reflex arc

Examples of reflex arc in the following topics:

• Components of a Reflex Arc

  • A reflex arc defines the pathway by which a reflex travels—from the stimulus to sensory neuron to motor neuron to reflex muscle movement.
  • The path taken by the nerve impulses in a reflex is called a reflex arc.
  • Most reflex arcs involve only three neurons.
  • There are two types of reflex arcs:the  autonomic reflex arc, affecting inner organs, and the somatic reflex arc, affecting muscles.
  • The path taken by the nerve impulses in a reflex is called a reflex arc.

• Reflexes and Diagnosis

  • A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus.
  • Scientific use of the term "reflex" refers to a behavior that is mediated via the reflex arc; this does not apply to casual uses of the term "reflex".
  • Generally, decreased reflexes indicate a peripheral problem, and lively or exaggerated reflexes a central one.
  • While the reflexes above are stimulated mechanically, the term H-reflex refers to the analogous reflex stimulated electrically, and Tonic vibration reflex for those stimulated to vibration.
  • While 2+ is considered normal, some healthy individuals are hypo-reflexive and register all reflexes at 1+, while others are hyper-reflexive and register all reflexes at 3+.

• The Peripheral Nervous System (PNS)

  • The somatic nervous system keeps the body adept and coordinated, both through reflexes and voluntary action.
  • Reflexes can be categorized as either monosynaptic or polysynaptic based on the reflex arc used to perform the function.
  • Monosynaptic reflex arcs, such as the knee-jerk reflex, have only a single synapse between the sensory neuron that receives the information and the motor neuron that responds.
  • Polysynaptic reflex arcs, by contrast, have at least one interneuron between the sensory neuron and the motor neuron.
  • An example of a polysynaptic reflex arc is seen when a person steps on a tack—in response, their body must pull that foot up while simultaneously transferring balance to the other leg.

• Autonomic Reflexes

  • Autonomic reflexes are unconscious motor reflexes relayed from the organs and glands to the CNS through visceral afferent signaling.
  • An example of referred pain from an autonomic reflex arc occurs when the bowel is suddenly distended.
  • The medulla's major ANS functions include respiration (the respiratory control center, or RCC), cardiac regulation (the cardiac control center, or CCC), vasomotor activity (the vasomotor center or VMC), and certain reflex actions (such as coughing, sneezing, vomiting and swallowing).
  • General visceral afferent sensations are mostly unconscious, visceral motor reflex sensations from hollow organs and glands that are transmitted to the CNS (see the following illustration for a depiction of a typical nerve fiber, including general visceral afferent fibers).
  • While the unconscious reflex arcs are normally undetectable, in certain instances they may send pain sensations to the CNS, masked as referred pain.

• Spinal Reflexes

  • Spinal reflexes include the stretch reflex, the Golgi tendon reflex, the crossed extensor reflex, and the withdrawal reflex.
  • Spinal reflexes include the stretch reflex, the Golgi tendon reflex, the crossed extensor reflex, and the withdrawal reflex.
  • This reflex has the shortest latency of all spinal reflexes.
  • The Golgi tendon reflex is a normal component of the reflex arc of the peripheral nervous system.
  • The crossed extensor reflex is a withdrawal reflex.

• Proprioceptive Sensations

  • An unconscious reaction is seen in the human proprioceptive reflex, or Law of Righting.
  • It provides the sensory component of the Golgi tendon reflex.
  • The Golgi tendon reflex is a normal component of the reflex arc of the peripheral nervous system.
  • In a Golgi tendon reflex, skeletal muscle contraction causes the agonist muscle to simultaneously lengthen and relax.
  • This reflex is also called the inverse myotatic reflex, because it is the inverse of the stretch reflex.

• Facial (VII) Nerve

  • In regards to the corneal reflex, the afferent arc is mediated by the general sensory afferents of the trigeminal nerve.
  • The efferent arc occurs via the facial nerve.
  • The reflex involves the consensual blinking of both eyes in response to stimulation of one eye.
  • Thus, the corneal reflex effectively tests the proper functioning of both cranial nerves V and VII.

• Gastrointestinal Reflex Pathways

  • The digestive system functions via a system of long reflexes, short reflexes, and extrinsic reflexes from gastrointestinal (GI) peptides working together.
  • In addition, there are three overarching reflexes that control the movement, digestion, and defecation of food and food waste: the enterogastric reflex, the gastrocolic reflex, and the gastroileal reflex.
  • When this occurs, it is called a short reflex.
  • The gastrocolic reflex is the physiological reflex controlling the motility, or peristalsis, of the gastrointestinal tract.
  • The gastroileal reflex is a third type of gastrointestinal reflex.

• Area and Arc Length in Polar Coordinates

  • Area and arc length are calculated in polar coordinates by means of integration.
  • If you were to straighten a curved line out, the measured length would be the arc length.
  • To find the area enclosed by the arcs and the radius and polar angles, you again use integration.
  • The curved lines bounding the region $R$ are arcs.
  • Evaluate arc segment area and arc length using polar coordinates and integration

• Reflexive