Integrative States

Nervous System Overview

  • Focus on sensory, motor, and integrative systems related to nerves.

Functions of the Nervous System

  1. Sensing the Environment

    • Detects changes in internal and external environments.

  2. Conveying Sensations

    • Sensations sent to the central nervous system (CNS) for modification and integration with incoming or stored information.

  3. Determining Motor Responses

    • Calculates appropriate responses to stimuli.

  4. Homeostasis Implications

    • Disruption in any component can lead to significant homeostatic disruptions.

Key Terms and Definitions

  • Sensation: The conscious or subconscious detection of changes in the environment.

  • Perception: The conscious awareness and interpretation of sensations.

  • Sensory Modality: A unique type of sensation (e.g., taste, smell).

  • Types of Senses:

    • General Senses: Includes somatic and visceral receptors.

    • Special Senses: Includes specialized receptors for smell, taste, vision, hearing, and equilibrium.

Sensory Reception Process

Transduction of Stimulus

  • Definition of Transduction: The process of converting stimulus energy into graded potentials.

  • Generation of Nerve Impulse: When graded potential reaches a threshold, it triggers action potentials.

Sensory Input Integration

  • Occurs in specific functional regions of the cerebral cortex.

  • Sensory receptors convert stimuli into graded potentials.

Types of Sensory Receptors

  1. Free Nerve Endings

    • Bare dendrites that detect pain, temperature, tickle, itch, and some touch sensations.

  2. Encapsulated Nerve Endings

    • Dendrites enclosed in connective tissue, specialized for pressure, vibration, and some touch sensations.

  3. Specialized Cells

    • Examples include hair cells (hearing), gustatory cells (taste), and photoreceptors (vision).

Sensory Graded Potentials

  • Amplitude varies with stimulus intensity:

    • Generator Potentials: Produced by free nerve endings and encapsulated nerve endings; they generate action potentials in sensory neuron's axon.

    • Receptor Potentials: Trigger neurotransmitter release from separate sensory cells.

  • Postsynaptic Potential: May trigger multiple action potentials.

Classification of Receptors

By Location and Origin of Stimulus

  • Exteroceptors: Receptors found at or near external surfaces.

  • Interoceptors: Receptors inside vessels, tissues, or organs.

  • Proprioceptors: Found in muscles, joints, and the inner ear; detect body position and movement.

  • Types of Stimuli Detected:

    1. Mechanoreceptors: Detect mechanical changes.

    2. Thermoreceptors: Respond to temperature changes.

    3. Nociceptors: Signal pain or tissue damage.

    4. Photoreceptors: Sensitive to light.

    5. Chemoreceptors: Respond to chemical changes.

    6. Osmoreceptors: Detect osmotic pressure of body fluids.

Sensory Adaptation

  • Definition: Decrease in receptor sensitivity during a sustained stimulus.

  • Types of Adaptation:

    • Rapid Adaptation: Sensitivity decreases quickly.

    • Slow Adaptation: Sensitivity decreases slowly, allowing continued monitoring.

Somatic Sensations

  • Result from stimulation of sensory receptors in skin, mucous membranes, muscles, tendons, joints, and the inner ear.

  • Cutaneous Sensations: Stimulation of skin sensory receptors, which include:

    • Tactile Sensations: Involve mechanoreceptors for touch, pressure, and vibration (e.g., Meissner corpuscles for hairless skin).

    • Thermal Sensations: Involve thermal receptors; cold receptors in the epidermis (10 to 40°C) and warm receptors in the dermis (32 to 48°C).

  • Pain Sensations: Elicited by nociceptors, with fast pain (sharp, acute) and slow pain (chronic, aching).

Localization of Pain

  • Fast Pain: Precisely located at the stimulated area.

  • Slow Pain: More diffuse, appearing to originate from a larger area.

  • Referred Pain: Pain perceived in areas distant from the site of injury, often due to shared nerve pathways.

Proprioception

  • Definition: Awareness of body movements and position.

  • Involves:

    • Muscle Spindles: Detect muscle length changes.

    • Tendon Organs: Monitor tension in tendons.

    • Joint Kinesthetic Receptors: Detect pressure and position in joints.

Somatic Sensory Pathways

  • Transmit sensory information to the primary somatosensory area in the cerebral cortex.

  • Pathway Order:

    1. First Order Neurons: From receptors to the CNS.

    2. Second Order Neurons: From spinal cord/brainstem to thalamus.

    3. Third Order Neurons: From thalamus to postcentral gyrus.

  • Types of Pathways:

    • Posterior Column: Conducts impulses for proprioception, touch, and vibration.

    • Spinothalamic Pathway: Conducts impulses for pain and temperature.

Primary Somatosensory Area

  • Located in the postcentral gyrus of the parietal lobe.

  • Receives sensory input from the opposite side of the body; precise localization of sensations occurs here.

Homunculus

  • Definition: Representation of body parts proportional to the number of sensory neurons; sensitive areas like lips and fingers occupy larger regions.

Motor System Overview

Primary Motor Area

  • Located in the precentral gyrus of the frontal lobe.

  • Controls voluntary movement; maps differ from sensory homunculus.

Motor Pathways

  • Lower Motor Neurons: Extend from the brain/spinal cord to skeletal muscles.

  • Upper Motor Neurons: Maintain muscle tone, posture, and balance.

  • Pathway Types:

    • Direct Pathways: Directly connect to lower motor neurons.

    • Indirect Pathways: Involve multiple synapses.

Types of Motor Pathways

  1. Lateral Corticospinal Pathway: Precise, skilled movements of hands and feet; decussate at the medulla.

  2. Anterior Corticospinal Pathway: Controls movements of the trunk/proximal limbs; decussate at different spinal cord levels.

  3. Corticobulbar Pathway: Controls head muscles; mixed pathways in terms of crossing over.

Basal Nuclei Functions

  • Receive input from sensory and motor areas; provide feedback to the motor cortex.

  • Roles include suppressing unwanted movement, maintaining balance, and coordinating rapid skilled movements.

Cerebellum Functions

  • Integrates sensory input to coordinate movements, maintain posture, and perform skilled activities.

  • Corrects discrepancies between intended and actual movements.

Wakefulness and Sleep

Reticular Activating System (RAS)

  • Part of the reticular formation; aids in wakefulness.

  • Influences arousal from sleep; increases cortical activity.

Circadian Rhythm

  • Regulates sleep-wake cycles, influenced by the hypothalamus.

  • Can be altered by lifestyle factors and environmental cues (light, activity).

Learning and Memory

Definitions

  • Learning: The ability to acquire new information or skills.

  • Memory: The ability to store and recall information or skills.

Memory Types

  1. Immediate Memory: Recall of current experiences for seconds.

  2. Short-Term Memory: Retain a few pieces of information for seconds to minutes.

  3. Long-Term Memory: Stored information that can last for years and retrieved later.

Memory Storage

  • Involves changes in neurons and synapses, particularly in the cerebral cortex and regions associated with the limbic system and basal nuclei for motor skills.