Contains approximately 86\,\text{billion} neurons
Average weight ≈ 1.4\,\text{kg} (soft, tofu-like texture)
Consumes >20\% of body energy while being 2\% of body mass
Generates about 12–25\,\text{W} of electrical power
Meninges (outer ➜ inner): dura mater, arachnoid, pia mater
Cerebrospinal fluid (CSF)
Produced in choroid plexus within ventricles
Circulates ventricles & sub-arachnoid space: cushioning, nutrient delivery, waste removal
Blood–brain barrier (BBB): tightly-packed capillary cells selectively allow nutrients, block toxins
Gyri (ridges) & sulci (grooves) increase cortical surface area; named & functionally relevant
Grey matter: neuronal cell bodies; white matter: myelinated axons
Key fissures: longitudinal (hemispheres), central (motor/sensory division), lateral (temporal separation)
Directions: dorsal/ventral, anterior/posterior (rostral/caudal), medial/lateral, superior/inferior, proximal/distal
Planes: frontal (coronal), horizontal, sagittal
Central nervous system (CNS): brain & spinal cord; protected by BBB & CSF
Peripheral nervous system (PNS): nerves & ganglia outside CNS
Somatic: afferent sensory + efferent voluntary motor (includes most cranial nerves)
Autonomic: involuntary; sympathetic (fight/flight) vs parasympathetic (rest/digest)
Forebrain
Telencephalon: cerebral cortex, basal ganglia, limbic structures
Diencephalon: thalamus, hypothalamus
Midbrain (mesencephalon): tectum (superior & inferior colliculi), tegmentum (red nucleus, substantia nigra)
Hindbrain
Metencephalon: cerebellum, pons
Myelencephalon: medulla oblongata
Outer grey layer; ≈16\,\text{billion} neurons; surface area ≈1.5\,\text{m}^2
Lobes & general functions (coarse):
Frontal: cognition, decision, voluntary movement
Parietal: somatosensation, spatial attention
Temporal: audition, language, memory
Occipital: vision
Cerebellum (posterior/inferior): balance & coordination (not a lobe but functionally distinct)
Primary areas: motor (precentral gyrus), somatosensory (postcentral gyrus), visual (occipital), auditory (temporal)
Association areas: premotor, prefrontal, language (Broca’s/Wernicke’s), multimodal integration
Six laminae (I–VI) from pia ➜ white matter
Layer IV: thalamic sensory input (prominent in primary sensory cortex)
Layer V: large pyramidal (Betz) cells, output to brainstem/spinal cord (motor cortex)
Columnar organisation: vertical information processing units
Basal ganglia: caudate, putamen, globus pallidus; movement gating, reward; implicated in Parkinson’s & Huntington’s
Limbic components
Hippocampus: formation of new declarative memories; adult neurogenesis
Amygdala: emotion (fear/anxiety), emotional memory, social processing
Cingulate gyrus (historically included)
Thalamus: major sensory relay to cortex; roles in sleep & consciousness
Hypothalamus: homeostasis (temperature, hunger, thirst, circadian), stress (HPA axis), controls pituitary (endocrine link)
Midbrain tectum: superior colliculus (visual-motor orienting), inferior colliculus (auditory)
Midbrain tegmentum: red nucleus & substantia nigra (motor modulation, dopamine)
Pons: sleep, arousal, cranial nerve nuclei, movement coordination
Medulla oblongata: autonomous vital functions (cardio-respiratory)
Cerebellum: coordination, posture, fine motor control, motor learning; receives corticospinal efferents & spinocerebellar afferents
86 billion neurons, 1.4 kg, >20\% energy use
Protective: meninges, CSF, BBB
CNS vs PNS; somatic vs autonomic
Key cortical lobes & primary areas
Six cortical layers; layer IV (input), V (output)
Basal ganglia = movement gating; limbic (hippocampus, amygdala) = memory & emotion
Thalamus = relay; hypothalamus = homeostasis & endocrine
Midbrain (colliculi), pons, medulla = brainstem functions
Cerebellum = coordination & motor learning