--- title: "Regional Anatomy of the Central Nervous System" description: "The brain and spinal cord contain regions with different cell groups and connections. Sensory and motor pathways cross the midline at different places. Tracing those routes helps explain a likely site" canonical: https://lightmysky.com/learn/science/regional-anatomy-of-the-central-nervous-system-mt_S9f5cUS8NZ source: https://lightmysky.com/learn/science/regional-anatomy-of-the-central-nervous-system-mt_S9f5cUS8NZ.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Regional Anatomy of the Central Nervous System The brain and spinal cord contain regions with different cell groups and connections. Sensory and motor pathways cross the midline at different places. Tracing those routes helps explain a likely site of damage from the functions lost and preserved, but a loss pattern does not always identify one location. Subject: Science · Area: The Human Body · Ages 19 to 20 Page: https://lightmysky.com/learn/science/regional-anatomy-of-the-central-nervous-system-mt_S9f5cUS8NZ ## Ready when they can - Name the major brain divisions and spinal cord regions, and describe their grey and white matter organisation. - Trace one ascending and one descending pathway, including where each crosses the midline - Infer a likely lesion region from a stated motor and sensory pattern, and explain the limits of that inference. ## Lesson: Mapping the control centre The central nervous system is the brain and spinal cord. Four major adult brain divisions are the cerebrum, diencephalon, brain stem and cerebellum. The diencephalon includes the thalamus and hypothalamus. The brain stem contains the midbrain, pons and medulla. Circuits in the pons and medulla help regulate breathing and heart rate. The cerebrum contains an outer grey cortex, deep grey nuclei and white matter connections. Grey matter includes neuron bodies, dendrites and synapses; white matter contains axon bundles. Basal nuclei are deep cell groups that help select, initiate and scale movements. The cerebellum uses sensory feedback to help coordinate movement and balance. Movement depends on connected regions working together. The cord has cervical, thoracic, lumbar, sacral and coccygeal regions. Its grey matter surrounds the central canal, with white matter outside. Dorsal horns process sensory input. Ventral horns contain motor neuron bodies whose axons reach skeletal muscles. Damage to these neurons weakens the muscles they supply. The withdrawal reflex you studied links sensory input to motor output through local cord circuits. *(drawing: These cells describe a local withdrawal route. They are not a spinal cross-section or a scale drawing.)* Two ascending routes carry different sensations. Fine touch, vibration and position signals ascend on the input side in the dorsal columns, relay in the medulla, then cross to the opposite thalamus and sensory cortex. Pain and temperature input relays in the dorsal horn. Second-order axons cross near entry and ascend on the opposite side in the spinothalamic pathway, then relay in the thalamus before reaching cortex. *(drawing: Follow the cells in order. This dorsal column route crosses after its medulla relay.)* Descending pathways travel toward the cord. Most corticospinal fibres from motor cortical areas cross in the lower medulla and descend in the opposite lateral corticospinal tract. They influence ventral horn motor neurons, often through interneurons. Motor neuron axons then reach muscles through ventral roots and peripheral nerves. Other descending pathways modify sensory processing, so descending does not always mean a muscle command. *(drawing: Most fibres entering the lateral corticospinal tract cross in the medulla. Spinal motor neurons provide the final route to muscle.)* A lesion is an area of damage. To propose its location, identify the functions lost and preserved, then trace the affected pathways and their crossings. Sensory loss with preserved movement suggests sensory involvement, but peripheral nerves and several CNS sites can produce it. Side and body level narrow the possibilities. Other examination findings and sometimes imaging are needed to distinguish them. A classic injury to one half of the cord causes limb weakness and loss of vibration or position sense on that side below the lesion. The lateral corticospinal fibres have already crossed; dorsal column fibres have not. Pain and temperature loss is on the opposite side, often starting one or two segments lower because those signals cross near entry. Together these findings suggest a cord side, not an exact vertebral level. *(drawing: Use the combined pattern. One lost function alone does not establish the lesion site.)* **Recap.** Identify the region and affected functions. Trace the pathways and their crossings, then check whether the combined findings support a likely lesion location. *Lesson, questions and flashcards written for this dataset. Factual reference study used Anatomy and Physiology sections 13.2, 14.2 and 16.4 and Introduction to Behavioral Neuroscience section 9.2. No source images are reproduced.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [The Brain: Regions and the Evidence for What They Do](https://lightmysky.com/learn/science/the-brain-regions-and-the-evidence-for-what-they-do-mt_BA_DGCDic8) - [Neurons & Brain Structure](https://lightmysky.com/learn/science/neurons-and-brain-structure-mt_okUMpHsV-P) ## Optional connections - [The Reflex Arc and Synapses](https://lightmysky.com/learn/science/the-reflex-arc-and-synapses-mt_evlgCVxTnK) ## Opens up - [The Autonomic Nervous System and Its Two Outflows](https://lightmysky.com/learn/science/the-autonomic-nervous-system-and-its-two-outflows-mt_bnVgu4T4E9) - [Motor Control: From Intention to Muscle](https://lightmysky.com/learn/science/motor-control-from-intention-to-muscle-mt_hrWOuRtPDl) - [Transmitter Systems and Two Kinds of Receptor](https://lightmysky.com/learn/science/transmitter-systems-and-two-kinds-of-receptor-mt_yXaSbrBxua)