Threat Detection and Nervous System Activation

His brain (specifically the amygdala and hypothalamus) immediately detected the danger. This triggered the sympathetic nervous system.

Signals were sent through nerves to his adrenal glands, which released adrenaline (epinephrine) and norepinephrine. These hormones caused:

• His heart rate and breathing rate to increase, supplying more oxygen and blood to his muscles.
• Blood diversion from non-essential organs to major muscle groups.
• Glucose release from the liver, providing immediate energy for muscle action.

The brain, through the motor neurons, sent rapid signals to his muscles.

• His quadriceps (front thigh muscles) contracted powerfully to straighten his knees, pushing his body forward.
• Simultaneously, his hamstrings (back thigh muscles) and gluteal muscles (buttocks) worked in sequence to propel his legs, creating a running stride.
• His calf muscles pushed off the ground, and his arm muscles swung rhythmically to maintain balance and add momentum. This coordinated effort of his nervous, endocrine, cardiovascular, respiratory, and muscular systems allowed Donald to run very fast and reach the safety of his home.