12. Sensory Physiology Flashcards
What are the two schemes that peripheral nerves are classified by?
electrical properites such as APs (ABC waves) physical properties such as fiber diameter/myelin (class 1/2/3/4)
A-alpha is a sensory afferent fiber type with a ____ diameter, ______ conduction velocity, and supply what?
Large diameter
Fast conduction velocity
Muscle spindle/golgi tendon
C sensory fibers are type IV/4 fibers with a ______ diameter, ______ conduction velocity and supplies what?
Small diameter
Slow conduction velocity
Skin/thermal receptors and nociceptors
A stimulus applied to a somatosensory receptor produces what? that when large enough leads to action potentials that can be carried into the CNS?
generator potential
info from all sensory systems are relayed through the thalamus on the way to the cerebral cortex. What is convergence and divergence?
Convergence is when two stimuli neurosn converge onto one receptor
Divergence is when one stimuli neuron relays info
The number of active receptors increases with increased intensity of the stimulus. The seonsory receptor tells how intense the stimulus is and?
transforms a signal of intesnsity into a digital pulse
What is it called when a stimulus persists for minutes leading to the neural response diminishing and losing sensation?
receptor adaptation
Receptors that respond to prolonged and constant stimulation are?
slowly adapting receptors
Receptors that respond only at beginning and end of a stimulus (only active when stimulus intensity inc/dec) are?
rapidly adapting receptors
Meissner Corpuscle
Receptor Type:
Sensation produced:
Receptive field size:
Receptor Type: Rapidly adapting
Sensation produced: tap/flutter
Receptive field size: small
Hair Follicle Receptors
Receptor Type:
Sensation produced:
Receptive field size:
Receptor Type: BOTH
Sensation produced: motion/direction
Receptive field size: N/A
Pacinian Receptor
Receptor Type:
Sensation produced:
Receptive field size:
Receptor Type: RA
Sensation produced: Vibration
Receptive field size: Large
Merkel Disk
Receptor Type:
Sensation produced:
Receptive field size:
Receptor Type: SA
Sensation produced: touch/pressure
Receptive field size: Small
Ruffini Corpuscle
Receptor Type:
Sensation produced:
Receptor Type: SA
Sensation produced: Skin stretch
What are individual mechanoreceptor fibers that convey information from a limited area of skin?
receptive fields
2-point discrimination is the ability to tell the difference between nearby stimuli. Where is tactile acuity the highest and lowest?
highest in fingertips and lips (smallest fields)
Lowest on calf, back, and thigh (largest receptive fields)
Where there is a lot of convergence of primary sensory neurons in one receptive fields the two stimuli will be received as one, but when there are fewer primary neurons converging in small receptive fields, what can be expected?
they will not converge and there will be point differentiation
Primary afferent neurotransmission is controlled by pre and postsynaptic inhibitory mechs, PRESYNAPTIC INHIBITION being more powerful. The inhibition is actually what?
a diminished excitatory signal
Presynaptic inhibition results in reduced NT release from the presynaptic terminal which improves?
the brains ability to localize the signal
When there are three primary neurons responding to a stimulus, the neuron closest to the stimuli will do what?
inhibits other 2, enhancing perception of stimulus
Somatotopic maps are not fixed. What does this mean?
We can train our senses to feel better. Ei: OMM hands over time will mature sensation and be able to feel things
Can also decrease senation d/t amputation/nerve probs
The cortex has 6 layers. the MAIN output neurons are the pyrimidal cells. Which layers are enlarge in primary somatocortex and are main site of input from thalamus?
Layers III and IV
Neurons that are stacked above and below eachother are fundamentally similar while neuronal columns that are side by side are?
significantly different from one another
The columns extend through all 6 layers, and each column deals with ONE sensory modality in one body part. What is the main input layer?
IV
Primary somatosensory cortex SI is in the post-central gyrus and aligns with brodmann areas 3a,3b 1 and 2. What is the main involvment of the SI?
integration of information for position sense as well as size shape discrimination
S2 receives input from S1 and is located in the wall of the sylvian fissure. The information received here allows?
comparisons between objects, different tactile senations and determining whether something becomes a memory
What area has a high level interpretation of sensory inputs, receives input from multiple areas, names objects and analyzes spatial coordinates of self in environment?
parieto-temporal-occiptal association cortex (PTO)
What establish parallel paths of sensation, linking primary and association areas of the sensory cortex, allowing for simultaneous processing of multiple sensations?
cortico-cortical projections
Corticofugal signals (flight) are transmitted AWAY from cortex to lower stations and does what?
Inhibits and supresses sensory input **CONTROLS TONE
What states that no matter where the afferent pathway is stimulated, the sensation that will occur is determined by the nature of the sensory receptor in the periphery connected to that pathway?
doctrine of specific nerve energies
What states that no matter where the afferent pathway is stimulated, the perceived sensation arises from the origin of sensation?
law of projections
What is the main difference between pain and nociception?
Nociception is a neural process encoding noxious stimuli (damaging or threatening stimulus)
Pain is unpleasant sensory and EMOTIONAL experience
What fibers are used for fast and slow pain trasmission?
Slow is C-fibers b/c no myelin
Fast is A-delta fibers b/c myelin
What are the four different pain characteristics?
somatic pain
muscle pain
deep pain
visceral pain
What is a high threshold sensory receptor of the PNS that is capable of making a noxious stimuli?
nociceptors
Nociceptors can relay thermal/mechanical/chemical pain, and many are poly modal meaning can respond to more than one. What is a silent nociceptor?
nociceptors that are rarely stimulated that can switch to respond to stimuli under chronic conditions
Nocicpetors usually have axons that are myelinated (A-delta) or unmyelinated (C fiber) with peripheral terminals as?
free nerve endings
What lacks specialized receptor cells, whose characterization cna further be broken down by molecular molecules?
free nerve endings
Free nerve endings of nociceptors can be peptidergic and non-peptidergic. What are main points of peptidergic free nerve endings? 3
- express substance P and CGRP which are responsive to NGF (nerve growth factor)
- most are visceral afferents
- half of cutaneous afferents (rest are nonpetidergic)
What are ligand gated nonselective cation channels permeable to CA2++**, Na and or K that sense nocious stimuli?
TRP (TRIP) receptors
What are the three TRP receptors we need to know?
TRPV1
TRPA1
TRPM8
What TRP is responsive to capsaicin and hot temperatures, causing pain d/t binding, increasing Ca through channel = depolarization = AP = PAIN?
TRPV1
What TRP is responsive to very cold temperatures and mustard/radish, causing pain d/t increase in Ca influx depolarization?
TRPA1
What TRP is responsive to cold temperatures and menthol, causing a influx of Ca leading to AP and pain?
TRPM8
Nav1.7- mechanosensitive sodium channel activates nociceptors, and if there is a type 1 mutation, what occurs?
the person becomes pain-insensitive!
What are some other noxious stimuli that activate nociceptors? 5
ATP H+ SP/CGRP Histamine Bradykinin
C fibers will release EAA and SP/GCRP at a dendrite to relay pain signals. What does A-delta fibers do?
Release EAA to bind non NMDA (all EAA for nociceptors) receptors such as AMPA receptors
Nociceptors are modulated by descending systems (dampens input) and local systems such as
gate control theory of pain
What does it mean in gate control theory when the gate is closed?
no pain is sensed because the inhibitory interneuron is blocking the nociceptive signal from moving foreward
The gate is open when there is a strong pain, C fibers stop inhibiting the pathway, allowing strong signal to be sent to brain. HOw can pain be modulated in this situation?
by simultaneous somatosensory input
What are the three steps of the gate theory during pain?
- AB fiber activated by normal stimuli (rubbing area hurt) central process of fiber in dorsal horn synapses on inhibitory interneuron, releasing EAA
- Activated interneuron releases glycine and inhibits secondary sensory neuron of the nociceptive path
- rubbing an area affected activates the Ab fibers
What are the 6 steps for descending inhibition?
- PAG are activated by opiates/EAA/cannabinoids
- Descending projections travel to Locus Coeruleus (NE) and Raphe nucleus (serotonin)
- Sero/NE released into dorsal horn activate inhib interneurons
- Local inhibitory interneurons release opiates
- Opiates activate mu receptors on pre synaptic C fiber
- Results in reduction of SP from C fiber and nociception
Just know these two steps for descending serotonergic and noradrenergic neruons…?
- activate local interneurons
2. suppress spinothalamic projection neurons (nociception) directly or indirectly via release of opiates
One route causing chronic pain and central sensitization is inflammation which releases WHAT, which upregulates NGF to increase the amount of pain?
BRADYKININ
What region of the brain intergrates all signals related to pain?
insular cortex
Damage to the insular cortex can cause what?
asymbolia - sensation of pain without emotion
Amygdala is important for the emotional part of pain. What input travels to hypothalamus and medulla, integrating physiological changes associated with visceral pain?
Visceral input
What are the three stimuli needed to activate skin nociceptors?
thermal, mechanical, and chemical
What are the two stimuli needed to activate joint nociceptors?
mechanical and chemical (inflamm)
What are the two stimuli needed to activate muscle nociceptors?
mechanical and chemical
What are the two stimuli needed to activate viscera nociceptors?
mechanical (distention/traction) and chemical
What types of pain are associated with cutaneous, deep, muscle, and visceral injuries?
Cutaneous: fast/sharp and slow/dull
Deep: dull and achy
Muscle: Fast and slow pain
Visceral: poor localization, STRETCH, reffered pain
What is the main signaling that diffuses visceral pain across multiple organs?
Antidromic signaling
