Neuroanatomy

Peripheral Autonomic Nervous System (ANS)

• Divided into Sympathetic (Fight or Flight), Parasympathetic (Rest and Digest), and Enteric Nervous System (ENS)
• Sympathetic Nervous System (SNS):
  • Increases heart rate, blood pressure, bronchodilation, and reduces gastrointestinal activity
  • Pathways: Short preganglionic fibers, long postganglionic fibers
  • Exception: Eccrine sweat glands use cholinergic transmission
• Parasympathetic Nervous System (PNS):
  • Enhances digestion, salivation, lacrimation, and sexual arousal
  • Pathways: Long preganglionic fibers, short postganglionic fibers
  • Major cranial nerves involved: III, VII, IX, X
• Enteric Nervous System (ENS):
  • Regulates gastrointestinal function independently of CNS
  • Components: Myenteric and submucosal plexuses in the GI tract

Visceral Afferents

• Physiological Afferents: Travel with parasympathetic nerves, monitor internal conditions
• Pain Afferents: Travel with sympathetic nerves, can cause referred pain

Cranial Nerves

• 12 bilaterally paired, numbered with Roman numerals
• CN I and II attach to the forebrain, others to the brainstem

Functional Components

• Afferent and Efferent Nuclei: Different nuclei are responsible for sensory (GSA, GVA, SSA, SVA) and motor functions (GSE, GVE, SVE)

Eye Control Nerves (III, IV, VI)

• Oculomotor (III): Innervates most eye muscles, parasympathetic control of pupil constriction
• Trochlear (IV): Innervates superior oblique muscle
• Abducens (VI): Innervates lateral rectus muscle, crucial for gaze stabilization

Trigeminal Nerve (CN V)

• Components: Sensory (GSA) and motor (SVE)

Sensory Pathways

• Primary Afferents: Sensory axons in peripheral nerves, carrying various types of sensation through "labelled lines"
• Peripheral Axons Classification: By size and function, e.g., C-fibres (nociception), Ia afferents, and Aβ afferents

Dorsal Root Ganglion (DRG)

• Structure and Function:
  • Contains cell bodies of sensory neurons
  • Different sizes of sensory neurons indicate different functions

Dermatomes

• Definition: Strips of skin supplied by specific spinal or cranial nerves
• Clinical Significance: Dermatomes are key landmarks in conditions like shingles (caused by herpes zoster)

Sensory Pathways to the Cerebral Cortex

• General Sensory (Somatosensory) Systems:
  • Primary Afferent Fibres: Carry sensory information to the spinal cord through dorsal roots
  • Ascending Sensory Tracts: Transmit sensory information to the cerebral cortex

Key Somatosensory Pathways

• Spinothalamic Tract (Anterolateral System):
  • Functions: Nociception (pain), temperature, and touch (non-discriminative)
  • Pathway: Primary sensory neurons in DRG, second-order neurons cross the midline to reach the thalamus
• Dorsal Column/Medial Lemniscus System:
  • Functions: Discriminative touch, conscious proprioception, and vibration sense
  • Pathway: Primary afferents in DRG, second-order neurons in dorsal column nuclei, axons in medial lemniscus to thalamus

Pathway Details

• Spinothalamic Tracts:
  • Located in the anterolateral quadrant of the spinal cord
  • Carry pain and temperature information
• Dorsal Columns:
  • Fasciculus Gracilis: Carries information from lower limbs
  • Fasciculus Cuneatus: Carries information from upper limbs above T6

Brainstem and Ascending Sensory Pathways

• Medulla:
  • Closed Medulla: Contains central canal, where dorsal column nuclei reside
  • Open Medulla: Medial lemniscus carries sensory information
• Pons and Midbrain:
  • Pons: Ascending pathways, including medial lemniscus and spinothalamic tract, are prominent

ANAT

• Basic Plan of the Nervous System:
  • Spinal Cord & Peripheral Nervous System
  • Brainstem (Medulla, Pons, Midbrain) & Cerebellum
  • Diencephalon (Thalamus, Hypothalamus)
  • Telencephalon (Cerebral Cortex, Cerebral Nuclei)

Developmental Anatomy

• Neural tube forms the CNS, with an axis of symmetry dividing dorsal (sensory) and ventral (motor) areas
• Early divisions of the neural tube form primary vesicles and the spinal cord, differentiating into various brain regions

Cerebral Cortex Development

• Human brain's distinctive shape due to the expansion of the forebrain and cerebral cortex

Spatial Axes in Neuroanatomy

• Embryological and adult posture axes help in describing brain anatomy: rostro-caudal, dorso-ventral, anterior-posterior, superior-inferior, and medial-lateral

Brainstem Anatomy

• Includes the Medulla, Pons, and Midbrain but excludes the Cerebellum
• Functions include vital bodily control (respiration, cardiovascular function) and movement coordination
• Cranial nerves (except for olfactory and optic) originate here

Thalamus and Hypothalamus

• Thalamus: Major relay station for sensory information to the cerebral cortex
• Hypothalamus: Controls physiological homeostasis and behaviors like feeding, drinking, and aggression

Basal Ganglia

• Involved in motor control and associated learning processes
• Consists of structures like the striatum and globus pallidus, important for initiating or suppressing movements

Cerebral Cortex

• Divided into four lobes: frontal, parietal, occipital, and temporal
• Six-layered structure facilitates various functions including sensory reception, motor output, and associative processes

Motor and Sensory Systems

• Motor pathways include the corticospinal pathway for voluntary movements
• Sensory pathways differentiate between general sensations and special senses like olfaction, taste, vision, and auditory processing

Sensory Pathways

• Primary Afferents: Sensory axons in peripheral nerves carrying various types of sensation through "labelled lines."
• Peripheral Axons Classification: By size and function, e.g., C-fibres (nociception), Ia afferents, and Aβ afferents.

Dorsal Root Ganglion (DRG)

• Structure and Function: Contains cell bodies of sensory neurons, with different sizes indicating different functions.

Dermatomes

• Definition: Strips of skin supplied by specific spinal or cranial nerves.
• Clinical Significance: Dermatomes are key landmarks in conditions like shingles (caused by herpes zoster).

Sensory Pathways to the Cerebral Cortex

• General Sensory (Somatosensory) Systems: Primary Afferent Fibres carry sensory information to the spinal cord through dorsal roots, which then transmit to the cerebral cortex via Ascending Sensory Tracts.

Key Somatosensory Pathways

• Spinothalamic Tract (Anterolateral System):
  • Functions: Nociception (pain), temperature, and touch (non-discriminative).
  • Pathway: Primary sensory neurons in DRG, second-order neurons cross the midline to reach the thalamus.
• Dorsal Column/Medial Lemniscus System:
  • Functions: Discriminative touch, conscious proprioception, and vibration sense.
  • Pathway: Primary afferents in DRG, second-order neurons in dorsal column nuclei, axons in medial lemniscus to thalamus.

Pathway Details

• Spinothalamic Tracts:
  • Located in the anterolateral quadrant of the spinal cord.
  • Carry pain and temperature information.
• Dorsal Columns:
  • Fasciculus Gracilis: Carries information from lower limbs.
  • Fasciculus Cuneatus: Carries information from upper limbs above T6.

Brainstem and Ascending Sensory Pathways

• Medulla:
  • Closed Medulla: Contains central canal, where dorsal column nuclei reside.
  • Open Medulla: Medial lemniscus carries sensory information.
• Pons and Midbrain:
  • Pons: Ascending pathways, including medial lemniscus and spinothalamic tract, are prominent.
  • Mitral and tufted cells relay signals from glomeruli to higher brain regions via the olfactory tract.

Integration of Gustation and Olfaction

• Orthonasal and Retronasal Olfaction:
  • Orthonasal Olfaction: Odor perception through the nostrils.
  • Retronasal Olfaction: Odor perception from the mouth during eating and drinking, contributing significantly to the sense of flavor.
• Multi-level Processing:
  • Broad Tuning: Initial receptor activation at the OR/OSN level.
  • Population Coding: In the glomeruli of the olfactory bulb.
  • Higher-Level Processing: Sharpening and modification of signals by mitral/tufted cells and cortical integration.

Interaction with Emotion and Memory

• Olfactory inputs directly project to limbic structures like the amygdala and hippocampus, which are involved in emotional responses and memory formation.

Exam Focus Areas

• Taste Bud Anatomy: Structure, types of cells, and their roles.
• Taste Transduction Mechanisms: Specific receptors and signaling pathways for each taste.
• Gustatory Pathway: From taste buds to the gustatory cortex, including relevant cranial nerves.
• Olfactory System Anatomy: Structure and function of the olfactory epithelium and olfactory bulb.
• Olfactory Transduction: Mechanisms of odor detection and signal transduction.
• Integration of Senses: How gustation and olfaction combine to create the perception of flavor and their connection to emotion and memory.

Vestibular System

• Introduction to the Vestibular System:
  • Key Points: Mostly operates unconsciously, provides spatial orientation information, deeply integrated with various brain circuits, interacts early with other sensory modalities, and essential for movement organization and supporting cognitive functions.

Pain and Nociception

• Nociception: Detection of noxious stimuli.
• Pain: A function of the cerebral cortex; acute pain is physiological, while chronic pain is pathological and difficult to treat.
• Gate Theory: Modulation of pain by mechanoreceptive afferents, influenced by descending fibers from the brain.

Influence on Nociception

• Periaqueductal Grey (PAG):
  • Influenced by the cerebral cortex.
  • Stimulation produces powerful analgesia.
• Raphe Nuclei:
  • Serotonin (5HT) Neurons: Modulate nociceptive transmission in the spinal cord.
  • Descending serotonergic fibers can adjust pain perception.
• Locus Ceruleus:
  • Noradrenergic Fibres: Descend to the spinal cord, exerting analgesic effects.

Clinical Considerations

• Congenital Insensitivity to Pain (CIP):
  • Patients with CIP have a mutant gene (SCN9A) and cannot respond to pain.
  • They often suffer severe injuries without feeling pain, demonstrating the importance of pain perception.

Upper Motor Neuron Lesions:

• Babinski Sign: Indicative of upper motor neuron damage.
• Lesions result in spastic paralysis and enhanced reflexes.

Other Clinical Conditions

• Tabes Dorsalis: Rare condition, sometimes seen in multiple sclerosis, damages specific sensory tracts, leading to loss of associated modalities.
• Ventrolateral Cordotomy: Surgical procedure to destroy spinothalamic tracts for pain relief, can lead to loss of other sensations and pain recurrence.
• Locked-in Syndrome: Often caused by basilar artery blockage, resulting in total paralysis but intact consciousness.

Key Points for Exams

• DRG and Dermatomes: Understand the structure and function, common in clinical cases like shingles.
• Spinothalamic and Dorsal Column Tracts: Fundamental pathways for various sensations.
• Pain Modulation: Gate theory, role of PAG, raphe nuclei, and locus ceruleus in pain perception.
• Clinical Conditions: Recognize symptoms and implications of lesions in sensory pathways.

Thalamus and Epithalamus

Gross Anatomy

• Lateral Geniculate Nucleus (LGN) and Medial Geniculate Nucleus (MGN) are two main divisions of the thalamus
• Divided into anterior, posterior, lateral, and medial nuclei

Sensory Relay Nuclei

• Relay sensory information (except olfaction) to the primary sensory cortex
• Pathways:
  • Somatosensation: spinal cord/brain stem/cranial nerve nuclei → Ventral Posterior (VP) thalamic nuclei → Primary somatosensory cortex (S1)
  • Vision: Retina → Lateral Geniculate Nucleus (LGN) → Primary visual cortex (V1)
  • Hearing: Cochlear nuclei → Medial Geniculate Nucleus (MGN) → Primary auditory cortex (A1)
  • Taste: Solitary nucleus → VP medial taste area
• Topographic mapping: preserved in projections to primary sensory cortex, resulting in topographic homunculus in S1
• Inputs: drivers (strong excitatory inputs, typically sensory) and modulators (weaker, activity-scaled inputs, typically cortico-thalamic axons)

Motor Nuclei

• Project to motor, premotor, and prefrontal cortices
• Inputs: from cortex (layers 5 & 6), basal ganglia, and cerebellum
• Segregated circuits:
  • Anterior (VL anterior nucleus): basal ganglia → supplementary motor area
  • Posterior (VL posterior nucleus): cerebellum → primary motor and premotor areas

Anterior Nuclei

• Involved in memory and navigation
• Nuclei: Anteromedial (AM), Anterodorsal (AD), Anteroventral (AV)
• Inputs: mammillary bodies (via mammillothalamic tract)
• Projections:
  • AM: anterior cingulate, retrosplenial cortex
  • AV: retrosplenial cortex, subiculum of hippocampus
  • AD: postrhinal, entorhinal cortices
• Functions:
  • AD: relays head direction signals
  • AV & AM: carry theta rhythm information

Association Nuclei

• Receive and integrate information primarily from cortical afferents
• Pulvinar:
  • Connected to many cortical areas, involved in visual attention and processing
  • Receives sub-cortical input from the superior colliculus
• Medio-dorsal Nuclei:
  • Connected to prefrontal cortex (PFC) and limbic structures
  • Integrate emotional, motivational states, and memory for decision-making

Reticular Nucleus

• Structure: a sheath of grey matter around the anterior portion of the thalamus
• Functions:
  • GABAergic neurons regulate thalamic activity
  • Essential for sleep spindles and likely involved in attention and sensory gating

Epithalamus

Pineal Gland

• Structure: unpaired, located in the diencephalon
• Functions:
  • Secretes melatonin, regulating circadian rhythms
  • Melatonin is driven by the suprachiasmatic nucleus (SCN) via the sympathetic ANS
• Evolutionary aspect: in some reptiles, the pineal gland is photosensitive, connected to the parietal eye

Habenula

• Structure: divided into medial and lateral portions
• Functions:
  • Medial Habenula (MH): inputs from limbic structures, influences dopamine and serotonin release
  • Lateral Habenula (LH): encodes negative motivational/emotional events, inhibits dopamine and serotonin release, potentially functioning as an "anti-reward" center
• Connectivity: inputs from limbic structures via the stria medullaris pathway

Basal Ganglia

• Comprises the putamen and globus pallidus
• Striatum includes the caudate nucleus and putamen
• Globus pallidus is divided into internal (GPi) and external (GPe) segments
• Sub-thalamic nucleus (STh) is embryologically part of the diencephalon
• Substantia nigra is located in the mesencephalon (midbrain)

Basal Ganglia Principal Neurons

• GABAergic neurons are all projection neurons in the cerebral nuclei that inhibit downstream targets
• Medium Spiny Neurons (MSNs) are:
  • D1-expressing MSNs: project to GPi, generally increase excitation via Gs-linked GPCRs
  • D2-expressing MSNs: project to GPe, generally inhibitory via Gi-linked GPCRs

Basic Pathways

• Direct Pathway:
  • Cortex → Striatum (D1 MSNs) → GPi → Thalamus → Cortex
  • Facilitates movement by reducing GPi inhibition on the thalamus
• Indirect Pathway:
  • Cortex → Striatum (D2 MSNs) → GPe → STh → GPi → Thalamus → Cortex
  • Inhibits movement by increasing GPi inhibition on the thalamus

Motor Control in More Detail

• Motor Planning and Execution:
  • Anterior regions of the motor thalamus (VL anterior nucleus) are involved in motor planning
  • Posterior regions (VL posterior nucleus) are involved in motor execution
• Direct Pathway:
  • Promotes movement by facilitating thalamic excitation of the cortex
  • Involves D1 MSNs in the striatum projecting to GPi, reducing GPi inhibition on the thalamus
• Indirect Pathway:
  • Inhibits movement by enhancing GPi inhibition of the thalamus
  • Involves D2 MSNs in the striatum projecting to GPe, which then inhibits the STh, reducing STh excitation of GPi

Dopamine's Role

• Dopamine from the substantia nigra pars compacta (SNc) modulates the activity of MSNs
• D1 Receptors:
  • Increase the activity of the direct pathway, promoting movement
  • Receive sub-cortical input from the superior colliculus
• Medio-dorsal Nuclei:
  • Connected to prefrontal cortex (PFC) and limbic structures
  • Integrate emotional, motivational states, and memory for decision-making

Reticular Nucleus

• Structure: A sheath of grey matter around the anterior portion of the thalamus
• Functions:
  • GABAergic neurons regulate thalamic activity
  • Essential for sleep spindles and likely involved in attention and sensory gating

Epithalamus

• The Pineal Gland:
  • Structure: Unpaired, located in the diencephalon
  • Functions:
    • Secrete melatonin, regulating circadian rhythms
    • Melatonin is driven by the suprachiasmatic nucleus (SCN) via the sympathetic ANS
  • Evolutionary Aspect: In some reptiles, the pineal gland is photosensitive, connected to the parietal eye
• The Habenula:
  • Structure: Divided into medial and lateral portions
  • Functions:
    • Medial Habenula (MH): inputs from limbic structures, influences dopamine and serotonin release
    • Lateral Habenula (LH): encodes negative motivational/emotional events, inhibits dopamine and serotonin release, potentially functioning as an "anti-reward" center
  • Connectivity: Inputs from limbic structures via the stria medullaris pathway

Exam Focus Areas

• Thalamic Sensory and Motor Nuclei: Understanding the pathways and functions
• Anterior Nuclei: Their role in memory and spatial navigation
• Association Nuclei: Pulvinar and medio-dorsal nuclei functions and connectivity
• Reticular Nucleus: Its regulatory role in thalamic activity and involvement in sleep spindles
• Epithalamus: Pineal gland's role in circadian rhythms and habenula's role in emotional regulation

Basal Ganglia

• Cerebral Nuclei: Striatum and globus pallidus
• Striatum: Divided into putamen and caudate nucleus; functionally similar
• Basal Ganglia: Cerebral nuclei + sub-thalamic nucleus, substantia nigra, ventral tegmental area (VTA)
• Thalamus is not part of the basal ganglia despite its role in the circuit
• D2 Receptors: Decrease the activity of the indirect pathway, also promoting movement

Nucleus Accumbens and the 'Affective' Basal Ganglia

• Nucleus Accumbens:
  • Function: Involved in reward, motivation, and affective processes
  • Connections:
    • Receives dopaminergic inputs from the VTA
    • Integrates information from the prefrontal cortex, hippocampus, and amygdala
  • Pathways:
    • Projects to the ventral pallidum and the thalamus, influencing motor and affective behaviors
• Affective Basal Ganglia:
  • Components: Include the nucleus accumbens and ventral pallidum
  • Roles: Regulate emotional and motivational aspects of behavior, in addition to motor control

Exam Focus Areas

• Anatomy and Terminology:
  • Understanding the components and divisions of the basal ganglia
• Motor Control Circuits:
  • Direct and indirect pathways and their roles in movement regulation
  • Dopamine's modulatory effects on these pathways
• Functional Roles:
  • Differences between motor planning and execution circuits within the basal ganglia
• Affective Roles:
  • Functions of the nucleus accumbens and its role in reward and motivation
  • The interplay between motor control and affective processes in the basal ganglia

Cerebral Cortex

• Principal Lobes, Sulci, and Gyri:
  • Lobes:
    • Frontal
    • Parietal
    • Temporal
    • Occipital
  • Sulci: Grooves in the brain that serve as landmarks
    • E.g., Central sulcus, Lateral sulcus, Parieto-occipital sulcus
  • Gyri: Ridges between sulci
    • E.g., Precentral gyrus (primary motor cortex), Postcentral gyrus (primary somatosensory cortex)

Fibre Pathways

• Types of Fibres:
  • Association Fibres: Connect different parts of the same hemisphere
    • Short (intralobar): Connect adjacent gyri
    • Long (interlobar): Connect different lobes
  • Commissural Fibres: Connect corresponding areas of both hemispheres
    • Corpus Callosum: Major commissural fibre bundle
    • Anterior Commissure: Connects temporal lobes

Cortical Mantle

• The cortical mantle consists of the isocortex (6 layers), allocortex (fewer layers), and periallocortex (transitional zone)
• Brodmann areas are regions defined by cytoarchitecture (e.g., BA17 = primary visual cortex, BA4 = primary motor cortex)

The Parietal Cortex and 'Dorsal Stream'

• Functions: spatial processing, somatosensory integration
• Key regions: primary somatosensory cortex (postcentral gyrus, BA1, 2, 3), topographically organized (homunculus)
• Secondary somatosensory cortex: associated with astereognosis (inability to recognize objects by touch)
• Disorders: unilateral spatial neglect (damage to right temporo-parietal junction), Gerstmann syndrome (left angular gyrus damage)

The Temporal Lobes and 'Ventral Stream'

• Functions: object recognition, memory, language comprehension
• Key regions: ventral temporal cortex (categorizing visual stimuli), fusiform face area (face recognition), parahippocampal place area (responds to scenes and landscapes)

Frontal Cortex: Motor Regions

• Primary motor cortex (precentral gyrus, BA4): controls voluntary movements, organized topographically (motor homunculus)
• Premotor cortex (BA6, lateral): planning and executing movements based on sensory cues
• Supplementary motor area (SMA, BA6, medial): involved in self-initiated movements, complex motor plans

Cerebellar Cortex

• Folia: highly convoluted folds creating gyri-like structures
• Layers: molecular layer (axons, dendrites, few interneurons), Purkinje cell layer, granule cell layer (thick layer with numerous small granule cells)

Deep Cerebellar Nuclei

• Fastigial nucleus: connected with flocculonodular lobe and some vermis (vestibulocerebellum, spinocerebellum)
• Emboliform nucleus: connected with vermis and paravermis (spinocerebellum)
• Globose nucleus: connected with vermis and paravermis (spinocerebellum)
• Dentate nucleus: connected with pontocerebellum, visible to the naked eye

The Intra-Cerebellar Circuit

• Microcircuitry: Purkinje cells (large dendritic trees contacted by one climbing fibre each), granule cells (receive input from mossy fibres), interneurons (stellate cells, basket cells, Golgi cells)
• Output: Purkinje cells project to deep nuclei, transmitting processed information out of the cerebellum

Functional Divisions in Detail

• Pontocerebellum (cerebrocerebellum): involved in planning and timing of movements, cognitive functions
• Cortico-ponto-cerebellar pathway: via the middle cerebellar peduncle
• Lesions can lead to alien limb syndrome and utilization behavior

Frontal Cortex: Prefrontal Regions

• Functions: executive function, decision making, social behavior
• Key regions: dorsolateral prefrontal cortex (dlPFC) (working memory, planning, response inhibition), orbitofrontal cortex (OFC) (evaluates stimuli, emotional responses)

Other Areas: Cingulate, Insula, Claustrum

• Cingulate cortex: emotional regulation, pain processing, cognitive functions
• Insula: taste, visceral sensations, emotional experience
• Claustrum: coordinates various cortical functions

Language

• Broca's area (BA44, 45): speech production, damage leads to Broca's aphasia
• Wernicke's area (BA22): language comprehension, damage leads to Wernicke's aphasia
• Arcuate fasciculus: connects Broca's and Wernicke's areas, important for language processing

Exam Focus Areas

• Anatomy and terminology: principal lobes, sulci, gyri, fibre pathways
• Functional localization: key regions in parietal, temporal, and frontal cortices and their functions
• Disorders: common disorders associated with damage to specific cortical areas (e.g., unilateral spatial neglect, prosopagnosia)
• Language areas: roles of Broca's and Wernicke's areas and the arcuate fasciculus in language processing

Limbic System

• Broca's 'Limbic Lobe' (1878): identified the limbic lobe as a structure closely linked to olfaction, considered a primitive part of the brain
• The Papez Circuit (1937): James Papez proposed that limbic structures mediate emotions, involving sensory cortex, thalamus, hippocampus, anterior thalamus, hypothalamus, and cingulate cortex
• Kluver-Bucy Syndrome: studied by Kluver and Bucy (1937) via temporal lobectomies in monkeys

Symptoms of Kluver-Bucy Syndrome

• Docility, hypo-emotionality, hyper-sexuality, visual agnosia, hyper-orality, and amnesia

Paul MacLean and the 'Limbic System'

• Introduced the 'visceral brain' concept, later termed the 'limbic system'
• Proposed the triune brain theory with three layers: reptilian (basal ganglia), paleo-mammalian (limbic system), and neomammalian (neocortex)

Modern View of the Limbic System

• Components:
  • Core structures: Cingulate gyrus, parahippocampal gyrus, hippocampus, amygdala, olfactory cortex, orbital, and medial prefrontal cortex, anteroventral insula
  • Closely associated: Hypothalamus, nucleus accumbens, ventral pallidum

Three Interconnected Circuits

Memory Circuit (Hippocampus)

• Anatomy: Includes hippocampus proper (CA1-3, dentate gyrus)
• Function: Memory encoding and retrieval
• Connections:
  • Inputs from medial septum via GABAergic (temporal pacing) and cholinergic (encoding mode) projections
  • Outputs via the fornix to mammillary bodies, anterior thalamus, and septum
• Theta Rhythm: Generated by the medial septum, crucial for memory encoding

Diencephalic Amnesia

• Caused by thiamine deficiency, often in chronic alcoholism
• Symptoms: Anterograde and retrograde amnesia
• Affected areas: Mammillary bodies, anterior thalamus, dorsomedial thalamus

Emotion Circuit (Amygdala)

• Anatomy: Sub-nuclei categorized into three groups: olfactory amygdala, central nucleus, and basolateral complex
• Functions: Processing emotionally significant stimuli and generating appropriate responses
• Pavlovian Fear Conditioning: Associates neutral stimuli with aversive events, mediated by basolateral amygdala and central nucleus

Nucleus Accumbens and the 'Affective' Basal Ganglia

• Function: Involved in reward, motivation, and affective processes
• Connections:
  • Receives dopaminergic inputs from the VTA
  • Integrates information from the prefrontal cortex, hippocampus, and amygdala
• Pathways:
  • Projects to the ventral pallidum and the thalamus, influencing motor and affective behaviors

Affective Basal Ganglia

• Components: Include the nucleus accumbens and ventral pallidum
• Roles: Regulate emotional and motivational aspects of behavior, in addition to motor control

Exam Focus Areas

• Anatomy and Terminology: Understanding the components and divisions of the basal ganglia
• Motor Control Circuits: Direct and indirect pathways and their roles in movement regulation
• Functional Roles: Differences between motor planning and execution circuits within the basal ganglia
• Affective Roles: Functions of the nucleus accumbens and its role in reward and motivation

Cerebral Cortex

I. Cerebral Cortex Anatomy

• Principal Lobes: Frontal, parietal, temporal, and occipital
• Sulci: Grooves in the brain that serve as landmarks (e.g., central sulcus, lateral sulcus, parieto-occipital sulcus)
• Gyri: Ridges between sulci (e.g., precentral gyrus, postcentral gyrus)

Fibre Pathways

• Types of Fibres:
  • Association Fibres: Connect different parts of the same hemisphere
  • Commissural Fibres: Connect corresponding areas of both hemispheres
  • Corpus Callosum: Major commissural fibre bundle
  • Anterior Commissure: Connects temporal lobes

Case Study: SM (Urbach-Wiethe Disease)

• Condition: Bilateral calcification of the amygdala
• Symptoms: Deficits in recognizing and reproducing fearful expressions, inappropriate social interactions, and lack of fear

Cingulate Cortex and Insula

• Cingulate Cortex:
  • Regions and Functions:
    • ACC (Anterior): Autonomic signaling, pain processing, conflict monitoring
    • MCC (Mid): Reward valuation, decision making
    • PCC (Posterior): Visuospatial orientation
    • RSC (Retrosplenial Cortex): Navigation, episodic memory
• Insula:
  • Functions: Multimodal sensory integration, interoception, emotional processing, empathy, and top-down autonomic control
  • Anatomy: Agranular, dysgranular, and granular subdivisions, containing von Economo neurons
  • Connections: Reciprocal connections with limbic structures, thalamus, prefrontal cortex, and basal ganglia

Cerebellar Cortex

• The cerebellar cortex has highly convoluted folds, creating gyri-like structures.
• The molecular layer contains axons, dendrites, and a few interneurons.
• The Purkinje cell layer is a thin layer of large Purkinje cell bodies.
• The granule cell layer is a thick layer with numerous small granule cells, approximately 60 billion in humans.

Deep Cerebellar Nuclei

• The fastigial nucleus is connected with the flocculonodular lobe and some vermis (vestibulocerebellum, spinocerebellum).
• The emboliform nucleus is connected with the vermis and paravermis (spinocerebellum).
• The globose nucleus is connected with the vermis and paravermis (spinocerebellum).
• The dentate nucleus is connected with the pontocerebellum and is visible to the naked eye.

Intra-Cerebellar Circuit

• Purkinje cells have large dendritic trees contacted by one climbing fiber each, which originate from the inferior olive and form multiple synapses.
• Granule cells receive input from mossy fibers and send parallel fibers that make weak synapses with many Purkinje cells.
• Interneurons, including stellate cells, basket cells, and Golgi cells, inhibit Purkinje cells and granule cells.

Output

• Purkinje cells project to deep nuclei, transmitting processed information out of the cerebellum.

Functional Divisions

Pontocerebellum (Cerebrocerebellum)

• The pontocerebellum is involved in planning and timing of movements and cognitive functions.
• It receives inputs primarily from the cerebral cortex via the pontine nuclei and projects to the dentate nucleus, then to the ventral lateral nucleus of the thalamus, and back to the motor cortex.
• The pontocerebellum uses the cortico-ponto-cerebellar pathway via the middle cerebellar peduncle.
• Dysfunctional pontocerebellum can lead to cerebellar hemispheric syndrome, characterized by lack of coordination, decomposition of movements, intention tremor, and speech issues.

Spinocerebellum

• The spinocerebellum regulates muscle tone and coordination of skilled voluntary movement.
• It receives proprioceptive information from muscles/tendons via spinocerebellar pathways (dorsal, ventral, cuneocerebellar).
• It projects to the interposed nuclei (globose and emboliform), then to the red nucleus and rubrospinal tract.
• The spinocerebellum uses spinocerebellar pathways through the inferior and superior peduncles and the rubrospinal tract for coordination of body-wide musculature.
• Dysfunctional spinocerebellum can lead to midline cerebellar syndromes, characterized by difficulty standing, unsteady walking, and gait issues.

Vestibulocerebellum

• The vestibulocerebellum maintains balance and controls eye movements.
• It receives inputs from the vestibular nuclei via the vestibulocerebellar tract.
• It projects to the fastigial nucleus and back to the vestibular nuclei.
• The vestibulocerebellum is involved in the vestibulo-ocular reflex (VOR) to stabilize vision during head movements.
• Dysfunctional vestibulocerebellum can lead to issues with balance and eye movements.

Exam Focus Areas

• Gross Anatomy: Understand the structure, divisions, and key landmarks of the cerebellum.
• Microcircuitry: Key cell types (Purkinje cells, granule cells, interneurons) and their connections.
• Functional Divisions: Pontocerebellum, spinocerebellum, and vestibulocerebellum.
• Dysfunctions: Recognize symptoms and underlying issues related to damage in each cerebellar division.

Hippocampus

• The hippocampus is part of the limbic system, involved in emotion, memory, and behavior.
• The hippocampus is located on the medial edge of the cortical sheet, forming part of the limbic system.

Coma and Consciousness

• Coma is a severe brain injury causing prolonged unconsciousness, assessed by the Glasgow Coma Scale.
• The Glasgow Coma Scale includes eye opening response, verbal response, and motor response.
• Brain injury and coma can be caused by brain swelling, vascular damage, and neuronal damage.
• The reticular activating system (RAS) and cerebral cortex are involved in maintaining consciousness.

Exam Focus Areas

• EEG Basics: Understanding EEG patterns and their relation to brain states.
• Sleep Stages and Physiology: Characteristics and functions of different sleep stages.
• Ascending Arousal System: Key components, neurotransmitters, and their roles in sleep and wakefulness.
• Sleep Disorders: Causes and symptoms of narcolepsy and encephalitis lethargica.
• Coma and Consciousness: Mechanisms, Glasgow Coma Scale, and the role of the RAS and cerebral cortex in maintaining consciousness.

Plasticity and Learning

• The cerebellum plays a critical role in motor learning and control.
• The cerebellum has a unique structure, containing over 50% of the brain's neurons despite only occupying 10% of the brain's volume.
• The cerebellum acts as a side loop on descending motor systems, modulating accuracy, force, timing, and sequencing of movements.

Organisation of the Hippocampal Cortex

• The hippocampus has a three-layered allocortex, including the dentate gyrus, CA3, CA1, and subiculum.
• The periallocortex (transition zone) consists of the presubiculum, parasubiculum, and entorhinal cortex.
• The proisocortex includes the perirhinal cortex and parahippocampal cortex.

Comparative Anatomy

• The hippocampus has a similar basic structure across mammals, but is more complex in primates.
• Humans have more cells in CA1 compared to rats, while rats have stronger commissural connections.

Intra-Hippocampal Connectivity

Tri-Synaptic Loop

• The perforant pathway connects the entorhinal cortex to the dentate gyrus.
• Mossy fibers connect the dentate gyrus to CA3.
• Schaffer collaterals connect CA3 to CA1.
• The loop returns from CA1 to the entorhinal cortex.

Complexity

• The perforant path projects to both the dentate gyrus and CA3.
• The temporo-ammonic pathway projects from the entorhinal cortex to CA1 and the subiculum.
• CA3 cells project to other CA3 cells, known as recurrent connectivity.

Output Connections

• The entorhinal cortex layers V and VI receive outputs from the hippocampus.

Cortical and Sub-Cortical Input Connections

Cortical Inputs

• The entorhinal cortex receives major input from cortical regions, processing diverse sensory inputs.

Sub-Cortical Inputs

• The medial septum provides cholinergic and GABAergic input, crucial for the theta rhythm.
• Direct inputs come from various neuromodulatory systems.

The Hippocampus and Memory

Case Study: Patient H.M.

• Patient H.M. had bilateral temporal lobe resection for epilepsy, resulting in profound anterograde amnesia and preserved procedural memory.

Types of Memory

• Preserved abilities include short-term memory, procedural learning, general intelligence, and language.
• Deficits include episodic memory and semantic memory.

Theories of Memory Formation

• The standard consolidation theory states that memories are stored long-term outside the hippocampus.
• The multiple trace theory states that rich, detailed autobiographical memories require an intact hippocampus.

Spatial Navigation and Cognitive Mapping

Cognitive Map Theory

• The hippocampus is involved in cognitive maps and spatial memory.
• Place cells fire when an animal is in a specific location, discovered by O'Keefe and Dostrovsky (1971).

Morris Water Maze

• The maze demonstrates spatial memory reliance on the hippocampus, and lesions impair spatial strategies.

Grid Cells and Head Direction Cells

• Grid cells, found in the entorhinal cortex, provide a coordinate system for navigation.
• Head direction cells fire based on an animal's head direction.

Exam Focus Areas

• Anatomy: Structure and layers of the hippocampus, allocortex vs. periallocortex.
• Connectivity: Tri-synaptic loop, perforant pathway, mossy fibers, and Schaffer collaterals.
• Memory Functions: Case studies (e.g., H.M.), types of memory, theories of memory consolidation.
• Spatial Navigation: Cognitive map theory, place cells, grid cells, and head direction cells.
• Clinical Relevance: Impact of hippocampal damage on memory and navigation.

Visual System Anatomy and Physiology

Anatomy of the Eye

• The eye consists of the cornea, lens, and retina.
• The retina contains photoreceptors (rods and cones).

Vision Problems

• Myopia is nearsightedness.
• Hyperopia is farsightedness.
• Astigmatism is an irregular curvature of the cornea or lens.

Retina and Photoreceptors

• Rods function in dim light, providing black-and-white vision.
• Cones function in bright light, enabling color vision and high visual acuity.
• Bipolar cells transmit signals from photoreceptors to ganglion cells.
• Ganglion cells form the optic nerve.

Color Opponency

• Mechanism: Red vs. green and blue vs. yellow color opposition.

Paul MacLean and the 'Limbic System'

• Paul MacLean expanded on Papez's theory, introducing the 'visceral brain' concept, later termed the 'limbic system'.
• He proposed the triune brain theory with three layers: reptilian (basal ganglia), paleo-mammalian (limbic system), and neomammalian (neocortex).

Modern View of the Limbic System

• Core structures include the cingulate gyrus, parahippocampal gyrus, hippocampus, amygdala, olfactory cortex, orbital, and medial prefrontal cortex.
• Closely associated structures include the hypothalamus, nucleus accumbens, ventral pallidum.

Three Interconnected Circuits

Memory Circuit (Hippocampus)

• Anatomy: Includes hippocampus proper (CA1-3, dentate gyrus).
• Function: Memory encoding and retrieval.
• Connections: Inputs from the medial septum, outputs via the fornix to mammillary bodies, anterior thalamus, and septum.
• Theta Rhythm: Generated by the medial septum, crucial for memory encoding.

Diencephalic Amnesia

• Korsakoff's Syndrome: Caused by thiamine deficiency, often in chronic alcoholism.
• Symptoms: Anterograde and retrograde amnesia.
• Affected areas: Mammillary bodies, anterior thalamus, dorsomedial thalamus.

Emotion Circuit (Amygdala)

• Anatomy: Sub-nuclei categorized into three groups: olfactory amygdala, central nucleus, and basolateral complex.
• Functions: Processing emotionally significant stimuli and generating appropriate responses.

Pavlovian Fear Conditioning:

• Associates neutral stimuli with aversive events, mediated by the basolateral amygdala and central nucleus.

Auditory System

• The cochlea is a spiral-shaped organ filled with fluid, containing hair cells that convert mechanical vibrations into electrical signals.
• Hair cells are sensory receptors that detect sound waves and convert them into neural signals.
• The auditory nerve carries electrical signals from the cochlea to the brainstem and then to the auditory cortex.

Central Auditory Pathway

• Auditory nerve fibers have properties such as frequency tuning, phase locking, and intensity coding.
• The cochlear nucleus is the initial site of auditory processing, where input converges and diverges.
• The superior olivary complex is responsible for sound localization and efferent projections to the cochlea.
• The inferior colliculus is an integration center, where almost all ascending auditory pathways converge.
• The medial geniculate nucleus (MGN) is a relay station for auditory information, with different divisions involved in primary auditory transmission, attention, and learning.

Auditory Cortex Organization

• The primary auditory cortex (A1) is located in Heschl's gyri and has a tonotopic organization.
• Area V5 (MT) is involved in processing object motion, and damage to this area can result in akinetopsia.
• Area V4 is involved in shape and color perception, and damage to this area can result in achromatopsia.
• The inferior temporal cortex (IT) responds to complex shapes, textures, and faces, and damage to this area can result in prosopagnosia.

Anatomy and Function of the Ear

• The outer ear collects and funnels sound to the eardrum through the ear canal.
• The pinna filters sound based on direction, aiding in sound localization and judgment of sound elevation and front-back location.
• The middle ear amplifies sound through impedance matching, lever action of ossicles, and the stapedius reflex.
• The inner ear contains the basilar membrane, which is sensitive to frequency, and hair cells that transduce sound into neural signals.

Visual Pathway

• The pathway from the retina to the brain involves the optic nerve, optic chiasm, and optic tract.
• Lesions in the visual pathway can result in various visual deficits, including loss of vision in one eye or one visual field.
• The superior colliculus is involved in eye movements and visual attention, while the lateral geniculate nucleus (LGN) relays information to the primary visual cortex (V1).
• The primary visual cortex (V1) is organized into six layers and processes visual information, with receptive fields, orientation selectivity, and movement and direction sensitivity.

Beyond the Primary Visual Cortex

• The dorsal stream ("where/how" pathway) is involved in perception of motion and location, and damage to this area can result in akinetopsia.
• The ventral stream ("what" pathway) is involved in object recognition and color perception, and damage to this area can result in achromatopsia and prosopagnosia.

Olfactory System

• The olfactory system involves the detection of odor molecules by olfactory receptors in the olfactory epithelium.
• The olfactory bulb is a primary olfactory cortex involved in odor identification and memory.
• Mitral and tufted cells relay signals from glomeruli to higher brain regions via the olfactory tract.
• The piriform cortex is a primary olfactory cortex involved in odor identification and memory.

Integration of Gustation and Olfaction

• Orthonasal olfaction involves odor perception through the nostrils, while retronasal olfaction involves odor perception from the mouth during eating and drinking.
• Broad tuning and population coding occur in the glomeruli of the olfactory bulb, and higher-level processing sharpens and modifies signals by mitral/tufted cells and cortical integration.
• Olfactory inputs directly project to limbic structures like the amygdala and hippocampus, which are involved in emotional responses and memory formation.

Vestibular System

• The vestibular system provides spatial orientation information, operates mostly unconsciously, and interacts early with other sensory modalities.
• The vestibular system is essential for movement organization and supporting cognitive functions.

Taste Sensation and Transduction

• Five basic tastes: salty, sour, bitter, sweet, and umami.
• Salty and sour tastes are detected by direct activation of ion channels.
• Bitter taste is detected by T2R receptors.
• Sweet taste is detected by T1R2 and T1R3 receptor combination.
• Umami taste is detected by T1R1 and T1R3 receptor combination.

Gustatory Pathway

• Taste information is detected by taste buds on the tongue and pharynx.
• Sensory neurons' peripheral fibers travel via the glossopharyngeal (CN IX), chorda tympani (branch of CN VII), and vagus nerves (CN X).
• Signals relay through the nucleus of the solitary tract (NST) in the brainstem to the ventral posteromedial nucleus (VPM) of the thalamus and then to the gustatory cortex.

Gustatory Cortex

• Located primarily in the insula and opercular regions.
• Further projections to the prefrontal cortex, orbitofrontal cortex, medial temporal lobe, and limbic structures.

Olfaction (Smell)

Anatomy and Function of Olfactory System

• Olfactory epithelium contains olfactory receptor neurons (ORNs), supporting cells, and basal cells.
• ORNs have a lifespan of approximately 40 days and are replaced by basal cells.
• Olfactory receptors are mostly G-protein coupled receptors (GPCRs).
• Humans have fewer than 500 olfactory receptor genes, yet can distinguish over 10,000 aromas.

Olfactory Transduction and Pathway

• Odorant molecules bind to receptors on ORNs, initiating a cascade that results in depolarization and action potential generation.
• ORN axons form the olfactory nerve, crossing the cribriform plate to synapse in the olfactory bulb.
• In the olfactory bulb, ORN axons converge on glomeruli, each receiving input from ORNs expressing the same receptor type.
• Mitral and tufted cells relay signals from glomeruli to higher brain regions via the olfactory tract.

Olfactory Bulb and Beyond

• Olfactory bulb projects to the piriform cortex, amygdala, entorhinal cortex, and other areas without thalamic relay.
• The piriform cortex is a primary olfactory cortex involved in odor identification and memory.

Integration of Gustation and Olfaction

• Orthonasal olfaction: odor perception through the nostrils.
• Retronasal olfaction: odor perception from the mouth during eating and drinking, contributing significantly to the sense of flavor.

Multi-level Processing

• Broad tuning: initial receptor activation at the OR/OSN level.
• Population coding: in the glomeruli of the olfactory bulb.
• Higher-level processing: sharpening and modification of signals by mitral/tufted cells and cortical integration.

Interaction with Emotion and Memory

• Olfactory inputs directly project to limbic structures like the amygdala and hippocampus, which are involved in emotional responses and memory formation.

Vestibular System

• Head rotation causes differential activation of hair cells in the left and right semicircular canals, leading to excitatory and inhibitory signals being sent to the vestibular nuclei.
• The Push-Pull System allows paired canals on each side to work together to detect head movements and stabilize gaze.

Cognition and Spatial Representation

• Vestibular inputs are widespread in the forebrain, crucial for spatial representation and abstract cognition.
• Areas involved include the parieto-insular vestibular cortex (PIVC), hippocampus, and other cortical regions.

Spatial Orientation and Navigation

• The vestibular system provides critical input for spatial orientation and navigation.
• It integrates with visual and proprioceptive information to maintain balance and orientation.

Effects of Vestibular Dysfunction

• Vestibular dysfunction can lead to issues with balance, spatial navigation, and cognitive functions.
• Studies show that vestibular loss can impair hippocampal function and spatial memory.

Exam Focus Areas

• Peripheral Anatomy: Structure and function of hair cells, otolith organs, and semicircular canals.
• Transduction Mechanisms: How hair cells convert mechanical stimuli into neural signals.
• Central Pathways: Projections from the vestibular nuclei to other brain regions and their functions.
• VOR: Mechanism and significance of the vestibulo-ocular reflex.
• Cognition: Vestibular contributions to spatial orientation, navigation, and cognitive processes.

Brain States and Modulatory Systems

• Brain states include sleep, arousal, and coma, understood through EEG and the neuroanatomy of wakefulness and sleep.

Electroencephalography (EEG)

• EEG detects summed activity of cortical neurons.
• Positive current flow into superficial dendritic regions creates superficial negativity.

Mechanosensory Cells

• Hair cells are ancient and common across species.
• Hair bundles, comprising stereocilia and often a kinocilium, are attached to various accessory structures in different sensory organs.

Hair Cell Function

• Hair cells in the vestibular labyrinth transduce mechanical stimuli into neural signals.
• Bending of stereocilia toward the kinocilium depolarizes the cell, increasing the firing rate in the afferent fiber.
• Bending away from the kinocilium hyperpolarizes the cell, decreasing the firing rate.

Balance and the Otolith Organs

• Otolith organs (utricule and saccule) detect linear acceleration and head tilt.
• Hair cells are embedded in a gelatinous layer covered with otoconia (calcium carbonate particles).
• The hair cells' orientation is arranged relative to the striola, a central line in the maculae.
• When the head tilts, gravitational forces on the otoconia bend the hair bundles, depolarizing or hyperpolarizing the hair cells based on their polarity.

Central Otolith Pathways

• Projections from the vestibular nuclei to various brain regions, including the spinal cord, reticular formation, cerebellum, and thalamus.
• Pathways are involved in maintaining balance, posture, and coordinating eye movements.

Tilt vs. Translation

• The vestibular system must distinguish between head tilt and linear acceleration.
• Sensory integration helps resolve ambiguities between tilt and translation.

Vision and the Semicircular Canals

• Semicircular canals detect angular acceleration.
• Each canal contains an ampulla with a crista, where hair cells extend into the cupula.
• Endolymph movement deflects the cupula during head rotation, displacing hair bundles.

Vestibulo-Ocular Reflex (VOR)

• The VOR stabilizes vision by coordinating eye movements with head movements.
• Mitral and tufted cells relay signals from glomeruli to higher brain regions via the olfactory tract.

Integration of Gustation and Olfaction

• Orthonasal olfaction involves odor perception through the nostrils.
• Retronasal olfaction involves odor perception from the mouth during eating and drinking, contributing significantly to the sense of flavor.
• Multi-level processing includes broad tuning, population coding, and higher-level processing.

Interaction with Emotion and Memory

• Olfactory inputs directly project to limbic structures like the amygdala and hippocampus, which are involved in emotional responses and memory formation.

Exam Focus Areas

• Taste Bud Anatomy: Structure, types of cells, and their roles.
• Taste Transduction Mechanisms: Specific receptors and signaling pathways for each taste.
• Gustatory Pathway: From taste buds to the gustatory cortex, including relevant cranial nerves.
• Olfactory System Anatomy: Structure and function of the olfactory epithelium and olfactory bulb.
• Olfactory Transduction: Mechanisms of odor detection and signal transduction.
• Integration of Senses: How gustation and olfaction combine to create the perception of flavor and their connection to emotion and memory.

Hypothalamic Nuclei

• Dorsal-Ventral (DV) axis: important for positional context
• Key nuclei and functions:
  • Paraventricular Nucleus (PVN): stress response, metabolism
  • Arcuate Nucleus (ARC): appetite regulation
  • Ventromedial Nucleus (VMN): satiety and female sexual behavior
  • Dorsomedial Nucleus (DMN): feeding, drinking, and body weight regulation
  • Lateral Nucleus (LN): hunger, arousal, and aggression
  • Mammillary Bodies (MB): memory and spatial navigation

Pituitary Gland

• Connection: infundibulum (pituitary stalk)
• Divisions:
  • Anterior Pituitary (Adenohypophysis): releases hormones via a two-step system
  • Posterior Pituitary (Neurohypophysis): direct hormone release from magnocellular neurons

Functional Systems

Endocrine Function

• Anterior Pituitary Hormones:
  • Hypothalamic Releasing/Inhibiting Hormones: control secretion of pituitary hormones
  • Key Hormones: Growth Hormone (GH), Thyroid-Stimulating Hormone (TSH), Adrenocorticotropic Hormone (ACTH), Prolactin, Luteinizing Hormone (LH), and Follicle-Stimulating Hormone (FSH)
• Posterior Pituitary Hormones:
  • Oxytocin: uterine contractions, milk ejection, and social bonding
  • Vasopressin (AVP/ADH): water retention and blood pressure regulation

Reproduction

• Sexual Behavior:
  • Males: Sexually Dimorphic Nucleus of the Preoptic Area (SDN-POA) involved in sexual behavior and testosterone regulation
  • Females: Ventromedial Nucleus (VMN) crucial for sexual receptivity, regulated by estrogen and progesterone
• Pair Bonding:
  • Oxytocin and Vasopressin: critical for pair bonding, differing receptor distributions in brain regions between monogamous and non-monogamous species

Feeding and Metabolism

• Arcuate Nucleus (ARC): central hub for hunger and satiety signals
• Neuropeptide Y (NPY) Neurons: stimulate hunger
• Pro-opiomelanocortin (POMC) Neurons: promote satiety
• Paraventricular Nucleus (PVN) and Lateral Hypothalamus (LHA):
  • PVN: signals satiety, releases oxytocin, thyrotropin-releasing hormone (TRH), and corticotropin-releasing hormone (CRH)
  • LHA: promotes feeding behavior, contains orexin neurons

Circadian Rhythm and Arousal

• Suprachiasmatic Nucleus (SCN): master clock for circadian rhythms
• Intrinsic Clock: regulated by feedback loops of clock genes
• Light Entrained: reset by light via retinohypothalamic tract
• Arousal Systems:
  • Orexin Neurons (LHA): increase wakefulness
  • Histaminergic Neurons (TMN): promote wakefulness, implicated in sleep disorders like narcolepsy

Memory and Navigation

• Mammillary Bodies (MB): part of the hypothalamus, crucial for memory formation and spatial navigation
• Connections: project to the anterior nuclei of the thalamus and the hippocampus, forming part of the Papez circuit