Chapter 13 - Touch 2 Flashcards
Nociceptors
- specialized sensory receptors sensitive to noxious stim
- pain - unpleasant sensory and emotional consequence of nociceptor activity
- free nerve endings
Subtypes:
- 1)myelinated A beta fibres respond to pressure or heat
- Slow and fast adapting
- 2)unmyelinated C type respond to intense pressure, tem, noxious chemicals
- Slow adapting
Noci-transducers
1) thermoTRP channels - canditate nociceptors (pain and temp)
ASIC - in nocicipter fibres that detect ineternal pain, mediates pain through pH change (lactic acid)
3. Ligand gated ATP receptors - open in response to extracellular ATP
Pleasant touch
- mediated by unmyelinated C tactile fibres CT
- preferential optimal rates in speeds of stroking that are pleasant
- induces emotional, hormonal behavior - connecting our social environment with physical feeling, reduces pain from thermal heat
Kinesthetic receptors
It provides info to the motor system - tells us where out limbs are and what kinds of movements we’re making
They are the terminal ends of nerve fibres in sensory neurons
- muscle spindles - rate at which fibres are changing lengths
- golgi tendon organs - provide signals about the tension in the muscles attached
- joint receptors - activated when a joing is bent at en extreme
Dorsal ganglion root (DRG)
- axons of many somatosensory receptors converge into a spinal nerve
- cell bodies are in the DRG
- AP travels from peripheral end along axon to central end where they enter dorsal horn
Spinal cord organization
- nerve fibres arising from the skin appear as labeled lines (particular touch sensation)
- signals enter dorsal horn which organized in many layers (laminee)
- organized somatopiclly - adjacent areas of the skin are connected to adjacent areas within the cord
- spinal cord is only channel for transmission of somatosensory
Shingles
- viral infection causes painful rash
- reactivated chickenpox travels along nerve pathway to brain
- example how important mapping tools are
How do signals get from afferent neuron to brain
Parallel processing of different qualities
- A alpha and A beta - DCML pathway - faster
- A delta and C go through spinothalamic pathway - slower
DCML pathway steps
- DRG neurons send their axons up the white matte of spinal cord (via dorsal colusm)
- central axons of DRG neurons synapse on dorsal column nuclei in the medulla (via medial leminscus)
- axons of second order neurons arch over the midline (decussate) to the other side of the brain and assend to the thalamus (via internal capsule)
- thalamic relay third order neurons project directly to the cerebral cortex
The spinothalamic pathway steps
- first order DRG neurons synapse on neurons in the dorsal horn
- axons of second order dorsal horn neurons cross midline in the spinal cord and ascend (via anterolateral pathway)
- most of the axons terminate on relay nucli in the medulla, midbrain, thalamus
- these neurons project to the cortex in a diffuse manner
Touch processing in the cortex
Primary somatosensory cortex S1
- area that recieves inputs from thalmus through intenal capsule
- in the postcentral gyrus posterior to the central sulcus, paritieal lobe
Secondary somatosensory cortex
- recives convergent projection from areas of S1
Motor area - control body parts are just in the front of central sucus
- adjacency enhances communication between somatosensory and motor control systems
Body representation in S1
A) Somatotopic organization
- somatotopic map - complete orderly representation of the body. adjacent areas on the skin have connection to adjacent areas in the brain
- contralteral mapping, nonlinear representation
B) sensory homunuculus spatial map
- cortical neurons also have receptive fields based on connected neurons
-receptive field size depends on the location in somatopic map
Columnar organization of the cerebral cortex
-cortex has 6 layers that are distinct in terms of:
- cellular compostition
- their input/output relationships
- somatosensory arrives at layer 4
Neural plasticity
Changes in the cortical map can occur in response to physiological changes in the sensory and motor function
Examples; monkeys being taught, using out phones and our thumgs, blind people through braile
Phantom limb syndrome
Illusion that a missing limb is still present
- felt when the face is touched
- functional reorganization of the somatotopic map after amputation
- S1 neurons that lost their input are innervated by tactile receptors from the face
