afferent neuron animate annoy anxiety aplomb apprehension assurance assure audacity autonomic nervous system axon backbone balance balanced personality balls beef up boldness bolster bottle bottom brace brace up brain brashness brass bravery brazenness buck up buttress case harden central nervous system cerebral cortex cheek cheer chirk up chutzpah confidence confirm constancy cool coolness courage craniosacral nervous system crust daring dauntlessness dendrite determination doughtiness effector organ efferent neuron effrontery embolden encourage equilibrium face fastness fearlessness firmness fortify fortitude forwardness fretfulness fright gall ganglion gird gray matter grit gumption guts gutsiness guttiness harden hardihood hardiness heart heart of oak hearten homeostasis hysteria impertinence imperturbability importunacy importunateness impudence insolence inspire inspirit internuncial neuron intestinal fortitude intrepidity invariability invigorate irritate medullary sheath mettle moxie nerve trunk nerves nervous system nervousness neuron peripheral nervous system pith plexus pluck presumption presumptuousness prop pushiness reassure refresh reinforce reinvigorate reliability resoluteness restrengthen rootedness sand sang-froid sauce secureness security self-assertion self-assertiveness self-expression self-expressiveness sensorium sensory area sensory cell shore up solar plexus solidity soundness spinal cord spirit spunk stability stable equilibrium stable state stamina staunchness steadfastness steadiness steady nerves steady state steel stiffen stout heart strengthen stress substantiality support sustain synapse temerity temper tenacity tension the heebie-jeebies thoracolumbar nervous system toughen toughness undeflectability undergird uniformity unshakable nerves unshakableness upset valor white matter will worry