Somatosensory System/ Ascending Tracts Flashcards
What are the 4 modalities of the somato-sensory system?
- Discriminative Touch
- Proprioception
- Nociception
- Temperature
What is divergent neural proccessing?
- Potential spreads to more than 1 system
- The axon gives off collaterals
What is the purpose of convergence?
To increase the contrast of the neural signal
What is the term for contrast enhancement ?
- Lateral inhibition
What are the 3 types of lateral inhibition?
- Feed forward
- Feedback
- Distal
What is feedforward control?
Lateral collaterals activate inhibitory cell off of primary neuron provide stimulation to inhibitory neurons. (no feedback)
What is local feedback inhibition?
Collaterals from inhibitory neurons receiving strong sensory input synapse on interneurons and inhibit analogous/ neighboring inhibitory neurons to better pinpoint the source of the stimulus.
What is distal feedback inhibition?
Axons from the motor and sensory areas of the cerebral cortex synapse on an interneuron that synapses on an inhibitory neuron targeting the secondary neurons of a somatosensory system, further inhibiting weaker input,
What is the overall purpose of convergence/ contrast enhancement?
- Inhibit weaker signals for stronger clarity of the more powerful sensory information
What is kinesthetic and position sense considered mysterious?
- We are unaware of it since it has no defined sensation that is identifiable
What 3 types of receptors combine to form awareness of joint position? What other signal contributes? Which is the primary receptor?
- Muscle spindles (primary)
- Skin/ SA ruffini endings
- Joint receptors (detect end of motion)
- Signals of central origins sense effort or will
Why are position and movements of joints separate senses?
- They share the same receptors, but central processing occurs in the different areas/ pathways
What 2 receptors are especially important in determining joint position?
- SA cutaneous receptors
- Tonic muscle spindles
What 3 receptors are especially important in determining movement?
- FA receptors
- Muscle spindles
- Golgi tendon organs
Where are receptors found for touch and pressure?
In the skin
What are the 3 primary sensory afferents for touch and pressure?
- Group II fast
- Group III and IV slow
Where is the origin of the fasciculus gracilis?
The dorsal root ganglions of T7 - S5
Do the fibers of the fasciculus gracilis cross?
No.
Where is the tract of the fasciculus gracilis found?
- Throughout the entire spinal cord
On what does the fasciculus gracilis synapse in the higher centers?
- The nucleus gracilis in medulla
What sensations run through the fasciculus gracilis?
- Conscious proprioception, discriminative touch, pressure, 2 point discrimination, kinesthetic sense
Where is the origin of the fasciculus cuneatus?
- Dorsal root ganglions of C1- T6
Do the fibers of the fasciculus cuneatus cross the spinal cord?
No.
Where is the tract of the fasciculus cuneatus found in the spinal cord?
Above T6
What does the fasciculus cuneatus synapse on in the higher centers?
- The nucleus cuneatus in the medulla
What sensations run through the fasciculus cuneatus?
- Consious proprioception, discriminative touch, pressure, 2 point discrimination, kinesthetic sense
What is the origin of the spinocervical thalamic tract?
- The lateral cervical nuclei of the dorsal horn (at C1, and above)
Do the fibers of the spinocervical thalamic tract cross?
Yes
What do the fibers of the spinocervical thalamic tract synapse on in the higher centers?
- Thalamus
What sensation runs through the spinocervical thalamic tract?
- Discrimitive touch
- Passive manipulation (somewhat)
What fascicle is the spinocervical thamalic tract analgous to?
- The fasciculus cuneatus (maybe?)
What is the origin of dorsal spinocerebellar tract?
- Laminae 7/ Clark’s Column of T1 - L2
What is Clark’s Column
- Ias, Ibs, and IIs, give off collaterals to interneurons, which exit the horn laterally and ascends up from the lateral portion of the spinal cord
Do the fibers of the dorsal spinocerebellar tract cross?
- No
Where do the dorsal spinocerebellar tracts synapse?
On the nuclei in L3 - C1
Where are the dorsal spinocerebellar tracts found in the spinal cord?
- Fibers are found throughout
What sensory information runs through the dorsal spinocerebellar tract?
- Ia, Ib, and II fiber propriception
- UNCONCIOUS proprioception
Where does the ventral spinocerebellar tract originate?
- Laminae 5 - 7 of L3 - L5 (Spinal border cells)
Do the fibers of the ventral spinocerebellar tract cross?
They double cross (in the spinal cord and cerebellum??), and end up on the same side
Where do the primary fibers of the ventral spinocerebellar tract synapse on their nuclei?
- L1 - S5
Where are fibers from the ventral spinocerebellar tract found in the spinal cord?
- Throughout the spinal cord
Where do the fibers of the ventral spinocerebellar tract synapse in the upper centers?
- The cerebellum
What fibers create the ventral spinocerebellar tracts?
- Ib, FRA from WRF
What sensory information travels through the ventral spinocerebellar tracts?
- Unconcious proprioception
- Movement
- Posture
Where does the cuneocerebellar tract originate?
- The accesory cuneate nucleus (collateral off fasciculus cuneatus)
What is the cuneocerebellar tract an analogue to?
- The dorsal spinocerebellar
Do the fibers of the cuneocerebellar tract cross?
No
Where are the fibers found of the cuneocerebellar tract found in the spinal cord?
- They are not present
On what structure does the cuneocerebellar tract synapse in the higher centers?
The cerebellum
What fibers make up the cuneocerebellar tract?
- Ia, Ib, and Grade II
What sensation runs through the cuneocerebellar tract?
- Ia, Ib, II proprioception
- Unconcious proprioception
Where does the rostrocerebellar tract originate?
- Laminae 7 of C4- C8
Do the fibers of the rostrocerebellar tract cross?
No
Where does the rostrocerebellar tract synapse in the higher centers?
On the cerebellum
What fibers make up the rostrocerebellar tract?
Ib, FRA from WRF
What sensory information travels through the rostrocerebellar tract?
- Unconcious proprioception
- Movement
- Posture
Which tracts location is not currently known?
Rostrocerebellar tract
How are the funiculi of the dorsal horn arranged?
- Somatotopically arranged
- Sacral to lumbar to thoracic to cervical from medial to lateral
Where does the spinoreticular tract originate?
- Posterior horn
Do the fibers of the 1st spinoreticular tract cross?
No
Where are fibers from the spinoreticular tract found in the spinal cord?
Throughout
What does the spinoreticular tract synapse on in the higher centers? (tract 1 and 2)
1: Medulla reticular formation
- Giganto and lateral reticular nucleus
2: Pons reticular formation
- Reticular pontis caudalis
What is the function of the 1st spinoreticular tract?
- Unconcious proprioception
What is the function of the 2nd spinoreticular tract?
- Maintanence of the state of conscioiusness
What is the origin of the spinovestibular tract?
- Dorsal root ganglia
Do the fibers of the 2nd spinoreticular tract cross?
Yes
Do the fibers of the spinovestibular tract cross?
Ues
What does the spinovenstibular tract synapse on in the higher centers?
- Vestibular nuclei
What sensation travels through the spinovestibular tract?
- Ia, Ib, II proprioception
- Unconcious proprioception
What is the origin of the spino-olivary tract?
- Dorsal root ganglia
Do the fibers of the spino-olivary tract cross?
Sometimes
Where are the fibers of the spino-olivary tract found?
C1 - C8
Where do the fibers of the spino-olivary tract synapse in the higher centers?
- Inferior olivary nucleus
What sensation travels through the spino-olivary tracts?
- Unconscious proprioception of the neck
What is the origin of the spinocortical tract?
Unknown
Do the fibers of the spinocortical tract cross?
No
Where are the fibers of the spinocortical tract found in the spinal cord?
Throughout
Where do the fibers of spinocortical tract synapse in the higher centers?
The cerebral cortex
What is the origin of the spinocervical tract?
Lamina III and IV
What is another name for the spinocervical tract?
- Morin’s tract
Do the fibers of the spinocervical tract cross?
No
Where do the fibers of the spinocervical tract synapse in the higher centers?
The lateral cervical nucleus
What sensation travels through the spinal cervical tract?
- Concious proprioception
- Tactile sensation
What are the 6 minor ascending tracts?
- Spinoreticular
- Spinoreticular
- Spinovestibular
- Spino-olivary
- Spinocortical
- Spinocervical/ Morin’s
What are the 3 interspinal reflex tracts?
- Fasciculus Septomarginalis
- Fasciculus Interfascicularis
- Fasciculus Proprius 1
Where does the fasciculus septomarginalis orginate from?
- The dorsal root ganglia
Do the fibers of the fasciculus septomarginalis cross?
- No
Where are the fibers of the fasciculus septomarginalis found?
L1 - S5
Where do the fibers of the fasciculus septomarginalis, and other interspinal reflex tracts synapse?
- On interneurons
- ACh endplates
What sensation travels through the fasciculus septomarginalis, and other interspinal reflex tracts?
- Proprioception interspinal reflexes
Where do the fibers of the fasciculus interfascicularis orginate?
The dorsal root ganglia
Do the fibers of the fasciculus interfascicularis cross?
No
Where are the fibers of the fasciculus interfascicularis found?
- C1 - T12
What type of sensory information travels trhough the fasciculus interfascicularis?
Proprioception Interspinal Reflexes
Where does the fasciculus proprius 1 originate?
- Dorsal root ganglia
- Laminae III and IV
Do the fibers of the fasciculus proprius 1 cross?
Probably; not sure
Where are the fibers of the fasciculus proprius 1 found in the spinal cord?
Throughout