Neuroanatomy

Neuroanatomy: Anatomy of the Nervous System

The Nervous System: Facts

  • Whole Body Distribution

    • Neurons: 86 billion

    • Connections per Neuron: 7,000

    • Total Synapses: 100 - 500 trillion

Course Outline

  • 1. Significance

  • 2. Definition

  • 3. A Plan for the Course

  • 4. Classification

    • Central vs. Peripheral

Significance of Neuroanatomy

  • Control Systems: Understanding how the nervous system governs body functions.

  • Localize Lesions: Identifying the locations of nervous system damage.

  • Procedures: Knowledge aiding in surgical and therapeutic interventional strategies.

Common Clinical Conditions

  • Vestibular Disease / Trigeminal Neuritis

  • Horner's Syndrome

  • Radial Nerve Paralysis

Nerves of the Abdominal Wall

  • Nerve root distributions (important for anatomical location):

    • T13, L1, L2, L3, L4, L5, L6

Epidural Anesthesia

  • High (Cranial) and Low (Caudal)

    • Caudal Epidural Injection: Performed at the first inter-coccygeal space

    • Spinal Cord Terminus: Ends at the 6th lumbar vertebra

    • Meninges End: Between 3rd and 4th sacral vertebra

Collection of Cerebrospinal Fluid (CSF) in Equine

  • Locations:

    • Atlanto-Occipital Space

    • Lumbo-Sacral Region

Comprehensive Overview of the Nervous System

  • The nervous system consists of nerves throughout the body, along with supportive cells that:

    • Collect information from all body regions/systems in response to various stimuli

    • Process this information

    • Send orders back to those regions/systems to prompt necessary sensory or motor responses

Course Plan

  • General Section

  • Special Section

  • Laboratories

  • Topics of Focus:

    • Classification

    • Development

    • Blood Supply

    • CSF

    • Meninges

    • Blood-Brain Barrier (BBB)

    • Efferent paths including General Somatic Efferent (GSE) and General Visceral Efferent (GVE)

    • Upper Motor Neuron (UMN) pathways and Afferent pathways covering General Somatic Afferent (GSA) and General Visceral Afferent (GVA) along with Proprioception, Vestibular, Cerebellum, Visual, Auditory, Limbic systems, Thalamus, Brain, and Spinal Cord sections.

General Neuroanatomy

  • Classification of Nerves:

    • Anatomically based

    • Functionally based

Anatomical Classification

  • Central Nervous System (CNS)

    • Components: Brain and Spinal Cord

  • Peripheral Nervous System (PNS)

    • Components: Cranial Nerves, Spinal Nerves, and Enteric Nervous System (ENS)

Peripheral Nervous System (PNS): Cranial Nerves

  • List of Key Cranial Nerves:

    • CN I: Olfactory

    • CN II: Optic

    • CN III: Oculomotor

    • CN IV: Trochlear

    • CN V: Trigeminal

    • CN VI: Abducens

    • CN VII: Facial

    • CN VIII: Vestibulocochlear

    • CN IX: Glossopharyngeal

    • CN X: Vagus

    • CN XI: Accessory

    • CN XII: Hypoglossal

Peripheral Nervous System (PNS): Spinal Nerves

  • Description of nerve root patterns including ventral and dorsal branches.

  • Lists various spinal nerve names including communication pathways.

Enteric Nervous System (ENS)

  • Anatomical Components:

    • Serosa

    • Muscularis externa

    • Myenteric plexus

    • Submucosal plexus

    • Mucosal layer

CNS vs. PNS

Constituents

  • CNS: Brain / Spinal Cord

  • PNS: Cranial Nerves / Spinal Nerves / ENS

Location

  • CNS: Enclosed within the Skull / Vertebral Column

  • PNS: Located outside the Skull and Vertebral Column

Development

  • CNS: Originates from the Neural Tube

  • PNS: Develops from Neural Crest

    • Neural Plate Development Process:

    1. Neuroectodermal Tissues: Differentiate from the ectoderm and thicken into the neural plate

    2. The Neural Plate Border separates ectoderm from neural plate

    3. The plate bends dorsally, forming a structure referred to as the neural crest.

    4. Neural Crest Cells differentiate to form most components of the PNS.

    5. Closure of the neural tube disconnects neural crests from the epidermis.

    6. The notochord, which provides initial support structure, degenerates, leaving remnants as the nucleus pulposus in spinal discs.

Regeneration

  • CNS: No capacity to regenerate

  • PNS: Some capacity to regenerate

Sites of Cell Bodies and Axons

  • Cell Body Components:

    • Soma

    • Dendrites

  • Axon Structure: Comprised of Axon, Telodendron, and Axon terminals

CNS: Locations of Cell Bodies

  • Found primarily in:

    • Brain: Cerebral Cortex

    • Spinal Cord: Gray Matter

CNS Cellular Organization

  • Cell Bodies in CNS: Aggregate into Nuclei

  • Axons in CNS: Aggregate into Tracts or Fasciculi

Nuclei and Tracts of the Brainstem

  • Highlight specific nuclei including Nucleus ambiguus and solitary tract among other cranial nerve nuclei.

Spinal Tracts

  • Includes posterior spinocerebellar tract, anterior spinocerebellar tract, DCML pathway, fasciculus gracilis and cuneatus, and anterior/lateral spinothalamic tracts.

PNS: Location of Cell Bodies and Axons

  • Cell Bodies: Aggregate in Ganglia

  • Axons: Separated by Connective Tissue

Sympathetic Ganglia Overview

  • Includes celiac plexus, ganglion, superior mesenteric plexus, sympathetic chain, aortic plexus, hypogastric plexus.

CNS Supportive Cells

  • Types of Cells:

    • Ependymal Cells: Generate CSF

    • Astrocytes: Regulate ions and neurotransmitter reuptake

    • Oligodendrocytes: Responsible for myelin formation

    • Microglia: Act as repair cells

PNS Supportive Cells

  • Types of Cells:

    • Satellite Cells: Help regulate the chemical environment

    • Schwann Cells: Produce myelin, facilitating efficient transmission of impulses

Functional Classification of Neurons

  • General Considerations: Neurons categorized based on

    • Functional role (sensory vs. motor)

    • Location of cell bodies

    • Direction of activity flow (afferent vs. efferent)

Anatomy of a Neuron

  • Parts of Neuron:

    • Soma (Cell Body)

    • Dendrites (Multiple, leading impulses to cell body)

    • Axon (Single, carrying impulses away from the cell body)

Functions of Neurons

  • Collect Inputs

  • Integration of Signals

  • Generation of New Signals

  • Transmission of Impulses

Functional Requirements for Neural Signals

  • Components Required:

    • Receptors: (e.g., skin/muscle)

    • Neurons: Afferent (receiving neuron), interneuron, efferent

    • Effector Organ: (e.g., muscle)

    • Response: (e.g., contraction)

Criteria for Functional Classification of Neurons

  • General function, number of dendrites, location of dendritic zone, direction of activity flow.

General Functions of Neurons

  • Types:

    • Sensory Neurons: Cell bodies are generally found in spinal ganglia (dorsal root)

    • Motor Neurons: Cell bodies from ventral root, dividing further into upper and lower motor neurons (UMN and LMN).

Cross-Sectional Anatomy of Spinal Cord

  • Visual representation showing the relationship between gray and white matter including dorsal and ventral roots and functional aspects of the nervous system.

Number of Neuronal Dendrites

  • Types based on structure:

    • Unipolar / Pseudounipolar: One axon splits; primarily sensory neurons (DRG, spinal nerves)

    • Bipolar: Rare structure found in areas like the retina/olfactory

    • Multipolar: One axon and many dendrites; usually motor neurons

Somatic & Visceral Systems

  • Somatic (Voluntary System): Sensory and motor functions relating to external environments.

  • Visceral System: Sensory and motor functions relating to internal organs, including the Autonomic Nervous System (ANS).

Upper Motor Neuron (UMN) Characteristics

  • Confined within the CNS, initiating voluntary movement, controlling muscle tone and posture.

Lower Motor Neuron (LMN)

  • Confined within the PNS, responsible for executing all motor functions

Afferent and Efferent Neurons

  • Afferent (Sensory): Transmit information from peripheral receptors to the CNS.

  • Efferent (Motor): Transmit signals from the CNS to the periphery, prompting responses.