Related Clues:

• Human stimulus pathway
• Brazenness
• See 17 Across
• Brass, so to speak
• Optic __
• Fearlessness
• Confidence
• Hero's quality
• Daredevil's asset
• Temerity
• Bottle
• Coolness under pressure
• AT&T's Telstar, e.g.
• ''Of all the ___!''
• 'The ___!' (perturbed cry)