Gross Brain lab Flashcards
corticospinal tract
principal efferent pathway.
corticospinal tract divides into…
anterior corticospinal tract and lateral corticospinal tract
major afferent, sensory pathways
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.
location of the primary motor cortex
along the pre-central gyrus just anterior to the central sulcus.
subcentral gyrus
bridge of tissue at the inferior extent of the central sulcus, just above the lateral fissure that unites the pre and post central gyri.
paracentral lobule
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.
pyramidal cells
cells in layer 5 of the primary motor cortex, especially large so called pyramidal.
Betz cells
giant pyramidal cells located within the 5th layer of the grey matter in the primary motor cortex. largest cells in CNS.
corona radiate
funnel shaped collection of white matter fibers in the cerebrum
derivation of DRG
neural crest cells
UMN syndrome presentation
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
LMN syndrome presentation
1) muscle weakness, hypotonia, hyporeflexia, areflexia are all immediate and long-lasting 2) FLACCID PARESIS
what do alpha motor neurons located medial in the ventral grey matter (of the anterior corticospinal tract) innervate?
core muscles important for posture
What do alpha motor neurons located laterally (in lateral corticospinal tract) in the ventral grey matter innervate?
muscles important for dexterity (put dexter on top of lateral corticospinal tract)
what does the precentral gyrus contain?
contains the primary motor cortex.
what does the postcentral gyrus contain
primary somatosensory cortex
cingulate sulcus
divides cingulate gyrus from preceneus and posterior paracentral gyrus
internal capsule
separates medial caudate from lateral globus pallidus. corticospinal tract constitutes a large part of the internal capsule.
upper motor neurons
neurons that go from cortex to spinal cord
lower motor neurons
motor neurons that travel from spinal cord to muscle
where do lateral corticospinal tract neurons in the spine originate?
contralateral motor cortex.
what is spinal shock?
initial damage to UMN, results in denervation of LMN and consequent loss of reflex arch
What is hyperreflexia?
following spinal shock, the reflex remerges after a couple days but in an exaggerated fashion (possynaptic neurons sends out more receptors on its surface).
What does spasticity indicate?
UMN injury
what do fasciculations indicate?
LMN injury
spastic paresis
term describing long term result of UMN injury
LMN consequences
flaccid paresis: weakness, hypotonia, areflexia
alpha motor neurons in the lateral grey matter innervate
distal muscles
alpha motor neurons in the medial grey matter innervate
core muscles impt for posture.
where do you start to see fasciculus cuneatus
above T6
location of primary motor cortex
precentral gyrus
location of primary somatosensory cortex
postcentral gyrus
what separates the frontal lobe from the parietal lobe
central sulcus
what separates the temporal lobe from the frontal and parietal lobes?
lateral sulcus
what forms the boundary between the parietal and occipital lobe?
imaginary line from parietooccipital sulcus to parietooccipital notch in the lateral aspect of the brain
where is primary visual cortex located?
calcarine sulcus
function of the anterior commisure
carries axons that connect the temporal lobe on one side with its counterpart on the other.
function of fornix?
axon tract in limbic system involved in memory formation and retrieval carrying info from hippocampus to hypothalamus.
midbrain consists of…
cerebral peduncles, superior + inferior colliculi, cerebral aqueduct, and some other structures
Where does conus medullaris lie in adult?
T12-L1
draw the anatomy of the corticospinal tract
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)
draw the anatomical pathway for relaying discriminative touch, vibration sense, and joint position sense (PCML)
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
understand the anatomical pathway for relaying pain and temperature sensation
(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.
explain the reason for dissociated sensory loss encountered in a Brown-Sequard syndrome
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.
What are the rules for determining level of spinal cord
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)
what is the ventral striatum?
this is where CAUDATE and PUTAMEN remain connected and striations are found within the internal capsule where separation is incomplete.
how many neurons does the corticospinal tract consist of?
2, upper and lower motor neurons
Explain the myotatic reflex
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.
what is the clinical significance of the ACS tract bilateral innervation of motor neurons?
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.
