Overview of Important Receptor Types

Information Processing by the Sensory Division

Sensory transduction mechanism -

1. Reception (stimulus)

Sensory receptor encoutners stimulus - receptors are highly specific (ex. thermoreceptor responds only to temp changes)

2. Ion channel gating

Bc. of stimulus the ion channels open/close. Can happen in two ways:

• Direct (Ionotropic) - physical stimulus (like stretching the skin), physically pulls the ion channel open

• Indirect (metabotropic) - stimulus triggers a complex chemical chain reaction (often involves G-proteins) inside the cell that eventually opens the channel

3. Ion flow (the current)

Once ions are open → ions flow across the cell membrane

Overview of Sensory Receptors

• Sensory cells use ion channels in their membranes to respond to stimuli

  • open or close depends on the sensory system involved

• Receptor potential (influx of ions in the intracellular space of the cell)

  • Analogous to the excitatory postsynaptic potential (EPSP)

  • For regulation and moderation: Hyperpolarizations are very important (IPSP - inhibitory postsynaptic potential)

  • They’re like graded potentials

    • larger sensory stimulus → greater the degree of depolarization → higher the frequency of action potentials

• Sensory neurons have different type of receptors

3 Classes of Receptors

Mechanoreceptors

• Stimulated by mechanical forces (like pressure)

• Cutaneous receptors

  • Receptors in the skin - for pain, heat, cold, touch, and pressure

  • Responds to stimuli at the border between internal and external environments

• Nociceptors

  • Transmits impulses perceived as pain

  • Sensitive to noxious substances + tissue damage

  • Most have free endings located thru the body (especially near surfaces)

  • Transient receptor potential (TRP) ion channel

        Nociceptor Pathways:

• Reflexive protective response

  • Integrated in spinal cord

  • Withdrawal reflex

• Ascending pathway to cerebral cortex

  • Becomes conscious sensation (pain or itch)

        Nociceptors: Pain and Itch

• Itch

  • Histamine activates C fibers → causes itch

  • From skin nociceptors

• Pain

  • Subjective perception

  • Fast pain (sharp + localized):

    • by A delta fibers

  • Slow pain (duller + more diffuse):

    • by C fibers

      • Strong pain - C fiber stops inhibition of the pathway → allows strogn signal to be sent to the brain

      • In abscence of input from C fibers (no stimuli), a tonically active inhibitory interneuron suppresses pain pathway

  • Pain can be modulated by simultaneous somatosensory input

• Proprioceptors

  • Monitor mucle length and tension

  • Provide info ab the relative position or movement of body parts

        Examples:

        Muscle spindles - monitor stretch on muscle. Knee jerk reflex

        Golgi tendon organs - monitor tension on tendons → Reflex inhibits motor neurons + prevents damage to tendons

• Baroreceptors

  • Monitor blood pressure

  • Located at carotic sinus and aortic arch

  • Detects tension or stretch in the walls of these blood vessels

  • Blood pressure decreases → frequency of impulses produced by baroreceptors decreases

    • results in increased heart rate and vasoconstriction

Chemoreceptors

• Detect chemicals or chemical changes

• Binds to particular chemicals in the extracellular fluid

• Membrane of sensory neuron becomes depolarized → produces action potentials

• Used in senses of taste and smell

• Important in monitoring the chemical composition of blood

    pH —

• Peripheral chemoreceptors

  • found in aortic and carotic bodies

  • sensitive to the pH of plasma

• Central chemoreceptors

  • Found in the medulla oblongata of the brain

  • Sensitive to the pH of cerebrospinal fluid

• Increased CO2 in blood → Lowers pH

  • Stimulates respiratory control center

Electromagnetic receptors

• React to heat and light energy

Integration by CNS

• Sensory information:

  • spinal cord → brain (by ascendingg pathways)

  • Directly to brain stem (by cranial nerves)

• Visceral reflex integrated in brain stem/spinal cord - usually dont reach conscious perception

• Perceptual threshold

• Each major division of the brain processes 1+ types of sensory information

  •    See image:

    

    Key points:

  • Most sensory pathways project to the thalamus

    • Thalamus modifies + relays info to cortical centers

  • Equilibrium pathways → project to cerebellum

    

    Key points:

  • Sensory pathways synapse in the thalamus

  • Sensations are perceived in the primary somatic sensory cortex

Class Notes 1/12/2026

Recitation: Focus on identifiying types of neurons

Homework: Due next week (Monday - 1/19)

(In this lecture we’ll focus on) Receptor types we’re using over and over again when it comes to regulation and moderation → mostly mechanoreceptors, chemoreceptors, etc.