Файл: Kaplan USMLE-1 (2013) - Anatomy.pdf

Clinical Correlate

Thalamic pain syndrome affects the ventral nuclear group. Patients present with burning, aching pain in contralateral limbs or body. Involvement of the dorsal column­

medial lemniscal part ofVPL increases the sensitivity to pain and presents as contralateral loss ofvibratory sense and gait ataxia. Thalamic pain syndrome is resistent to analgesic medications.

Medialnucleargroup (partoflimbicsystem)

Input is from the amygdala, prefrontal cortex, and temporal lobe; output is to the prefrontal cortex and cingulate gyrus. The most important nucleus is the dorso­ medial nucleus.

Ventral nucleargroup

MotorVentralNuclanteriori nucleus (VA): Input to VA is from the globus pallidus, substantia nigraVentral. Outputlateralisnucleusto the premotor(VL): and primary motor cortex.

Input to is mainly from the globus pallidus and

VL

the dentate nucleus of the cerebellum. Output is to the primary motor cortex (Brodmann area 4).

SVentralsoryposterolateralNuclei (VPL) nucleus: Input to VPL conveying somatosensory and nociceptive information ascends in the medial lemniscus and spinothalamic

tract. Output is to primary somatosensory cortex (Brodmann areas 3, 1, and 2) ofVentralthe parieposteromedialal lobe. (VPM) nucleus: Input to VPM is from the ascending tri­

geminal and taste pathways. Output is to primary somatosensory cortex (Brod­

Medialmann argeniculateas 3, 1 , andbody2)(nucleus):ofthe parietal lobe.

Inputis from auditoryinformation that ascends Lateralfrom thegeniculatei ferior colliculusbody (nucleus):. O tput is to primary auditory cortex.

Input is from the optic tract. Output is in the form ofthe geniculocalcarine or visual radiations that project to the primary vi­ sual (striate) cortex in the occipital lobe.

Midline and lntralaminar Nuclei

Midline and intralarninar nuclei receive input from the brain-stem reticular for­ mation, and from the spinothalarnic tract. Intralaminar nuclei send pain informa­ tion to the cingulate gyrus.

These nuclei appear to be important in mediating desynchronization ofthe elec­ troencephalogram (EEG) duringbehavioral arousal.

EPITHALAMUS

The epithalamus is the part ofthe diencephalon located in the region ofthe poste­ rior commissure that consists of the pineal body and the habenular nuclei.

The pineal body is a small, highlyvascularized structure situated above the poste­ rior commissure and attached by a stalk to the roof ofthe third ventricle.

The pineal body contains pinealocytes and glial cells but no neurons. Pinealo­ cytes synthesize melatonin, serotonin, and cholecystokinin.

The pineal gland plays a role in growth, development, and the regulation of cir­ cadian rhythms.

Environmental light regulates the activity ofthe pineal gland through a retinal-su­ prachiasmaticpineal pathway.

The subthalamus is reviewed with the basal ganglia.

ChapterSummary

•The diencephalon is divided into 4 parts: thalamus, hypothalamus, epithalamus, and subthalamus.

•The thalamus is the major sensory relay for many sensory systems. The long tracks of spinal cord and the trigeminal system synapse in the ventral posterolateral (VPL) and ventral posteromedial (VPM) nuclei, respectively. Auditory input is to the medial geniculate body, and the visual input is to the lateral geniculate body. Motor projections from the basal ganglia and cerebellum synapse in the ventral anterior and ventral lateral nuclei.

•The hypothalamus contains nuclei that have fiber connections with many areas ofthe nervous system, including the pituitary gland in the anterior and tuberal regions ofthe hypothalamus. Other areas control eating, drinking, body temperature, and provide connections with the limbic system.

•The epithalamus consists mainly ofthe pineal gland, which plays a major role in the regulation of circadian rhythms.

•The subthalamic projections are important circuits related to the basal ganglia.

Chapter 9 • Diencephalon

Clinical Correlate

Precocious Puberty

In young males, pineal lesions may cause precocious puberty.

Pineal Tumors

Pineal tumors may cause obstruction of CSF flow and increased intracranial pressure. Compression ofthe upper midbrain and pretectal area by a pineal tumor results in Parinaud syndrome, in which there is impairment of conjugate vertical gaze and pupillary reflex abnormalities.

Section IV • Neuroscience

Note

The internal granular layer is the site oftermination of the thalamocortical projections. In primary visual cortex, these fibers form a distinct Line of Gennari. The internal pyramidal layer gives rise to axons that form the corticospinal and corticobulbar tracts.

I.Molecular layer

II. External granular layer

Ill. External pyramidal layer

IV. Internal granular layer

V. Internal pyramidal layer

VI. Multiform layer

(layer of polymorphic cells)

t t t

Figure IV-1 0-5. The Six-Layered Neocortex

LANGUAGE AND THE DOMINANT HEMISPHERE

Most people (about 80%) are right-handed, which implies that the left side ofthe brain has morehighlydeveloped hand-controlling circuits. In thevast majorityof right-handed people, speech and language functions are also predominantly or­ ganized in the left hemisphere. Most left-handed people show language functions bilaterally, although a few, with strong left-handed preferences, show right-sided speech and language functions.

BLOOD SUPPLY

The cortex is supplied by the 2 internal carotid arteries and the 2 vertebral arter­ ies (Figures IV-10-6 and IV-10-7). On the base (or inferior surface) ofthe brain, branches of the internal carotid arteries and the basilar artery anastomose to form the circle of Willis. The anterior part of the circle lies in front of the optic chiasm, whereas the posterior part is situated just below the mammillary bodies. The circle ofWillis is formedby the terminal part ofthe internal carotid arteries; the proximalparts ofthe anterior and posterior cerebral arteries and the anterior and posterior communicating arteries. The middle, anterior, and posterior cere­ bralarteries,which arise from the circle ofWillis, supplyall ofthe cerebral cortex, basal ganglia, and diencephalon.

The internal carotid arteryarises from thebifurcation ofthe common carotidand enters the skull through the carotid canal. It enters the subarachnoid space and terminates by dividing into the anterior and middle cerebral arteries.