Somatic sensory systems Flashcards
Sensory systems

In general, what are the 2 ways in which a signal can be transmitted in response to a sensory stimulus?

Tell me about the sensory systems of the senses?

What are the sensory and motor components?
What part of the nervous system are they a part of?
Where does the sensory stimulus that effects them come from?
Where does the signal go to?

Whats a first order neuron?
First order neurons – These are pseudounipolar neurons which have cells bodies within the dorsal root ganglion. They have one axon which splits into two branches, a peripheral branch (which extends towards the peripheries) and a central branch (which extends centrally into spinal cord/brainstem).
Tell me about the dorsal root ganglion (DRG) neuron
- Where it enters
- branches and their destination
- where their cell bodies are located
- myelination and diameter
Dorsal root ganglion (DRG) neurons
- Mechanosensory. Enters dorsal root and joins dorsal column
- Pain and temperature fiber makes a connection upon entrance
- Two axon branches depart from the soma.
- One branch runs to the periphery (PNS) and the other to the spinal cord (CNS)
- The cell bodies (somas) of all somatosensory fibres from the body are located in the dorsal root ganglia (DRG).
- Signals from face: somas in trigeminal ganglion.sa
- First order sensory neurons are pseudo unipolar.
- Two axon branches
- Mechanosensory neurons are myelinated and have large diameters

Tell me about mechanosensory neurons
- myelinated
- have large diameters
- touch
- Merkel, meissner, pacinian, ruffini cells
- 6-12 µm
- 35-75 m/s

somatic sensory system organisation

What receptors does the skin contain?
mechanoreceptors, nociceptors and thermoceptors
Tell me about the different compoents of the skin and whether they are located in the epidermis or dermis

The major classes of somatic sensory receptors

Classes of somatosensory afferents
tell me…
- Their sensory function
- Receptor type
- axon type
- diameter
- conduction velocity

The sensory transduction cascade, where the energy of a stimulus is converted into an electrical signal consists of several key steps. What are these key steps?

What is the sensory system stimulus strength encoded by?
The stimulus strength is encoded by the amplitude of the generator potential and the frequency of action potentials

What are the two types of sensory system receptors?
Tell me about eah
Tonic and phasic receptors
Tonic= static
Phasic= dynamic

Tell me the Sensory system receptors subtypes?
- Non encapsulated fibres with touch and injurious force
- Touch first respond but then quiet down
- With force they are persistent and don’t turn off. These fibres also response do temperature. Pain receptor will be continuously on

Tell me the key features of the following sub-types…
- Hair follicles
- Meissner corpuscel
- Pacinian corpuscle
- Merkel cell-neurite complex
- Ruffini corpuscle
- Encapsulated receptors
- Low-threshold (or high-sensitivity)
- Innervated by relatively large myelinated axons (type Aβ)
- Rapid central transmission of tactile information

Tell me the key features and characteristics of the Meissner’s corpuscle…
- Connective tissue capsule.
- Several lamellae of Schwann cells.
- 40% of the sensory innervation of the human hand (glabrous skin).
- Dynamic deformation.
- Movement of textured objects are moved across the skin (~50 Hz).
Tell me the key features and characteristics of the pacinian corpuscle…
- 10–15% of the cutaneous receptors in the hand.
- Present in subcutaneous tissue (bone and gut).
- Onion-like capsule / lamella separated by a fluid-filled space.
- Discrimination of fine surface textures / high-frequency vibration of the skin (250–350 Hz).
- Dynamic qualities of mechanical stimuli
- less abundant than the Meissners corpuscle
How does mechano- transduction work?
- stretch-sensitive cation channels
- Depolarisation of afferent neuron
- If you want to read more on this look at: Delmas et al 2011 Molecular mechanisms of mechanotransduction

What makes up 25% of the mechanoreceptors in the hand (fingertips)
Merkel cell- neurite complex
Tell me about the Merkel-cell neurite complex and the Ruffini complex…
- Static discrimination of shapes, edges, and rough textures. Light pressure.
- Ruffini’s corpuscles, 20% of the receptors in the human hand. also in ligaments and tendons.

What is meant by a receptive field?
The ability to distinguish 2 simultaneously applied stimuli as distinct is called 2-point discrimination and it is a measure of spatial acuity

Whats meant by two-point discrimination?
Two-point discrimination (2PD) is the ability to discern that two nearby objects touching the skin are truly two distinct points, not one. It is often tested with two sharp points during a neurological examination and is assumed to reflect how finely innervated an area of skin is.









































