Somatosensory + Processing

What is sensation?

The neural process of receiving and processing stimuli.

What is perception?

What your brain makes of the information it receives.

What is the key distinction between sensation and perception?

Sensation concerns receiving/processing sensory stimuli, whereas perception concerns the brain’s interpretation of that sensory information.

Why can sensation and perception differ?

The same stimulus does not always produce the same experience or perception.

What five sensory-system tasks are visibly listed on the slide?

Transduction, transmission, inference, deduction, and follow-up.

What is transduction in a sensory system?

Converting information into neural signals.

What is transmission in a sensory system?

Passing sensory information on to the brain.

What question is addressed by inference?

“Did something just happen?”

What questions are addressed by deduction?

“What was it?” and “Where was it?”

What question is addressed during sensory follow-up?

Whether to pay more or less attention.

What is the complete sequence of sensory-system tasks shown?

Transduction → transmission → inference → deduction → follow-up.

What are the four qualities of sensory information?

Modality, intensity, duration, and location.

What does modality describe?

What type of sensation it is.

What examples of sensory modalities are written in the annotation?

Touch, pressure, vibration, pain, temperature, and proprioception.

What does intensity describe?

How strong the stimulus/sensation is.

What does duration describe?

How long the stimulus lasts.

What does location describe?

Where the stimulus happened.

What five factors influence the success or failure of sensory processing?

Fatigue, adaptation, sensitization, overlap/redundancy, and damage/overload.

How can fatigue influence sensory processing?

When you are tired, it can change your perception of sensory information.

What is the basic purpose of sensory adaptation according to the annotations?

It allows the brain to focus on what is important and new rather than continuously focusing on an unchanging stimulus.

What everyday example of sensory adaptation is written on the slide?

When you walk outside after being in a dark room, your eyes feel weird at first but then adapt to the light.

Why should sensory systems not adapt to everything?

Because we should not adapt to a dangerous stimulus.

What is sensitization?

A very strong or exaggerated response to a stimulus.

What is overlap/redundancy in sensory processing?

Multiple or repeated sensory inputs can provide overlapping information.

According to the annotation, what happens when overlap/redundancy occurs more often?

The more often a stimulus signal occurs, the more likely it is to be noticed or detected.

How can damage/overload interfere with sensory processing?

Too much going on- overstimulated

What two major CNS structures are shown between peripheral sensory input and the thalamus/cortex?

The spinal cord and brainstem.

Through what ganglion does mechanical sensation from the face travel?

The trigeminal ganglia.

Through what ganglia does mechanical sensation from the body travel?

The dorsal root ganglia.

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What type of receptors detect touch, pressure, and vibration?

Mechanoreceptors.

Which sensory fiber type is associated with touch, pressure, and vibration?

Aβ (A-beta) fibers.

Complete the modality chain for touch/pressure/vibration.

Mechanical stimulus → mechanoreceptors → skin → Aβ fibers.

What types of stimuli are associated with pain in the handwritten notes?

Chemical, thermal, and physical stimuli.

What receptor type is associated with pain?

Nociceptors.

What type of stimulus is associated with temperature sensation?

A thermal stimulus.

What receptor type is associated with temperature?

Thermal receptors.

Which sensory fibers are associated with pain and temperature?

Aδ (A-delta) and C fibers.

Complete the pain classification shown in the notes.

Chemical/thermal/physical stimulus → nociceptors → skin → Aδ and C fibers.

Complete the temperature classification shown in the notes.

Thermal stimulus → thermal receptors → skin → Aδ and C fibers.

What sensory modality provides information related to muscles, spindles, and Golgi organs?

Proprioception.

What structures are listed under proprioception in the handwritten notes?

Muscle spindle and Golgi organ.

What type of receptors are associated with proprioception?

Proprioceptors.

Which fiber class is associated with proprioception in the handwritten notes?

Aα (A-alpha) fibers.

Complete the proprioception classification shown in the notes.

Muscle-related stimulus/stretch → proprioceptors → Aα fibers.

What functional problem is described for a person with a lesion affecting proprioception?

They may know how to perform certain actions but not know where the relevant body part is positioned.

What is sensory transduction?

The conversion of a stimulus into neural signals.

What form do all sensory fibers use to transmit nerve impulses?

Action potentials.

Do all sensory receptors have the same sensitivity to all sensory stimuli?

No. Different sensory receptors have differing sensitivities to different types of sensory stimuli.

What is a receptor potential?

A change in a sensory receptor’s membrane potential caused by receptor activation.

Give the sequence shown for sensory transduction at the receptor.

Stimulus activates receptor → ions move across the membrane → membrane voltage changes → receptor potential occurs.

How are receptor potential and action potential distinguished on this slide?

Receptor activation first produces a receptor potential/change in membrane potential, while sensory fibers transmit nerve impulses as action potentials.

What structural type are sensory neurons according to the annotation?

Pseudounipolar neurons.

What is structurally distinctive about a pseudounipolar sensory neuron?

It has one process that leaves the soma and splits into two branches.

Where are dorsal root ganglion sensory-neuron cell bodies located relative to the CNS?

In the dorsal root ganglia, outside the central nervous system.

Give the complete action-potential route through the pseudounipolar DRG neuron.

Initiates in distal process in the periphery → bypasses the cell body → propagates along the proximal process/axon → reaches synaptic terminal in the dorsal horn of the spinal cord.

What are the two possible structural forms of the distal section of a sensory axon?

It may be a bare nerve ending or be encapsulated by a receptor structure.

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Which fiber types are associated with nociceptors in the diagram?

Aδ/C fibers.

Which fiber type is associated with proprioceptors in the diagram?

Aα fibers.

Which fiber type is associated with mechanoreceptors in the diagram?

Aβ fibers.

What do the dorsal root ganglia contain?

The sensory neurons of the somatosensory system.

What is the functional direction of the dorsal root?

Afferent entry — sensory information enters.

What is the functional direction of the ventral root?

Efferent exit — motor information exits.

Compare dorsal and ventral roots by information direction and function.

Dorsal root = afferent sensory entry; ventral root = efferent motor exit.

Compare the ganglia shown for sensory information from the face versus the body.

Face → trigeminal ganglia; body → dorsal root ganglia.

How are sensory axons classified according to the slide?

According to their diameter.

What properties are governed/associated with sensory axon diameter?

Myelination and conduction velocity.

What general relationship connects axon size, myelination, and speed?

Larger sensory axons have more myelination and faster conduction than smaller axons.

What sensory function is associated with the largest and most myelinated afferents in the table?

Proprioception.

What receptor type is listed for proprioception?

Muscle spindle.

What afferent axon types are listed for proprioception?

Ia and II.

What axon diameter is listed for proprioceptive Ia/II afferents?

13–20 μm.

What conduction velocity is listed for proprioceptive Ia/II afferents?

80–120 m/s.

Which sensory function is associated with Aβ afferents?

Touch.

What receptor types are listed for touch in the table?

Mechanoreceptors but more specifically: Merkel, Meissner, Pacinian, and Ruffini cells.

What axon diameter is listed for Aβ touch afferents?

6–12 μm.

What conduction velocity is listed for Aβ touch afferents?

35–75 m/s.

What sensory functions are associated with Aδ fibers in the table?

Pain and temperature.

What receptor type is listed for Aδ pain and temperature afferents?

Free nerve endings.

What axon diameter is listed for Aδ fibers?

1–5 μm.

What conduction velocity is listed for Aδ fibers?

5–30 m/s.

What type of pain is associated with Aδ fibers in the annotation?

Initial, sharp pain.

How are Aδ fibers characterized in terms of size/myelination in the handwritten notes?

They are small and have low myelination compared with the larger sensory fibers.

What sensory functions are associated with C fibers in the table?

Pain, temperature, and itch.

What receptor type is listed for C fibers?

Free nerve endings.

What axon diameter is listed for C fibers?

0.2–1.5 μm.

What conduction velocity is listed for C fibers?

0.5–2 m/s.

What does the annotation say about myelination of C fibers?

They are the thinnest and have no myelin sheath.

What type of pain is associated with C fibers in the annotation?

Slow, dull, persistent pain.

Rank the sensory afferent groups shown from largest to smallest axon diameter.

Ia/II proprioceptive fibers → Aβ → Aδ → C.

Compare Aδ and C fibers in terms of pain sensation.

Aδ → initial/sharp pain; C → slow, dull, persistent pain.

What explains the general progression from fast proprioceptive signaling to slow C-fiber signaling in the table?

Decreasing axon diameter and myelination are associated with decreasing conduction velocity.

Match touch with its stimulus, receptor class, and fiber type.

Mechanical stimulus → mechanoreceptor → Aβ fiber.

Match pain with its receptor and fiber types.

Nociceptor/free nerve ending → Aδ and C fibers.