CNS Neuroanatomy 4

Longitudinal fissure

Deep midline groove separating the left and right cerebral hemispheres; defines the border between hemispheres and orients cortical lobes.

Central sulcus

Major sulcus separating the frontal lobe (anterior) from the parietal lobe (posterior); key landmark to identify precentral (motor) and postcentral (sensory) gyri.

Lateral sulcus (Sylvian fissure)

Deep fissure separating the temporal lobe from the frontal and parietal lobes; retracting it exposes the insula.

Parieto-occipital sulcus

Sulcus separating the parietal lobe from the occipital lobe; used to define posterior cortical borders on the medial surface.

Precentral gyrus (primary motor cortex)

Cortical strip anterior to the central sulcus composed of pyramidal cells that initiate voluntary motor commands to upper motor neurons.

Postcentral gyrus (primary somatosensory cortex)

Cortical strip posterior to the central sulcus that receives somatic sensory input for touch, pressure, pain, temperature, and proprioception.

Primary motor cortex (M1)

Region in the precentral gyrus whose pyramidal neurons (upper motor neurons) send direct corticospinal projections for fine, discrete voluntary movements.

Primary somatosensory cortex (S1)

Region in the postcentral gyrus that receives and maps tactile, proprioceptive, and nociceptive input from the body; organized somatotopically.

Premotor cortex

Association motor area anterior to M1 that plans, sequences, and prepares learned movements using memory of motor programs; influences M1.

Supplementary motor area

SMA; medial/anterior cortical area involved in internally generated movement planning and coordinating bilateral or complex sequences before execution.

Somatosensory association area

Posterior to S1; integrates sensory input to interpret size, shape, texture, and spatial relationships for perception and object recognition.

Visual cortex (primary)

Cortical area in the occipital lobe (calcarine fissure region) that receives and initially processes visual information from the thalamus.

Visual association area

Surrounding occipital regions that interpret and recognize visual patterns, objects, and complex features by integrating primary visual inputs.

Auditory cortex (primary)

Temporal lobe region that receives and processes basic auditory information such as frequency and intensity.

Auditory association area

Temporal lobe regions that interpret complex sounds and recognize auditory patterns like speech and music.

Gustatory cortex

Region involved in processing taste information; contributes to perception of flavor and taste quality.

Olfactory cortex

Medial temporal lobe area that processes smell; closely linked to limbic structures for memory and emotion.

Insula

Deep cortical region within the lateral sulcus involved in interoception, emotion, sensory-motor integration, and aspects of cognition.

Gyri and sulci

Gyri are cortical ridges and sulci are grooves; together they increase cortical surface area and provide anatomical landmarks for lobes and functional areas.

Cerebral lobes (frontal, parietal, temporal, occipital)

Major cortical divisions each associated with dominant functions: frontal—motor and executive; parietal—somatosensation; temporal—auditory/olfactory; occipital—vision.

Corpus callosum

Large commissural fiber bundle connecting homologous cortical areas of left and right hemispheres, enabling interhemispheric communication.

Association fibers

White-matter tracts that interconnect cortical areas within the same hemisphere (e.g., arcuate fibers, longitudinal fasciculi) to integrate local and long-range cortical processing.

Commissural fibers

White-matter tracts that connect corresponding cortical regions between the two hemispheres; the corpus callosum is the largest example.

Projection fibers

White-matter tracts that connect the cerebral cortex with subcortical structures (diencephalon, brainstem, spinal cord); include corticospinal fibers within the internal capsule.

Internal capsule

Compact bundle of projection fibers between basal nuclei and thalamus that conveys ascending sensory and descending motor information between cortex and lower CNS.

Arcuate fibers

Short association fibers that interconnect neighboring gyri within the same lobe to support local cortical integration.

Longitudinal fasciculi

Long-range association tracts linking frontal lobe with more posterior cortical areas to coordinate higher-order functions.

Gray matter vs white matter

Gray matter contains neuronal cell bodies and synapses; white matter consists of myelinated axon bundles that transmit signals between regions.

Basal nuclei (basal ganglia) overview

Deep gray-matter structures embedded in cerebral white matter that modulate motor control, procedural learning, and subconscious movement regulation.

Caudate nucleus

Part of basal nuclei involved in motor control, learning, and aspects of emotion and cognition; follows lateral ventricle contours.

Putamen

Part of the lentiform nucleus; regulates voluntary movements and procedural learning by interacting with globus pallidus and cortex.

Globus pallidus

Part of the lentiform nucleus with internal and external segments; provides inhibitory output to thalamus to fine-tune and limit movement.

Subthalamic nucleus

Role within basal nuclei circuitry that modulates motor output and prevents involuntary movements by interacting with globus pallidus.

Substantia nigra

Dopamine-producing midbrain structure that influences basal nuclei function and facilitates smooth voluntary movement; degeneration causes parkinsonian symptoms.

Basal nuclei function in motor control

They integrate cortical input to select and inhibit motor programs, regulate muscle tone, and refine learned movement patterns via reciprocal loops with thalamus and cortex.

Pyramidal tract (corticospinal tract)

Direct descending pathway from primary motor cortex through internal capsule and medullary pyramids to spinal ventral horn to control voluntary, fine distal movements.

Upper motor neuron vs lower motor neuron

Upper motor neurons originate in cortex and descend to synapse on lower motor neurons; lower motor neurons in spinal ventral horn innervate skeletal muscle.

Extrapyramidal tracts (overview)

Indirect descending motor pathways (rubrospinal, vestibulospinal, reticulospinal, tectospinal) that modulate posture, tone, reflexes, and gross movements.

Rubrospinal tract

Extrapyramidal pathway originating in red nucleus that influences limb flexor tone and assists in motor coordination, particularly in nonprimates and as a supplementary pathway in humans.

Vestibulospinal tracts

Brainstem-originating extrapyramidal tracts that facilitate extensor tone and postural adjustments in response to vestibular input.

Reticulospinal tract

Extrapyramidal pathway from the reticular formation that modulates muscle tone, reflexes, and automatic posture and gait patterns.

Tectospinal tract

Extrapyramidal descending tract from superior colliculus that coordinates head and eye movements in response to visual stimuli.

Four tasks for motor control

1. Idea to move (cortical and limbic initiation) 2. Program movement (premotor and SMA) 3. Execute movement (M1 → corticospinal → LMN → muscle) 4. Feedback and refinement (sensory systems, cerebellum, basal nuclei).

Flow of voluntary movement (conceptual pathway

Idea and motivation from limbic and association areas → motor planning in premotor cortex and SMA → execution by M1 sending signals via pyramidal tract → LMNs in ventral horn → muscle contraction → sensory feedback to cortex, cerebellum, thalamus, basal nuclei for correction and learning.

Role of cerebellum in movement

Provides real-time feedback and error correction to ensure smooth coordination, timing, and learning of movements by comparing intended vs actual movement and adjusting motor output.

Sensory neuron categories

Somatic sensory neurons: detect external stimuli; visceral sensory neurons: monitor internal organs; receptors: exteroceptors (external), interoceptors (internal state), proprioceptors (body position and movement).

Proprioceptors

Specialized receptors in muscles, tendons, and joints that inform the CNS about limb position and movement, essential for coordinated motor execution and feedback.

Somatotopy (cortical maps)

Ordered mapping of body parts onto cortical areas (motor and sensory homunculi) where cortical area size reflects the precision required for that body part.

Borders of cortical lobes by fissures (study rule)

Use longitudinal fissure to separate hemispheres; central sulcus for frontal/parietal border; lateral sulcus for temporal from frontal/parietal; parieto-occipital sulcus for parietal/occipital border.

Association areas (definition and role

Regions adjacent to primary cortices that integrate sensory or motor information, enable recognition, planning, and higher-order interpretation rather than primary reception or execution.

Motor program concept

Stored sequences of neural activity in premotor and SMA based on practice and memory that are recruited to produce coordinated skilled movements via M1 output.

Relationship: basal nuclei, thalamus, cortex loop

Basal nuclei receive cortical input, process and inhibit or facilitate specific motor programs, send output via thalamus back to cortex to modulate motor initiation and selection.