1. The Peripheral Nervous System
Nervous structures outside the brain and spinal cord
Nerves allow the CNS to receive information and take action
Functional components of the PNS
Sensory inputs and motor outputs
Categorized as somatic or visceral
Sensory inputs also classified as general or special
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2. Functional Organization of the PNS
Figure 14.1
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3. Basic Structural Components of the PNS
Sensory Receptors: pick up stimuli from inside or outside the body
Motor Endings: axon terminals of motor neurons
Innervate effectors (muscle fibers and glands)
Nerves and Ganglia:
Nerves – bundles of peripheral axons
Ganglia – clusters of peripheral neuronal cell bodies
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4. Structural Organization of PNS in Region of a Spinal Nerve
Peripheral Nerve Endings:
Afferent: Sensory Receptors
Efferent: Somatic Motor
Efferent: Autonomic Nervous System

5. Peripheral Sensory Receptors
Structures that pick up sensory stimuli
Initiate signals in sensory axons
Two main categories of sensory receptors
Special nerve endings of sensory neurons
Monitor general sensory information
Independent receptor cells – specialized epithelial cells or small neurons
Sensory receptors can be classified in three ways:
Type of stimulus detected
Location
Structural Complexity
Monitor most types of special sensory information

6. Classification by Type of Stimuli
Mechanoreceptors – respond to mechanical forces
Thermoreceptors – respond to temperature changes
Chemoreceptors – respond to chemicals in solution
Photoreceptors – respond to light – located in the eye
Nociceptors – respond to harmful stimuli that result in pain
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7. Classification by Location
Exteroceptors: sensitive to stimuli arising from outside the body
Located at or near body surfaces
Include receptors for touch, pressure, pain, and temperature
Interoceptors: – (visceroceptors) receive stimuli from within the body
internal viscera & blood vessels
Monitor a variety of stimuli such as chemical changes, stretching of tissue & temperature
Proprioceptors: – monitor degree of stretch
Located in musculoskeletal organs

8. Classification by Structure
Simple:
Vast majority
Modified dendritic extensions of sensory neurons
Found in skin, mucous membranes, muscles & connective tissue
Complex:
Associated with the special senses (vision, hearing, smell & taste)
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9. General Sensory Receptors (simple receptors)
Widely distributed
Nerve endings of sensory neurons monitor:
Touch, pressure, vibration, stretch
Pain, temperature, proprioception
Divided into two groups
Free dendritic (nerve) endings
Encapsulated dendritic (nerve) endings
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10. Abundant in epithelia and underlying connective tissue
Free Nerve Endings
Abundant in epithelia and underlying connective tissue
Most are unmyelinated with a small diameter
Respond to pain and temperature
Monitor affective senses
Two specialized types of free nerve endings
Merkel discs – lie in the epidermis
Slowly adapting receptors for light touch
Hair follicle receptors – wrap around hair follicles
Rapidly adapting receptors
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11. Encapsulated Nerve Endings
Consist of one or more end fibers of sensory neurons
Enclosed in connective tissue
Mechanoreceptors
Include four main types:
Meissner’s corpuscles
Pacinian corpuscles
Ruffini’s corpuscles
Proprioceptors – monitor stretch in locomotory organs
Muscle spindles
Golgi tendon organs
Joint kinesthetic receptors

12. Three Types of Proprioceptors
Muscle spindles – measure the changing length of a muscle
Imbedded in the perimysium between muscle fascicles
Golgi tendon organs – located near the muscle-tendon junction
Monitor tension within tendons
Joint kinesthetic receptors
Sensory nerve endings within the joint capsules
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13. Structure of Receptors in Skin
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14. Innervation of Skeletal Muscle
Motor axons innervate skeletal muscles
Neuromuscular junctions (motor end plates)
Similar to synapses between neurons
Acetylcholine diffuses across the synaptic cleft
Binds with molecules on the sarcolemma
Motor axons branch to innervate muscle fibers
Motor unit – a motor neuron and all the muscle fibers it innervates

15. The Neuromuscular Junction
Figure 14.5a, b
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16. Innervation of Visceral Muscle and Glands
Simpler than neuromuscular junctions of skeletal muscle
Near the smooth muscle or gland it innervates
Visceral motor axon swells into a row of varicosities
Visceral motor responses
Slower than somatic motor reflexes

17. Attach to the brain and pass through foramina of the skull
Cranial Nerves
Attach to the brain and pass through foramina of the skull
Numbered from I–XII
Cranial nerves I and II attach to the forebrain
All others attach to the brain stem
Primarily serve head and neck structures
The vagus nerve (X) extends into the abdomen
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18. The 12 Pairs of Cranial Nerves
Figure 14.8
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19. Sensory nerves of smell
CN I: Olfactory Nerves
Sensory nerves of smell
Table 14.2
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20. Sensory nerve of vision
CN II: Optic Nerve
Sensory nerve of vision
Table 14.2
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21. CN III: Oculomotor Nerve
Innervates four of the extrinsic eye muscles
Table 14.2
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22. Innervates an extrinsic eye muscle
CN IV: Trochlear Nerve
Innervates an extrinsic eye muscle
Table 14.2
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23. Provides sensory innervation to the face
CN V: Trigeminal Nerve
Provides sensory innervation to the face
Motor innervation to chewing muscles

24. CN VI: Abducens Nerve Abducts the eyeball Table 14.2
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25. Innervates muscles of facial expression Sensory innervation of face
CN VII: Facial Nerve
Innervates muscles of facial expression
Sensory innervation of face
Taste
Table 14.2
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26. CN VIII: Vestibulocochlear Nerve
Sensory nerve of hearing and balance
Table 14.2
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27. CN IX: Glossopharyngeal Nerve
Sensory and motor innervation of structures of the tongue and pharynx
Taste
Table 14.2
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28. CN X: Vagus Nerve (pneumogastric nerve)
A mixed sensory and motor nerve
Main parasympathetic nerve
“Wanders” into thorax and abdomen
Table 14.2
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29. An accessory part of the vagus nerve
CN XI: Accessory Nerve
An accessory part of the vagus nerve
Somatic motor function of pharynx, larynx, neck muscles
Table 14.2
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30. CN XII: Hypoglossal Nerve
Runs inferior to the tongue
Innervates the tongue muscles
Table 14.2
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31. 31 pairs – contain thousands of nerve fibers
Spinal Nerves
31 pairs – contain thousands of nerve fibers
Connect to the spinal cord
Named for point of issue from the spinal cord
8 pairs of cervical nerves (C1-C8)
12 pairs of thoracic nerves (T1-T12)
5 pairs of lumbar nerves (L1-L5)
5 pairs of sacral nerves (S1-S5)
1 pair of coccygeal nerves (Co1)
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32. Spinal Nerves Posterior View
Figure 14.9
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33. Spinal Nerves
Connect to the spinal cord by the dorsal root and ventral root
Dorsal root – contains sensory fibers
Cell bodies – located in the dorsal root ganglion
Ventral root – contains motor fibers arising from anterior gray column (cell bodies in gray matter of spinal cord – no ganglia)

34. Spinal Nerves Branch into dorsal ramus and ventral ramus
Rami communicantes connect to the base of the ventral ramus
Lead to the sympathetic chain ganglia (gray and white ramus)
Dorsal and ventral rami contain sensory and motor fibers

35. Innervation of the Skin: Dermatomes
Dermatome – an area of skin
Innervated by cutaneous branches of a single spinal nerve
Upper limb – skin is supplied by nerves of the brachial plexus
Lower limb
Lumbar nerves – anterior surface
Sacral nerves – posterior surface

36. Map of Dermatomes – Anterior & Posterior View

37. A reflex is a rapid, predictable motor response to a stimulus
Reflex Activity
A reflex is a rapid, predictable motor response to a stimulus
The basic reflex is unlearned, unpremeditated and involuntary,
Some reflexes we are aware of (pulling away from hot pot) and others, usually visceral, we are not
In addition to basic reflexes there are also learned or acquired reflexes (automatic actions of an experienced driver)
Reflexes occur in highly specific neural paths called reflex arcs
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38. The Reflex Arc Receptor: site of stimulus action
Sensory Neuron: transmits afferent impulses to the CNS
Integration Center: synapse between sensory & motor neuron or multiple synapses within a chain of interneurons
Motor Neuron: conducts the afferent impulses from integration center to effector organ
Effector: the muscle fiber or gland cell that response to the efferent impulses in a characteristic way

39. Spinal reflexes are somatic reflexes mediated by the spinal cord
In the stretch reflex the muscle spindle is stretched and excited by either an external stretch or an internal stretch
The Golgi tendon reflex produces muscle relaxation and lengthening in response to contraction
The flexor, or withdrawal, reflex is initiated by a painful stimulus and causes automatic withdrawal of the threatened body part from the stimulus
They crossed extensor reflex is a complex spinal reflex consisting of an ipsilateral withdrawal reflex and a contralateral extensor reflex
Superficial reflexes are elicited by gentle cutaneous stimulation

40. The Stretch Reflex

41. Deep Golgi Tendon Reflex

42. Disorders: Anencephaly
Various degrees of absence of the various of the skull bones, cerebrum and the brain stem
One of the most common neural tube defects. Neural tube.
Occurs early in the development when the upper part of the neural tube fails to close.
Possible causes include environmental toxins and low intake of folic acid by the mother during pregnancy.
Often results in miscarriage, if child survives to birth he/she will be totally vegetative and unable to see, hear or process sensory input. Death will occur soon after birth.

43. Disorders: Shingles Viral infection
Childhood chicken pox dormant in spinal ganglia
Often brought on by stress
Mostly experienced by those over 50
Unilateral patch of skin blisters and discoloration along the path of one or more spinal nerves
Most commonly around the waist. The symptoms may persist for 3 to 6 months.

44. Disorders: Cerebal Palsy
Group of neuromuscular disorders in which the voluntary muscles are poorly controlled or paralyzed due to brain damage
Can result in spasticity, speech difficulties, seizures, deafness or reduced cognitive ability
Can be due to lack of oxygen during delivery, smoking or drug use, or maternal infection during pregnancy

45. Disorders: Spina Bifida & Lumbar Myelomeningocele
Incomplete formation of vertebral arches, usually in lumbosacral region
Laminae & spinal processes missing in at least one vertebrae
In the severe form, spina bifida cyctica, it can result in a sac-like cyst protruding dorsally
The cyst may contain meninges and CSF and possibly portiosns of the spinal cord and spinal root nerves
primary functional deficits are lower limb paralysis and sensory loss, bladder and bowel dysfunction, and cognitive dysfunction

46. Disorders :Migraine Headache
Relates to sensory innervation of cerebral arteries
Arteries dilate
Compresses and irritates sensory nerve endings
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47. Disorders: Poliomyelitis
“polio” means gray matter
caused by Poliovirus hominis.
CNS infection, but its major effect is on the peripheral nerves and the muscles they supply.
virus infects the motor neurons in the anterior horn of the central gray matter of the spinal cord.
The infection causes degeneration of the motor neurons, which results in paralysis and atrophy of the muscles innervated by those nerves.

48. Disorders: Anesthetic leprosy
Bacterial infection of the peripheral nerves caused by Mycobacterium leprae.
Infection results in anesthesia, paralysis, ulceration, and gangrene

49. Disorders :Myasthenia Gravis
Progressive weakening of the skeletal muscles
An autoimmune disorder
Antibodies destroy acetylcholine receptors
Ptosis due to weakness of eyelid muscles
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