Exam 4 Review:  Chapter 13:  Proprioception and Types of Reflexes

muscle tone - The normal degree of vigor and tension in maintained in skeletal muscles by involuntary spinal reflexes; the resistance of skeletal muscle to passive elongation or stretch.

 

stretch reflex - A (usually) monsynaptic ipsilateral segmental reflex contraction of a muscle in response to stretching of an attached tendon or of the muscle itself; the receptors involved are golgi tendon organs and muscle spindles respectively; the stretch reflex is fast and has a fast onset and offset; it is important in anti-gravity responses; keeping the limbs extended so that one does not fall down; gravity exerts tension on the extensor muscles and they contract and keep the limbs straight.

 

 

muscle spindle - A special mechanoreceptor organ involved in proprioception consisting of a group of sensory nerve endings wrapped around special muscle cells termed spindle fibers ("intrafusal fibers") which have lost the capacity to contract; stretching the spindle fibers initiates nerve impulses in the sensory neurons which are transmitted to the spinal cord where various connections can be made to interneurons or motor neurons and the impulses may be routed to higher centers, e.g., the cerebellum and thalamus.

 

 

tendon organ = Golgi tendon organ - A proprioceptive receptor which is located within the tendons found on each end of a muscle; these organs are composed of skeletal muscle cells ("extrafusal muscle fibers") which enter a funnel-like capsule that is filled with collagen fiber bundles; nerve endings are entwined throughout these collagen fibers, and are triggered when tension in the muscle is transferred to the collagen fibers of the Golgi tendon organ; it responds to increased muscle tension or contraction as exerted on the tendon, by inhibiting further muscle contraction; when muscle contraction is excessive, the Golgi tendon organ protects against muscle damage; the proprioceptive sensory neuron of a Golgi tendon organ projects to the motor neurons located within the ventral horn of the spinal cord, where the inhibition occurs; unlike the muscle spindle, Golgi tendon organs do not respond to a change in muscle length, but rather in muscle tension.

 

 

ipsilateral - Located on or affecting or relating to the same side of the body.  For example, many somatic reflexes, such as stretch reflexes, receive a stimulus on one side of the body and the motor response which follows is returned to muscles on the same side of the body

 

contralateral  - Located on or affecting or relating to the opposite side of the body; e.g., the crossed extensor reflex (see below).

 

reciprocal innervation - Innervation so that the contraction of a muscle or set of muscles (as of a joint) is accompanied by the simultaneous inhibition of an antagonistic muscle or set of muscles; specific reflex arcs exist so that agonists/prime movers and antagonists do not generally contract simultaneously; the Golgi or Deep Tendon Reflex is an example of reciprocal innervation.  aka reciprocal inhibition.

 

 

tendon reflex - A type of monosynaptic ipsilateral segmental stretch reflex action in which a muscle is made to contract by a blow upon its tendon, e.g., the patellar reflex, the Achilles tendon reflex, the biceps reflex; its absence is generally a sign of disease.

 

flexor reflex = withdrawal reflex - A type of protective polysynaptic ipsilateral segmental reflex in which a painful stimulus triggers the contraction of ipsilateral flexor muscles (and the ipsilateral extensors are inhibited) which takes the limb or structure away from source of the pain; these reflexes have a slower onset and a longer response than the stretch (extensor) reflexes.

 

 

intersegmental reflex arc - A polysynaptic neuron pathway which  involves sensory impulses being received in one segment of the spinal cord and then stimulating interneurons which route the sensory information to motor neurons in both superior and inferior segments of the spinal cord in order to permit innervation of a variety of muscles in the reflex action.

 

crossed extensor reflex - A polysynaptic contralateral segmental reflex that is usually associated with the same painful stimulus which triggered a flexor/withdrawal reflex; in the crossed extensor reflex, the contralateral extensors contract (and the ipsilateral flexors are inhibited) which tends to adjust for any shift in the center of gravity so that balance is maintained and body weight is properly supported.

 

patellar (knee jerk) reflex - A monosynaptic ipsilateral segmental stretch reflex,  resulting from a sharp tap on the patellar tendon, in which proprioceptive sensory information from muscle spindles in the quadriceps muscles of the thigh are routed to the appropriate spinal segments where motor impulses to the quadriceps muscle of the thigh cause a reflex extension of the leg.

 

 

Achilles (ankle jerk) reflex - A monosynaptic ipsilateral segmental stretch reflex in which a reflex plantar flexion (downward movement) of the foot is produced by a spasmodic contraction of the gastrocnemius and soleus muscles of the calf in response to sudden extension of the leg or the striking of the Achilles' tendon above the heel.

 

 

Babinski sign or reflex = plantar reflex - A ipsilateral segmental reflex in which there is extension upward of the toes and the abduction of the toes when the sole of the foot is stroked firmly on the outer side from the heel to the front; normal in infants under the age of 2 years but a sign of brain or spinal cord injury or disease in older persons.

 
normal in infants pathological in adults

 

abdominal reflex - The reflex ipsilateral contraction or quivering of the muscles of the abdominal wall and deviation of the umbilicus towards the stimulus in response to stimulation of the overlying skin; babies do not exhibit the abdominal reflex until about 6 months; absence of abdominal reflex is one of the "classic" criteria used in diagnosing MS.

List

2. four different reflex arcs and indicate if they are: reciprocally innervated (inhibition or activation), ipsilateral or contralateral, segmental or intersegmental.

 

Reflex Reciprocally Innervated (Inhibition or Activation) Ipsilateral or Contralateral Segmental or Intersegmental
Patellar Tendon (stretch) inhibition ipsilateral segmental
Achilles Tendon (stretch) inhibition ipsilateral segmental
Golgi Tendon activation ipsilateral segmental
Flexor inhibition ipsilateral segmental
Crossed Extensor inhibition contralateral segmental
Pupillary inhibition ipsilateral and contralateral n/a

 

 

Explain:

2.  The purpose of detecting and reporting proprioceptive sensory information to the CNS, and how the organization of this information takes place.

         Proprioception is the unconscious perception of movement, position, location and spatial orientation of the body and its parts arising from stimuli within the body itself.  There are various specific mechanoreceptors which respond to the stretching of a muscle, a tendon, or a ligament or respond to the movement of special structures in the inner ear.   The mechanism is involved in the automatic and largely unconscious self-regulation and coordination of postural and other muscular movements.  Proprioceptive sensations trigger reflexes which may protect body parts from injury as well.