
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Given an ellipse $C$: $\dfrac {x^{2}}{a^{2}}+ \dfrac {y^{2}}{b^{2}}=1(a > b > 0)$, where its left and right vertices are $A$ and $B$ respectively, and the length of its major axis is $8$. Let $T$ be a point on the ellipse, and the product of the slopes of lines $TA$ and $TB$ is $- \dfrac {3}{4}$.  
(Ⅰ) Find the equation of ellipse $C$;  
(Ⅱ) Let $O$ be the origin, and a moving line passing through point $M(0,2)$ intersects the ellipse $C$ at points $P$ and $Q$. Find the range of values for $\overrightarrow{OP} \cdot \overrightarrow{OQ}+ \overrightarrow{MP} \cdot \overrightarrow{MQ}$.

Present the answer in LaTex format: \boxed{Your answer}
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