Gross Brain lab

Question 1

corticospinal tract

Answer 1

principal efferent pathway.

Question 2

corticospinal tract divides into…

Answer 2

anterior corticospinal tract and lateral corticospinal tract

Question 3

major afferent, sensory pathways

Answer 3

dorsal colmun/medical lemniscal system (aka posterior column/medial lemniscal system) and anterolateral system/spinothalamic tract. The dorsal column = PCML. It consists of the gracile fasciculus and cuneate fasciculus.

Question 4

location of the primary motor cortex

Answer 4

along the pre-central gyrus just anterior to the central sulcus.

Question 5

subcentral gyrus

Answer 5

bridge of tissue at the inferior extent of the central sulcus, just above the lateral fissure that unites the pre and post central gyri.

Question 6

paracentral lobule

Answer 6

contains both primary somatosensory cortex and primary motor cortex of which both habor somatotropy corresponding to the lower extremity. If you were to trace you’re fingure of the central sulcus, the flat patch where it ends is the paracentral lobule. At this point there’s no longer an anatomical boundary between motor and sensory areas of the cortex. How to find it from medial view of half cortex: find corpus collosum, and then you’ll see the cingulate gyrus that parallels the corpus collosum, just outside of that is the cingulate sulcus, follow the cingulate sulcus, this will have a ramus that curves up into the cortex, in front of that is the paracentral lobule.

Question 7

pyramidal cells

Answer 7

cells in layer 5 of the primary motor cortex, especially large so called pyramidal.

Question 8

Betz cells

Answer 8

giant pyramidal cells located within the 5th layer of the grey matter in the primary motor cortex. largest cells in CNS.

Question 9

corona radiate

Answer 9

funnel shaped collection of white matter fibers in the cerebrum

Question 10

derivation of DRG

Answer 10

neural crest cells

Question 11

UMN syndrome presentation

Answer 11

1) immediate muscle weakness and hypotonia, hyporeflexia or areflexia 2) spasticity and HYPERreflexia in days to weeks (including extensor plantar response: Babinski) 3) SPASTIC PARESIS

Question 12

LMN syndrome presentation

Answer 12

1) muscle weakness, hypotonia, hyporeflexia, areflexia are all immediate and long-lasting 2) FLACCID PARESIS

Question 13

what do alpha motor neurons located medial in the ventral grey matter (of the anterior corticospinal tract) innervate?

Answer 13

core muscles important for posture

Question 14

What do alpha motor neurons located laterally (in lateral corticospinal tract) in the ventral grey matter innervate?

Answer 14

muscles important for dexterity (put dexter on top of lateral corticospinal tract)

Question 15

what does the precentral gyrus contain?

Answer 15

contains the primary motor cortex.

Question 16

what does the postcentral gyrus contain

Answer 16

primary somatosensory cortex

Question 17

cingulate sulcus

Answer 17

divides cingulate gyrus from preceneus and posterior paracentral gyrus

Question 18

internal capsule

Answer 18

separates medial caudate from lateral globus pallidus. corticospinal tract constitutes a large part of the internal capsule.

Question 19

upper motor neurons

Answer 19

neurons that go from cortex to spinal cord

Question 20

lower motor neurons

Answer 20

motor neurons that travel from spinal cord to muscle

Question 21

where do lateral corticospinal tract neurons in the spine originate?

Answer 21

contralateral motor cortex.

Question 22

what is spinal shock?

Answer 22

initial damage to UMN, results in denervation of LMN and consequent loss of reflex arch

Question 23

What is hyperreflexia?

Answer 23

following spinal shock, the reflex remerges after a couple days but in an exaggerated fashion (possynaptic neurons sends out more receptors on its surface).

Question 24

What does spasticity indicate?

Answer 24

UMN injury

Question 25

what do fasciculations indicate?

Answer 25

LMN injury

Question 26

spastic paresis

Answer 26

term describing long term result of UMN injury

Question 27

LMN consequences

Answer 27

flaccid paresis: weakness, hypotonia, areflexia

Question 28

alpha motor neurons in the lateral grey matter innervate

Answer 28

distal muscles

Question 29

alpha motor neurons in the medial grey matter innervate

Answer 29

core muscles impt for posture.

Question 30

where do you start to see fasciculus cuneatus

Answer 30

above T6

Question 31

location of primary motor cortex

Answer 31

precentral gyrus

Question 32

location of primary somatosensory cortex

Answer 32

postcentral gyrus

Question 33

what separates the frontal lobe from the parietal lobe

Answer 33

central sulcus

Question 34

what separates the temporal lobe from the frontal and parietal lobes?

Answer 34

lateral sulcus

Question 35

what forms the boundary between the parietal and occipital lobe?

Answer 35

imaginary line from parietooccipital sulcus to parietooccipital notch in the lateral aspect of the brain

Question 36

where is primary visual cortex located?

Answer 36

calcarine sulcus

Question 37

function of the anterior commisure

Answer 37

carries axons that connect the temporal lobe on one side with its counterpart on the other.

Question 38

function of fornix?

Answer 38

axon tract in limbic system involved in memory formation and retrieval carrying info from hippocampus to hypothalamus.

Question 39

midbrain consists of…

Answer 39

cerebral peduncles, superior + inferior colliculi, cerebral aqueduct, and some other structures

Question 40

Where does conus medullaris lie in adult?

Answer 40

T12-L1

Question 41

draw the anatomy of the corticospinal tract

Answer 41

3rd neuron: fibers start in cortex and funnel in structure known as corona radiata –> split components of basal ganglia and are called internal capsule –> enter midbrain, where they form a stalk-like white matter bundle called the crus cerebri (also known as cerebral peduncle) –> continue through pons –> reemerge on ventral surface of medulla as the pyramid –> continue their caudal descent in the spinal cord until they reach a second neuron (alpha motor neuron)

Question 42

draw the anatomical pathway for relaying discriminative touch, vibration sense, and joint position sense (PCML)

Answer 42

1st neuron: detects sensation in dermis of skin –> travels to soma in DRG –> travels into posterior horn and UP posterior column –> at the level of the MEDULLA axons synapse with neurons in the gracile nucleus and cuneate nucleus 2nd neuron: start in nucleus gracilis and nucleus cuneatus –> cross over to form medial lemniscus –> travel up rest of brainstem and then synapse at thalamus 3rd neuron: starts in thalamus –> travels up posterior limb of internal capsule –> axons synapse in primary sensory cortex

Question 43

understand the anatomical pathway for relaying pain and temperature sensation

Answer 43

(anterolateral system/lateral spinothalamic tract) primary afferent (with cell body in DRG) enters spinal segment through a dorsal rootlet, where it may ascend or descend in a small band of white matter near the dorsal root entry zone called Lissauer’s fasciculus –> axon then terminates on a second neuron in substantia gelatinosa –> second neuron projects its axon across the midline via the ventral white commisure –> ascends in spinal column until it reaches third order neuron in VPL thalamus –> third neuron innervates somatosensory cortex.

Question 44

explain the reason for dissociated sensory loss encountered in a Brown-Sequard syndrome

Answer 44

loss of vibration sense/proprioception on IPSILATERAL side due to PCML tract injury (fibers travel up spinal cord before decussating) AND CONTRALATERAL loss of pain and temperature sensation. due to ALS injury (second neuron fibers immediately decussate). Weakness (corticospinal tract damage) is IPSILATERAL.

Question 45

What are the rules for determining level of spinal cord

Answer 45

1) presence of fasciculus cuneatus (indicates you’re above T6) 2) density of grey matter in the anterior horn (means you’re in cervical or lumbar enlargement) 3) present of lateral horn (T1-L2)

Question 46

what is the ventral striatum?

Answer 46

this is where CAUDATE and PUTAMEN remain connected and striations are found within the internal capsule where separation is incomplete.

Question 47

how many neurons does the corticospinal tract consist of?

Answer 47

2, upper and lower motor neurons

Question 48

Explain the myotatic reflex

Answer 48

muscle spindle/stretch receptors axons enter the spinal cord via dorsal rootlets. They ascend in a column of white matter but before they do so, they give off a branch that directly innervates alpha motor neurons in the ventral grey matter.

Question 49

what is the clinical significance of the ACS tract bilateral innervation of motor neurons?

Answer 49

damage to one hemisphere may affect contralateral muscles for dexterity, but the core muscles will remain innervated because ACS fibers from intact hemisphere innervate these LMNs bilaterally.