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.