Sensation: Pain and Fine Touch

Senses

What are the ways in which the body perceives external stimuli?

- Sight

- Hearing

- Taste

- Touch

- Smell

Additional:

- Balance

- Thermoreception (hot/cold)

- Pain

- Proprioception

What are the 5 general senses (+ other possible ones)?

Proprioception

What is a sense of what position your body is in at any time?

receptive

Differential sensitivity of receptors allows each receptor to be highly _______________ to one type of stimulus and appraises the nervous system of one kind of modality of sensation with an adequate stimulus

receptor potential

Regardless of the type of stimulus, the effect on all receptors is the same: a change in the electrical potential of the receptor or the ____________ _______________

appropriate

Light, sound, heat, cold, mechanical deformation, pain - all produce a change in electrical potential in the _______________ receptor type

Adequate Stimulus

What is the physical energy to which a receptor is tuned?

Light

What is the adequate stimulus on the rods and cones of the eye?

Sound

What is the adequate stimulus on the hair cells of the ear?

Deformation

What is the adequate stimulus on receptors that sense touch?

Changes in muscle length

What is the adequate stimulus for muscle spindle receptors?

Changes in muscle tension

What is the adequate stimulus for the Golgi tendon organ?

proportional

Receptor potential amplitude and action potential frequency are _______________ to stimulus intensity (bright light = signals from many dendrites to stimulate the action potential is strong)

Adaptation

What is the property of the receptor where an initial high rate of response (action potentials) is followed by a lower response rate with a continued stimulus (ex. don't think about the feeling of the clothes you are wearing)?

Pain (never want to desensitize to harmful actions = why receptors sensitize with chronic pain)

What nerve fibers show little if any adaption?

• Exteroceptors

• Proprioceptors

• Interoceptors

What are the classes of receptors?

Interoceptors

What class of receptors detect stimuli from inside the body and include receptors that respond to pH, oxygen level in arterial blood, carbon dioxide concentration, osmolality of body fluids, distention and spasm (e.g., gut), and flow (e.g., urethra)?

Proprioceptors

What class of receptors are located in skeletal muscles, tendons, ligaments and joint capsules; are sensitive to muscle stretch, muscle tone, position and angle of joints; and provide a sense of body position - "self" receptors?

• Muscle spindle

• Golgi tendon organ

• Joint receptor

• Vestibular hair cell

What are places where proprioceptors are often found?

Exteroceptors

What class of receptors detect stimuli near the outer surface of the body and include those from the skin that respond to cold, warmth, touch, pressure and vibration and also includes special receptors for hearing and vision?

- Mechanoreceptors (mechanosensitive ion channels, touch)

- Thermoreceptors (heat, cold)

- Nociceptors (pain, damaging stimuli)

- Chemoceptors (taste and smell)

What are examples of exteroceptors?

• Pacinian corpuscle - vibration

• Meissner's corpuscle - touch

• Hair-follicle receptor - touch

• Merkel's disk - pressure

• Tactile disk - pressure

• Ruffini's corpuscle - pressure

What do the following mechanoreceptors sense:

- Pacininan corpuscles

- Meissner's corpuscles

- Hair-follicle receptor

- Merkel's disk

- Tactile disk

- Ruffini's corpuscles

Meissner's corpuscles, Pacinian corpuscles

Mechanreceptors are spread throughout the layers of the skin to get a complete picture of the sensation. For example, _____________ _________ are located near the epidermis and sense light touch, while __________ __________ are deeper in the dermis and can sense deep touch

Tactile localization

What is the ability to identify where on the body a stimulus originates?

Tactile discrimination

What is the ability to distinguish the presence of two close stimuli (2-point discrimination)?

Somatosensory cortex

What is the region of the brain with surfaces devoted to organizing sensory information from differenet parts of the body (spatial organization)?

Enlarged face and hands = more than 1/2 the somatosensory cortex

What is enlarged in the sensory homunculus - a representation of what we would look like if we grew in proportion to our sensory processing?

Dermatomes

What are skin areas innervated by spinal nerves (well conserved across species)?

Pain

What is an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage?

protective, aversive

Pain usually elicits a _____________ or ____________ reaction which removes the organism from the stimulus

Nociception

__________________ is the ability to detect damaging stimuli, typically used when discussing animal studies

free nerve endings

Nociceptors or pain receptors are __________ _________ ____________ which can be found in superficial skin, periosteum, muscle, arterial walls, joint surfaces, viscera, meninges

- noxious mechanical stress

- extremes of temperature

- ischemia

- inflammatory chemicals (bradykinin, H+, K+, histamine, serotonin, prostaglandins, acetylcholine, or proteolytic enzymes)

What are potential stimuli that will excite nociceptors?

Fast pain

What type of pain is transmitted by A-delta fibers, is acute, bright or pricking pain with a short latency (well localized, not blocked by narcotics well)?

Slow pain

What type of pain is transmitted by C fibers, is burning, aching, or throbbing pain and can be chronic, slow, or diffuse (blocked by narcotics)?

myelinated A-fibers

What kind of fibers carry a sharp pain to the spinal cord (fast) = gives you the information to get away from the stimulus?

unmyelinated C-fibers

What kind of fibers carry a continuous pain to the spinal cord in a slower manner?

dorsal, dorsal

The fibers from nociceptors bring the signal first to the ________ root ganglion and then into the _______ horn of the spinal cord

Dorsal horn of the spinal cord

What is the first synaptic relay for pain information from the periphery?

Ascending nociceptive pathway

What nociceptive pathway brings the sense of pain up the spinal cord to the brain?

Descending inhibitory pathway

What pathway allows the brain to shut down the sense of pain (times of intense stress)?

descending

The brain plays a major role in _______________ control of pain.

1. The midbrain periaqueductal gray matter (PAG) and periventricular areas

2. The medullary raphe nuclei in the (rostral ventromedial medulla, RVM)

3. The spinal cord dorsal horn

Where is it thought that an intrinsic or endogenous analgesia system exists?

PAG - periaqueductal gray matter

Stimulation of the midbrain ________ produces a selective suppression of pain in animals and man

morphine

Administration of ____________ into the PAG produces analgesia

opioid

The PAG is rich in ___________ receptors and endogenous ____________ peptides (enkephalins).

centrifugal

The PAG produces analgesia by modifying the pain response of "nociceptive" cells in the spinal cord - _____________ modulation of sensory function

endogenously

The PAG is activated ________________ by pain or stress and inhibits dorsal horn pain transmission cells

NRM - nucleus raphe magnus

What in the RVM is activated by the PAG and by opioids?

enkephalin

PAG neurons release ____________ onto NRM neurons

serotonin (5HT)

NRM neurons release _______________ onto dorsal cord neurons.

- Analgesia

- Release of enkephalins

What occurs if the NRM is stimulated?

substance P

In the spinal cord dorsal horn, __________ is released by nociceptor afferents onto pain transmission cells.

opiates

Substance P release is inhibited by ___________ with receptors for them present in the SCDH

inhibit

5HT from NRM stimulates enkephalin neurons, which presynaptically and postsynaptically ________ pain afferents

GCPRs

The opioid receptors are ____________ allowing them to perform many different actions on the cell (close Ca+ channels, open K+ channels) resulting in a shut down of pain

Injecting so that they spread all over the body (where there are many opiod receptors) leads to side effects = would be better to only put them where they are needed in the brain

Why is there such an issue with the use of opioids?

pain, reward

Opioid receptors are found both in the __________ and _________ networks of the brain (one of the drivers of addiction)

Transient Receptor Potential (TRP) Channels

What are the bare or encapsulated nerve endings associated with A-delta and C fibers that aid in temperature sensation?

bulbs of Krause

What are the cold receptors that can sense 20-45 C?

Ruffini organs

What are the warm receptors that can sense 30-50 C?

extreme

Pain is produced at ______________ temperatures

TRPV1

Free nerve endings in the epidermal layer of the skin contain a sensor on their outer membrane called ____________ - a single protein molecule that can respond to both heat and capsaicin by opening an ion channel

capsaicin

The "hot" chemical in hot (capsicum) peppers is __________, which activates TRPV1 receptors

TRPM8

There are free nerve endings in the epidermis that contain a different sensor - ____________ - that responds to both menthol and cooling