In movies, knocking someone unconscious can look like this:
It can be a PG-13 way to take care of a bad guy, who wakes up sometime later with only a headache.
(However, more realistic depictions can be found, usually in war movies.)
In real life, it looks more like this:
What isn't shown is that in reality a person knocked unconscious is usually knocked out only for a few seconds, minutes at most.
If a person is knocked out for longer than that, this may indicate severe brain damage, which could lead to loss of function, life-long debilitation, coma, and death. Essentially, a blow hard enough to knock a person unconscious is classified as a Traumatic Brain Injury (TBI). Since most guards,henchmen,etc.in movies are knocked out for extended periods of time, it quite possible that they may suffer severe brain damage.
Also the force (Scientific American has one pro boxer's punch at 400kg)required to knock someone out might also break the skull or kill the person. Even wikipedia's article on boxing states that there is no clear line drawn between the force needed to knock someone out and the force needed to kill that person.
So, knocking someone unconscious by hitting them in the head is clearly not as practical or consequence-free as tv and movies might lead one to believe.
The most common causes of being knocked unconscious are related to either falls or vehicle crashes. However, direct trauma to the head is another cause, the CDC lists assault as accounting for 10% of reported cases. (Fact: Chuck Norris is responsible for 9.7%)
What is TBI?
Traumatic brain injury is the most
common cause of death and disability
in young people. There is much hope
for improvement in early care and
functional outcome by use of
scientific evidence-based guidelines.
Traumatic brain injury is graded as
mild, moderate, or severe on the basis
of the level of consciousness or
Glasgow coma scale (GCS) score after
resuscitation (panel). Mild traumatic
brain injury (GCS 13–15) is in most
cases a concussion and there is full
neurological recovery, although many
of these patients have short-term
memory and concentration
difficulties.1 In moderate traumatic
brain injury (GCS 9–13) the patient is
lethargic or stuporous, and in severe
injury (GCS 3–8) the patient is
comatose, unable to open his or her
eyes or follow commands. Patients with
severe traumatic brain injury
(comatose) have a significant risk of
hypotension, hypoxaemia, and brain
swelling. If these sequelae are not
prevented or treated properly, they
can exacerbate brain damage and
increase the risk of death. source
In reality, TBI consists of more than just the initial impact.
Step 1: Impact
The main thing to keep in mind is:
Although TBI is a problem of major
medical and socioeconomic
significance, its pathogenesis is
incompletely understood, and it is
often difficult to reconstruct the
events leading to the primary and
secondary lesions of varying severity
and regional distribution that
constitute TBI source
This means that while there are some general aspects and theories we can apply broadly to patients with TBI, it is by no means a cut-and-dry phenomenon, and individual cases show great variation.
At the time of the initial impact, the brain is injured in two places, the place of the impact and the side opposite the place of impact. This happens because the brain is surrounded by fluid and can be moved if if enough force is applied.
In movies, it is this intial impact which renders the victim unconscious, however in reality, this is not always the case.
Step 2: Secondary Injuries:
In reality, the person may not be rendered unconscious by the primary injury. However, they may become unconscious later due to the secondary injuries. Secondary injuries are typically caused by bleeding or swelling within the skull which compresses the brain.
The principal mechanisms of TBI are
classified as (a) focal brain damage
due to contact injury types resulting
in contusion, laceration, and
intracranial haemorrhage or (b)
diffuse brain damage due to
acceleration/deceleration injury types
resulting in diffuse axonal injury or
brain swelling.2404649 Outcome from
head injury is determined by two
mechanisms/stages: (a) the primary
insult (primary damage, mechanical
damage) occurring at the moment of
impact. In treatment terms, this type
of injury is exclusively sensitive to
preventive but not therapeutic
measures. (b) The secondary insult
(secondary damage, delayed
non-mechanical damage) represents
consecutive pathological processes
initiated at the moment of injury with
delayed clinical presentation.
Cerebral ischaemia and intracranial
hypertension refer to secondary
insults and, in treatment terms, these
types of injury are sensitive to
therapeutic interventions. source
Some common occurrences in head injuries:
The word "concussion" has many different meanings to patients, families, and physicians. One definition:a condition in which there is a traumatically induced alteration in mental status, with or without an associated loss of consciousness (LOC).
A broader definition for concussion: A traumatically induced physiologic disruption in brain function that is manifest by LOC, memory loss, alteration of mental state or personality, or focal neurologic deficits.
While there are many individual variations, concussions usually result in relatively temporary impairment of neurologic function
Again, things are not so clear cut when dealing with concussions, and post-concussion syndromes:
Post concussive syndrome (PCS), a
sequela of minor head injury (MHI),
has been a much-debated topic. Muddled
by conflicting findings regarding
symptom duration, an absence of
objective neurologic findings,
inconsistencies in presentation,
poorly understood etiology, and
significant methodologic problems in
the literature, postconcussive
syndrome (PCS) remains controversial.
Depending on the definition and the
population examined, 29-90% of
patients experience postconcussive
symptoms shortly after the traumatic
(One symptom of concussions is nausea/vomiting which you don't see in movies too often.)
A hematoma is a swelling of blood
confined to an organ or tissue, caused
by hemorrhaging from a break in one or
more blood vessels. As a cerebral
hematoma grows, it damages or kills
the surrounding brain tissue by
compressing it and restricting its
blood supply, producing the symptoms
of stroke. The hematoma eventually
stops growing as the blood clots, the
pressure cuts off its blood supply, or
They are classified from small to massive depending on diameter and volume. Effects vary according to size and location.
White arrows are pointing to the hematoma.
Black arrows point to subdural bleeding
White arrow points to the midline shift of the brain.
The build-up of blood in the skull is putting extensive pressure on the brain. Enough bleeding will essentially "crush" the brain, causing the brainstem to herniate.
Diffuse Axonal Injury
Basically this is extensive damage to the white matter.
Diffuse axonal injury is one of the
most important types of brain damage
that can occur as a result of
non-missile head injury. Increasing
experience with fatal non-missile head
injury in man has allowed the
identification of three grades of
diffuse axonal injury. In grade 1
there is histological evidence of
axonal injury in the white matter of
the cerebral hemispheres, the corpus
callosum, the brain stem and, less
commonly, the cerebellum; in grade 2
there is also a focal lesion in the
corpus callosum; and in grade 3 there
is in addition a focal lesion in the
dorsolateral quadrant or quadrants of
the rostral brain stem. source
Diffuse axonal injuries can occur at the time of the initial impact, or develop during the minutes or hours after the injury.
Length of time unconscious correllates to severity of the brain injury
Post-traumatic amnesia(PTA) is defined as the time from the initial injury until the patient can demonstrate conscious memory of what is going on around him/her.
The duration of PTA was the best
predictor of outcome selected in this
model for all endpoints and elements
of the physical examination provided
additional predictive value. source (medscape link)
Age is also a factor in predicting outcome...
Duration of PTA appears to be a useful
variable in predicting specific
functional outcome in the TBI
population receiving inpatient
rehabilitation services. The use of
age as a factor in addition to
duration of PTA enhances the
prediction of functional outcome.
Most movies simply cherry-pick the most convenient aspects of head injury to advance their plot. Either the person will only be unconscious for a very short time and wake up relatively fine, or the person will be unconscious for an extended time, but likely suffer severe consequences.