Spinal Cord and the Somatic Motor System-Lecture 13 & 14 Exam 3

Question 1

Divisions/Segments of the Spinal Cord

Answer 1

-Cervical (C1 – C8)
-Thoracic (T1 – T12)
-Lumbar (L1 – L5)
-Sacral (S1 – S5)

Question 2

Cross-Sectional Spinal Cord Anatomy

Answer 2

White Matter & Gray Matter

Question 3

Dorsal/Posterior Horn

Answer 3

-Somatic sensory (afferent) neurons travel through the spinal nerve then through the dorsal/posterior root & synapse in the dorsal horn
-Carry sensory information from the body to the spinal cord

Question 4

Dorsal/Posterior Root Ganglia

Answer 4

Contains sensory neuron cell bodies

Question 5

Ventral/Anterior Horn

Answer 5

-Contains somatic motor neuron cell bodies
-Somatic motor (efferent) axons travel through the ventral root then
through the spinal nerve to skeletal muscles
-Transmit voluntary motor information from spinal cord to skeletal muscles

Question 6

Dorsal Root

Answer 6

Above & diagonal of ventral root

Question 7

Ventral Root

Answer 7

Below & diagonal of dorsal root

Question 8

Spinal Nerve

Answer 8

Where dorsal root and ventral root come close to contact heading towards somatic neurons

Question 9

Lateral Corticospinal Tract (descending)

Answer 9

Voluntary motor control of skeletal muscles

Question 10

Lateral Spinothalamic Tract (ascending)

Answer 10

Sensory info about pain & temperature

Question 11

Ventral Spinothalamic Tract (ascending)

Answer 11

Sensory info about touch

Question 12

White Matter (outer portion)

Answer 12

Myelinated axons (fiber tracts)

Question 13

Gray Matter (inner portion)

Answer 13

-Neuron cell bodies, unmyelinated axons, axon terminals
-Dorsal (posterior) horn: sensory neuron axon terminals
-Ventral (anterior) horn: motor neuron cell bodies
-Lateral horn: (between T1 and L2) ANS cell bodies

Question 14

Components of Neuromuscular Junction

Answer 14

-Somatic Motor Neuron
-Synaptic Cleft
-Skeletal Muscle Fiber

Question 15

Somatic Motor Neuron

Answer 15

-Presynaptic axon terminal with ACh-filled vesicles
-Cell body originates in the ventral horn of the spinal cord
-Synapses directly onto skeletal muscle (target) & releases ACh
-Axon branches at its terminal end to innervate more than one skeletal
muscle fiber

Question 16

Skeletal Muscle Fiber

Answer 16

Postsynaptic membrane (motor end plate) with nicotinic receptors

Question 17

Synaptic Cleft

Answer 17

The gap between neurons that allows chemical signals to pass between them

Question 18

Steps Involved in Ach Release & Binding to Nicotinic Receptor on the Motor Endplate to Initiate a Skeletal Muscle Contraction

Answer 18

1. A stimulus depolarizes the somatic
   motor neuron
2. Action potential arrives at the axon
   terminal causing voltage-gated Ca2+
   channels to open
3. Ca2+ entry causes synaptic vesicles to
   fuse with the membrane and release ACh into the synaptic cleft (exocytosis)
4. Two molecules of ACh bind to a nicotinic receptor on the motor end plate of the skeletal muscle fiber
5. ACh binding leads to the opening of a cation channel allowing Na+ to flow into and K+ out of the muscle fiber
   6.Na+ influx depolarizes the muscle fiber triggering muscle contraction
6. ACh is deactivated by acetylcholinesterase (AChE)

Question 19

Pharmacology of the Nervous System to Determine Agonists Molecules (direct or indirect)

Answer 19

-Direct agonists bind to target receptors and mimic the action of the NT
-Indirect agonists increase secretion, block reuptake, or block degradation of NT

Question 20

Pharmacology of the Nervous System to Determine Antagonists Molecules (direct or indirect)

Answer 20

-Direct antagonists bind to target receptors and block NT binding and action
-Indirect antagonists decrease secretion, increase reuptake, or increase degradation of NT