Il medico controlla il cervello.

Because Italian normally uses articles with singular count nouns. So:

• il medico = the doctor
• il cervello = the brain

English sometimes leaves articles out in places where Italian does not, but in a simple sentence like this, the articles are expected.

Il is the normal masculine singular definite article before most consonants.

So you get:

• il medico
• il cervello

Italian uses lo only before certain sounds, such as:

• z → lo zio
• s
  • consonant → lo studente
• gn → lo gnomo
• ps → lo psicologo
• x → lo xilofono

Since medico and cervello do not begin with those special sounds, il is correct.

Italian often leaves out subject pronouns when they are not needed. This is called being a pro-drop language.

Here, il medico already tells you who is doing the action, so there is no need to add lui.

• Il medico controlla il cervello = The doctor checks the brain
• Lui controlla il cervello would mean He checks the brain, but it is not necessary here

Because controlla is the third person singular present form of controllare.

The present tense endings for regular -are verbs are:

• controllo = I check
• controlli = you check
• controlla = he/she checks
• controlliamo = we check
• controllate = you all check
• controllano = they check

So il medico controlla means the doctor checks.

It can mean both in different contexts, but very often controllare means to check, to inspect, or to examine.

So in a sentence like this, the most natural sense is usually checks or examines, not controls.

That is a very common point of confusion for English speakers because controllare looks like the English word control, but it is often used more like check.

In this sentence, il medico is masculine singular.

For a woman, Italian commonly uses:

• la dottoressa
• and in modern usage also la medica

So depending on context, you might hear:

• La dottoressa controlla il cervello
• La medica controlla il cervello

For this sentence as written, though, il medico is masculine.

Because it is the direct object: the thing being checked.

Italian commonly uses the same basic order as English in simple sentences:

subject + verb + object

So:

• Il medico = subject
• controlla = verb
• il cervello = object

That makes this sentence very straightforward in structure.

No. Direct objects in Italian normally do not take a preposition.

So:

• Il medico controlla il cervello = correct

The doctor is directly acting on the brain, so no extra word like a or di is needed there.

Yes, but the sentence as written is the most neutral and standard order.

The normal pattern is:

Il medico controlla il cervello.

Italian can change word order for emphasis, contrast, or style, but beginners should treat this version as the default and safest one.

A rough pronunciation guide is:

• controlla → kon-TROL-la
• cervello → cher-VEHL-lo

A few useful points:

• In cervello, ce sounds like che in English chess
• The stress in both words is on the second-to-last syllable
• The double consonants, especially ll, are pronounced a bit longer than single ones

So try to avoid saying them too quickly or flattening the double consonants.

The plural forms are:

• il medico → i medici
• il cervello → i cervelli

If the subject becomes plural, the verb changes too:

• I medici controllano il cervello = The doctors check the brain
• I medici controllano i cervelli = The doctors check the brains

So both the article and the noun change, and the verb changes to match the plural subject.