PSB3340 EXAM 3: CH 8 General Principles of Sensory Processing

How is the notion of Five Senses challenged from the neurobiological perspective?

• Each sensory processes multiple features of one stimulus

• Each sensory system has multiple types of sensory receptors

• Example: pressure, temperature, balance, pain, proprioception

What are the submodalities of somatosensation?

• Touch

  • pressure, vibration, and texture

• Proprioception

  • sense of body position and movement

• Temperature

  • detects hot and cold

• Pain (Nociception)

What types of sensation are processed from the inner ear

• Auditory

  • sound waves

  • cochlea

  • hair cells in the organ of corti convert vibrations to electrical signals

  • signals travel auditory nerve to brain

• Vestibular (Balance)

  • head movements and position

• both info is sent to the vestibulochochlear nerve (cranial nerve VIII!

Distinguish sensory receptors and neurotransmitter receptors.

• Sensory receptors detect specific physical stimuli

  • Don’t have axons, have cell bodies that synapse on dendrites or cell bodies of other neurons

  • convert stimuli into eletrical signals thru transduction

• Neurotransmitter receptors detect chemical signals released by neurons

  • mediate communication between neurons by initiating post synaptic potentials

What is meant by sensory salience?

• How noticeable or attention grabbing a particular stimulus is to the sensory systems

• ex: brighter lights, unexpected stimuli,etc

What is the Doctrine of Specific Nerve Energies?

• Johannes Muller hypothesized that Each sensory nerve, no matter how it is stimulated, produces its own specific type of sensation.

• concluded that the brain is funcitonally divided and specific nerves convey specific types of info

• all sensory info is eventually encoded as action potentials

• For example:

  • Stimulating the optic nerve (even by pressure or electricity) will cause you to see light (a visual sensation), even if no light is present.

  • Stimulating the auditory nerve will produce a sound sensation.

Do sensory receptors fire action potentials? Explain

✅ Some do fire action potentials directly:

• These receptors generate action potentials themselves, especially in unipolar neurons (e.g., mechanoreceptors in skin or olfactory receptors).

• They convert a stimulus into an electrical signal called a receptor potential, and if it's strong enough, it triggers an action potential that travels along the sensory neuron's axon to the CNS.

🛑 Others do not fire action potentials directly:

• These receptors (e.g., photoreceptors in the retina, hair cells in the ear) don’t fire action potentials.

• Instead, they produce graded potentials (like depolarization or hyperpolarization) and release neurotransmitters to activate adjacent neurons, which then fire action potentials.

In general terms, how does sensory information reach the brain?

1. reception: absorption of physical energy by sensory receptor

   1. hair cells in your ear bend from sound waves

2. transduction: conversion of physical energy to electrochemical pattern in neurons

   1. touch receptors convert pressure into depolarization > action potentials

3. coding: turning the signal into a pattern of neural activity that tells your brain what the stimulus is

   1. brighter light causes more frequent firing in certain neurons

Define umwelt.

the way a species perceives the world

ex: dogs can hear higher frequencies than us

Do all sensory modalities occupy brain regions equally in size? Explain

Sensory modalities do not take up equal brain space. The brain allocates more space to senses and body parts that are more important or require more precise processing.

How do neurons encode stimulus frequency?

• Neurons encode frequency (like the pitch of a sound or the rate of a flickering light) by:

  • Phase locking: Neurons fire in sync with each wave cycle (used in hearing).

  • Population coding: Different neurons are tuned to specific frequencies — kind of like channels on a radio.

✅ Example: In the cochlea, different parts respond to different sound frequencies — high pitch = base of cochlea, low pitch = apex.

How do neurons encode stimulus intensity?

• range fractionation: different receptor cells are “specialists” in particular segments on an intensity scale

• more intense stimuli leads to more action potentials firing per second

How do neurons encode stimulus location?

• position of excited receptors on sensory surface

  • if a bug is on ur back, a receptor there will get excited

  • receptor pathways convey a specific position (labeled lines)

  • cells at all levels of the nervous system are arranged in an orderly, maplike manner

• relative time of arrival of the stimulus at the two receptors, or the relative intesity is directly related to location of stimulus

• comparing inputs of multiple receptive fields inputs

What is a receptive field?

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

Function of receptive field

1. localize stimuli: where is it coming from

2. discriminate detail: close apart

3. filter sensory input: analyze compelx stimuli, some receptive fields respond best to specific shapes, angles, or directions of motion

What is lateral inhibition?

Interconnected neurons inhibit their neighbors, enhancing contrast at the edges of regions

Whats the function of lateral inhibition

Sharpens the acuity of sensory recognition

Describe the mechanisms of adaptation to a stimulus

1. receptors become less sensitive and stop firing action potentials

2. neuron slows it firing rate cause ion channels change, affecting firing

3. thalamus or cortex may inhibit the sensory input when its no longer meaningful

Hierarchical processing

• sensory info is processed in stages w each stage handling increasingly complex features of the stimulus

• spinal cord > brainstem > thalamus > primary sensory cortical areas to nonprimary sensory cortical areas or nonprimary sensory cortical areas

Which receptors show slow or no adaptation to a stimulus?

Tonic

they keep firing as long as the stimulus is present

detecting duration

ex: pain, pressure, proproception

Which receptors undergo rapid adaptation

Phasic

respond quickly at the beginning or end of a stimulus

then stop firing even if stimulus continues

touch, smell, temp

why do organisms adapt to sensory stimulus exposure

so we dont get overstimulated

describe plasticity in cortical maps

brains ability to reorganize and adapt the structure and function of its cortical areas in response to experience, learning, injury, or environmental changes

ex: monkey experiment where their somatosensory input got bigger

Describe the pathways that process sensory information

Sensory information enters the CNS through the brainstem or spinal cord and then reaches the thalamus. The thalamus transmits the information to the cerebral cortex; the cortex directs the thalamus to suppress some sensations. Primary sensory cortex swaps information with nonprimary sensory cortex. This organization is present in all sensory systems except smell, which bypasses the thalamus, going directly to cortex

Describe the organization of somatosensory inputs through the dorsal column system

1. Feel it → Receptors

• Fine touch, pressure, proprioception

• Uses mechanoreceptors/proprioceptors

2. Climb it → Dorsal Columns (1st-order neurons)

• No synapse yet

• Climb up spinal cord on the same side (ipsilateral)

• Two tracks:

  • Gracilis = Ground (legs/lower body)

  • Cuneatus = Ceiling (arms/upper body)

3. Flip it → Medulla (2nd-order neurons)

• Synapse at nucleus gracilis/cuneatus

• FLIP sides here! (Decussation = crossing over)

• Now it's contralateral

4. Ship it → Medial Lemniscus → Thalamus

• Axons ride the medial lemniscus through the brainstem

• Synapse at the VPL of the thalamus

5. Sense it → Somatosensory Cortex

• Final stop: Postcentral gyrus

• Body map = Sensory homunculus

  • Medial = legs

  • Lateral = face/hands

Describe the organization of somatosensory inputs through the ventral spinothalamic tract

1. Receptors (Feel it)

• Mechanoreceptors in the skin detect crude touch/pressure.

• Signals travel via Aδ and C fibers (slower than dorsal column fibers).

2. First-Order Neurons (Enter spinal cord)

• Enter via the dorsal root of the spinal cord.

• Synapse immediately in the dorsal horn (unlike dorsal column where they ascend first).

3. Second-Order Neurons (Cross it)

• After synapsing, these neurons decussate (cross over) in the spinal cord (usually within 1–2 segments).

• They then ascend contralaterally in the ventral (anterior) funiculus as the ventral spinothalamic tract.

4. Thalamus (Relay station)

• The tract ascends to the ventral posterolateral nucleus (VPL) of the thalamus.

• Still somatotopically organized: lower body more lateral, upper body more medial (opposite of cortex layout).

5. Third-Order Neurons (To the brain!)

• From the thalamus, third-order neurons project to the primary somatosensory cortex in the postcentral gyrus.

Epicritic Touch

-fine and discriminative touch

-proproception

What’s included in epicritic touch

Pacinian corpuscle: sudden, deep pressure
- Meissner corpuscle: sudden, light touch
- Ruffini corpuscle: gradual, stretch
- Merkel’s Disk: gradual, light touch
- proprioceptors (muscle spindles, GTOs,
joint proprioceptors)

Protopathic touch

non discriminating, pain, and temperature

whats included in protopathic touch

temp and pain, free nerve endings that respond to tissue damage, release intracellular K+ from nerve itself, bradykinins, histamine due to damage

ascending pain fibers release substance P (and others)
- analgesia mediated by descending projections from PAG, raphe etc.
- descending analgesic action mimicked by opiate drugs
- pain may also sensitize (inflammation, neuralgia)

meissener’s corpuscles

• Location: Dermal papillae (fingertips, palms, lips)

• Stimulus: Light touch & low-frequency vibration

• Adaptation: Rapid

• Function: Detect texture & fine touch, especially changes over time

merkel’s discs

• Location: Epidermis (especially fingertips)

• Stimulus: Sustained pressure & texture

• Adaptation: Slow

• Function: Detect shape, edges, and steady touch (e.g., reading Braille)

pacinian corspucles

• Location: Deep dermis & subcutaneous tissue

• Stimulus: Deep pressure & high-frequency vibration

• Adaptation: Very rapid

• Function: Detect sudden changes or vibration (e.g., power tools, phone vibrations)

ruffini endings

• Location: Deep dermis, ligaments, tendons

• Stimulus: Skin stretch

• Adaptation: Slow

• Function: Detect continuous pressure and stretching (important for grip adjustment)

hair follicle receptors

• Location: Wrapped around hair follicles

• Stimulus: Hair displacement

• Adaptation: Rapid

• Function: Detect light touch via hair movement (e.g., a breeze or bug on skin)

What is the current knowledge about the stimuli to which pain receptors respond?

responsive to tissue damage, release of intracellular K+ from nerve itslef, bradykinins, histamine

Describe descending pathways for analgesia (pain relief)

1 activate periaqueductal gray to process both emotional and sensory info related to pain

2 pag neurons signal rostral ventromedial medulla, integrates pain info and coordinates the modulation of spinal pain transmission thru two groups of neurons

-on cells: facilitate pain transmission by increasing nociceptive signaling

-off cells: inhibit pain transmission by suppressing nociceptive signaling

3 rvm sends descending projections to the spinal cord that release serotonin and norepinephrine

4 release of serotonin and norepinephrine interacts w/ specific receptors on primary nociceptive neurons

transient receptor potential vanilloid type 1 (TRPV1):

a receptor that binds to capsaicin (spicy chemical) to transmit the burning sensation from chili peppers and normally detects sudden increase in temp

TRPM8: (cool-menthol receptor)

• 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.

  • responds to cool temps rather slowly

  • located on small C fibers

Describe the range of treatments that are currently used to control pain

social rejection and pain

• social rejection activates the anterior cingulate cortex and that the extent to which a person is upset by rejection correlates with activation of this region

• more distress or feelings of rejection the participant felt, the greater the activity in anterior cingulate

strategies to alleviate pain

• cannabis

  • when endogenous cannabinoid receptors and free nerve endings of nociceptors are stimulated by Cannabis sativa, pain is reduced significantly

• opiates

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

    • brain will release substances that work like opiates