Somatosensory Pathways Flashcards
What are exteroreceptors?
Receptors in the skin that respond to stimuli impinging on the body
What are proprioceptors?
Receptors in joints and muscles that respond to the body’s own movement
What are nociceptors?
Receptors that respond specifically to tissue damage
In which spinal laminae do proprioceptors synapse?
V and VI
In which spinal laminae do exterorecptors synapse?
III and IV
In which spinal laminae do nociceptors synapse?
I and II
What are sensory receptors?
Sensory receptors are present on the ends of sensory nerve fibres, usually surrounded by a capsule which determines the stimulus which the fibre will respond to (due to differing capsule shape and structure)
What is the sensory capsule?
The capsule is made of connective tissue which grows around the nerve terminal and it alters the effect of movement on the nerve ending, making a receptor either slowly or rapidly adapting
What are ‘rapidly adapting’ sensory receptors?
Receptor responds at the beginning of a stimulus and fatigues after a second or so, even if the stimuli is sustained
What are ‘slowly adapting’ sensory receptors?
Receptor continues firing to a sustained stimulus but at a gradually reducing rate
Where are sensory receptors in the skin most often found?
In the epidermal-dermal junction
What is the role of Merkel receptors?
Sustained touch and pressure
What is the role of Meissner’s corpuscles?
Sensitivity to light touch
What is the role of Pacinian corpuscles?
Selectively sensitive to vibration (onion-like capsule)
What is the role of Ruffini corpuscles?
Sensitive to pressure/stretch
What is the role of Peritricheal receptors?
Detect hair displacement
Define ‘receptive field’
The area of skin innervated by a single nerve fibre
How does the brain determine the location of a stimulus?
The brain uses information from many receptors simultaneously to determine the location of the stimulus
How do chemoreceptors differ from touch receptors?
They do not have capsules around their endings but form ‘free’ nerve endings very fine nerve plexus in the dermis and other tissues. These free nerve endings respond to chemical stimuli. The parent fibre of such afferents is either type Aδ or type C.
Describe the DCML tract (information it conveys, deficits, decussation and passage)
•Ascending (sensory) pathway
•Contralateral deficits above medulla
•Carries information about proprioception (joint sense) and discriminative touch
•Decussation: secondary afferents decussate at the medulla after the primary afferents synapse in the gracile/cuneate nuclei
Passage - medulla –> thalamus –> somatosensory cortex
What makes up the medial lemniscus?
Trigeminal nucleus lies adjacent to gracile and cuneate nuclei in lower medulla; axons from cells in the trigeminal nucleus join axons from the gracile and cuneate nuclei –> cross over as internal arcuate fibres to form the medial lemniscus
What is the role of the VPM nucleus in the thalamus?
Relays information from the face to the cortex
What is the role of the VPL nucleus in the thalamus?
Relays information from the limbs to the cortex (in an ordered map - homunculus)
Where is the somatosensory cortex?
A strip of cortex immediately posterior to the central sulcus and is parallel to the motor cortex (post-central gyrus)
