1/17 Britton Somatosensory Neurotransmission: Touch, Pain, and Temperature Flashcards
Sensory Receptors-Basic Function
1) sensory receptors are _______
2) sensory receptors covert stimuli in the environment (touch, temp, pressure) into _____ _____ in sensory neurons
3) the conversion process is called _____ ______
- transducers
- action potentials
- sensory transduction
______ like muscle spindles and golgi tendon organs relay info about muscle length and tension
Proprioceptors
Rods and cones in the retina that respond to light
Photoreceptors
_______are stimulated by chemicals in the environment (taste, smell) as well as internal chemical in plasma
Chemoreceptors
______ are cutaneous receptors for touch and pressure
Mechanoreceptors
________- detect the sensations of warm and cold
Thermoreceptors
________-mediate potentially harmful stimuli such as pain, extreme heat, and extreme cold
Nociceptors
Each of the principal types of sensation that we can experience-pain, touch, sight, sound, is called _______ of sensation
Modality
The nature of the sensory receptor varies between:
Sensory modalities
the sensory receptor may be a _____ ______ at the end of a peripheral nerve
Specialized structure
many sensory receptors are ______ _____ cells
Specialized epithelial cells (touch, vision, taste, hearing)
Not smell
if the sensory receptor is a specialized structure where will it synapse?
On a 1st order neuron
the sensory receptor may be ____ _____ endings of 1st order neurons
free nerve endings (touch, temp, pain, smell)
When the receptor is also the 1st order neuron where does it synapse?
There is no need for a synapse
Sensory receptors on the skin are:
Cutaneous receptors that mediate the sensations of touch, pressure, pain, temperature
Sensory receptors on the skin: associated sensory nerves are classified as _____ fibers according to ______
A-beta, A-Delta, and C fibers; diameter and degree of myelination
What are the 3 sensory receptors associated with the skin?
Mechanoreceptors, Thermoreceptors, and Nociceptors
What types of sensory receptors are associated with mechanoreceptors and what is their associated afferent type?
Most are A-beta; only outlier is free nerve endings, which are A-delta and C fibers
what type of sensory receptors are associated with thermoreceptors and what is their associated afferent type?
Warm receptors - C fibers
Cold receptors - A-delta
Warm receptors (thermoreceptors) are _______
Free nerve endings
What type of sensory receptors are associated with nociceptors and what is their associated afferent type?
A-delta, except polymodal (free nerve endings) are C fibers
Classification of Neuron Fibers
Structural Classification: (3 different types of neurons)
- unipolar
- bipolar
- multipolar
Classification of Neuron Fibers
Functional
- sensory
- interneuron
- motor neuron
Classification of Neuron Fibers
Direction from CNS
- afferent
- efferent
Classification of Neuron Fibers
Chemical
- adrenergic
- cholinergic
- GABAergic
Classification of Neuron Fibers
Diameter and myelination
Speed of conduction (A, B, and C fibers)
_____ can be classified according to their conduction velocity
Nerve fibers
What type of nerve fiber is the fastest and has the largest diameter?
A-alpha fibers
A-alpha fibers are _____ neurons
Motor
Which type of nerve fiber is the slowest?
Type C (slow pain)
Postganglionic autonomic nerves, olfaction
_____ fibers are unmyelinated
Type C
What results in faster conduction velocites?
larger size (diameter) and myelination
Sensory afferent nerve fibers are _______ in many aspects.
What nerve fibers are associated?
Heterogenous
A-Beta
A-Delta
C fibers
What type of nerve fibers have a medium conduction velocity and a medium diameter?
- A-beta (touch and pressure)
- A-Gamma (motor neurons to muscle spindles)
What type of nerve fibers have a small diameter and a medium conduction velocity?
- A-delta; touch, pressure, temp, fast pain
- B-preganglionic autonomic nerves
Sensory mechanoreceptors sense:
Touch and pressure
Name the sensory mechanoreceptors on the skin
Free nerve endings
Merkel discs
Pacinian corpuscle
Meissner’s corpuscle
Hair-end organ
Ruffini endings
_____ _____ is the critical first step in all sensory processing
Sensory transduction
What activates a sensory receptor?
Environmental stimuli such as pressure or temperature, which gets converted into a neuronal AP
The transduction process couples ______ detection (activation of a receptor) to the opening or closing of _____ channels in the receptor membrane. This leads to:
Stimulus; ion channels; current flow across the membrane (changes membrane potential)
Current flow across the membrane will result in:
A change in membrane potential
A change in membrane potential in a sensory receptor will cause a _____ ______, which will increase or decrease the likelihood that neuronal APs will occur
Receptor potential
Another name for receptor potential
Generator potential
the _______ is the non-propagated depolarizing potential recorded in a sensory receptor after an adequate stimulus is applied
Receptor potential
The _______ is the non-propagated depolarizing potential recorded in a sensory receptor after an adequate stimulus is applied
Receptor potential
What makes the receptor potential a graded response?
The magnitude of the receptor potential is proportional to the strength of the stimulus
True or false: the receptor potential is a graded response, which is different from the all or nothing neuronal AP
True - as the stimulus increases, the magnitude of the receptor potential also increases
When a receptor potential reaches a critical ______ in stimulus strength, an AP is generated in the sensory nerve
Threshold
The strength of a stimulus is then conveyed in the sensory nerve by the ______ of AP
Frequency
what is it called when a receptor stimulus is converted to a recognizable sensation
Sensory coding
The quality and strength of a sensory stimulus is determined by?
Properties of the sensory receptors
What are the 4 attributes of stimuli that all sensory systems encode?
- modality
- intensity
- duration
- location (receptive field)
Modality
Mode of stimuli that can be sensed by the receptor
What are examples of mechanical modalities?
Touch, pressure, vibration
What are examples of chemical modalties?
- Bradykinin
- Prostaglandin
- pH
- histamine
What are the temperature modalities?
Hot and cold
What is the intensity of a stimulus coded by? (2 things)
- the # of receptors activated
- the frequency of APS (stronger stimuli produce a HIGHER frequency of APs)
What is population coding?
The number of receptors activated
What is frequency coding?
Frequency of APs
Sensory Coding: Duration
1. ________ is a decrease in the size of the receptor potential with a constant stimulus
2. _____ ______ receptors keep stimulating APs as long as the stimulus is present
3. _____ ______ receptors respond maximally but briefly when a stimulus is presented; their response ______ if the stimulus is maintained
- Adaptation
- Slowly Adapting Receptors
- Rapidly Adapting Receptors; decreases
Examples of slowly adapting receptors
Merkel disc, Ruffini corpuscle (detect sustained pressure)
Examples of rapidly adapting receptors
Meissner’s and Pacinian corpuscle (can detect next pressure quickly applied)
The ______ ______ of a sensory neuron is the region of the skin within which a tactile stimulus evokes a sensory response in its axon
Receptive field
The accuracy by which tactile stimuli can be sensed varies in different regions of the body is called:
Mechanosensory discrimination
How big is the receptive field of mechanosensory neurons on the fingertips?
1-2mm
How big is the receptive field on the palms?
5-10 mm
How can the variation of receptive fields be measured?
Two point discrimination test
Two Point Discrimination Test
1) a technique that measures the _______ inter-stimulus distance required to perceive 2 simultaneously applied stimuli as ______
2) measures the ______ distance on the skin between neighboring receptive fields for touch
1) minimal, distinct
2) minimum
Smaller discrimination point means:
Smaller receptive field
Mechanosensory discrimination is due to:
- density of mechanoreceptors
- size of receptive fields
Mechanoreceptors in the fingertips are 3-4x _______ and ______ than in other areas of the hand
More numerous and dense
Mechanoreceptor: Free Nerve Ending
Name the associated afferent nerve type, location, adaptation, and modality
- A-delta, C
- Superficial, all skin
- Modality: light touch
- Adaptation: slow
Mechanoreceptor: Merkel’s Disk
Name the associated afferent nerve type, location, adaptation, and modality
- A-beta
- Superficial, all skin
- Adaptation: slow
- Modality: pressure
Mechanoreceptor: Pacinian Corpuscle
Name the associated afferent nerve type, location, adaptation, and modality
- A-beta
- Deep, all skin
- Adaptation: Rapid
- Modality: vibration
Mechanoreceptor: Meissner’s Corpuscle
Name the associated afferent nerve type, location, adaptation, and modality
- A-beta
- Superficial, Glabrous Skin
- Adaptation: rapid
- Modality: vibration
Mechanoreceptor: Hair Follicle Receptor
Name the associated afferent nerve type, location, adaptation, and modality
- A-beta
- Superficial, hairy skin
- Adaptation: slow
- Modality: bending of hair
Mechanoreceptor: Ruffini’s ending
Name the associated afferent nerve type, location, adaptation, and modality
- A-beta
- Deep, hairy skin
- Adaptation: slow
- Modality: pressure
_____ _______ gives us the ability to differentiate information through the sense of touch
Tactile discrimination
Thermoreceptors examples
- Warm receptors (free nerve endings)
- Cold receptors
Nociceptors examples
Mechanical, Thermal, Polymodal (all free nerve endings)
Nociceptors and thermoreceptors are relatively ___________ on _______ or _______ in hairy or glabrous skin and deep tissues
unspecialized; unmyelinated C fibers; myelinated A-delta fibers
Like mechanoreceptors, _______ transduce a variety of stimuli into _____ potentials
nociceptors
receptor
(stimuli can be tissue damage from a cut, strong mechanical pressure, extreme heat, etc.)
nociceptors are often referred to as ______ _____ fibers
Polymodal nerve fibers (different modes of pain detected)
Nociceptors detect ______ stimuli
Noxious (harmful, injurious)
1) nociceptors express a wide variety of _____ channels that transduce the ______ potential into a ______
2) the resulting _____ potential (depolarization) triggers the activation of _____ channels which will generate a _______ neuronal AP
1) ion, receptor, neuronal AP
2) receptor, ion, propagating
Sensory Transduction at Nociceptors: the transduction process couples _______ to _______ in the receptor membrane
stimulus detection (activation of a receptor) to the opening or closing of ion channels
Sensory transduction involves a complex of molecular ________ present on distinct subsets of nerve fibers
Transducers (ion channels)
Ion channels involved in transduction
- Acid sensing channels (ASIC)
- Purinergic Ion channels
- Piezo mechanosensitive channels
- ANO1 (Ca2+-gated chloride channels)
- Transient Receptor Potential channels (TRP)
Acid sensing ion channels (ASIC) activated by:
Protons (H+)
Purinergic ion channels activated by:
ATP
Piezo mechanosensitive channels activated by:
Mechanical sensation
Activation of nociceptors leads to current flow across the membrane, generates a ______ potential, which will result in neuronal APs
Receptor potential
Transient Receptor Potential Channels (TRP)
- these are a ______ of ion channels
- TRP channels that open in response to stimuli result in _______ and the generation of _____ potentials
- TRP channels are found on _____ _____ _____ of polymodal neurons (temp and pain sensing)
- superfamily
- depolarization, receptor
- free nerve endings
TRP-V (TRP-vanilloid) - what modalities does this channel respond to?
What is this channel stimulated by?
- responds to heat and pain
- stimulated by capsaicin, the spice in chili peppers
TRP Channels: Heat, Cold and Pain Transducers
TRP-M (TRP-melastatin) is stimulated by?
Stimulated by cold and menthol
TRP channels are localized to:
Trigeminal, vagal, and dorsal root ganglia
TRP channels transduce what stimuli into _____ fluxes?
- Visual, chemical, thermal, mechanical, painful, and osmotic stimuli
- Ca2+ fluxes
Examples of TRP channels
- TRP-V
- TRP-M
- TRP-A
TRP Channels: Heat, Cold and Pain Transducers
TRP-A (TRP-ankyrin repeat)
What modality does this channel respond to?
what is this a transducer for?
responds to heat
transducer for pungent chemicals
______ blocks TRPV1 which is a major component of ______
Cetylpyridinium chloride; Scope mouthwash
The discovery of TRPV1 in sensory neurons
The majority of transducers belong to the thermo-sensitive _____ family of ion channels
TRP family of ion channels
What are the 3 types of pain that are generally distingushed?
Nociceptive, inflammatory, neuropathic
Inflammatory pain is associated with ______ caused by tissue inflammatory conditions, which can lead to:
damage; chronic pain syndromes
Neuropathic pain
1) a ______ pain state, characterized by _____ and or _____ nerve injury
2) can lead to?
3) tends to be refractory to:
1) chronic, peripheral and/ or central nerve
2) chronic pain syndromes characterized by hyperalgesia, allodynia, fibromyalgia
3) pharmacological treatment
Types of nociceptive pain
Fast and slow
Fast pain (sharp, pricking) - ____ localized and transmitted by _____ fibers
Well; A-delta
Slow pain (dull, aching) - _____ localized, transmitted by ______
Poorly; C fibers
Inflammatory mediators induce pain by activating ______
Nociceptors
Examples of neuropathic pain
traumatic nerve injury
diabetic neuropathy
chemotherapy induced peripheral neuropathy (CIPN)
What is an ‘inflammatory soup’
describes the mixture of substances released from damaged tissue, immune cells, and bacteria
Nociceptor activation and transduction is triggered through a wide variety of ____ channels
what are some of the ion channels that get activated?
Ion; GPCR’s, RTK’s, ligand gated ion channels. other channels and pores
Nociceptors arise from cell bodies in the _______ that send ____ axonal process to the periphery and the other into the _______
DRG or trigeminal ganglion; 1; spinal cord or brainstem
The nociceptive signal is transmitted to the _____ synapse in the spinal _____ horn by releasing a variety of neurotransmitters at the synapse, such as:
- Central
- Dorsal
- Substance P, Glutamate, Calcitonin, Calcitonin gene related peptide (CGRP)
1) Dental pulp contains:
2) What types of fibers are present?
1) abundant sensory fibers of TG neurons
2) A-delta and C fibers
The nociceptive signal is conducted through either _____ or _____ to the _______ of the ______
- myelinated A-delta fibers
- unmyelinated C fibers
- lamina I and II of the dorsal horn in the spinal cord
Characteristics of A-delta fibers in DENTAL PAIN
Myelination:?
Location of terminals:?
Pain Characteristics: ?
- Yes
- Principally in region of pulp-dentin junction
- Sharp, pricking
characteristics of C- fibers in DENTAL PAIN
Myelination:?
Location of terminals:?
Pain Characteristics: ?
- No
- Distributed throughout pulp
- Burning, aching, less bearable than A-delta fiber sensations
Sensory Pathways
Steps Involved in Transmitting Sensory Info
1) information transmitted from _____ receptors to the _____ cortex via a series of neurons
2) order of sensory afferent neurons
3) synapses are made in _____ ______
1) peripheral, cerebral
2) 1st, 2nd, 3rd, 4th order sensory afferent neurons
3) relay nuclei
Relay Nuclei
1) often ______ pathways, where 2 or more neurons synapse with the 1 neuron
2) ______ may also be located in the relay nuclei
3) the relay nuclei process the info they receive via _______ which may be excitatory or inhibitory? (give examples)
1) converging
2) interneurons
3) interneurons
Excitatory: ACh
Inhibitory: GABA and Glycine
Sensory Pathways
1) _______ are closest to the sensory receptor
2) cell bodies are located in a ______ or _______ ganglion
1) 1st order or primary sensory neurons
2) DRG or cranial nerve ganglion
EXCEPT: auditory, olfactory, and visual systems
In some cases, the 1st order neuron is also the receptor cell, termed-
Free nerve endings
2nd order neurons
1) axons of the 2nd order neurons (descend/ascend) from the spinal cord to the next relay located in the ______
2) en route, the axons of 2nd order neurons ______ _____ _____ (decussation) either in the spinal cord or in the brain stem
1) ascend, thalamus
2) cross the midline-decussation
3rd Order Neurons are typically located in the ______
Thalamus
4th Order Neurons reside in the _____ area of the ______ cortex
Sensory area of the cerebral cortex
What is the sensory nerve that innervates the orofacial region?
trigeminal nerve (CN V)
______ stimuli in teeth are transmitted in primary ______ neurons (1st order neurons) located in the trigeminal ganglion via ______ order neurons in the brain stem to the brain
noxious, afferent, 2nd
What are the 2 major ascending somatosensory pathways?
- Dorsal Column-Medial Lemniscal (DCML)
- Lateral Spinothalamic Tract (LST)
What sensory information is relayed in the DCML pathway
Mechanoreceptors, proprioceptors
What sensory information is relayed in the LST pathway
Thermoreceptors, nociceptors
Somatosensory sensations from all areas of the body go to the _____ cortex
Sensory
______ ______ is a neurological ‘map’ of the portions of the cortex dedicated to processing sensory information from different regions of the body
Sensory homunculus
