As I write this, our thoughts are with those in Boston who were affected by the bombings at the 2013 Boston Marathon.

In my 20 years living in the Boston area, I cheered on the runners on many occasions and now, even from far way, these events feel close to home.

Experiencing trauma can have a dramatic effect on our bodies and our minds. And although it’s a different experience to witness a trauma on television, it still can affect us.

When you perceive a threat, the body activates the stress response. The stress response occurs in both your body and brain.

The body’s response to acute stress is a preparation for emergency. Adrenaline and other hormones are released. The body shuts down processes associated with long-term care. When under immediate threat, digestion, reproduction, cell repair and other body tasks related to long-term functioning are unimportant.

Of immediate importance is survival. Increased blood sugar can provide extra energy for muscles. Increases in cortisol counter pain and inflammation. Blood pressure increases. Blood is diverted from our extremities to our major muscles to provide us with extra strength. Increased endorphins can help us ignore physical pain.

You can see the effects of these changes to the body in many of the symptoms of stress, such as racing heart, dizziness, nausea, shortness of breath, shaking, feeling hot and flushed, and sweating.

But it is the impact of trauma on the mind that is often the most disturbing. Traumatic events can leave us feeling unsafe. They can disrupt our beliefs and assumptions about the world. Your sense of your ability to control your life may be shattered. You may question how much influence you have over your life and your life choices.

A trauma, such as the one the occurred at the Boston Marathon, can leave us distrustful of other people. You may question your basic trust of other people in the world. Trauma can affect your ability to be intimate with others and may impact your feelings of self-worth. Those who survive the trauma often feel guilt and wonder why they lived when others were less fortunate.

As we grow, change and have varied experiences throughout life, our beliefs and assumptions typically evolve over time. With trauma, those beliefs and assumptions that we use to make sense of the world around us change nearly instantaneously.

It’s common to experience a wide range of psychological symptoms, including intrusive thoughts, worry, difficulty sleeping, trouble focusing, bouts of crying, blame or self-judgment and lack of satisfaction.

The effects of trauma also can cause intense emotion, including extreme emotional fluctuations, unhappiness, anxiety, loneliness, anger, and irritability.

Multiple traumas or repeatedly being exposed to life-threatening events can have a further impact on your body and mind. Parts of the brain can become sensitized, causing you to be on high alert and to perceive threats all around, leaving you jumpy and anxious.

Other parts of the brain associated with memory can actually shrink, making it difficult to consolidate and form new memories. Prolonged stress can effect the development of a number of health issues, including diabetes, obesity and hypertension. And repetitive stress affects our moods, brings on anxiety disorders, and affects our experience of chronic pain and our ability to control food intake.

But when horrible events occur, such as those that occurred at the 2013 Boston Marathon, we also see the generosity and caring that is a large part of human nature.

Countless individuals ran to help without a second thought. First responders, medics, EMTs and even bystanders jumped into action to do what they could to save lives. Runners crossed the finish line and kept on running straight to give blood.

As we deal with the impact of violence, we can also keep in our minds the heroes and the strength of the human spirit that brings us together when we are faced with senseless tragedy.

Image: Wikimedia Commons: Aaron “tango” Tang