The is the fatty substance that insulates and protects the axon.

The answer you are looking for is the Myelin

Myelin SheathExplanation:

The Myelin sheath is made of fatty tissue that wraps itself around the axon of the nerves so as to provide protection, insulation and better transmission to the electrical signals across it. The fact that it comprises of fatty substances gives it the properties it needs to provide these functions.

The average resting heart rate (hrrest) for a 34 year old is 73 beats per minute2. 34 year old males average heart rates of 71 bpm while females average slightly higher at 76 bpm2. the normal resting heart rate range for all adults and children 10 and over is between 60 and 100 beats per minute3. 90% of 34 year olds resting pulses fall within the range of 54 to 92 bpm. in general, an adult's resting heart rate will be lower for those in better athletic condition.