Mod 3 Flashcards
Ascending sensory pathways
Spinothalamic (ALS)
DCML
Spinocerebellar
Anterior and posterior spinocerebellar pathways
Carry subconscious proprioception
- receptors of muscles, joints, tendons, and skin
- ipsilateral trunk and lower extremity
First order neuron: carries signals from receptor to dorsal horn
- cell body in dorsal root ganglia
Second order neuron: carries signals from the dorsal horn to the cerebellum
- cell body in the dorsal horn
Anatomy of the thalamus
Relay signals to the ipsilateral cerebral cortex
- specific relay nuclei
- sensory relay nuclei
- motor relay nuclei
- association nuclei
- nonspecific nuclei
Vascular supply of the thalamus
Posterior cerebral artery
Anterior choroidal artery
Function of the ALS
Carry sensory signals to the cerebral cortex
Neurons travel by the direct or indirect path.
Direct path carries pain, temperature, and crude touch to the thalamus.
Indirect path carries pain to others structures before they reach the thalamus.
- reticular formation
- hypothalamus
- superior colliculus
- brainstem
Neurons of ALS
First order: receptor to dorsal horn
Second order: dorsal horn to thalamus
Third order: thalamus to cerebral cortex
Indirect path of ALS
Reticular system: alerts patient to injury, elicits response –> evade injury
Mesencephalon: modulates pain reception
- transmits to the amygdala, emotional component of pain
Superior colliculus: turn head/eyes toward pain stimulus
Hypothalamus: autonomic response
- increases heart rate
- endocrine release of stress hormones
DCML
In posterior funiculus
Fine touch, vibration, and proprioception
Fasciulus gracillis - on either side of midline carrying signals to LE
Fasciculus cuneatus - lateral to FG carrying UE signals
Neurons of DCML
First order: receptor to medulla
Second order: dorsal horn to thalamus
Third order: thalamus to cerebral cortex
Specificity theory
Proposed that the somatosensory system could be divided according to specific receptors for tactile, hot, cold, and pain
Pattern theory
Suggested that in addition to the type of input (fibers, pathways, or anatomic structures), the pattern of impulses in the nervous system modulates pain perception
Gate control theory
Endogenous pain modulatory mechanisms could enhance or reduce perception
Diffuse noxious inhibitory controls
Observation that a localized nociceptive stimulation can produce a diffuse analgesic effect over the rest of the body, an analgesic approach known as counter-irritation.
Path of light
Cornea
Anterior chamber
Pupil
Lens
Vitreous humor
Retina
Neurons of the eyeball
Photoreceptors: light energy transduced to electrical energy
First order: bipolar cells
Second order: ganglion cells which form the optic nerve
Third order: in the thalamus which sends projections to the visual cortex
Light stimulates a sensory signal which travels the following path
Optic nerve
Optic chiasm
Optic tract
LGN of the thalamus
Optic radiations
Visual cortex
Secondary: subconscious vision
- superior colliculus: saccadic eye movement
- pretectal area: autonomic reflexes
- hypothalamus: circadian rhythms
- reticular formation: arousal/vision
PLR: Constriction
Afferent: CN II
Efferent: CN III
- light –> optic nerve/optic tract
- pretectal midbrain —> bilateral EW nucleus
- bilateral ciliary ganglia –> constrictor muscles
PLR: Dilation
- hypothalamus
- spinal cord
- superior cervical ganglia
- internal carotid artery plexus
- dilator muscles
Convergence accommodation reflex
Light –> optic nerve –> optic tract –> visual cortex –> bilateral midbrain
- Convergence: CN III to medial rectus
- Accommodation: CN III to ciliary muscles
- Constriction: CN III to pupillary sphincter
Corneal blink reflex
Afferent: CN V1 (unilateral)
Efferent: CN VII (bilateral)
Pathway of sound
Sound waves create oscillations
- external auditory canal
- tympanic membrane
- ossicles vibrate, pusing on the structures of the inner ear
- oval window
- scala vestibuli
- scala tympani
- round window
Chochlea
The cochlear duct is between the scala vestibuli and the scala tympani.
It contains the receptors for transducing fluid wavs into electrical signals.
Ascending auditory pathway
the auditory pathway travels along CN VIII to immediately become a bilateral signal which goes to the thalamus then the auditory cortical areas.
Vestibular system
The bony labyrinth contains the organs of the vestibular system
Two sets of vestibular organs:
- semicircular canals
- otolith organs
Semicircular canals
As the head moves, the fluid inside the canals moves, pushing on the ampulla of the canal.
Otolith organs
In the vestibule
- saccule
- utricle
Function: respond to linear movement
Receptors of the otolith organs
Hair cells embedded in a gelatinous membrane. Movement causes hair cells to bend, depolarizing sensory neurons.
Otoliths sit on top of the membrane, causing the membrane to move in response to gravity.
Afferent projections to the vestibular nuclear complex
Vestibular nerve
Cerebellar nuclei
Contralateral vestibular nucleus
Spinal cord (spinovestibular fibers)
Pretectal nuclei (eye movement coordination)
Efferent projections to the vestibular nuclear complex
Motor nuclei of CN III, IV, VI: extraocular movements and eye reflexes
Cerebellum: integrates sensory movement and coordinates movement
Reticular formation: reflex motor activity
Spinal cord: postural adjustments
Vestibular labyrinth: modulate the afferent signals
