dcml

1. Somatic
sensations and
mechanical
receptors

2. • Classify somatic sensations
• Classify mechanical receptors

3. Classification of Sensations
 The somatic senses are the nervous mechanisms that collect
sensory information from all over the body.
 Special senses, which mean specifically vision, hearing, smell, taste,
and equilibrium.

4. CLASSIFICATION OF
SOMATIC SENSES
 The mechanoreceptive somatic senses, which
include both tactile and position sensations.
 The thermoreceptive senses, which detect heat
and cold
 The pain sense, which is activated by any factor
that damages the tissues.

5. Mechanoreceptive somatic senses
 The tactile senses include touch, pressure, vibration, and tickle
 the position senses include static position and rate of movement

6. Detection and Transmission of
Tactile Sensations
 Touch, pressure, and vibration are all detected by the
same types of receptors called tactile receptors.
 There are at least six entirely different
types of tactile receptors

7. Free nerve endings
 Free nerve endings, which
are found everywhere in
the skin and in many other
tissues, can
 detect touch and pressure

8. Meissner’s corpuscle
 Elongated encapsulated
nerve ending of a large
(type AB) myelinated nerve
fiber.
 Inside the capsulation are
many branching terminal
nerve filaments.
 These corpuscles are
present in the non hairy
parts of the skin .
 Meissner’s corpuscles adapt
in a fraction of a second
after they are stimulated,
 Detect low frequency
vibration.

9. Merkel’s discs
 The hairy parts and non
hairy part of the skin also
contain moderate
numbers of expanded tip
receptors
 they transmit an initially
strong but partially
adapting signal and then a
continuing weaker signal
 adapts only slowly.
 Therefore, they are
responsible for giving
steady-state signals

10. Iggo dome receptor
 Merkel’s discs are often
grouped together in a
receptor organ called the
Iggo dome receptor, which
projects upward against
the underside of the
epithelium of the skin

11. Hair end-organ
 This receptor adapts
readily and, like Meissner’s
corpuscles, detects mainly
 (a)movement of objects
on the surface of the body
or
 (b)initial contact with the
body.

12. Ruffini’s end-organs
 multibranched,
encapsulated endings,
 These endings adapt very
slowly
 They are also found in
joint capsules and help to
signal the degree of joint
rotation
 Found in skin and deeper
tissues

13. Pacinian corpuscles
 Lie both immediately
beneath the skin and deep
in the fascial tissues of the
body.
 They are stimulated only by
rapid local compression of
the tissues because they
adapt in a few hundredths
of a second.
 Important for detecting
tissue vibration or other
rapid changes in the
mechanical state of the
tissues.

14. Transmission of Tactile Signals in
Peripheral Nerve Fibers
 Transmit their signals in type A-beta nerve fibers that
have transmission velocities ranging from 30 to 70
m/sec.
 free nerve ending tactile receptors transmit signals
mainly by way of the small type A-delta myelinated
fibers that conduct at velocities of only 5 to 30 m/sec.
 Some tactile free nerve endings transmit by way of
type C unmyelinated fibers (up to 2 m/sec;) these
send signals into the spinal cord and lower brain
stem, mainly the sensation of tickle.

15. Detection of Vibration
 Pacinian corpuscles can detect signal vibrations from
30 to 800 cycles per second and they also transmit
their signals over type A-beta nerve fibers.
 Meissner’s corpuscles detect vibrations from 2 to 80
cycles per seconds

16. TICKLE AND ITCH
 rapidly adapting mechanoreceptive free nerve
endings elicit only the tickle and itch sensations.
 These sensations are transmitted by very small type C,
unmyelinated fibers similar to those that transmit the
aching, slow type of pain.

17.  Receptors afferents dorsal root
ganglia gray column ascending tracts
thalamus sensory cortex

21.  Dorsal Column–Medial Lemniscal
System
 1. Touch sensations requiring a
high degree of localization of the
stimulus
 2. Touch sensations requiring
transmission of fine gradations of
intensity
 3. Phasic sensations, such as
vibratory sensations
 4. Sensations that signal
movement against the skin
 5. Position sensations from the
joints
 6. Pressure sensations having to
do with fine degrees of judgment
of pressure intensity
 Anterolateral System
 1. Pain
 2. Thermal sensations, including
both warmth and cold sensations
 3. Crude touch and pressure
sensations capable only of crude
localizing ability on the surface of
the body
 4. Tickle and itch sensations
 5. Sexual sensations

27. OBJECTIVES:
 Understand Structure of spinal cord and thalamus
 Understand the structure of sensory cortex and
clinical application when sensory cortex is not
working

28. Functional anatomy of spinal cord

36. OBJECTIVES
 Understand the structure of sensory cortex and
clinical application when sensory cortex is not
working
 Understand the pathway of two main Ascending
pathways

39. Molecular layer
External granular layer
External pyramidal layer
Internal granular layer
Internal pyramidal layer
Polymorphic layer

40. Functions of Somatosensory
Area I
 Localize and discriminate
discretely the different
sensations in the different
parts of the body
 judge critical degrees of
pressure against the body
 judge the texture, weights,
shapes or forms of objects by
touch. This is called
stereognosis.
 Judge the shape by drawing.
Bilateral excision of
somatosensory area
Pt is unable to
 Localize and discriminate
discretely the different
sensations in the different parts
of the body
 judge critical degrees of
pressure against the body
 judge the texture, weights,
shapes or forms of objects. This
is called astereognosis.
 Judge the shape by drawing.
Agraphaesthesia

41. Effect of Removing the Somatosensory Association Area—(5,7)
Amorphosynthesis
 The person loses ability to recognize complex
objects and complex forms felt on the opposite
side of the body.
 He or she loses most of the sense of form of his
or her own body parts on the opposite side
forgets that it is there .
 When feeling objects, the person tends to
recognize only one side of the object and
that the other side even exists.

42. Ascending tracts
1. Dorsal column medial-
leminiscal system
2. Anterolateral tract
3. Anterior and posterior
spinocerebellar
4. Cuneocerebellar
5. Olivocerebellar
6. Spinotectal
7. Spinoreticular
8. Visceral afferents

43.  Dorsal Column–Medial
Lemniscal System
 Touch sensations requiring a high
degree of localization and
discrimination of the stimulus
 Phasic sensations, such as
vibratory sensations
 Sensations that signal movement
against the skin
 Position sensations from the joints
 Pressure sensations having to do
with fine degrees of judgment of
pressure intensity
 Anterolateral System
 Pain
 Thermal sensations, including
both warmth and cold sensations
 Crude touch and pressure
sensations capable only of crude
localizing ability on the surface of
the body
 Tickle and itch sensations
 Sexual sensations

45. Transmission in the Dorsal Column–
Medial
Lemniscal System
 Anatomy of the Dorsal Column–Medial Lemniscal
System
 nerve fibers entering the dorsal columns pass
uninterrupted up to the dorsal medulla, where they
synapse in the dorsal column nuclei (the cuneate and
gracile nuclei).

47. SPINOTHALAMIC TRACT

50. Lesions of Dorsal Column Tract
 Sensory ataxia
 Loss of vibration
 Loss of tactile discrimination
 Loss of tactile localization

51.  Dorsal Column–Medial Lemniscal
System
 Touch sensations requiring a high
degree of localization of the
stimulus
 Touch sensations requiring
transmission of fine gradations of
intensity
 Phasic sensations, such as
vibratory sensations
 Sensations that signal movement
against the skin
 Position sensations from the
joints
 Pressure sensations having to do
with fine degrees of judgment of
pressure intensity
 Anterolateral System
 Pain
 Thermal sensations, including
both warmth and
cold sensations
 Crude touch and pressure
sensations capable only of crude
localizing ability on the surface of
the body
 Tickle and itch sensations
 Sexual sensations

52. Organization in dorsal column and anterolateral
pathways
Dorsal column system
 Composed of
large,myelinated nerve
fibers that transmit signals
to the brain at velocities of
30 to 110 m/sec,
 high degree of spatial
orientation of the nerve
fibers with respect to their
origin
 Fine gradation of intensity
 Termination VPL & SC
Anterolateral Pathway
 The velocities of transmission
are only one third to one half
those in the dorsal column–
medial lemniscal system,
ranging between 8 and 40
m/sec;
 The degree of spatial
localization of signals is poor;
 The gradations of intensities are
also far less accurate
 Termination in RN, ILN, VPL, SC

53.  Anterior and posterior spinocerebellar
 Cuneocerebellar
 Olivocerebellar
 Spinotectal
 Spinoreticular
 Visceral afferents

54. Judgment of Stimulus
Intensity
 Spatial & temporal summation
 Lateral inhibition increases contrast

55. Judgment of Stimulus
Intensity by sensory cortex
 Weber-Fechner Principle
Interpreted signal strength = Log (stimulus) +
constant
 Power Law
Interpreted signal strength = K (stimulus-k)y

60.  Position sense
1. Static
2. Rate of movement called kinesthesia
 Receptors
1. Muscle spindles
2. Golgi tendon organs
3. Ruffni’s endings
4. Pacinian

61.  Texture meissner & merkel
 Localization meissner & merkel
 Discrimination meissner
 Vibration meissner & pacinian
 Prolonged touch merkel’s
 Prolonged deep touch & pressure ruffni’s

62.  Dermatome
Segment of skin supplied by the spinal nerve