SomatoSensory I Flashcards
What sensations does the somatosensory convey?
- Touch
- Propioception
- Heat, Cold
- Pain, Itch
How is the Central nervous system connected to the Peripheral nervous system?
The CNS (Brain and spinal cord) is connected to the body via spinal (31 pairs) and cranial nerves (Both apart of the peripheral nervous system)
Describe the peripheral nerve structure
Think of a nerve as a bundle of axons
- Epineurium is the connective tissue ensheathing the whole nerve
- Within the nerves, axon bundles may be in separate fascicles surrounded by…
List the different spinal cord and spinal nerves
Briefly describe the Dorsal root ganglion cells
Dorsal root ganglion cells are the sensory receptors of the somatosensory system
Describe the anatomical structure of the dorsal root ganglion cells
Broadly two anatomically and functionally distinct systems
- Large fibres (large diameter, myelinated, fast conduction): tactile and proprioceptive
- Small fibres (small diameter, thinly myelinated or unmyelinated, medium or slow conduction): temperature, pain, itch, crude touch
What does the quality of sensation depend on?
Quality of sensation depends on afferent fibre type such as specificity
- mechanosensitive fibre insensitive to thermal stimulation
- Thermosensitive fibres sensitive to warming or cooling
- Example of cold receptor responding to skin cooling from 34 to 26°C (A) and warming back to 34°C
What are the different receptors of the somatosensory system?
- Propioception
- Tactile afferents (discriminative touch)
Describe the proprioception receptor
- A-α afferents: large diameter, myelinated, fast conducting (<100 m/s) muscle fibres
Describe Tactile afferents (discriminative touch) receptors
A-β afferents: Large diameter, myelinated, 2nd fastest conducting (30-70 m/s). They include:
- Superficial: Meissner’s corpuscles, Merkel’s discs
- Deep: Ruffinni corpuscles, Pacinian Corpuscles
What are the 2 types of proprioceptors of the somatosensory system?
Proprioception - Muscle spindle
Tactile afferents Golgi tendon organ - Specialised sensory ending is skin
Free nerve endings - Low resolution tactile, temperature
In what mechanosensory afferent classes are tactile information encoded in?
- Small receptive fields (Dermis/Epidermis): Merkels disks, meissner’s corpuscles
- Large receptive fields (Dermis): Ruffini’s corpuscles, Pacinian corpuscles
Which of these 4 examples are slow adapting and fast adapting?
Slow adapting
- Merkels disks (Small RF): Pressure, Light touch
- Ruffini’s corpuscles (Large RF): Skin stretch
Rapidly adapting
- Meissner’s corpuscles (Small RF): Vibrarion, light touch
- Pacinian corpuscles (Large RF): Vibration
What are the 2 major central pathways of the somatosensory system?
Dorsal column: Medial lemniscal system (DCML)
- mediates discriminative touch, vibration, proprioception
- Inputs from A-β and A-α afferent fibres
Spinothalamic tract: STT also known as anterolateral system
- coarse touch, temperature, pain
- Inputs from A-δ and C fibres
Describe the route map for the DCML central pathway
- Primary afferents enter spinal cord and ascend ipsilaterally to brain stem
- 1st synapse is in the dorsal column nuclei of medulla
- 2nd order neurons cross and ascend contralaterally to thalamus
- 2nd synapse is in the VIP nuclei of…
