Touch :) [done]

Describe the structure of sensory neurons and how is this different from a stereotypical neuron?

• sensory neurons are pseudounipolar meaning that they do not have dendrites, and instead have a single axon that bifurcates into one bilateral neuron that projects to the CNS and one that projects to the skin

• This means that sensory information is detected by the axon rather than a dendrites like in a stereotypical neuron.

• This it’s important because due to the extreme length of these cells, axons and AP propagation of the signal is way more efficient than graded potentials and passive depolarization that is used in stereotypical neurons.

What are mechanoreceptors and how do they work?

• specialized ion channels that change their shape in response to stretching of the membrane to open and allow ions to flow into the cell

List the 5 different encapsulated sensors

• hair follicle endings

• Merkel cells

• Meissner’s corpuscles

• Pacinian corpuscles

• Ruffini’s endings

Where are hair follicle endings located, are they rapid or slowly adapting and what is their function?

• dermis

• Rapid

• Detect movement of hairs

Loco, rapid/slowly adapting, and function merkel cells

• base of epidermis

• Slowly

• Sense shape and texture of objects

Meissner’s corpuscles loco, rapid/slowly adapting, function

• top of dermis

• Rapid

• Important for detecting light touch, movement or objects rubbing against skin, and for maintaining grip

Pacinian corpuscles loco, rapid/slowly adapting, function

• lower dermis and subcutaneous layer

• Rapid

• Important for detecting deep pressure and use of tools

Raffini’s endings loco, slowly or rapid adapting, function

• deep in dermis

• Slowly adapting

• Important for detecting skin stretch

How does the amount of myelination (or type of axon fiber) relate to the function of different sensory neurons?

• more myelination is needed for sensory information that is critical for functioning (proprioception & movement)

• Lower (or no) myelination is seen in fibers used to communicate pain to protect against over stimulation of sensory information and pain signals that could send the body into shock when not needed

How do we perceive pain and how does this differ from how we perceive tactile information?

• we perceive pain through nociceptors on free nerve endings (unencapsulated), only activated by intense stimuli and transmitted through slower fibers

• Touch has encapsulated endings and fast fibers

• This is because we don’t want to perceive everything we touch as painful

How is temp perceived?

• through TRP (transient receptor potential) channels that open/close in a response to specific temperature

• Found on free nerve endings and projected to CNS through slower fibers like pain

• This is because we do not need to respond quickly to temperature fluctuations typically

Why might some plants evolve to contain used that activate TRP channels

• defense mechanims against mammals and fungi while still allowing birds to consume their fruit

• Their fruit might lead to a sensation of pain like in chili peppers (capsaicin)

• Capsaicin does not activates bird’s TRP channels and so they feel no burning sensation from it