1. Exercise 16: Human Reflex Physiology

2. The Reflex Arc
1. Reflex—rapid, predictable, and involuntary response to a stimulus

3. 2. 5 Essential Components of the Reflex Arc
Stimulus at distal end of neuron
Skin
Spinal cord
(in cross section)
Interneuron
Receptor
Effector
Sensory neuron
Motor neuron
Integration center
(a)
Figure 7.11a

4. The Reflex Arc Figure 7.11a, step 1 Skin
Stimulus at distal end of neuron
Skin
Receptor
(a)
Figure 7.11a, step 1

5. The Reflex Arc Figure 7.11a, step 2 Skin
Stimulus at distal end of neuron
Skin
Receptor
Sensory neuron
(a)
Figure 7.11a, step 2

6. The Reflex Arc Figure 7.11a, step 3 Skin Spinal cord
Stimulus at distal end of neuron
Skin
Spinal cord
(in cross section)
Interneuron
Receptor
Sensory neuron
Integration center
(a)
Figure 7.11a, step 3

7. The Reflex Arc Figure 7.11a, step 4 Skin Spinal cord
Stimulus at distal end of neuron
Skin
Spinal cord
(in cross section)
Interneuron
Receptor
Sensory neuron
Motor neuron
Integration center
(a)
Figure 7.11a, step 4

8. The Reflex Arc Figure 7.11a, step 5 Stimulus at distal end of neuron
Skin
Spinal cord
(in cross section)
Interneuron
Receptor
Effector
Sensory neuron
Motor neuron
Integration center
(a)
Figure 7.11a, step 5

9. Simple Reflex Arc Figure 7.11b–c
Sensory receptors (stretch receptors in the quadriceps muscle)
Sensory (afferent) neuron
Sensory receptors (pain receptors in the skin)
Spinal cord
Sensory (afferent) neuron
Synapse in ventral horn gray matter
Inter- neuron
Motor (efferent) neuron
Motor (efferent) neuron
Effector (quadriceps muscle of thigh)
Effector (biceps brachii muscle)
(b)
(c)
Figure 7.11b–c

10. 3. 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

11. Simple Reflex Arc Figure 7.11b, step 1
Sensory receptors (stretch receptors in the quadriceps muscle)
Spinal cord
(b)
Figure 7.11b, step 1

12. Simple Reflex Arc Figure 7.11b, step 2
Sensory receptors (stretch receptors in the quadriceps muscle)
Sensory (afferent) neuron
Spinal cord
(b)
Figure 7.11b, step 2

13. Simple Reflex Arc Figure 7.11b, step 3
Sensory receptors (stretch receptors in the quadriceps muscle)
Sensory (afferent) neuron
Spinal cord
Synapse in ventral horn gray matter
(b)
Figure 7.11b, step 3

14. Simple Reflex Arc Figure 7.11b, step 4
Sensory receptors (stretch receptors in the quadriceps muscle)
Sensory (afferent) neuron
Spinal cord
Synapse in ventral horn gray matter
Motor (efferent) neuron
(b)
Figure 7.11b, step 4

15. Simple Reflex Arc Figure 7.11b, step 5
Sensory receptors (stretch receptors in the quadriceps muscle)
Sensory (afferent) neuron
Spinal cord
Synapse in ventral horn gray matter
Motor (efferent) neuron
Effector (quadriceps muscle of thigh)
(b)
Figure 7.11b, step 5

16. Simple Reflex Arc Figure 7.11c, step 1
Sensory receptors (pain receptors in the skin)
Spinal cord
(c)
Figure 7.11c, step 1

17. Simple Reflex Arc Figure 7.11c, step 2
Sensory receptors (pain receptors in the skin)
Spinal cord
Sensory (afferent) neuron
(c)
Figure 7.11c, step 2

18. Simple Reflex Arc Figure 7.11c, step 3
Sensory receptors (pain receptors in the skin)
Spinal cord
Sensory (afferent) neuron
Inter- neuron
(c)
Figure 7.11c, step 3

19. Simple Reflex Arc Figure 7.11c, step 4a
Sensory receptors (pain receptors in the skin)
Spinal cord
Sensory (afferent) neuron
Inter- neuron
Motor (efferent) neuron
(c)
Figure 7.11c, step 4a

20. Simple Reflex Arc Figure 7.11c, step 4b
Sensory receptors (pain receptors in the skin)
Spinal cord
Sensory (afferent) neuron
Inter- neuron
Motor (efferent) neuron
Effector (biceps brachii muscle)
(c)
Figure 7.11c, step 4b

21. Simple Reflex Arc Figure 7.11b–c
Sensory receptors (stretch receptors in the quadriceps muscle)
Sensory (afferent) neuron
Sensory receptors (pain receptors in the skin)
Spinal cord
Sensory (afferent) neuron
Synapse in ventral horn gray matter
Inter- neuron
Motor (efferent) neuron
Motor (efferent) neuron
Effector (quadriceps muscle of thigh)
Effector (biceps brachii muscle)
(b)
(c)
Figure 7.11b–c

23. Types of Reflexes and Regulation
Somatic reflexes
Activation of skeletal muscles
Example: When you move your hand away from a hot stove
A “stretch reflex” is a muscle contraction in response to stretching within the muscle
“Superficial reflexes” are motor responses to scraping of the skin.

24. 4. Somatic Reflexes (Activation of skeletal muscles)
Achilles Reflex-
Simple stretch reflex
Cord-mediated
Corneal Reflex
Patellar Reflex
Simple stretch reflex
Cord-mediated
Plantar (Babinski) Reflex
Superficial cord reflex

25. 5. 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

26. 5. Somatic reflex involving higher brain centers
Example: pupillary light reflex

27. Patellar Reflex
Striking 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 spinal
From 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.

28. Superficial reflexes
Superficial 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.

29. Plantar Reflex
Plantar Reflex: Flexion of the toes in response to stroking of the outer surface of the sole, from heel to little toe.

30. Plantar Reflex

31. Corneal Reflex Cranial Nerve V “trigeminal nerve”
Protect the eyeball from damage

32. Autonomic reflexes Autonomic reflexes Smooth muscle regulation
Heart and blood pressure regulation
Regulation of glands
Digestive system regulation
An 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

33. 5. Example of Autonomic Reflex: Pupillary Light Reflex
Receptor = retina of the eye
Afferent Fibers = in Cranial Nerve II,
“optic nerve”
Efferent impulses = carried by cranial nerve III
“ oculomoter nerve”
Effector = smooth muscles of the iris
Function =protects the retina from excessive illumination, which is damaging to the photoreceptors

34. Pupillary Light Reflex

35. Autonomic Reflexes
May 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.

36. 9. Pupillary Response
Ipsilateral: 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.

37. 9. 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?

38. 10. 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.

39. Types of Reflexes and Regulation
Patellar, or knee-jerk, reflex is an example of a two-neuron reflex arc
Figure 7.11d

40. 6. Reflex Arc of Patellar Reflex
Receptors
Afferent Nerves
Integration Center
Efferent Nerve
Effector
Stretch receptors in quadriceps muscle
Afferent neuron
Spinal Cord
Efferent neuron (Femoral Nerve)
Quadriceps muscle of the thigh

41. 6. Reflex Arc of Achilles Reflex
Receptors
Afferent Nerves
Integration Center
Efferent Nerve
Effector
Stretch receptors in Achilles Tendon
Afferent neuron
Spinal Cord
Efferent neuron (Tibial Nerve, S1-S2)
Gastrocnemius muscle

42. 7. Effect of Muscle Fatigue on Patellar Reflex
The intensity of the response is less

43. Differences Between Somatic and Autonomic Nervous Systems
Nerves
Somatic: one motor neuron
Autonomic: preganglionic and postganglionic nerves
Effector organs
Somatic: skeletal muscle
Autonomic: smooth muscle, cardiac muscle, and glands

44. PNS: Differences Between Somatic and Autonomic Nervous Systems
Neurotransmitters
Somatic: always use acetylcholine
Autonomic: use acetylcholine, epinephrine, or norepinephrine

45. Autonomic Nervous System
Motor subdivision of the PNS
Consists only of motor nerves
Also known as the involuntary nervous system
Regulates activities of cardiac and smooth muscles and glands
Two subdivisions
Sympathetic division
Parasympathetic division

46. PNS: Comparison of Somatic and Autonomic Nervous Systems
Figure 7.27

47. Anatomy of the Sympathetic Division
Originates from T1 through L2
Ganglia are at the sympathetic trunk (near the spinal cord)
Short pre-ganglionic neuron and long post-ganglionic neuron transmit impulse from CNS to the effector
Norepinephrine and epinephrine are neurotransmitters to the effector organs

48. PNS: Anatomy of the Autonomic Nervous System
Figure 7.28

49. PNS: Sympathetic Pathways
Figure 7.29

50. Anatomy of the Parasympathetic Division
Originates from the brain stem and S1 through S4
Terminal ganglia are at the effector organs
Always uses acetylcholine as a neurotransmitter

51. Autonomic Functioning
Sympathetic—“fight or flight”
Response to unusual stimulus
Takes over to increase activities
Remember as the “E” division
Exercise, excitement, emergency, and embarrassment

52. Autonomic Functioning
Parasympathetic—“housekeeping” activites
Conserves energy
Maintains daily necessary body functions
Remember as the “D” division
digestion, defecation, and diuresis

53. Effects of the Sympathetic and Parasympathetic Divisions of the ANS
Table 7.3 (1 of 2)

54. Effects of the Sympathetic and Parasympathetic Divisions of the ANS
Table 7.3 (2 of 2)