Somatosensory System (7) EXAM 2 Material Flashcards by Colleen Patterson

Sensory information from the skin and musculoskeletal systems

Somatosensation

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What type of sensory info do we get from the skin? (Called superficial, cutaneous or exteroceptive)

Pain, touch, temperature

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What type of sensory info do we get from the musculoskeletal system?

Pain, Proprioception

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Proprioception

Provides information regarding stretch of muscles, tension on tendons, position of joints and deep vibration.

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What does the speed of processing information depend on?

Diameter of axons, degree of myelination and number of synapses in the pathway.

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Functions of receptors in PNS::

Transduction of stimulus into an electrical signal (so brain can process the information)

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Where are the somatosensory receptors?

At the distal end of peripheral neurons

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What type of somatosensory receptor continues to fire during entire presentation of the stimulus?

Slow adapting / tonic

ex: Yoga - stretching

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What type of somatosensory receptor adapts quickly to stimulus and stops responding?

Fast adapting / Phasic

ex: Wearing a watch, we don’t notice it unless attention is called to it

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Receptor Density

Number of receptors within a given area of body surface

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Area of skin innervated by a single afferent neuron is called what?

Receptive field

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Large receptive fields of somatosensors:

Borders are difficult to define; often cover a large area (ex: Back, stomach)

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Small receptive fields of somatosensors:

Borders are sharply defined; cover small area

ex: Pads of fingers

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Do distal or proximal regions tend to have greater density of receptors. Also, smaller or larger receptive fields?

Distal regions have GREATER density of receptors than proximal regions and smaller receptive fields.

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Mechanoreceptors

Touch

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Which kind of receptor responds to mechanical deformation of receptor?

Mechanoreceptor

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Which kind of receptor deals with body part position and movement?

Proprioceptors

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Thermoreceptors

Temperature:

Responds to heat or cooling

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Chemoreceptors

Chemicals:

Responds to substances released by cells

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Nocioceptors

Pain:
Sensitive to stimuli that damage or can damage
(Subclass of other types of receptors)

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What are the three prime components of somatosensory pathways?

Receptors, Sensory Pathways, Brain Centers

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Which pathway distinguishes info about location and type of stimulation to cortex? (Temperature, texture, detail)

Conscious relay pathway

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Divergent Pathway

Transmit info to many areas of the brainstem and cerebrum

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Unconscious pathway

Brings unconscious proprioceptive and other movement-related information to cerebellum.
(Ex: Walking on something bumpy)

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Which type of neurons are counted in the somatosensory pathway?

Only projection neurons are counted (the long ones)

Are interneurons counted in the somatosensory pathway?

What is the pathway usually named after?

Often the origin and termination of the tract that contains the second neuron in the system

Primary somatosensory cortex =

Post-central gyrus

What sensory info does the post-central gyrus discern?

Touch, size, texture and shape of objects

What type of representation does the post-central gyrus use?

Somatotopic: Homunculus (Body on brain)

Most lateral on the primary somatosensory cortex?

Face

Most Medial on primary somatosensory cortex?

In middle area on primary somatosensory cortex?

Primary afferent fiber classification:

Afferent

Classification of conduction velocity of afferent fibers?

A, B, C (A is fastest, C is slowest)

Classification of diameter of afferent fibers?

I - IV (I is fastest, IV is slowest)

T or F, first order neurons are pseudounipolar?

True, they DONT receive info from other neurons

Sensory root that enters into the SC in the dorsal horn

Dorsal root

What type of matter is the dorsal horn?

Gray matter

What type of matter is the dorsal column?

White matter

The area of skin innervated by axons from cell bodies in a single dorsal root?

Dermatomes: | These are overlapping (allows room for injury)

Function of Dorsal Column-Medial Lemniscal Tract (DCML)

1. Discriminative Touch - ability to discriminate b/w two closely spaced points touching the skin. 2. Vibration 3. Conscious Proprioception - awareness of movements and relative position of body parts.

Receptor types in DCML

Mechanoreceptors and Proprioceptors, NO nocioceptors

Where does the 1st order neuron (DCML) convey info from and to?

Conveys info from receptor on skin to the medulla

Where are the cell bodies of the 1st order neuron (DCML)

Dorsal Root Ganglia

Is the diameter of the 1st order neuron (DCML) large or small??

Large

1st order neuron of DCML: Ipsilateral or contralateral projection into dorsal column?

Ipsilateral projection into dorsal column

Fasciculus Cuneatus

Axons from upper limbs - more lateral

Fasciculus Gracilis

Axons from lower limbs - more medial

Where does the 1st order neuron of DCML synapse?

Nucleus cuneatus or nucleus gracilis

Where does the 2nd order neuron of DCML convey info from and to?

Conveys info from Medulla to Thalamus

Where are the cell bodies of the 2nd order neuron of DCML?

Nucleus gracilis or cuneatus

Where does the decussation of the DCML occur? Is it 1st, 2nd or 3rd order neuron that does this?

At the level of the medulla | 2nd order

What does the 2nd order neuron (DCML) ascend as?

The medial lemniscus

Where does the 2nd order neuron (DCML) project to/decussate to?

VPL (Ventral Posterolateral Nucleus) of the thalamus

Where does the 3rd order neuron (DCML) convey info from and to?

Conveys info from VPN of Thalamus to the cortex

Where are the cell bodies of the 3rd order neuron (DCML) located?

VPL of thalamus

Where does the 3rd order neuron (DCML) project to/decussate to?

Projects through internal capsule to primary somatosensory cortex

DCML mnemonic

De Cussates (in the) Medu Lla

Anterolateral System: Spinothalamic Tract (STT) Functions

1. Discriminate (fast) pain 2. Discriminate temperature 3. Coarse touch (skin to skin touch)

Types of receptors in STT tract?

Nocioceptors (Mechanoreceptors, Thermoreceptors)

Where does the 1st order neuron of the STT convey info to/from?

Conveys info from skin receptor to dorsal horn

Where are the cell bodies of the 1st order neuron (STT)?

Dorsal root ganglion

What does the Tract of Lisseauer do? what Tract is it in?

It conveys info up or down 1-2 levels (protective) | It's in the Spinothalamic Tract (STT)

Where does the 1st order neuron of the STT synapse?

Ipsilateral dorsal horn

Where does the 2nd order neuron of the STT convey info to and from?

Conveys info from dorsal horn to thalamus

Where are the cell bodies of the 2nd order neuron (STT) located?

Ipsilateral dorsal horn

When does the STT tract decussate?

During the 2nd order neuron

Where does the 2nd order neuron (STT) decussate to?

The anterolateral white matter of the SC

Where does the 2nd order neuron (STT) ascend and where does it ascend to?

Ascends in the anterolateral white matter tract area. | Ascends to VPL of Thalamus

Where does the 3rd order neuron (STT) convey info from and to?

Conveys info from Thalamus to Cortex

Where are the cell bodies of the 3rd order neuron (STT) located?

In the VPL of the Thalamus

Where does the 3rd order neuron (STT) project through?

Projects through Internal capsule to primary somatosensory cortex

What information does the Trigeminal Thalamic Tract sense?

Fast pain, discriminative touch, temperature information from the face

Divergent Anterolateral Tracts: How is the info from these pathways NOT organized?

The information from these pathways are not somatotopically organized

Divergent Anterolateral Tracts:

1. Spinomesencephalic Tract 2. Spinoreticular Tract 3. Spinolimbic Tract

Activity in divergent anterolateral tracts results in what?

Looking at cause of pain, arousal, withdrawal, autonomic and affective responses to pain (non discriminative)

Which divergent anterolateral tract is involved in turning the head and eyes toward the noxious input?

Spinomesencephalic Tract

Which divergent anterolateral tract is involved in pain stimuli commanding attention and interfering with sleep?

Spinoreticular Tract

Which divergent anterolateral tract is involved in emotions, personality, movement, etc?

Spinolimbic Tract

What are the unconscious relay tract to cerebellum called?

Spinocerebellar Tracts

What information do the spinocerebellar tracts transmit?

Information from proprioceptors transmitted to cerebellum

What are the spinocerebellar tracts critical for?

Unconscious adjustments to movement and posture.

Neuropathy Compression (Class I)

Large, myelinated fibers affected first | Tingling or prickling occurs as the blood supply increases once compression relieved.

Neuropathy Complete Severance (Class II)

Lack of sensation in the distribution of nerve | Pain may occur

Ataxia

Incoordination that is not due to weakness

Sensory Ataxia

Lesion in peripheral sensory nerve, dorsal root or column of spinal cord, or medial lemnisci

Sensory Ataxia problems

Balance, incoordination, impaired conscious proprioception and vibration

Complete SCI (spinal cord lesion)

Loss of sensation one or two levels BELOW the level of the lesion (and all the way down)

Brown-Sequard Syndrome

Incomplete SC lesion - "hemisection" (damage to left OR right half) of the SC.

Results of Brown-Sequard Syndrome: Contralateral

Interruption of pain and temperature sensation CONTRALATERAL to the lesion (and below)

Results of Brown-Sequard Syndrome: Ipsilateral

1. Lack of discriminative touch and conscious proprioception IPSILATERAL to lesion (and below) 2. IPSILATERAL paralysis

Brain Stem Lesions

Only in the upper midbrain is all loss contralateral (because all sensation tracts have crossed).

Thalamic Lesions

Everything has deccesated so there is a decreased or loss of sensation on CONTRALATERAL body or face

Somatosensory cortex or internal capsule lesions

CONTRALATERAL decrease or loss of discriminative sensations

Tactile Defensiveness

Aversive response to seemingly non-noxious tactile stimuli

How does tactile defensiveness manifest itself in observable behaviors?

Overreaction to touch --> tantrums, avoiding touch of both people and objects.

What is tactile defensiveness hypothesized to be due to lack of?

Lack of inhibition