Reflex Arc http://www.learner.org/channel/courses/biology/images/archive/detail/1968_d.jpg

The Reflex Arc Often it is critical that we react quickly to a stimulus. For example, if you go outside on a bright day, your pupils will constrict ( ) to protect your eyes from damage. This is the pupillary reflex. Often it is critical that we react quickly to a stimulus. For example, if you go outside on a bright day, your pupils will constrict ( ) to protect your eyes from damage. This is the pupillary reflex. Often it is critical that we react quickly to a stimulus. For example, if you go outside on a bright day, your pupils will constrict ( ) to protect your eyes from damage. This is the pupillary reflex. Often it is critical that we react quickly to a stimulus. For example, if you go outside on a bright day, your pupils will consytrict ( ) to protect your eyes from damage. This is the pupillary reflex. A doctor may test your knee-jerk (patellar) reflex. They use a rubber hammer to stretch your patellar ligament (the ligament that joins your quadricep muscle to your kneecap). This stimulus causes your quadricep to contract so your leg extends. A doctor may test your knee-jerk (patellar) reflex. They use a rubber hammer to stretch your patellar ligament (the ligament that joins your quadricep muscle to your kneecap). This stimulus causes your quadracep to contract so your leg extends. A doctor may test your knee-jerk (patellar) reflex. They use a rubber hammer to stretch your patellar ligament (the ligament that joins your quadricep muscle to your kneecap). This stimulus causes your quadracep to contract so your leg extends. http://faculty.washington.edu/chudler/chreflex.html

The Reflex Arc Reflexes are automatic, we don’t have to think about them. The message does not have to go to the brain for a response to occur, it is sent directly to the spinal cord. Since there is no processing needed by the brain, these reactions can be very quick. Reflexes are automatic, we don’t have to think about them. The message does not have to go to the brain for a response to occur, it is sent directly to the spinal cord. Since there is no processing needed by the brain, these reactions can be very quick. Reflexes are automatic, we don’t have to think about them. The message does not have to go to the brain for a response to occur, it is sent directly to the spinal cord. Since there is no processing needed by the brain, these reactions can be very quick. spinal cord

The Reflex Arc There are only 3 neurons involved in a reflex arc. The small number of neurons involved makes the response faster. There are only 3 neurons involved in a reflex arc. The small number of neurons involved makes the response faster. spinal cord interneuron motor neuron sensory neuron

The Reflex Arc The electrical message that travels along each axon is converted to a chemical one at each synapse. Step 1: Stimulus sensed by a receptor. stimulus receptor Step 2: An action potential travels down the sensory neuron. sensory neuron Step 3: The interneuron transfers the message from the sensory neuron to the motor neuron. interneuron motor neuron How many synapses are there? Step 4: The motor neuron sends the message to the muscle. muscle Fewer synapses means that the response is faster. Step 5: The muscle contracts. Figure 7 pg. 520

Let’s review that ... Sensory receptor http://www.pageout.net/user/www/k/p/kpetti/0802.MOV

Let’s review that ... Sensory receptor Sensory neuron http://www.pageout.net/user/www/k/p/kpetti/0802.MOV

Let’s review that ... Interneuron Sensory receptor Sensory neuron http://www.pageout.net/user/www/k/p/kpetti/0802.MOV

Let’s review that ... Interneuron Sensory receptor Sensory neuron Motor neuron Sensory neuron Sensory receptor http://www.pageout.net/user/www/k/p/kpetti/0802.MOV

Let’s review that ... Interneuron Sensory receptor Sensory neuron Motor neuron Effector Sensory neuron Sensory receptor http://www.pageout.net/user/www/k/p/kpetti/0802.MOV

Read pgs. 520 Do. Q#4 and 5 pg 521