2The Reflex Arc1. Reflex—rapid, predictable, and involuntary response to a stimulus
32. 5 Essential Components of the Reflex Arc Stimulus at distal end of neuronSkinSpinal cord(in cross section)InterneuronReceptorEffectorSensory neuronMotor neuronIntegration center(a)Figure 7.11a
4The Reflex Arc Figure 7.11a, step 1 Skin Stimulus at distal end of neuronSkinReceptor(a)Figure 7.11a, step 1
5The Reflex Arc Figure 7.11a, step 2 Skin Stimulus at distal end of neuronSkinReceptorSensory neuron(a)Figure 7.11a, step 2
6The Reflex Arc Figure 7.11a, step 3 Skin Spinal cord Stimulus at distal end of neuronSkinSpinal cord(in cross section)InterneuronReceptorSensory neuronIntegration center(a)Figure 7.11a, step 3
7The Reflex Arc Figure 7.11a, step 4 Skin Spinal cord Stimulus at distal end of neuronSkinSpinal cord(in cross section)InterneuronReceptorSensory neuronMotor neuronIntegration center(a)Figure 7.11a, step 4
8The Reflex Arc Figure 7.11a, step 5 Stimulus at distal end of neuron SkinSpinal cord(in cross section)InterneuronReceptorEffectorSensory neuronMotor neuronIntegration center(a)Figure 7.11a, step 5
9Simple Reflex Arc Figure 7.11b–c Sensory receptors (stretch receptors in the quadriceps muscle)Sensory (afferent) neuronSensory receptors (pain receptors in the skin)Spinal cordSensory (afferent) neuronSynapse in ventral horn gray matterInter- neuronMotor (efferent) neuronMotor (efferent) neuronEffector (quadriceps muscle of thigh)Effector (biceps brachii muscle)(b)(c)Figure 7.11b–c
103. Why test your reflexes?Reflexes determine the general health of the motor portion of the nervous system.Whenever reflexes are exaggerated, distorted, or absent, nervous system disorders are indicated.Reflex changes often occur before the pathological condition has become obvious
11Simple Reflex Arc Figure 7.11b, step 1 Sensory receptors (stretch receptors in the quadriceps muscle)Spinal cord(b)Figure 7.11b, step 1
23Types of Reflexes and Regulation Somatic reflexesActivation of skeletal musclesExample: When you move your hand away from a hot stoveA “stretch reflex” is a muscle contraction in response to stretching within the muscle“Superficial reflexes” are motor responses to scraping of the skin.
255. Cord- Mediated Reflexes Muscle stretch (myotatic) reflexes are mediated purely at the spinal cord level, with monosynaptic connections between muscle spindle afferents and motor neurons to the muscle that was stretched.Examples: Achilles and plantar
27Patellar ReflexStriking the patellar tendon with a tendon hammer just below the patella stretches the quadriceps muscles in the thigh. This stimulates stretch sensory receptors to trigger an afferent impulse in a sensory nerve fiber of the femoral nerve which synapses at the level of L4 in the spinalFrom there, an motor neuron conducts an efferent impulse back to the quadriceps femoris muscle, triggering contraction. This contraction causes the leg to kick.This reflex helps maintain posture and balance, allowing one to walk without consciously thinking about each step.The patellar reflex is an example of the monosynaptic reflex arc. There is no interneuron in the pathway.
28Superficial reflexesSuperficial reflexes are motor responses to scraping of the skin.Plantar Reflex is a normal reflex that involves plantar flexion of the foot (toes move away from the shin, and curl down.)Babinski's reflex occurs when the big toe moves toward the top of the foot and the other toes fan out after the sole of the foot has been firmly stroked.This reflex, or sign, is normal in younger children, but abnormal after the age of 2.
29Plantar ReflexPlantar Reflex: Flexion of the toes in response to stroking of the outer surface of the sole, from heel to little toe.
31Corneal Reflex Cranial Nerve V “trigeminal nerve” Protect the eyeball from damage
32Autonomic reflexes Autonomic reflexes Smooth muscle regulation Heart and blood pressure regulationRegulation of glandsDigestive system regulationAn autonomic reflex is one that involves the response of an organ, such as the peristaltic contraction of the smooth muscle of the intestines, that is not controlled consciously
335. Example of Autonomic Reflex: Pupillary Light Reflex Receptor = retina of the eyeAfferent Fibers = in Cranial Nerve II,“optic nerve”Efferent impulses = carried by cranial nerve III“ oculomoter nerve”Effector = smooth muscles of the irisFunction =protects the retina from excessive illumination, which is damaging to the photoreceptors
35Autonomic ReflexesMay be spinal (e.g., urination and defecation) or modified by higher brain structures.The thalamus, hypothalamus and brain stem are in charge of multiple reflexes – HR, BP, breathing, eating, osmotic balance, temperature, vomiting, gagging, sneezing.All are polysynaptic.
369. Pupillary ResponseIpsilateral: A reflex in which the response occurs on the side of the body that is stimulated.Contralateral: A reflex in which the response occurs on the opposite side of the body that is stimulated.
379. Test For Cranial Nerves II and III Normally, both pupils should constrict with light shone into either eye alone. If not working:Optic nerve damage?Oculomotor nerve damage?
3810. Somatic vs Autonomic Reflexes Somatic Reflexes are all reflexes that stimulate skeletal muscles.Autonomic Reflexes stimulate smooth muscles, cardiac muscle, and glands of the body, and they regulate body functions such as digestion and blood pressure.
39Types of Reflexes and Regulation Patellar, or knee-jerk, reflex is an example of a two-neuron reflex arcFigure 7.11d
406. Reflex Arc of Patellar Reflex ReceptorsAfferent NervesIntegration CenterEfferent NerveEffectorStretch receptors in quadriceps muscleAfferent neuronSpinal CordEfferent neuron (Femoral Nerve)Quadriceps muscle of the thigh
427. Effect of Muscle Fatigue on Patellar Reflex The intensity of the response is less
43Differences Between Somatic and Autonomic Nervous Systems NervesSomatic: one motor neuronAutonomic: preganglionic and postganglionic nervesEffector organsSomatic: skeletal muscleAutonomic: smooth muscle, cardiac muscle, and glands
44PNS: Differences Between Somatic and Autonomic Nervous Systems NeurotransmittersSomatic: always use acetylcholineAutonomic: use acetylcholine, epinephrine, or norepinephrine
45Autonomic Nervous System Motor subdivision of the PNSConsists only of motor nervesAlso known as the involuntary nervous systemRegulates activities of cardiac and smooth muscles and glandsTwo subdivisionsSympathetic divisionParasympathetic division
46PNS: Comparison of Somatic and Autonomic Nervous Systems Figure 7.27
47Anatomy of the Sympathetic Division Originates from T1 through L2Ganglia are at the sympathetic trunk (near the spinal cord)Short pre-ganglionic neuron and long post-ganglionic neuron transmit impulse from CNS to the effectorNorepinephrine and epinephrine are neurotransmitters to the effector organs
48PNS: Anatomy of the Autonomic Nervous System Figure 7.28