10/28 - Sensory System- Central Processing

Question 1

DRG NEURON:

Proprioception Peripheral process:

Answer 1

Large diameter, heavily myelinated axons carry information from muscle spindles/joint receptors

Question 2

DRG NEURON:

Touch, Vibration Peripheral process:

Answer 2

Slightly smaller diameter, myelinated axons, carry information from cutaneous receptors

Question 3

Enters through dorsal root and courses directly to posterior column where they ascend to the brainstem forming the fasciculus gracilis or fasciculus cuneatus.

Answer 3

DRG NEURON’s Central process

Question 4

TOUCH Modalities

Answer 4

Low Threshold Cutaneous,
Joint & Muscle Receptors.

Touch, Pressure, Vibration, Fine Form and Texture Discrimination, Form Recognition of 3-dimensional objects (Stereognosis)

Conscious Awareness of Body Position (Proprioception)

Limb Movement In Space (Kinesthesia)

Question 5

Proprioception

Answer 5

Conscious Awareness of Body Position

Question 6

Stereognosis

Answer 6

Form Recognition of 3-dimensional objects

Question 7

Input From Lower Limb & Trunk (T6-S5) Forms the ___ .

Answer 7

Fasciculus Gracilis

Question 8

Input From Upper Limb & Trunk (C1-T5) Forms the ____ .

Answer 8

Fasciculus Cuneatus

Question 9

TOUCH PATHWAY

1ST ORDER NEURON:

Answer 9

DORSAL ROOT GANGLIA CELLS

Primary afferent axons enter via dorsal root to enter ipsilateral posterior column.

Below T5 only fasciculus gracilis.

Above T5, 2 tracts – fasciculus gracilis (FG) and fasciculus cuneatus (FC).

Question 10

TOUCH PATHWAY:

2ND ORDER NEURONS

Answer 10

2ND ORDER NEURONS ARE IN CAUDAL MEDULLA IN N. GRACILIS AND N. CUNEATUS.

Axons arising from neurons in these nuclei CROSS the midline and form the MEDIAL LEMNISCUS.

Question 11

TOUCH PATHWAY:

3RD ORDER NEURON

Answer 11

3RD ORDER NEURON IN THALAMUS (VENTRAL POSTERIOR LATERAL NUCLEUS, VPL).

Axons arising from these neurons project to primary sensory (parietal) cortex

Question 12

1st-order sensation neurons will always be in a ganglion.

Answer 12

EITHER a DRG or TRIGEMINAL Ganglion (or other cranial nerve ganglion).

Question 13

Axons from the MAIN SENSORY NUCLEUS, carrying touch information from the ____, cross the midline and join the ______ in the PONS.

Answer 13

Axons from the MAIN SENSORY NUCLEUS, carrying touch information from the FACE, cross the midline and join the MEDIAL LEMNISCUS in the PONS.

Question 14

Axons from the _____, carrying touch information from the FACE, terminate in the _____.

Answer 14

Axons from the MAIN SENSORY NUCLEUS, carrying touch information from the FACE, terminate in the VPM of the THALAMUS.

Question 15

UNCROSSED TRIGEMINAL AXONS

Answer 15

Small number of axons remain uncrossed as the dorsal trigeminal tract.

These carry information from the inside of the oral cavity and end in VPM.

Their significance is unknown.

Question 16

Do the axons from the spinal trigeminal nucleus (pain and

temparature) join the medial leminiscus?

Answer 16

NO.

Axons from the MAIN SENSORY NUCLEUS, (touch from the FACE) join the MEDIAL LEMNISCUS.

Question 17

What tract is conserned with the Location and Intensity of pain & temperature sensory input

Answer 17

SPINOTHALAMIC TRACT

Question 18

1st ORDER NEURON of the

SPINOTHALAMIC TRACT

Answer 18

DORSAL ROOT GANGLIA CELLS.

Primary afferent axons enter via dorsal root and SYNAPSE
on neurons in the superficial portion of the dorsal horn

Question 19

2nd ORDER NEURON of the

SPINOTHALAMIC TRACT

Answer 19

NEURONS IN DORSAL HORN OF SPINAL CORD AT ALL LEVELS.

Axon CROSSES MIDLINE and forms spinothalamic
(anterolateral) tract in the anterior half white matter of the spinal cord.

Question 20

3rd ORDER NEURON of the

SPINOTHALAMIC TRACT

Answer 20

NEURONS IN THALAMUS VPL (VENTRAL POSTERIOR LATERAL NUCLEUS).

Axons arising from these neurons project to primary
sensory (parietal) cortex and insular cortex.

Question 21

SPINOTHALAMIC TRACT

Answer 21

Carries Discriminative Aspects of Pain/Temperature:

Location & Intensity of sensory input.

Question 22

PAIN PATHWAYS FROM THE FACE:

1st ORDER NEURONS

Answer 22

Axons enter in the pons and descend via the Spinal Trigeminal Tract to the medulla where they synapse on 2nd order neurons in the Spinal Trigeminal Nucleus.

Question 23

PAIN PATHWAYS FROM THE FACE:

2nd ORDER NEURONS

Answer 23

Axons of 2nd order neurons, located in Spinal Nucleus of V,
CROSS the midline and join the Contralateral Spinothalamic Tract as it courses rostrally through the pons and midbrain

Axons from trigeminal nucleus terminate in ventral posterior
medial (VPM) nucleus of the thalamus.

Question 24

Postcentral-Gyrus

Answer 24

= Primary Sensory Cortex

= S1 of the Parietal Lobe

Question 25

More posterior gyri of the Parietal Lobe are involved in what?

Answer 25

sensory association

Question 26

More posterior gyri involved in sensory association areas specialize in what?

Answer 26

spatial orientation and directing attention.

Question 27

On the somatotopic map, sensory input from what body parts are centralized in the deep fissure that separates the 2 hemispheres?

Answer 27

lower extremeties: feet, toes, legs, genitals

Question 28

Moleunculus

Answer 28

The mole sensory cortex maps the area of the appendages very precisely and in such a way that a cross section of that part of the brain looks almost like a 2-dimensional image of the appendages.

Question 29

Information Flow in the Somatosensory Cortex

Answer 29

>>> Brainstem via Ascending pathways (Trigeminal, Medial Lemniscus, Spinothalamic tract, etc.) >>> to VPM/VPL >>>to S1 (primary sensory cortex) or SA (association areas).

Question 30

Area 3: Basics

Answer 30

Obligatory first step in cortical processing of somatosensory information. The primary part of the primary cortex. Intensity, localization....

Question 31

Area 3: 4 Specifics

Answer 31

1. Almost entirely buried in the central sulcus – forms posterior wall of the sulcus. 2. Receives majority of thalamocortical input 3. LOCALIZES sensory input (i.e., area of skin being touched) and INTENSITY of stimulus. 4. Lesions of Area 3 result in profound deficits in all forms of tactile sensations mediated by cutaneous mechanoreceptors

Question 32

Primary Somatosensory Cortex includes what Brodman's Areas?

Answer 32

Areas 1, 2, and 3

Question 33

Area 1

Answer 33

the exposed part of S1 Lesions in Areas 1 result in partial deficits and an inability to use tactile information to discriminate texture.

Question 34

Area 2

Answer 34

buried in postcentral sulcus Lesions in Areas 2 result in partial deficits and an inability to use tactile information to discriminate size & shape of an object.

Question 35

Areas 1 & 2:

Answer 35

1. Receives less input from thalamus and more from Area 3 2. More complex receptive field – responds to Limb Position, or Shape of object touching skin rather than localizing area of skin being touched or intensity of pressure (role of Area 3).

Question 36

SECONDARY SOMATOSENSORY CORTEX

Answer 36

Adjacent to insula in the upper bank of the lateral sulcus. 1. Input from all areas of S1. Little from VPL/VPM of the Thalaumus. 2. Lesions in S1 eliminate responses of neurons in S2. 3. Have bilateral receptive fields 4. Contains pain sensitive neurons. 5. Projects to limbic structures (amygdalya, hippocampus). 6. Plays a role in tactile learning and memory

Question 37

Brodmann’s areas 5 and 7

Answer 37

Brodmann’s areas 5 and 7 are posterior to S1. They make up the bulk of the parietal lobe. 5 & 7 are Somatosensory Association Areas

Question 38

ASSOCIATION AREA OF CORTEX | AREAS 5 AND 7

Answer 38

Higher level integration – combine input from different sensory receptors

Question 39

Lesions of Areas 5,7

Answer 39

produce complex sensory deficits TACTILE AGNOSIA – Cannot identify object based on touch. May sense you are touching it but cannot determine what it is.

Question 40

TACTILE AGNOSIA

Answer 40

Cannot identify object based on touch. May sense you are touching it but cannot determine what it is.

Question 41

PARIETAL NEGLECT SYNDROME

Answer 41

• Failure to recognize side of body contralateral to injury. • Primarily occurs when RIGHT parietal association area is involved. Right Parietal Lesion >>> Deficit is on Left side of the body • May not bathe contralateral side of body or shave contralateral side of face * Deny own limbs * Objects in contralateral visual field ignored

Question 42

APRAXIA

Answer 42

Unable to use sensory information needed to plan movements. Usually occurs with lesions to the right parietal association area. Apparent paralysis although muscles are functional and connections from motor cortex are intact. May not be able to touch their nose when directed, but will scratch their nose if it itches

Question 43

BUCCOFACIAL OR OROFACIAL APRAXIA

Answer 43

Cannot carry out movements of the face on demand, such as licking the lips, sticking out the tongue, or whistling.

Question 44

IDEATIONAL APRAXIA

Answer 44

Cannot carry out learned complex tasks in the proper order, such as putting on socks before putting on shoes.

Question 45

IDEOMOTOR APRAXIA:

Answer 45

Cannot voluntarily perform a learned task when given the necessary objects. For instance, if given a screwdriver, the person may try to write with it as if it were a pen.

Question 46

APRAXIA

Answer 46

The inability to execute a voluntary motor movement despite being able to demonstrate normal muscle function.

Question 47

PATIENT GL

Answer 47

Claimed “loss of tactile sensation but could still sense temperature & pain” Objective testing revealed.... • Could NOT detect vibration on palm or arm • Could NOT detect stroking on palm BUT • COULD detect stroking on arm ``` Stroking arm felt WEAKER than for control subjects and NO discriminations (e.g., direction) could be made ``` BUT the sensation was described as PLEASANT Thus, the DISCRIMINATIVE content of the stroking sensation on arm was DIMINISHED but the emotional impact of the stroking was NOT DIFFERENT compared to control subjects

Question 48

Sensory localization illuminated by patient with specific loss of myelinated Aβ fibers… PATIENT GL

Answer 48

Autoimmune syndrome resulting in loss of large diameter sensory fibers in spinal nerves. Cranial nerves remained intact.

Question 49

There ARE some C fibers with low-threshold touch sensitivity: exclusively in hairy skin

Answer 49

Exclusively located in hairy skin. Slow stroking most effective in activating these cells. This is why Patient GL could feel a little on her arm, nut not in her hand.

Question 50

Brain area activated by low threshold C Fibers.....

Answer 50

(for pain and pleasant sensation of stroking) in Patient GL is Insular cortex but NOT S1 or S2 (Area activated by gentle stroking of forearm)

Question 51

VPM

Answer 51

Face, Trigeminal

Question 52

VPL

Answer 52

Body, Spinothalamic, Touch

Question 53

Anterolateral system:

Answer 53

Discriminative multiple tracts that convey different aspects of pain including location and intensity of painful stimulus, emotional response to pain, autonomic response to pain, increased attention to painful input.

Question 54

Spinothalamic tract:

Answer 54

Discriminative Tract that conveys conscious awareness of nature of a painful stimulus (burning, stinging, aching) and where it is located. Also conveys temperature information. As in the periphery, this information is conducted by small diameter, lightly myelinated axons.

Question 55

Reticular formation throughout brainstem

Answer 55

attention

Question 56

Periaqueductal grey

Answer 56

intrinsic pain control mechanisms

Question 57

Hypothalamus

Answer 57

autonomic response

Question 58

Limbic system

Answer 58

emotion, memory

Question 59

Two distinct aspects of the experience of pain:

Answer 59

Affective | Discriminative

Question 60

Most of these do not reach the level of the cerebral cortex with the exception of one pathway that involves the limbic system and the midline thalamic nuclei.

Answer 60

This pathway is more involved in interpreting “pleasantness” or “unpleasantness” of a painful stimulus rather than recording it’s physiological intensity.

Question 61

Other aspects of pain are mediated by other pathways. These end in:

Answer 61

1. Reticular formation throughout brainstem (attention) 2. Periaqueductal grey (intrinsic pain control mechanisms) 3. Hypothalamus (autonomic response) 4. Limbic system (emotion, memory)

Question 62

INSULAR CORTEX

Answer 62

BURIED DEEP IN THE LATERAL SULCUS. COVERED BY GYRI FROM THE TEMPORAL, PARIETAL AND FRONTAL LOBES. CONTAINS GUSTATORY, AUTONOMIC, PAIN, VESTIBULAR AREAS.

Question 63

Pain information terminates in 2 areas:

Answer 63

Primary somatosensory cortex (SI) and anterior cingulate cortex (ACC). The latter is emotional response (level of “unpleasantness”). Also input to insular cortex (not shown).

Question 64

MODULATION OF PAIN

Answer 64

GATE- CONTROL THEORY: Initial site of modulation is at the level of the spinal cord where there are interactions between nociceptive and non-nociceptive afferents. This controls transmission at site of origin. PREMISE: Dorsal horn neurons in laminas 1 and 5 receive convergent input from both nocicpetive and non-nociceptive afferents (i.e., large myelinated axons from touch receptors). A- beta afferents inhibit dorsal horn neurons by activating inhibitory interneurons. A-delta and C fibers excite dorsal horn neurons and inhibit an inhibitory interneuron through a circuitous pathway involving several other interneurons.

Question 65

MODULATION OF PAIN: GATE-CONTROL THEORY:

Answer 65

Initial site of modulation is at the level of the spinal cord where there are interactions between nociceptive and non-nociceptive afferents. This controls transmission at site of origin.

Question 66

MODULATION OF PAIN PREMISE:

Answer 66

Dorsal horn neurons in laminas 1 and 5 receive convergent input from both nocicpetive and non-nociceptive afferents (i.e., large myelinated axons from touch receptors). A- beta afferents inhibit dorsal horn neurons by activating inhibitory interneurons. A-delta and C fibers excite dorsal horn neurons and inhibit an inhibitory interneuron through a circuitous pathway involving several other interneurons.

Question 67

Gate Theory of Pain Modulation

Answer 67

A-beta fiber and C fiber terminate on the same dorsal horn neuron. C fiber inhibits the interneuron (not directly) and the dorsal horn neuron is activated. A-beta activates an inhibitory interneuron that suppresses the dorsal horn neuron and pain is not transmitted. Think about rubbing a painful site to relieve pain. Basis for use of transcutaneous electrical stimulation (TENS) to relieve pain. Stimulation is in range to activate large diameter processes within painful area.

Question 68

Pain transmission may be modulated by descending afferents including those arising in the:

Answer 68

Periaqueductal Gray | Midline reticular formation

Question 69

Input to ___ from ascending axons in spinothalamic tract.

Answer 69

Input to Periaqueductal Gray from ascending axons in spinothalamic tract.

Question 70

Modulate the Transmission of Information in Pain Pathways.

Answer 70

a. Regulates our ability to focus attention on particular sensory modality such as pain. b. Pathway involves input to PAG from ascending pain pathways. From PAG output is to reticular formation and then to dorsal horn of spinal cord to inhibit pain pathways. c. Opiate receptors are found throughout PAG and raphe nuclei. Activated by drugs such as morphine or endogenous opiates such as enkephalin and dynorphin released from local inhibitory interneurons.

Question 71

Morphine

Answer 71

– opioid derivative | – has been known to have analgesic effects

Question 72

Areas that control pain are excited by exogenous application of opioids.

Answer 72

Neurons in PAG and dorsal horn express opioid receptors.

Question 73

All 3 of the major classes or endogenous opioid peptides are present in the PAG including:

Answer 73

Endorphins Enkephalins Dynorphins

Question 74

CINGULATE AND INSULAR CORTEX

Answer 74

* Cingulate & insular cortex more important for “motivational & emotional” aspects of pain… * Pain has most obvious motivational/emotional impact * BUT so do other somatosensory submodalities, e.g. touch * Touch signals also activate insular cortex

Question 75

Descending systems modulate the transmission of ascending pain signals

Answer 75

Axons from neurons in the PAG synapse on neurons in the lower part of the brainstem, e.g., raphe nuclei which release serotonin. These excite an inhibitory interneuron that contains enkephalin which contacts the terminal of the C-fiber. ENK inhibits release of excitatory transmitter onto dorsal horn projection neuron, blocking further transmission of the pain signal.

Question 76

insular cortex

Answer 76

In each hemisphere of the mammalian brain the insular cortex (also called insula, insulary cortex, or insular lobe) is a portion of the cerebral cortex folded deep within the lateral sulcus (the fissure separating the temporal lobe from the parietal and frontal lobes). The insula is another region of the brain that remained little understood for a long time because of its position deep in the folds of the cortex. Also, because it was not associated with the “higher” brain functions, it was of less interest to scientists who were investigating consciousness.