ascending pathways Flashcards
types of senses
- special
- general
general senses
spread through the body
special senses
localized by their respective sensory organ
5 special senses and their CN
- olfaction (CNI)
- vision (CNII)
- taste (CNVII, IX)
- hearing (CNVIII)
- vestibular (CNVIII)
general sense types
- interoception
- exteroception
- proprioception
interoception
pain, temp, touch pressure of the viscera
exteroception
pain, temp, touch pressure of environmental stimuli
proprioception
position sense from joints, tendons, ligaments
general sense information detected via
- nociceptors
- thermoreceptors
- mechanoreceptors
- chemoreceptors
- baroreceptors
nociceptors
monitor tissue damage
thermoreceptors function and location
- monitor temperature
- found in skin, muscle liver and hypothalamus
mechanoreceptors
- monitor contact and pressure
- found mostly in the skin
chemoreceptors
monitor chemical composition of body fluids (O2, CO2, pH)
baroreceptors
- subset of mechanoreceptors
- monitor changes in pressure of tubular organs (vessels, ureters, bowel)
motor areas
- precentral gyrus of frontal lobe
- primary motor cortex (directs voluntary movements)
sensory areas
- postcentral gyrus of the parietal lobe
- primary somatosensory cortex (receives somatic sensory information)
somatic sensory information
touch, pressure, pain, vibration, taste, temp
dermatome
- area of skin supplied by a particular spinal nerve
- correspond to the entry or exit point of ventral (motor) and dorsal (sensory) rootlets
if a spinal nerve is cut …
sensation is lost in the dermatome
symptoms that follow a dermatome may indicate ?
pathology that involves the related nerve root
ganglia
cell bodies lining the nerves in the peripheral nervous system
nuclei
cell bodies in the central nervous system
types of ascending somatosensory pathway in the spinal cord
- spinothalamic (anterolateral)
- medial lemniscus (dorsal column-medial lemniscus pathway)
- spinocerebellar
spinothalamic (anterolateral) pathway function
pain and temp, crude touch
medial lemniscus (dorsal column-medial lemniscus) pathway function
- fine touch
- conscious proprioception
spinocerebellar pathway function
proprioception
somatosensory axons are relayed to the ?
primary somatosensory sortex
3 orders of neurons in the ascending pathways
- PNS (dorsal root ganglion)
- CNS (grey matter spinal cord)
- CNS (ventral posterolateral thalamus)
interoception, exteroception, and proprioception from the trunk and limbs are delivered to the CNS by ?
1st order neurons (PNS)
divergence of pathway depend on ?
sensory modality
pain and temp, crude touch pathways
- decussate in spinal cord
- ascend contralaterally via the spinothalamic tract to the primary somatosensory cortex
tactile and proprioceptive pathways
- ascend ipsilaterally via the fascilia gracile and cuneatus
- decussate in the brainstem
- ascend contralateral to the primary somatosensory cortex via the medial lemniscus pathway
spinocerebellar pathway
- ipsilateral
- ventral spinocerebellar double crosses
- dorsal spinocerebellar does not cross
spinothalamic system
- lateral spinothalamic tract
- anterior spinothalamic tract
- appreciation of mild noxious stimulus
lateral spinothalamic tract function
pain and temp
anterior spinothalamic tract
- crude touch, pressure, tickle, itch
- limbs and trunk
- decussate immediately
spinothalamic system lesion result
contralateral loss of sensation below lesion
medial lemniscus system
- fien touch and proprioception
- limbs and trunk
- ascend ipsilaterally to the medulla before decussating
- high degree of spatial orientation
medial lemniscus system lesion result
- below decussation of its fibers = loss of sensation ipsilaterally
- above decussation = lose sensation contralaterally
primary somatosensory cortex properties
contralateral, disproportionate, inverted
trigeminothalamic tract nerves
- trigeminal nerve
- facial nerve
- glossopharyngeal nerve
- vagus nerve
trigeminal nerve supplies…
face/oral cavity
facial nerve supplies…
skin around ear
glossopharyngeal nerve supplies…
- upper pharynx
- post 1/3 of tongue
vagus nerve supplies…
- external auditory meatus
- tympanic membrane
trigeminothalamic tract
- enter brainstem
- synapse at trigeminal nuclear complex
- decussate before ascending to post central gyrus
trigeminal nuclear complex
midbrain, pons, medulla
peripheral receptors and sensation structures served by the trigeminothalamic tract
- Cornea
- Mucocutaneous tissues around mouth and nostrils.
- Oral and nasal mucosae
- Paranasal sinuses
- Tongue (anterior two thirds)
- Teeth and gums
- Dura of anterior and middle cranial fossae
- Skin of face to the vertex except angle of jaw
- Parts of external ear
primary sensory neurons
- trigeminal ganglion (semilunar)
- unipolar neurons similar to dorsal root ganglion cells
- 3 nerve roots give rise to: ophthalmic nerve (CNV-1), maxillary nerve (CNV-2), and mandibular nerve (CNV-3)
- peripheral distribution of 3 branches (back of head and angle of the jaw not supplied by CNV, areas around ear supplied by CNSVII, IX, X)
trigeminal nerve (CNV) branches
- ophthalmic nerve (CNV-1)
- maxillary nerve (CNV-2)
- mandibular nerve (CNV-3)
second order trigeminal neurons
- principal (chief) trigeminal nucleus
- spinal (descending) trigeminal nucleus
principal (chief) trigeminal nucleus
- mediates fine touch stimuli (two point discrimination), joint position, and vibration
- located in the middle of pons lateral to the motor nucleus of trigeminal nerve
spinal (descending) trigeminal nucleus
mediates pain and temp
axons of the second order neurons form the ? pathway to the ?
trigeminothalamic; ventroposteromedial nucleus of the thalamus
third order neurons in ? project to ?
thalamus; postcentral gyrus (primary sensory cortex)
peripheral nerve lesion cause
neuritis
peripheral nerve lesion result
- primary order neurons affected
- disease or dysfunction of nerves (problems in any normal nerve function)
- loss of function (numbness, tremor, gait)
- gain of function (tingling, pain, itching, crawling, pins and needles)
- hypersensitivity
neuritis
inflammation of the PNS
neuritis causes
- physical/chemical injury
- infection (herpes, shingles, lyme)
- radiation
- nutritional deficiency
sensory system lesions
- dissociated sensory loss
- all ascending axons decussate in the spinal cord (STT) or lower brainstem (MLP) so lesions in the upper brainstem result in the loss of contralateral sensation
dissociated sensory loss
deficit in pain/temp or touch/proprioception
spinothalamic tract lesion
contralateral loss of pain/temp sensation below level of the lesion
medial lemniscus pathway lesion
ipsilateral loss of touch/ proprioception below the level of the lesion
syringomyelia
- disrupts the decussating fibers of the spinothalamic system
- usually in cervical and upper thoracic regions
- usually not the ascending fibers of the dorsal column-medial lemniscal system
- cape-like distribution of loss of pain, temp, crude touch sensation from above lesion
brown-sequard syndrome
- caused by spinal cord tumor, trauma, ischemia, infectious or inflammatory diseases (tuberculosis, MS)
- contralateral loss of pain and temp, sensation, and ipsilateral loss of position and vibration sensation
are spinal cord injuries rarely limited to a particular tract
yes
incomplete spinal cord lesion characterized by
hemisection of the spinal cord
neuropathic pain
- complex, chronic state accompanied by tissue injury affecting the STT
- nerve fibers may be damage, dysfunctional, or injured
- causes: spinal cord injury, MS, stroke
referred pain
- pain perceived at a location other than the site of the painful stimulus
- pain from an internal organ coincides with the part of the body served by somatic sensory neurons
- why we have chest/arm pain with a heart attack
STT and somatosensory cortex cannot discern clearly ?
whether pain is coming from body wall or viscera
