Chapter 12 – Nervous Tissue

Divisions of the Nervous System

The nervous system is divided into several major components, each with distinct functions and structures. Understanding these divisions is essential for identifying their roles in physiological processes.

• Central Nervous System (CNS): Consists of the brain and spinal cord; responsible for processing and integrating information.

• Peripheral Nervous System (PNS): Includes all neural tissue outside the CNS; subdivided into:

  • Afferent Division: Transmits sensory information to the CNS.

  • Efferent Division: Carries motor commands from the CNS to effectors.

  • Somatic Nervous System: Controls voluntary movements.

  • Autonomic Nervous System: Regulates involuntary functions (e.g., heart rate, digestion).

Structure and Function of Neurons

Neurons are the basic functional units of the nervous system. Each part of a neuron has a specific role in signal transmission.

• Cell Body: Contains the nucleus and organelles; integrates incoming signals.

• Dendrites: Receive signals from other neurons.

• Axon: Conducts electrical impulses away from the cell body.

• Myelin Sheath: Insulates axons, increasing the speed of impulse transmission.

• Axon Hillock: Initiates action potentials.

Cell Membrane Features

The cell membrane regulates the movement of molecules and ions, maintaining the neuron's internal environment.

• Selective Permeability: Only certain molecules can cross the membrane easily.

• Transport Proteins: Facilitate movement of ions and molecules across the membrane.

Ion Channels and Membrane Potentials

Ion channels are proteins that allow specific ions to pass through the membrane, influencing the neuron's electrical properties.

• Ligand-Gated Ion Channel: Opens in response to chemical signals.

• Leak Potassium Channel: Allows passive movement of K+ ions.

• Leaky Sodium Channel: Allows passive movement of Na+ ions.

• Sodium-Potassium Pump: Actively transports Na+ out and K+ in.

• Voltage-Gated Channels: Open or close in response to changes in membrane potential.

Key Equations:

• Resting membrane potential:

• Nernst equation for ion equilibrium:

Action Potentials and Synaptic Transmission

Action potentials are rapid changes in membrane potential that propagate along axons. Synaptic transmission involves the release of neurotransmitters.

• Action Potential: All-or-none electrical event; involves depolarization and repolarization.

• EPSP (Excitatory Postsynaptic Potential): Increases likelihood of action potential.

• IPSP (Inhibitory Postsynaptic Potential): Decreases likelihood of action potential.

Neurotransmitters and Their Functions

Neurotransmitters are chemicals that transmit signals across synapses.

• GABA: Main inhibitory neurotransmitter in the CNS.

• Acetylcholine: Involved in muscle activation and autonomic functions.

• Epinephrine/Norepinephrine: Involved in fight-or-flight response.

Neurotransmitter Removal and Glial Cells

Neurotransmitters are removed from the synaptic cleft by enzymatic breakdown or reuptake.

• Enzymatic Breakdown: Enzymes such as acetylcholinesterase degrade neurotransmitters.

• Astrocyte Reabsorption: Glial cells help remove neurotransmitters and maintain homeostasis.

Types of Neurons

Neurons are classified based on structure and function.

• Bipolar Neuron: One axon and one dendrite; found in sensory organs.

• Unipolar Neuron: Single process; common in sensory pathways.

• Multipolar Neuron: Multiple dendrites and one axon; most common type.

• Motor Neuron: Transmits signals to muscles.

• Sensory Neuron: Transmits sensory information to CNS.

Blood Brain Barrier and CSF Barrier

The blood-brain barrier protects the brain from harmful substances, while the CSF barrier regulates the composition of cerebrospinal fluid.

• Tight Junctions: Found in endothelial cells of brain capillaries.

Chapter 13 – The Spinal Cord

Spinal Cord Anatomy

The spinal cord is a major pathway for information traveling between the brain and body. It is organized into regions and contains both white and gray matter.

• Cervical, Thoracic, Lumbar, Sacral Regions: Each region is associated with specific spinal nerves.

• Conus Medullaris: Tapered end of the spinal cord.

• Filum Terminale: Fibrous extension anchoring the spinal cord.

• Cauda Equina: Bundle of spinal nerves below the conus medullaris.

White Matter vs. Gray Matter

White matter contains myelinated axons, while gray matter contains neuron cell bodies and unmyelinated fibers.

• White Matter: Transmits signals up and down the spinal cord.

• Gray Matter: Processes information locally.

Ascending and Descending Tracts

Tracts are bundles of axons that carry information to and from the brain.

• Ascending Tracts: Carry sensory information to the brain (e.g., fasciculus cuneatus, spinothalamic tract).

• Descending Tracts: Carry motor commands from the brain (e.g., corticospinal tract).

Dorsal and Ventral Roots

Dorsal roots carry sensory information into the spinal cord, while ventral roots carry motor information out.

• Dorsal Root: Sensory input.

• Ventral Root: Motor output.

Meninges and Spaces

The spinal cord is protected by three layers of meninges: dura mater, arachnoid mater, and pia mater.

• Dura Mater: Outermost, tough layer.

• Arachnoid Mater: Middle, web-like layer.

• Pia Mater: Innermost, delicate layer.

• Subarachnoid Space: Contains cerebrospinal fluid (CSF).

Chapter 14 – The Brain & Cranial Nerves

Embryonic Development of the Nervous System

The nervous system develops from embryonic structures called vesicles, which give rise to different regions of the brain.

• Primary Vesicles: Prosencephalon, Mesencephalon, Rhombencephalon.

• Secondary Vesicles: Telencephalon, Diencephalon, Metencephalon, Myelencephalon.

Lobes and Regions of the Brain

The brain is divided into lobes, each with specialized functions.

• Frontal Lobe: Motor control, decision making.

• Parietal Lobe: Sensory processing.

• Temporal Lobe: Auditory processing, memory.

• Occipital Lobe: Visual processing.

White Matter vs. Gray Matter in the Brain

White matter consists of myelinated axons; gray matter consists of neuron cell bodies and dendrites.

• White Matter: Transmits signals between brain regions.

• Gray Matter: Processes information.

Functional Regions of the Cerebrum

Different regions of the cerebrum are responsible for specific functions.

• Primary Motor Cortex: Controls voluntary movements.

• Basal Nuclei: Regulate movement and coordination.

• Primary Somatosensory Cortex: Processes sensory input.

• Auditory Cortex: Processes sound.

• Visual Cortex: Processes visual information.

• Broca's Area: Speech production.

• Wernicke's Area: Language comprehension.

• Limbic System: Emotion and memory.

Brain Structures and Communication

The hemispheres of the cerebrum communicate via the corpus callosum.

• Corpus Callosum: Large bundle of axons connecting the left and right hemispheres.

Encephalography and Brain Waves

Encephalography is a technique used to measure electrical activity in the brain.

• EEG (Electroencephalogram): Records brain waves; useful for diagnosing neurological disorders.

• Brain Waves: Alpha, Beta, Delta, Theta; each associated with different states of brain activity.

Additional info:

• SNARE proteins are involved in vesicle fusion during neurotransmitter release.

• Glial cells include astrocytes, oligodendrocytes, microglia, and ependymal cells, each with specialized functions in CNS support.

• Differences between sulci, gyri, and fissures: Sulci are shallow grooves, gyri are raised ridges, and fissures are deep grooves in the brain.