Glossary
Each definition paraphrases its source, which is linked after it.
- Action potential
- An all-or-none electrical pulse in a neuron's membrane: depolarisation past threshold, then repolarisation. Betts et al. 2022, §12.4 · More
- Alar ligaments
- Paired ligaments from the dens to the base of the skull that limit rotation and side bending; with the transverse ligament they stabilise the craniocervical junction. Offiah and Day 2016 · More
- Anterior (ventral) horn
- The front part of the cord's grey matter, which sends motor signals to the skeletal muscles. Betts et al. 2022, §13.2 · More
- Anulus fibrosus
- The fibrous outer layer of an intervertebral disc. Betts et al. 2022, §7.3 · More
- Arachnoid mater
- A membrane of thin fibrous tissue forming a loose sac around the brain and spinal cord, beneath the dura. Betts et al. 2022, §13.3 · More
- ASIA Impairment Scale (AIS)
- The grade of a spinal cord injury in the standard examination, from A (neurologically complete: no sacral sparing) to E (a previous injury with an intact follow-up examination); C and D separate motor incomplete injuries by key muscle strength below the level. Kirshblum et al. 2021; Snider et al. 2025; Snider et al. 2025 · More
- Atlas (C1)
- The first cervical vertebra, which supports the skull on top of the column. Betts et al. 2022, §7.3 · More
- Axis (C2)
- The second cervical vertebra; its dens is the axis about which the head turns. Betts et al. 2022, §7.3 · More
- Betz cell
- A large neuron of the primary motor cortex that synapses with lower motor neurons in the brainstem or spinal cord. Betts et al. 2022, §14.3 · More
- Brain–computer interface (BCI)
- A non-muscular channel for sending messages and commands, built from recordings of brain activity. Wolpaw et al. 2002 · More
- Brain–spine interface
- A digital bridge that converts cortical activity recorded above a spinal cord injury into stimulation of the cord below it. Lorach et al. 2023 · More
- Cauda equina
- The bundle of lower nerve roots in the canal below the end of the cord, named for its resemblance to a horse's tail. Betts et al. 2022, §13.2 · More
- Central pattern generator (CPG)
- A spinal network that can, under some conditions, produce basic coordinated rhythmic locomotor movements even without descending or peripheral input. Guertin 2013 · More
- Cobb angle
- The angle of a sideways curve of the spine; it equals the sum of the tilts of the upper and lower end vertebrae. Wang et al. 2018 · More
- Conus medullaris
- The tapered lower end of the spinal cord; in a study of 629 adults its most common level was L1. Nakashima et al. 2021 · More
- Corticospinal tract
- The descending pathway from the motor cortex to the lower motor neurons of the cord; most of its fibres cross at the pyramidal decussation. Betts et al. 2022, §14.3 · More
- Craniosacral outflow
- The parasympathetic division's connections, from brainstem nuclei and the lateral horn of the sacral cord. Betts et al. 2022, §15.1 · More
- Decussation
- A crossing of fibres to the other side of the nervous system, such as the pyramidal decussation of the corticospinal tract. Betts et al. 2022, §14.3
- Dorsal root
- The root through which sensory axons enter the spinal cord. Betts et al. 2022, §13.4 · More
- Dorsal root ganglion
- A cluster of sensory neuron cell bodies on the dorsal root; the cells are unipolar. Betts et al. 2022, §13.4
- Dura mater
- A thick fibrous layer and strong protective sheath over the entire brain and spinal cord. Betts et al. 2022, §13.3 · More
- Extrapyramidal system
- The descending connections between the brain and the cord other than the corticospinal tract: the tectospinal, reticulospinal, vestibulospinal and rubrospinal tracts. Betts et al. 2022, §14.3 · More
- Filum terminale
- A fibrous continuation of the spinal cord that anchors the conus medullaris to the coccyx. Sharma et al. 2026 · More
- Gate control theory
- Melzack and Wall's 1965 theory that a gating mechanism in the dorsal horn modulates the transmission of pain signals, and that the brain can influence it through descending fibres. Katz and Rosenbloom 2015; Fink and Raffa 2025 · More
- Herniated disc
- Protrusion of the nucleus pulposus backwards through a weakened anulus fibrosus; most common at L4–L5 and L5–S1. Betts et al. 2022, §7.3 · More
- Information transfer rate
- Bits carried per selection (or per minute) by a brain–computer interface, from the number of targets and the accuracy. Wolpaw et al. 1998; Wolpaw et al. 2002 · More
- Intervertebral disc
- A fibrocartilaginous pad that fills the gap between adjacent vertebral bodies. Betts et al. 2022, §7.3 · More
- Intervertebral foramen
- The opening between adjacent vertebrae, formed by notches in their pedicles, through which a spinal nerve exits. Betts et al. 2022, §7.3
- Key sensory point (ISNCSCI)
- One standard spot per segment and side where light touch and pinprick are tested in the examination after spinal cord injury. Rupp et al. 2021; Kirshblum et al. 2011 · More
- Lateral horn
- Grey matter found only in the thoracic, upper lumbar and sacral cord, containing autonomic motor neurons. Betts et al. 2022, §13.2 · More
- Ligamentum flavum
- Short, paired, elastic ligaments behind the cord that join the laminae of neighbouring vertebrae. Betts et al. 2022, §7.3 · More
- Lower motor neuron
- The motor neuron in the ventral horn (or a cranial motor nucleus) whose axon reaches the skeletal muscle. Betts et al. 2022, §14.3
- Micturition reflex
- A spinal reflex in which bladder stretch receptors signal the sacral cord, leading to detrusor contraction and sphincter relaxation; voluntary control can override it. Betts et al. 2022, §25.2 · More
- Nucleus pulposus
- The gel-like centre of an intervertebral disc; its high water content resists compression and declines with age. Betts et al. 2022, §7.3
- Pelvic incidence
- A fixed angle of a person's pelvis that equals pelvic tilt plus sacral slope, which both change with posture. Lazennec et al. 2011 · More
- Phrenic nerve
- The nerve that drives the diaphragm, connected to the spinal cord at cervical levels 3 to 5. Betts et al. 2022, §15.2; Betts et al. 2022, §13.4 · More
- Pia mater
- A thin fibrous membrane directly on the surface of the brain and spinal cord. Betts et al. 2022, §13.3
- Posterior (dorsal) horn
- The back part of the cord's grey matter, responsible for sensory processing. Betts et al. 2022, §13.2 · More
- Sacral sparing
- Preserved sensation (light touch or pinprick at S4–5, or deep anal pressure) or voluntary anal contraction in the lowest sacral segments; its presence makes an injury incomplete. Snider et al. 2025; Kirshblum et al. 2021 · More
- Saltatory conduction
- Conduction along a myelinated axon, where the action potential jumps from node to node; faster than continuous conduction. Betts et al. 2022, §12.4 · More
- Spinal cord segment
- The part of the cord that gives off one pair of spinal nerves; there are 31 pairs. Segment levels do not match vertebral levels. Betts et al. 2022, §13.4 · More
- Tectorial membrane
- The thin upward extension of the posterior longitudinal ligament, from the axis to the clivus of the skull. Offiah and Day 2016; Lee et al. 2022 · More
- Thoracolumbar outflow
- The sympathetic division's connections, which emerge from the thoracic and upper lumbar spinal cord. Betts et al. 2022, §15.1 · More
- Threshold
- The membrane potential a depolarisation must reach to fire an action potential, about −55 mV in the textbook neuron. Betts et al. 2022, §12.4
- Upper motor neuron
- A motor neuron with its cell body in the primary motor cortex, synapsing on a lower motor neuron. Betts et al. 2022, §14.3 · More
- Vertebral foramen
- The large opening between the vertebral arch and body, which contains the spinal cord. Betts et al. 2022, §7.3