Receptors and Somatic Sensations Flashcards

Practice flashcards covering sensory receptors, mechanoreceptors, nerve fiber classification, and the mechanisms of sensory transduction based on the lecture notes.

What is the definition of a sensory receptor?

Sensory receptors are transducers that convert different forms of energy in the environment into action potentials (AP).

What comprises a sense organ?

A sense organ consists of a receptor and the non-neural cells that surround it.

What are the three categories of general senses?

(a) Exteroceptive senses (external world information), (b) Proprioceptive senses (body/limb position and movement), and (c) Interoceptive senses (internal organ stimuli).

Which sensory modality is the only exception to the obligate relay in the thalamus?

Olfaction (smell).

Describe the three-neuron pathway for sensations reaching the cortex.

The first-order neuron goes from the receptor to the spinal cord or medulla; the second-order neuron ascends to the thalamus; and the third-order neuron relays the signal from the thalamus to the sensory cortex.

How are mechanoreceptors defined and what are some examples?

They detect mechanical deformation (compression or stretching) of the receptor or adjacent tissues. Examples include Merkel's discs, Meissner's corpuscles, Pacinian corpuscles, Ruffini corpuscles, and hair-follicle plexuses.

Which cutaneous corpuscular receptor is categorized as nonencapsulated?

Merkel's disc.

Match the mechanosensitive afferent types (FA1, SA1, SA2, FA2) to their corresponding receptors.

FA1 terminates in Meissner's corpuscles; SA1 terminates in Merkel's discs; SA2 terminates in Ruffini's endings; FA2 ends in Pacinian corpuscles.

How much more common are cold-sensitive spots compared to heat-sensitive spots in the skin?

There are $4-10$ times more cold-sensitive spots than heat-sensitive spots.

What is the location and detection function of Meissner's corpuscles?

Found in nonhairy (glabrous) skin, fingertips, and lips; they detect light touch, low-frequency vibration, and texture.

What are Merkel's discs, and where are they located?

They are expanded tip receptors (forming Iggo dome receptors) located in fingertips and hairy skin parts; they detect steady-state touch and texture.

What is the specific function of Pacinian corpuscles?

Located in the dermis and facial tissues, these lamellated receptors are rapidly adapting and detect pressure and tissue vibrations.

In proprioception, what is the difference between static position sense and dynamic proprioception?

Static position sense is the conscious perception of body part orientation; dynamic proprioception (kinesthesia) is the sense of the rate of movement.

How many nuclear bag and nuclear chain fibers are typically found in a muscle spindle?

Each spindle usually contains $1-3$ nuclear bag muscle fibers and $3-9$ nuclear chain fibers.

What is the difference between primary and secondary sensory nerve endings in muscle spindles?

The primary ending ($17\,\mu m$) is excited by both nuclear bag and chain fibers and responds to both length (static) and rate of change (dynamic). The secondary ending ($8\,\mu m$) is usually only excited by nuclear chain fibers and responds to length (static).

Define Teloceptors and provide examples.

Teloceptors are concerned with stimuli at a distance. Examples include rods and cones for vision, the olfactory bulb for smelling, and the organ of Corti for audition.

What are some examples of interoceptors (visceroceptors)?

Baroreceptors (aortic arch/carotid sinus), vagal nerve endings (lungs/pharynx), thermostatic cells (hypothalamus), chemoreceptors (carotid/aortic bodies), and osmoreceptors.

What is the difference between rapidly adapting (phasic) and slowly adapting receptors?

Rapidly adapting receptors (e.g., Pacinian corpuscles) detect changes in stimulus strength; slowly adapting receptors (e.g., muscle spindles, Mercy’s discs) detect continuous stimulus strength.

Which nerve fiber types are associated with Muscle Spindles and Golgi Tendon Organs?

Muscle spindle primary endings (annulo-spiral) use $Ia$ ($A\alpha$); Golgi Tendon Organs use $Ib$ ($A\alpha$); Muscle spindle secondary endings (flower-spray) use Type $II$ ($A\beta$).

Identify the diameter and conduction velocity for General Classification Type $A\alpha$ fibers.

Diameter: $12\text{ – }30\,\mu m$; Conduction velocity: $70\text{ – }120\,m/s$.

Describe the properties of Group C nerve fibers.

Smallest diameter ($0.3\text{ – }1.3\,\mu m$), slowest conduction velocity ($0.7\text{ – }2.3\,m/s$), and long spike duration; they transmit pain, temperature, tickle, and itch.

What is the 'Label line principle'?

A principle stating that nerve fibers are specific for transmitting only one modality of sensation because each nerve tract terminates at a specific point in the CNS.

Define the 'Law of Projection'.

No matter where a sensory pathway is stimulated, the conscious sensation produced is referred to the location of the receptor.

Where is the first action potential generated in a cutaneous sensory neuron?

At the first node of Ranvier (rather than the axon hillock).

What is the 'adequate stimulus' for a receptor?

The particular form of energy to which a receptor is most sensitive and has the lowest threshold.

How does the receptor potential (RP) differ from an action potential (AP)?

The RP is a graded, non-propagated, localized change that does not obey the all-or-none law, whereas the AP is propagated and obeys the all-or-none law.

Which nerve fiber types are most susceptible to hypoxia, pressure, and local anesthetics?

Hypoxia: Group B; Pressure: Group A; Cocaine/Anesthetics: Group C.

How do mechanoreceptors achieve adaptation?

By readjustment in their structure or by accommodation (inactivation of $Na^+$ channels).

Identify the four classes of low-threshold mechanosensitive afferents in the skin.

FA1 (Meissner's corpuscles), FA2 (Pacinian corpuscles), SA1 (Merkel's discs), and SA2 (Ruffini's endings).