The Nervous System

Main Components of the Nervous System

Brain Regions

  • Cerebrum

  • Cerebellum

  • Spinal Cord

Peripheral Nerves and Plexuses

  • Brachial Plexus: A network of nerves that conduct signals to and from the upper limb.

  • Musculocutaneous Nerve: Supplies the anterior compartment of the arm.

  • Radial Nerve: Innervates the extensor muscles of the arm and forearm.

  • Intercostal Nerves: Supply the intercostal muscles and skin of the thorax.

  • Median Nerve: Innervates most of the forearm flexors.

  • Iliohypogastric Nerve: Supplies muscles and skin of the lower abdomen.

  • Subcostal Nerve: Supplies part of the abdominal wall.

  • Lumbar Plexus: Supplies nerves to the lower back and abdomen.

  • Genitofemoral Nerve: Supplies sensation to the genitalia and inner thigh.

  • Obturator Nerve: Innervates the thigh's adductor muscles.

  • Ulnar Nerve: Supplies the little finger side of the hand and forearm.

  • Sacral Plexus: Supplies nerves to the pelvis and lower limbs.

  • Femoral Nerve: Supplies the anterior compartment of the thigh.

  • Pudendal Nerve: Innervates the pelvic floor.

  • Sciatic Nerve: Supplies the posterior compartment of the thigh.

  • Common Peroneal Nerve: Supplies the lower leg and foot.

  • Muscular Branches of Femoral Nerve: Innervate quadriceps and sartorius muscles.

  • Saphenous Nerve: Provides sensory innervation to the leg.

  • Tibial Nerve: Innervates muscles in the back of the lower leg and the plantar surface of the foot.

  • Deep Peroneal Nerve: Innervates the muscles of the anterior compartment of the leg.

  • Superficial Peroneal Nerve: Supplies the lateral compartment of the leg.

Functionality of the Nervous System

Major Functions

  1. Sensory Input: Utilizes millions of sensory receptors to monitor stimuli both externally and internally.

  2. Integration: The processing and interpretation of sensory input for appropriate response.

  3. Motor Output: Activation of “effector organs” (muscles and glands) to respond to stimuli.

Nervous Systems in Different Animals

Simple Nervous Systems

  • Characterized by lack of centralization.

Examples:

  • Radial Nerve: Found in organisms such as sea stars.

  • Nerve Net: A decentralized network that transmits signals without a central brain, such as in sea anemones.

  • Neural Ring: Found in specific echinoderms.

Advanced Nervous Systems

  • Centralization into a defined brain and spinal cord.

Examples:

  • Earthworm (Annelida): Features central nervous systems with segmental nerves.

  • Flatworm (Platyhelminthes): Exhibits more complex nervous structures for motor control.

  • Squid (Mollusca): Showcases advanced cephalization with a developed brain and ganglia.

Vertebrate Nervous System Structure

Major Divisions

  1. Central Nervous System (CNS)

    • Composed of:

      • Brain: The integrating and command center located in the cranium.

      • Spinal Cord: Encased in the vertebral canal, relays information to and from the brain.

  2. Peripheral Nervous System (PNS)

    • Connects the CNS to the rest of the body, carrying information both ways.

    • Divided into:

    • Sensory Division: Carries sensory information from receptors to CNS.

    • Motor Division: Carries motor information from CNS to muscles.

Composition of Nervous Tissue

Cells in Nervous Tissue

  1. Neurons

    • Specialized for transmitting nerve impulses.

  2. Supporting Cells (Glial Cells)

    • Various types that assist neurons in their functions.

Characteristics of Neurons

  1. Non-dividing: Neurons are not replaced or regenerated after birth.

  2. Long-living: Neurons must last throughout a human's life (with some exceptions in the cerebral cortex).

  3. High Metabolic Rate: Require significant amounts of oxygen and nutrients due to their active metabolism.

Structure of a Neuron

  • Soma (Cell Body)

  • Dendrites: Receive signals from other neurons.

  • Axon: Transmits impulses away from the cell body.

  • Myelin Sheath: Insulating layer that speeds up impulse transmission.

  • Node of Ranvier: Gaps in the myelin sheath where depolarization occurs.

  • Chemical Synapse: Junction facilitating communication between neurons.

Synaptic Transmission and Communication

Synapse Definition

  • A junction between neurons that allows for information transfer which is typically unidirectional, ensuring controlled flow.

Mechanism of Synaptic Transmission

  • Neurons communicate via neurotransmitters released into the synaptic cleft, leading to action potentials in the receiving cell.

  • Action Potential: Electrical impulses generated along the axon upon reaching a synapse.

Impulse Transmission in Neurons

Electrical Signals

  • Transmitted through an uneven exchange of ions across the neuron's membrane, causing electric potential to build.

Structure of the Central Nervous System

Overview

  • Comprising mainly of the brain and spinal cord, the CNS functions as the central control center.

Brain Composition

  • Brain tissues are categorized into:

    • Grey Matter: Contains neuron cell bodies.

    • White Matter: Comprised of myelinated axons.

Organizational Regions of the Brain

  1. Cerebral Hemispheres: Major part of the brain responsible for various higher functions.

  2. Diencephalon: Relay center for information and visceral control.

  3. Brain Stem: Responsible for basic life functions and passage of nerve fibers.

  4. Cerebellum: Coordinates motor control and balance, accounting for 11% of brain mass.

Functional Areas of the Cerebral Cortex

  1. Motor Areas: Controls voluntary movement.

  2. Sensory Areas: Process sensory information leading to perception.

  3. Association Areas: Integrate information leading towards conscious actions.

Lobes of the Cerebral Cortex

  • Frontal Lobe: Involved in movement planning, recent memory, some aspects of emotion.

  • Temporal Lobe: Responsible for hearing and advanced visual processing.

  • Parietal Lobe: Processes body sensations.

  • Occipital Lobe: Responsible for vision.

Reflexes and Their Role in the Nervous System

Reflex Definition

  • Reflex: An automatic response of the body to stimuli, often controlled by the spinal cord, allowing for quick reactions independent of brain input.

Peripheral Nervous System Details

Overview

  • The PNS encompasses all nervous structures outside of the CNS, including cranial and spinal nerves.

Divisions of the PNS

  • Sensory Division: Carries information from the sensory receptors to the CNS.

  • Motor Division: Carries commands from the CNS to the effectors (muscles and glands).

Sensory Pathways

Sensory Receptors

  • Mechanoreceptors: Detect pressure.

  • Thermoreceptors: Respond to temperature changes.

  • Pain Receptors: Indicate tissue damage.

Sensory Pathway Composition

  • Comprises sensory organs, neurons, and corresponding brain areas.

Special Sensory Pathways

Examples

  • Olfaction (Smell): Contains approximately 5 million receptors in humans.

  • Vision: Certain animals, such as bloodhounds, possess a significantly higher number of olfactory receptors (200 million).

Comparison of Sensory Capabilities in Animals

Unique Sensory Abilities

  • Some animals, such as bees, can perceive ultraviolet light, giving them unique perspectives of their environment compared to human sensory input.

Advanced Sensory Capabilities

Echolocation in Bats

  • Bats utilize echolocation as a method for navigation and hunting, a sense not employed by humans.

Dopamine and Drugs

Drug Addiction and Dopamine Mechanisms

  • Explores the relationship between dopamine signaling and drug addiction, emphasizing the neurological pathways involved.