1. Sensory Pathways and the Somatic Nervous System
Chapter 15
Neural Integration I:
Sensory Pathways and the Somatic Nervous System

2. fig. 15-1

3. Sensory
Motor
General (15)
Somatic (15)
Special (17)
Autonomic (16)

4. most associated with the skin
General senses
Special senses
smell
sight
taste
hearing
special “sense”
organs
temperature
pain
touch
pressure
vibration
proprioception
most associated with the skin

5. General senses
receptors distributed throughout the body
relatively simple

6. receptors send info to CNS
General senses
receptors send info to CNS
arriving info is called sensation
our awareness of it is perception

7. interface between environment
Sensory receptors
interface between environment
and the
body
translate stimulus into an AP
transduction

8. Sensory receptors
receptors have selective sensivity
chemical
physical touch
light
heat transfer
receptors may or may not have accessory structures associated with them

9. size of receptive field
Sensory receptors
receptive field
area monitored by a receptor
size of receptive field
70 mm
1 mm
specificity
fig. 15-2

10. Sensory receptors stimulus receptor transduction stimulus changes
membrane potential
receptor potential
(+ or -)
greater stimulus means larger receptor potential
if stimulus is large enough to get to threshold is is called generator potential ( generates an AP)
transduction

11. Sensory receptors
stimulus
receptor
action potential
CNS
for processing and
interpretation
(cortical areas)

12. receptor 2
receptor A
receptor B
labeled line
cortex

13. a “line” carries the same “type” (modality) of information
interpretation is based on which “line” information travels on

14. receptor 2
receptor A
receptor B
labeled line
optic nerve
cortex
shut eyes and rub them gently

15. When CNS receives info…
which “line” type of stimulus
where “line” ends perception
all other attributes (strength, duration, variation) are determined by the frequency and pattern of AP’s

16. receptor types:
tonic: always “on”
phasic: only on with stimulus
some receptors combine the two
greater stimulus higher freq.
lesser stimulus lower freq.

17. adaptation
reduction in sensitivity in the presence of a constant stimulus
peripheral
central
change in receptor activity
inhibition of nuclei in pathway

18. peripheral adaptation
phasic receptors
(aka fast-adapting receptors)
example: thermoreceptors
you usually don’t notice room
temperature unless it changes

19. central adaptation example: smell
you walk into a room and notice a new smell…
…but not for long

20. about 1% of sensory information coming in reaches our awareness
adaptation reduces the amount of information reaching the cerebral cortex
about 1% of sensory information coming in reaches our awareness

21. 100 Keys (pg 498)
“Stimulation of a receptor produces action potentials along the axon of a sensory neuron. The frequency or pattern of action potentials contains information about the strength, duration, and variation of the stimulus. Your perception of the nature of that stimulus depends on the path it takes inside the CNS.”

22. General senses (from chapter 12)
exteroceptors
proprioceptors
interoceptors
outside
position
inside

23. based on nature of stimulus
General senses
classification
based on nature of stimulus
nociceptors
thermoreceptors
mechanoreceptors
chemoreceptors
pain
heat flow
physical distortion
chemical concentration

24. General senses nociceptors common in: skin joint capsules
coverings of bones
around blood vessel walls
free nerve endings
large receptive fields

25. nociceptors sensitive to: extreme temperature mechanical damage
dissolved chemicals
(like those release by damaged cells)
stimulation causes depolarization

26. nociceptors two fiber types convey info type A fast pain (cut, etc.,)
easy to localize
type C
slow pain (“burning, aching”)
difficult to localize

27. nociceptors tonic receptors no significant peripheral adaptation
as long as the stimulus is present, it will hurt
but central adaptation can occur
(perception of pain may decrease)

28. nociceptors
sensory neurons bringing in pain info use glutamate and/or substance P as their neurotransmitter
these nts can cause facilitation (?)
pain may be disproportional
(feels worse than it should)
pain can be reduced by endorphins and enkephalins (inhibit activity in pathway) [neuromodulators chpt. 12]

29. nociceptors
endorphins
pain centers use substance P
as nt.
endorphins bind to presynaptic membrane and inhibit substance P release, reducing perception of pain

30. to here 3/9
lec # 24

31. thermoreceptors
free nerve endings in the dermis
skeletal m.
hypothalamus
liver
warm receptors or
cold receptors

32. thermoreceptors
phasic receptors
active when temperature is changing, quickly adapting to stable temperature
detect transfer of heat
heat loss from skin cool
heat gain to skin warm

33. mechanoreceptors
contain mechanically regulated ion channels (chapter 12)

34. c. mechanically regulated channels
closed
mechanical
stimulus-
opens
remove
stimulus-
closed
fig c

35. mechanoreceptors
three classes
tactile receptors
baroreceptors
proprioceptors
touch, pressure, vibration
pressure changes
(gut, genitourinary)
position of joints/muscles

36. mechanoreceptors
tactile receptors
fine touch/pressure
crude touch/pressure
small (narrow) receptive field
detailed information
sensitive
wide receptive field
poor localization

37. fig. 15-3

38. tactile receptors
range of complexity
free nerve endings
root hair plexus
tactile discs
tactile corpuscles (Meissner’s)
lamellated corpuscles (pacinian)
Ruffini corpuscles

39. tactile receptors
free nerve endings
in epidermis of skin
cornea of eye
sensitive to touch and pressure
tonic receptors
small receptive field

40. tactile receptors
root hair plexus
around each hair follicle
sense movement of hair
adapt quickly

41. tactile receptors
tactile discs
sensitive, tonic receptors
in epidermis
fine touch and pressure

42. tactile receptors
tactile corpuscles (Meissner’s)
fine touch, pressure , vibration
adapt quickly
surrounded by Schwann cells
in dermis of skin
eyelids, fingertips (sensitive areas)

43. tactile receptors
lamellated corpuscles (pacinian)
sensitive to deep pressure
high-frequency vibrations
adapt quickly
nerve ending is encapsulated
by layers of supporting cells
(onion)
dermis, pancreas, fingers…

44. tactile receptors
Ruffini corpuscles
pressure and skin distortion
located deep in the dermis
tonic, little if any adaptation

45. fig. 15-3

46. sensivitity can be altered
infection
disease
damage to pathway
e.g., damage to a spinal nerve
would affect an entire dermatome

47. tickle and itch
closely related to touch and pain

48. baroreceptors
free nerve endings in the walls of organs that stretch
e.g., blood vessels
when pressure changes they expand or contract
changes activity of receptors

49. proprioceptors
muscle spindles
Golgi tendon organs
receptors in joint capsules
stretch reflex
monitor tendon tension
free nerve endings in joints

50. proprioceptors
no adaptation
continuously send info to CNS
most processed at subconscious level

51. chemoreceptors
respond to chemicals dissolved in the surrounding fluids
respiratory centers in brain
pH, CO2 levels in blood
carotid bodies and aortic bodies
pH, CO2, O2 levels in blood

52. Pathways in the CNS spinothalamic tract corticospinal tract
spine to thalamus
=sensory
corticospinal tract
cortex to spine
=motor

53. Pathways in the CNS
sensory pathways
neurons involved
first order neuron
second order neuron
third order neuron
sensory neuron (DRG)
in CNS (crosses over)
in thalamus

54. Pathways in the CNS
sensory pathways
Somatic sensory pathways
carry sensory info
from skin and muscles of
body wall, head, neck, limbs

55. Pathways in the CNS
sensory pathways
Somatic sensory pathways
posterior column pathway
anterolateral column pathway
spinocerebellar pathway

56. fig. 15-4

57. The Posterior Column Pathway
fine touch
pressure
vibrations
proprioception

58. The Posterior Column Pathway
inferior half of body
first order neuron in DRG
up the fasciculus gracilis to the
nucleus gracilis of med. oblong.
superior half of body
first order neuron in DRG
up the fasciculus cuneatus to the
nucleus cuneatus of med. oblong.

59. The Posterior Column Pathway
second order neuron in nucleus ?
cross to other side and ascend to
the ventral nucleus of thalamus
third order neuron in thalamus
project to the primary sensory cortex

60. fig. 15-4
fig. 15-5a

61. The Anterolateral Pathway
“crude” touch
pressure
pain
temperature

62. The Anterolateral Pathway
first order neuron in DRG
synapses on 2nd order neuron
in dorsal horn of spinal cord
second order neuron
cross to opposite side and ascend

63. The Anterolateral Pathway
second order neuron
cross to opposite side and ascend
anterior spinothalamic tract
lateral spinothalamic tract
crude touch and pressure
to ventral nucleus of thalamus
pain and temperature

64. The Anterolateral Pathway
second order neuron in spinal cord
cross to other side and ascend to
the ventral nucleus of thalamus
third order neuron in ventral thalamus
project to the primary sensory cortex

65. fig. 15-4
fig. 15-5b

66. The Anterolateral Pathway
phantom pain ?
activity along pathway, even if “limb” is not there
referred pain?
viceral pains sensations may stimulate neurons of AL pathway

67. fig. 15-6

68. The Spinocerebellar Pathway
posterior s.c. tracts
axons from same side to cerebellum
anterior s.c. tracts
axons cross over and
ascend to cerebellum
information goes to Purkinjie cells
in the cerebellum (proprioception)

69. fig. 15-4
fig. 15-7

70. 100 Keys (pg. 507)
Most somatic sensory information
is relayed to the thalamus for processing. A small fraction of the arriving information is projected to the cerebral cortex and reaches our awareness.

71. to here 3/12
lec # 25

72. Pathways in the CNS
sensory pathways
Somatic sensory pathways
posterior column pathway
anterolateral column pathway
spinocerebellar pathway

73. fig. 15-4

74. Pathways in the CNS
sensory pathways
Somatic sensory pathways
posterior column pathway
anterolateral column pathway
spinocerebellar pathway

75. Pathways in the CNS
sensory pathways
Somatic sensory pathways
Visceral sensory pathways
info from interoceptors
(internal organs)

76. Pathways in the CNS
Somatic sensory pathways
Visceral sensory pathways
nociceptors, thermoreceptors,
tactile receptors, baroreceptors, chemoreceptors

77. Somatic sensory pathways Visceral sensory pathways
Pathways in the CNS
Somatic sensory pathways
Visceral sensory pathways
CN V, VII, IX, X carry info from
pharynx, mouth, palate, larynx, trachea and esophagus
project to solitary nucleus
(medulla oblongata)

78. Somatic sensory pathways Visceral sensory pathways
Pathways in the CNS
Somatic sensory pathways
Visceral sensory pathways
T1 to L2 abdominal organs
S2 to S4 pelvic organs
first order neurons project to interneurons which travel up the anterolateral pathway to sol. nuc.
usually subconscious

79. Pathways in the CNS sensory pathways motor pathways
the somatic nervous system (SNS)
autonomic nervous system (ANS)
voluntary
involuntary

80. motor pathways in the CNS
the somatic nervous system (SNS)
always involve at least two neurons
upper motor neuron
lower motor neuron
inside CNS (+ or -)
stimulates a motor unit

81. motor pathways in the CNS
motor information follows
one of three main pathways:
corticospinal pathway
medial pathway
lateral pathway

82. motor pathways in the CNS
corticospinal pathway
(aka., pyramidal system)
upper motor neurons are
pyramidal cells in primary motor cortex
synapse on lower motor neurons
(ventral horn of spinal cord)
also project to other control centers

83. motor pathways in the CNS
corticospinal pathway
three pairs of tracts:
corticobulbar tracts
to motor nuclei of
CN III, IV, V, VI, VII, IX, XI, XII
conscious control of eye, jaw and face muscles…

84. motor pathways in the CNS
corticospinal pathway
three pairs of tracts:
corticobulbar tracts
lateral corticospinal tracts
anterior corticospinal tracts

85. fig. 15-9

86. Pathways in the CNS
motor pathways
motor information follows
one of three main pathways:
corticospinal pathway
medial pathway
lateral pathway

87. fig. 15-8

88. corticospinal pathway medial pathway
Pathways in the CNS
motor pathways
corticospinal pathway
medial pathway
neck
trunk
proximal
limbs
muscle tone
gross movement

89. reflexive head position
Pathways in the CNS
motor pathways
medial pathway
UMN in:
vestibular nuclei
(hind)
superior colliculus
(mid)
reticular formation
(brain stem)
posture &
balance
reflexive head position
various

90. Pathways in the CNS motor pathways lateral pathway
control of muscle tone
precise movement of distal limbs
UMN in red nucleus (mid)
descend down rubrospinal tract

91. Basal Nuclei background patterns of movement
(walking, running, etc.)
adjust activities of UMN in cortex
normally:
inactive
active
two populations:
ACh stimulatory
GABA inhibitory
inhibited

92. Cerebellum monitors (sensory): proprioception visual
vestibular (balance)
spinocerebellar tract
superior colliculus
vestibular nucleus
output
continually adjusts UMN activity

93. Several conditions ALS cerebral palsy anencephaly
amyotrophic lateral sclerosis
(aka Lou Gerhig’s disease)
degeneration of UMN’s and/or LMN’s
atrophy of muscle
cerebral palsy
affect voluntary muscle performance
trauma, exposure to drugs etc., genetics
cerebrum, cerebellum, basal nuclei, hippocampus, thalamus
abnormal motor skills, posture, speech…
anencephaly
lack of higher brain development

94. 100 Keys (pg. 513)
“Neurons of the primary motor cortex (UMN) innervate motor neurons in the brain and spinal cord (LMN) responsible for stimulating skeletal muscles. Higher centers in the brain can suppress or facilitate reflex responses; reflexes can complement or increase the complexity of voluntary movements”