1. The Peripheral Nervous System and Reflex Activity: Part D13
The Peripheral Nervous System and Reflex Activity: Part D

2. Reflex Arc Components of a reflex arc (neural path)
Receptor—site of stimulus action
Sensory neuron—transmits afferent impulses to the CNS
Integration center—either monosynaptic or polysynaptic region within the CNS
Motor neuron—conducts efferent impulses from the integration center to an effector organ
Effector—muscle fiber or gland cell that responds to the efferent impulses by contracting or secreting

3. 1 2 3 4 5 Stimulus Skin Interneuron Receptor Sensory neuron
Integration center 4
Motor neuron 5
Effector
Spinal cord
(in cross section)
Figure 13.14

4. Spinal somatic reflexes
Spinal Reflexes
Spinal somatic reflexes
Integration center is in the spinal cord
Effectors are skeletal muscle
Testing of somatic reflexes is important clinically to assess the condition of the nervous system

5. Quadriceps (extensors) Hamstrings (flexors)1
Quadriceps strongly
contracts. Golgi tendon
organs are activated. 2
Afferent fibers synapse
with interneurons in the
spinal cord.
Interneurons
Quadriceps
(extensors)
Spinal cord
Golgi
tendon
organ
Hamstrings
(flexors) 3a
Efferent impulses
to muscle with
stretched tendon are
damped. Muscle
relaxes, reducing
tension. 3b
Efferent
impulses to
antagonist
muscle cause
it to contract. +
Excitatory synapse –
Inhibitory synapse
Figure 13.18

6. Superficial Reflexes Plantar reflex
Stimulus: stroking lateral aspect of the sole of the foot
Response: downward flexion of the toes
Tests for function of corticospinal tracts

7. Superficial Reflexes Babinski’s sign Stimulus: as above
Response: dorsiflexion of hallux and fanning of toes
Present in infants due to incomplete myelination
In adults, indicates corticospinal or motor cortex damage