biol 642 lecture 2012 so ma to sensory i

8/2/2019 BIOL 642 Lecture 2012 So Ma to Sensory I

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Somatosensory processes

Key Ideas

A. Sensory receptors convert stimulus energy to electrical energy within thenervous system (action potentials). A process called stimulus transduction.

B. Receptor potential: The electrical signal produced within a sensoryneuron by a stimulus. The amplitude and duration of the receptor potential isgraded.

C. Modality specific: Sensory receptor neurons tend to be responsive to aspecific type of stimulus or stimulus modality; therefore, stimulation of sensoryneuron is a reliable indicator of stimulus modality. This is known as labeled line

coding. Stimulation of a sensory neuron either electrically or by a normalstimulus is always interpreted in the same way.

D. Receptive fields: the area of skin innervated by a neuron in whichstimulation will drive a response in that neuron


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Decussation: crossing of

the fibers associated with

a pathway from one side of

the body to the other


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1. Stretch receptors contained in muscle spindles fibers detect stretchof the muscle. Essentially, deformation of the plasma membrane of

receptor neuron physically pulls open ion channels in the

membrane, allowing ions to enter the cell and depolarizing it .


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There are several different types of

sensory receptor neurons

involved in somatosensation.

Each, except some multimodal

neurons involved in nocioception,

are myelinated.

A: Meissner corpuscle

B: Merkel disk

C: Pacinian corpuscle

D: Ruffini corpuscle

E: Free nerve endings (pain)

SA I (Merkel)

The distribution of the different types of mechanoreceptors is not

uniform over the surface of the hand. The more dense the stipples, the

more more dense the distribution of the receptors.


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Somatosensory neurons respond

differently to the same stimulus. The

pattern of action potentials in

response to a given stimulus can be

either continuous or transient.

Reponses can even be generated inresponse to the onset and offset of the

stimulus, but not to the continued

presence of the stimulus.

Merkels disk

Meissners corp.

Cells have receptive

fields. These

correspond to the

areas on the skin

surface over which a

stimulus can induce

a response in a

specific

somatosensory

neuron. The size of

the receptive fielddiffers for different

types of

somatosensory

neurons.


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The greater the number ofreceptors and the smaller

the size of the receptive

field, the greater the

resolution of the sensory

process. That is, the

smaller the receptive

field, the greater the

acuity of the sensory

process (the ability to

discern that pressure on

two points on the skinsurface are distinct from

one another.


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biol 642 lecture 2012 so ma to sensory i

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