Neuroanatomy Overview

Comprises the brain and spinal cord, enclosed within the skull and vertebral canal respectively, surrounded by the meninges and cerebrospinal fluid (CSF).

• Composed of grey matter (neuronal cell bodies, dendrites, synapses) and white matter (myelinated axons), arranged differently in the brain (grey matter predominantly cortical/peripheral, with deep nuclei) versus the spinal cord (grey matter central, white matter peripheral).

• Comprises the cranial nerves (I-XII, except the optic nerve, which is a CNS tract), spinal nerves and their roots/plexuses, and the peripheral distribution of the autonomic nervous system.
• Functionally connects the CNS to the rest of the body, carrying motor output and sensory input.

• Comprises the cerebral hemispheres (cerebrum), diencephalon, brainstem (midbrain, pons, medulla), and cerebellum: collectively enclosed within the cranial cavity.

• The connecting stalk between the cerebrum/diencephalon and the spinal cord, comprising the midbrain, pons, and medulla oblongata, housing most cranial nerve nuclei (III-XII), major ascending/descending tract relay points, and the reticular formation (vital cardiorespiratory/consciousness-regulating centres).

• A distinct structure attached to the brainstem via three paired peduncles, primarily coordinating movement, balance, and motor learning.

• Extends from the foramen magnum (continuous with the medulla) to approximately the L1-L2 vertebral level in adults (conus medullaris), housing segmental grey matter and ascending/descending white matter tracts.

• A continuous, CSF-filled cavity system within the brain: paired lateral ventricles → third ventricle → cerebral aqueduct → fourth ventricle → continuous with the spinal cord's central canal and the subarachnoid space.

• Three protective membrane layers surrounding the CNS: dura mater (outermost, tough), arachnoid mater (middle, web-like), pia mater (innermost, closely applied to neural tissue).

• Internal carotid system (anterior circulation, anterior and middle cerebral arteries) and vertebrobasilar system (posterior circulation, posterior cerebral arteries, cerebellar arteries, brainstem perforators), unified via the circle of Willis.

• Dorsal column-medial lemniscus (fine touch, proprioception, vibration) and spinothalamic tract (pain, temperature, crude touch), the two principal ascending pathways, each with a distinct decussation pattern and clinical lesion signature.

• Corticospinal tract (voluntary limb/trunk movement) and corticobulbar tract (voluntary cranial nerve motor nuclei control), plus extrapyramidal pathways (rubrospinal, vestibulospinal, reticulospinal, tectospinal); full detail in Section 11.

• Twelve paired nerves (I-XII): extracranial/peripheral course and distribution.

• The nervous system is broadly organised around parallel, hierarchically arranged systems: sensory (peripheral receptor → ascending pathway → thalamus → primary sensory cortex), motor (motor cortex → descending pathway → brainstem/spinal cord → peripheral effector, modulated by the cerebellum and basal ganglia), and autonomic (hypothalamic/brainstem control → sympathetic/parasympathetic outflow → visceral effectors), each of these three systems is explored in dedicated sections throughout this content.