The Reflex Arc Reflex—rapid, predictable, and involuntary response to a stimulus Occurs over pathways called reflex arcs Occur without the use of the brain Brain is usually “advised” that the reflex has occurred (Sometimes resulting in a secondary response- OUCH, which occurs after the reflex)

Simple Reflex Arc Figure 7.11c, step 1 Sensory receptors (pain receptors in the skin) Spinal cord (c) Figure 7.11c, step 1

Simple Reflex Arc Figure 7.11c, step 2 Sensory receptors (pain receptors in the skin) Spinal cord Sensory (afferent) neuron (c) Figure 7.11c, step 2

Simple Reflex Arc Figure 7.11c, step 3 Sensory receptors (pain receptors in the skin) Spinal cord Sensory (afferent) neuron Inter- neuron (c) Figure 7.11c, step 3

Simple Reflex Arc Figure 7.11c, step 4a Sensory receptors (pain receptors in the skin) Spinal cord Sensory (afferent) neuron Inter- neuron Motor (efferent) neuron (c) Figure 7.11c, step 4a

Simple Reflex Arc Figure 7.11c, step 4b Sensory receptors (pain receptors in the skin) Spinal cord Sensory (afferent) neuron Inter- neuron Motor (efferent) neuron Effector (biceps brachii muscle) (c) Figure 7.11c, step 4b

2 Types of Reflexes and Regulation 1. Somatic reflexes Activation of skeletal muscles Examples: Gag Reflex This reflex helps to prevent choking. Withdrawal Reflex Sharp, sudden pain causes the affected arm or leg to be withdrawn. Scratch Reflex An irritant to the skin causes scratching movement to relieve the itch.

2. Autonomic reflexes Smooth muscle regulation Heart and blood pressure regulation Regulation of glands Digestive system regulation Saliva Sweating Pupil dilation For more examples see next slide