Spinal shock was first explored by Robert Whytt in 1750 as a loss of

sensation Sensation (psychology) refers to the processing of the senses by the sensory system. Sensation or sensations may also refer to: In arts and entertainment In literature *Sensation (fiction), a fiction writing mode *Sensation novel, a British ...

accompanied by motor

paralysis Paralysis (: paralyses; also known as plegia) is a loss of Motor skill, motor function in one or more Skeletal muscle, muscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory d ...

with initial loss but gradual recovery of

reflexes In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a Stimulus (physiology), stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous s ...

, following a

spinal cord injury A spinal cord injury (SCI) is damage to the spinal cord that causes temporary or permanent changes in its function. It is a destructive neurological and pathological state that causes major motor, sensory and autonomic dysfunctions. Symptoms of ...

(SCI) – most often a complete transection. Reflexes in the spinal cord below the level of injury are depressed (hyporeflexia) or absent (areflexia), while those above the level of the injury remain unaffected. The 'shock' in spinal shock does not refer to circulatory collapse, and should not be confused with neurogenic shock, which is life-threatening. The term "spinal shock" was introduced more than 150 years ago in an attempt to distinguish arterial hypotension due to a hemorrhagic source from arterial hypotension due to loss of sympathetic tone resulting from spinal cord injury. Whytt, however, may have discussed the same phenomenon a century earlier, although no descriptive term was assigned. __TOC__

Phases of spinal shock

Ditunno et al. proposed a four-phase model for spinal shock in 2004 as follows: Phase 1 is characterized by a complete loss—or weakening—of all reflexes below the SCI. This phase lasts for a day. The

neurons A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

involved in various

reflex arc A reflex arc is a neural pathway that controls a reflex. In vertebrates, most sensory neurons synapse in the spinal cord and the signal then travels through it into the brain. This allows for faster reflex actions to occur by activating spinal mo ...

s normally receive a basal level of excitatory stimulation from the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

. After an SCI, these cells lose this input, and the neurons involved become hyperpolarized and therefore less responsive to stimuli. Phase 2 occurs over the next two days, and is characterized by the return of some, but not all, reflexes below the SCI. The first reflexes to reappear are polysynaptic in nature, such as the

bulbocavernosus reflex The bulbocavernosus reflex (BCR), bulbospongiosus reflex (BSR) or "Osinski reflex" is a polysynaptic reflex that is useful in testing for spinal shock and gaining information about the state of spinal cord injuries (SCI). ''Bulbocavernosus'' i ...

. Monosynaptic reflexes, such as the deep tendon reflexes, are not restored until Phase 3. Restoration of reflexes is not rostral to caudal as previously (and commonly) believed, but instead proceeds from polysynaptic to monosynaptic. The reason reflexes return is the hypersensitivity of reflex muscles following

denervation Denervation is any loss of nerve supply regardless of the cause. If the nerves lost to denervation are part of neural communication to an organ system or for a specific tissue function, alterations to or compromise of physiological functioning ca ...

– more receptors for neurotransmitters are expressed and are therefore easier to stimulate. Phases 3 and 4 are characterized by hyperreflexia, or abnormally strong reflexes usually produced with minimal stimulation.

Interneurons Interneurons (also called internuncial neurons, association neurons, connector neurons, or intermediate neurons) are neurons that are not specifically motor neurons or sensory neurons. Interneurons are the central nodes of neural circuits, ena ...

and

lower motor neurons Lower motor neurons (LMNs) are motor neurons located in either the anterior grey column, anterior nerve roots (spinal lower motor neurons) or the cranial nerve nuclei of the brainstem and cranial nerves with motor function (cranial nerve lower ...

below the SCI begin sprouting, attempting to re-establish synapses. The first synapses to form are from shorter

axons An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see spelling differences) is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action pot ...

, usually from interneurons – this categorizes Phase 3. Phase 4 on the other hand, is soma-mediated, and will take longer for the soma to transport various growth factors, including proteins, to the end of the axon.

Autonomic effects

In spinal cord injuries above T6, neurogenic shock may occur, from the loss of autonomic innervation from the brain. Parasympathetic is preserved but the synergy between sympathetic and parasympathetic system is lost in cervical and high thoracic SCI lesions. Sacral parasympathetic loss may be encountered in lesions below T6 or T7. Cervical lesions cause total loss of sympathetic innervation and lead to vasovagal

hypotension Hypotension, also known as low blood pressure, is a cardiovascular condition characterized by abnormally reduced blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood and is ...

and bradyarrhythmias – which resolve in 3–6 weeks.

Autonomic dysreflexia Autonomic dysreflexia (AD) is a life-threatening medical emergency characterized by hypertension and cardiac arrhythmias. This condition is sometimes referred to as autonomic hyperreflexia. Most cases of AD occur in individuals with spinal cord ...

is permanent, and occurs from Phase 4 onwards. It is characterized by unchecked sympathetic stimulation below the SCI (from a loss of cranial regulation), leading to often extreme

hypertension Hypertension, also known as high blood pressure, is a Chronic condition, long-term Disease, medical condition in which the blood pressure in the artery, arteries is persistently elevated. High blood pressure usually does not cause symptoms i ...

, loss of

bladder The bladder () is a hollow organ in humans and other vertebrates that stores urine from the kidneys. In placental mammals, urine enters the bladder via the ureters and exits via the urethra during urination. In humans, the bladder is a distens ...

or bowel control,

sweating Perspiration, also known as sweat, is the fluid secreted by sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distributed over much of the ...

headaches A headache, also known as cephalalgia, is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Head ...

, and other sympathetic effects.

References

{{shock types Spinal cord disorders