1. Reflex Arc

2. 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.

3. 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

4. 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

5. 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

6. Let’s review that ... Sensory receptor

7. Let’s review that ... Sensory receptor Sensory neuron

8. Let’s review that ... Interneuron Sensory receptor Sensory neuron

9. Let’s review that ... Interneuron Sensory receptor Sensory neuron
Motor neuron
Sensory neuron
Sensory receptor

10. Let’s review that ... Interneuron Sensory receptor Sensory neuron
Motor neuron
Effector
Sensory neuron
Sensory receptor

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