What are antibiotics? Antibiotics are chemical or biological substances either produced by microorganisms or are produced artificially to kill or inhibit growth of other microorganisms. They are used at very low concentrations.

What are different types? As there are innumerable antibiotics that are presently in use, different people classify them differently for e.g. those that kill or those just inhibit action of microorganisms, according to their chemical nature, according to types of organisms they kill, according to no of different types of microorganisms, their mechanism of action and so hence and so forth. Hence sulfadiazine and others are sulfonamides while isoniazid is nicotinic acid derivatives, etc. tetracyclines are bacteriostatic while vancomycin is bactericidal.

How do they work? Some antibiotics for e.g. penicillins inhibit cell wall synthesis of bacteria, some like acyclovir inhibit DNA synthesis, some like sulfonamides interfere with metabolism and still others like tetracyclines inhibit protein synthesis. Similarly there are many others with different mechanism of action meant to be targeted at specific function of bacteria or virus.

Neurologists and neurosurgeons cringe when they hear sports-reporters make comments like, "Johnny had a CAT scan and it showed that he didn't have a concussion." The truth is that CAT scans don't show concussions. They do show other serious consequences of head injuries, like bleeding within brain, or hemorrhages that compress brain. But concussions—while no less real—are invisible to brain-imaging tests like CAT scans and MRIs.

So what is a concussion? If a blow to head caused unconsciousness, a concussion occurred. Most people know this. But a concussion can occur even when there is no loss of consciousness. Other symptoms after a head-injury indicating a concussion include:

1. impaired attention, e.g. vacant stare, slowness to respond, easy distractibility
2. slurred speech, or speech that doesn't make sense
3. clumsiness or unsteadiness
4. disorientation, e.g. walking in wrong direction, forgetting day of week
5. excessive emotional reaction, e.g. easy tears, overly upset
6. memory impairment, e.g. asking same question repeatedly, can't memorize new facts

You'll notice that all these symptoms share a common feature—an alteration in brain function. The normal brain processes, which depend on proper signaling among brain's 20 billion brain cells, are out of whack.

There can also be physical damage to brain's cells. Because brain-cells are so tiny, brain scans don't detect them. Injuries causing more severe concussions can tear apart cells' axons (the long filaments that carry coded messages over long distances within brain). As you can imagine, these rips in very fabric of brain can cause lasting impairments in brain function or require long periods of time for recovery.