Cranial Nerves Overview

CN I Olfactory Nerve

• Sensory nerve responsible for sense of smell
• Nerve endings are triggered by odor molecules
• Nerve impulse sent to olfactory bulb
• Terminates in olfactory cortex (inferior/medial temporal lobe)
• Clinical concerns: anosmia, hyposmia, hyperosmia
• Individuals with traumatic brain injury (TBI) may experience smell complaints due to damage to CN I tract at the base of the skull

CN II Optic Nerve

• Sensory nerve responsible for vision
• Originates in photoreceptor layer of retina, which transduces light energy into electrical signals
• Travels through optic nerve, optic chiasm where fibers cross over, and optic tract
• Terminates in occipital lobe
• Clinical concerns: visual field cuts, which may occur in aphasia or TBI due to damage to optic radiations

CN III Occulomotor Nerve

• Motor nerve responsible for eye movements, pupillary light reflex, and accommodation reflex
• Originates in oculomotor nucleus and Edinger-Westphal nucleus
• Fibers travel ventrally through brainstem
• Terminates in various eye muscles, pupillary sphincter, and ciliary muscle
• Pupillary light reflex controls amount of light entering eye
• Accommodation reflex adjusts lens shape for near vision and convergence

CN IV Trochlear Nerve

• Motor nerve responsible for eye movements
• Originates in trochlear nucleus
• Fibers travel ventrally through the brainstem
• Terminates in superior oblique muscle
• Controls downward and inward eye movement

Corticobulbar Tract

• The corticobulbar tract consists of upper motor neuron (UMN) fibers that connect the cerebral cortex to the motor nuclei of the cranial nerves.
• The UMNs in the corticobulbar tract originate in the cerebral cortex and descend to the brainstem.
• The lower motor neurons (LMN) in the corticobulbar tract originate in the brainstem and project to the muscle units of various muscles.

Lesions to the Corticobulbar Tract

• Lesions to the corticobulbar tract can result in both upper motor neuron (UMN) and lower motor neuron (LMN) lesion signs.
• UMN lesion signs differ from LMN lesion signs.

Dysarthrias

• Dysarthrias are motor speech disorders that result from impairments in various systems due to damage within the central nervous system (CNS) or peripheral nervous system (PNS).
• Dysarthrias affect the following systems:
  • Respiratory
  • Phonatory (voice)
  • Resonatory
  • Articulatory (speech)
  • Prosodic

Spastic Dysarthria

• Spastic dysarthria is due to damage to the upper motor neuron (UMN) system.
• Prominent speech characteristics include:
  • Low pitch
  • Slow rate
  • Strained-strangled quality

Flaccid Dysarthria

• Flaccid dysarthria is due to damage to the lower motor neuron (LMN) system or the motor unit.
• Prominent speech characteristics include:
  • Hypernasality
  • Continuous breathiness
  • Nasal emission
  • Audible inspiration
  • Short phrases

Motor Weakness Terms

• Paresis refers to weakness (partial paralysis).
• -plegia refers to no movement or paralysis.
• Hemi- refers to one side of the body.
• Para- refers to both legs.
• Quadri- refers to all four limbs.

Motor Weakness Terminology

• Hemiplegia: No movements on one side of the body.
• Hemiparesis: Weakness in movements on one side of the body.
• Paraplegia: No movements in both legs.
• Quadriplegia: No movements in all four limbs.

This quiz covers the essential aspects of the first three cranial nerves: the Olfactory, Optic, and Oculomotor nerves. Explore their functions, clinical concerns, and pathways in the nervous system. Understand the implications of injuries affecting these sensory and motor nerves.