Monosynaptic reflexes do not require a neuron between the pre-synaptic and post-synaptic neuron, and do not require input from the brain. These reflexes can be triggered even in brain-dead individuals. The knee-jerk reflex is an example of a monosynaptic reflex.

The accommodation reflex is used to adjust the focus of the eye. The acoustic reflex reduces sound intensity by adjusting the bones of the middle ear. The suckling reflex is the complicated reflex of an infant mammal being able to breast feed. Somatic reflexes are a broad category simply involving muscle reflexes. Some of these reflexes involve input from the brain, while others (like the knee-jerk reflex) do not.

The sympathetic nervous system is activated during times of stress, and is responsible for initiating the "fight or flight" response. Part of this response in an increase in heart rate, allowing better conduction of blood and delivery of oxygen throughout the body.

The other answer options are effects of parasympathetic stimulation, which allows for rest. During this time, the body stores energy from glucose into glycogen, and allows for digestion and reproduction.