Somatosensory System

Where is the somatosensory cortex located?

in the post central gyrus

Sensory Neurons aka Receptor Neurons aka Sensory Afferents

perform sensory transduction

convert stimuli into electrical signals

Can a stimulus be detected without the presence of a receptor?

no bruh

Somatosensory System

info about what body is doing, where it is, and what’s going on in the environment

Where does the somatosensory system encode and process information from?

skin, muscles, viscera (internal organs)

What are Somatosensory Afferents/Neurons?

pseudounipolar neurons with soma, axon, NO DENDRITES

How does information travel along somatosensory afferent’s axon?

2 directions:

towards spinal cord

towards skin/muscle

What determines the size of receptor field and type of stimulus that activates a neuron?

the type of receptor ending

2 Types of Receptor Endings

1. Mechanoreceptors

2. Free Nerve Endings

What stimuli do mechanoreceptors respond to?

touch, vibration, pressure

mechanical stimulus

What stimuli do free nerve endings respond to?

pain, temp, itch

Receptive Field

chance of APs firing depends on size and type of receptor ending

smaller receptive field = more spatial accuracy

Spatial Accuracy

how well can you tell location of stimuli distinctly from one another

Two-Point Discrimination

ability to distinguish between two different stimuli

Why do smaller receptive fields have better spatial accuracy?

smaller field = more precise in detecting stimuli

fingers have smallest receptive fields + highest spatial accuracy

3 Steps of Mechanoreceptor Sensory Transduction

1. skin stretches with mechanical stimuli

2. allows Na+/Ca2+ channels to open and ions flow through

3. afferents are depolarized, APs fire

What is a Receptor Potential aka Graded Potential?

initial touch = graded/receptor potentials

When do APs fire?

when graded potential is strong enough due to strong stimuli

How do we detect the difference between stimuli of differing intensities? Why does a light touch feel different than a firmer touch?

1. frequency of APs firing due to higher/lower intensity of touch

2. receptor field size

What does it mean when there’s a more intense touch?

more APs are firing

Slowly Adapting Receptors

continue to respond throughout entire duration of stimulus

Rapidly Adapting Receptors

respond to ON/OFF of stimulus but not its continued duration

respond when stimulus is added + when stimulus is removed

Proprioception

information about limb and body position of in space

essential for accurate movement

3 Classes of Proprioceptors

1. Muscle Spindles

2. Golgi Tendon Organs

3. Joint Receptors

Muscle Spindles

found in skeletal/cardiac muscles

active when stretched (fire more APs)

Golgi Tendon Organ

in the tendon

active when contracted (fire less APs, still depolarize)

Joint Receptors

used to detect angle in which joints move

Somatotopic Maps

more circuitry devoted to more important functions

(more circuitry for hands + facial expressions)

Cortical Remapping

circuitry is redistributed after amputation