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Somatic Sensory System, Dorsal column pathway, Spino pathway, 1st order,…
Somatic Sensory System
Primary Afferent Axons
AKA 1st Order neurons
First sensory neurons ALL have these axons
Cell bodies found in dorsal root ganglion
Differ depending on sense👁
Info goes UP dorsal myelinated sensory axons⬆️
Types
A-Alpha
Diameter = 13-20 μm 📏
Fastest🐇
⚡️Conduction Speed = 80-120 m/sec
Sensory receptors📢
Proprioceptors of skeletal muscle💪
Group I
A-Beta
Diameter = 6-12 μm📏
⚡️Conduction Speed = 35-75 m/sec
Sensory receptors📢
Mechanoreceptors of skin
Touch👋
Pressure
Vibration🔊
Group I
A-Delta
Diameter = 1-5 μm📏
⚡️Conduction Speed = 5-30 m/sec
Sensory receptors🔊
Pain😫
Temperature🌡
Group III
C-fibers
Diameter = 0.2-1.5 μm📏
Slowest🐢
Only one that is unmyelinated
⚡️Conduction Speed = 0.5-2 m/sec
Sensory receptors🔊
Pain😫
🌡Temperature
Group IV
Diff diameters correlates w/ conduction velocity + type of sensory receptor
Somatosensory Cortex
Processing Areas
3b
Where all info comes in + gets sorted📦
3a
Body position👤
Gets info from proprioceptors
1
Texture + touch👋
2
Shape + size of an object🎁
Located in postcentral gyrus behind central sulcus in parietal lobe
"Parent of parietal lobe"
Somatopy = mapping body's surface onto cortex🗺
Similar to motor cortex
Not proportional in terms of body part size
Proportional to sensitivity of body part
Face + hands == extremely sensitive🙈
More brain tissue devoted to processing their sensory info + more receptors🧠
Touch
👋
Mechanoreceptors
Vary depending on what they are detecting
Touch👋
Pressure
Vibration🔊
Surrounded by non-neuronal tissue
Dorsal Column Medial Lemniscal Pathway
3 neurons
Consists of A-Alpha + A-Beta axons
Ascends ipsilaterally
Same side as it came in
Deals w/ touch, vibration, + proprioception
1st neuron :black_flag:
Primary afferent axon
Cell body in dorsal root ganglion
Goes from dorsal root to dorsal part of spinal cord⬆️
Running up on SAME side
1st Synapse
Dorsal column nuclei
2nd neuron
Cell body in brain stem
Crosses sides @ level of brain stem 🔀
2nd Synapse
VP nucleus in thalamus
3rd neuron
1 more item...
A-Alpha are same EXCEPT they synapse in medulla
Right next to dorsal column nuclei @ its level
Pain
😫
Detects strong mechanical pressure that hurts + very high or very low temps that hurt
Consists of A-delta axons + C-fibers
A-Delta
Detect "1st pain"
More intense, but short-lasting💉
Ex. papercut📃
Reaches brain 1st b/c its myelinated
C-fiber
Detect "2nd pain"
Less intense, but longer-lasting
Ex. throbbing pain😖
Nociceptors = pain receptors
Ligand-gated ion channels
If cells break open💥
Ligands bind inside + cause pain
Free nerve endings in skin
Spinothalamic Pathway
3 neurons
Deals w/ pain + temp
Consists of A-Delta + C-fibers
Ascends contralaterally
Opposite side as it came in
1st neuron :black_flag:
Primary afferent axon
Cell body in dorsal root ganglion
Goes from dorsal root to dorsal part of spinal cord⬆️
1st Synapse
Dorsal part of spinal cord
shorter axon
2nd neuron
Crosses over to opposite side @ same level of spinal cord as it comes in🔀
Bypasses medulla
2nd Synapse
Thalamus
3rd neuron
1 more item...
Descending Regulation of Pain
⬇️
Comes from brain to control how much pain
Helps for high stress situations + excessive pain
PAG = stress parts of brain
Starts in midbrain :black_flag:
cell bodies send axon to synapse @ Raphe nuclei (medulla)
sends axon to synapse @ short inhibitory opioid inter-neuron
Enkephalin (opioid peptide neurotransmitter) - inhibitory interneuron that synapses w/ C-fiber
2nd neuron in spinothalamic pathway
Opioid meds (ex. oxycontin) bind to receptors here💊
🥵
Temperature
🥶
Thermoreceptors = temp-sensitive receptors
More suited for recognizing temps near body temp👤
Found in A-Delta axons + C-fiber
Trp = transient receptors channels that open @ specific temp
Normally open in response to diff temps, but can be tricked by certain substances👻
Menthol = active ingredient in mint🍀
can bind to COLD receptors + open them up🥶
Capsaicin = active ingredient in peppers🌶
can bind to HOT receptors + open them up🥵
Brown-Séquard Syndrome = when half of spinal cord is damaged
Results in paralysis + loss of touch sensation, vibration + proprioception on same side as injury❌👋
💥Damage == LEFT side
Crosses over AFTER injury🔀
👈Won't feel LEFT side❌
Loss of pain + temp sensation on opposite side of injury❌🌡
💥Damage == LEFT side
Crosses over RIGHT AWAY🔀
❌Won't feel RIGHT side👉
Loss of sensory info below injury
🦽
Dorsal column pathway
Spino
pathway
1st order
Spinal cord pathways
Mechano
Processing areas
Pain graph
Brown Sequard