Cerebellum: Anatomy and Function

Function of the Cerebellum

• Movement and posture are coordinated by comparing intended movements to actual movements and making necessary adjustments
• Operates nonconsciously without directly controlling muscles
• Damage to the cerebellum results in poor coordination and postural control
• Influences cognitive, emotional, and social capabilities

Anatomy of the Cerebellum

• The cerebellum has three lobes: anterior, posterior, and Flocculonodular
• The cerebellum contains three regions, the midline Vermis, Paravermis and the Lateral Hemisphere
• The cerebellum links to the brainstem via three peduncles
• The superior peduncle serves as a major output pathway
• The middle peduncle receives cortical input
• The inferior peduncle integrates spinal cord and vestibular input

Functional Regions & Movement Control

• Movement is categorized into equilibrium (balance), gross limb movements, and fine, distal, voluntary movements
• The vestibulocerebellum influences balance and eye movements, and is linked to the Flocculonodular Lobe
• The spinocerebellum is linked to the Vermis and Paravermis and influences gross limb movements
• The cerebrocerebellum is involved in fine motor control and planning and is linked to the posterior and lateral anterior lobes

Pathways & Tracts

• High-accuracy sensory input reaches the cerebellum via the posterior spinocerebellar tract (lower body proprioception) and the cuneocerebellar tract (upper body proprioception)
• Internal feedback tracts consist of the anterior spinocerebellar tract (lower limb motor feedback) and the rostrospinocerebellar tract (upper limb motor feedback)

Clinical Signs of Cerebellar Dysfunction

• Ataxia (uncoordinated movement) is the most common sign of cerebellar damage
• Damage to the vestibulocerebellum causes balance issues like nystagmus, unsteadiness and truncal ataxia
• Damage to the cerebrocerebellum causes fine motor deficits like finger ataxia and dysarthria
• Damage to the spinocerebellum causes limb and gait impairments such as unsteadiness, truncal ataxia, ataxic gait, dysdiadochokinesia, dysmetria, and action tremor

Non-Motor Functions of the Cerebellum

• Cognitive functions include goal-directed behavior as well as language optimization and visuospatial skills
• Emotional and social functions include emotional memory storage and social behavior regulation

Cerebellar Disorders

• Developmental disorders affect coordination and cognition
• Degenerative disorders consist of Spinocerebellar Ataxia (SCA) and Multiple System Atrophy (MSA)
• Acquired disorders include Multiple Sclerosis (MS), stroke, tumors, alcoholic cerebellar degeneration, and brainstem/cerebellum compression due to Foramen Magnum issues

Brainstem

• The brainstem integrates sensory/motor functions, regulates autonomic functions, and links the brain to the spinal cord
• There are four rules of the brainstem
• There are 2 cranial nerves in the midbrain, 4 in the pons, and 4 in the medulla
• Sensory tracts begin with "S" (spinothalamic, spinocerebellar, sympathetic)
• Motor nuclei are divided by 12 (CN 3, 4, 6, 12 are medial motor nuclei)
• Medial structures start with "M" (motor tracts, medial lemniscus)
• Brainstem tracts
• Sensory tracts include the spinothalamic tract which carries pain/temperature without crossing in the brainstem and the DCML which crosses in the medulla
• Motor tracts consist of the corticospinal tract that decussates(crosses) in the medulla and the corticobulbar tract which synapses with cranial nerve nuclei
• Autonomic tracts include the sympathetic tracts which pass unmodified and parasympathetic tracts where some axons synapse

Brainstem Anatomy & Cranial Nerves

• Midbrain Key Structures
• Superior Cerebral Peduncles connect to the cerebellum
• Substantia Nigra and PPN are part of basal ganglia circuits
• The Red Nucleus is responsible for cognitive motor control
• The Periaqueductal Grey modulates pain and emotional responses
• Midbrain Cranial Nerves
• CN III (Oculomotor) controls eye movement and pupil constriction
• CN IV (Trochlear) moves eye downward and medially

Pons

• Key Structures
• The Middle Cerebral Peduncle connects the pons to the cerebellum
• Vertical tracts are mostly unchanged.
• Pons Cranial Nerves
• CN V (Trigeminal) controls facial sensation and chewing
• CN VI (Abducens) controls eye abduction
• CN VII (Facial) controls facial expressions, taste, salivation, and tear production
• CN VIII (Vestibulocochlear) influences balance and hearing

Medulla

• Key Structures
• Pyramids (corticospinal tract decussation).
• Olives (inferior olivary nucleus).
• Inferior Cerebral Peduncle (connects medulla to cerebellum).
• Medulla Cranial Nerves
• CN IX (Glossopharyngeal) supports swallowing, taste, and blood pressure regulation
• CN X (Vagus) influences swallowing and visceral regulation (heart rate, digestion)
• CN XI (Accessory) supports shoulder and neck movement
• CN XII (Hypoglossal) controls tongue movement

Brainstem Clinical Considerations

• Brainstem lesions can impact vital functions (respiration, heart rate) and cause the "4 Ds"
• "4 Ds": dysphagia, dysarthria, diplopia and dysmetria
• Consciousness can be impacted by reticular formation damage
• Cranial nerve disorders include Bell's Palsy from facial nerve damage that causes facial paralysis and facial synkinesis post-recovery

Autonomic Nervous System (ANS)

• The ANS flow of information travels: sensory input, to the emotion system, to the reticular formation, to the hypothalamus, to the spinal cord and then to sympathetic/parasympathetic output

Sympathetic Nervous System (SNS)

• The "fight or flight" response causes:
• Increased body temperature from epinephrine increasing metabolism, and norepinephrine constricting blood vessels
• Increased heart rate and blood pressure via norepinephrine (T1-T4)
• Airway dilation through respiration (T1-T4)
• Digestive inhibition decreasing peristalsis and blood flow (T5-T12)
• Bladder retention (L1-L2)

Parasympathetic Nervous System (PNS)

• The "rest and digest" response causes:
• Decreased cardiac activity
• Increased digestion and secretions (saliva, tears, stomach acid)
• Bladder and bowel control (promotes emptying - S2-S4)
• Sexual function (erection and lubrication)

Clinical Correlations in ANS

• Dysautonomia conditions
• Horner’s Syndrome: Loss of sympathetic innervation to the face.
• Blood Pressure Regulation Issues.
• Body Temperature Dysregulation (Hyper/hypothermia).
• Bladder and Bowel Dysfunction.
• Emotional Dysregulation (autonomic emotional dissociation)

Basal Ganglia Structure and Function

• Key roles for motor control, decision-making, judgment, emotional processing, and learning
• Input areas consist of the Caudate, Putamen, and Subthalamic nucleus who receive signals
• Output areas consist of the Substantia nigra and Globus pallidus who send signals

Basal Ganglia Circuits

• There are five circuits that influence goal-directed behavior, social behavior, emotion/motivation, motor function, and oculomotor function
• Oculomotor circuit controls eye movement for reading and watching videos
• Motor circuits helps control skeletal muscle contraction, muscle force, multi-joint movement, and movement sequencing

Motor Control Pathways

• There are three pathways that regulate movement
• The stop (hyperdirect) pathway which suppresses ongoing movement
• The go (direct) pathway which facilitates voluntary movement
• The no-go (indirect) pathway which suppresses competing movements
• Glutamate, GABA and dopamine are neurotransmitters
• Glutamate is excitatory
• GABA is inhibitory
• Dopamine modulates movement pathways

Basal Ganglia Disorders

• Hypokinetic disorders (excess inhibition): Parkinson’s Disease
• There are symptoms such as tremor, rigidity, bradykinesia, postural instability, and cognitive and emotional changes
• This is caused by a dopamine loss in the substantia nigra which results in overactivity of inhibitory pathways
• Can be treated with dopamine medications, deep brain stimulation, and therapy

Hyperkinetic Disorders

• Hyperkinetic disorders (reduced inhibition): Huntington’s Disease
• There are symptoms that include jerky, involuntary movements (chorea), and cognitive decline
• This is caused by overactivity of the Go pathway, which leads to excessive movement
• Nerve cells degenerate in the striatum and cortex

Cerebrum & Cognition

• The cerebral cortex controls sensory perception, motor control, and higher cognitive skills
• Sensory discrimination, complex sensory analysis, motor planning, and behavior regulation are of key importance

Sensory and Motor Areas

• The Primary Sensory Cortex is responsible for processing basic sensory input (e.g., touch, sound, vision)
• The Secondary Sensory Cortex is responsible for analyzing and interpreting sensory data
• The Motor Cortex controls voluntary movements
• The Association Cortex integrates sensory input with emotions and memory

Motor Planning & Execution

• The Primary Motor Cortex executes movements
• The Premotor Cortex manages posture and movement preparation
• The Supplementary Motor Area handles movement sequencing
• Broca’s Area is responsible for speech production

Association Areas & Higher Cognitive Functions

• The Prefrontal Cortex handles personality, decision-making, and memory processing
• The Lateral Prefrontal Cortex controls executive functions such as the the ability to set goals
• The Medial Prefrontal Cortex regulates emotions such as self-awareness

Clinical Disorders

• Sensory and Motor Disorders include agnosia, optic ataxia, dysarthria, apraxia, and paresis
• Epilepsy is Characterized by sudden excessive neural activity
• Psychiatric Disorders include:
• OCD: Hyperactivity in the amygdala and reduced lateral prefrontal cortex activity.
• PTSD: Increased amygdala and insula activity.
• Bipolar Disorder: Abnormal amygdala and prefrontal cortex function.
• Schizophrenia: Structural abnormalities in the frontal and temporal lobes.

Memory & Consciousness

• There are 3 types of memory
• Working Memory controls Short-term retention of relevant information
• Declarative Memory controls encoding, consolidation, and retrieval
• Procedural Memory stores skills and habits
• There are different attention types such as selective, divided, sustained, and switching attention

Neurotransmitters

• Serotonin regulates arousal
• Dopamine controls motivation and cognition
• Norepinephrine directs attention
• Acetylcholine helps in goal-based focus

Communication & Spatial Awareness

• Communication Disorders affect speech production and comprehension
• Spatial Neglect manifests as personal (body-related) or spatial (environment-related)

Intellectual & Neurodegenerative Disorders

• Cognitive Disabilities include Trisomy 21 and phenylketonuria
• Learning Disabilities include dyslexia and other intelligence-related impairments
• Dementia includes Alzheimer's, frontotemporal dementia, and Parkinson's-related dementia