Lecture 4 Levels of Control and Reflex Arcs - Anatomy
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Questions and Answers

What is the primary function of sensory cells in a reflex arc?

  • To inhibit reflex responses
  • To monitor muscle contractions
  • To translate environmental energy into action potentials (correct)
  • To perform voluntary movements

    • Which component of the reflex arc is responsible for integrating sensory input with motor output?

  • Effectors
  • Sensory nerve fibers
  • Motor nerve fibers
  • Coordinating center (CNS) (correct)

    • What aspect of reflex arcs is affected by a malfunctioning component?

  • The response will not be voluntary
  • The response may become more variable (correct)
  • The response will always be maintained
  • The response will become stronger

    • In the context of reflex arcs, what does frequency coding allow the CNS to determine?

    <p>The intensity of the stimulus</p> Signup and view all the answers

    In which part of the nervous system are somatic reflex arcs primarily integrated?

    <p>Spinal cord</p> Signup and view all the answers

    What type of muscle is primarily involved in somatic reflex arcs?

    <p>Skeletal muscle</p> Signup and view all the answers

    Which of the following disruptions would most likely indicate an issue in motor nerve fibers?

    <p>Weakness in muscle contractions</p> Signup and view all the answers

    What condition might result from a malfunction in receptors involved in a reflex arc?

    <p>Loss of sensitivity to stimuli</p> Signup and view all the answers

    What is the primary function of sensory (afferent) nerves?

    <p>Conduct action potentials from the receptor to the CNS</p> Signup and view all the answers

    How do sensory nerves enter the spinal cord?

    <p>Through dorsal roots</p> Signup and view all the answers

    In the context of reflexes, what is a monosynaptic reflex?

    <p>Involves a direct connection between sensory and motor neurons</p> Signup and view all the answers

    What role do Golgi organs play in muscle response?

    <p>Sense tension in tendons</p> Signup and view all the answers

    During the knee jerk reflex, which muscle contracts as a response?

    <p>Quadriceps</p> Signup and view all the answers

    What happens to the triceps during the activation of the biceps in a resting position?

    <p>They relax due to inhibition</p> Signup and view all the answers

    What is the role of motor (efferent) nerves in muscle control?

    <p>To carry action potentials from the CNS to target effectors</p> Signup and view all the answers

    Which of the following describes the role of interneurons during a reflex?

    <p>Inhibit or facilitate communication between sensory and motor neurons</p> Signup and view all the answers

    What is the role of the cerebellum in the control of body movement?

    <p>It monitors the execution of movements.</p> Signup and view all the answers

    Which component of a reflex arc is responsible for converting environmental energy into action potentials?

    <p>Sensory cells/receptors</p> Signup and view all the answers

    What symptom might indicate a loss of proprioception in an individual?

    <p>Poor coordination and balance</p> Signup and view all the answers

    Which of the following levels of control is primarily responsible for conscious movements?

    <p>Higher centers (Cerebral cortex)</p> Signup and view all the answers

    What happens if any component of a reflex arc malfunctions?

    <p>The response may be altered or diminished.</p> Signup and view all the answers

    In the context of a somatic reflex arc, which type of muscle is primarily affected?

    <p>Skeletal muscle</p> Signup and view all the answers

    Which structure in the spinal cord is directly involved in local integration during a somatic reflex?

    <p>Interneurons</p> Signup and view all the answers

    What is the function of Golgi organs in relation to muscle activity?

    <p>Monitor muscle tension</p> Signup and view all the answers

    What is the role of the middle segment of intrafusal fibers in muscle spindles?

    <p>It acts as a stretch receptor for detecting changes in muscle length.</p> Signup and view all the answers

    During a knee jerk reflex, which process ensures that the opposite muscle relaxes?

    <p>Inhibition of motor neurons via interneurons.</p> Signup and view all the answers

    What is the primary function of Golgi organs in the context of muscle response?

    <p>Sensors for muscle contraction strength.</p> Signup and view all the answers

    Which structure carries action potentials from the central nervous system to the effectors?

    <p>Motor (efferent) nerve.</p> Signup and view all the answers

    In the context of reflexes, what distinguishes monosynaptic from multisynaptic reflexes?

    <p>Monosynaptic reflexes have direct connections without interneurons.</p> Signup and view all the answers

    What reflex mechanism is involved when the triceps muscle is inhibited during bicep contraction?

    <p>Interneuronal feedback inhibition.</p> Signup and view all the answers

    What type of reflex arc involves a direct sensory to motor neuron communication?

    <p>Monosynaptic reflex arc.</p> Signup and view all the answers

    In which part of the body are the cell bodies of sensory nerves located?

    <p>In ganglia outside of the spinal cord.</p> Signup and view all the answers

    Study Notes

    Levels of Control of Body Movement

    • Three levels: higher, middle, and lower
    • Higher Centers: Cerebral cortex (conscious)
    • Middle Level: Sensorimotor cortex, cerebellum (monitors execution), basal ganglia (semi-voluntary movements)
    • Lower Level: Spinal cord (site of somatic reflex arcs)

    Components of a Reflex Arc

    • Automatic, involuntary response to a stimulus
    • Five components:
      • Sensory cells/receptors
      • Sensory nerve fibers
      • Coordinating center (CNS)
      • Motor nerve fibers
      • Effectors (muscle or gland cells)

    Somatic (Skeletal Muscle) Reflex Arcs

    • Five Components: Receptors, sensory nerve, coordinating center in the central nervous system (CNS), motor nerve, target organ response
    • Receptors
      • Transduce environmental energy, like heat, cold, pressure, stretch, and tension
      • Convert energy into action potentials
      • Frequency of action potentials is proportional to intensity (frequency coding)
    • Sensory (afferent) Nerve
      • Conducts action potentials from the receptor to the CNS
      • Cell body is in ganglion outside of the spinal cord
      • Enters the spinal cord via dorsal roots
    • CNS Synapses
      • Can be monosynaptic (muscle spindle reflex) or multisynaptic (elaborate reflexes)
    • Motor (efferent) Nerve
      • Carries action potentials from the CNS to the target organ
      • Via ventral roots
      • Cell body within the CNS
    • Target Organ Response
      • Can be skeletal muscle (e.g. knee jerk reflex) or multiple targets (e.g. scratching)

    Stretch and Tendon Reflex

    • Stretch Reflex
      • Changes in muscle length detected by muscle spindles
      • Modified muscle fibers called spindle or intrafusal fibers act as stretch receptors
      • Sensory nerve makes excitatory synaptic contact with motor neurons serving the same muscle, causing muscle shortening
    • Tendon Reflex
      • Changes in tendon length detected by Golgi organ
      • Senses tension in tendons
      • Muscle contraction pulls tendon, squeezing the Golgi organ, activating sensory fibers
      • Sensory nerve contacts an inhibitory interneuron in the spinal cord, inhibiting motor neurons serving the same muscle

    Antagonistic Muscle Groups

    • Skeletal muscles are organized in antagonistic muscle groups
    • Reflex targets both groups

    Knee Jerk Reflex

    • Protective reflex to prevent tendon injury
    • Quadriceps muscle contraction in response to tapping the patella ligament
    • Requires relaxation of opposing flexor muscles (via activation of inhibitory interneurons)

    Calf with Neurologic Abnormalities

    • Gradual onset of hind leg lameness
    • No withdrawal responses in hind legs
    • Weakness, poor muscle tone
    • Loss of proprioception (lack of awareness of body position in space)
    • Problem likely in the spinal cord, perhaps due to cord compression or an abscess

    Key Concepts

    • Reflex arcs are responsible for automatic, involuntary responses
    • They are essential for maintaining posture, coordinating movements, and protecting the body from injury
    • Understanding reflex arcs is crucial for diagnosing and treating neurological disorders

    CNS Control of Movement

    • Three levels of control:
      • Higher centers – cerebral cortex (conscious).
      • Middle level:
        • Sensorimotor cortex.
        • Cerebellum (monitors execution of movement).
        • Basal ganglia (semi-voluntary movements).
      • Lower level – Spinal cord (site of somatic reflex arcs).
    • Tensions in muscles and tendons, and angles of joints, send sensory information back to CNS (proprioception).

    Components Involved in the Control of Skeletal Muscles

    • Dark pink = components involved in planning and programming of movements.
    • Light pink = components responsible for the execution of movements.
    • Somatic reflex arc involves local integration in the spinal cord.

    Concept of a Reflex

    • An automatic or unconscious response of effectors (muscle or gland) to a stimulus.
      • Involuntary.
      • Unvarying response.
    • Contains five fundamental components:
      • Sensory cells / receptors.
      • Sensory nerve fibers.
      • Coordinating center (CNS).
      • Motor nerve fibers.
      • Effectors (muscle or gland cells).
    • Malfunction of any one component leads to the alteration in the response.

    Somatic (skeletal muscle) Reflex Arcs

    • Receptors:

      • Transduce environmental energy.
        • Skin – heat, cold, pressure.
        • Muscle (spindle) – stretch.
        • Tendon (Golgi) - tension.
      • Convert energy into action potentials (AP).
      • Frequency of APs proportional to intensity of energy transduced (frequency coding) – enables CNS to detect intensity.

    • Sensory (afferent) nerve:

      • Conduct AP from the receptor.
      • Cell body in ganglion outside of spinal cord.
      • Enter spinal cord via dorsal roots.

    • Coordinating center = CNS synapses:

      • Monosynaptic (muscle spindle reflex).
      • Multisynaptic (elaborate reflexes).

    • Motor (efferent) nerve:

      • Carries APs from CNS to target (effectors) organs.
      • Via ventral roots.
      • Cell body within the CNS.

    • Target organ response:

      • Skeletal muscle e.g. knee jerk (patella) reflex.
      • Multiple targets (scratching).

    Stretch and Tendon Reflex

    • Changes in muscle length detected by muscle spindles.
      • Modified muscle fibers = spindle or intrafusal fibers, the middle segment acts as stretch receptor by pinching the bare end of the sensory neuron (act as receptor) sensory afferent nerve spinal cord muscle shortening.
      • Sensory nerve makes excitatory synaptic contact with motor neurons serving the same muscle (extrafusal  fibers).
    • Changes in tendon length detected by Golgi organ, senses tension in tendons.
      • Muscle contracts pulls tendon squeezes bare end of neuron (receptors) sensory nerve contacts with an inhibitory interneuron in spinal cord inhibits motor neurons serving the same muscle.

    Stretch and Tendon Reflex: Antagonistic Muscle Groups

    • Skeletal muscles organized in antagonistic muscle groups.
    • Reflex will target both.
      • Resting position.
      • Biceps stretched by added weight AP in sensory neuron enters spinal cord activates biceps motor nerve and, via interneuron inhibits triceps motor nerve.
      • Biceps contract, triceps relax posture restored.

    Knee Jerk Reflex

    • Same protective reflex concept to prevent tendon injury.
    • Quadriceps muscle contraction in response to “tapping” of the patella ligament brief leg extension.
    • Requires relaxation of opposing flexor muscles (via activation of inhibitory interneurons).

    Calf with Neurologic Abnormalities

    • Cord compression abscess of vertebral body (L4).

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    Neurophysiology III: Reflex Arcs PDF

    Description

    Explore the intricate systems of body movement control through this quiz that covers the three levels of movement: higher, middle, and lower centers. Additionally, test your knowledge on the components of somatic reflex arcs and their respective functions within the central nervous system.

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