Parent:

Adult:

Child

Nurturing Parent:

Controlling Parent:

Adult:

Internal ego states can occur together with external ego states and can be spotted when the behavioural aspects of a communication seem intuitively out of line with what we feel is happening.

Internal Child

Needs, wants and feelings, which are collected and stored. Emotions can be recalled when an incident triggers an emotional response from the past. We may display these emotions through our natural child, or choose another ego state if we feel this is more appropriate.

Internal Parent:

Storage of behaviour copied from others, together with associated beliefs, values and opinions.

Internal Adult:

Processes received information and compares this with the reaction generated by our Internal Adult and Internal Child. Makes choices and balanced decisions. Channels of communication

Complementary transactions continue indefinitely.
Crossed transactions result in a break in communication.

4 channels of good communication (we usually prefer one or two):

Adult - Adult problem-solving
Nurturing Parent - Natural Child nurturing
Natural Child - Natural Child having fun, being creative
Controlling Parent - Adapted Child giving instructions

Adequate channels:

Nurturing Parent - Nurturing Parent discussing how to care for  others
Controlling Parent - Controlling Parent agreeing what rules to apply to others 
Adapted Child - Adapted Child being compliant or rebellious together 

Crossed transactions are only useful to make a significant change in a communication. This is more successful if you adopt one of the 4 preferred channels first.
Ulterior transactions have a hidden message, picked up by our Internal Child. The behavioural outcome is determined by the psychological (ulterior) level of the transaction (ie the secret agenda carries the most weight).