Human Phys - Chapter 11: Sensory Physiology

1. What is the basic sensory pathway?

Stimulus → transduction → receptor potential → action potentials → brain → perception

• Transduction = converting a stimulus into an electrical signal

• Receptor potential = graded potential in the receptor

Easy: Stimulus → convert → graded → AP → perceive

Transduction

converting a stimulus into an electrical signal

Receptor potential

graded potential in the receptor

What is an adequate stimulus?

The type of stimulus a receptor responds to best.

Examples:

• Chemoreceptor → chemicals

• Mechanoreceptor → pressure/movement

• Thermoreceptor → temperature

• Photoreceptor → light

Easy: adequate stimulus = receptor’s favorite stimulus

Chemoreceptor

Chemicals

Mechanoreceptor

Pressure/movement

Thermoreceptor

temperature

Photoreceptor

Light

What is a receptive field?

The area where a stimulus can activate a sensory neuron.

Small receptive fields = more precise/sensitive

Large receptive fields = less precise

Easy: small field = sharp location

How does convergence affect two-point discrimination?

More primary neurons converging onto one secondary neuron → larger receptive field → worse ability to distinguish 2 nearby points.

Easy:

More convergence = less precision

Less convergence = more precision

What 4 properties of a stimulus does the CNS encode?

Modality = what kind

Location = where

Intensity = how strong

Duration = how long

Easy: M-L-I-D

Your professor basically organizes the whole section around these four.

What is labeled-line coding?

Each sensory pathway stays associated with a specific type of sensation.

Example: activating a cold pathway is interpreted as cold.

Easy: The pathway tells the brain WHAT it is.

Your professor specifically notes that modality and receptive-field information stay organized as signals travel toward the brain.

What is lateral inhibition?

The strongest sensory pathway inhibits neighboring pathways, making the stimulus location easier to pinpoint.

Easy: Strongest signal tells its neighbors to shut up. 😭

How is stimulus intensity coded?

Stronger stimulus causes:

• a larger receptor potential

• higher frequency of action potentials

• often activation of more receptors

Important: APs themselves do not get bigger.

Easy: Stronger = bigger graded potential + faster AP firing

Tonic vs phasic receptors?

Tonic = slowly adapt and keep firing while stimulus is present.

Phasic = rapidly adapt and mainly respond when the stimulus changes.

Easy:

Tonic = stays ON
Phasic = detects CHANGE

Tonic

slowly adapt and keep firing while stimulus is present.

Stays ON

Phasic

rapidly adapt and mainly respond when the stimulus changes.

detects CHANGE

11.2 — Somatic Senses Flashcards

What are the 4 somatic senses?

• Touch

• Proprioception

• Temperature

• Nociception

Easy: touch, position, temp, pain/itch

Where are primary somatic sensory neuron cell bodies?

In the dorsal root ganglia.

Easy: DRG = sensory cell bodies

Where do pain, temperature, and coarse touch cross?

In the spinal cord.

Easy: pain/temp cross early

Where do fine touch, vibration, and proprioception cross?

In the medulla.

Easy: fine touch crosses later

Why does the left side of the body go to the right brain?

Because sensory pathways cross the midline.

Easy: body side → opposite brain side

What is the basic somatosensory pathway to the cortex?

Primary neuron → secondary neuron → thalamus → tertiary neuron → somatosensory cortex

Easy: 1 → 2 → thalamus → 3 → cortex

What does the somatosensory cortex do?

It tells the brain where the sensation came from.

More sensitive body parts get more cortex space.

Easy: more sensitive = more brain space

What do Pacinian corpuscles detect?

Vibration

They adapt quickly.

Easy: Pacinian = vibration

What do Meissner corpuscles detect?

Light touch / stroking

Easy: Meissner = light touch

What do Ruffini corpuscles detect?

Skin stretch

Easy: Ruffini = stretch

What do Merkel receptors detect?

Steady pressure and texture

Easy: Merkel = pressure + texture

What are nociceptors?

Free nerve endings that detect harmful or damaging stimuli.

They can respond to:

• chemical

• mechanical

• thermal stimuli

Easy: nociceptor = damage detector

What is fast pain?

• sharp

• well localized

• carried by Aδ fibers

• Aδ fibers are myelinated

Easy: Aδ = fast + sharp

What is slow pain?

• dull

• diffuse

• carried by C fibers

• C fibers are unmyelinated

Easy: C = slow + dull

Which fiber is linked to itch?

C fibers

Histamine in the skin can activate C fibers and cause itch.

Easy: C = slow pain + itch

What is referred pain?

Pain from an internal organ that feels like it comes from somewhere else on the body.

Easy: organ hurts → brain feels it somewhere else

Why does referred pain happen?

Visceral and somatic pain signals converge onto the same pathway, so the brain can confuse where the pain came from.

Easy: same pathway = wrong location

What is a classic referred pain example?

Heart pain can be felt in the left arm/chest area.

Easy: heart → left arm

How can touch reduce pain?

Touch signals can help inhibit pain signaling in the spinal cord.

Easy: rub it → pain feels less

Your professor literally notes this on the slide.

Why can pain cause sweating, nausea, or other body reactions?

Pain pathways also connect with the hypothalamus and limbic system.

Easy: pain affects emotion + body responses