RF, Hypothalamus, Limbic And Olfactory Systems

Question 1

What contains the principal discharge pathways for olfactory/limbic systems and hypothalamus? It plays an important role as a mediator of somatic and visceral motor components of autonomic, emotional, and behavioral responses

Answer 1

Reticular formation

Question 2

Describe the ascending reticular activating system (ARAS)

Answer 2

Consists of sensory and motor reticular nuclei along with corticoreticular and reticulocortical pathways
Important in sleep, arousal, alertness, and attention
Projects to widespread area of cerebral cortex via intralaminar reticular nuclie, which play integral role in energizing cortex

Question 3

What is the rubrospinal tract (RST)?

Answer 3

Part of corticorubrospinal pathway that functions as the principal descending pathway of extrapyramidal system
Initially descends from premotor cortex to red nucleus
Involved with lateral corticospinal tract for fine manipulative and independent movements of digits of hands and feet (fractionation of movement)

Question 4

What is the medial reticulospinal tract?

Answer 4

Part of corticoreticulospinal pathway from premotor cortex
Involved in nonvolitional movements of axial and proximal limb musculature associated with posture and locomotion
Medial pontine reticular nuclei

Question 5

What is the lateral reticulospinal tract?

Answer 5

Part of corticoreticulospinal pathway from premotor cortex
Involved in nonvolitional movements of axial and proximal limb musculature associated with posture and locomotion
Links hypothalamus to visceral nuclei of lower brainstem and spinal cord
Medullary reticular nucleus

Question 6

What is the effector (via reticular pathways) of various visceral and somatic motor responses associated with emotional behavior?

Answer 6

Hypothalamus

Question 7

Describe Korsakoff’s Syndrome (Wernicke’s encephalopathy)

Answer 7

Results from bilateral destruction of mammillary bodies and dorsal medial nucleus of thalamus
May be a sequela of long-term chronic alcoholism or pituitary tumors (for tumors, bitemporal hemianopsia is usually present)
Primary deficit is impairment of recent memory

Question 8

What makes up the entorhinal cortex? What does it do?

Answer 8

Uncus and rostral parahippocampus
Chief input to hippocampus and acts as a critical integrator and mediator of information to hippocampus
Important link in Papez memory circuit
Neocortical representation of external sensory world and person’s memory seem to merge here

Question 9

What does the amygdala do?

Answer 9

Pivotal information processing center for olfactory, somatosensory, viscerosensory, and emotional expressions
Projects to hypothalamus and septal areas

Question 10

What does the septal area refer to?

Answer 10

Collective term encompassing septum pellucidum, cortical areas inferior to rostrum of corpus callosum and anterior to lamina terminalis and associated underlying nuclei
Receives fibers from medial olfactory stira, amygdala via stria terminalis, and hippocampus vis fornix

Question 11

What does the Papez circuit do?

Answer 11

Plays a critical role in storage and retrieval of recent memory

Question 12

Describe the fornix

Answer 12

Large fiber bundle that descends toward hypothalamus and septal area
It is split by anterior commissure into precommissural (terminate in septal area and hypothalamus) and postcommissural (terminate in mammillary body as part of Papez circuit) fibers

Question 13

What does the cingulum connect?

Answer 13

Septal area, cingulate gyrus, parahippocampus

Question 14

What are characteristics of prefrontal syndrome?

Answer 14

Apathy, indifference, alterations in mood, inability to predict consequences of own behavior

Question 15

Describe hippocampal amnesia

Answer 15

Due to bilatearl lesions of hippocampi
Can be due to herpes
Pyramidal cells of CA1 region of hippocampus (Sommer’s sector) are vulnerable to hypoxic or ischemic injury
Axons of these neurons form fornix and also send recurrent collaterals to entorhinal cortex

Question 16

Describe olfactory hallucinations

Answer 16

Imaginary disagreeable odor, movements of lips and tongue, and a dreamy state of consciousness
Sensations may be mildly pleasant or curious
Odors (hallucinations) may disturb individual and disrupt activities like sleep

Question 17

Describe uncal herniation

Answer 17

Within cranial vault, any unilateral lesion that increases hemispheric volume is likely to cause a herniation of uncus or parahippocampal gyrus through ipsilateral tentorial notch (between brainstem and free edge of tentorium cerebelli)
A space-occupying mass, such as a tumor or hematoma, may force uncus to herniate through incisura

Question 18

Describe compression of oculomotor nerve

Answer 18

Pupillary dilation, external strabismus, and complete ptosis

Question 19

Describe compression of abducens nerve

Answer 19

Gaze is down and in

Question 20

Describe compression of cerebral peduncle

Answer 20

Herniation pushes contralateral cerebral peduncle against sharp edge of tentorium cerebelli (Kernohan’s notch)
Spastic hemiplegia on same side of original lesion

Question 21

Describe compression of posterior cerebral artery

Answer 21

Contralateral incongruent homonymous hemianopia with macular sparing

Question 22

Describe compression of ARAS

Answer 22

Decreasing levels of consciousness

Question 23

Describe stretching of brainstem blood vessels

Answer 23

Post-traumatic thrombosis of brainstem may cause Weber’s or Benedickt’s syndromes

Question 24

Describe communicating hydrocephalus

Answer 24

CSF blockage from infratentorial to supratentorial regions