What happens when the sympathetic division of nervous system is stimulated?
Stimulation of sympathetic division of the autonomic nervous system results in widespread effects throughout the body, preparing it for a quick response to stressful or emergency situations. It produces a state known as "fight-or-flight" response, characterized by increased alertness and mobilization of resources to effectively respond to potential threats or challenges. Here's what happens when the sympathetic division is stimulated:
1. Activation of Adrenal Medulla: The sympathetic nervous system stimulates the adrenal medulla, which releases hormones epinephrine (adrenaline) and norepinephrine (noradrenaline) into the bloodstream. These hormones act as chemical messengers and enhance the body's response to stressors.
2. Cardiac Changes:
- Increased Heart Rate: The heart rate increases to pump more oxygen-rich blood to tissues and muscles, supplying them with the necessary energy for action.
- Increased Contraction Strength: The force of heart contractions increases, ensuring efficient pumping of blood to meet the demands of heightened activity.
3. Vasodilation and Vasoconstriction:
- Vasoconstriction: Blood vessels supplying non-essential organs like the digestive system constrict, redirecting blood flow to essential organs like skeletal muscles, brain, and heart.
- Vasodilation: Blood vessels in the skeletal muscles dilate, allowing for increased blood supply to meet the energy needs of muscles during a response.
4. Respiratory System:
- Increased Respiratory Rate: Breathing quickens to provide more oxygen to the bloodstream, supporting increased energy expenditure.
5. Sweat Gland Activation: Sweating is triggered to cool down the body, as increased activity and metabolic processes can generate heat.
6. Pupil Dilation: The pupils dilate to improve visual acuity, increasing the amount of light entering the eye for better vision.
7. Inhibition of Salivary and Digestive Functions: Salivation decreases to conserve energy and direct more resources toward the immediate response. Digestion is slowed down, as energy is needed for the fight-or-flight response rather than digestion.
8. Adrenal Gland Activation: The sympathetic division stimulates the adrenal cortex to release additional hormones like cortisol, which supports the body's response to stress and helps regulate energy levels.
9. Relaxation of the Urinary Bladder: The bladder's sphincter muscles relax to facilitate urination, reducing the urge to urinate during times of stress.
10. Piloerection (Goosebumps): In some animals, the sympathetic division can cause the erection of hair follicles, creating the effect known as "goosebumps."
Overall, the stimulation of the sympathetic division leads to a series of physiological changes aimed at mobilizing energy resources, increasing alertness, and preparing the body for immediate action in response to perceived threats or challenges.