Neurophysiology 5

Question 1

What is the somatic nervous system?

Answer 1

Is traditionally considered a division within the PNS.
However, an important point is that somatic refers to a functional division, whereas peripheral refers to an anatomic division.
The somatic nervous system is responsible for our conscious perception of the environment and for our voluntary responses to that perception by means of skeletal muscles.
Peripheral sensory neurons receive input from environmental stimuli, but the neurons that produce motor responses originate in the CNS

Question 2

What is sensation?

Answer 2

Sensation is the activation of sensory receptor cells at the level of the stimulus.
Receptors are the cells or structures that detect sensations.
Stimuli in the environment activate receptor cells located in the PNS

Question 3

What is perception?

Answer 3

Perception is the central processing of sensory stimuli into a meaningful pattern.
Perception is dependent on sensation, but not all sensations are perceived

Question 4

What are sensory receptors?

Answer 4

A transmembrane protein receptor mediates a physiological change in a neuron, most often through the opening of ion channels or changes in the cell signaling processes.
Transmembrane receptors are activated by ligands. E.g., a molecule in food can serve as a ligand for taste receptors.
Other transmembrane proteins are sensitive to mechanical or thermal changes (not accurately called receptors).
Physical changes in these proteins increase ion flow across the membrane, and can generate a graded potential or an AP in the sensory neurons

Question 5

How are sensory receptors classified?

Answer 5

Structural classification:
Based on cell type and their position in relation to stimuli they sense.

Functional classification:
Based on thetransductionof stimuli, or how the stimulus (mechanical, light, or chemical) changes the cell membrane potential.

Question 6

Describe the specialized sensory receptors

Answer 6

Specialized sensory receptor cells (e.g. the photoreceptors of the eye) are:
located in specialized receptor organs,
produce receptor potentials,
contain synaptic specializations, and
release neural transmitters.

Specialized sensory receptors may be modified neurons (e.g. the photoreceptors and olfactory receptors) or modified epithelial cells (e.g. taste receptors and the auditory and vestibular hair cells).

Question 7

Explain the structural classifications of sensory receptors

Answer 7

Based on cell type
Can either be:
1. A neuron with afree nerve ending :: Dendrites are embedded in tissue that would receive a sensation. E.g. pain and temperature receptors in the dermis of the skin.
2. A neuron with an encapsulated ending:: The sensory nerve endings are encapsulated in connective tissue that enhances their sensitivity. E.g. lamellated corpuscles that respond to touch and pressure
3. A specializedreceptor cell :: Has distinct structural components that interpret a specific type of stimulus. E.g.photoreceptors in the retina

Based on Position (in Relation to Stimuli)
1. Exteroceptor: located to receive a stimulus in the external environment, e.g. the somatosensory receptors located in the skin.
2. Interoceptor: interprets stimuli from internal organs and tissues, e.g. receptors that sense BP changes in the aorta or carotid sinus.
3. Proprioceptor:located near a moving part of the body (e.g. a muscle) that interprets the positions of the tissues/joints as they move.

Question 8

Explain the functional classifications of sensory receptors

Answer 8

Based on Transduction of Stimuli
Of generally 3 types:
1. Ions and macromolecules that affect transmembrane receptor proteins when these diffuse across the cell membrane.
2. Physical variations in the environment that affect receptor cell membrane potentials.
3. Electromagnetic radiation from visible light. For humans, the only electromagnetic energy that is perceived by our eyes is visible light. Some other organisms have receptors that humans lack, such as the heat sensors of snakes, the ultraviolet light sensors of bees, or magnetic receptors in migratory birds

Based on Type of Stimuli Transduced
1. Chemoreceptor interprets chemical stimuli, such as an object’s taste or smell.
2. Osmoreceptorresponds to solute concentrations of body fluids.
3. Nociceptor interprets the presence of chemicals from tissue damage, or similar intense stimuli and this is felt as pain.
4. Mechanoreceptor interprets physical stimuli, such as pressure, vibration, the sensation of sound and body position (balance).
5. Thermoreceptor is either sensitive to temperatures above (heat) or below (cold) normal body temperature.