Topic 4 - Sensory Systems

Part 1 - Visual, Part 2 - vestibular, Part 3 - Somatosensory [touch, pain, temp, proprioception]e

What are Ruffini Endings?

They are Large receptors in dermis layer

What do Ruffini Endings do?

Detect stretch and deformation

How big is Ruffini Endings receptive field

Large receptive field

Are Ruffini Endings Slow adapting?

YES

* react to sustained deformations

What are Merkel's Disks

Small receptors in epidermis, common in fingers

What do Merkel disk do?

Detect fine touch and pressure

How big are Merkel disk receptive field?

Small receptive field

Are Merkel disk slow adapting?

YES

* react to sustained deformations

What is Two-Point Discrimination?

Sensitivity to discriminate small points varies greatly across the body
it is more sensitive in important places

Can't distinguish two separate points when they are very close together, feels like one point

How is Two-Point Discrimination Accomplished?

- Greater density of mechanoreceptors
- Smaller field size (Meissner corpuscles + Merkels disks)
- Greater brain tissue devoted to these areas

What are Primary Afferent Axons?

Enter spinal cord at DORSAL root

Cell bodies lie in DORSAL root ganglion --> Pseudo-unipolar neruons

What are the four types of Primary Afferent Axons?

A-alpha [Proprioceptors]
A-beta [touch/mechanoreceptors]
A-delta [pain, temp]
C axons [temp, pain]

What are the various sizes of Primary Afferent Axons?

All A's are myelinated
- larger + myelination = faster

C's are NOT myelinated
- smaller and slower

What are the two A-Beta branches?

Directly ASCENDING the spinal cord to brain

SYNAPSES with second-order sensory neuron (for reflexes)

What is the Dorsal Column-Medial Lemniscal Pathway (DCML) pathway?

1. Ascending branch goes up the dorsal column

2. Synapse on the dorsal column nuclei in the medulla

3. Dorsal column nuclei axons decussate and ascend the medial lemniscus

4. Synapse in the VP nucleus of the thalamus

5. Neurons in the VP nucleus project to somatosensory cortex

What type of information does the DCML pathway send?

Touch Information

How many neuron pathways and synapses points does the DCML have to reach S1?

3 neuron pathways
- 1st order, 2nd order, 3rd order

3 synapse points
- first to second, second to third, third to cortex

What is a Herniated Disc?

A slipped, ruptured, bulging disc
can compress a nerve root

What are the Symptoms of Herniated Disc?

Pain - Back and Leg
Numbness or tingling
Weakness

What is the treatment for Herniated Disc?

Rest, physical therapy, pain meds

Surgical - Discectomy/Microdiscectomy

What is Lateral Inhibition?

^^Inhibit adjacent inputs to enhance tactile sensitivity^^

Increases contrast to __**allow for more precise/finer location of sensations**__

* minimize the firing rate of sensory information close to it but maximize the information that is precisely where is it happening

What is Sensory Gating?

It is ^^**Corticothalamic Feedback**^^ influences sensory processing

* cortex to thalamus

Cortex helps to filter irrelevant or repetitive information

__"feel what you want to feel"__

what is the Primary Somatosensory Cortex [3b]

Receives inputs from VP Nucleus

Highly responsive to somatosensory input

Damage impairs sensations

Electrical stimulus creates sensations

What is the Somatosensory 3a?

Dense thalamus input, but more body position

What is Somatosensory 1 & 2 ?

Receives infor from 3b
- trying to integrate things together

Generally related to texture, size, and shape
- starting to combine

What is Posterior Parietal Cortex?

Allows for processing of basic sensory information and integration with other senses

What is the Posterior Parietal Cortex Area 5?

Sensory integration with planing and organizing of movement

what is the Posterior Parietal Cortex Area 7?

Sensory information for object recognition and spatial relationships

What is a Nociceptor?

A receptor of painful stimulus

What are Nociceptor activated by?

Activated by stimulus that may damage tissue
- strong mechanical stimulus, temp extremes, oxygen deprivation, chemicals: even substance released by damaged cells [lactic acid, histamine, etc]

Does Nociception mean Pain?

NO

Nociception --> sensory process that provides the signals that MAY trigger pain

Pain -> sore, aching, throbbing sensations we "feel"

they can exist without each other

What are the types of Nociceptors?

Mechanical Nociceptors
Thermal Nociceptor
Chemical Nociceptor
Polymodal Nociceptor

What are Mechanical Nociceptors?

Respond to damage such as cutting, crushing, or pinching

What are Thermal Nociceptors?

Respond to extreme temperatures

What are Chemical Nociceptors?

Respond to histamine and other chemicals

What are Polymodal Nociceptors?

Respond to equally to all kinds of damaging stimuli

Characteristics of the Fast pain?

(nociceptor, fiber, pain, localization, tming)

Nociceptor --> Mechanical and Thermal
Fiber --> Myelinated A-delta fibers
Pain --> Sharp, prickling sensations
Localization --> Easily localized
Timing --> Fast, occurs first

Characteristics of Slow pain?

(nociceptor, fiber, pain, localization, tming)

Nociceptor --> Polymodal
Fiber --> unmyelinated C fibers
Pain --> dull, aching, burning sensations
Localization --> poorly localized
Timing --> slow, occurs second and for longer time

What information does the Spinothalamic tract carry to the brain?

Carries **nociceptive information** to the brain

Where are the Spinothalamic tract cell bodies located and where do axons enter?

Cell bodies located in dorsal root ganglion

Axons enter dorsal horn of spinal cord

what is the Spinothalamic tract pathway?

1. Enter zone of Lissauer [ascend or descend slightly]
- travels up a bit then enters spinal cord; does not instantly synapse

2. Synpase in the substantia gelatinosa [in dorsal horn]

3. Second order neurons in the spinal cord immediately decussate

4. ascend to the brain in the ventrolateral lateral surface of spinal cord

5. synapse with VP nucleus in thalamus

6. information projected to somatosensory cortex

What is Afferent Pain Regulation?

Pain being reduced by the activity of mechanoreceptors
- mechanical information coming in can over ride pain information

What is gate control theory of pain?

Neurons in the spinothalamic tract may be inhibited by A-alpha or A-beta sensory nerves (touch) in the dorsal horn of the spinal cord

What is decending regulation of pain?

Brain can do powerful things when it comes to controlling pain (strong emotion, stress etc.)
- brain is trying to minimize pain
- could be to major stress response

What is the Periaqueductal Gray Matter (PAG) Pathway?

1. Receives input from many areas in the cortex (often emotional)
2. Neurons descend to medulla (raphe nuclei)
3. Neurons descend to spinal cord to depress activity

** sends information down to spinal cord and synapses in dorsal horn**

What is Hyperalgesia?

Reduction in the Pain threshold, increases sensitivity or spontaneous pain

What is Primary Hyperalgesia?

super-sensitivity within the damaged area

what is secondary Hyperalgesia?

super-sensitivity in the surrounding area

What is the primary change that occurs peripherally in Hyperalgesia?

Inflammation
- bodies attempt to eliminate injury and stimulate healing

A variety of neurotransmitters, peptides, lipids, etc, are released which can attach to receptors in/around injury to lower their threshold for activation

How is Allodyina different from Hyperalgesia?

Alloydina is similar BUT pain response from stimuli that would normally NOT cause pain

What is Central Sensitization?

Amplification of neural signalling (e.g. nociceptive info) within the CNS that elicits pain hypersensitivity or even normal stimuli (allodyina)

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**using pathways over and over causes them to become hypersensitive (chronic injuries/pain)**

What is Referred Pain ?

^^**Cross-talk**^^ between sensory neurons

* convergence of visceral and somatic afferent neurons

ex. heart attack --> feel in left arm

What are Thermoreceptors?

Varying sensitivities to hot and cold temps
- Hot temps = C Fibers
- Cold temps = A-delta + C fibers

Adapt to long durations of stimuli

Follow same pathways as Pain

What is Proprioception?

Our perception of the location and movement of our body
Allows us to control limb and joint position for optimal movement

Group 1 Neruons (from muscle) myelinated fibers

What are the two primary receptors for Proprioception?

Muscle spindle --> amount of stretch in a muscle

Golgi tendon organ --> amount of force

What is Conscious Proprioceptive information pathway?

Dorsal Column medial lemniscus pathway (DCML)

What is Unconscious Proprioceptive information pathway ?

Spinocerebellar tracts --> to cerebellum

Spinal interneurons --> Spinal reflexes

Where is the Primary visual cortex located?

Broadman’s area 17

Occipital lobe → posterior parietal lobe

What is the Primary visual cortex?

first area of the cortex to receive visual information

What are the two main pathways of the primary visual cortex?

Dorsal stream + ventral stream

What is the Dorsal stream?

* object recognition W/ TOUCH
* Processing visual motion

What type of visual motion does the Dorsal stream process?

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* Navigation
* perceiving the direction and speed of objects


* Directing eye movement
* sense motion and quickly react
* motion perception
* interpretation of moving objects

What is the ventral stream?

Information passed toward the temporal lobe

Processing of vision other than motion

Relating more to object preception W/ VISION --> identifying objects

What type of vision other than motion does the ventral stream process?

* Object perception + facial recognition
* not only recognize features but remember faces

What is the Vestibular System?

* Balance, equilibrium, posture
* Based on motion of hair cells
* Humans = Vestibular Labyrinth

What are the parts of the vestibular system?

* Otolith organs ---> acceleration and tilt
* Semicircular Canals ---> head rotation
* Use hair cells to detect changes

What do the Otolith organs measure?

Measures Acceleration and Tilt --> depend on direction they deflect

Parts of the otolith organs?

* Macula --> epithelium-filled pouch w/ hair cells
* Kinocilium --> tallest, most important cilia
* measures things in respect to how far
* Otoconia (ear stones) --> calcium carbonate crystals
* provide weight on top
* squish fluid as moves around

What is the Macular Orientation?

__**Array of hair cell orientation**__ within Otolith organs

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Allows __**measures of all possible linear movements**__

* measure tilt in all directions

What are the types of Macular Orientation?

* Saccular macula --> vertically oriented
* Utricular macula --> horizontally oriented

What do the semicircular canal measure?

__**Measures head rotation**__ → angular acceleration

* three canals on each side → help sense all possible head rotation

Principle of inertia

Push-Pull activation of vestibular axons

prolonged dizziness will keep fluid in motion \[dizziness --> opposite direction\]

What are the parts of the semicircular canals?

* Crista ampullaris -->
* cupula \[bubble\] fill of cilia found within an ampulla \[bulge\]

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* Endolymph
* reacts slowly to quick rotations which deflect the cupula + cilia
* as rotation occurs fluid will remain where it is or start moving crista in one direction

What is the Central Vestibular Pathway?

\*\*Pathway of vestibular information and reflexes to control head, body, eye movement


1. Otolith organs + semocicular canals
2. Vestibulochochlear nerve \[VIII\] --> vestibular + cochlear nerve

* biopolar neurons


3. vestibular nuclei

* dorsolateral regions of medulla
* integrate with other information \[visual/motor\]


4. Send out information above and below

* cerebellum, VP of thalamus, extraocular motor neurons, limbs, neck, trunk

Where does the Central Vestibular Pathways Sends info out to...

* cerebellum
* thalamus \[VP Nucleus\]
* Extraocular motor neurons
* Limbs
* Neck and Trunk

The Cerebellum receives what type of information from the Central Vestibular Pathway?

Vestibular sensations needed for FINE MOVEMENTS, coordinating movement patterns

The Thalamus receives what type of information from the Central Vestibular Pathway?

* projects to post-central gyrus
* info received by the cortex maintains a representation of the body in space

The Extraculor motor neurons receives what type of information from the Central Vestibular Pathway?

* Reflexive eye movements
* Primary goal --> maintain gaze \[eye needs to know how head is moving so keep tract at what we are looking at\]

The Limbs receives what type of information from the Central Vestibular Pathway?

* reflective limbs movements
* primary goal --> keep body upright

The Neck & Trunk receives what type of information from the Central Vestibular Pathway?

* reflexive neck/trunk movements
* primary goal --> keep head upright

What is the function of the Vestibulo-Ocular reflex (VOR)

to fixate line of sight on visual target during head movement

What is the mechanism of the Vestibulo-Ocular reflex (VOR)

senses rotation of head, commands compensatory movement of eyes in opposite direction

Vestibular Connections - horizontal eye movements

* head rotate to left, eye rotate to right
* one semicircular canal will increase FR and one will decrease FR
* key is push and pull --> one inhibits, one excites
* job is to control extra ocular muscles
* eyes moving to right = muscles on right side of eyes need to contract, inhibit muscles on the left side
* Semicircular canals change FR to control ocular muscles
* Excitation and Inhibition cross over

What are the Vestibular Changes in the __**Otolith organs**__ with Age

* loss of cilia --> sensations and organs not as efficient
* alterations in otoconia (size and shape) --> crystal carbonate breakdown \[stone crumble\]

What are the Vestibular Changes in the __**Semicircular canals**__ with Age

* loss of cilia, to a greater extent than otolith organs
* greater impact in VOR

What are the Vestibular Changes in the __**Central changes**__ with Age

occurs around 60 years age

* vestibular nuclei --> slow loss of neurons
* Cerebellum --> slow loss or change in connectivity

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Overall leads to a reduction in sensory info for controlling head, eyes, body and balance = increased fall risk

What is Benign Paroxysmal Positional Vertigo \[BPPV\]

* Benign = Harmless in long term
* Paroxysmal = sudden onset/recurrence of symptoms (

Causes of Benign Paroxysmal Positional Vertigo \[BPPV\]

* otoconia (ear stones) migrating into semicircular canals \[displaces in organs\]
* disrupting the cupula located in ampulla

Treatment of Benign Paroxysmal Positional Vertigo \[BPPV\]

* often resolves on own
* specific head manoeuvers can repositon debris out

Causes of Vestibular Neuronitis?

inflammation of vestibular nerve

Symptoms of Vestibular Neuronitis?

* vertigo for several days
* does NOT affect hearing

Treatment of Vestibular Neuronitis?

* anti-nausea medication until inflammation reduces
* steroids to reduce inflammation
* physical therapy/activity can help the body compensate

Cause of Labyrinthitis?

* inflammation of entire inner ear due to infection

Symptoms of Labyrinthitis

* vertigo last for several days
* DOES affect hearing

Treatment of Labyrinthitis

* treat infection
* anti-nausea medication until inflammation reduces
* physical therapy/activity can help body compensate

Cause of Meniere's Disease

* excessive fluid up in inner ear

Symptoms of Meniere's Disease

* sudden episodes of --> tinnitus, hearing loss, vertigo
* each episode can last minutes to hours
* may occur in clusters, then subside for years

Treatment of Meniere's Disease

* no cure --> mange symptoms
* can lead to permanent hearing loss but rare

What are Mechanoreceptors in Skin?

Somatosensory receptor

* Receptive to physical distortion

What are the 4 primary Mechanoreceptors in Skin

* Pacinian Corpuscles
* Mesissner's Corpuscles
* Ruffini endings
* Merkels Disk

What do Mechanoreceptors vary by?

* Receptive field (large vs small)
* Adaptation (rapid vs slow)