lumbar vertebrae the five vertebrae between the thoracic vertebrae and the sacrum. vertebra magÂ´na the sacrum. odontoid vertebra the second cervical vertebra, or axis. vertebra plaÂ´na a condition of spondylitis in which the body of the vertebra is reduced to a sclerotic disk.
Generally, in the early stages of drowning, very little water enters the lungs: a small amount of water entering the trachea causes a muscular spasm that seals the airway and prevents the passage of both air and water until unconsciousness occurs.
Assuming a normally fit person, otherwise conscious and uninjured, who is drowning in warm (21C/70F) water, I would estimate 2-3 minutes before full loss of consciousness, and 5-10 minutes before brain damage, and 15 minutes before irrecoverable death.