General Senses & Spinal Cord 1 - PHYL 301

Receptors

Detect environmental changes (stimuli)

Sensory Receptors

Cells, often nurons

• Detects stimulus

Cellular Receptors (Receptor Protein)

Proteins on cells

• Protein on or inside the cell and responds to a signal

General Senses

• Can be sensed in multiple locations

• proprioception

• pain

• temperature

• pressure

• vibration

• touch (fine, crude, light)

Special Senses

• Located in specialized organs

• vision (sight)

• audition (hearing)

• gustation (taste)

• olfaction (smell)

• quilibrioception (balance)

Nociceptors

Painful Stimuli

Thermoreceptor

Temperature (cold or hot)

chemoreceptors

chemical concentrations (e.g., pH, O2 , CO2 )

osmoreceptors

osmotic pressure

mechanoreceptors

stretch & distortion

tactile receptors

touch

baroreceptors

pressure

proprioceptors

body position

What is nociception?

Nociception is the nervous system’s detection and transmission of signals about potential or actual tissue damage

• Nociceptors can respond to extreme heat or cold, strong mechanical forces such as a pinprick, or irritating chemicals

• Pain is the conscious experience that can result from that signaling

Stimulus

Change detectable by the body

Afferent neurons

• Have sensory receptors at peripheral endings

  • Respond to stimuli from external world and internal environment

  • Sensory neurons that cary information towards nervous system

Receptor potentials

Local, graded change in voltage caused by a stimulus

• Can lead to action potentials and senesory transduction (stimulus into signal to send toward CNS)

What happens when stimulus alters receptor membrane permeability?

Graded Receptor Potenital

• Summation of receptor potenails lead to action potenials

• Receptor potentials may also open nearby voltage-gated Na+ channels

Tonic Receptors

• Slowly adapt to stimuli

“tone” = montone = long

Tonic Receptors Examples

• Merkel’s discs (light sustained touch)

• Ruffini corpuscles (stretch, sustained pressure)

Phasic Receptors

• Quickly adapt to stimuli

“phase" = just a phase, short and quick

Phasic Receptors Examples

• Hair plexuses

• Pacinian corpuscles (vibration & deep pressure)

• Meissner’s corpuscles (light touch)

Which category of sensory receptors rapidly adapts to a constant simtulus, decreasing their response over time (adapting over time)?

Phasic Receptors

Tactile Receptors

• Related to touch

• Hair receptor (root hair plexus)

• Merkel’s disc ~ Tonic/sustained

• Pacinian corpuscle

• Ruffini endings (corpuscle) ~Tonic/sustained

• Meissner’s corpuscle

Free Nerve Endings

• Stimulated by

  • Touch

  • Temperature

  • Pain

• Found in dermis and deeper layers of epidermis

• How you sense things naked

Root Hair Plexuses

• Mechanoreceptor neurons (stretch & distortion)

• Wrap around hair follicles

• Detect hair movement

• Structure: sensory nerve endings wrapped around hair follicles

if you feel the wind blowing through your hair

Tactile Discs (Merkel cells)

• Oval-shaped discs

• Reach into stratum basale (epidermis)

• Stimulated by

  • pressure

  • position where you’re being touched

  • (deep) touch pressing more than light touch

“erked” = annoying and deep

Tactile (Meissner’s) Corpuscles

• Nerve endings surrounded by connective tissue capsule

• Located in papillae of the dermis (Papillary layer under epidermis, ret underneath )

• Stimulated by

  • Light, fine touch

  • Vibration

“meiSS"“ = super smooth = light

mice is nice

Lamellated (Pacinian) Corpuscles

• Encapsulated nerve endings

  • Dozens of connective tissue layers (like an onion)

  • Gelatinous fluid between layers

• Located in deep dermis

• Stimulated by

  • Pressure

  • Vibration

• Mechanism of adaptation in Pacinian corpuscle

  • Receptor ending consisting of concentric layers of connective tissue wrapped around the peripheral terminal of an afferent neuron

Bulbous (Ruffini) Corpuscles

• Nerve endings weaving through collagen bundles surrounded by a capsule

• Located in dermis

• Stimulated by

  • Stretch

  • Joint position

“bulb & ruff” = bubble weaves through collagen

Visceral afferents

Carries subconscious input

• Internal

Sensory afferents

Carries conscious input

• Outer bodily sensations

What does a labeled somatosensory pathway tell the brain, and what do first-, second-, and third-order mean?

The label tells the brain what you felt (modality) and where you felt it (location), like light touch on your left index finger.
First-, second-, and third-order tell you the order of the neurons that relay the signal toward the sensory cortex.

What is Acuity?

• “Accuracy”

• Influenced by receptive field size and lateral inhibition

  • Smaller = more precise

• Fingertips have higher acuity; two points may feel like one on back

Receptive field

Region of the skin surface surrounding the somesthetic sensory neuron

Lateral inhibition

Each activated signal pathway inhibits the pathways next to it

• Strongest signal at contact point, but smaller weaker signals nearby

Perception

• conscious awareness of surroundings

  • Derived from interpretation of sensory input

Exteroreceptors - General Sense Receptor

Detect external stimuli

Interoreceptors - General Sense Receptor

Detect internal stimuli

Proprioception

• General sense of body position and movement

• Uses proprioceptor neurons & mechanoreceptor nerve endings

  • muscle spindles - changes in muscle length (stretch)

  • Golgi tendon organs - tension in tendon (muscle to bone)

  • joint receptors - joint movement

• How your body knows where it is with you eyes closed

Nociceptors Stimulation

• pain perception, motivational & emotional responses

• Brings awareness of current or impending cell/tissue/body damage

  • Stores memories of pain to avoid reoccuring

• Subcategories:

  • mechanical, thermal, chemical, and polymodal

A-Delta Fibers

• myelinated, small

• “fast” pain (e.g., pricking by sharp points)

• Axon of Nociceptors

“A” = first = fast

C Fibers

• unmyelinated, small

• “slow” pain (e.g., dull achey, long lasting)

“C"“= see long = slow

What do cell receptor proteins do for sensory receptor cells?

Cell receptor proteins detect stimuli for sensory receptor cells

• Different types of ion channels

• Stimulus → Cell Receptor → Sensory Cells

Stimulus → Cell Receptor → Sensory Cells

• Thermoreceptors

• Chemoreceptors

• Mechanoreceptors

Stimulus → Cell Receptor → Sensory Receptor (Cell)

• Temperature → Tempertature-gated ion channels → thermoreceptors

• Chemicals → ligand-gated ion channels → chemoreceptors

• Stretch, distortion, or pressure → mechanically-gated ion channles → mechanoreceptors

Analgesic System

• Analgesia: blocking or relief from pain

• Suppresses pain pathways as they enter spinal cord

• Endorphins released during exercise

  • Reduces substance P relief

• Stress-induced analgesia

• Acupuncture analgesia