Nervous System Integration & Control

• In biological terms, this integration allows organisms to:

  • Respond to stimuli
  • Maintain homeostasis
  • Perform complex behaviors
  • Adapt to environmental changes
• Hierarchy of Biological Organization

  Living organisms are organized in a hierarchical structure:

  1. Cells
  2. Tissues
  3. Organs
  4. Organ systems
  5. Organism

  Each level integrates with the others to create a functional living being.
• Emergent Properties


  Emergent properties are characteristics that arise from the interaction of components in a system, which are not present in the individual parts alone.
• Consider a cheetah as a predator:

  • Muscular system: Provides strength and speed
  • Skeletal system: Supports the body and allows movement
  • Nervous system: Coordinates movements and processes sensory information
  • Circulatory system: Supplies oxygen and nutrients to muscles
• The Brain as a Central Information Integration Organ


  The brain is the body's command center, responsible for:

  1. Processing multiple inputs:
  2. Learning and memory:
• Processing multiple inputs:

  • Integrates sensory information from various sources
  • Combines this information to create a coherent perception of the environment
• Learning and memory:

  • Forms new neural connections based on experiences
  • Stores and retrieves information
• The integration of organs through these systems allows for complex behaviors and adaptations that wouldn't be possible with individual organs working in isolation. This integration is key to an organism's survival and success in its environment.
• The Spinal Cord as an Integrating Centre

  The spinal cord is not just a conduit for signals between the brain and body; it's also a crucial integrating centre for unconscious processes.
• Conscious Processes

  • Require active attention and awareness
  • Controlled by the cerebral cortex
  • Examples: solving a math problem, deciding what to eat
• Unconscious Processes

  • Occur without conscious awareness or control
  • Many are controlled by the spinal cord
  • Examples: reflexes, some aspects of posture control, basic locomotion patterns
• Sensory Input to the Central Nervous System

  Sensory neurons play a crucial role in conveying information from the environment to the central nervous system (CNS).
• Pathway of Sensory Information

  1. Receptor cells detect stimuli (e.g., light, sound, pressure)
  2. Sensory neurons transmit this information as electrical signals
  3. Signals travel to the spinal cord or directly to the brain
  4. Information is processed in the CNS
• Types of Sensory Information

  • Exteroceptive: from the external environment (e.g., touch, sight, hearing)
  • Interoceptive: from internal organs (e.g., blood pressure, stomach distension)
  • Proprioceptive: about body position and movement
• The integration of sensory information in the spinal cord and brain allows for rapid, appropriate responses to environmental stimuli, which is crucial for survival. This system's efficiency is due to the combination of unconscious spinal reflexes and conscious brain-mediated responses.
• Output from Cerebral Hemispheres to Muscles

  The cerebral hemispheres are responsible for initiating voluntary movements through a pathway involving motor neurons.
• Process of Motor Output


  1. Decision to move is made in the cerebral cortex
  2. Signal travels through the motor cortex
  3. Passes through the brainstem and spinal cord
  4. Motor neurons carry the signal to specific muscles
  5. Neurotransmitters are released at the neuromuscular junction
  6. Muscle fibers contract in response
• Muscle Contraction

  Muscles contract through a process called the sliding filament theory:

  1. Motor neuron releases acetylcholine at the neuromuscular junction
  2. This triggers an action potential in the muscle fiber
  3. Calcium is released within the muscle cell
  4. Myosin heads bind to actin filaments
  5. Myosin pulls the actin, causing the muscle to shorten
• Nerve Structure


  Nerves are bundles of nerve fibers that contain both sensory and motor neurons.
• Components of a Nerve (Transverse Section)

  1. Protective Sheath (Epineurium): Outer layer of connective tissue
  2. Fascicles: Bundles of nerve fibers
  3. Perineurium: Surrounds each fascicle
  4. Endoneurium: Surrounds individual nerve fibers
  5. Nerve Fibers:

  • Myelinated: Covered in myelin sheath for faster conduction
  • Unmyelinated: Lack myelin sheath, slower conduction
• Myelinated:


  • Faster conduction due to saltatory conduction
  • Action potential "jumps" between nodes of Ranvier
• Unmyelinated:


  • Slower conduction
  • Action potential travels continuously along the axon
• The structure of nerves, with their mixture of sensory and motor fibers, allows for efficient bidirectional communication between the central nervous system and the rest of the body. This organization is crucial for coordinated responses to stimuli and execution of complex behaviors.
• Pain Reflex Arc

  A reflex arc is a neural pathway that produces a rapid, involuntary response to a stimulus. The pain reflex arc is a crucial protective mechanism.
• Components of a Pain Reflex Arc

  1. Receptor: Free nerve endings in the skin (pain receptors)
  2. Sensory neuron: Carries signal to the spinal cord
  3. Interneuron: In the grey matter of the spinal cord
  4. Motor neuron: Carries signal from spinal cord to effector
  5. Effector: Skeletal muscle
• Example of Process of a Pain Reflex Arc

  When you touch a hot object with your hand:

  1. Pain receptors (free nerve endings) in your hand detect the heat
  2. Sensory neurons transmit this information to your spinal cord
  3. In the grey matter of the spinal cord, the signal synapses with an interneuron
  4. The interneuron then synapses with a motor neuron
  5. The motor neuron sends a signal to the skeletal muscles in your arm
  6. Your arm muscles contract, pulling your hand away from the hot object
• The Role of the Cerebellum

  The cerebellum, located at the back of the brain, plays a crucial role in coordinating skeletal muscle contraction and maintaining balance.
• Key Functions of the Cerebellum

  1. Motor Coordination: Integrates inputs from various parts of the brain and spinal cord to produce smooth, coordinated movements
  2. Balance and Posture: Processes information from the inner ear, eyes, and proprioceptors to maintain balance
  3. Motor Learning: Helps in learning and refining motor skills
  4. Timing and Precision: Ensures movements are performed with the correct timing and precision
• The pain reflex arc and the cerebellum's function demonstrate different levels of motor control. Reflex arcs provide rapid, involuntary responses, while the cerebellum allows for more complex, learned motor behaviors. Both are crucial for an organism's survival and effective interaction with its environment.
• Nervous System

  • Sends electrical signals (action potentials)
  • Fast transmission (milliseconds)
  • Specific target cells
  • Short-term effects