Ch. 6: Somatosensory System Flashcards
What is Exteroception?
Discrimitive touch
Outside sensation
What is Proprioception?
Ability to know where you are in space
(Gives Cerebellum something to compare plan to)
What is Sensation?
Raw modality
(touch or pin prick)
What is Perception?
Making meaning of sensation
What so Sensory Receptors respond to?
A variety of stimuli
What are “modality-specific” receptors?
Have a modality gated channel at the end
What are the 3 types of “Modality Receptors?”
- Mechanoreceptors
- Chemoreceptors
- Thermoreceptors
What do Mechanoreceptors sense?
- Touch
- Pressure
- Vibration
- Stretch
What do Chemoreceptors sense?
Chemical in extracellular fluid cause AP to start
What do Thermoreceptors sense?
Hot and cold temperatures
What are Nociceptors?
- Sense Pain!
- High threshold
- Need STRONG stimulus to activate
- Subset of: Mechano-, Chemo- and Thermoreceptors
What does a Phasic Receptor sense?
- Detect Change
- start and stop of movement or touch
- “Fast” adapting
What does a Tonic Receptor sense?
- Sustained contact
- detecting continuous duration of touch
- “Slow adapting”
Somatosensory Peripheral Neurons are our named neurons.
What is their morphology?
- Pseudounipolar
- Peripheral axon projection
- Central axon projection
What do Ia, Ib, II somatosensory neurons do?
- Proprioception
- Muscle spindle and muscle tendon
- Muscle length
What does an A-beta somatosensory neuron do?
- Exteroception
- “touch” of skin and subcutaneous tissue
- Discriminative touch - “I can describe and locate it”
What does an A-delta somatosensory neuron do?
- “Fast,” local pain & temp (superficial and deep)
- sense mechanical touch → cant describe, just scream!
What does a C somatosensory neuron do?
- “Slow.” non-localized pain & temp (superficial and deep)
- smaller = slower
- say “dang that hurts”
- Ex: stub toe, lightining bolt pain = A-delta, then it aches = C
What is a Receptive Field in cutaneous innervation?
Area of skin innervated by peripheral branch or sensory neurons
In cutaneous innervation, what parts of the body have the highest Density of receptors?
- Fingers, face, toes
- More dense = more iscriminative touch
What receptors make up Fine Touch?
What do they do?
- Combo of specialized receptor + A-beta afferent {biggest touch axon}
- Discriminative touch - describe & locate pain
What are the 2 different types of fine touch receptors?
What do they do?
- Cutaneous (smaller receptive fields) - SUPERFICIAL
- light touch, vibration, pressure, hair movement
- Subcutaneous (larger receptive fields) - DEEP
- touch, vibration, stretch of skin
What named receptors make up Coarse Touch?
What do they do?
- Free nerve endings + A-delta & C affernt
- mediated by free nerve endings
- A-delta: fast pain
- C: slow pain
What named receptors sense Temperature?
- free nerve ending + A-delta & C afferent
What named receptors sense Pain?
- free nerve ending + A-delta & C afferent
What is the spinal nerve made up of?
- Where ventral and dorsal roots come together
- all sensory, motor and autonomic
What happens when there is damage to a spinal nerve?
damage causes sensory loss in a dermatomal pattern
What axons feed a peripheral nerve?
Axons from more than one spinal level
(mixing occurs in plexus)
What happens when a peripheral nerve is damaged?
Sensory loss presents as a subsection of one or many dermatomes BUT, not a whole dermatome
In the muscle spindles, what do the Nuclear Bag Fibers sense?
Change and rate of change of muscle length
In the muscle spindles, what do the Nuclear Chain Fibers sense?
change of muscle length
In the muscle spindles, what do the Group Ia sensory axons innervate?
- Wrap center of bag and chain fibers
- “Primary endings”
- All info about length, change of length and rate of change of length
In the muscle spindles, what do Group II sensory axons innervate?
- End of chain fibers
- ONLY give info about length
Where are Intrafusal Muscle Fibers located?
What do they do?
- Inside the spindle at the ends of each bag and chain fiber
- Keep muscle fiber sensative to length
Where are Extrafusal Muscle Fibers located?
What do they do?
- Outside of spindle! (outside of the picture and not shown)
- Move muscle, contract
What motor neurons innervate Intrafusal Muscle Fibers?
What is their purpose?
- A-Gamma Motor Neurons
- Keep spindle sensative to new changes in length
What are Golgi Tendon Organs (GTO’s)?
What do they do?
- Specialized mechanoreceptors in the tendons of the muscles
- Senses tension
- More tension = More AP’s
What Sensroy Axon innervates the Golgi Tendon Organs (GTO’s)?
Group Ib
In the joint, what do Capsule Receptors do?
Where are they located?
- Detect Joint Movement
- mechanoreceptors - detect passive movement and extreme ranges
In the joint, what do Ligament Receptors do?
Where are they located?
- Sense tension in ligaments
- Located in ligaments
In the joint, what do Free Nerve Endings do?
Where are they located?
- Sense pain and inflammation
- Inside joint line and back on knee
What contributes to our sense of proprioception?
Deep
- Muscle Spindles - length, change of length
- Tendon Receptors - tension on muscle/MSK info
- Joint Receptors - position & stress on joints
Superficial
- Cutaneous Mechanoreceptors - weightbearing
Conscious Relay carries what sensory info?
Where does the info end up?
- Light touch
- Concious proprioception
- “Fast” pain
Ends in cerebral cortex → can characterize and localize
Divergent Pathways carry what sensory info?
Where does the info end up?
- “Slow” Pain
- Emotional and Autonomic responses to pain
End subcortical
Unconscious Relay carries what sensory info?
Where does the info end up?
- Unconsciouse proprioception
- Deep singals from muscles, tendons and joints
End in Cerebellum
What are Projection Neurons?
- MAIN neurons of pathway
- Labeled where they are in the chain (1st order, 2nd order, 3rd order)
Where are 1st Order Projection Neurons located?
- First in line
- Peripheral
- Psuedo-unipolar
Where are 2nd and 3rd Order Projection Neurons located?
- 2nd and 3rd in line
- Central
What are Interneurons?
- Tiny, not part of relay
- Introduce synapses → can turn up/down, gather/disperse
What are High Fidelity Pathways?
- Discriminative
- High degree of somatotopic organization (body map)
**End in Cortex or Cerebellum**
What are Low Fidelity Pathways?
- Non-driminative
- Low degree of somatotopic organization (body map)
**End in Subcortical - autonomic & emotional areas**
What are the 3 types of pathways to the brain?
- Conscious Relay
- Divergent Pathways
- Unconscious Relay
What is processed in the Primary Cortex?
Where is it located?
- Where sensation comes to consciousness
- Post central gyrus of the parietal lobe
What is processed in the Association Cortex?
Where is it located?
- Makinging meaning of sensation
- Other parts of Parietal lobe
When someone punches you, what pathway tells you WHERE they hit you?
What type of relay is this?
Spinothalamic
Conscious Relay
(Anterolateral columns, A-delta → fast pain and fast temp)
When someone punches you, what pathway TURNS your head to the source of pain?
What type of relay is this?
Spinomesencephalic (superior colliculus)
Divergent Pathway
(Anterolateral Columns, C → slow pain)
When someone punches you, what pathway increases AROUSAL in response to pain?
What type of relay is this?
Spinoreticular
Divergent Pathway
(Anterolateral Columns, C → slow pain)
When someone punches you, what pathway activates the SUBCORTICAL autonomic and emotional responses to pain?
What type of relay is this?
Spinolimbic
Divergent Pathway
(Anterolateral Columns, C → slow pain)
What pathway sends proprioceptive info to cerebellum for movement correction?
What type of pathway is this?
Spinocerebellar
(Unconcious Pathway, Ia, Ib, II → proprioception)
High Fidelity
