily. Involuntary spasms are ones that either occur spontaneously or in response to sensory input below in the injury site. Voluntary spasms are mass movements that can be induced by the person and are indicative of some supraspinal influence on the spinal cord. Spasms may be associated with spasticity.
. Increased reflexes or muscle tone. Spasticity is usually assessed clinically by the Ashworth scale which scores the stiffness and rigidity of muscles in response to movement. Deep tendon reflexes are often exaggerated or may go into repetitive oscillations called clonus. Complex multi-muscle reflexes such as the Babinsky reflex may appear.
. Every segment of the spinal cord has associated spinal roots that enter and exit the spinal cord in the dorsal and ventral side. The dorsal and ventral roots join together as they approach the dura mater and become a single root outside of the spinal canal. The dorsal spinal root is associated with a dorsal root ganglion which contains the cell bodies of the sensory neurons that send axons into the peripheral nerve and into the spinal cord. The ventral spinal root contains motor axons that go from the spinal cord to muscles.
spinal shock - a temporary physiological state that can occur after a spinal cord injury in which all sensory, motor, and sympathetic functions of the nervous system are lost below the level of injury. Spinal shock can lower blood pressure to dangerous levels and cause temporary paralysis.
. This spinal tract goes from the spinal cord to the thalamus. The spinothalamic neurons are situated in the dorsal gray horn and send axons that cross over to the opposite lateral column (i.e. neurons in the left dorsal horn send axons to the right lateral column and vice versa), ascend in the lateral column all the way to the thalamus
stem cell - special cells that have the ability to grow into any one of the body's more than 200 cell types. Unlike mature cells, which are permanently committed to their fate, stem cells can both renew themselves and create cells of other tissues.
. These are receptors in striated muscles that sense muscle stretch. The receptors are specialized muscle fibers called spindles. Dorsal root ganglion neurons send axons that innervate these spindles. Stretching of the spindle activates the axons to send messages to the spinal cord.
Subluxation-Incomplete or partial dislocation.
synapse - a specialized junction between two nerve cells. At the synapse, a neuron releases neurotransmitters that diffuse across the gap and activate receptors situated on the target cell.
T-cell - an immune system cell that produces substances called cytokines, which stimulate the immune response. thoracic - the part of the spine at the upper-back to mid-back level.
. This brain structure is located in the center of the brain. It receives sensory information from the body and from other sensory organs. For example, thalamic neurons receive sensory information from the spinothalamic tract, the dorsal column nuclei, the brainstem nuclei, and other central nervous system structures. They relay the sensory information to the cerebral cortex cortex.
vertebrae - the 33 hollow bones that make up the spine.
Teardrop Fracture-Bursting type of fracture of cervical region; produces a characteristic anterior-inferior bone chip; fragment resembles a "teardrop" on x-ray film; associated with flexion and compression forces.
Tenotomy-Surgical section of a nerve; used to reduce spasticity
(Anterior). This refers to parts of the anatomy that are towards the front of the body. The word “ventral” is usually applied to quadriped (four-legged) animals whereas the word “anterior” (meaning front) is usually used for humans. Ventral is opposite of dorsal.
. The white matter of the spinal cord is organized into columns: two dorsal columns (left and right), lateral columns, and ventral columns. The ventral columns (also called anterior columns) carry vestibulospinal and reticulospinal tracts.
. Spinal cord gray matter has four “horns”, two dorsal horns and two ventral horns. Thus, the ventral horn refers to the gray matter in the spinal cord that is close to the front (anterior) side of the cord. The ventral horn contains mostly motor neurons that send their axons out the ventral roots to innervate muscle.
. Each segment of the spinal cord has four roots, two dorsal roots and two ventral roots. The ventral roots contain the axons of motoneurons that go out to innervate muscle.
. The vestibulospinal tract goes from neurons in the vestibular nucleus to the spinal cord. The vestibular nucleus is situated in the brainstem, receives information from the vestibular organs in the ear, and is responsible for detecting the position and acceleration of the head. It is a crucial for balance and posture. The vestibulospinal tract innervate mostly extensor motoneurons responsible to maintaining anti-gravity muscle activities.
Weight-supported ambulation. This refers to suspending people or animals in a harness and placing them to walk on a treadmill. A variety of techniques may be used to facilitate walking, including manual manipulation and electrical stimulation of muscle, nerve, or spinal cord. Weight-supported ambulation on treadmill has been reported by many groups now to be able to improve or restore overground locomotion in people with chronic spinal cord cord injury.