Lecture 11: Sensory Physiology Flashcards
What 2 things can be used to classify a peripheral nerve?
Contribution to an action potential. (Letter)
Fiber diameter, myelin thickness. (Number)
Aalpha nerve
Classification:
Fiber diameter:
Conduction velocity:
Classification: Ia, Ib
Fiber diameter: large
Conduction velocity: fast
C nerve
Classification:
Fiber diameter:
Conduction velocity:
Classification: IV
Fiber diameter: small
Conduction velocity: slow
What is a generator potential?
A stimulus, when large enough, can trigger an AP to be carried over a distance into the CNS.
Receptor adaptation
When a stimulus persists for awhile, the neural response diminishes and sensation is lost.
Slowly adapting receptors
Receptors that respond to prolonged and constant stimulation
Rapidly adapting receptors
Receptors that respond only at beginning or end of stimulus when the intensity of stimulus increases or decreases.
Meissner’s corpuscle
Adaptation rate:
Sensation produced:
Receptive field size:
Receptor Adaptation rate: RA
Sensation produced: tap, flutter
Receptive field size: small
Hair follicle receptors
Adaptation rate:
Sensation produced:
Receptive field size:
Receptor Adaptation rate: RA or SA
Sensation produced: motion, direction
Receptive field size: N/A
Pacinian corpuscle
Adaptation rate:
Sensation produced:
Receptive field size:
Receptor Adaptation rate: RA
Sensation produced: vibration
Receptive field size: large
Merkel disk
Receptor Adaptation rate:
Sensation produced:
Receptive field size:
Receptor Adaptation rate: SA
Sensation produced: touch, pressure
Receptive field size: small
Ruffini corpuscle
Receptor Adaptation rate:
Sensation produced:
Receptive field size:
Receptor Adaptation rate: SA
Sensation produced: skin stretch
Receptive field size: large
Where is tactile acuity highest?
Small receptor fields (fingertips, lips, etc).
Where is tactile acuity lowest?
Large receptor fields (calf, thigh, back, etc)
Pre-synaptic inhibition
Diminishes excitatory signal.
- GABA –> influx of Cl-.
- Hyperpolarization
- Less Ca++
- Less NT release
What is the use for pre-synaptic inhibition? How?
It helps the brain localize the signal.
The activated neuron can send collateral branches to inhibit nearby neurons, which would enlarge the sensory area.
3 roles of cortical processing
Initial processing of signal.
Integration of the initial processing into larger schemes.
Emotional response to the processing.
What is interesting about the somatotopic maps?
They can be changed (i.e. magnified (OMM) or diminished (amputation, severed nerve)).
What layers of the cortex are enlarged in the primary sensory cortex?
III and IV
What layers of the cortex are the main site of termination of axons from the thalamus?
III and IV
Each column within the cortex deals with what?
One sensory modality in one part of the body (Meissner’s of arm, free nerve endings leg, etc).
How does sensory info arrive at its column in layer IV?
Via the thalamus
What is S1 involved in?
Integration of the info for position sense, and size and shape discrimination.
What is S2 involved in?
Comparisons between objects, sensations, etc. and whether or not something becomes a memory.
PTO
High level interpretation of sensory inputs from many areas.
Analyzes spatial coordinates of self in environment. Names objects.
Once it receives sensory, what does the primary sensory cortex send projections to?
Mostly back to thalamus, but also to other parts of cortex.
What do the thalamic projections from the primary sensory cortex do?
Permits focusing activities
What is the function of cortico-cortical projections?
It allows for linking of primary and association areas of sensory cortex.
Allows for simultaneous processing multiple sensations.
What is the corticofugal signal?
Transmits back from cortex to thalamus, medulla or SC.
Typically inhibitory and suppresses sensory input.
Pain vs nociception
Pain: both the sensory and emotional unpleasantness from a harm.
Nociception: Neural process of encoding noxious stimuli.
Fast pain is done by:
A-delta fibers
Slow pain is done by:
C-fibers
3 types of pain
Thermal
Mechanical
Chemical
Silent nociception
Nociceptors that are not generally activated
Phenotype switching
Induction of nociceptive receptors where they otherwise are not.
Free nerve endings have which kind of fibers? (2)
C fibers
A-delta fibers
Peptidergic free nerve endings
Peptides expressed:
Responsive to:
What kind of pain?
Peptides expressed: SP, CGRP.
Responsive to: NGF (nerve growth factor)
What kind of pain? Chronic inflammation and visceral pain.
Non-peptidergic free nerve endings
Peptides expressed:
Responsive to:
What kind of pain?
Peptides expressed: no neuropeptides
Responsive to: GDNF
What kind of pain? Diabetic neuropathy
TRP receptors are permeable to? (3)
Ca++
Na+
K+
TRPV1
Capsaicin, and heat
TRPA1
Menthol
TRPM8
Allyl isothiocyanate and coldness.
Other receptors sensing pain (3)
Na 1.7 channel: Mechanosensitive sodium channel.
P2X: ATP activated.
ASIC: activated by H+.
Gate theory of pain
Rubbing the spot that hurts.
No pain is sensed because the inhibitory interneuron is blocking the nociceptive signal (activates the A-beta fiber which activates an interneuron which is inhibitory).
Descending inhibition
NE and serotonin activates inhibitory interneurons which release opiods on presynaptic C-fibers which leads to reduced nociception/ALS.
What mediates chronic pain, or subthreshold pain?
Bradykinin
Role of insular cortex
Interpretation of pain.
Integrates all signals referred to pain.
Asymbolia
No emotional attachment to pain
Where does visceral input travel?
With ANS to hypothalamus and medulla.
Types of pain associated with: Skin: Joints: Muscle: Viscera:
Skin: thermal and chemical
Joints: mechanical and chemical
Muscle: mechanical and chemical
Viscera: mechanical and chemical
How does referred pain occur?
Many afferents converge in the dorsal horn. If they synapse on the same 2nd neurons, then the pain is perceived in many places.
