Neuroscience Chapter 4 Quiz

Ventricles and Basal Ganglia

• Ventricles are cavities in the brain filled with cerebrospinal fluid.
• They provide a useful landmark for identifying the position of basal nuclei and white matter tracts.
• The ventricle system is composed of the lateral ventricles, the third ventricle, the cerebral aqueduct, and the fourth ventricle.
• The lateral ventricles are the largest and extend into all lobes of the cerebrum: frontal, parietal, occipital, and temporal.
• The third ventricle is located in the diencephalon and connects to the lateral ventricles via the interventricular foramina.
• The cerebral aqueduct connects the third ventricle to the fourth ventricle.
• The fourth ventricle is located in the brainstem and connects to the subarachnoid space via the lateral apertures and the median aperture.

Basal Nuclei

• Basal nuclei are clusters of neuronal cell bodies located in the deep brain regions, involved in motor control, learning, and cognition.
• The caudate nucleus and putamen are collectively referred to as the striatum, which is primarily involved in receiving input from the cortex and sending projections to the globus pallidus.
• The globus pallidus is a nucleus located medial to the putamen, responsible for output projections to the thalamus and brainstem.
• The subthalamic nucleus, located ventral to the thalamus near the cerebral peduncle, plays a role in regulating basal ganglia activity.
• The substantia nigra, also located in the midbrain, is involved in movement control and is associated with dopamine production.
• The two parts of the substantia nigra are the pars compacta and the pars reticularis.
• The internal capsule, a large white matter tract, runs between the caudate nucleus, putamen and thalamus.
• The internal capsule carries important motor pathways from the cortex to the brainstem and spinal cord, including the corticospinal tract and corticobulbar tract.

Blood Supply of the Internal Capsule

• The internal capsule is primarily supplied by the middle cerebral artery (MCA) and its perforating branches.
• Blockage of the MCA or its perforating branches can lead to a stroke that affects a large area of the internal capsule, potentially resulting in significant motor deficits due to damage to the corticospinal and corticobulbar tracts.

Corticobulbar Tract and Cranial Nerve Nuclei

• The corticobulbar tract connects the cerebral cortex (upper motor neurons) to the cranial nerve nuclei (lower motor neurons) in the brainstem.
• This pathway controls the muscles of the face, tongue, and neck, mediating voluntary movements of these structures.
• Cranial nerve nuclei receive both ipsilateral and contralateral input, allowing for some compensation in case of injury to one side of the brain.
• Exceptions to this bilateral innervation rule involve the facial nerve (CNVII) and hypoglossal nerve (CNXII).
• The facial nerve nucleus has a superior part that receives input from both sides of the brain and an inferior part that receives input only from the contralateral side.
• Damage to the dominant side of the brain can result in facial droop and weakness on the contralateral side of the face.
• The hypoglossal nerve (CNXII), which controls tongue movements, also has a superior part receiving bilateral input and an inferior part (genioglossus) receiving primarily contralateral input.
• A lesion on one side of the brain can cause the tongue to deviate towards the weakened side when protruded.

Organisation of White Matter in the Cortex

• The white matter of the brain is organized into three types of fibers: association fibers, projection fibers, and commissural fibers.
• Association fibers connect different regions within the same hemisphere of the brain.
• Projection fibers transmit information between the cerebral cortex and other brain regions or the spinal cord.
• Commissural fibers connect corresponding regions of the two hemispheres.
• The internal capsule is a major pathway for projection fibers; it carries motor, sensory, and other signals between the cortex and lower brain structures.

Basal Nuclei and Eye Movements

• Eye movements are regulated by specialized brain areas, including frontal eye fields, supplementary eye fields, and parietal eye fields.
• These eye fields contribute to planning and executing eye movements, and they pass through the basal nuclei pathways.
• The basal nuclei can modify and adjust these eye movements based on input from the cortical regions.
• Damage to the cortical eye fields can cause strabismus (deviation of eye gaze) toward the affected side.

Basal Nuclei and Motor Control

• Basal nuclei play a crucial role in controlling and refining motor activity, working in conjunction with the motor cortex and other brain regions.
• They receive input from the cortex, process this information, and send signals to the thalamus and brainstem, which influence motor function and movement planning.
• The two main pathways within the basal nuclei are direct and indirect.
• The direct pathway enhances motor activity, while the indirect pathway inhibits motor activity.
• Both pathways involve a series of interconnected neurons within the basal nuclei, leading to a delicate balance between excitation and inhibition.

Parkinson's Disease

• Parkinson's disease is a neurodegenerative disorder characterized by tremors, muscle rigidity, slow movements (bradykinesia), and postural instability.
• It is associated with the loss of dopamine-producing neurons in the substantia nigra pars compacta, leading to an imbalance in the basal ganglia circuits and a reduction in dopamine signaling.

Huntington's Disease

• Huntington's disease is a neurodegenerative disorder caused by a genetic mutation responsible for the production of an abnormal protein that accumulates in the brain.
• It primarily affects the striatum and other basal ganglia structures, leading to uncontrolled movements (chorea), cognitive decline, and behavioral changes.

Basal Ganglia: Indirect Pathway

• The indirect pathway inhibits thalamic output, modulating cortical activity.
• This applies to both the thalamus and brainstem.
• The direct and indirect pathways work in parallel to refine and select cortical programs.

Substantia Nigra Pars Compacta (SNc)

• The SNc contains dopaminergic neurons that modulate the basal ganglia.
• Dopamine has different effects on inhibitory neurons depending on the receptors expressed.
• Dopamine inhibits the indirect pathway (D2 receptors) and stimulates the direct pathway (D1 receptors).
• This ultimately increases thalamic output by reducing inhibition on the indirect pathway and stimulating the direct pathway.

Parkinson's Disease

• Parkinson's disease results from the loss of dopaminergic neurons in the SNc.
• By the time symptoms appear, approximately 70% of these neurons are lost.
• This leads to decreased thalamic output, causing bradykinesia (slowing of movements).
• The loss of function in these loops can also result in tremor and involuntary movements.

Parkinson's Disease: Diagnosis

• Clinical Inspection:
  • Reduced spontaneous movements, including hand gestures and eye blinking.
  • Resting tremor.
  • Fidgeting and crossing/uncrossing legs (dyskinesia), a complication of long-term Levodopa therapy.
• Tests:
  • Bradykinesia: Assess rapid alternating movements (e.g., hand flipping, finger pinching).
  • Rigidity: Passive manipulation of limbs, particularly the wrist or elbow.
  • Tremor: Resting, postural, and kinetic.
  • Gait and Balance: Reduced step length, shuffling gait, loss of balance during turns, and loss of heel strike.

Huntington's Disease

• Huntington's disease is caused by a mutation in the Huntington gene.
• It leads to atrophy of the putamen, caudate, and other basal nuclei.
• This results in movement disorders, cognitive deficits, and psychiatric problems.

Huntington's Disease: Symptoms

• Movement Disorders:
  • Chorea: Involuntary jerking movements.
  • Rigidity and dystonia: Similar to upper motor neuron lesions.
  • Abnormal eye movements: Difficulty initiating movements.
  • Impaired gait, posture, and balance.
  • Difficulty with speech and swallowing.
• Cognitive Disorders:
  • Difficulty organizing, prioritizing, and focusing.
  • Perseveration: Difficulty shifting thoughts, behaviors, or actions.
  • Lack of impulse control.
  • Lack of awareness of one's behaviors and abilities.
  • Slowness in processing thoughts and finding words.
  • Difficulty learning new information.
• Psychiatric Disorders:
  • Depression: Feelings of sadness, apathy, irritability, and social withdrawal.
  • Obsessive Compulsive Disorder.
  • Mania: Overactive mood with elevated self-esteem.
  • Bipolar Disorder.

Basal Nuclei Topography

• Caudate Nucleus: Associated with association cortices, including the prefrontal and temporal lobes.
• Putamen: Primarily associated with motor and sensory functions.
• Nucleus Accumbens: Involved in the limbic system, contributing to neuropsychiatric symptoms.

Midbrain, Pons, and Medulla Reflexes

• Midbrain Rostral/Caudal:
  • Pupillary Light Reflex: Constriction of both pupils, afferent via optic nerve, efferent via oculomotor nerve.
  • Pretectal Nucleus: Receives afferent fibers for the pupillary light reflex.
• Pons Rostral/Caudal:
  • Corneal Reflex: Afferent via trigeminal nerve, efferent via facial nerve.
  • Jaw Jerk Reflex: Afferent via trigeminal nerve, efferent via ?
• Medulla Rostral/Caudal:
  • Salivation and Gag Reflex: Afferent and efferent via cranial nerves IX and X.
  • Vestibulo-ocular Reflex: Reflexive eye movements in response to head movement.

Mapping Visual Field Defects

• Left Optic Nerve Lesion: Monocular vision loss in the left eye.
• Left Optic Radiation Lesion:
  • Anterior Bundle (Meyer's Loop): Affects the inferior retinal quadrant, causing a superior visual field defect.
  • Superior Bundle: Affects the superior retinal quadrant, causing an inferior visual field defect.
  • Macular Sparing: Suggests a more anterior lesion.

Cerebellar Pontine Angle Infarct

• Result in ipsilateral cerebellar dysfunction, cranial nerve deficits, and potentially lateral medullary symptoms if the infarct extends.
• Ipsilateral Cerebellar Dysfunction:
  • Impaired coordination of voluntary movements.
  • Dysmetria: Difficulty judging distance and range of motion.
  • Dysdiadochokinesis: Difficulty performing rapid alternating movements.
  • Intention tremor: Worsening tremor as the limb approaches its target.
  • Hypotonia: Decreased muscle tone.
• Cranial Nerve Deficits:
  • Facial nerve palsy: Weakness or paralysis of facial muscles.
  • Vestibulocochlear nerve: Hearing loss, tinnitus, and vertigo.
  • Trigeminal nerve: Sensory impairment of the face.
  • Abducens nerve: Lateral gaze paralysis.

Imaging Quizzes Week 12 Anatomy

• Station 1:
  • CT Brain: Identify structures like the left ventricle, choroid plexus, and cerebral aqueduct.
  • CSF Flow: Understand how CSF circulates from the cerebral aqueduct to the subarachnoid space.
• Station 2:
  • CT Brain: Recognize subdural hematomas, midline shift (e.g., of the septum pellucidum), sulci effacement, and cerebral/cerebellar herniation.
  • Types of Herniation: Understand the different types of herniation (subfalcine, transtentorial, cerebellar tonsil, axial, lateral).
• Station 3:
  • CT Brain: Label the major arteries supplying the brain (e.g., anterior cerebral artery, middle cerebral artery, posterior cerebral artery, basilar artery, vertebral artery).
• Station 4:
  • CT Brain: Identify the hyperdense middle cerebral artery (MCA) as a sign of MCA infarct.
  • Basal Ganglia: Label the caudate nucleus, putamen, globus pallidus, and internal capsule.

Week 12 Anatomy Pre-Lab Questions

• Labeling the Ventricular System: Locate the anterior, superior, inferior, and posterior horns of the lateral ventricles, the third ventricle, the cerebral aqueduct of Sylvius, and the fourth ventricle.
• Labeling Axial Images: Identify the position of structures in axial images, from rostral to caudal, including the lateral ventricles, caudate nucleus, temporal lobes, and occipital lobes.
• Fiber Types: Categorize fibers as commissural, projection, or association based on their location and function.
• Basal Ganglia Structures: Label the caudate nucleus, putamen, globus pallidus externa/interna, subthalamic nucleus, and substantia nigra on an axial image.
• Blood Supply of the Brain: Label the main arteries supplying the brain, including the anterior cerebral artery, anterior communicating artery, internal carotid artery, middle cerebral artery, posterior communicating artery, posterior cerebral artery, superior cerebellar artery, basilar artery, posterior inferior cerebellar artery, anterior spinal artery, and vertebral artery.

Specimen Notes Week 12

• Claustrum: A thin sheet of neurons and glial cells that connects to the cerebral cortex and subcortical regions.
• Substantia Nigra Degeneration (Parkinson's Disease):
  • Effects: Reduction in dopamine production, leading to motor (tremor, rigidity, bradykinesia, postural instability) and non-motor (cognitive impairment, depression, anxiety, REM sleep disorder) symptoms.
• Cerebral Vascular Accidents (CVAs):
  • Anterior Cerebral Artery (ACA) Occlusion: Symptoms include contralateral lower limb weakness and sensory loss, urinary incontinence, impaired judgment, personality changes, abulia, and transcortical motor aphasia.
  • Middle Cerebral Artery (MCA) Occlusion: Symptoms include contralateral hemiparesis and hemisensory loss, homonymous hemianopia, global aphasia, apraxia, neglect syndrome, and Gerstmann syndrome.
  • Posterior Cerebral Artery (PCA) Occlusion: Symptoms include visual field defects, contralateral hemiparesis, and sensory loss.

Posterior Cerebral Artery (PCA) Lesions

• May cause Homonymous hemianopia (similar to Middle Cerebral Artery (MCA) lesions)
• May cause visual agnosia (difficulty recognizing objects)
• May cause prosopagnosia (difficulty recognizing faces)
• May cause color agnosia (difficulty recognizing colors)
• May cause alexia without agraphia (difficulty reading, but can write)
• May cause memory impairment, due to involvement of the hippocampus and parahippocampal gyrus
• May cause thalamic syndrome (sensory loss, pain, and some movement disorders)

Spinal Cord Pathways

• Spinothalamic Tract: Transmits pain and temperature information.
  • Sensory information enters spinal nerve, cell body in dorsal root ganglion
  • Neuron projects into dorsal horn
  • Relay neuron ascends through spinal cord after crossing to the other side, traveling in the ventrolateral white matter (spinothalamic tract).
  • Pathway continues up the spinal cord, through the medulla hole and the brainstem to the thalamus
• Dorsal Column Medial Lemniscus (DCML): Transmits light touch and proprioception.
  • Sensory information enters spinal nerve, cell body in dorsal root ganglion
  • Axon ascends through the dorsal column (divided into the cuneate fasciculus for the upper limb and the gracile fasciculus for the lower limb).
  • Axons synapse at the cuneate or gracile nucleus in the medulla, then cross and decussate through the medial lemniscus (a white matter pathway).
• Corticospinal Tract: Transmits motor signals from the motor cortex to the spinal cord.
  • Motor neuron resides in the ventral horn
  • Axon leaves via the ventral root and joins the spinal nerve
  • Axon originates in the precentral gyrus (or premotor or supplementary motor area)
  • Travels through the corticospinal tract, crosses over to the lateral side of the spinal cord to innervate muscles.

Spinal Cord Blood Supply

• Anterior Spinal Artery: Supplies the ventral 2/3 of the spinal cord.
• Posterior Spinal Arteries: Supplies the posterior 1/3 of the spinal cord.
• Radicular Arteries: Connect the anterior and posterior spinal arteries and form a network.

Spinal Cord Injury

• Transverse Myelitis: Inflammation of the spinal cord
• Multiple Sclerosis: Autoimmune disorder that attacks the myelin sheath of neurons.
  • Can affect the anterior 2/3 of the spinal cord, causing bilateral loss of pain and temperature sensation below the lesion.
  • If only some myelin is affected, some sensation/motor might still be present.
  • Bilateral motor issues may present, potentially with preserved proprioception if the damage is restricted to the anterior side
  • A complete spinal cord injury will affect all pathways bilaterally.

Extrapyramidal Tracts

• Rubrospinal Pathway: Originates in the red nucleus (midbrain), crosses to the other side, and projects down the lateral aspect of the medulla and spinal cord to synapse on motor neurons.
  • Receives input from the cerebellum
  • Involved in maintaining tone in flexor compartments and complex reflexes in the limbs.
  • Involved in inhibiting contraction of antigravity muscles (extensors).
  • Injuries above the red nucleus can present with decorticate posturing (flexion of upper limbs, drawing of limbs towards the core, extension of legs).
• Tectospinal Tract: Originates in the superior colliculus (midbrain), crosses to the contralateral side, and runs in the anterior medial part of the spinal cord to innervate muscles.
  • Receives input from the retina and visual association areas
  • Involved in reflex eye movements in response to visual stimuli or head position.
  • It contributes to maintaining posture in response to visual stimuli, mainly in head and neck muscles.
• Reticulospinal Tract: Originates in the reticular formation (pons), primarily ipsilateral (some bilateral input).
  • Involved in extrapyramidal control of lower motor neurons.
  • Medial nuclei drive excitatory motor control.
  • Lateral nuclei inhibit motor control through interneurons.
  • Important for postural control and modulating heart rate and respiratory rates.
  • Part of the autonomic nervous system.
  • Injury below the red nucleus, particularly in the pontine/medullary region, creates a decerebrate posture (extended and internally rotated arms).
• Vestibulospinal Tract: Originates in the vestibular nuclei (inner ear, receives input from vestibular ganglion).
  • Involved in maintaining posture and balance, and controlling eye movements (vestibulo-ocular reflex) in coordination with the medial longitudinal fasciculus (MLF).
  • Lateral tract drives tone in antigravity muscles.
  • Medial tract assists in postural adjustments related to head and eye movements.
  • Damage to the vestibular nuclei impairs the vestibulo-ocular reflex.

Clinical Cases

• Case 1: Patient experiences temporary visual disturbance, clumsiness, slurring of speech, and difficulty with motor control.
  • Likely diagnosis: Atherosclerosis in the left internal carotid artery with potential emboli.
  • Symptoms point to disruption of the ophthalmic artery (for vision), anterior cerebral artery (for right-sided motor symptoms), and the middle cerebral artery (for speech and motor control).
  • Possible cause: Blockage or occlusion in the internal carotid artery, middle cerebral artery, or anterior cerebral artery, as well as potential emboli.
• Case 2: Patient with multiple sclerosis experiences dizziness, tingling, and blurry vision.
  • Diagnosis: Multiple sclerosis.
  • Likely cause: Demyelination of neurons within the central spinal cord, affecting spinothalamic and sensory pathways.
• Sports Injury Case: Patient experiences decorticate posturing.
  • Likely cause: Injury to the red nucleus, likely caused by a stroke or trauma.
  • Decorticate posturing is a result of unmodulated flexor activity and inability to inhibit extensor function.

Glasgow Coma Scale

• A scoring system used to assess the level of consciousness in patients.
• Assesses eye opening, verbal response, and motor response.
• Scores range from 3 to 15.

Glasgow Coma Scale (GCS)

• GCS used to assess level of consciousness
• Score based on eye opening, verbal response, and motor response
• Anything less than 8 indicates coma and requires immediate medical attention

Concussion

• Repeated concussions can cause injuries to the white matter and long tracts
• Tua Taigivaloa has sustained multiple concussions but passes all protocols
• Debate on whether he is safe to play despite ongoing concussions

Ventricular system

• Identify major components of the ventricular system
• Appreciate main cisterns where Cerebrospinal Fluid (CSF) may accumulate
• Understand how typical ventricular anatomy changes due to:
  • Midline shift
  • Subfalcine herniation
  • Transtentorial herniation

Cerebral Circulation

• Identify major arteries contributing to cerebral circulation
• Recognize hyperdense middle cerebral artery sign on CT
• Understand how imaging can visualize the extent of a lesion

Basal Ganglia

• Components include caudate, globus pallidus, and putamen
• Anterior and posterior limbs of the internal capsule pass through these structures
• Parkinson’s disease associated with resting tremors
• Cerebellar dysfunction associated with action tremors

Tremors

• Parkinson's resting tremor - pill rolling
• Cerebellar tremors - worse at the end of a movement, high amplitude, zigzagging movements
• Cerebellar tremors can also cause rapid uncontrollable eye movements
• Cerebellar testing includes finger-to-nose and heel-to-shin tests
• Parkinson's can be investigated through vascular tumor scans
• Positron emission tomography (PET) scans can visualize the loss of dopaminergic receptors

Parkinson's Treatment

• Levodopa + carbidopa: Inhibit dopa decarboxylase enzyme peripherally
• Anticholinergics and MAOB inhibitors can be used to manage the condition

Cerebellar Dysfunction Treatment

• Thalamic deep brain stimulation used to address cerebellar dysfunction

Tracts

• Visceral tracts cross the longitudinal fissure to join hemispheres via the corpus callosum and anterior/posterior commissures
• Association tracts connect regions within one hemisphere
• Short association tracts connect regions within one lobe, while long tracts connect across lobes (e.g., arcuate fasciculus, superior longitudinal fasciculus)
• Major tracts include:
  • Corticospinal
  • Corticopontine
  • Corticobulbar
  • Dorsal Column Medial Lemniscus (DCML)
  • Medial Lemniscus

Internal Capsule

• Acts as a highway for fibers traveling through the brain
• Composed of anterior, posterior limbs, and genu
• Runs through the caudate, globus pallidus, and putamen
• Posterior limb carries corticospinal tract and some somatosensory fibers from the thalamus to the cortex
• Damage to this region affects contralateral motor and sensory function
• Most corticobulbar tracts (cranial nerves) pass through the genu

Middle Cerebral Artery (MCA)

• Branch of the internal carotid artery
• Largest of the three cerebral arteries
• Supplies most of the brain except the outer layers
• M1 segment supplies the basal ganglia
• M2 segment passes through the insula cortex
• M3 segment loops back on itself (opercular segment)
• M4 segment wraps around the entire cortex, supplying motor, sensory, auditory, and posterior limb regions
• Infarction in this area is devastating, causing significant functional impairments

Test your knowledge on key anatomical structures and relationships within the brain in this Neuroscience Chapter 4 Quiz. Questions cover the connections between upper and lower motor neurons, the role of the basal nuclei, and the anatomy surrounding the ventricles. Challenge yourself and deepen your understanding of neuroscientific concepts.