Ascending Pathways Flashcards
five special senses
- olfaction
- vision
- taste
- hearing
- balance
cranial nerve for olfaction
olfactory nerve (I)
cranial nerve for vision
optic nerve (II)
cranial nerve for taste
facial (VII) and glossopharyngeal (IX) nerves
cranial nerve for hearing
vestibulocochlear nerve (VIII)
cranial nerve for balance
vestibulocochlear nerve (VIII)
three types of general senses
- interoception
- exteroception
- proprioception
interoception
pain, temperature, touch pressure of viscera
exteroception
pain, temperature, touch pressure of external world
proprioception
position sense from joints/ligaments/tendons
5 types of sensory receptor for general senses
- nociceptors
- thermoreceptors
- mechanoreceptors
- chemoreceptors
- Baroreceptors
what do nociceptors do
monitor tissue change
what do thermoreceptors do
monitor temperature - found in skin, liver muscle, and hypothalamus
what do mechanoreceptors do
monitor contact and pressure, found mostly in the skin
what do chemoreceptors do
monitor chemical compositition of body fluids
what do baroreceptors do
- subset of mechanoreceptors
- monitor changes in pressure of tubular organs (vessels, ureters, bowel)
dermatome
area of skin supplied by a specific spinal nerve
each corresponds to an entry or exit point of ventral (motor) and dorsal (sensory) rootlets
how many dermatomes are there
31
dermatone pathology
symptoms that follow a dermatome (rash, pain) may indicate pathology involving the nerve root eg. shingles
where are somatosensory axons relayed to
post central gyrus (primary somatosensory cortex)
1st order neurons
- PNS
- found in dorsal root ganglia
2nd order neurons
- CNS
- found in spinal cord
3rd order neurons
- CNS
- found in thalamus
three different types of ascending somatosensory pathways in spinal cord
- Spinothalamic (STT)
- Medial Lemniscus (MLT)
- Spinocerebellar
what does the STT relate to
pain, temperature, crude touch
what does the MLT relate to
fine touch and conscious proprioception
what does the spinocerebellar tract relate to
proprioception
what does the trigeminal nerve innervate
face and oral cavity
what does the facial nerve innervate
skin around ear
what does the glossopharyngeal nerve innervate
upper pharynx and posterior 1/3 of tongue
what does the vagus nerve innervate
external auditory meatus and tympanic membrane
four cranial nerves involved in the trigeminothalamic tract
- trigeminal
- facial
- glossopharyngeal
- vagus
trigeminal tract pathway
- four cranial nerves enter brainstem
- these synapse at the trigeminal nucleur complex (midbrain, pons, and medulla)
- they decussate here
- then ascend to post central gyrus
nine periperac receptors and sensation structures served by trigeminal system
- cornea
- muscoctaneous tissues around nose and mouth
- oral and nasal mucosae
- paranasal sinuses
- tongue (anterior 2/3)
- teeth and gums
- dura of anterior and middle cranial fossae
- skin of face to vertex except angle of jaw
- parts of external ear
primary sensory neurons
trigeminothalamic tract
unipolar neurons similar to dorsal root ganglion cells
what nerve roots give rise to primary sensory neurons
- ophthalmic CN V-1
- maxillary CN V-2
- mandibular CN V-3
where do second order neurons originate
two brain stem nuclei:
principle trigeminal nucleus
spinal trigeminal nucleus
principle trigeminal nucleus
- mediates fine touch stimuli (two point discrimination), joint position and vibration
- located in the middle of the pons just lateral to the motor nucleus of trigeminal nerve
what is neuritis
inflammation of PNS
five causes of neuritis
- physical injury
- infection (herpes, shingles, leprosy, guillain-barre syndrome, lyme disease, bells palsy)
- chemical injury
- radiation
- nutritional deficiencies
what two types of sensory function damage can occur
neuritis
- loss of function (numbness, tremor, gait abnormality)
- gain of function (tingling, itching, crawling, pins and needles)
dissaociated sensory loss
deficit in modality of pain/temperature or touch/proprioception
STT lesion
contralateral loss of pain/temperature sensation below the level of the lesion
MLP lesion
ipsilateral loss of touch/proprioception below the level of the lesion
what is syringomyelia
disruption of the decussating fibres of the spinothalamic system (usually in cervical and upper thoracic regions) but not usually the ascending fibres of the dorsal column-medial lemniscal system
syringomyelia symptoms
cape like distribution of loss of pain, temperature and crude touch sensation from above the lesion
what is Brown-Sequard Syndrome
incomplete spinal cord lesion characterised by a hemisection of the spinal cord
causes of Brown-Sequard Syndrome
- spinal cord tumour
- trauma (puncture wound to neck or back)
- ischemia (obstruction of bloos vessel)
- infection/inflammatory diseases (TB or MS)
Brown-Sequard Syndrome symptoms
contralateral loss of pain and temperature sensation (STT)
ipsilateral loss of position and vibrating sensation, as well as parasthesia (ML)
neuropathic pain
complex, chronic pain state that is usually accompanied by a tissue injury affecting the STT
causes of central neuropathic pain
- spinal cord injury
- MS
- some strokes
what is referred pain
pain perceived at a location other than the site of the painful stimulus
