- 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
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