Flashcards in Week 2 Sensory Receptors, Sensory Pathways, Lesions Deck (29)
Define stimulus transduction.
The process by which a sensory receptor converts the sensory stimulus into an electrical signal that is carried by sensory axons
What is a graded potential (aka generator potential or receptor potential)?
-changes in ion fluxes across the membrane in varying degrees (not all or none)
-an increase in magnitude of a receptor potential (stimulus energy) causes an increase in frequency of action potentials
Define adaptation or desensitization.
-decrease in frequency of action potentials in a sensory neuron despite maintenance of the stimulus at constant strength
What is the difference between rapidly adapting (phasic) receptors and slowly adapting (tonic) receptors?
-rapidly adapting: response quickly to onset of stimulus then decreases over time or may stop responding. important for indicating change in stimulus. E.g. putting on a sock, then forgetting it is on your feet
-slowly adapting: responses that maintain response to stimulus over time, e.g. receptors in joints/muscles that convey positional info, receptors that measure oxygen tension in blood
What are the 4 attributes coded for by a sensory stimulus?
1. modality (what it is)
-touch, temperature, pain receptors
2. location (where it is)
-related to size of receptive fields of neurons
-conveyed via freq of action potentials
How do receptive fields of neurons convey the degree of acuity of a particular sense?
-overlapping receptive fields give more precise location (e.g. if recorded by 3 neurons, stimulus is at the intersection of those receptive fields)
-size of receptive field: small on fingertips and large on back (less able to distinguish between two points close together) [2 point discrimination]
-lateral inhibition: ability of excited neuron to reduce activity of it neighbors and sharpen spatial profile of excitation
Where is neuron 1 and its axons for the DC/ML pathway?
Neuron 1 is in DRG
Its axons for C1-T5 are in Fasciculus cuneatus in spinal cord
Its axons for T6-S5 are in Fasciculus gracilis in the spinal cord
Where is neuron 2 and its axons for the DC/ML pathway? Where is neuron 3?
Neuron 2 is the Nucleus cuneatus and Nucleus gracilis in the lower medulla. Its axons take the ML pathway after decussation. Neuron 3 is VPL in the thalamus.
Where is neuron 1 and its axons for the STT pathway?
Neuron 1 is DRG
Its axons doesn't have a name
Where is neuron 2 and its axons for the STT pathway? Where is neuron 3?
Neuron 2 is nucleus proprius in the dorsal horn where the axons of neuron 1 enter the spinal cord.
Axons of neuron decussate 1-2 segments above nucleus proprius through white commissure and follow STT tract to Neuron 3-VPL in thalamus
Where is neuron 1 and its axons for the TL (trigeminal lemniscus) pathway?
Neuron 1: trigeminal ganglion
Its axons aren't named
Where is neuron 2 and its axons for the TL pathway? Where is neuron 3?
Neuron 2: Chief/main sensory nucleus of V in mid pons
The axons decussate in the mid pons and follow the TL pathway
Neuron 3: VPM in thalamus
Where is neuron 1 and its axons for the TTT (Trigeminal thalamic tract) pathway?
Neuron 1: trigeminal ganglion
The axons follow spinal tract of V in mid pons-descending to lower medulla
Where is neuron 2 and its axons for the TTT pathway? Where is neuron 3?
Neuron 2: Spinal nucleus of V
Axons follow TTT pathway, decussating in lower medulla and ascending to Neuron 3
Neuron 3: VPM in thalamus
What is the sensory pathway for taste?
Neuron 1: sensory ganglion of VII, IX, and X
Neuron 1 axons: solitary tract
Neuron 2: nucleus solitarius
Neuron 2 axons central tegmental tract
Neuron 3: insula, SS1 for tongue
List the four sensory pathways for the head/neck and body and what sensory information they carry.
1. DC/ML: fine touch, proprioception, vibration, and 2 point discrimination
2. STT: temperature and pain
1. TL: fine touch, proprioception, vibration, and 2 point discrimination
2. TTT: temperature and pain
What type of injury does a decreased deep tendon reflex indicate? What type of injury does a increased deep tendon reflex indicate?
decreased reflex: Peripheral injury
increased reflex: CNS injury
Identify the connections that mediate the corneal blink reflex.
-afferent limb: opthalmic nerve (V) innervates cornea and conveys sensation of touch
-sensory nuclei are parts of spinal trigeminal nucleus and chief sensory nucleus that projects laterally to the facial motor nuclei (VII)
-efferent limb: cranial nerve VII to orbicularis oculi muscles that contract to close eye
What are the features of isolated peripheral nerve lesion (mononeuropathy)?
-Sensory: numbness and loss of light touch, pinprick, and vibration sense in a targeted dermatome or area of an individual limb or trunk dermatome
-motor: weakness or loss of limb or digit movements, possible atrophy of muscle. decreased deep tendon reflex
-common causes: contusion, crush, or laceration of a ventral rams of a peripheral nerve
What are the features of distal symmetrical polyneuropathy? [degeneration of distal axons]
-Sensory: bilateral sensory loss-Glove and/or stocking distribution in all modalities. vibration may be earliest sensor modality effected
-motor: muscle wekaness, areflexia, flaccid paralysis
-Common causes: metabolic diseases (diabetes), deficiency syndromes, acute inflammatory disease causing demyelination, chemical toxins (cancer drugs)
What are the features of radiculopathy?
-lesion at spinal nerve at intervertebral foramen
-numbness and pain along course of nerve or dermatome
-causes: compression of nerve root/area of spinal nerve, disc herniation
What are the features of transverse cord lesion?
-Sensory: bilateral loss of all sensory modalities at and below the lesion
-motor: upper motor neuron syndrome bilateral
-common causes: trauma, tumors, multiple sclerosis
What are the features of a hemicord lesion: brown-sequard syndrome?
-Sensory: loss of vibration and proprioception ipsilateral to lesion (DC/ML pathway). Loss of pain and temperature contralateral but slightly below lesion (STT pathway)
-motor: upper motor neuron syndrome ipsilateral to lesion
-common causes: penetrating injury, lateral compression from tumor
What are the features of a central cord syndrome (springomyelia-small lesion)?
-Sensory: segmental loss of pain and temperature bilaterally at the level of lesion. Lose crossing fibers in 1-2 segments (STT)
-motor: only occur with larger lesion that effects the anterior horns of spinal cord
-common causes: central cavitation can be congenital or acquired due to trauma, tumor, etc.
What are the features of a posterior cord syndrome?
-sensory: loss of vibration and position sense below the level of the lesion (DC/ML). Pain and temp normal (STT unaffected)
-motor: only occur with larger lesion that affects corticospinal tract
-common causes: compression from posterior located tumor, vitamin B12 deficiency, tabes dorsal is (tertiary syphilis), multiple sclerosis
What are the features of anterior cord syndrome?
-sensory: loss of pain and temperature below the level of lesion (STT). vibration and position sense normal.
-motor: upper motor syndrome due to damage to anterior horns of spinal cord and corticospinal tract
-common causes: trauma, MS, ant spinal artery infarct
What are the features of a medial medullary lesion in the brain stem?
-sensory: contralateral loss or decrease in vibration and position sense (ML)
-motor: contralateral loss or weakness in arm and leg (pyramid). ipsilateral tongue weakness (CN 12)
-common causes: infarct of paramedic branches of ant spinal or vertebral artery
What are the features of a lateral medullary lesion (wallenberg's syndrome)?
-ipsilateral loss of pain and temperature to face (TTT)
-contralateral loss of pain and temp to body (STT)
-unilateral horner's syndrome-ipsilateral eye
-hoarseness, difficulty swallowing, loss of gag reflex