CN I Flashcards
(27 cards)
Contents of Olfactory epithelium
- Olfactory receptor cells = bipolar neurons which are the FIRST ORDER NEURONS of olfactory pathway
- Sustentacular cells = support cells
- basal cells = stem cells
Describe Olfactory receptor cells
- Only nerve cells that are EXPOSED to enviornement
- located in epithelium instead of being enclosed in a ganglion
- regenerated every 30-60 days thoughout a lifetime
- give rise to SLOWEST-conducting (unmyelinated) axons of the NS
Describe the fibers that make up CN I
- Axons of olfactory receptor cells form bundles called OLFACOTRY FILA
- All Olfactory fila form Cranial Nerve I on each side
- Olfactory Fila pass through cribiform plate of the ethmoid bone and terminate/synpase in the overlying olfactory bulb in the anterior cranial fossa
why do our nostrils open above the orifice of the oral cavity
- olfactory system serves as a last resort “alarm” system which protects us from ingesting food that might make us sick
what are the contents of the olfactory bulbs
- second order neurons = axons run in olfactory tract and give off collaterals to the anterior olfactory nucleus
–> Mitral cells
–> Tufted cells
- Interneurons = modulate olfactory input
Describe the olfactory projection sequence
- sequence of ONLY 2 neurons from receptor to cortex:
1) olfactory receptor cells (first order enurons)
2) mitral and tufted cells (projections neurons in the olfacotry bulb)
**Only system which does NOT project to thalamus prior to cerebral cortex**
Describe the Primary olfactory cortex projections
- Sends projections to:
–> hypothalamus = integrates endocrine and autonomic functions
–> amygdala of limbic system = processing of learning, memory, emotions and drives
–> Cortical areas = associated with memory
–> olfactory association cortex = interprets the significant of scent/odor
Lesion to olfactory receptor cells
- Olfactory receptor cell axons may be damaged due to fracture of ethmoid bone
RESULT:
- Anosmia = complete loss of sense of smell
- Hyposmia = partial loss of smell
- Parosmia (dysosmia) = distorted perception of odors
describe the visual pathway
1) Bipolar cells in the retina are first order neurons
2) Ganglion cells in the retina are second order neurons and give rise to axons that exit the eyeball to form OPTIV NERVE (heavily mylinated)
3) optic nerve passes through optic canal to enter cranial vault
4) optic nerves converge to form the optic chiasm
5) optic chiasm diverges to form the optic tract
6) Most terminate in the lateral geniculate nucleus (LGN) of thalamus; some terminate in superior colliculus or pretectal area and hypothalamus
7) LGN contains THIRD ORDER ENURONS which give rise to GENICULOCALCARINE TRACT (optic radiation) which run to the primary visual cortex
What lesion will result in Total blindness in Ipsilateral eye
- Optic nerve on Ipsilateral side
what type of lesion would result in Bitemporal (heteronymous) hemianopia
- Only CROSSED fibers at optic chiasm
result of Ipsilateral (right) nasal hemianopia
- Ipsilateral lesion of only one UNCROSSED FIBER
Result of Binasal (heteronymous) hemianopia
- Lesion in both sides of UNCROSSED FIBERS
Result of Left (homonymous) Hemianopia
- Right Optic tract lesion
OR
- Right LGN lesion
OR
- Right Optic radiation (upper and lower division)
**CONTRALATERAL**
Result of Left lower (homonymous) quadrantanopia
- lesion of the Right optic radiation - UPPER DIVISION ONLY (to cuneus)
–> CONTRALATERAL
Result of Left upper (homonymous) quadrantanopia
- Right Optic radiation lesion - LOWER DIVISON ONLY (to lingual gyrus/Meyers loop)
–> contralateral
what is the result of an occlusion in the Posterior cerebral artery
- produces a lesion in the PRIMARY VISUAL CORTEX (area 17) located in the medial surface of the occipital lobe on the banks of the calcarine sulcus (H)
- Result = Left (homonymous) hemianopia with MACULAR SPARING
What is the blood supply to the area of the brain that receives visual info from macula
- located in the posterior pole of the primary visual cortex
- receives blood supply from POSTERIOR CEREBRAL ARTERY with collateral blood supply contributed by MIDDLE CREREBRAL ARTERY
what are the 2 factors that support macular sparing
1) dual blood supply of the visual cortex - if PCA becomes occluded, the MCA nourishes the macular cortical region
2) macular cortical region is quite extensive, so its rare that a single infarction (vascular lesion) will produce a lesion large enough to damage ENTIRE CORTICAL AREA
What is the Function of Cranial nerve XI
- SVE/GSE = SKELETAL MOTOR to laryngeal muscles, SCM and trapezius
- GP = General proprioception (position sense) from SCM and trapezius muscles
describe Aberrant vagal fibers
- Arise from NULCEUS AMBIGUUS (SVE; in medulla)
- lower part of nucleus ambiguus contains the cell bodies of motor neurons (LMN) whose axons exit the nucleus
–> Join the main trunk of VAGUS NERVE and follows those fibers to innervate the LARYNGEAL MUSCLES
-
describe the Course Spinal accessory nerve
- ORIGIN = spinal accessory nucleus of the spinal cord C1-C5 levels
- Fibers arsing from spinal cord levels C1-C5 gatther to form SPINAL ACCESSORY NERVE
- Ascends to the foramen magnus to enter cranium
- Meet up with ABERRANT VAGAL FIBERS and run together through the JUGULAR FORAMEN to various muscles
(nucleus continuous superiorly with the nucleus ambiguus of the medulla)
If a person where to turn his/her head to the right, which SCM would contract?
- THE LEFT SCM CONTRACTS
Compare winging of scapula due to lesion of CN XI and Long thoracic nerve
CN XI lesion–> causes winging of the scapula
- more priminent during ABDUCTION OF THE AFFECTED ARM
LONG THORACIC Lesion
- More prominent during ANTERIOR ELEVATION OF THE ARMS and PUSHING UP AGAINST AN IMMOVABLE OBJECT (a wall or peice of furniture)
