Biomedical Science for Osteopathy: Neuroscience Study Guide

Cerebral Regions and Selected Cranial Nerves

• Frontal Lobe: Identify this lobe and associate it with voluntary motor control, executive functions, planning, behaviour, and speech production within the dominant hemisphere.

• Parietal Lobe: Identify this lobe and associate it with somatosensory processing, sensory integration, and aspects of spatial attention and language processing.

• Temporal Lobe: Identify this lobe and associate it with auditory processing, memory, and aspects of language comprehension.

• Occipital Lobe: Identify this lobe and associate it with visual processing.

• Precentral Gyrus / Primary Motor Cortex: Recogise this cortical gyrus located anterior to the central sulcus. It is associated with voluntary skeletal movement.

• Postcentral Gyrus / Primary Somatosensory Cortex: Recognise this cortical gyrus located posterior to the central sulcus. It is associated with conscious somatic sensation.

• Cingulate Gyrus: Identify this gyrus on a medial brain view. It is recognized as part of the limbic system and is involved in emotion, motivation, and the integration of autonomic and cognitive responses.

• Corpus Callosum: Identify this major commissural white-matter tract on a midsagittal brain view. It connects the two cerebral hemispheres.

• Cranial Nerves $I-XII$: Students must know the basic function of all twelve cranial nerves and identify their specific origin within the Central Nervous System ($CNS$).

Ventricles, Cerebrospinal Fluid (CSF), and Meninges

• Lateral Ventricles: These are paired ventricles identifiable on models and sagittal/coronal representations. They have a direct relationship with the cerebral hemispheres.

• Third Ventricle: A midline structure that must be distinguished from the lateral and fourth ventricles.

• Interventricular Foramen: This is the communication pathway through which each lateral ventricle connects with the third ventricle.

• Cerebral Aqueduct: This passage travels through the midbrain and connects the third ventricle to the fourth ventricle.

• Fourth Ventricle: Located between the pons/upper medulla and the cerebellum.

• Choroid Plexus: The specific structure responsible for the production of most $CSF$ within the ventricles.

• Arachnoid Villi / Granulations: Projections that return $CSF$ from the subarachnoid space into the dural venous sinuses.

• CSF Flow Sequence: The correct order of flow is from the lateral ventricles, through the interventricular foramen to the third ventricle, through the cerebral aqueduct to the fourth ventricle, into the subarachnoid space, and finally to the venous return via arachnoid granulations.

• Dura Mater: The tough, outermost meningeal layer surrounding the brain and spinal cord.

• Arachnoid Mater: The middle meningeal layer that bridges over surface contours.

• Pia Mater: The delicate, innermost layer that is closely adherent to the $CNS$ tissue.

• Epidural Space: In the vertebral canal, this space exists outside the dura and contains fat and the venous plexus.

• Subarachnoid Space: The space located between the arachnoid and pia mater. It is filled with $CSF$ and contains blood vessels and trabeculae.

• Falx Cerebri: A sickle-shaped dural fold located in the longitudinal fissure, separating the two cerebral hemispheres.

• Falx Cerebelli: A smaller sickle-shaped dural fold that separates the two cerebellar hemispheres.

Spinal Cord Gross Anatomy, Roots, and Levels

• Spinal Cord Orientation: On a cross-section, identify dorsal/posterior versus ventral/anterior. The dorsal columns are located as posterior white matter situated between the dorsal horns.

• Anterior / Ventral Funiculus: The anterior white matter located between the anterior median fissure and the ventral horn regions. It contains multiple ascending and descending tracts rather than a single function.

• Posterior / Dorsal Funiculus: This dorsal white column is associated with fine touch, vibration, and conscious proprioception.

• Lateral Funiculus: These lateral white matter regions contain major ascending and descending tracts.

• Anterior / Ventral Horn: Grey matter containing lower motor-neuron ($LMN$) cell bodies that supply skeletal muscle.

• Dorsal / Posterior Horn: Grey matter involved in receiving and processing sensory afferent information.

• Lateral Horn: An autonomic grey-matter projection that is most prominent in the thoracic and upper lumbar regions of the spinal cord.

• Dorsal Root: Sensory nerve fibres entering the cord; must be distinguished from the ganglion.

• Dorsal Root Ganglion: The swelling along the dorsal root that contains primary sensory-neuron cell bodies.

• Ventral Root: Motor fibres leaving the spinal cord.

• Thoracic Cross-Section: Characterized by relatively small, rounded grey horns, a distinct lateral horn, and a higher white-to-grey matter ratio than lumbar or sacral levels.

• Cervical Cross-Section: Characterized by a large overall diameter, abundant white matter, and enlarged ventral horns at cervical enlargement levels.

• Lumbar Cross-Section: Characterized by a higher proportion of grey matter and large ventral horns at enlargement levels.

• Sacral Cross-Section: Characterized by a small overall size, a very high grey-to-white matter ratio, and broad grey horns.

• Conus Medullaris: The tapered inferior end of the spinal cord, typically terminating near the $L1-L2$ vertebral level in adults.

• Cauda Equina: A bundle of lumbar, sacral, and coccygeal nerve roots that descend below the conus medullaris.

• Filum Terminale: A thin strand of pia mater extending from the conus medullaris that helps anchor the inferior spinal cord.

• Denticulate Ligament: Tooth-like lateral extensions of the pia mater that stabilise the spinal cord by attaching to the dura mater.

Spinal Pathways and Lesion Reasoning

• Dorsal-Column Fasciculi: Consists of the Fasciculus Gracilis and Fasciculus Cuneatus.

  • Fasciculus Gracilis: Carries lower-body information and is present throughout the entire length of the cord.

  • Fasciculus Cuneatus: Carries upper-trunk and upper-limb information, appearing at approximately level $T6$ and above.

• Sensory Modalities: The dorsal-column pathway carries discriminative/fine touch, vibration, and conscious proprioception. These must be distinguished from pain, temperature (spinothalamic), and unconscious proprioception (spinocerebellar).

• Pathway Sequence (Dorsal Column): Peripheral receptor \rightarrow dorsal root ganglion \rightarrow ipsilateral dorsal column \rightarrow gracile/cuneate nuclei in the medulla \rightarrow sensory decussation \rightarrow medial lemniscus \rightarrow thalamus \rightarrow primary somatosensory cortex.

• Medial Lemniscus: The continuation of dorsal-column information in the brainstem after the fibres synapse and cross (decussate) in the medulla.

• Dorsal / Posterior Spinocerebellar Tract: Located in the dorsolateral funiculus; carries ipsilateral unconscious proprioceptive information to the cerebellum.

• Lateral Spinothalamic Tract: Located in the anterolateral cord; carries pain and temperature information from the contralateral body after crossing within the spinal cord.

• Lateral Corticospinal Tract: Located in the posterolateral funiculus; associated with voluntary motor control, particularly movement of distal limbs.

• Rubrospinal Tract: A smaller descending tract located near the lateral corticospinal system, associated with motor influence from the red nucleus.

• Modality-to-Tract Matching:

  • Pain/Temperature: Lateral Spinothalamic Tract.

  • Unconscious Proprioception: Dorsal/Posterior Spinocerebellar Tract.

  • Conscious Proprioception: Dorsal Columns (Fasciculus Gracilis/Cuneatus).

  • Voluntary Movement: Lateral Corticospinal Tract.

Neurovasculature and Stroke

• Main Stroke Types:

  • Ischaemic Stroke: The more common broad category of stroke.

  • Haemorrhagic Stroke: Less common, involving bleeding within the brain tissue or subarachnoid space.

• Ischaemic Mechanisms: Primarily caused by thrombosis (local clot formation) or embolism (clot traveling from elsewhere). Common contributors include atherosclerosis and cardiac embolic sources.

• Haemorrhagic Stroke Presentation: Can produce focal neurological deficits, headache, vomiting, or altered consciousness.

• Major Cerebral Arteries:

  • Anterior Cerebral Artery ($ACA$): Specific cortical distribution territory.

  • Middle Cerebral Artery ($MCA$): Specific cortical distribution territory.

  • Posterior Cerebral Artery ($PCA$): Specific cortical distribution territory.

• Laterality: A hemispheric lesion results in contralateral body findings because the major corticospinal and somatosensory pathways cross (decussate) before reaching their final targets.

• Venous Sinuses: Identify these structures and understand the drainage pathway of the brain.

• Vertebral Arteries: Paired arteries that ascend to the cranial cavity and join to form the basilar artery.

• Basilar Artery: A midline artery located on the ventral surface of the pons, formed by the union of the vertebral arteries.

• Spinal Artery Blood Supply: The spinal cord is generally supplied by the anterior spinal artery, posterior spinal arteries, and radicular arteries.

Brainstem and Midbrain Localisation

• Brainstem Divisions: Consists of the midbrain, pons, and medulla oblongata (ordered rostral to caudal).

• Midbrain External Anatomy:

  • Dorsal Aspect: Tectum, comprising the superior and inferior colliculi.

  • Ventral Aspect: Cerebral peduncles.

• Midbrain Internal Organisation: Includes the tectum, tegmentum, cerebral aqueduct, substantia nigra, and crus cerebri/cerebral peduncles.

• Substantia Nigra: The dopaminergic substantia nigra pars compacta is linked to movement initiation. Dysfunction here is the hallmark of Parkinson disease.

• Cerebral Aqueduct: Connects the third and fourth ventricles; obstruction can impair $CSF$ flow (hydrocephalus).

• Medial Lemniscus: Damage to this structure in the brainstem results in contralateral loss of discriminative touch, vibration, and proprioception.

• Superior Colliculus / Tectospinal System: Involved in the reflexive orientation of the eyes, head, and neck toward visual stimuli.

• Crus Cerebri and Corticospinal Fibres: Damage to descending corticospinal fibres in the cerebral peduncle results in contralateral upper-motor-neuron ($UMN$) weakness of the body.

• Periaqueductal Grey ($PAG$): Contributes to descending pain modulation. Damage may reduce the body's endogenous inhibition of nociceptive signalling.

• Pons: The rounded middle segment of the brainstem; features the basilar sulcus on its ventral surface.

• Medulla Oblongata: The caudal brainstem segment continuous with the spinal cord.

• Medullary Pyramids: Paired ventral elevations containing corticospinal fibres.

Basal Ganglia and Parkinson Disease

• Basal Ganglia Structures: Caudate nucleus, putamen, globus pallidus ($GP$), subthalamic nucleus ($STN$), and substantia nigra ($SN$).

• Dorsal Striatum: Composed of the caudate nucleus and the putamen.

• Putamen: The lateral component of the dorsal striatum.

• Caudate Nucleus: Features a head, body, and tail relationship to the lateral ventricle.

• Globus Pallidus: Located medial to the putamen. The internal segment ($GPi$) is a principal output nucleus of the motor loop.

• Functional Groups:

  • Striatum: Principal input group.

  • $GPi$ and $SNr$ (Substantia Nigra Reticulata): Major output nuclei.

  • $GPe$ (Globus Pallidus Externus), $STN$, and $SNc$ (Substantia Nigra Pars Compacta): Intrinsic and modulatory nuclei.

• Body-Movement Loop Sequence: Cerebral cortex \rightarrow striatum \rightarrow $GPi/SNr$ \rightarrow thalamus \rightarrow motor cortex.

• Direct Pathway: Facilitates selected movement by reducing the inhibitory basal-ganglia output to the thalamus.

• Indirect Pathway: Suppresses competing or unwanted movements.

• Dopamine Role: Released from the $SNc$, it facilitates movement by promoting direct-pathway activity and reducing indirect-pathway activity.

• Limbic Loop: Associated with motivation, reward, reinforcement, and emotion-related behaviour.

• Parkinson Pathology: Involves the degeneration of dopaminergic neurons in the $SNc$, leading to altered basal-ganglia output and reduced movement facilitation.

• Parkinson Motor Terminology:

  • Bradykinesia: Slowness of movement.

  • Akinesia: Absence of movement.

  • Micrographia: Abnormally small handwriting.

  • Freezing: Temporary inability to move.

  • Resting Tremor: Tremor occurring when the limb is at rest.

  • Rigidity: Increased resistance to passive movement.

  • Postural Instability: Impaired balance and coordination.

• Medication Overview: The combination of levodopa and carbidopa is used. Levodopa serves as a dopamine precursor, while carbidopa reduces the conversion of levodopa to dopamine in the periphery (outside the brain).

Cerebellum and Cerebellar Dysfunction

• Core Cerebellar Role: Does not initiate movement; instead, it coordinates timing, force, accuracy, balance, and motor learning.

• Laterality: Cerebellar lesions typically produce ipsilateral (same side) limb coordination deficits due to the organization and double-crossing of cerebellar motor circuits.

• Functional Regions:

  • Cerebrocerebellum: Lateral hemisphere; involved in motor planning, complex/sequential movement, and skilled limb activity.

  • Spinocerebellum: Comprises the vermis (trunk/proximal control) and intermediate zones (ipsilateral distal-limb coordination).

  • Vestibulocerebellum: Flocculonodular lobe; involved in balance, gaze stability, vestibulo-ocular control, vertigo, and nystagmus.

• Ataxia: Defined as incoordination rather than primary weakness. Includes appendicular (limb) ataxia and gait/truncal ataxia.

• Dysmetria: The overshoot (hypermetria) or undershoot (hypometria) of a target during goal-directed movement. Assessed via finger-to-nose or heel-to-shin tests.

• Dysdiadochokinesia: Impaired ability to perform rapid alternating movements; associated with ipsilateral hemispheric/intermediate-zone dysfunction.

• Intention Tremor: A tremor that worsens as the limb approaches a target (distinguishable from Parkinsonian resting tremor).

• Additional Cerebellar Signs: Hypotonia (low muscle tone), rebound phenomenon, scanning or ataxic dysarthria (speech impairment), nystagmus (involuntary eye movement), broad-based gait, and truncal instability.

• Anatomical Features:

  • Primary Fissure: Separates the anterior and posterior lobes.

  • Horizontal Fissure: Runs around the lateral margin, separating superior and inferior surfaces.

  • Folia: Narrow transverse folds of the cerebellar cortex.

  • Arbor Vitae: Branching internal white matter.

  • Deep Cerebellar Nuclei: Embedded in white matter; major output structures are the dentate, interposed, and fastigial nuclei.

• Cerebellar Peduncles:

  • Middle Cerebellar Peduncle: The largest; connects pons to cerebellum and carries pontocerebellar afferent input.

  • Superior and Inferior Peduncles: Distinguished by their specific brainstem connections and broad input/output roles.

Multiple Sclerosis and Meningitis

• Multiple Sclerosis (MS) Classification: An immune-mediated inflammatory demyelinating disorder of the $CNS$.

• MS Pathology: Demyelination leads to slowed or blocked neural conduction. Symptoms vary depending on the location of the lesions.

• Common MS Manifestations: Examples include optic neuritis (visual disturbance), sensory changes, weakness, ataxia, fatigue, and bladder dysfunction.

• Meningitis Concept: Inflammation of the meninges, usually caused by infection. Bacterial meningitis is a medical emergency.

• Common Meningitis Features: Headache, fever, neck stiffness (nuchal rigidity), photophobia, nausea/vomiting, altered mental state, and potentially a rash or seizures. The classic triad of fever, neck stiffness, and altered mental state is not present in every patient.

• Bedside Signs of Meningeal Irritation:

  • Nuchal Rigidity: Passive neck flexion reveals pain or stiffness.

  • Kernig's Sign: Patient is supine with hip and knee flexed; attempted extension of the knee produces pain or resistance.

  • Brudzinski's Sign: Passive neck flexion produces involuntary flexion of the hips and knees.

• Clinical Safety: Traditional signs have limited sensitivity; a negative test does not rule out meningitis. Suspected cases require urgent medical escalation, not musculoskeletal treatment.

Pain Mechanisms and Ibuprofen

• Pain vs. Nociception:

  • Pain: A personal sensory and emotional experience.

  • Nociception: The neural processing of potentially damaging stimuli. Pain should not be inferred solely from sensory-neuron activity.

• Somatic Nociceptive Pain: Defined as pain arising from actual or threatened damage to non-neural somatic tissue due to the activation of nociceptors.

• Somatic Nociceptive Characteristics: Anatomically plausible localisation, clear relation to movement or loading, proportionate aggravating/relieving factors, local tenderness, and mechanical/intermittent behavior.

• Peripheral Neuropathic Pain: Defined as pain caused by a lesion or disease of the peripheral somatosensory nervous system.

• Peripheral Neuropathic Characteristics: Described as burning, electric, shooting, or lancinating; associated with tingling/dysaesthesia, allodynia (pain from non-painful stimuli), hyperalgesia (increased pain from painful stimuli), sensory loss, and follow a dermatomal or peripheral-nerve distribution.

• Nurofen / Ibuprofen: Contains ibuprofen and belongs to the Non-Steroidal Anti-Inflammatory Drug ($NSAID$) class.

• NSAID Mechanism: These drugs inhibit the enzyme cyclooxygenase and reduce the production of prostaglandins, which effectively reduces inflammatory pain and peripheral sensitisation.

• Contraindications / Major Cautions for Ibuprofen:

  • Serious $NSAID$ hypersensitivity.

  • Active or recurrent peptic ulcers or gastrointestinal ($GI$) bleeding.

  • Severe renal (kidney) impairment.

  • Use during the late stages of pregnancy.

• Medication Safety: Safe advice depends on specific formulation, dose, patient comorbidities, and concurrent medicines. Prescribing is not required for osteopathy students, but safety knowledge is essential.