People are staring. Quick, cover your parietal!
The parietal lobe is a multi-fuction region at the top-back of the head. It processes pain, temperature and pressure information. It processes visual information it receives from the occipital lobe (the dorsal stream). And it provides a 3-D view of your environment.
Visual information from the occipital lobe helps you know where things are and how to reach them. Data from occipiatal lobe is compared to data obtained directly from the optic chiasm and superior colliculus. You get fast response to moving objects and a clear, if slower, understanding of where everything is.
Temperature and pain information is routed to the parietal lobe but it is less clear how this information is organized and processed. Touch information is clearly mapped but pain isn’t. Pain also invloves the frontal lobe for determining context and significance.
NOTES
Parietal Lobe
- Mechanical Senses
- Vestibular sensations (inner ear)
- Tactile Sensations
- Itch, touch, pressure, pain
- 1. Vestibular sensations
- Measures
- Position-movement of head
- Pressure, bending
- Spatial orientation
- Balance
- Signals come from:
- Semicircular canals
- Neck muscle “stretch” receptors
- Utricle (gravity)
- Sends signals to
- control eye movement
- keep you upright
- Labyrinth of inner ear
- Two major components
- Semicircular canal system
- rotational movements
- Otoliths
- linear accelerations
- Semi-Circular Canals
- Responsive to acceleration
- Detects rotational movements
- Detect head rotation
- fluid pushes hair cells
- 3D Structure
- Orthogonal
- Lateral (horizontal) = pirouette
- Superior (anterior) = head-heel
- Inferior (posterior) = cartwheel
- Push-pull system
- Sense all directions of rotation
- Three pairs work together
- 3 on left side & 3 on right side
- push-pull fashion
- Otolith Organs
- Linear accelerations
- Two on each side
- Utricle
- Saccule
- Utricular signals = eye move
- Saccular signals = posture
- Contain otoconia crystal
- Heavier than its gel layer
- Displaced during linear acceleration
- Deflects ciliary bundles
- Vestibular system projects to cerebellum
- Cerebellum to eye muscles, etc
- Also to thalamus & eyes
- Projects to spinal cord
- reflex reactions of limbs and trunk
- regain balance
- Sensations
- Vertigo
- Dizziness
- Whirling or spinning
- Feeling of motion when stationary
- Nausea and vomiting
- Trouble walking
- Three sensations
- Objective = world moving
- Subjective = you’re moving
- Pseudovertigo = rotation
- Common complaints
- 20%-30% of population
- Patients of all ages
- More common as get older
- 1. Peripheral Vertigo
- Most common cause
- Cold or flu
- Chemicals
- Head trauma
- Motion sickness
- 2. Central Vertigo
- Central Nervous System
- Cervical spine injury-disease
- Parkinson’s disease
- Migraine headaches
- Multiple sclerosis
- Epilepsy
- Tumors
- Prognosis
- Slow improvement
- No improvement
- Measures
- Itch
- Result of tissue damage
- release of histamine
- Contact with certain plants
- Itch Process
- Single spinal pathway
- slower than other tactile senses
- activates neurons in spinal cord
- produce a chemical called gastin-releasing peptide
- Why Itch
- Alert to remove irritation
- Scratch irritant off skin
- Not type of pain
- Opiates less pain & increase itch
- Correlated
- Vigorous scratching causes pain
- Reduce pain, reduce itch
- Similar to pain but not
- Both use unmyelinated neurons
- Same nerve bundle
- Both originate in skin but two distinct systems
- Both use unmyelinated neurons
- Itch receptors
- Only on top two skin layers
- Epidermis
- Epidermal
- Itch on top, pain under skin?
- No itch in muscles or joints
- Sensitivity
- Evenly distributed across skin
- Similar density to that of pain
- Neuropathic
- Itch can originate at any point along afferent pathway
- Damaged nervous system
- Diseases or disorders
- CNS or PNS
- Causes
- Multiple sclerosis
- Opioid use
- Psychogenic
- Psychiatric Itch
- Hallucinations & delusions
- Obsessive-compulsive
- Neurotic scratching
- Pain can reduce itch
- Rubbing, scratching
- Electric shock
- Noxious heat
- Chemicals
- Pain & itch sensitivity
- Negatively correlated
- More sensitive to pain
- Less sensitive to itch
- Central sensitization
- Spinal cord input (noxious $)
- Allodynia = exaggerated pain
- Hyperalgesia = extra sensitivity
- Contagious Itch
- Want to scratch
- Talking about it
- See someone scratch
- Mirror neurons?
- Treating Itch
- Itch-scratch-itch cycle
- Self-contagion
- Result of tissue damage
- Touch
- Skin Mapping
- 4 findings:
- 1. Sensations not continuous across skin
- Localized in discrete points
- 2. Number of pain spots > number of pressure > number for temperature
- 3. Localization shifts over time
- 4. Specific sensations do not always directly correspond with the type of receptor found at that location in the skin
- Somato-sensation
- 3 types of tactile sensations
- 1. Temperature
- 2. Pressure
- 3. Pain
- Skin Mapping
- 1. Temperature
- Two independent systems
- Cold
- Warm
- Not Hot
- Hot is not the extreme of warm
- Both warm and cold spots respond to “hot” stimuli
- Physiological zero
- Current skin temperature
- things you touch are compared to your current skin temperature
- Current skin temperature
- Structure
- Free endings of touch neurons
- Non-specialized endings
- Not so much separate neuron
- warmth receptors are slow; unmyelinated C-fibers
- cold uses both
- C-fibers (unmyelinated)
- A delta fibers (thin myelinated)
- How it works
- Warm = increase firing rate
- Cooling = decrease warm rate
- Cold = both
- = increase cool firing rate
- = decrease warm firing rate
- Some cold receptors
- Brief pulse at high temp
- paradoxical response
- Paradoxical cold
- Can’t distinguish extreme hot from extreme cold
- Temperature receptor location
- Skin
- Bladder
- Cornea
- Pre-optic & hypothalamic regions
- Core temp
- Path
- Up spinal cord
- To thalamus
- Two independent systems
- 2. Touch
- Pressure
- Light & Deep
- Use internal organ feedback
- Use touch receptors
- Meissner’s corpuscles
- Unmyelinated nerve endings
- Slow vibrations; texture changes
- Lips, finger tips, palm, foreskin
- Close to surface
- Onset & offset
- Touched a coin
- Merkel’s discs
- Sustained touch and pressure
- Close to surface
- Fingertips
- Slow adapting
- Still holding coin
- Ruffini’s end organs
- Sustained pressure
- Slow adapting
- Deep in skin
- Skin stretch
- Where coin is
- Pacinian corpusles
- Fast vibrations; deep pressure
- Fast adapting (joint position)
- Sudden displacements
- Onset & onset
- Coin leaves hand
- Pressure on receptor
- opens sodium channels in axon
- action potential if enough NT
- Touch perception
- Cutaneous rabbit illusion
- Tapped very rapidly 6x on wrist and then 3x near elbow
- sensation of rabbit hopping from the wrist to elbow with extra illusory stop in between
- Damage to somatosensory cortex (Alzheimer’s)
- impaired body perception
- trouble putting clothes on
- Pressure
- Pain
- All tactile senses except pain adapt quickly
- Survival function of pain
- Independent systems
- Sharp and dull
- Treatment for one not usually effective for the other
- A. Sensing Pain
- Nociceptors
- Bipolar neurons
- Cells in dorsal root of spinal cord
- Send signals on to brain
- Signal skin damage
- Muscles, joints and organs
- Degree of pain depends on:
- Sensitivity of receptors
- Level of stimulation
- Several types of nociceptors
- 1. Thermal nociceptors (extreme)
- 2. Mechanical nociceptors
- Respond to intense pressure
- Not Pacinian corpuscles (touch only)
- 3. Silent nociceptors
- Respond to inflammation chem
- Once activated are sensitive to thermal and mechanical stresses too
- 4. Polymodal nociceptors
- Respond to everything
- Thermal
- Mechanical
- Chemical stresses
- Axons that carry pain info, vary in diameter
- Myelinated faster than unmyel.
- Thicker the faster
- A-alpha
- Largest
- Insulated
- Muscles sensations
- Proprioception
- A-beta
- 2nd largest
- Insulated
- Touch
- A-delta
- Smallest of alphas; nearly as small as Cs
- Thinly insulated
- Pain, heat, touch
- “Good pain” = do something and it will go away
- Put down hot frying pan
- C fibers
- Smallest
- Unmyelinated
- Slowest
- Heat & itch
- Diffuse, dull, chronic pain
- “Bad pain” = removing $ doesn’t remove pain
- Signals damaged tissue
- ********************
- Example
- Stub (hurt) your toe
- 1. moving your foot
- A-alpha propreioceptive info
- 2. sensation of hitting object
- A-beta nerve fibers
- 3. pain of tissue damage
- A-delta and C-nerve fibers
- Primary afferent axons
- Vary in diameter
- A-alpha largest myelinated
- A-beta 2nd largest myelinated.
- A-delta 3rd largest myelinated.
- C fibers smallest unmyelinated
- Vary in speed
- A-alpha 265 mph
- A-beta 165 mph
- A-delta 75 mph
- C fibers 2 mph
- Vary in diameter
- ***************
- Rare Condition: Congenital Insensitivity To Pain
- Born without sense of pain
- Continue activity after injury
- Not detect broken bones-gash
- Often get pressure sores & damaged joints
- B. Relieving pain
- Capsaicin
- disrupts steady $ of pain cells
- Steroids (cortisone injections)
- Relieve pain & joint inflame
- Released by adrenal gland
- Steroid hormone that suppresses immune system
- Which reduces inflammation but stops trying to heal you
- Non-steroidal anti-inflam. drugs
- Tissue damage causes inflame
- Releases prostaglandins that trigger pain
- Capsaicin
- ************
- Prostaglandins
- Proteins
- Synthesized by 3 major enzymes
- Cyclooxygenase 1 (Cox-1)
- Cyclooxygenase 2 (Cox-2)
- Cyclooxygenase 3 (Cox-3)
- All three are blocked by:
- aspirin
- ibuprofen (Advil, Motrin)
- naproxen (Aleve)
- Acetaminophen (Tylenol)
- Blocks Cox 3 only
- Doesn’t irritate stomach
- Not likely cause of Reye’s syndrome; aspirin, children with viral infections?
- ************
- Non-steroidal anti-inflam drugs (NSAIDs)
- Opioids (opiates)
- Good news: Effective
- Bad news: Addictive
- Hydrocodone
- Most used opioid treat of pain
- Morphine = cancer pain
- Opioids (opiates)
- Social Pain
- Romantic breakup
- similar to physical pain
- Emotional pain
- experienced in cingulate cortex
- can be relieved by Tylenol
- Romantic breakup
- Parietal lobes
- Named for overlying bone (parietal bone)
- Above occipital lobe
- Behind frontal lobe
- Integrates sensory information
- Spatial sense
- Navigation
- 1. Somatosensory Cortex
- Visual
- Auditory
- Olfactory
- Gustatory
- 2. Posterior Parietal Cortex
- Also called Somatosensory Assoc. Cortex
- Multimedia
- Dorsal stream of vision
- Where stream of spatial vision
- How stream of visual action
- Used by oculomotor system for targeting eye movements
- Spatial location
- Organized in gaze-centered coordinates
- ‘remapped’ when eyes move
- Input from multiple senses
- Encode location of a reach target
- Manipulation of hands
- Shape, size & orientation of objects to be grasped
- Damage to right hemisphere
- Problems with visualization
- Imagery
- Neglect of left-side space
- Neglect left side of the body
- Damage to left hemisphere
- Problems in mathematics
- Reading
- Writing
- Understanding symbols
Parietal lobes
Named for overlying bone (parietal bone)
Above occipital lobe
Behind frontal lobe
Integrates sensory informationSpatial sense
Navigation
1. Somatosensory CortexVisual
Auditory
Olfactory
Gustatory
2. Posterior Parietal CortexAlso called Somatosensory Assoc. Cortex
Multimedia
Dorsal stream of visionWhere stream of spatial vision
How stream of visual action
Used by oculomotor system for targeting eye movements
Spatial locationOrganized in gaze-centered coordinates
‘remapped’ when eyes move
Input from multiple senses
Encode location of a reach target
Manipulation of hands
Shape, size & orientation of objects to be grasped
Damage to right hemisphereProblems with visualization
Imagery
Neglect of left-side space
Neglect left side of the body
Damage to left hemisphereProblems in mathematics
Reading
Writing
Understanding symbols
TACTILE SENSATIONS
Ascending pathways
1. Lemniscal System
Pressure information
Small receptive fields
Rapid transmission in long axons
Travels up the back of the spinal chord
Travels to somatosensory I in the Parietal lobe
(front part of parietal lobe)
SSI is organized into the sensory humunculus
the greater the sensitivity of a body part the greater the area of the brain devoted to it
2. Spinothalamic System
(Extralemniscal)
Pain & temperature information
Large receptive fields (dermatomes)
Small axons and slower transmission
Travels up sides of spinal chord
Travels to somatosensory II in the parietal lobe
– (back part of parietal lobe)
SSII does not have a neat organization
Many overlapping representations
een neurons. These separations are called synapses. Structurally, synapses are intercellular spaces (between cells). They are small separations between neurons.
