General Principles of Sensory Processing, Touch, and Pain

Chapter 8

Sensory Receptor Organs

An organ (such as the eye or ear) specialized to detect particular stimuli

Stimulus

A physical event that triggers a sensory response

Receptor Cells

A specialized cell that responds to a particular energy or substance in the internal or external environment and converts energy into a change in the electrical potential across its membrane

Adequate Stimulus

The type of stimulus for which a given sensory organ is particularly adapted

Mechanical Sensory System

Touch, Pain, Hearing, Vestibular, Joint, Muscle

Visual Sensory System

Seeing, visible radiant energy

Thermal Sensory System

Cold, Warmth

Chemical Sensory System

Smell, Taste, Common chemical, Vomeronasal

Electrical Sensory System

Electroreception, differences in density of electrical currents

Magnetic Sensory System

Magnetoreception, orientation of earth’s magnetic field

Specific Nerve Energies

The doctrine that the receptors and neural channels for the different senses are independent and operate in their own special ways and can produce onlt one particular sensation each

Labeled Lines

The concept that each nerve input to the brain reports only a particular type of information

Sensory Transduction

The process in which a receptor cell converts the energy in a stimulus into a change in the electrical potential across its membrane

Receptor Potentials

Also called generator potential, a local change in the resting potential of a receptor cell that mediates between the impact of stimuli and the initiation of action potentials

Pacinian Corpuscle

Also called lamellated corpuscle, a skin receptor cell type that detects vibration

Threshold

The stimulus intensity that is just adequate to trigger an action potential

Piezo

A family of proteins that respond to mechanical stretch by opening channels to let cations in to depolarize the cell

Coding

The rules by which action potentials in a sensory system reflect a physical stimulus

Range Fractionation

A method of stimulus intensity perception in which intensity values are encoded by an array of cells, each specialized to detect a particular range of intensities

Somatosensory

Referring to body sensation, particularly touch and pain sensation

Adaptation

The subsequent loss of receptor sensitivity as stimulation is maintained

Tonic Receptors

A receptor in which the frequency of action potentials declines slowly or not at all as stimulation is maintained

Phasic Receptors

A receptor in which the frequency of action potentials drops rapidly as stimulation is maintained

Sensory Pathway

The chain of neural connections from sensory receptor cells to the cortex

Thalamus

The brain regions that surround the third ventricle and trade information with the cortex

Receptive Field

The stimulus region and features that affect the activity of a cell in a sensory system

Primary Sensory Cortex

For a given sensory modality, the region of cortex that receives most of the information about that modality from the thalamus or, in the case of olfaction, directly from the secondary sensory neurons

Primary Somatosensory Cortex

Also called somatosensory 1, the gyrus just posterior to the central sulcus, in the parietal lobe, where sensory receptors on the body surface are mapped; primary cortex for receiving touch and pain information

Secondary Somatosensory Cortex

Also called somatosensory 2, the region of the cortex that receives direct projections from somatosensory 1

Attention

Also called selective attention. A state or condition of selective awareness or perceptual receptivity, by which specific stimuli are selected for enhanced processing

Cingulate Cortex

A region of medial cerebral cortex that lies dorsal to the corpus callosum

Epidermis

The outermost layer of the skin, over the dermis

Dermis

The middle layer of the skin, between the epidermis and the hypodermis

Hypodermis

The innermost layer of the skin, under the dermis

Tactile

Of or relating to touch

Meissner Corpuscles

A skin receptor cell type that detects light touch

Merkel Discs

A skin receptor cell type that detects fine touch

Ruffini Endings

A skin receptor cell type that detects stretching of the skin

Dorsal Column System

A somatosensory system that delivers most touch stimuli via the dorsal columns of spinal white matter to the brain

Dorsal Column Nuclei

Collections of neurons in the medulla that receive somatosensory information via the dorsal columns of the spinal cord. These neurons send their axons across the midline and to the thalamus

Pain

The discomfort normally associated with tissue damage

Congenital Insensitivity to Pain

The condition of being born without the ability to perceive pain

Nociceptors

A receptor that responds to stimuli that produce tissue damage or pose the threat of damage

Free Nerve Endings

An axon that terminates in the skin without any specialized cell associated with it and that deducts pain and or changes in temperature

Capsaicin

A compound synthesized by various plants to deter predators by mimicking the experience of burning

Transient Receptor Potential Vanilloid Type 1 (TRPV1)

Also called vanilloid receptor 1. A receptor that binds capsaicin to transmit the burning sensation from chili peppers and normally detects sudden increases in temperature

Transient Receptor Potential Type M3 (TPRM3)

A receptor found in some free nerve endings, that opens its channel in response to rising temperature

A delta Fibers

A moderately large, myelinated, and therefore fast-conducting axon, usually transmitting acute pain information

C Fibers

A small, unmyelinated axon that conducts information slowly and adapts slowly

TRPM8

Also called cool-menthol receptor 1, a sensory receptor found in some free nerve endings, that opens an ion channel in response to a mild temperature drop or exposure to menthol

Nav1.7

Also called SCN9A. A voltage gated sodium channel used almost exclusively by nociceptors to initiate action potentials

Anterolateral System

Also called spinothalamic system. A somatosensory system that carries most of the pain and temperature information from the body to the brain

Glutamate

An amino acid transmitter, the most common excitatory transmitter

Substance P

A peptide transmitter implicated in pain transmission

Natriuretic Peptide B

A peptide neurotransmitter used by neurons reporting itch to the spinal cord

Neuropathic Pain

Pain caused by damage to peripheral nerves, often difficult to treat

Migraines

Intense headaches, typically perceived from one half of the head, that recur regularly and can be difficult to treat

Calcitonin Gene-Related Peptide

A neuropeptide that has been implicated in migraine headaches

Analgesia

Absence or reduction in pain

Cannabis

Dried leaves and flowers of the plans, typically smoked to obtain THC for a psychoactive effect, and CBD to induce a feeling of relaxation

Opiates

A class of compounds that exert an effect like that of opium, including reduced pain sensitivity

Endogenous Opioids

A family of peptide transmitters produced in various regions of the brain that bind to opioid receptors and act like opiates. The three kinds are enkephalins, endorphins, and dynorphins

Endorphins

One of three kinds of endogenous opioids, substances that reduce pain perception

Enkephalins

One of three kinds of endogenous opioids, substances that reduce pain perception

Dynorphins

One of three kinds of endogenous opioids, substances that reduce pain perception

Opioid Receptors

A receptor that responds to endogenous and/or exogenous opiates

Periaquecuctal Gray

The neuronal body-rich region of the midbrain surrounding the cereral aqueduct that connects the third and fourth ventricles. It is involved in pain perception

Placebo

A substance that is known to be ineffective or inert but that, when administered like a drug, can sometimes bring relief.

Naloxone

A potent antagonist of opiates that may be administered to people who have taken drug overdoses. It blocks receptors for endogenous opioids

Nocebo

An inert substance that causes discomfort due to the patients expectations