Effects of Alcohol on the Central Nervous System

Ethanol generally decreases the activity of the central nervous system. In relation to alcohol, the most important neurotransmitters in the brain are glutamate, gamma-aminobutyric acid (GABA), dopa-mine, and serotonin.

Glutamate is the major excitatory neurotransmitter in the brain. Ethanol inhibits the N-methyl-d-aspartate (NMDA) subset of glutamate receptors. Ethanol thereby reduces the excitatory effects of glutamate. GABA is the major inhibitory neuro-transmitter in the brain. Alcohol facilitates the action of the GABA-a receptor, increasing inhibition. Changes to these receptors seem to be important in the development of tolerance of and dependence on alcohol.

Dopamine is involved in the rewarding aspects of alcohol consumption. 'Enjoyable' activities such as eating or use of other recreational drugs also release dopamine in the nucleus accumbens of the brain. Serotonin is also involved in the in reward processes and may be important in encouraging alcohol use.

The most obvious effects of ethanol intoxication on the central nervous system begin with behavior modification (e.g., cheerfulness, impaired judgment, and loss of inhibitions). These 'excitatory' effects result from the disinhibition described previously (inhibition of cells in the brain that are usually inhibitory). As a result of these effects, it is well recognized that driving under the influence of ethanol is unsafe. However, the definition of what is safe or acceptable varies between countries (Table 8) and often changes.

The effects of ethanol are dose dependent (Table 9) and further intake causes agitation, slurred speech, memory loss, double vision, and loss of coordination. This may progress to depression of consciousness and loss of airway protective reflexes, with danger of aspiration, suffocation, and death.

Table 8 Legal limits of blood ethanol concentrations for drivinga Legal limitb Blood ethanol concentration mg/dl mmol/l

Table 8 Legal limits of blood ethanol concentrations for drivinga Legal limitb Blood ethanol concentration mg/dl mmol/l

Norway and Sweden

20

4.3

France, Germany, Italy,

50

11

and Australia

United Kingdom, United

80

17

States, and Canada

Russia

"Drunkenness"

aEthanol impairs judgment and coordination. It is well recognized that driving under the influence of ethanol is unsafe. However, the definition of what is safe or acceptable varies between countries and can change as a result of social, political, or scientific influences.

^Legislation regarding legal limits of blood ethanol for driving may change.

Table 9 Relationship between amount of ethanol consumed, blood ethanol concentration (BEC), and effect of ethanol on the central nervous system

Alcohol

Possible BEC

Effect

consumed

(units)

1-5

10-50 mg/dl

No obvious change in behavior

2-11 mmol/l

2-7

30-100 mg/dl

Increased self-confidence;

7-22 mmol/l

loss of inhibitions

Impaired judgment, attention,

and control

Euphoria

Mild sensorimotor impairment,

delayed reaction times

Sociability

Legal limits for driving

generally fall within this

range (see Table 8)

8-15

90-250 mg/dl

Loss of critical judgment

20-54 mmol/l

Impairment of perception,

memory, and

comprehension

Reduced visual acuity

Reduced coordination,

impaired balance

Drowsiness

11-20

180-300 mg/dl

Disorientation

39-65 mmol/l

Exaggerated emotional states

Disturbances of vision and

perception of color, form,

motion, and depth

Confusion

Increased pain threshold

Further reduction of

coordination, staggering

gait, slurred speech

15-25

250-400 mg/dl

Loss of motor functions

54-87 mmol/l

Markedly reduced response to

stimuli

Marked loss of coordination,

inability to stand/walk

Stupor

Incontinence

Impaired consciousness

22-30

350-500 mg/dl

Unconsciousness

76-108 mmol/l

Reduced or abolished reflexes

Incontinence

Coma

Cardiovascular and respiratory

depression (death possible)

38

>600 mg/dl

>130 mmol/l

Respiratory arrest

Death

Approximate amounts of alcohol required by a 70 kg male to produce the corresponding blood ethanol concentration and intoxicating effects of ethanol. One unit of alcohol contains 8g of ethanol.

Adapted with permission from Morgan MY and Ritson B (2003) Alcohol and Health: A Handbook for Students and Medical Practitioners, 4th edn. London: Medical Council on Alcohol.

This sequence of events is particularly relevant in the hospital setting, where patients may present intoxicated with a reduced level of consciousness. It is difficult to determine whether there is coexisting pathology such as an extradural hematoma or overdose of other drugs in addition to ethanol. Although measurement of BEC is helpful (Table 9), it is safest to assume that alcohol is not responsible for any disturbance in consciousness and to search for another cause.

Alcohol No More

Alcohol No More

Do you love a drink from time to time? A lot of us do, often when socializing with acquaintances and loved ones. Drinking may be beneficial or harmful, depending upon your age and health status, and, naturally, how much you drink.

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