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ANATOMY & PHYSIOLOGY INSTRUCTOR: FRED WENDLER
PERIPHERAL NERVOUS SYSTEM-
REFLEX ACTIVITY
BASED ON THE BOOKS HUMAN ANATOMY & PHYSIOLOGY, NINTH EDITION BY ELAINE N. MARIEB AND KATJA HOEHN; WITH ILLUSTRATIONS FROM HUMAN ANATOMY & PHYSIOLOGY, NINTH EDITION BY ELAINE N. MARIEB AND KATJA HOEHN; ANATOMY AND PHYSIOLOGY FROM OPENSTAX COLLEGE, ISBN 1- 938168 - 13 - 5
What is a reflex?
- A reflex is a predictable, pre-programmed, involuntary motor response to a specific stimulus
- Reflexes use a neural pathway called a reflex arc
- Reflex arcs have a minimum of 5 parts
Reflex Arc
- Components of a reflex arc (neural path)
- Receptor—site of stimulus action
- Sensory neuron—transmits afferent impulses to CNS
- Integration center—one or more synapses within CNS
- Motor neuron—conducts efferent impulses from integration center to effector organ
- Effector—muscle fiber or gland cell that responds to efferent impulses by contracting or secreting
Reflex Classification
• Reflexes can be classified by multiple
ways
- Development of reflex
- Nature of response
- Complexity of neural circuit
- Processing site of reflex
Reflexes – Classified by Development Acquired Reflexes
- Also called ‘learned’ reflex
- Learned result from practice and repetition
- Example: driving
Reflexes Classified by Nature of Response
• Can be classified as
- Autonomic reflexes
- Somatic reflexes
Somatic Reflexes
- Reflexes that stimulate skeletal muscles
- Provide involuntary control of skeletal muscles
- Spinal Reflexes
- Stretch reflexes (patellar reflex)
- Superficial reflexes (plantar reflex)
- Cranial Nerve Reflexes Tests
Reflex Classified by the Complexity of Neural Circuit
- Monosynaptic reflex
- Simplest reflex
- Involves 2 neurons with 1 synapse
- Sensory neuron synapses directly of motor neuron
- Examples are:
- Patellar reflex
- Ankle jerk reflex
Classification Based on Site of Processing Reflex
- Spinal Reflex
- Processing of reflex occurs in spinal cord
- Cranial Reflex
- Processing of reflex occurs in brain
Spinal Reflexes
- Spinal somatic reflexes
- Reflexes are mediated by the spinal cord
- Integration center in spinal cord
- Effectors are skeletal muscle
- Testing of somatic reflexes important clinically to assess condition of nervous system
Stretch Reflexes
- How stretch reflex works
- Stretch reflex is activated by tapping the tendon the muscle is attached to
- Sensory neurons synapse directly with motor neurons in spinal cord
- motor neuron causes stretched muscle to contract
Stretch Reflexes
- Reciprocal inhibition also occurs
- Example: In patellar reflex
- Stretch reflex muscle (quadriceps) contracts
- antagonists (hamstrings) relax
Figure 13.18 Stretch Reflex (2 of 2) Slide 10 Patellar ligament Patella Hamstrings (flexors) Muscle spindle Quadriceps (extensors) Spinal cord (L 2 – L 4 ) Tapping the patellar ligament stretches the quadriceps and excites its muscle spindles. Afferent impulses (blue) travel to the spinal cord, where synapses occur with motor neurons and interneurons. The motor neurons (red) send activating impulses to the quadriceps causing it to contract, extending the knee. The interneurons (green) make inhibitory synapses with ventral horn neurons (purple) that prevent the antagonist muscles (hamstrings) from resisting the contraction of the quadriceps. The patellar (knee-jerk) reflex—an example of a stretch reflex 1 2 3a 3b 3b 1
- 2 3a 3b - Inhibitory synapse
- Excitatory synapse Elaine N. Marieb and Katia Hoehn; HUMAN ANATOMY & PHYSIOLOGY, Ninth Edition; Pearson Education, Inc.; Boston, 2013.
The Flexor Reflex
- Flexor (withdrawal) reflex
- Initiated by painful stimulus
- Causes automatic withdrawal of threatened body part
- Protective reflex
