Sensory Processing Pathways Flashcards
Sensation
process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment
In short = our brain receives input from PNS.
Sensory Pathway Nerves
Sensory pathways regarding bodily sensation = spinal nerves
Sensory pathways regarding head, larynx, pharynx, soft palate & tongue = cranial nerves
Both are a part of the peripheral nervous system (PNS)
The body has more sensory fibers than motor fibers
Somasensation
refers to pain, temperature, touch, and proprioception arising from the body
1) PNS ascending fibers carry information (somasensation) and travel through the spinal cord, brainstem and thalamus
2) From the thalamus, it will travel to the appropriate primary cortices
Somatic Sensation Types
Three categories:
1. Mechanoreception 2. Thermoreception 3. Nociception
Somatic Receptor Types
Types of receptors:
1. Encapsulated endings 2. Free nerve endings 3. Expanded tip endings
Three-Neuron Organization
First order: with their cell bodies in the DRG, collect sensory information from the periphery and send it the 2nd order neuron in CNS.
Second order: Can either be in the spinal cord or in the brainstem. Will send information to the __________.
take note
Third order: From the VPL it will travel to Primary Sensory Cortex or to specific cortices
Three-Neuron Organization
First order: with their cell bodies in the DRG, collect sensory information from the periphery and send it the 2nd order neuron in CNS.
Second order: Can either be in the spinal cord or in the brainstem. Will send information to the thalamus
Third order: From the VPL it will travel to Primary Sensory Cortex or to specific cortices
Sensory Impulse Decussation
Once 2nd order neuron reached, impulse decussates
Above the level of decussation, the neurons in a somatosensory pathway represent the contralateral (i.e., opposite) side of the body or face.
When an afferent pathway is damaged somewhere below the site of decussation, the sensory loss will be on the side ipsilateral to the lesion (i.e., the loss is on the same side as the lesion or ipsilesional).
Ascending Pathways
Can be divided into two systems:
- Dorsal column-medial lemniscal system (Epicritic System)
- Anterolateral System (Protopathic System)———————
Fasciculus Gracilis:
discriminative touch from lower half of body
1st order = DRG at the sacral – midthoracic level, will travel ipsilateral to the Nucleus Gracillis of medulla
2nd order = at Nucleus Gracilis will cross midline. Will form medial lemniscus tract and travel up the brainstem (medulla, pons, midbrain) to enter the VPL nucleus of thalamus 3rd order = At VPL, sensory pathway will lead to the Primary Sensory Cortex and associated areas
Epicritic System
- Ventral posterolateral nucleus (VPL)
- Fasciculus Gracilis: transmits sensation from the lower half of the body from the sacral to midthoracic regions
- Fasciculus Cuneatus: transmits sensation from the upper half of the body from midthoracic region and up.
Fasciculus Cuneatus:
discriminative touch from upper half of body
Ist order= DRG above midthoracic level, will travel ipsilateral to the Nucleus cuneatus of Medulla
2nd order= at Nucleus Cuneatus will cross midline. Will form medial lemniscus tract and travel up the brainstem (medulla, pons, midbrain) to VPL nucleus of thalamus. 3rd order= At VPL, Sensory pathway Primary Sensory Cortex & associated areas.
Lateral Spinothalmic:
Part of the Anterolateral (or Protopathic) System
pain and temperature
Ist order: DRG at S,L,T or C level of the spinal cord will travel to the Nucleus Proprius & Substantia gelatinosa in the dorsal horn of spinal cord
2nd order: At Nucleus Proprius and Substantia gelatinosa will cross midline to the white commissure (forming the lateral Spinothalmic tract) and will travel through brainstem to VPL of thalamus
3rd order: At VPL, fibers will travel and project into the upper 2/3 of Primary Sensory Cortex
Ventral (or Anterior) Spinothalmic:
Part of the Anterolateral (or Protopathic) System
Diffuse/light touch and pressure
1st order: DRG at S, L, T, or C level of spinal cord will travel to the Nucleus Proprius & Substantia gelatinosa in the dorsal horn of spinal cord
2nd order: At Nucleus Proprius and Substantia gelatinosa will cross midline to the ventral gray matter (forming the Ventral Spinothalmic tract), travel through brainstem and eventually reach the VPL of Thalamus
3rd order: At the thalamus, it has projections to different thalamic nuclei:
-Ventrolateral (VL), Mediodorsal (MD), Ventral Posteromedial (VPM)
and finally travel to VPL to the upper 2/3 of Primary Sensory Cortex
Anterolateral (or Protopathic) System
- Ventral (or Anterior) Spinothalmic
2. Lateral Spinothalmic
Cranial Nerves as Sensory Pathway
Cranial nerves are the primary sensory pathway for:
- skin of face - anterior portion of the scalp - anterior 2/3 of tongue - outer surface of eardrum
Mediates pain, temperature, touch, pressure and proprioception for the oral and cranial areas
Sensory Nerves for Face/Head
Trigeminal (sensory, 3 branches), Facial (taste, ant 2/3), Vagus, Glossopharyngeal (taste, post 1/3)
Cranial nerves generally don’t deccussate (a few do, but most don’t); Spinal nerves always deccussate
Which cranial nerve is the primary sensory nerve for the face and head? Trigeminal (all braches)
Agnosia
disorder of recognition caused by a cerebral injury
-thought to occur at the sensory association areas of cerebral cortex
Visual agnosia – recognize people/objects/colors by sight
Auditory agnosia – inability to comprehend speech or nonspeech sounds
A type of AA - Pure word Deafness – in the absence of aphasia; very rare
Tactile agnosia – inability to recognize objects by touch
Agnosia results from brain damage in areas involved in spatial processing, integration of visual and motor information, and attention. However, agnosia may affect a person’s ability to recognize speech or name objects and thus present with some similarities to Wernicke’s aphasia or anomia.
Sensation Perception
Conscious sensation occurs in the VPL (Ventral Posterolateral Nucleus of thalamus) for body and VPN (Ventral Posteromedial Nucleus of thalamus) for face/head
The PSC denotes where in the body the sensation derives.
Pain is processed in the thalamus/limbic system
Area near the thalamus that deals with emotional processing? Limbic system (emotional pain may be a part of sensory processing)
While much of this is conscious, there are also ascending systems that convey unconscious information involved in coordination (proprioception) and brain stem reflexes that is unconscious.
Sensory Perception Areas of Thalamus
VPL – sensory processing for most of the body
VPM – SP for the face
Pulvinar and LP – visual stimuli
Pain Perception
Three common types of altered responses to pain: hyper, hypo, and analgesia
Analgesia -Lack of pain sensation
Hyperalgesia – increased pain or tenderness
Hypoalgesia- decreased sense of pain or tenderness
Referred Pain – often occurs with issues with the heart – pain in the arm
chart in book shows where referred pain often occurs
pain in some areas may indicate a prblm with another area of the body
Phantom Limb
A phenomenon related to pain
-If a limb or substantial part of a limb is amputated, the patient may continue to have shooting pain/ tingle-feeling
2 rationales:
1) the peripheral afferent neurons continues to grow, until it reaches scar tissue where it forms a Neuroma (hypersensitive neuronal knot).
2) difficult to forget years of associated sensory processing.
Spatial Perception
Proprioception – awareness of limb position in space.
It is important for development of skilled movements such as speech and writing; provides the cortex with an awareness of the spatial positioning of body parts and the body during movement
Kinesthesia – awareness of limb movement
- important for skilled movements and provides information re: direction and limb movements
- aids fine/discriminative touch analysis
- helps discriminate between two or multiple points of touch and deep pressure touch
Romberg tests; while standing with feel together, measure amount of sway w/ eyes open & close
Mechanoreception
touch, pressure, vibration, and proprioception
Thermoreception
cold and heat
Nociception
pain
Encapsulated endings
tactile (discriminative touch, vibration)
Free nerve endings
pain, temperature, some tactile
Expanded tip endings
tactile (touch, pressure), temperature
