Nervous System Organization Study Notes

Chapter 15: Nervous System Organization

15.1 The Organization and Evolution of Nervous Systems

• Overview of Nervous System Organization

  • Central Nervous System (CNS)

  • Peripheral Nervous System (PNS)

• Incoming Stimulus Pathway:

  • Afferent neuron

  • Integrating center (e.g., brain, ganglia)

  • Interneuron

  • Efferent neuron

  • Sensory receptors (e.g., mechanoreceptors, photoreceptors)

  • Effector organs (e.g., muscles, glands)

• Patellar (Knee) Reflex Arc:

  • Output process:

  • Sensors

  • Integrating centers

  • Output pathways

  • Components:

  • Quadriceps muscle

  • Sensory neuron

  • Spinal cord

  • Dorsal root neuron/ganglion

  • White matter

  • Hamstring muscle

  • Motor neuron

  • Gray matter

  • Interneuron

15.2 The Vertebrate Nervous System: A Guide to the General Organizational Features of Nervous Systems

• Structure of Nervous Systems:

  • CNS consists of the brain and spinal cord.

  • PNS includes peripheral nerves and ganglia.

• Divisions of the Peripheral Nervous System:

  • Somatic Nervous System:

  • Controls skeletal muscles (conscious)

  • Incoming sensory information involves:

    • Touch, hearing, vision, olfaction

  • Autonomic Nervous System:

  • Controls involuntary functions and reflexes (unconscious)

  • Divisions include:

    1. Sympathetic: Energy-expending

    2. Parasympathetic: Energy-conserving

    3. Enteric

• Functions of the Autonomic Nervous System:

  • Controls effectors like smooth muscle, cardiac muscle, and glands, including:

  • Gastric acid secretion

  • Heart pacemaker regulation

  • Functions of brown adipose tissue and adaptations in fish (swim bladder and chromatophores).

Anatomy of the Sympathetic and Parasympathetic Divisions

• Sympathetic Division Functions:

  • Dilates pupils

  • Inhibits salivation

  • Constricts blood vessels

  • Relaxes airways

  • Accelerates heart rate

  • Stimulates secretion by sweat glands

  • Inhibits digestion

  • Stimulates secretion of glucose from the liver

  • Modulates immune responses

• Parasympathetic Division Functions:

  • Constricts pupils

  • Stimulates salivation

  • Inhibits secretion by sweat glands

  • Constricts airways

  • Slows heartbeat

  • Stimulates digestion

  • Stimulates gallbladder function

  • Inhibits gut motility

  • Stimulates secretion of epinephrine and norepinephrine from the adrenal gland.

• Dual innervation of organs:

  • Most organs receive input from both autonomic nervous systems.

The Central Nervous System

• Components of the Central Nervous System:

  • Brain (cerebrum, cerebellum, brainstem)

  • Spinal Cord (cervical, thoracic, lumbar, sacral, coccygeal nerves)

• Gray Matter vs. White Matter in Spinal Cord:

  • Gray Matter: Dorsal root, dorsal horn

  • White Matter: Afferent and efferent axons

Major Brain Division and Functionality

• Functional Organization of the Brain:

  • Four principles of functional organization apply to most vertebrate brains:

  1. Brain function is localized

  2. Brains have maps

  3. Size matters

  4. Expansion of forebrain areas during vertebrate evolution

• Major Brain Divisions and Functions:

  • Forebrain:

  • Telencephalon:

    • Cerebral cortex (higher sensory/motor functions)

    • Hippocampus (learning/memory)

    • Basal ganglia (motor control)

    • Limbic system (emotions)

  • Diencephalon:

    • Thalamus (sensory relay)

    • Hypothalamus (homeostasis, endocrine regulation)

  • Midbrain:

  • Mesencephalon:

    • Superior colliculus (visual integration)

    • Inferior colliculus (auditory integration)

  • Hindbrain:

  • Metencephalon:

    • Cerebellum (motor coordination)

    • Pontine motor nuclei (descending motor control)

  • Myelencephalon:

    • Medulla oblongata (autonomic functions, respiratory control)

Brain Mapping and Homunculus

• Motor Homunculus:

  • Illustrates disproportionate representations of body areas in the brain (e.g., face, hands).

• Sensory Homunculus:

  • Reflects sensory receptor distribution on body surface, mapped to somatosensory cortex (posterior to central sulcus).

Variability in Brain Structure and Function Across Vertebrates

• Relative Sizes of Brain Regions:

  • Structures are consistent but vary in size across different vertebrate species (e.g., fish, amphibians, mammals).

• General Observations:

  • Midbrain, forebrain, and cerebellum are prominent brain structures across vertebrates but differ in relative size and function.