Practice Questions on Chapter 13 [There is some repetition of questions]
1. Describe the structure of a GTO. Draw and describe reflex connections of 1b
afferents. [~ 1 page of total writing + figures; make sure of the connections in the spinal
cord--what is in the intermediate zone and what is in the ventral horn]
GTO is located at junction between extrafusal fibers, and muscle tendon. It consists of
interwoven collagen fibers. It is innervated by a 1b afferent that becomes unmyelinated
once it enters the GTO capsule. • As the muscle is contracted, the 1b afferent in the GTO is activated.
• Action potential is sent to the spinal cord via the dorsal root.
• It bifurcates. One pathway goes up via the dorsal column to the medulla
ipsilaterally and synapses; then travels contralaterally and synapses in the Ventro-
Posterior Lateral nucleus of the Thalamus. Third order neuron goes from VPL of
Thalamus to Areas 3, 2, 1 of the primary somatosensory cortex.
• The second pathway travels into the gray matter of the spinal cord and divides in
the intermediate area. At least one branch will excite an antagonist muscle, while
others will inhibit agonist muscles. Interneurons for these connections are in the
intermediate region, but motoneurons they eventually synapse with will be
located in the ventral horn. 2. Draw and describe the ascending connections of 1a and Ib afferents [< 0.3 page of
wring + a figure]
Pretty much the same?? 3. Compare/contrast the ipsilateral spinal reflex connections from 1a, 1b and pain
afferents. [~ 1 page of writing + three detailed figures.]
Ipsilateral connections from Ia and Ib:
• Ia or II Spindle afferents make monosynaptic connections for agonists that are to
• For both Ia and Ib, motoneurons only lead to muscles on the same side of body
(right or left) from where the afferent originates from
• Ascends ipsilaterally to the medulla, and the cross-over is between the medulla
• Multiple interneurons in the gray matter for both excitation pathways, and
• Flexors are activated, and extensors inhibited for ipsilateral efferents. Flexors
inhibited and extensors excited for contralateral efferents (side where afferent
comes from pulls away, while the other side stiffens) • Ascends to the Thalamus contralaterally.
• No synapse in the medulla
• Everything else pretty much the same!
4. Describe flexor reflex and crossed extensor reflex for pain afferents from my left hand.
[~1 page of writing + one figure].
Afferent signal goes to spinal cord and synapses multiple times in intermediate zone.
Then it diverges, and on the ipsilateral side, it excites flexors, and inhibits extensors. A
divergence travels to the contralateral side and excites extensors, and inhibits flexors in
the right hand. The afferent then leaves the spinal cord via the ventral horn and ascends to
thalamus and then Primary Somatosensory cortex (areas 3, 1, 2)
5. Draw and describe the ascending connections from the hand to SI for group I, II, III &
IV afferents [1 figure, and ~ half a page of writing] [ 20 minutes]
6. Define homunculus (sensory and motor). [1-2 sentences]
Sensory homunculus: Visual representation of your S1 on different areas that receive
sensory information in disproportionate amounts. Areas where that are more sensitive
have larger representation in the sensory homunculus. This is a representation of humans
Motor homunculus: Visual representation of Area 4 of disproportionate amounts of fine
control of the body’s muscles. Muscles involved in more precise movements have greater
representation in the Motor Homunculus. This is a representation of humans
7. What is somatotopic representation in the cortex for somatic afferents and efferents?
Where in the cortex are they located? Why does your brain see you in a distorted
manner? [ half a page + an approximate figure]
Somatotopic representation in the cortex for somatic afferents and efferents means that
adjacent parts of the body are adjacent in their representation in their respective cortexes.
Somatic afferents are located in