• Thalamus
• Hypothalamus
• Subthalamus
• Optic Tract
• anterior extension of diencephalon

Thalamus

General Info

• Consists of multiple nuclei
• Sensory relay to cortex
• speech/language functions
• Massa Intermedia; thalamic adhesion

• Thalamic adhesion
• Connect right/left thalami
• Present in 70-80% of people

• Relay sensory information to cortex
• gross sensory processing (mostly unconscious)
• Integrate motor information
• From basal ganglia, cerebellum, limbic system
• To primary and pre-motor cortex
• Regulate cortically-mediated cognitive functions
• Inputs to/from brainstem reticular formation

• Thalamo-cortico-thalamic look
• reverberating circuit
• Project and retain information

• ~120
• Specific
• Bi-directional connections to specific cortical areas
• Sensorimotor and cognitive processes
• Non-specific
• No direct connection to cortex
• Connected to brainstem arousal systems

1. Medial (mediodorsal) nuclear complex
2. Lateral nuclear complex
3. Ventral nuclear complex
4. Lateral geniculate body
5. Medial geniculate body

• Input from: mammilary glands, hippocampus, cortical areas
• Output to: cortical association areas, prefrontal, orbitofrontal, limbic, hippocampus, hypothalamus

• Mood, emotion, cognition, personality
• Development of emotion, judgement/reasoning, memory, language
• Intergrate visceral information with affect, emotion, though processes, personality and judgement
• Regular mood based on sensory input and stored experiences
• Sensory and motor learning

• Input from: visual cortex, superior colliculus, midbrain, visual reflex center, inferiuor parietal
• Output to: inferior parietal, angular and supramarginal gyri
• Language formulation and processing, reading, writing
• Visual reflexes

• Input from spinal cord, somatosensory for body (below the neck)
• Primary sensory relay
• VPL/VMP output to primary sensory area

• Relay station for visual input
• Fibers of CN II (optic nerve) to occipital lobe

• Relay station for auditory input
• Fibers from inner ear (via CN VIII and brain stem) to temporal lobe

• Sensations
• Pain
• Temperature
• Touch
• Proprioception (where you are in space)
• Pathways
• Sensors in skin, muscles, joints, blood vessels

• Mix of afferent and efferent fibers
• Spinal nerve splits -> dorsal and ventral spinal nerve fibers
• Dorsal root ganglion
• Dorsal horn

Somatosensation: Ascending fibers

• Pain, touch, temperature, proprioception
• through spinal cord, brian stem, thalamus
• To primary sensory (somatotopically organized)
• Conscious perception of sensation
• To association areas (superior parietal)
• Analyzes and intergrates sensations

• Classified based on modality or adaptability
• Quick adapting
• Initial response fades over time
• Non-adapting
• Continuous response over time

• Mechanoreceptive
• Tactile: rouche, pressure, vibration
• Fine discriminative (localizable)
• Diffuse (unlocalizable)
• Kinesthetic (limb movement)
• Thermoreception
• Nociception

• Anterior: non-localizable (diffuse/crude) touch
• Lateral: pain and temperature

• Final touch, vibration, proprioception
• Funiculi Gracilis and Cuneatus

Spinal pathways:

Anterolateral spinalthalamic tract

First Order neurons

• Dendrites in periphery
• Cell bodies in spinal DRG
• Synapse in ipsilateral spinal cord

Spinal pathways:

Anterolateral spinalthalamic tract

Second order neurons

• Cell bodies in spinal cord
• Axons cross over and ascend in contralateral spinal cord
• Synapse in thalamus (VPL)

Spinal pathways:

Anterolateral spinalthalamic tract

Third Order Neurons

• Cell bodies in thalamus
• Axons ascend to parietal lobe (primary sensory area)

Dorsal Column Medial Lemniscal Tract (DC-ML)

First Order Neurons

• Dendrites in the periphery
• Cell bodies in DRG
• Synapse in the medulla

Dorsal Column Medial Lemniscal Tract (DC-ML)

Second Order Neurons

• Cell bodies in the medulla
• Axons cross over and ascend in contralateral brain stem
• Synapse in the Thalamus (VPL)

Dorsal Column Medial Lemniscal Tract (DC-ML)

Third Order Neurons

• Cell bodies in the thalamus
• Axons ascend to parietal lobe (primary sensory area)

• DCML
• Late developing
• Travel in cuneatus and gracilis
• Discriminative touch
• Decussates at medulla

• Anterolateral
• Early developing
• Pain, temperature, diffuse touch
• Decussate in spinal cord

DC-ML system

General Info

What sensory info is carried

• Large myelinated fibers
• Precise map of body system
• Lesions -> predictable loss of sensation
• Fasciculus Gracilis - lower body
• Fasciculus Cuneatus - upper body
• Fine discriminate touch
• Graphesthesia
• Stereognosis
• Vibration sense
• Proprioception, kinethesia

DC-ML system:

Cortical representation

• Post-central gyrus
• Somatotopic organization
• Conscious awareness
• Lesion -> reduced perception of touch and localization
• Somasthetic association cortex (BA 5,7)
• Inferior parietal lobule; temporo-parieto-occipital region
• Lesion -> reduced touch perception, tactile agnosia, reduced sensory discrimination

Sensory neurons and pathways:

Anterolateral system

• Lateral spinothalamic tract - pain and temp
• Anterior spinothalamic tract - unlocalizable touch
• 3 neuron pathway

Lateral spinothalamic tract

Pain and Temp

• Connections to thalamus
• VPL
• Intralaminar nuclei - connections to limbic system
• Mediates emotional responses to pain
• Influenced by descending reticulatar projections
• Periaqueductal gray matter
• modulate pain perception
• visceral responses to pain
• Nausea, fainting, changes in heart rate and respiration

Lateral spinothalamic tract

Phantom limb pain

Peripheral neuron regrowth -> growth tip encounters scar tissue (stump) -> forms hypersenstive neuroma -> sensations "recorded" in brain as from missing limb

Lateral spinothalamic tract

Referred pain

• Damage to one site "felt" in another site
• Visceral pain = poorly localized
• No specific visceral pathways in CNS
• Heart attach -> pain in chest/arm

Lateral spinothalamic tract

First order neurons

• Dendrites in periphery
• Cell bodies in spinal DRG
• Axons enter spinal cord
• Synapse in dorsal horn

Lateral spinothalamic tract

Second Order neurons

• Cell bodies in dorsal horn
• Axons cross midline in spinal cord
• Ascend in contralateral lateral spinothalamic tract
• Synapse in thalamus (VPL)

Lateral spinothalamic tract

Third Order Neurons

• Cell bodies in thalamus
• Axons ascend to parietal lobe (primary sensory area)

Anterior Spinothalamic Tract:

General info

• Diffuse touch - no specific location
• Feels touch, but can't localize or describe it
• back up for Dorsal column

Anterior Spinothalamic Tract:

First order neurons

• unipolar neurons
• Dendrites in periphery
• Cell bodies in DRG
• Axons enter spinal cord
• Synapse in dorsal horn

Anterior Spinothalamic Tract:

Second order neurons

• Cell bodies isn dorsal horn
• Axons cross midline in spinal cord
• ascend in contralateral anterior spinothalamic tract
• Multiple axon collaterals to reticular formation
• Synasep in the thalamus (VPL) 

Anterior Spinothalamic Tract:

Third order neurons

• Cell bodies in thalamus
• Axons ascend to parietal lobe (primary sensory area)

Spinocerebellar tracts

General info

• Unconscious proprioception
• Position, range, diretion of limb movements
• Backup for consciuos DC-ML system
• Modify, monitor ongoing movements through cerebellum

• 2 neuron system
• First order
• Dendrites in periphery
• Cell bodies in spinal DRG
• axons enter spinal cord
• Synapse in dorsal horn
• Second Order
• cell bodies in dorsal horn
• axons ascend in spinocerebellar tracts
• May cross over in spinal cord and then cross back over in medulla
• Synapse in ipsilateral cerebellum

• Nerves innervate specific regions
• Each pair of spinal nerves -> body region
• Dermatome (sensory)
• areas innervated by afferent nerve
• Myotome (motor)
• areas innervated by efferent nerve

• Direct sensory-motor connection
• Stimulation of sensory nerve ending
• Travel through axon into dorsal horn
• Synpases on motor nerve
• Travel through axon out through ventral root
• Signal muscle to contract

• Inhibition of antagonist muscle to allow movement of primary muscle (agonist muscle)

Spinal cord lesions:

Complete transection

• Bilateral loss of all sensory and motor below lesion

Spinal cord lesions:

Spinal Hemisection

• Brown-Sequard syndrome
• Damage to 1 side of spinal cord (R or L)
• Ipsilateral paralysis
• Ipsilateral loss of touch sensation
• Contralateral loss of pain and temp

Auditory System:

Mechanics

• Sound waves -> create vibration
• movement of tympanic membrane
• Pressure waves -> mechanical energy
• movement of ossicles
• Mechanical energy -> hydraulic energy
• movement of fluid in cochlea
• Nerve impulses
• movement of hair cells in cochlea -> auditory nerve (CN VIII)
• Cranial nerve -> thalamus (MGB) -> temporal lobe (Heschel's gyrus)

• air filled cavity
• ossicles (malleus, incus, stapes)
• Eustacian tube - opens into nasopharynx
• Oval window - entry into cochlea, covered by stapes footplate
• Round window - entry into cochlea

• Body Labyrinth: cavities within temporal bone
• Semicircular canals
• Cochlea
• Membraneous labyrinth: fluid filled canals/ducts
• Housed within body labyrinth

Ear anatomy: inner ear

Cochlea

• Snail shaped structure, coiled around modiolus
• Cavities:
• Scala vestibuli
• Reisner's membrane
• Scala media (cochlear duct)
• Basilar membrane
• Scala typmani

• Vestibuli/tympani: filled with perilymph
• High sodium cencentration (like CSF)
• Scale media: filled with endolymph
• High posassium concentration (like intracellular fluid)

• Hair cells = primary auditory receptors
• outer hair cells (3 rows)
• Inner hair cells (1 row)
• Tectorial membrane

• Stereocilia
• extend from hair cells
• end in proximity to tectorial membrane

• Basilar membrane displaced by fluid movement
• Creates mechanical displacement of cilia
• Cilia bend -> increase permeability to K+ ions
• K+ moves into hair cells
• Opens calcium channel -> calcium moves into hair cells
• Triggers release of Ntx Glutamate
• Glutamate binds to receptors on cochlear nerve endings
• Depolarizes cochlear nerve
• Axon potential send up CN VIII

• Cochlea to brainstem
• Cochlear nerve (CN VIII)
• Axons travel through internal auditory meatus
• Enter brainstem and ponto-medullary junction

• Brainstem to Cortex
• Cochlear nuclei (dorsal/ventral)
• Some via trapezoid body
• Superior olivary complex
• through lateral lemniscus
• Inferior colliculus
• Medial geniculate body
• Heschel's gyrus

Central Auditory Pathway:

Cochlear nuclei

• 80% cross over
• Some through trapezoid body

Central Auditory Pathway:

Superior Olivary Nucleus

• Receives ipsilateral and contralateral stimuli
• comparisons of timing and intensity for localization

Central Auditory Pathway:

Lateral Lemniscus

• Tracts
• Some synapses in pons

Central Auditory Pathway:

Inferior colliculus

• Commissural fibers between R/L colliculi
• Integration with superior colliculi
• Startle reflexes

Central Auditory Pathway:

Medial Geniculate body

• From ipsilateral inferior colliculus

Central Auditory Pathway:

Heschel's gyrus

• From ipsilateral MGB

Central Auditory Pathway:

Information processing

• Contralateral projections (80%)
• Integration of monaural and binaural information
• aids in sound localization

• BA 41
• Heschel's gyrus
• Dorsal surface of superior temporal gyrus
• Tonotopic organization
• ]Functions: auditory discrimination based on timing

• Association area
• BA 42
• Lateral surface of superior temporal gyrus
• Functions: processing timing patterns and spatial attributes

• Deep in sylvian fissure, around superior temporal gyrus
• Large in L than R hemispher

• BA 22
• Connected to BA 41/42
• Recognizes language stimuli
• Interpret meaning
• Compare stimuli to auditory memories
• Comprehend spoken language

• Coordinate head and eye movement toward sound
• Pathways:
• Inferior colliculus -> superior colliculus

• Feedback circuits
• Refine pitch eprception
• lateral inhibition -> sharpen reception of specific frequences
• Suppress responses to competing background noise

• Problem with conduction of sound waves in outer/middle ear

• Damage to sensory mechanism (cochlea - hair cells) or neural pathway (CN VIII)
• Causes
• Noise exposure
• Meniere's diesease
• Presbycusis
• Acoustic neuroma
• Vestibular schwannoma

Central Auditory Impairment:

Left Hemisphere

• Unilateral Left temporal lobe lesions
• Wernicke's area
• Pure word deafness
• Cortical deafness

Central Auditory Impairment:

Wernicke's area

• Wernicke's aphasia
• Impaired comprehension, jargon, empty speech

Central Auditory Impairment:

Pure word deafness

• Isolates primary auditory area from association areas
• Speech sounds like noise, uninterpretable
• reading, writing, speaking are presevered
• auditory perception of noises are preserved

Central Auditory Impairment:

Cortical deafness

• Bilateral damage to Heschel's gyrus
• Inability to hear despite intact peripheral auditory system and pathways to the cortex

Central Auditory Impairment:

Right Hemisphere

• Unilateral right temporal lobe lesions
• Impairments in interpreting prosody

• Inner Ear
• Semicircular ducts/canals
• Vestibule: utrile and Saccule
• Brainstem
• Vestibular nuclei (medulla)
• Medial Longitudinal fasciculus
• Brainstem reticular formation and RAS
• Cerebellum
• Spinal Cord

• 3 seperate canals
• At right angles (X,Y, and Z axis)
• Anterior posterior lateral

• Utricle and Saccule
• Contain hair cells
• Otolithic membrane
• gelatinous mass w/calcium crystals
• Canals and vestibule
• physiology
• Similar to cochlear hair cells

• Fibers course through internal auditory meatus
• Join with auditory nerve fibers
• lies next to facial nerve
• enters brainstem

Vestibular projections

From Vestibular nuclei to:

Medial Longitudinal fasciculus

• To cranial nerve nuclei for eye movement
• CN III, IV, VI (3,4,6)
• Congugate eye movement
• Head/eye position, visual fixation with head movement

Vestibular projections

From Vestibular nuclei to:

Cerebellum

• Flocculonodular lobe, vermis
• Cerebellovestibular; spinocerebellar tracts
• Integrated connections for balance, equilibrium, proprioception

Vestibular projections

From Vestibular nuclei to:

Spinal Cord

• Includence axial muscles; muscle tone to cunteract gravity
• Vestibulospinal, spinocerebellar tracts
• Integrated connections for balance, equilibrium, proprioception

Vestibular projections

From Vestibular nuclei to:

• Other projections
• Retcular formation, recticular activating system
• visceral automatic activities
• Thalamus
• Cortex
• Motor system ?
• Frontal eye fields
• middle frontal gyrus
• volitional eye movements
• Parietal lobe ?
• Temporal lobe ?

• Enlarged area at base of each canal
• Crista - sensory organ within the ampulla (contains hair cells)
• Cupula gelatinous structure encasing cilia

• Utricle/saccule
• Maculae
• Otolithic membrane
• otoconia

• Calcium crystals
• located on surface of otolithic membrane

• Movement of head -> movement of fluid in semicircular canals
• Fluid moves in opposite directions on R/L sides of head
• Fluid presses against cupula
• Movement of cupula -> movement of cilia
• Cilia bend toward dinocilium -> open K+ channels
• K+ enters cells, causes depolarization
• Signals opening of Ca++ chanels, Ca moves in
• Ca signals release of neurotransmitter
• Cilia bend away from kinocilium -> hyperpolarization

• Utricle set horizontally; saccule vertically
• Movement of head -> shifting of otolithic membrane
• movement enhanced by otoconia
• cilia bend toward kinocilium -> open K+ channels
• K+ enters cell, causes depolarization
• signals opening of Ca++ channels, Ca moves in
• Ca signals release of neurotransmitter

• Similar to cochlear hair cells
• Hair cells, cilia arranged by height (kinocilium=tallest)
• Resting state (cilia in neutral position) -> some K+ channels open, causing regular action potentials
• Bend cilia towards kinoclium -> open K channels -> depolarization -> increase # of action potentials
• Bend cilia way from kinocilium -> close K channels -> hyperpolization -> decrease # of action potentials