Lecture 2.1 10/9

Question 1

What are the 3 main somatosensory and motor pathways? List what each does

Answer 1

1) Lateral corticospinal tract: Motor
2) Anterolateral columns: Sensory; pain, temperature and crude touch
3) Posterolateral columns: Sensory; vibration, fine touch, proprioception

Question 2

Where are the primary motor and somatosensory cortexes?

Answer 2

On either side of the central sulcus; primary motor is precentral and primary somatosensory is postcentral.

Question 3

1) What do adjacent regions on the cortex correspond with?
2) What is this somatotopic organization of the cortex called?

Answer 3

1) Adjacent lesions on the body surface.
2) Homunculus

Question 4

1) What makes up the spinal cord?
2) What are its two areas of enlargement? What do they give rise to?

Answer 4

1) Butterfly shaped central gray matter, surrounded by ascending and descending white matter columns
2) Cervical and lumbosacral enlargements; give rise to the nerve plexuses for the arms and legs (most nerves here)

Question 5

1) What does the white matter of the spinal cord contain
2) Where is the spinal cord the thickest?

Answer 5

1) White matter columns contain the dorsal, lateral and anterior columns
2) In the cervicothoracic area

Question 6

1) What form the anterior spinal artery? Where is it? What does it supply?
2) What form the posterior spinal arteries? What do they supply?
3) What else is involved in forming the anterior and posterior spinal arteries?

Answer 6

1) Vertebral arteries; runs along ventral surface; supplies most of the cord
2) Vertebral arteries; supply the dorsal surface of the cord
3) Radicular arteries

Question 7

Where is venous return for the spinal cord?

Answer 7

The epidural space

Question 8

1) How are the descending motor pathways of the spine divided?
2) What is the most important descending motor pathway of the nervous system? What does it do?

Answer 8

1) Into medial and lateral motor systems
2) Lateral corticospinal tract; controls the movement of extremities

Question 9

1) What can lesions of the lateral corticospinal tract cause?
2) Where does it start? Where does it cross over?

Answer 9

1) Dramatic deficits depending on level of lesion
2) Starts in the precentral gyrus travels down through spinal cord, but crosses at the level of medulla and spinal cord junction (pyramidal decussation)

Question 10

Define pyramidal decussation. What percent of the corticospinal tract is involved?

Answer 10

~85% of corticospinal tract crosses over to the lateral white matter spinal cord at medulla/spinal cord junction at level of foramen magnum and forms the lateral corticospinal tracts

Question 11

1) Where is pyramidal decussation?
2) What percent of the corticospinal tracts are not involved in this? Where do they go and what do they form?

Answer 11

1) At medulla/spinal cord junction
2) ~15% continue into the spinal cord ipsilaterally without crossing and enter the anterior white columns to form the anterior corticospinal tract

Question 12

1) What is the internal capsule? What is it made of?
2) What does it appear as? Where is it? Where does it go?

Answer 12

1) 2 internal structures (made of compacted nerve fibers) in the brain with 3 sections/ limbs
2) Appear as “V”s pointing inward surrounding the thalamus that continues into the midbrain

Question 13

1) Where is the corticospinal tract in the brain?
2) What can a lesion or stroke of the internal capsule cause? Why?

Answer 13

1) In the posterior limb of the internal capsule
2) because these fibers are so compact, a lesion/stroke of internal capsule can cause weakness of the entire contralateral side of the body from face to lower extremity

Question 14

Where may a lesion occur in the brain if it causes weakness of the entire contralateral side of the body from face to lower extremity? Why?

Answer 14

Internal capsule; because its fibers are so compact

Question 15

1) What does the ANS control?
2) What kind of pathways does it have?
3) What are its divisions?
4) What do its two divisions use?

Answer 15

1) Automatic and visceral body functions
2) Only efferent pathways
3) Sympathetic and parasympathetic
4) Each of the two divisions uses different neurotransmitters

Question 16

1) Where on the spinal cord does the sympathetic nervous system arise from?
2) What kind of functions does it control? Give 4 examples

Answer 16

1) Thoracolumbar division; arises fromT1-L2 or T2-L3
2) “Fight or flight” functions such as increasing heart rate, BP and pupil size, and bronchodilation

Question 17

1) Where on the spinal cord does the parasympathetic nervous system arise from?
2) What kind of functions does it control? Give 3 examples

Answer 17

1) Craniosacral arises from nuclei between S2-S4
2) “Rest and digest”: increase gastric secretions and peristalsis, slow down HR, and decrease pupil size

Question 18

1) What do sympathetic neurons release to their target organs?
2) What do parasympathetic neurons release?

Answer 18

1) Sympathetic: release norepinephrine to the end organs
2) Parasympathetic: release acetylcholine

Question 19

What 3 things control the sympathetic and parasympathetic nervous systems?

Answer 19

Hypothalamus, brainstem nuclei, and the amygdala

Question 20

What are the two main somatosensory pathways?
Where are they?

Answer 20

1) One posterior column-medial leminiscal system
2) Two anterolateral systems (includes spinothalamic tract)
-They’re 2 additional “long tracks” in the spinal cord

Question 21

What is the third long track of the spinal cord?

Answer 21

Corticospinal tract

Question 22

1) What 3 things does the Posterior column-medial leminiscal pathway convey?
2) Where does it decussate?
3) Where does the medial lemeniscal pathway go?

Answer 22

1) Proprioception, vibration sense, and fine touch
2) In lower medulla
3) Ascends to the brainstem, thalamus, internal capsule and on to the somatosensory cortex

Question 23

1) What 3 things does the anterolateral pathway convey?
2) Where does it decussate?
3) What does it consist of?

Answer 23

1) Pain, temperature sense and crude touch
2) At anterior commissure of the spinal cord
3) 3 tracts, the best known is the spinothalamic tract

Question 24

1) What does the spinothalamic tract do?
2) Where does it relay information?
3) What would a lesion here cause?

Answer 24

1) Mediates pain and temperature sensation
2) Relays information through the thalamus to the primary somatosensory cortex.
3) A loss of pain and temperature sensation in the contralateral side below the level of the lesion.

Question 25

What type of lesion would cause a loss of pain and temperature sensation in the contralateral side below the level it occurs at?

Answer 25

A lesion in the spinothalamic tract

Question 26

1) Why is it important to treat lesions or suspected trauma/damage to the spinal cord as an emergency?
2) What is the most common cause of spinal cord lesions? What can cause this?

Answer 26

1) Spinal cord lesions affect motor, sensory and autonomic pathways and they need to be treated quickly to prevent permanent damage
2) External compression: from degenerative spinal disease, trauma or metastatic cancer

Question 27

1) What can affect the integrity of the posterior spinal cord?
2) Define posterior cord syndrome and what it causes

Answer 27

1) Vit B12 deficiency
2) Lesions (trauma, compression, multiple sclerosis) of the posterior columns; cause loss of vibration sense, and proprioception below the level of the lesion

Question 28

What type of lesion would cause loss of vibration sense, and proprioception below the level of the lesion

Answer 28

Posterior cord syndrome (lesions like trauma, compression, or multiple sclerosis of the posterior columns)

Question 29

1) What is anterior cord syndrome? What does it cause?
2) What is a common cause of this syndrome?

Answer 29

1) Damage to the anterior cord; causes loss of pain and temperature sensation below the level of the lesion
2) Anterior spinal artery infarct

Question 30

What might an anterior spinal artery infarct cause? What would that cause?

Answer 30

Anterior cord syndrome; loss of pain and temperature sensation below the level of the lesion

Question 31

1) Define dermatome
2) Why is knowing dermatomes useful?

Answer 31

1) A peripheral region innervated by sensory fibers from a single nerve root level
2) Can help you localize lesions clinically

Question 32

Give 4 examples of dermatomes

Answer 32

T4: nipple line
T10: umbilicus
C6: thumb (6 shooter)
S5: perianal

Question 33

1) What are neuropathies?
2) Where is their pathology?
3) What does it usually affect?
4) Is the damage always permanent?

Answer 33

1) A nerve disorder
2) In the axons, myelin sheath or both.
3) Usually both motor and sensory nerve fibers
4) Can be permanent or reversible.

Question 34

1) Define radiculopathy
2) What does it feel like?

Answer 34

1) Neuropathy affecting spinal nerve roots
2) Burning, tingling pain that often radiates down a limb or dermatome

Question 35

List some common causes of neuropathies

Answer 35

Diabetes, infections (Lyme disease,) HIV, varicella-zoster (shingles), toxins, malnutrition, immune disorders (Gullain-Barre) or hereditary

Question 36

1) What is cauda equina syndrome? What can it cause?
2) What can impairment of S2-S4 cause? Is it urgent?

Answer 36

1) Impaired function of nerve roots below L1-L2; sensory loss in S2-S5 is called saddle anesthesia
2) Bladder disfunction, constipation, fecal incontinence, and loss of erections; needs to be treated promptly to avoid permanent damage

Question 37

1) What is saddle anesthesia?
2) Impairment at what spinal level can cause can cause bladder disfunction, constipation, fecal incontinence and loss of erections?

Answer 37

1) Sensory loss in S2-S5 (due to cauda equina syndrome)
2) S2-S4

Question 38

1) What does the thalamus do? Where is it?
2) Why is it important?
3) What is it made of and shaped like? What is it divided into?

Answer 38

1) Processing station in the center of the brain.
2) Almost all pathways projecting into the cerebral cortex relay through here
3) Deep gray matter structures shaped like eggs divided into several groups of nuclei that have different functions

Question 39

1) What does the thalamus have connections with?
2) What does it convey?

Answer 39

1) All regions of the cerebral cortex
2) Information from other parts of the nervous system and periphery to the cortex