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1. Reflex
 Reflex is an action that is performed without conscious thought as a
response to a stimulus.
 Rapid, predictable, involuntary responses to stimuli
1. Somatic Reflexes: stimulate skeletal muscles
 Eg. jerking away hand from hot object
2. Autonomic Reflexes: regulate smooth muscles, heart, glands
 Eg. salivation, digestion, blood pressure, sweating
 Reflex arc
 It is the nerve pathway involved in a reflex action, including at its
simplest a sensory nerve and a motor nerve with a synapse
between them.

2. Reflex Arc
1) Receptor - reacts to stimulus
2) Sensory Neurons - afferent impulses to CNS
3) Integration centers - synapses in CNS
4) Motor Neurons - efferent impulses from Integration centers to
effector
5) Effector - muscle or glands

5. ReflexActivities
Patellar (Knee-jerk)
Reflex
Pupillary Reflex
Gently tap your quadriceps tendon, which is located immediately below your
knee cap, with a reflex hammer
Optic nerve --brainstem--muscles
constrictpupil
• Useful for checking brain stem
function and drug use

6. Other Reflexes
Stimulus (receptors) Response (effector)
The aroma of your favorite
food
Salivation
A nasty odor Nausea
A bright light shining in your
eye
Pupils get smaller
An insect flying towards your
eye
Blinking

7. Voluntary Reactions
• More neurons and synapses are involved --
longer response times
Reflex = Involuntary Reaction Voluntary Reaction

9. References
• Elaine N. Marieb, Human Anatomy and Physiology
9th Edition .
• Dr. Henry Gray and Dr. HenryVandyke Carter , Grays
Anatomy for Students 40th Edition.
• Various internet sources.