Lecture 35: Major Neuroanatomical Pathways II

Question 1

Peripheral receptors encode somatosensory information through what type of neurons

Answer 1

Pseudounipolar neurons

Question 2

Where are the cell bodies of pseudounipolar neurons located

Answer 2

Dorsal root ganglia

Question 3

Axons of pseudounipolr neurons have ___ and ___ parts or branches

Answer 3

Local (reflex) and ascending branches (all the way to brain)

Question 4

Peripheral receptors are distributed throughout the ___ and ___

Answer 4

Dermis and epidermis

Question 5

What are local circuits

Answer 5

Paths of local control in spinal cord

Sensory neuron—> interneuron—> motor neuron

Question 6

What are central pathways

Answer 6

Axon tracts to and from the brain that carry motor commands or sensory information

Question 7

What are sensory tracts

Answer 7

Carry information on stimuli ascending to the brainstem and cortex

Question 8

What are motor tracts

Answer 8

Leave the cortex and descend through the spinal cord carrying motor commands

Question 9

Are reflexes an example of a central pathway or local circuits

Answer 9

Local circuits

Question 10

What are two somatosensory pathways

Answer 10

1. Dorsal column/ medial lemniscal system
2. Anterolateral system/spinothalamic tract

Question 11

What is the dorsal colum/medial lemniscal system

Answer 11

Senses tactile (touch) and conscious proprioception

Question 12

Where do the axons cross in the dorsal column/medial lemniscal pathway

Answer 12

Axons traveling towards the thalamus cross to the contralateral side in the medulla

Question 13

What is the anterolateral system/spinothalamic tract

Answer 13

Senses pain, itch, temperature, non-conscious proprioception, unpleasant sensations

Question 14

Where do axons cross in anterolateral system/spinothalamic tract

Answer 14

Axons cross to contralateral side of spinal cord at the level of entry before changing direction and ascending toward thalamus

Question 15

What are muscle spindle sensory receptors

Answer 15

Encapsulated intramural fibers with both sensory and motor innervation that are distributed throughout the muscle

Continuously detect tension and changes in length within the muscle itself

Question 16

What are golgi tendon organs

Answer 16

Detect tension within tendons (produced by muscle contraction) when nerve fibers intertwined with collagen fibrils fold and touch

Question 17

Where do muscle spindle receptors and golgi tendon organs send stretch information to

Answer 17

Dorsal horn of the spinal cord along pseudounipolar neurons

Question 18

What is the motor unit

Answer 18

One LMN and the skeletal muscle fibers it innervates

Question 19

Where do lower motor neurons originate

Answer 19

Brainstem and spinal cord

Question 20

Local circuits are composed of neurons located at each ____

Answer 20

Spinal cord level

Question 21

Are motor neuron cell bodies located in ventral or dorsal horn

Answer 21

Ventral

Question 22

What is the sequence of patellar reflex

Answer 22

1. Patellar tendon hit which stretches the tendon and increases tension within the quadriceps muscle
   2-3. Stretch sensory signal sent as action potential along pseudounipolar neuron to Dorsal horn
2. Synapse on LMN in ventral horn
3. Axons carry action potential to quadriceps
4. Synapse at motor endplates—quadriceps contract, lower leg extends stifle joint

Question 23

What is the role of inhibitory interneurons

Answer 23

Inhibit LMNs that innervate antagonist muscle of stretched muscle which inhibits muscle contraction

Question 24

In order to maintain correct muscle tension to maintain posture against gravity if you contract quadriceps to prevent joint collapse what muscle must be inhibited by inhibitory interneuron

Answer 24

Bicep femoris

Question 25

Describe the flexor reflex- withdrawal reflex from a negative stimulus

Answer 25

1. Painful stimulus encountered
2. Excitatory interneurons excite LMN that innervate ipsilateral flexor muscles
3. Inhibitory interneurons inhibit LMN’s that innervate ipsilateral extensor Muscles

Question 26

Describe the Postural Reflex

Answer 26

When tested or affected limb is raised the contralateral limb will extend

Question 27

Describe ipsilateral and contralateral flexion and extension during withdrawal reflex

Answer 27

Excitatory neurons on ipsilateral side will innervate flexor muscles to remove limb from stimulus. While sending inhibitory neurons to ipsilateral extensors

Excitatory neurons on contralateral side will innervate extensor muscles to support flexed contralateral limb