Lab 6: The Nervous System

General Overview

• Major Topics: Key Objectives
  • Divisions of the nervous system: Central vs. Peripheral
  • Structures of a neuron and a nerve
  • Structures of the spinal cord
  • Understanding reflexes
  • Structures of the brain
  • Naming cranial and peripheral nerves, and associated muscles
  • Structures of the eye and ear
  • Dissections: Brain and eye specimens

Nervous System Divisions

Central Nervous System (CNS)

• Composed of the brain and spinal cord

Peripheral Nervous System (PNS)

• Includes all nerves outside the CNS (nerves & ganglia)
  • Nerves: Bundles of axons in connective tissue
  • Ganglia: Swellings/clusters of neuron cell bodies

Structure of a Neuron

• Cell Body (Soma): Contains nucleus and nucleolus
• Dendrites: Tree-like structures receiving electrical information
• Axon: Long process transmitting information from Soma
  • Schwann Cells: Produce myelin sheath around axon
  • Nodes of Ranvier: Gaps between Schwann cells
• Terminal Arborizations (Axon Terminals): End branches releasing neurotransmitters
• Synaptic Knobs: End of axon terminals, where synapses happen

Types of Neurons

Sensory Neurons (Afferent)

• Pick up sensations (touch, temperature, pain)
• Carry signals toward CNS

Motor Neurons (Efferent)

• Carry instructions from CNS to muscles or glands

Interneurons

• Found within CNS
• Process and integrate information
• Majority of neurons (~90%)

Neuron Morphologies

Multipolar Neurons

• Many dendrites, one axon
• Most common (interneurons & motor neurons)

Unipolar Neurons

• One process, axonal
• Sensory neurons

Structure of a Nerve

• Epineurium: Outer connective tissue layer
• Perineurium: Surrounds bundles (fascicles) of axons
• Endoneurium: Surrounds individual axons
• Fascicles: Bundles of axons
• Myelin: Conductive sheath produced by Schwann cells

Spinal Cord

General Structure

• About the diameter of a pencil
• Ends around L1 vertebra
• 31 pairs of spinal nerves
  • Cervical (8), Thoracic (12), Lumbar (5), Sacral (5), Coccygeal (1)
• Enlargements: Cervical and Lumbar areas
• Conus Medullaris: End of spinal cord
• Cauda Equina: Nerve roots in vertebral canal below the conus medullaris

Meninges and Spaces

• Dura Mater: Tough outer layer
  • Epidural Space: Above dura mater, fat & blood vessels
• Arachnoid Mater: Middle, spider web appearance
  • Subarachnoid Space: Contains cerebrospinal fluid (CSF)
• Pia Mater: Delicate inner layer, closely follows the spinal cord

Gray and White Matter

• Gray Matter: Butterfly shape
  • Dorsal Horn: Posterior part
  • Lateral Horn: Middle part
  • Ventral Horn: Anterior part
  • Gray Commissure: Connects two sides
• White Matter: Surrounds gray matter
  • Columns (funiculi): Dorsal, ventral, lateral
  • Tracts: Groups of axons, ascending (sensory) and descending (motor)

Reflexes

• Automatic, involuntary responses
• Reflex Arc: Pathway of reflex action
  • Sensory input -> Spinal cord (interneuron processing) -> Motor output
  • Examples: Patellar reflex, stepping-on-object reflex

Brain Structure

Functional Areas

• Frontal Lobe: Thinking, memory, behavior, movement
• Parietal Lobe: Language, touch
• Occipital Lobe: Sight
• Temporal Lobe: Hearing, learning, feelings
• Insula: Taste (hidden within lateral sulcus)
• Brainstem: Breathing, heart rate, temperature
• Cerebellum: Balance, coordination

Mid-Sagittal View Key Structures

• Corpus Callosum: Thick band of white matter
• Thalamus: Relays sensory & motor signals
• Hypothalamus: Regulates homeostasis
• Pons & Medulla Oblongata: Part of brainstem
• Foramen Magnum: Transition to spinal cord

Cranial Nerves

• 12 pairs of cranial nerves
  • Numbered using Roman numerals (I-XII)
  • Functions vary among olfaction, vision, taste, hearing, movement, etc.
• Learn function and control areas, e.g., CN XI (Accessory Nerve): Controls trapezius, sternocleidomastoid

Eye Structure

• Three Main Layers:
  • Sclera: White outer layer
  • Choroid: Middle layer, vascular
  • Retina: Inner network, contains photoreceptors
• Optic Nerve (CN II): Transmits visual info to brain
• Anterior Cavity: Contains aqueous humor
• Posterior Cavity: Contains vitreous humor
• Cornea: Transparent front part
• Lens: Focuses light, may appear cloudy in specimens

Ear Structure

Outer Ear

• Pinna (Auricle): Collects sound
• External Auditory Canal
• Tympanic Membrane (Eardrum)

Middle Ear

• Ossicles: Malleus, Incus, Stapes
• Oval Window: Leads to inner ear

Inner Ear

• Vestibule & Semicircular Canals: Balance
• Cochlea: Hearing
• Cranial Nerve VIII (Vestibulocochlear Nerve): Transmits auditory and balance info

Dissections

Sheep Brain

• Identify dura mater and other structures
• Note comparative anatomy to human brain (orientation differences)

Eye Dissection

• Identify and label structures
• Submit labeled images or video walkthrough of dissection