(06) Spinal Reflexes & Neuronal Integration

Question 1

_____ = an inherent, subconscious, relatively consistent responses to a particular stimulation.

_____ = an inherent, subconscious, relatively consistent responses to a particular stimulation, involving the cerebellum and cerebral cortex; e.g., hopping reaction & tactile placing reaction.

Examples of spinal reflexes, involving spinal nerves and the spinal cord, include:
—_____: limb flexes to withdraw from a noxious stimulus
— _____: muscle stretch is resisted by reflex contraction of the muscle
— _____: pricking skin triggers contraction of cutaneus trunci (panniculus) m.

Answer 1

• Reflex
• Reaction
• withdrawal reflex
• myotatic reflex
• panniculus reflex

Question 2

Reflex responses are determined by _____ which “hard-wire” _____ to _____. Interneurons organize efferent neurons (motor units) into meaningful movement components, which can be utilized by either_____ or _____.

Also, interneurons form _____ for _____ movements. Locomotor pattern generators exist in the _____ (e.g., on a treadmill, hind limbs exhibit stepping even in a cat that has its spinal cord transected in the thoracic region, i.e., isolated from the brain).

Since “_____” and “_____” compete for control of the same _____, they cannot be _____ of one another. Thus, brain activity will influence _____ responses, introducing variation and making clinical reflex evaluation an interpretive art.

Answer 2

• interneurons, afferent input, efferent output, spinal input, descending pathways
• pattern generators, repetitive, spinal cord
• voluntary movement, involuntary reflex/reaction, interneurons circuits, independent, spinal reflex

Question 3

(Withdrawal Reflex = Flexor (Crossed Extensor) Reflex)

— _____(1) participates in both _____ (2) and _____ (3);

— divergent _____ propagates to several segments and _____ (B);

— _____ feedback prolongs the _____ beyond the time of the _____ (A);

— individual interneurons are either _____ or _____ (black cells) in their effect;

— antagonists are _____ while agonists are_____ (_____ innervation) (D);

— _____ pathways (C) modify _____ (reflex is not independent of brain control).

Answer 3

• primary afferent neuron, reflexes, ascending pathways
• interneuronal circuit, right and left sides
• positive, reflex, stimulus
• excitatory, inhibitory
• inhibited, excited, reciprocal
• descending, reflex circuit

Question 4

NOTE:

• As the reflex is tested clinically, the crossed extension component disappears after the first _____ weeks of age because _____ pathways _____ and _____ extension. But, later in life, the normally inhibited crossed extension reappears if “_____” damage to _____ fibers removes the inhibition (crossed extension is _____).
• The withdrawal reflex is often elicited to assess _____ (the more synapses a reflex has, the more vulnerable it is to _____).

Answer 4

• 3, descending, mature, inhibit, upstream, descending, abnormal
• depth of anesthesia, suppression by anesthesia

Question 5

(BACKGROUND INFORMATION ABOUT PROPRIOCEPTION)

Proprioceptors are _____, located in _____ & joint _____. Proprioceptors provide:

• _____ about the status of muscles & joints,
• _____ (sense of position & movement), and
• _____

Muscle & tendon proprioceptors:

free nerve endings: ___

(Golgi) _____ organs: located in series with _____ (tension detector) muscle spindles: located in _____ (length detector)

Answer 5

• mechanoreceptors, muscles/tendons, capsules/ligaments
• subconscious feedback
• conscious kinesthesia
• pain
• pain
• tendon, muscle fibers, muscle belly

Question 6

III. Muscle Spindle:

A. Muscle spindles are:

• elaborate _____ positioned in
_____ with muscle fibers;

• designed to signal _____
• about _____ long & _____ wide.

Morphologically, a muscle spindle consists
of a connective tissue capsule enclosing:

— two kinds of _____,

— two kinds of _____ muscle fibers,

— two kinds of _____ neurons.

B. Intrafusal muscle fibers:
(vs. typical extrafusal muscle fibers)

• very small, anchored in _____
• do not contribute at all to _____
• center of each fiber is packed with ____ & lacks _____
• polar regions are _____ and innervated by _____
• two kinds of ____:

nuclear bag fibers — central region is
_____; fiber extends beyond the _____;

nuclear chain fibers — smaller, central
region contains _____.

C. Mechanoreceptors within muscle spindle :

They are activated by stretch of the _____, which is stretched either

1) by contraction of _____ of intrafusal muscle fibers, or
2) by passive stretch of the _____ (including the intrafusal fibers)

Answer 6

(A)

• proprioceptors, parallel
• muscle length
• 3mm, 0.5 mm
• mechanoreceptors
• intrafusal
• gamma efferent

(B)

• endomysium
• whole muscle tension
• nuclei, myofilaments
• striated, gamma neurons
• intrafusal muscle fibers
• dilated, capsule
• chain of nuclei

(C)

• central region
• polar regions
• whole muscle

Question 7

There are two types of mechanoreceptors:

1] primary (_____) endings —
— spiral around _____ (nuclear) regions;
— endings of large nerve fibers (type __);
— initially _____ reflects rate of stretch;
— then steady _____ reflects degree of
stretch

2] secondary endings —
— _____” formations adjacent to _____;
— endings of _____ nerve fibers;
— AP frequency is _____ to degree
of stretch.

Answer 7

• annulospiral, central, IA, AP frequency, AP frequency
• “flower-spray, nuclear chain regions, type II, proportional

Question 8

IV. Myotatic Reflex:
Clinically, a myotatic reflex is elicited by abruptly tapping a _____ (e.g., the patellar tendon). Suddenly deforming/displacing a tendon effectively _____ the associated muscle.

When a whole muscle is suddenly stretched (as a result of _____), _____ receptors in muscle _____ are simultaneously excited, triggering a volley of _____ in __ afferent axons. Within the CNS, the axons activate excitatory synapses on _____ that innervate the muscle that was stretched. Also, alpha motor neurons to antagonistic muscles are inhibited via _____. As a result, the stretched muscle immediately _____.

Thus, the myotatic reflex functions to _____ muscle stretch. Since _____ are by passed in eliciting the contraction, the response is rapid, localized, and relatively resistant to hypoxia, fatigue, drugs, etc.

Answer 8

• tendon, stretches
• tendon deformation, annulospiral, spindles, action potentials, IA, alpha motor neurons, interneurons, contracts
• oppose, interneurons