Nervous System Booklet 1

The Nervous System

Unit Overview

  • Unit Title: The Nervous & Endocrine Systems
  • Biology Level: 30
  • Textbook Reference: Chapter 13
  • Themes: Equilibrium and Systems
    • Purpose: Examines biological processes that allow interactions between humans and their environment to maintain equilibrium.
    • Nervous System Role: Contributes to homeostasis via responses to internal and external stimuli.
    • Endocrine System Role: Maintains homeostasis through hormone release into the bloodstream.
    • Focus: Interaction between nervous and endocrine systems, especially the functioning of central and peripheral nervous systems in sensing and responding to the environment.

General and Specific Outcomes

  • General Outcome: Students will explain how the nervous system controls physiological processes.
  • Specific Outcomes for Knowledge:
    • Describe structure and function of neurons and myelin sheaths, including:
    • Formation and transmission of action potentials (all-or-none response and intensity of response).
    • Transmission of signals across synapses.
    • Main chemicals and neurotransmitters involved: norepinephrine, acetylcholine, and cholinesterase.
    • Identify principal structures of the central and peripheral nervous systems, explaining their functions in the voluntary (somatic) and involuntary (autonomic) systems:
    • Key Structures Include:
      • Cerebral hemispheres and lobes
      • Cerebellum
      • Pons
      • Medulla oblongata
      • Hypothalamus
      • Spinal cord
      • Sympathetic and parasympathetic nervous systems
      • Sensory-somatic nervous system
    • Describe organization of neurons into nerves and the composition/function of reflex arcs using examples such as the patellar reflex and pupillary reflex.

Organization of the Nervous System

  • Two Main Divisions:
    1. Central Nervous System (CNS):
    • Comprises brain and spinal cord.
    • Functions as coordinating center for incoming and outgoing information.
    1. Peripheral Nervous System (PNS):
    • Carries information between organs and CNS.
    • Connects the CNS to the rest of the body.

Anatomy of a Nerve Cell

  • Types of Nerve Cells:
    1. Glial Cells (Neuroglial Cells):
    • Provide structural support and metabolism for nerve cells.
    1. Neurons:
    • Functional unit of the nervous system.
    • Requires ATP, and glial cells assist in ATP production.

Structure of a Neuron

  • Key Parts of Neuron:
    • Dendrites:
    • Receive information from the environment or other neurons.
    • Conduct nerve impulses towards the cell body.
    • Cell Body:
    • Contains the nucleus and organelles.
    • Axon:
    • Extension of cytoplasm conducting nerve impulses away from the cell body to other neurons or effectors.
    • Only one axon per neuron, which may branch into terminal branches.
    • Can contain myelin sheath for insulation and faster impulse transmission.
    • Myelin Sheath:
    • Glistening white coat of fatty protein insulating the axon, formed by Schwann cells in PNS.
    • Areas between myelin sections are nodes of Ranvier, facilitating faster impulse conduction.
    • Damage to myelin can lead to disorders like Multiple Sclerosis.
    • Neurilemma:
    • Thin outer membrane surrounding the axon promoting regeneration of damaged axons.

Types of Neurons

  1. Sensory Neurons:
    • Receive information from sensory receptors and relay it to CNS.
    • Cell bodies located in clusters called ganglia outside the spinal cord.
  2. Interneurons:
    • Link neurons to other neurons within the brain and spinal cord.
    • Integrate and interpret sensory information, facilitating connections between sensory and motor neurons.
  3. Motor Neurons:
    • Relay information to effectors (muscles or glands) that respond to stimuli.

The Reflex Arc

  • Definition: The simplest nerve pathway, heavily involved in involuntary and often unconscious reactions to stimuli perceived as dangerous.
  • Components of a Reflex Arc:
    1. Sensory receptor
    2. Sensory neuron
    3. Interneuron
    4. Motor neuron
    5. Effector (typically muscles)
  • Function: Facilitates quick protective responses while sending secondary signals to the brain for processing.
  • Events:
    • Arrival of stimulus activates receptor.
    • Information is processed in the spinal cord.
    • Final response occurs through motor neuron activation.

Electrochemical Impulses

  • Nature of Impulses: Created through the movement of ions.
    • Significant ions include Sodium (Na+) and Potassium (K+), which are prevalent around neurons.

Resting Potential

  • Defined as the voltage difference across a nerve cell membrane during rest, typically about -70 mV.
  • Mechanism: Sodium-potassium pump actively transports Na+ out and K+ into the cell (3 Na+ ions out for every 2 K+ ions in).
  • Channel dynamics allow for differential permeability, with more K+ channels than Na+ channels, maintaining the polarized state of the neuron.

Action Potential

  • Describes the rapid rise and fall of electrical potential across a cell membrane as response to stimuli:
    1. Depolarization: Na+ channels open, causing the inside of the cell to become positively charged.
    2. Repolarization: K+ channels open, allowing K+ to exit, returning the membrane back to negative.
    3. Hyperpolarization: K+ channels close slowly, causing temporary excess negativity inside the cell.
    4. Refractory Period: Time after action potential during which another impulse cannot occur (1 - 10 ms).

Synaptic Transmission

  • Neurons do not touch; a gap called a synapse exists.
  • Neurotransmitters: Chemicals released from presynaptic neurons that bind to receptors on postsynaptic neurons facilitating the transmission of signals.
  • Major neurotransmitters include:
    • Acetylcholine: Primarily excitatory.
    • Norepinephrine: Excitatory or inhibitory in function.
    • Dopamine, Serotonin, GABA:
    • Each associated with specific functions within the CNS and PNS.

The Central Nervous System (CNS)

  • Components:
    • Brain
    • Spinal Cord
  • Protection:
    • Enclosed in bones (skull & vertebrae).
    • Surrounding meninges (three layers of protection).
    • Cerebrospinal fluid for shock absorption and nutrient transport.

The Peripheral Nervous System (PNS)


  • Comprised of sensory-somatic and autonomic nervous systems.

  • Sensory-Somatic Nervous System: Controls voluntary movements and sensory information transfer to the CNS.

  • Autonomic Nervous System: Regulates involuntary body functions, subdivided into sympathetic (fight-or-flight response) and parasympathetic (rest-and-digest response).

  • Sympathetic vs. Parasympathetic Functions:

FunctionSympatheticParasympathetic
Heart RateIncreasesDecreases
Digestive TractInhibits peristalsisStimulates peristalsis
EyesDilates pupilsConstricts pupils
LiverStimulates glucose releaseNo effect

Summary of the Nervous System

  • Structural Components:
    • Neuron Types: Sensory neurons, interneurons, motor neurons.
    • Key Structures: Dendrites, axons, myelin sheaths, nodes of Ranvier, neurilemma, reflex arcs.
    • Central Nervous System Components: Brain and spinal cord; divided into forebrain, midbrain, hindbrain. Each division has specific parts and functions vital for maintaining bodily functions and homeostasis.
    • Peripheral Nervous System Components: Sensory-somatic and autonomic systems, each regulating different types of activities and responses.