Reflex Arcs and Sensory Receptors

Reflex Arc Components

  • Reflex arcs are fundamental components of the nervous system, responsible for reflex actions.
    • Key components include:
    • Stimulus: The change in the environment that initiates the reflex.
    • Receptor: Specialized cell or nerve ending that detects the stimulus.
    • Response: The resulting action or movement produced by the motor output.
    • Effector: The muscle or gland that produces the response.

Types of Reflexes

  • Stretch Reflex: A type of reflex that occurs when a muscle is stretched.
    • Example: Knee-jerk reflex when hitting the patellar tendon.
  • Pupillary Reflex: A reflex which controls the diameter of the pupil in response to light intensity.
    • Involves receptors in the retina which detect light stimulus, leading to constriction of the pupil via muscle contractions.

Electromyography

  • Electromyography: A technique used to evaluate and record the electrical activity of muscle cells during contraction.
    • Important concepts include:
    • Electrical activity of muscle cells: Refers to action potentials generated by muscle fibers.
    • Recruitment of Motor Units: The process of activating multiple motor units to increase muscle strength during contraction.
    • Electromyogram (EMG): The definitive recording that displays the electrical activity from the muscle.

Exercise 22: General Sensations

  • Vital terms associated with general sensations include:
    • Transduction: The process whereby sensory receptors convert stimulus energy into electrical signals.
    • General Senses: Senses that provide information about the body's condition in the environment, these include touch, temperature, pain, and proprioception.
    • Receptive Field: The specific area where a stimulus will activate a sensory neuron.
    • Adaptation: The decrease in sensitivity to a continuous stimulus over time.
    • Threshold: The minimum stimulus intensity needed to activate a sensory receptor.

Classification of Receptors

  • According to Stimulus Source:

    • Exteroceptors: Receptors that respond to stimuli from outside the body (e.g., touch, temperature).
    • Interoceptors: Receptors that monitor internal body conditions (e.g., blood pressure, hunger).

  • According to Type of Stimulus:

    • Mechanoreceptors: Respond to mechanical pressure or distortion (e.g., touch, sound).
    • Photoreceptors: Detect light and are essential for vision (e.g., rods and cones in the retina).
    • Thermoreceptors: Sensitive to temperature changes (heat and cold).
    • Chemoreceptors: Detect chemical stimuli (e.g., taste and smell).
    • Nociceptors: Sensory receptors for painful stimuli.

Cutaneous Receptors

  • Cutaneous Receptors: A subtype of mechanoreceptors located in the skin that respond to tactile stimuli, temperature, and pain.

Exercise 23: Special Senses: Vision

  • Extrinsic Eye Muscles:

    • There are six extrinsic muscles that control eye movement, including:
    • Lateral Rectus (contracts when looking laterally to the right).
    • Medial Rectus (contracts when looking medially).
    • Superior Rectus and Inferior Rectus (control elevation and depression).
    • Superior Oblique and Inferior Oblique (control rotation).

  • Internal Anatomy of the Eye:

    • Students should refer to models and pictures for highlighted structures in the manual.
    • Layers of the Eye include:
    • Fibrous Layer: Provides structure; includes the sclera and cornea.
    • Vascular Layer: Contains the choroid, ciliary body, and iris.
    • Inner Layer: The retina, where photoreceptors (rods and cones) are located, crucial for vision.
    • Ganglion Cells in the retina converge to form the Optic Nerve (CN II).

Supertasters Lab

  • The experiment assessed taste sensitivity using taste receptors.
    • Students tested themselves to evaluate differences in taste perception—what types of receptors were involved?

Exercise 25: Special Senses: Hearing

  • Terms Related to Hearing:

    • Hair Cells: Specialized mechanoreceptors found in the cochlea that convert sound vibrations into electrical signals. They also function as exteroceptors.
    • Tectorial Membrane: A membrane that stimulates hair cells in the cochlea during sound wave transduction.
    • Basilar Membrane: A membrane that runs the length of the cochlea; it vibrates in response to sound waves, aiding in sound detection.
    • Organ of Corti: The sensory organ within the cochlea that contains hair cells responsible for auditory transduction.
    • Cochlear Nerve (CN VIII): The nerve carrying auditory sensory information from the cochlea to the brain.

  • Identify Structures of the Ear: Students should refer to models and images for the structures of the ear as detailed in the manual.

  • Microscopic Structure of the Cochlea: Should be examined using a model. Consult the manual for highlighted structures' details.

  • Refer to Table 25.1 for a comprehensive identification of structures and functions of the ear.