M2, M3, M4, and M5 in the Glasgow coma scale

[Bill_H]

Another question here on comas made me read up a bit on them. Apparently, there’s a scale where one can measure how deep a coma is called the Glasgow coma scale. Quoting from Wikipedia:

The Glasgow Coma Scale (also known as Glasgow Coma Score or simply GCS) was devised by doctors to assess head trauma and, importantly, to help keep track of patients’ progress over a period of time. The scale is comprised of three tests: eye, verbal and motor responses. The three values separately as well as their sum are considered. The lowest possible GCS (the sum) is 3 (deep coma) whilst the highest is 15 (fully awake person).

Best eye response: (E)

1. No eye opening
2. Eye opening to pain
3. Eye opening to speech
4. Eyes opening spontaneously

Best verbal response: (V)

1. No verbal response
2. Incomprehensible sounds
3. Inappropriate words
4. Confused
5. Orientated

Best motor responses: (M)

1. No motor response
2. Extension to pain (decerebrate response)
3. Flexion to pain (decorticate response)
4. Withdraws from pain (pulls part of body away when pinched)
5. Localises pain (pulls examiner’s hand away)
6. Obeys commands

The Eye and Verbal response parameters seem obvious. But the motor responses 2, 3, 4 and 5 aren’t clear to me. Why is it that one is considered in a deeper coma if they’ll extend when they feel pain, as compared to if they withdraw?

What’s the logic behind the definitions of M2, M3, M4, and M5?

Thanks.