-result from damage to motor neurons or their peripheral axons.
(1) Flaccid paralysis
(3) Muscle atrophy
(4) Fasciculations and fibrillations
9. The proprioceptive pathway for trunk and limbs carries highly localized deep sensations (body posture, movement, vibration and pressure as well as two-point discrimination) from receptors to the cortex. The axons, with their first-order neurons in the spinal ganglia, reach the CNS through the posterior roots of spinal nerves and collect sensory information from different body areas. Axons from the spinal ganglia ipsilaterally ascend within the fasciculus gracilis or fasciculus cuneatus in the spinal cord. The fasciculus gracilis transmits deep sensations from the lower half of the body (below the fifth thoracic segment). Fasciculus cuneatus fibers carry deep sensations from the upper body and enter the spinal cord above the level of fourth thoracic segment. These fibers ipsilaterally ascend in the posterior funiculus of spinal cord toward the brainstem and terminate at the gracile nucleus and cuneatus nucleus, the second-order neurons. The internal arcuate fibers, the second order fibers from the nuclei gracilis and cuneatus, travel anteromedially and cross the midline just above the pyramid in the medulla. After crossing, the internal arcuate fibers form the medial lemniscus. The medial lemniscus ascends along the midline and posterior to pyramidal tract through the medulla oblongata. The medial lemniscus is horizontally arranged in the pontine tegmentum. Then it posterolaterally migrates in the midbrain to enter the ventral posterolateral nucleus of the dorsal thalamus, the third-order neurons. The axons carrying the information from the thalamus to the sensory cortex through the anterior posterior limb of the internal capsule are collectively known as projection fibers, central thalamic radiations. They terminate in the upper two-thirds of the postcentral gyrus, the primary somesthetic area in the parietal lobe.
10. What effects would lesion in the optic nerve have on monocular blindness in the eye? A chiasmatic lesion (often owing to a pituitary tumor or a lesion around the sella turcica) can injure the decussating axons of retinal ganglion cells within the optic chiasm. These axons originate in the nasal halves of the two retinas. Thus, this type of lesion produces bitemporal hemianopsia, characterized by blindness in the lateral or temporal half of the visual field for each eye. A pathology encroaching on the lateral edge of the optic chiasm selectively interrupts the fibers from the ipsilateral temporal portion of the retina, resulting in nasal hemianopsia in the corresponding eye. Lesions behind the optic chiasm cause a field defect in the temporal field of one eye, together with a field defect in the nasal (medial) field of the other eye. The result is a homonymous hemianopsia in which the visual field defect is on the side opposite the lesion.
11. The light stimulus acting upon the retinal photoreceptors gives rise to activity in retinal ganglion cells, the axons of which form the optic nerve. Activity is conducted through the optic chiasma and along the optic tract, and the majority of fibers end in the lateral geniculate nucleus of the thalamus. However, a small number of fibers leave the optic tract before it reaches the thalamus and synapse in the pretectal area by short neurons which synapse bilaterally with preganglionic parasympathetic neurons in the accessory nucleus of oculomotor nerve (Edinger-Westphal's nucleus) complex in the rostal midbrain. Efferent impulses pass along parasympathetic fibers of the oculomotor nerve to the orbit where they synapse in the ciliary ganglion. Postganglionic fibers (short ciliary nerve) pass to the eyeball to supply sphincter pupillae, which reduces the size of the pupil when it contracts. So light shone on the retina of one eye causes both pupils to constrict normally. The response in the eye stimulated is called the direct papillary light reflex,, while that in the opposite eye is known as the indirect (or consensual) papillary light reflex.
12. The corticospinal tract originates the pyramidal cells of the superior and middle parts of the precentral gyrus and anterior part of the paracentral lobule. It travels through the posterior limb of internal capsule of the telencephalon, and then descends through the intermediate 3/5 of the cerebral peduncles of the midbrain. Later it runs through the basilar part of the pons and continues to the pyramids in the medulla oblongata. About 75% to 90% of the corticospinal tract crosses pyramidal decussation at the caudal end of the medulla oblongata. After crossing, these fibers descend into the lateral corticospinal tract in the lateral funiculus of the spinal cord. These fibers terminate on the interneuron and lower motor neurons in the ipsilateral anterior gray horns of the spinal cord, and mainly control musculature of the limbs. About 10% to 15 % of the corticospinal tract does not cross in the pyramidal decussation but descends in the anterior funiculus of the spinal cord (the anterior corticospinal tract). These fibers cross or uncross above the level of mid-thoracic segments, close to the anterior horns of spinal cord, and control the skeletal muscles of trunk. Up to 3% of the decending fibers in the lateral corticospinal tract are uncrossed. The ipsilateral decending projections mainly control musculature of trunk. Some axons of upper motor neurons (the pyramidal cells in the inferior part of the precentral gyrus) that conduct impulses for the control of skeletal muscles in the head extend through the genu of the internal capsule to the midbrain, where they join the corticobulbar tracts in the right and left of cerebral peduncles. Some of the axons in the corticobulbar tracts decussated at the midplane in the brainstem, whereas others have not. The axons terminate the bilateral motor nuclei of the cranial nerves (nucleus of oculomotor nerve, nucleus of trochlear nerve, motor nucleus of trigeminal nerve, nucleus ambiguus, accessory nucleus, superior part of the facial nucleus), and the contralateral hypoglossal nucleus and the inferior part of the facial nucleus.
(Li Feng, Ding Wenlong)
Multiple Choice Questions
1. An obstruction in the interventricular foramen would interfere with the flow of cerebrospinal fluid into the.
39. All of the following arteries are branches of the internal carotid artery except the.
A. anterior cerebral arteries
B. middle cerebral arteries
C. ophthalmic arteries
D. posterior cerebral arteries
E. posterior communication arteries
1. Blockage of the flow of cerebrospinal fluid (CSF) within the cerebral aqueduct (of Sylvius) normally would result in the enlargement of all of the following ventricular spaces except the.
A. third ventricle
B. fourth ventriclee
C. right lateral ventricle
D. interventricular foramen
E. left lateral ventricle
2. During childbirth, an excessive anteroposterior compression of the head may tear the anterior attachment of the cerebral falx from the tentorium of cerebellum. The bleeding that follows is likely to be from which of the following venous sinuses?
A. occipital sinus
B. sigmoid sinus
C. straight sinus
D. superior sagittal sinus
E. transverse sinus
3. An infant was found to have hydrocephalus. Studies revealed that the hydrocephalus was caused because CSF could not get out of the third ventricle. The blocked passage was the.
A. central canal
B. cerebral aqueduct
C. interventricular foramen
D. lateral foramen
E. medial foramen
4. A patient is suspected of having bacterial meningitis. A lumbar puncture is performed to remove cerebrospinal fluid for analysis. The fluid would be removed from the.
A. epidural space
B. subarachnoid space
C. intervertebral foramen
D. spinal canal
E. subdural space
5. It is decided to image the spinal cord and spinal nerve rootlets by doing a myelogram (injection of a radio-opaque dye into the subarachnoid space followed by a radiograph). In order to inject the dye without injury to the spinal cord, the injection is usually done below which vertebral level?
6. You have been asked to assess the neurological deficit that might exist in a patient diagnosed with cavernous sinus thrombosis. You will focus your examination on cranial nerves related to the sinus that includes all the following except.
A. abducent (CN Ⅵ)
B. facial (CN Ⅶ)
C. oculomotor (CN Ⅲ)
D. ophthalmic division of the trigeminal nerve (CN Ⅵ)
E. trochlear (CN Ⅳ)
7. While riding her bicycle on campus without a helmet a student is hit by a car and falls, hitting her head on the pavement. She is brought to the Emergency Room in an unconscious state with signs of a closed head injury. Tests reveal blood in her cerebrospinal fluid taken from a spinal tap. Diagnosis is of torn cerebral veins as they pass from the brain to the superior sagittal sinus. From which of the following was the bloody fluid taken?
A. cavernous sinus
B. epidural space
C. subarachnoid space
D. subdural space
E. vertebral venous plexus
8. A 35-year-old man was admitted to the hospital complaining of double vision (diplopia), inability to see close objects, and blurred vision in the fight eye. A vertebrohasilar angiogram revealed an aneurysm of the superior cerebellar artery close to its origin on the right side. The doctor attributed the symptoms to the compression of an adjacent cranial nerve by the aneurysm The compressed nerve is the.
A. abducent (CN Ⅵ)
B. oculomotor (CN Ⅲ)
C. optic (CN Ⅱ)
D. trigeminal (CN Ⅴ)
E. trochlear (CN Ⅳ)
9. During an intramural baseball game a player is hit on the head, between the eye and the ear. He immediately loses consciousness, wakes up momentarily and then becomes comatose. He is rushed to the ER and immediately given a CT scare The scan shows a skull fracture and an accumulation of blood between the dura and the cranial bone on the side of his head, compressing his cerebrum. He is rushed to surgery where a hole is bored into his skull to relieve the pressure. After a few tense hours, he regains consciousness and has an uneventful recovery. The hemorrhage from the fracture would be described as
10. An 84-year old woman suffers a stroke, with paralysis on the right side of her body. Neurological tests show that the intracerebral hemorrhage has interrupted the blood supply to the posterior part of the frontal, the parietal and medial portions of the temporal lobes of the left cerebral hemisphere. Which vessel was involved?
A. anterior cerebral artery
B. great cerebral vein
C. middle cerebral artery
D. middle meningeal artery
E. posterior cerebral artery
A. contains cerebrospinal fluid
B. innermost layer of the spinal meninges
C. contains a quantity of loose areolar tissue
D. sensitive to pain
E. dense fibrous connective tissue
1. pia mater
2. subarachnoid space
A. the posterior communicating artery
B. the anterior cerebral artery
C. the middle cerebral artery
D. the anterior choroidal artery
E. the posterior cerebral artery
3. Which is not included in the circle of Willis?
4. Which is not the branch of internal carotid arteries?