Sensory receptors and exteroception - Restrepo

Question 1

What are the two types of receptors that sense vibration touch? What is the receptive field size for each? Are these considered slow or fast adaptation?

Answer 1

Fast adapting receptors sense vibratory touch. These are the Meissner corpuscle and the Pacinian corpuscle. THe Pacinian corpuscle resides deeper in the tissue (P-profunda) and has a larger receptive field than the meissner corpuscle.

Fast adapting neurons fire when pressure is applied, and again when pressure is released, which is why they can sense vibration.

Question 2

What do Ruffini’s endings and Merkel discs sense? What is the receptive field size of each? Is this a slow or fast adapting receptor? What is the AP pattern when activated?

Answer 2

Ruffini endings reside deeper in the tissues along with the pacinian corpuscles, and hence have a relatively large receptive field. They sense how the skin is stretched (shear–> grip, for example). APs are fired consistently when these endings are stetched.

Merkel discs detect fine touch of some type. They are also slow adapting, but with a small receptive field.

Question 3

What happens to the rod photoreceptor cells in the retina? How are they stimulated and activated?

Answer 3

The rod cells do not fire APs. Their resting membrane potential is -40mV due to high levels of cGMP which keep a gated cation channel open. When the photon receptor is activated (conversion to trans retinal), cGMP is degraded and the cell HYPERPOLARIZES, leading to DECREASED NEUROTRANSMITTER RELEASE which the brain interprets as light.

Question 4

Describe the myelination, conduction speed, and name the fiber that carries signals from muscle and tendon.

Answer 4

Aα. Heavily myelinated, very fast (60-120m/s)

Question 5

Describe the myelination, conduction speed, and name the fiber that carries signals from mechanoreceptors in the skin.

Answer 5

Aβ. Myelinated, fast (30-60 m/s).

Question 6

Describe the myelination, conduction speed, and name the fiber that carries sharp pain and cold temperature.

Answer 6

Aδ. Lightly myelinated, not so fast. (4-30 m/s)

Question 7

Describe the myelination, conduction speed, and name the fiber that carries warm temperature, burning pain, itch, crude touch

Answer 7

C. Unmyelinated (0.4-2 m/s)