Nerve PathwaysNerve Pathways

Chapter 9: Nervous SystemChapter 9: Nervous System

Unit 3: Integration and Unit 3: Integration and CoordinationCoordination

Nerve PathwaysNerve Pathways

Nerve PathwaysNerve Pathways are the routes are the routes nerve impulses follow as they travel nerve impulses follow as they travel through the nervous system.through the nervous system.

– Nerve pathways that require only a few Nerve pathways that require only a few neurons are called neurons are called Reflex ArcsReflex Arcs..

Reflex arcs are the structural and Reflex arcs are the structural and functional basis for involuntary actions functional basis for involuntary actions called called ReflexesReflexes..

Parts of the Reflex ArcParts of the Reflex Arc

The reflex arc consists of the The reflex arc consists of the following structural components:following structural components:

ReceptorReceptor

Sensory neuronSensory neuron

InterneuronInterneuron

Motor neuronMotor neuron

EffectorEffector

Reflex Arcs in GeneralReflex Arcs in General

ReceptorsReceptors sense specific types sense specific types of internal or external change.of internal or external change.

– Sensory FibersSensory Fibers send this send this information to information to InterneuronsInterneurons found found within the CNSwithin the CNS

Interneurons communicate with Interneurons communicate with Motor Motor NeuronsNeurons whose fibers pass outward whose fibers pass outward from the CNS.from the CNS.

– EffectorsEffectors respond to stimulation by motor respond to stimulation by motor neurons and produces reflex or behavioral neurons and produces reflex or behavioral action.action.

Reflex BehaviorReflex Behavior

ReflexesReflexes are automatic subconscious are automatic subconscious responses to changes within or outside responses to changes within or outside the body.the body.

– Maintain homeostasis by controlling Maintain homeostasis by controlling involuntary processes:involuntary processes:

Heart rate, breathing rate, blood pressure, and Heart rate, breathing rate, blood pressure, and digestion.digestion.

– Also carry out automatic processes:Also carry out automatic processes:

Swallowing, sneezing, coughing, and vomitingSwallowing, sneezing, coughing, and vomiting

Patella Tendon ReflexPatella Tendon Reflex

This reflex employs only two neuronsThis reflex employs only two neurons

– A sensory neuron communicating directly A sensory neuron communicating directly with a motor neuron.with a motor neuron.

The knee-jerk reflex helps to maintain upright The knee-jerk reflex helps to maintain upright posture.posture.

– If the knee begins to bend (force of gravity) while If the knee begins to bend (force of gravity) while the person is standing still:the person is standing still:

The quadriceps femoris group is stretchedThe quadriceps femoris group is stretched

The reflex is triggeredThe reflex is triggered

The leg straightens out againThe leg straightens out again

Events of the Knee-Events of the Knee-Jerk ReflexJerk Reflex1.1. Strike the patella ligamentStrike the patella ligament

2.2. Quadriceps femoris grouping Quadriceps femoris grouping (attached to the patella by a tendon) (attached to the patella by a tendon) is pulled slightlyis pulled slightly

3.3. Stretch stimulates stretch receptors Stretch stimulates stretch receptors within the muscleswithin the muscles

4.4. Impulse travels along sensory neuron Impulse travels along sensory neuron into the spinal cordinto the spinal cord

Events ContinuedEvents Continued

5.5. Sensory neuron forms a synapse with Sensory neuron forms a synapse with a motor neuron in the spinal corda motor neuron in the spinal cord

6.6. Impulse continues along the motor Impulse continues along the motor neuronneuron

7.7. Impulse reaches the quadriceps Impulse reaches the quadriceps femoris groupfemoris group

8.8. Muscle group contracts in response, Muscle group contracts in response, and the leg extendsand the leg extends

Withdrawal ReflexWithdrawal Reflex

The The Withdrawal ReflexWithdrawal Reflex occurs when occurs when a person unexpectedly touches a body a person unexpectedly touches a body part to something painful.part to something painful.

– A protective measure because it limits A protective measure because it limits tissue damage caused by touching tissue damage caused by touching something harmful.something harmful.

This reflex employs three types of neurons:This reflex employs three types of neurons:

– Sensory NeuronSensory Neuron

– Interneuron (within the reflex center)Interneuron (within the reflex center)

– Motor NeuronMotor Neuron

Withdrawal ReflexWithdrawal Reflex

1.1. Skin receptors are activatedSkin receptors are activated

2.2. Skin receptors send information Skin receptors send information to sensory neuronto sensory neuron

3.3. Sensory impulses are sent to the Sensory impulses are sent to the spinal cordspinal cord

4.4. Impulse passes to an Impulse passes to an interneuron in the reflex centerinterneuron in the reflex center

Withdrawal Reflex Withdrawal Reflex ContinuedContinued

5.5. The interneuron directs the impulse The interneuron directs the impulse to the motor neuronsto the motor neurons

6.6. Motor neurons transmit signals to Motor neurons transmit signals to flexor muscles in the injured part, flexor muscles in the injured part, and the muscle contracts in and the muscle contracts in responseresponse

7.7. Antagonist extensor muscles are Antagonist extensor muscles are inhibitedinhibited