Sensory Systems (Lecture 6)
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| Dermatomes | 31 pairs of spinal nerves, sensory and motor that innervate the regions of the body accordingly
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| Types of Sensation | Mechanoreceptive (Tactile), Thermoreceptive (Temperature), Nociceptive (Pain)
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| Free nerve endings sense | pain, temperature, some tactile
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| Free nerve endings are located | throughout body (skin, tissue, visceral organs)
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| Free nerve endings | Can send information at slow rate for long periods of time (constant dull ache)
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| Encapsulated endings sense | tactile
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| Free nerve endings are located primarily | in skin of fingertips, palms, bottom of feet, lips, genitalia
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| Free nerve endings have | a fluid filled layer around fluid, displaced fluid stimulates nerve
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| Free nerve endings are | Most sensitive, primarily mechanical
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| Free nerve ending Meissner Corpuscles | closer to skin surface, light touch sensation primarily in hands and feet
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| Free nerve ending Pacinian | larger endings, more responsive to deep pressure
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| Expanded tip endings sense | tactile and temperature
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| Expanded tip endings are located | in dermas (skin) and joints
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| Expanded tip ending Ruffini Endings | spindle shaped, sensitive to skin stretch, contribute to sense of finger position movement (i.e. gripping), in deeper layers monitors angle change in joints
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| Expanded tip ending Merkel Receptors | extremely sensitive to tissue displacement, feel find details in fingertips
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| Three neuron organization of a sensory pathway: First order neurons | cell bodies in dorsal root ganglion of spinal cord transmit sensory information from the periphery to second order neurons
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| Three neuron organization of a sensory pathway: Second order neurons | most cell bodies in brainstem (though some may be in spinal cord), cross at midline and transmit to third order neurons
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| Three neuron organization of a sensory pathway: Third order neurons | cell bodies in thalamus (not vestibular or olfactory), most information projects to postcentral gyrus (sematosensory cortex), if the sensory information is taste then to gustatory cortex, if hearing then auditory cortex, and if visual then visual cortex
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| Touch decussates | ipsilaterally in medulla
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| Pain and temperature decussate | at the level of the spinal cord and ascend contralaterally
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| DCML (dorsal column medial leminiscus) PATHWAY | Made up of encapsulated nerve fibers that carries mechanosensory (touch) info from posterior third of head and from the rest of the body
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| DCML (dorsal column medial leminiscus) FUNCTION | Primarily for proprioception, fine touch discrimination, and sense of vibration
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| DCML (dorsal column medial leminiscus): Fasciculus Gracilis | mediates touch from lower half of body
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| DCML (dorsal column medial leminiscus): Fasciculus Cuneatus | mediates discriminative touch from upper half of the body
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| DCML (dorsal column medial leminiscus)DAMAGE | fine touch sensation and proprioception damage to whichever dermatome is affected
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| Anterolateral System: Lateral Spinothalamic Tract PATHWAY | free nerve endings Anterolateral System: Lateral Spinothalamic Tract FUNCTION
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| Anterolateral System: Lateral Spinothalamic Tract DAMAGE | decreased contralateral sense of pain, phantom limb
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| Anterolateral System: Anterior Spinothalamic Tract PATHWAY: | contains all three types of nerve endings
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| Anterolateral System: Anterior Spinothalamic Tract FUNCTION | General touch sensation, diffuse; Back up sensory system to DCML
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| Anterolateral System: Anterior Spinothalamic Tract DAMAGE: | no obvious clinical deficit but useful for telling if there is damage to DCML
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| Trigeminal Nerve (V) PATHWAYS | contains all three types of nerve endings
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| Nerve ending types | Encapsulated: fine discriminative touch, Free nerve endings: pain and temperature; All types: diffuse touch
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| Trigeminal Nerve Three branch FUNCTIONS: | Opthalamic: mediates from nose to half of scalp; Maxillary: from midface; Mandibular: from mandible side of face and part of outer ear
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| Trigeminal Nerve DAMAGE: | trigeminal neuralgia (excruciating chronic pain)
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| Central Visual PATHWAYS: | from retina to primary visual cortex. Nasal and temporal quadrants, and upper and lower portions as well. Temporal fibers project to ipsilateral cortex, nasal fibers decussate contralaterally.
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| Central Visual Damage: Homonymous | similar regions
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| Central Visual Damage: Heteronymous | two different regions of visual field
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| Central Visual Damage: Homonymous hemainopsia | same field of each eye, damage to optic tract (ex. homonymouse right hemianopsia)
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| Central Visual Damage: Monocular blindness | Blindness in one eye, damage to optic nerve
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| Central Visual Damage: Bitemporal hemianopsia | Opposite fields affected in each eye, damage to optic chiasm
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| Central Visual Damage: Nasal hemianopsia | blindness in both nasal visual fields, have peripheral vision, damage to optic chiasm
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| Central Visual Damage: Superior quadrantanopsia | blindness in upper quadrant, damage to optic tract
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| Central Visual Damage: Inferior quadrantanopsia | blindness in lower quadrant, damage to optic tract
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| Central Visual PATHWAYS: | Optic chiasm: enters cortex, Lateral geniculate body in Thalamus, Primary visual cortex (Broadman Area 17)
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| Central Auditory: Pathway from cochlea | Cochlear nuclear complex: tone, phase, timing, press. lvls; Sup. olivary com.: localize; Lat. lem.: pri. ascending aud. pthwy; In. coll.: analyze complex patterns; Med. geniculate bdy: thalamus (relay aud. info to pri. aud. cor.); Pri. aud. cor. (41,42)
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| Central Auditory DAMAGE | Hearing impairments: sensorimotor hearing loss; Central auditory impairments;
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| Central Auditory DAMAGE: Lower brainstem | sound localization issues (superior olivary), sound discrimination issues (lateral leminiscus);
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| Central Auditory DAMAGE: Upper brainstem | decreases reflexive response to sudden and loud noises and also difficulty selecting and attending to auditory stimuli (inferior colliculus)
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| Central Auditory DAMAGE: Cortical lesions | Wernicke's aphasia or auditory discrimination problems with specific phonemes
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| Vestibular System | body equilibrium
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| Vestibular System Components:Semicircular canal system | interconnected fluid (lymph) filled ducts, control equilibrium
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| Vestibular System Components: Vestibulo-ocular reflex | how eye is fixated while the body and head are moving
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| Vestibular System Components: Otolithic organs | sensitive to gravity and linear acceleration (horizontal and vertical acceleration)
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| Vestibular System Components: Vestibular nuclear complex | primary afferent vestibular projections to cerebellum, located in the floor of the medulla and behind the fourth ventricle, receives information from semicircular canals and otolithic organs
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| Vestibular System Components: Cerebellum | regulates head and neck in space, monitors posture reflexes
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| Vestibular System Damage | Motion sickness, Vertigo
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| Vestibular System Damage: Labyrinth dysfunction (within semicircular canals) | vertigo, disequilibrium, nystagmus, nausea
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| Vestibular System Damage: Benign positional vertigo | spinning sensation when head moved
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| Vestibular System Damage: Nystagmus | involuntary and irregular eye movement
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| Vestibular System Damage: Meniere disease | caused by high lymph pressure in semicircular canals and otolithic organs, symptoms are tinnitus, hearing loss, vertigo, eventually deafness
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