7.3 Somatosensory System Flashcards
What is the direction information passes thought a neuron?
Dendrite - cell body - axon
What kinds of neurons are primary sensory, interneurons and motor neurons?
Primary sensory: unipolar or pseudounipolar
Interneurons: bipolar
Motor neurons: multipolar
How is the unipolar sensory neuron distributed?
the nerve endings with specalised sensory receptors, cell bodies in the peripheral ganglia and the central processes enter the CNS and synapse
How do we discriminate different information?
Receptor type, fibre type and pathways
What are the nerve endings in Glabrous skin?
Meissner (FA1/RA) Pacinian (FA2/PC) Merkel (SA1) Ruffini (SA2) Free nerve endings
What are the nerve endings in hairy skin?
Hair follicle afferents
Merkel (SA1)
Ruffini (SA2)
Free nerve endings
Where are the nerve endings located ?
Meissner, Merkel superficial
Pacinian and Rufini deep
Which receptors transmit fine touch information?
Meissner and Merkel
What type of receptor, where, what do they respond to and function - Meissner
FA1, glaborous skin and upper dermis, change in pressure, fine touch (texture and motion)
What type of receptor, where, what do they respond to and function - Pacinian
FA2, glaborous skin , deep dermis, changes in pressure, event detection, high frequency vibrations
What type of receptor, where, what do they respond to and function - Merkel
SA1, glaborous and hairy skin, upper dermis, pressure status, fine touch (shape/form of edges and points/dots)
2nd derivative discrimination
What type of receptor, where, what do they respond to and function - Ruffini
SA2, glaborous and hairy skin, lower dermis, skin stretch, proprioception
What type of receptor, where, what do they respond to and function - free nerve endings
galborous and hairy skin, upper dermis, mechanical, temperature, tissue damage, sensitisation
Function: noxious hot/cold, mechanical trauma, itch and chemical irritants
What influences the sensitivity of the skin?
type of receptor, numerical density and distribution
What are the proprioceptors and what is their respective function?
Golgi tendon organs (1b): sense tension (force of contraction or stretch); inhibits alpha motor neuron activity to reduce muscle tone
Muscle spindles (1a and IIa): sense stretch in the muscle length, results in activation of alpha motor neurons to initiate the jerk/myotatic reflexes
Where do sensory fibres have their cells bodies and where do they enter the spinal cord?
DRG
A central process that enters the spinal cord ini the dorsal horn
Where do large diameter fast conducting nerves send their information?
DORSAL COLUMNS
Where do small diameter, slow conducting fibres send their information?
Spinothalamic
Where does all sensory information pass through?
Thalamus
What information does the Ventral posterolateal thalamus receive?
Afferents from the entire body
What information does the VPM region of the thalamus recurve
Information from the face via the trigeminal
What does the anterior group of the thalamus do?
Attention and learning
What does the medial thalamus do?
Planning and active memory
What are the inputs and outputs to the VPL
In - medial lemniscus and spinothalamic tract (spinal nerves from limbs and trunk)
Out - somatosensory cortex
What are the inputs and outputs for the VPM
In - medial lemniscus and trigeminal system (face, ocular surface, tongue, oral cavity and masa, cavity)
Out - somatosensory
What information travels where in the dorsal column system?
Gracile from lower body
Cuneate from upper
Where does information from the dorsal column system go?
Comes in the medulla, form and accurate course to the medial lemniscus on contra lateral side, ascend through brainstem and end up on the VPL before projecting to the primary somatosensory cortex
What are broad and areas of the primary somatosensory cortex?
1: cutaneous (FA1 and 2)
2: deep receptors from muscles/joints/some cutaneous
3a: mainly muscle spindles
3b: mainly cutaneous (RA1 and SA1)
