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Neuronal Control of Breathing

Breathing is controlled by nerves that originate from the cervical and thoracic levels of the spinal cord. Due to the numerous muscles and nerves involved, the respiratory function that is affected depends on the level and severity of the injury. Table 1 outlines the associated muscles involved in inspiration and expiration that are affected by injuries at various levels; subsequent patient outcomes for these injuries are also detailed. Information for this table was adapted from Warren et al. (2014) and Mansel and Norman (1990).

Table 1: Effect of Level of Injury on Respiratory Function

Table 1. Effect of Level of Injury on Respiratory Function

LevelAssociated Muscles for Inspiration and Pulmonary FunctionAssociated Muscles for ExpirationPatient Outcomes
C1Sternocleidomastoid and accessory muscles

(C1-C4)

Complete injury above C3 usually results in paralysis and denervation of all muscles required for inspiration and expiration. Life-long ventilation usually required.
C2
C3Diaphragm

(C3-C5)

 

Tidal volume is reduced from injury at or above this level

C4An injury from C3-C5 results in variable inability to inspire and expire. Often ventilated. May be able to wean from ventilation in time, depending on other factors.
C5Pectoralis major muscle

(C5-T1)

C6Scalenes accessory

(C4-C8)

Patients experience more difficulty with expiration than inspiration. May not experience respiratory failure, but often experiences muscle fatigue. Often ventilated initially but can usually achieve independent breathing.
C7
C8
T1External intercostals

(T1-T11)

 

These muscles are responsible for producing vital capacity. Vital capacity reduced by up to 53%, peak expiratory flow rate reduced by up to 42%, and forced expiratory volume is reduced up to 49% of what is seen in healthy individuals.

 

Internal intercostal muscles

(T1-T11)

Patients experience more difficulty with expiration than inspiration. Patients experience a reduced ability to cough in an injury at or above this level.
T2
T3
T4
T5
T6Abdominal muscles and internal intercostals

(T6-T12)

T7
T8
T9
T10
T11
T12