The feature of arousal and fear is controlled by the brain area called “Hypothalamus”. When the brain thinks something is dangerous, the hypothalamus releases neurotransmitters, triggering the firing of neurons throughout the brain and the release of chemicals throughout the body.

The hypothalamus activates two systems:

•          Autonomic Nervous System (ANS): A network of nerves that connects the brain and spinal cord to the body’s organs. It controls automatic actions like breathing, heartbeat, blood pressure, and sweating.

•          Endocrine System: A system of glands that release hormones into the blood to affect different organs.

These two systems work together to create arousal and fear. They do this through two main pathways:

1.        Sympathetic Nervous System pathway

2.        Hypothalamic-Pituitary-Adrenal (HPA) pathway

1. Sympathetic Nervous System Pathway

When we face danger, the hypothalamus activates the sympathetic nervous system. It is a group of ANS fibers that makes our heartbeat faster and creates other changes that cause fear or anxiety.

It works in two ways:

•          Directly: It stimulates organs like the heart to beat faster.

•          Indirectly: It signals the adrenal glands (on top of the kidneys), especially the adrenal medulla, to release chemicals called epinephrine (adrenaline) and norepinephrine (noradrenaline). These chemicals act as hormones and travel through the blood to prepare the body for action.

When the danger is gone, a second group of ANS fibers, called the parasympathetic nervous system reduce heartbeat to normal level and other body process to normal.

Both systems work together to control our fear and arousal responses.

2. Hypothalamic-Pituitary-Adrenal (HPA) Pathway

The second way our body reacts to stress is through the HPA pathway. Here’s how it works:

1.        When you face stress, the hypothalamus sends a signal to the pituitary gland.

2.        The pituitary gland releases a hormone called ACTH (adrenocorticotropic hormone), also known as the body’s main stress hormone.

3.        ACTH then triggers the adrenal cortex (the outer part of the adrenal glands) to release corticosteroids, including cortisol.

4.        These hormones travel through the blood to different organs and cause arousal and fear reactions.

The reactions in these two pathways together are called the fight-or-flight response. This name is used because they prepare our body to either fight the danger or run away from it.