Lecture 9 - Touch and sound

Somatosensory system

Detects touch, pressure, vibration, temperature, pain, and body position (proprioception)

Mechanoreceptors

Specialized receptors for touch, pressure, vibration

Why so many types? Different receptors detect different pressures, vibrations, textures, and speeds

Open nerve endings

Not mechanoreceptors; detect pain and temperature;

Hot vs cold receptors respond to different temperature ranges

Receptive fields (somatosensory)

Area of skin a neuron responds to

Spatial scale = size of receptive field
Temporal scale = adaptation speed (fast vs slow adapting neurons)

Primary somatosensory cortex (S1)

Processes touch info from body; somatotopically organized

Somatotopic map / Homunculus

Map of body in cortex; larger areas for body parts with more sensory receptors (hands, lips)

Anterior cingulate cortex (ACC)

Processes pain; involved in pain perception & inhibition

Somatosensory pathway: pain vs touch

Touch → receptor → spinal cord → thalamus → S1
Pain → receptor → spinal cord → thalamus → S1 + ACC

Motor cortex

Works with somatosensory system for movement control

Auditory system

Detects air pressure waves and converts them to neural signals

Outer ear

Funnels & filters sound waves toward eardrum

Middle ear

Contains ear drum & ossicles (malleus, incus, stapes); transmits air waves → fluid waves in cochlea

Inner ear

Converts fluid waves → neural signals via hair cells in cochlea

Cochlea

Spiral-shaped organ; contains basilar membrane, tectorial membrane, Organ of Corti, and hair cells (mechanoreceptors)

Basilar membrane

Vibrates at different locations depending on frequency → enables tonotopy

Tectorial membrane

Membrane that hair cells move against, triggering mechanoreceptors

Hair cells

Mechanoreceptors in cochlea; convert mechanical motion → neural signals

Organ of Corti

Houses hair cells; sits on basilar membrane

Tonotopic map

Organization of frequency along cochlea and auditory cortex

Auditory pathway

Cochlea → brainstem → thalamus → primary auditory cortex (A1)

Primary auditory cortex

Processes sound info; organized by frequency (tonotopy)

Hertz (Hz)

Unit of frequency; cycles per second; used to measure pitch of sound