1. The Peripheral Nervous System and Reflex Activity: Part A13
The Peripheral Nervous System and Reflex Activity: Part A

2. Peripheral Nervous System (PNS)
All neural structures outside the brain
Sensory receptors
Peripheral nerves and associated ganglia
Motor endings

3. Central nervous system (CNS)
Peripheral nervous system (PNS)
Sensory (afferent)
division
Motor (efferent) division
Somatic nervous
system
Autonomic nervous
system (ANS)
Sympathetic
division
Parasympathetic
division
Figure 13.1

4. Sensory Receptors
Specialized to respond to changes in their environment (stimuli)
Activation results in graded potentials that trigger nerve impulses
Sensation (awareness of stimulus) and perception (interpretation of the meaning of the stimulus) occur in the brain

5. Classification of Receptors
Based on:
Stimulus type
Location
Structural complexity

6. Classification by Stimulus Type
Mechanoreceptors—respond to touch, pressure, vibration, stretch, and itch
Thermoreceptors—sensitive to changes in temperature
Photoreceptors—respond to light energy (e.g., retina)
Chemoreceptors—respond to chemicals (e.g., smell, taste, changes in blood chemistry)
Nociceptors—sensitive to pain-causing stimuli (e.g. extreme heat or cold, excessive pressure, inflammatory chemicals)

7. Classification by Location
Exteroceptors
Respond to stimuli arising outside the body
Receptors in the skin for touch, pressure, pain, and temperature
Most special sense organs

8. Classification by Location
Interoceptors (visceroceptors)
Respond to stimuli arising in internal viscera and blood vessels
Sensitive to chemical changes, tissue stretch, and temperature changes

9. Classification by Location
Proprioceptors
Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles
Inform the brain of one’s movements

10. Classification by Structural Complexity
Complex receptors (special sense organs)
Vision, hearing, equilibrium, smell, and taste (Chapter 15)
Simple receptors for general senses:
Tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense
Unencapsulated (free) or encapsulated dendritic endings

11. Unencapsulated Dendritic Endings
Thermoreceptors
Cold receptors (10–40ºC); in superficial dermis
Heat receptors (32–48ºC); in deeper dermis

12. Unencapsulated Dendritic Endings
Nociceptors
Respond to:
Pinching
Chemicals from damaged tissue
Temperatures outside the range of thermoreceptors
Capsaicin

13. Unencapsulated Dendritic Endings
Light touch receptors
Tactile (Merkel) discs
Hair follicle receptors

14. Table 13.1

15. Encapsulated Dendritic Endings
All are mechanoreceptors
Meissner’s (tactile) corpuscles—discriminative touch
Pacinian (lamellated) corpuscles—deep pressure and vibration
Ruffini endings—deep continuous pressure
Muscle spindles—muscle stretch
Golgi tendon organs—stretch in tendons
Joint kinesthetic receptors—stretch in articular capsules

16. Table 13.1

17. From Sensation to Perception
Survival depends upon sensation and perception
Sensation: the awareness of changes in the internal and external environment
Perception: the conscious interpretation of those stimuli

18. Sensory Integration
Input comes from exteroceptors, proprioceptors, and interoceptors
Input is relayed toward the head, but is processed along the way

19. Levels of neural integration in sensory systems:
Sensory Integration
Levels of neural integration in sensory systems:
Receptor level—the sensor receptors
Circuit level—ascending pathways
Perceptual level—neuronal circuits in the cerebral cortex

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

21. Processing at the Receptor Level
Receptors have specificity for stimulus energy
Stimulus must be applied in a receptive field
Transduction occurs
Stimulus energy is converted into a graded potential called a receptor potential

22. Processing at the Receptor Level
In general sense receptors, the receptor potential and generator potential are the same thing
stimulus 
receptor/generator potential in afferent neuron
action potential at first node of Ranvier

23. Processing at the Receptor Level
In special sense organs:
stimulus 
receptor potential in receptor cell
release of neurotransmitter
generator potential in first-order sensory neuron
action potentials (if threshold is reached)

24. Adaptation of Sensory Receptors
Adaptation is a change in sensitivity in the presence of a constant stimulus
Receptor membranes become less responsive
Receptor potentials decline in frequency or stop

25. Adaptation of Sensory Receptors
Phasic (fast-adapting) receptors signal the beginning or end of a stimulus
Examples: receptors for pressure, touch, and smell
Tonic receptors adapt slowly or not at all
Examples: nociceptors and most proprioceptors

26. Processing at the Circuit Level
Pathways of three neurons conduct sensory impulses upward to the appropriate brain regions
First-order neurons
Conduct impulses from the receptor level to the second-order neurons in the CNS
Second-order neurons
Transmit impulses to the thalamus or cerebellum
Third-order neurons
Conduct impulses from the thalamus to the somatosensory cortex (perceptual level)

27. Processing at the Perceptual Level
Identification of the sensation depends on the specific location of the target neurons in the sensory cortex
Aspects of sensory perception:
Perceptual detection—ability to detect a stimulus (requires summation of impulses)
Magnitude estimation—intensity is coded in the frequency of impulses
Spatial discrimination—identifying the site or pattern of the stimulus (studied by the two-point discrimination test)

28. Main Aspects of Sensory Perception
Feature abstraction—identification of more complex aspects and several stimulus properties
Quality discrimination—the ability to identify submodalities of a sensation (e.g., sweet or sour tastes)
Pattern recognition—recognition of familiar or significant patterns in stimuli (e.g., the melody in a piece of music)

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

30. Perception of Pain
Warns of actual or impending tissue damage
Stimuli include extreme pressure and temperature, histamine, K+, ATP, acids, and bradykinin
Impulses travel on fibers that release neurotransmitters glutamate and substance P
Some pain impulses are blocked by inhibitory endogenous opioids

31. Structure of a Nerve
Cordlike organ of the PNS
Bundle of myelinated and unmyelinated peripheral axons enclosed by connective tissue

32. Connective tissue coverings include:
Structure of a Nerve
Connective tissue coverings include:
Endoneurium—loose connective tissue that encloses axons and their myelin sheaths
Perineurium—coarse connective tissue that bundles fibers into fascicles
Epineurium—tough fibrous sheath around a nerve

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

34. Classification of Nerves
Most nerves are mixtures of afferent and efferent fibers and somatic and autonomic (visceral) fibers
Pure sensory (afferent) or motor (efferent) nerves are rare
Types of fibers in mixed nerves:
Somatic afferent and somatic efferent
Visceral afferent and visceral efferent
Peripheral nerves classified as cranial or spinal nerves

35. Contain neuron cell bodies associated with nerves
Ganglia
Contain neuron cell bodies associated with nerves
Dorsal root ganglia (sensory, somatic) (Chapter 12)
Autonomic ganglia (motor, visceral) (Chapter 14)

36. Regeneration of Nerve Fibers
Mature neurons are amitotic
If the soma of a damaged nerve is intact, axon will regenerate
Involves coordinated activity among:
Macrophages—remove debris
Schwann cells—form regeneration tube and secrete growth factors
Axons—regenerate damaged part
CNS oligodendrocytes bear growth-inhibiting proteins that prevent CNS fiber regeneration

37. Endoneurium Schwann cells The axon becomes fragmented at1
The axon
becomes
fragmented at
the injury site.
Droplets
of myelin
Fragmented
axon
Site of nerve damage
Figure 13.4 (1 of 4)

38. Macrophages clean out the dead axon distal to the injury. Schwann cell2
Schwann cell
Macrophage
Figure 13.4 (2 of 4)

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

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