Cranial Nerve VIII

Transmits auditory information from cochlea.

Sound Waves

Vibrations characterized by frequency and amplitude.

Frequency

Pitch measured in Hertz (Hz) of oscillations.

Amplitude

Loudness determined by magnitude of oscillations.

Cochlea

auditory structure

Organ of Corti

coverts mechanical energy from sound waves into neural signals

Basilar Membrane

• Codes sound frequency through its shape.
• narrowest at middle ear = shorter fivers for higher frequencies
• widest at free end = longer hairs for lower frequencies

Hair Cells

Sensory cells that generate neural signals.

Auditory Pathway (from choclear nuceli)

reticular formation --> inferior colliculus --> medial geniculate body

Cochlear Nuclei

First relay station for auditory signals.

Inferior Colliculus

Integrates auditory information from both ears.

Medial Geniculate Body

Thalamic relay for auditory signals to cortex.

Primary Auditory Cortex

Processes complex sounds, sound localization, selective attention to specific sounds, discrimination of auditory patterns, performance of difficult auditory tasks

Auditory Patterns

Recognition and discrimination of sound sequences.

Round Window

Flexible membrane that relieves cochlear pressure.

Oval Window

Membrane transmitting vibrations from stapes to cochlea.

Reticular Formation

Regulates arousal and attention to auditory stimuli.

Auditory Nerve

Transmits signals from cochlea to brainstem.

Olfactory receptors

Hair cells in nostrils detecting odors.

Olfactory pathway

olfactory receptors --> olfactory bulb --> Primary olfactory cortex/amygdala/parahippocampal gyrus

Amygdala sends olfactory information to (3 places)

1. Hypothalamus (hunger)
2. Medial parahippocampal gyrus (quality of aromas and odors)
   Sends to secondary olfactory area in orbitofrontal cortex (frontal lobe) for value judgements
3. Lateral parahippocampal gyrus (declarative memory)

Primary olfactory cortex

Initial processing area for olfactory signals.

Orbitofrontal cortex

Processes value judgments of odors.

Visual system

System responsible for sight and visual processing.

Eye movement control

Regulates movements for visual targeting.

Lens

Refracts light before it enters the pupil.

Pupil

Opening for light entry, controlled by ciliary bodies.

Retina

Receptors that convert light into neural signals

Optic nerve (CN II)

First order neuron in visual pathway.

Visual pathway

Sequence of neural connections for vision.

Optic chiasm

Point where retinal axons cross to opposite cortex.

Lateral geniculate nucleus

Thalamic relay for visual information.

Primary visual cortex

Processes basic visual features like shape.

Dorsal stream

Visual pathway for action and movement adjustments.

Ventral stream

Visual pathway for object recognition.

Tectal system

Midbrain structure for auditory and visual reflexes.

Eye movement system

• Normal eye movements require synthesis of information concerning
  • head movements (vestibular), visual objects (visual info)
  • eye movement and position (proprioception)
  • selection of visual target (brainstem & cortical areas)

Conjugate Movements

Both eyes move in the same direction.

Vergence Movements

Eyes move toward or away from midline.

Gaze Stabilization

Maintains stable vision during head movements.

Nystagmus

Involuntary oscillating movements of the eyes.

Optokinetic Nystagmus

Reflex elicited by moving moving visual stimuli.

Physiologic Nystagmus

Normal response elicited by head rotation or stimulation.

Saccades

Fast eye movements between visual targets.

Smooth Pursuits

Eye movements tracking a moving object.

Convergence

Eyes aim at midline for closer objects.

Optic Nerve Lesion

Causes total vision loss in ipsilateral eye.

Optic Chiasm Lesion

Results in bitemporal hemianopia.

Complete Optic Tract Lesion (before LGN)

Leads to contralateral homonymous hemianopia.

Incomplete Optic Tract Lesion (after LGN)

Causes partial vision loss in contralateral field.

Ciliary Muscles

Contract to increase lens curvature for focus.

Frontal Eye Fields

Involved in voluntary eye movement control.

Superior Colliculus

Processes visual information for saccades.

Eye movement system objectives

• Keeping the position of the eyes stable during head movements to ensure that the environment does not appear to bounce.
• Directing the gaze at visual targets

Eye movements are either

• Conjugate (both eyes move in the same direction)
• Vergence (eyes move toward the midline or away from the midline)