Neuroscience Week 3: Somatosensory Systems Flashcards
Mechanical Receptors
6 listed
- Meissner Corpuscles
- Merkel Discs
- Hair Follicle receptors
- Ruffini endings
- Pacinian corpuscles
- Muscle spindles
Nociceptors examples
2 listed
- A𝛿 mechanical; heat
- C-polymodal
Thermoreceptors example
free nerve endings
Meissner Corpuscles Function
Tactile: shape/surfaces. Stereognosis
Merkel Discs Function
Tactile: indentation. Two-point sense, graphesthesia, flutter (low frequency)
Hair Follicle receptors Function
Tactile in hairy skin
Ruffini Endings Function
Stretching & Shapes. Stereognosis, pressing or squeezing
Pacinian Corpuscles Function
Vibrations. High Frequency
Muscle Spindles Function
Proprioception. Limb position, motion sense
Vibration high frequency
256 vibrations / sec
Vibration Low Frequency
125 vibration/sec light flutter
A𝛿 Mechanical Receptor function
heat, pinprick at or >45C, damaging chemical information
C-polymodal Receptor Function
Tissue damage
The termperature sensing warning device
Noiception: a warning device
A. Nociceptive spinal reflexes triggered at ~45°C (113°F)
B. Maintenance >/= 45°C (113°F) is tissue damaging
Pain Perception
- moments after the nociceptive reflex withdrawal the stimulus is perceived as pain
- Delay in perception is due to the time required to relay nociceptive signals via the spinothalamic tract to the 3rd order neurons in the thalamus, and they relay from thalamus to somatosensory cortex
- Nociceptive reflexes and the “pain threshold” serve a protective role
Pain as a Recuperative Healing Mechanism
Induces disuse of the injured area to promote healing
Myelination of Aα and function
- Heavily myelinated
- limb position and motion
Myelination of Aß and function
low threshold stimuli
gentle touch
modest myelinated
Myelination of Aδ fibers
Lightly myelinated
first fast pain
Bright and well localized pain
sets off protective reflexes
C fiber Myelination and function
Unmyelinated
smaller than Aδ fibers
conduct about 1yd/sec
poorly localized
long pain, dull, aching
Triggers disuse of the injured site
protection for healing
much more proportionality 70%
Which nerve fibers set off protective reflexes
Aδ fibers
Identify pathway and where the 2nd order neuron is located
Fill in
motion is passive motion so someone is moving your arm
Funiculus vs Fasciculus
Funiculus is a fiber bundle
Fasciculus is a thinner fiber bundle
many fasciculi make up a funiculus
Identify
Dorsal columns- medial lemniscus pathway
- ascend fasiculus gracilis
- fibers from T6 and above will ascend in the cuneate fasiculus (general sense from upper trunk and upper limbs) synapse on nucleus cuneatus of medulla
- fibers below T6 ascend in the fasiculus gracilis (general sense from the lower trunk and lower limbs) synapse on nucleus gracilus of medulla
- medial meniscus is the name of the fiber tracts after the decussation in the medulla
3D diagram of the dorsal columns - ML pathway
Spinothalamic Tract
pain and temperature from the body
primary neurons dorsal root ganglion
2ndary ipsilateral dorsal horn
decussate
3rtiary in thalamus to the primary somatosensory cortex
pay attention to where lesions are in relation to decussation
Spinothalamic tract 3D diagram
if there was a lesion at the ventral white commissure would have deficits bilaterally because both sides decussate there
Tract responsible for unconscious proprioception
Spinocerebellar
Identify
know the blood supply
Identify
know the blood supply
Identify
know the blood supply
Vertebral-basilar system
- Know Vertebral-Basilar system
- vertebral arteries
- Posterior inferior cerebellar artery (PICA)
Blood Supply to the spinal cord
both posterior spinal arteries supply the dorsal columns
if in the anterior spinal would have ipsilateral motor deficits and contralateral pain and temp deficits
Draw and label each pathway and include 1st 2nd3rd order neurons and location of decussations
Question 1
Question 2
Question 3
Question 4
Question 5
Question 6
Question 7
