isya ga nou wo kensasimasu.

It is read:

いしゃ が のう を けんさします。

Word by word:

• 医者 = いしゃ = doctor
• が = subject marker
• 脳 = のう = brain
• を = object marker
• 検査します = けんさします = examines / inspects / performs an examination on

が marks the grammatical subject — the person or thing that performs the action.

So in:

医者が脳を検査します。

the doctor is the one doing the examining.

A very literal breakdown is:

• 医者が = the doctor / it is the doctor who
• 脳を = the brain
• 検査します = examines

を marks the direct object of the verb — the thing that the action is done to.

So:

• 脳を = the brain as the thing being examined

In other words:

• the doctor is the subject
• the brain is the object

This is very common in Japanese:

• X が Y を verb
• X does the verb to Y

Because Japanese normally puts the main verb at the end of the sentence.

So while English says:

The doctor examines the brain.

Japanese says, in effect:

Doctor + subject marker + brain + object marker + examines

This subject–object–verb pattern is one of the basic word-order differences between Japanese and English.

検査します means to inspect, to examine, or to perform a medical/technical examination. It sounds more formal and specific than a simple verb like 見る (to look at / see).

So:

• 脳を見ます = looks at the brain
• 脳を検査します = examines the brain, likely in a medical or technical sense

Since 医者 is a doctor, 検査します fits well in a medical context.

Yes.

検査 is a noun meaning inspection, examination, or test.
When combined with します, it becomes a verb phrase:

• 検査する = to examine / to inspect / to perform an examination
• 検査します = polite present/future form

This is a very common pattern in Japanese, especially with words of Chinese origin:

• 勉強します = study
• 練習します = practice
• 説明します = explain
• 検査します = examine

Because this sentence is simply marking the subject with が, not setting up a topic with は.

• が focuses on who does the action
• は marks the topic and often gives a contrast or broader statement

Compare:

• 医者が脳を検査します。 = The doctor examines the brain / It is the doctor who examines the brain
• 医者は脳を検査します。 = As for the doctor, he/she examines the brain or Doctors examine the brain

Both are possible, but the nuance changes.

Yes, it can, but the nuance changes.

医者が脳を検査します。

• emphasizes the doctor as the subject
• can answer a question like Who examines the brain?

医者は脳を検査します。

• makes doctor the topic
• can sound like a general statement about doctors, or a contrast with someone else

So they are not always interchangeable, even if both may translate similarly in simple English.

No, Japanese does not normally use articles like the and a.

So:

• 医者 can mean a doctor or the doctor
• 脳 can mean a brain or the brain

The exact meaning depends on context.

That is why one Japanese sentence can be translated into English in several ways:

• A doctor examines the brain.
• The doctor examines the brain.
• Doctors examine the brain.

Context tells you which is most natural.

Yes. 医者 normally means doctor in the medical sense.

It is not used for a person with a PhD the way English doctor can be.

So for Japanese learners, it is useful to remember:

• 医者 = medical doctor
• not usually doctor in the academic-title sense

Also, 医者 is gender-neutral. It can mean a male or female doctor.

Yes. 検査します is in the polite -ます form.

So the sentence is polite and neutral enough for normal conversation, explanations, or textbook examples.

The plain form would be:

医者が脳を検査する。

That plain form might be used in:

• casual speech
• dictionary form
• written explanations
• subordinate clauses

Yes, grammatically it is natural.

However, in real life, it may sound a little context-dependent because examining the brain is quite specific. Japanese often omits details that are understood from context, but here the sentence is still fine as a simple example sentence.

It sounds like:

• a medical explanation
• a textbook example
• a statement about what a doctor is doing

So it is natural enough, especially for study purposes.