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CNS brain basics notes

Central Nervous System (CNS) - Brain Basics

General Overview

  • CNS comprises: Brain + Spinal Cord.

  • Originates from Ectoderm (one of the three germ layers: Ectoderm, Mesoderm, Endoderm).

  • Development Steps:i. Formation of Neural Plate with Neural Folds.ii. Creation of Neural Groove with Neural Crests (becomes PNS).iii. Development of Neural Tube (becomes CNS - Brain and Spinal Cord).

  • Brain enlarges and twists during development.

Main Parts of the Brain

  • Cerebrum (Telencephalon): Divided into 2 Cerebral Hemispheres, characterized by a wrinkled surface (convolutions).

  • Diencephalon

  • Brain Stem: Comprises Midbrain, Pons, Medulla Oblongata.

  • Cerebellum: Positioned behind the Brain Stem, distinct from it.

Brain Structure

  • Cerebral Cortex: The outermost layer (1/8 inch thick) responsible for conscious thought; consists mainly of Gray Matter (Neuron Cell Bodies).

  • White Matter: Below the Cortex, containing myelinated axons.

  • Fissures & Sulci:

    • Fissures: Deep (e.g., Longitudinal Fissure separates hemispheres).

    • Sulci: Shallow (e.g., Central Sulcus separates frontal and parietal lobes).

Cerebral Lobes

  1. Frontal Lobe: Involved in body movements (Motor Function).

  2. Parietal Lobe: Responsible for body sensations (Somatosensory).

  3. Temporal Lobe: Associated with hearing and smell (Olfaction).

  4. Occipital Lobe: Processes vision.

  5. Insula Lobe: Involved in taste.

Functional Areas

  • Primary Motor Cortex: Located in the Precentral Gyrus (Frontal Lobe).

  • Primary Somatosensory Cortex: Located in the Postcentral Gyrus (Parietal Lobe).

  • Broca’s Area: Related to speech production (often on the left).

  • Wernicke’s Area: Involved in language comprehension; damage can result in 'Word Salad'.

Neural Fibers and Communication

  • Types of Axons:

    1. Commissural Fibers: Communication between hemispheres (e.g., Corpus Callosum).

    2. Association Fibers: Connections within a hemisphere.

    3. Projection Fibers: Linking brain regions to the lower brain and spine; includes pyramidal neuron axons.

Cerebellum

  • Coordination center located behind the brainstem, characterized by Folia (Gyri) and Vermis (connects hemispheres).

  • Ipsilateral connections (same side of the body); does not communicate directly with the cerebrum about its functions.

Limbic System

Overview

  • Center for emotions, spread across the medial surfaces of the cerebral hemispheres.

  • Hypothalamus: Connects the Autonomic Nervous System (ANS) with emotions; influences psychosomatic responses.

Limbic System Structures

  • Cingulate Gyrus: Important for emotional processing.

  • Amygdaloid Body: Associated with emotion (e.g., rage) and memory.

  • Hippocampus: Memory processing; responds to emotional stimuli and sensory triggers, such as smells.

Neural Communication

  • Neural Fibers (Axons): Typically myelinated, which appears white; form tracts.

  • Communication types:

  1. Commissural Fibers (e.g., Corpus Callosum).

  2. Association Fibers (within a hemisphere).

  3. Projection Fibers (ascending and descending pathways).

Brain Ventricles

Structure and Function

  • Formed from the hollow neural tube, including 4 ventricles filled with cerebrospinal fluid (CSF).

  • Lateral Ventricles: Right and left top ventricles.

  • Third Ventricle: Surrounded by the Diencephalon, resembles a cartoon character (e.g., Woody Woodpecker).

  • Fourth Ventricle: Located between the Pons and Medulla Oblongata, and the Cerebellum.

CSF Circulation

  • CSF is produced in the choroid plexus in all ventricles and circulates through brain and spinal cord.

  • CSF is drained via Arachnoid Granulations into the Superior Sagittal Sinus.

Pathologies

  • Hydrocephalus: Accumulation of CSF leading to head enlargement if untreated; treated through shunting.

Meninges and Protection

Meningeal Layers

  1. Dura Mater: Two layers; the outermost (periosteal) is attached to the skull, the innermost layer extends around the spinal cord.

  2. Arachnoid Mater: Spider-web-like structure containing CSF.

  3. Pia Mater: Thin, delicate layer that directly covers the brain's surface.

Spaces

  • Subdural Space: Located beneath the Dura Mater; can accumulate blood and form hematomas.

  • Subarachnoid Space: CSF-filled area that can also lead to hematomas if blood vessels rupture.

Dural Septa

  • Falx Cerebri: Separates the two cerebral hemispheres.

  • Falx Cerebelli: Separates cerebellar hemispheres.

  • Tentorium Cerebelli: Supports cerebrum over the cerebellum.

Pathologies

  • Meningitis: Inflammation of the meninges that can be sampled via lumbar puncture.

  • Encephalitis: Inflammation of the brain itself.

Reticular Activating System (RAS)

Function

  • Maintains wakefulness and arousal; damage can lead to permanent coma.

  • Filters out sensory stimuli to manage awareness and focus.

EEG (Electroencephalogram)

Brain Waves

  1. Alpha Waves: Awake, calm, and relaxed.

  2. Beta Waves: Alert and active thinking.

  3. Theta Waves: Uncommon in awake adults, seen in children.

  4. Delta Waves: High amplitude, indicative of deep sleep; may signal brain damage if present in awake adults.

Seizures and Consciousness

Seizures

  • Absence Seizures: Short loss of consciousness (Petit Mal).

  • Tonic-Clonic Seizures: Intense convulsions and loss of consciousness (Grand Mal).

Levels of Consciousness

  1. Alert: Maximum alertness.

  2. Drowsiness: A state of lethargy.

  3. Stupor: Near-unresponsiveness.

  4. Coma: Extended unresponsiveness.

Sleep Disorders

  • Narcolepsy: Sudden REM sleep attacks.

  • Insomnia: Difficulty in initiating sleep.

  • Sleep Apnea: Temporary cessation of breathing during sleep.

Memory Stages

  1. Short-Term Memory (STM): Limited capacity for daily function.

  2. Long-Term Memory (LTM): Relatively unlimited capacity, but memories can change over time.

Brain Trauma and Disorders

Types of Brain Injury

  • Coup Injury: Impact on one side of the brain.

  • Contracoup Injury: The brain bounces and impacts the opposite side.

  • Concussion: Temporary functional change; multiple can cause cumulative damage.

  • Contusion: Permanent damage.

Degenerative Disorders

  1. Alzheimer’s Disease: Progressive brain degeneration characterized by plaques and tangles.

  2. Parkinson’s Disease: Lack of dopamine leading to motor difficulties and tremors.

  3. Huntington’s Disease: Genetic and fatal, producing chorea movements.

Additional Notes on Mental Health

  • Anxiety Disorders: Impact everyday function; includes panic attacks and phobias.

  • Severe Mental Illnesses: Schizophrenia, severe depression.

  • Cerebral Palsy: Neuromuscular disability from oxygen deprivation at birth.

  • Microcephaly: Congenital small brain; often linked with mental retardation.