Central Nervous System: Structure, Function, and Key Terminology

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Central Nervous System (CNS)

General Regions and Terminology

The central nervous system (CNS) consists of the brain and spinal cord, serving as the main control center for processing and integrating information in the body.

Brain: The primary organ of the CNS, responsible for processing sensory information, initiating responses, and higher cognitive functions.
Spinal Cord: A long, thin bundle of nervous tissue that transmits signals between the brain and the rest of the body.
Sensory Input: Information received from sensory receptors about internal and external environments.
Integration: The process by which the CNS interprets sensory input and determines an appropriate response.
Motor Output: Commands sent from the CNS to muscles or glands to elicit a response.

Major Brain Regions

Cerebrum: The largest part of the brain, responsible for voluntary actions, sensory perception, and higher mental functions.
Diencephalon: Contains structures such as the thalamus and hypothalamus; involved in sensory relay and homeostasis.
Cerebellum: Coordinates movement and balance.
Brainstem: Connects the brain to the spinal cord and controls vital functions such as breathing and heart rate.

White Matter vs. Gray Matter

White Matter: Composed of myelinated axons; responsible for communication between different brain regions.
Gray Matter: Contains neuron cell bodies, dendrites, and unmyelinated axons; involved in processing and integration.
Nuclei: Clusters of neuron cell bodies within the CNS.
Tracts: Bundles of axons in the CNS that transmit signals.

Surface Features of the Cerebrum

Sulcus (plural: sulci): Shallow grooves on the brain surface.
Gyrus (plural: gyri): Raised ridges between sulci.

Lobes of the Cerebrum

Frontal Lobe: Involved in voluntary movement, planning, reasoning, and problem-solving.
Parietal Lobe: Processes sensory information such as touch, temperature, and pain.
Temporal Lobe: Responsible for auditory processing and memory.
Occipital Lobe: Main center for visual processing.
Insular Lobe (Insula): Involved in taste, visceral sensation, ++++++++++++ ooqand emotional processing.

Cerebral Cortex: Functional Areas

Central Sulcus: Separates the frontal and parietal lobes.
Lateral Fissure: Divides the temporal lobe from the frontal and parietal lobes.
Precentral Gyrus: Contains the primary motor cortex; controls voluntary movements.
Postcentral Gyrus: Contains the primary somatosensory cortex; processes sensory input from the body.
Longitudinal Fissure: Divides the right and left cerebral hemispheres.
Right/Left Hemisphere: The two halves of the cerebrum, each controlling opposite sides of the body.
Prefrontal Cortex: Involved in complex behaviors, decision-making, and personality.
Frontal Eye Field: Controls voluntary eye movements.
Premotor Cortex: Plans and coordinates complex movements.
Primary Motor Cortex: Initiates voluntary muscle movements.
Primary Somatosensory Cortex (S1): Receives and processes sensory information from the body.
Primary Auditory Cortex: Processes auditory information.
Auditory Association Cortex: Interprets sounds and language.
Primary Visual Cortex: Receives visual information from the eyes.
Visual Association Area: Interprets visual stimuli.
Somatosensory As++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++sociation Cortex (S2): Integrates sensory information for perception.
Broca’s Area: Controls speech production (usually in the left hemisphere).
Wernicke’s Area: Involved in language comprehension.

Basal Nuclei

The basal nuclei are deep gray matter structures involved in regulating movement and coordination.

Globus Pallidus
Corpus Striatum
Caudate Nucleus
Putamen

Function: Modulate voluntary motor activity and inhibit unwanted movements.

White Matter Tracts of the Cerebrum+

Commissural Fibers: Connect corresponding areas of the two hemispheres (e.g., Corpus Callosum).
Projection Fibers: Connect the cerebrum with lower brain regions and spinal cord (e.g., Internal Capsule, Corona Radiata).
Association Fibers: Connect different parts of the same hemisphere.

Limbic System

The limbic system is a group of structures involved in emotion, memory, and motivation.

Fornix
Limbic Lobe
Cingulate Gyrus
Parahippocampal Gyrus
Hippocampus: Essential for memory formation.
Amygdala: Involved in emotion, especially fear and aggression.

Diencephalon

Thalamus: Relay station for sensory information.
Hypothalamus: Regulates homeostasis, endocrine functions, and autonomic nervous system.
Epithalamus: Contains the pineal gland; involved in circadian rhythms.
Subthalamus
Pituitary Gland: Major endocrine gland controlled by the hypothalamus.
Pineal Gland: Secretes melatonin, regulates sleep-wake cycles.

Cerebellum

Anterior Lobe
Posterior Lobe
Flocculonodular Lobe
Folia: Thin, leaf-like gyri of the cerebellum.
Cerebellar Peduncle: Connects cerebellum to brainstem.
Arbor Vitae: Tree-like arrangement of white matter.
Left/Right Cerebellar Hemisphere
Cerebellar Cortex: Outer gray matter layer.

Function: Coordinates voluntary movements and maintains pos

ture and balance.

Midbrain

Superior Colliculus: Visual reflexes.
Inferior Colliculus: Auditory reflexes.
Reticular Formation: Regulates arousal and consciousness.
Crus Cerebri
Tegmentum
Substantia Nigra: Produces dopamine; involved in movement control.
Tectum
Mammillary Bodies: Involved in memory processing.

Brainstem

Midbrain
Pons: Relays signals between cerebrum and cerebellum; regulates breathing.
Medulla Oblongata: Controls vital autonomic functions (e.g., heart rate, respiration).

Meninges and Spaces

The meninges are protective membranes surrounding the brain and spinal cord.

Periosteal Dura Mater: Outer layer attached to the skull.
Meningeal Dura Mater: Inner layer of dura mater.
Arachnoid Mater: Middle, web-like layer.
Pia Mater: Thin, delicate inner layer adhering to the brain and spinal cord.
Dural Sinus: Venous channels between layers of dura mater.
Falx Cerebri: Separates cerebral hemispheres.
Superior Sagittal Sinus: Major dural venous sinus.
Tentorium Cerebelli: Separates cerebrum from cerebellum.
Falx Cerebelli: Separates cerebellar hemispheres.
Epidural Space: Between skull and dura mater.
Subdural Space: Between dura mater and arachnoid mater.
Subarachnoid Space: Between arachnoid and pia mater; contains cerebrospinal fluid (CSF).
Cerebrospinal Fluid (CSF): Cushions and nourishes the CNS.
Arachnoid Trabeculae: Web-like extensions in the subarachnoid space.
Arachnoid Granulation: Structures that absorb CSF into the venous system.

Ventricular System

Lateral Ventricles: Paired cavities in each cerebral hemisphere.
Third Ventricle: Located in the diencephalon.
Fourth Ventricle: Located between the brainstem and cerebellum.
Interventricular Foramen: Connects lateral ventricles to the third ventricle.
Cerebral Aqueduct: Connects third and fourth ventricles.
Central Canal: Runs through the spinal cord.
Choroid Plexus: Produces CSF.
Ependymal Cell: Lines ventricles and helps circulate CSF.

Blood Brain Barrier (BBB)

Blood Brain Barrier: Selective barrier that protects the brain from harmful substances in the blood.
Astrocyte: Glial cell that supports the BBB.
Tight Junction: Specialized connections between endothelial cells that restrict passage of substances.

Spinal Cord Anatomy

Denticulate Ligament: Extensions of pia mater that anchor the spinal cord.
Cervical Enlargement: Region where nerves to the upper limbs arise.
Lumbar Enlargement: Region where nerves to the lower limbs arise.
Conus Medullaris: Tapered end of the spinal cord.
Cauda Equina: Bundle of spinal nerves below the conus medullaris.
Filum Terminale: Fibrous extension anchoring the spinal cord to the coccyx.
Posterior Median Sulcus: Shallow groove on the dorsal side.
Anterior Median Fissure: Deep groove on the ventral side.
Posterior (Dorsal) Horn: Contains sensory neurons.
Anterior Horn: Contains motor neurons.
Posterior Root Ganglion: Contains cell bodies of sensory neurons.

White Matter Tracts of the Spinal Cord

Posterior Funiculus
Lateral Funiculus
Anterior Funiculus
Posterior Columns: Ascending tracts for fine touch and proprioception.
Fasciculus Gracilis: Carries sensory information from lower body.
Fasciculus Cuneatus: Carries sensory information from upper body.
Spinocerebellar Tracts: Convey proprioceptive information to the cerebellum.
Anterior/Posterior Spinocerebellar Tract
Anterolateral System: Includes spinothalamic tract; transmits pain and temperature.
Spinothalamic Tract: Carries pain and temperature sensations.
Corticospinal Tracts: Major descending motor pathways.
Reticulospinal Tracts
Tectospinal Tracts
Vestibulospinal Tracts

Neural Circuits

First-Order Sensory Neuron: Transmits sensory information from receptors to the CNS.
Second-Order Sensory Neuron: Relays information from the spinal cord or brainstem to the thalamus.
Third-Order Sensory Neuron: Projects from the thalamus to the cerebral cortex.
Interneuron: Connects neurons within the CNS; involved in processing and integration.
Upper Motor Neuron: Originates in the cerebral cortex or brainstem and projects to lower motor neurons.
Lower Motor Neuron: Projects from the spinal cord to skeletal muscles.

Example: Pathway of Voluntary Movement

Upper motor neuron in the primary motor cortex sends a signal down the corticospinal tract.
Signal synapses with a lower motor neuron in the anterior horn of the spinal cord.
Lower motor neuron innervates skeletal muscle, causing contraction.

Additional info:

The CNS is protected by the skull, vertebral column, meninges, and cerebrospinal fluid.
Damage to specific regions of the CNS can result in characteristic neurological deficits (e.g., Broca's aphasia, Parkinson's disease).