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1. 13 The Peripheral Nervous System and Reflex Activity: Part A

2. Stretched muscle spindles initiate a stretch reflex,causing contraction of the stretched muscle andinhibition of its antagonist. The events by which muscle stretch is damped The sensory neurons synapse directly with alphamotor neurons (red), which excite extrafusal fibersof the stretched muscle. Afferent fibers alsosynapse with interneurons (green) that inhibit motorneurons (purple) controlling antagonistic muscles. 2 When muscle spindles are activatedby stretch, the associated sensoryneurons (blue) transmit afferent impulsesat higher frequency to the spinal cord. 1 Sensoryneuron Cell body ofsensory neuron Initial stimulus(muscle stretch) Spinal cord Muscle spindle Antagonist muscle 3a 3b Efferent impulses of alpha motor neuronscause the stretched muscle to contract,which resists or reverses the stretch. Efferent impulses of alpha motorneurons to antagonist muscles arereduced (reciprocal inhibition). Figure 13.17 (1 of 2), step 3b

3. The patellar (knee-jerk) reflex—a specific example of a stretch reflex 2 Quadriceps(extensors) 3a 3b 3b 1 Patella Musclespindle Spinal cord(L2–L4) Tapping the patellar ligament excitesmuscle spindles in the quadriceps. 1 Hamstrings(flexors) Patellarligament 2 Afferent impulses (blue) travel to thespinal cord, where synapses occur withmotor neurons and interneurons. 3a The motor neurons (red) sendactivating impulses to the quadricepscausing it to contract, extending theknee. +– Excitatory synapseInhibitory synapse 3b The interneurons (green) makeinhibitory synapses with ventral horn neurons (purple) that prevent theantagonist muscles (hamstrings) fromresisting the contraction of thequadriceps. Figure 13.17 (2 of 2)

4. + Excitatory synapse – Inhibitory synapse Interneurons Efferent fibers Afferent fiber Efferent fibers Extensor inhibited Flexor inhibited Arm movements Flexor stimulated Extensor stimulated Site of reciprocal activation:At the same time, the extensor muscles on the opposite side are activated. Site of stimulus: a noxious stimulus causes a flexor reflex on the same side, withdrawing that limb. Figure 13.19

5. Filaments of olfactory nerve (I) Frontal lobe Olfactory bulb Olfactory tract Optic nerve (II) Temporal lobe Optic chiasma Infundibulum Optic tract Facial nerve (VII) Oculomotor nerve (III) Trochlear nerve (IV) Vestibulo- cochlear nerve (VIII) Trigeminal nerve (V) Glossopharyngeal nerve (IX) Abducens nerve (VI) Vagus nerve (X) Cerebellum Accessory nerve (XI) Medulla oblongata Hypoglossal nerve (XII) (a) Figure 13.5 (a)

6. Cervical plexus Cervical nerves C1 – C8 Brachial plexus Cervical enlargement Thoracic nerves T1 – T12 Intercostal nerves Lumbar enlargement Lumbar nerves L1 – L5 Lumbar plexus Sacral plexus Sacral nerves S1 – S5 Cauda equina Coccygeal nerve Co1 Figure 13.6

7. Gray matter White matter Dorsal and ventral rootlets of spinal nerve Ventral root Dorsal root Dorsal root ganglion Dorsal ramus of spinal nerve Ventral ramus of spinal nerve Spinal nerve Rami communicantes Sympathetic trunk ganglion Anterior view showing spinal cord, associated nerves, and vertebrae. The dorsal and ventral roots arise medially as rootlets and join laterally to form the spinal nerve. Figure 13.7 (a)

8. Dorsal ramus Ventral ramus Spinal nerve Rami communicantes Intercostal nerve Dorsal root ganglion Sympathetic trunk ganglion Dorsal root Ventral root Branches of intercostal nerve • Lateral cutaneous • Anterior cutaneous Sternum (b) Cross section of thorax showing the main roots and branches of a spinal nerve. Figure 13.7 (b)

9. Roots (ventral rami): C4 Dorsal scapular C5 Nerve to subclavius C6 Suprascapular Upper Posterior divisions C7 Trunks Middle C8 Lateral Lower Cords T1 Posterior Long thoracic Medial pectoral Medial Lateral pectoral Axillary Upper subscapular Musculo- cutaneous Lower subscapular Thoracodorsal Radial Medial cutaneous nerves of the arm and forearm Median Ulnar (a) Roots (rami C5 – T1), trunks, divisions, and cords Posterior divisions Roots Anterior divisions Trunks Figure 13.9 (a)

10. C2 C3 C2 C4 C3 C5 C6 C4 C7 C8 T1 C5 C5 T2 T1 T3 T2 T4 T3 T5 T4 T2 T2 T6 T5 T7 T6 T8 T9 T7 T10 T8 C6 C6 C5 C5 T11 T9 T12 C7 C7 T10 L1 C6 C6 S1 L2 C8 T11 C8 L3 S2 L5 L4 S3 T12 L1 L1 C6 S4 C6 S5 S2 C7 C7 C8 S3 C8 L2 L2 S1 S2 S2 S1 L1 L3 L3 L2 L5 L5 L4 L4 L3 L5 L5 L4 S1 S1 Anterior view (b) Posterior view L4 L4 L5 L5 S1 Figure 13.12

11. Heart Lungs and diaphragm Liver Heart Gallbladder Liver Appendix Stomach Pancreas Small intestine Ovaries Colon Kidneys Urinary bladder Ureters Figure 14.8

12. Axon Myelin sheath Endoneurium Perineurium Epineurium Fascicle Blood vessels (b) Figure 13.3b

13. Endoneurium Schwann cells 1 The axon becomes fragmented at the injury site. Droplets of myelin Fragmented axon Site of nerve damage Figure 13.4 (1 of 4)

14. Macrophages clean out the dead axon distal to the injury. 2 Schwann cell Macrophage Figure 13.4 (2 of 4)

15. Axon sprouts, or filaments, grow through a regeneration tube formed by Schwann cells. 3 Aligning Schwann cells form regeneration tube Fine axon sprouts or filaments Figure 13.4 (3 of 4)

16. The axon regenerates and a new myelin sheath forms. 4 Site of new myelin sheath formation Schwann cell Single enlarging axon filament Figure 13.4 (4 of 4)

17. Table 13.1

18. Table 13.1

19. Perceptual level(processing in cortical sensory centers) 3 Motor cortex Somatosensory cortex Thalamus Reticular formation Cerebellum Pons Medulla Circuit level (processing in ascending pathways) 2 Spinal cord Free nerve endings (pain, cold, warmth) Muscle spindle Receptor level (sensory reception and transmission to CNS) 1 Joint kinesthetic receptor Figure 13.2