Notes on Brain and Nervous System Organization

Organization of the Brain and Nervous System

  • Nervous System Overview: Divided into the Central Nervous System (CNS) and Peripheral Nervous System (PNS).
  • Blood Brain Barrier: A separation between CNS and PNS.
Central Nervous System (CNS)
  • Components: Includes the Brain and Spinal Cord.
Peripheral Nervous System (PNS)
  • Components:
    • Cranial nerves
    • Spinal nerves
    • Sensory nerves
  • Soma: The body of the neuron.
Somatic Nervous System
  • Involved in voluntary muscles, transmitting both sensory and motor information to and from the CNS.
    • Parasympathetic: Calming responses.
    • Sympathetic: Fight or flight responses.
Autonomic Nervous System (ANS)
  • Hypothalamus Functions: Controls the 4 F's - Fight, Flight, Food, and Fornication.
  • Sends and receives messages regulating involuntary physiological processes like heart rate and digestion.

Anatomy and Planes of the Brain

  • Directional Terms:
    • Rostral/Anterior: Front-facing
    • Caudal/Posterior: Back-facing
    • Superior/Dorsal: Top/above
    • Inferior/Ventral: Below/bottom
  • Planes:
    • Horizontal Plane
    • Sagittal Plane
    • Coronal Plane

Brain Organization

  • Hierarchical Model:
    • Basic functions are managed by lower regions (hindbrain) while complex functions are managed by higher regions (forebrain).
    • Forebrain: Responsible for feelings, thoughts, and complex functions.
    • Midbrain: Involved in eye movements and regulating sleep cycles.
    • Hindbrain: Controls basic life functions (breathing, heart rate, etc.) via structures like the medulla oblongata and cerebellum.
Cerebellum
  • Comprises 10% of brain volume; contains 50% of the neurons.
  • Critical for motor coordination, spatial reasoning, and some cognitive functions.
  • If absent, symptoms include delayed speech, poor reactions, and emotional processing difficulties.
Neurons and Their Organization
  • The brain is divided into left and right hemispheres connected by the Corpus Callosum (tract of ~200 million myelinated axons).
  • Each hemisphere has four lobes:
    • Frontal Lobe: Involved in planning movement, reward, and decision-making.
    • Parietal Lobe: Processes sensory information, touch, and speech.
    • Occipital Lobe: Handles visual information processing.
    • Temporal Lobe: Responsible for language encoding, auditory information, and memory encoding.
Gyri and Sulci
  • Gyri: Ridges of the brain.
  • Sulci: Grooves between the gyri; their complexity indicates brain function.
  • Longitudinal Sulcus: Divides the hemispheres; structures close to it are medial; those further away are lateral.
Central and Precentral Gyri
  • Central Sulcus: Separates frontal and parietal lobes.
    • Precentral Gyrus: The motor cortex area controls voluntary movements.
    • Postcentral Gyrus: The somatosensory cortex responsible for sensation.

Cells of the Nervous System

  • Neuron Theory: All living organisms consist of cells, with neurons being specialized for signal transmission.
  • Neurons: Over 86 billion in humans, adapted for receiving, conducting, and transmitting signals.
Neuron Structure
  • Major Components:
    • Soma: Contains genetic information and organelles.
    • Dendrites: Receive signals from other neurons.
    • Axon: Transmits electrical impulses to other neurons.
    • Synaptic Terminals: Convert electrical signals into chemical signals at synapses.
Neurotransmission Methods
  • Electrical Impulses: Current flows within neurons.
  • Chemical Neurotransmission: Involves the release of neurotransmitters for communication.
  • Myelination: Insulates axons, speeding up signal transmission and forming white matter in the brain.
Types of Glial Cells
  • Astrocytes: Maintain the blood-brain barrier and regulate blood flow.
  • Microglia: Act as immune defense.
  • Myelinating Glia: Oligodendrocytes (CNS) and Schwann Cells (PNS) found in myelin formation.

Neurotransmitter Release and Signaling

  • Synapse: The junction where communication occurs. Neurotransmitters are released upon action potentials.
  • Receptors: Fundamental for transducing signals in target cells.
  • Ionotropic vs. Metabotropic Receptors:
    • Ionotropic: Fast response through ion channels.
    • Metabotropic: Slower, via intracellular signaling cascades.
Post-Synaptic Potentials
  • EPSP: Excitatory potentials make action potential more likely.
  • IPSP: Inhibitory potentials decrease action potential likelihood.
  • Integration: The outcome (action or not) depends on how EPSPs and IPSPs sum up before reaching action potential threshold.

Memory and Learning

  • Types of Memory:
    • Declarative: Episodic (events) and Semantic (facts).
    • Non-declarative: Skills, conditioning, priming.
  • Memory Consolidation: Transition from short-term in the hippocampus to long-term in the cortex.
  • Hippocampus: Critical for learning and memory processes.
  • Plasticity: Synaptic strength increases via long-term potentiation (LTP), a mechanism vital for memory formation.

Pathologies

  • Alzheimer’s Disease: Characterized by neurodegeneration, presence of amyloid plaques, and tau tangles, leading to memory loss and cognitive decline.