Week 8 - The Anatomy of the Brainstem & Spinal Cord Flashcards
What is the termination level of the spinal cord in adults?
Approximately the level of the disc between vertebrae LI and LII
Common variations exist where the spinal cord has terminated as high as vertebra TXII and as low as between LII and LIII.
What is the conus medullaris?
The cone-shaped distal end of the spinal cord
It originates a bunch of nerve roots known as the cauda equina.
What is the cauda equina?
A bunch of nerve roots originating from L2-L5, S1-S5, and C1
It innervates the pelvis and lower limbs.
How many pairs of mixed spinal nerves are attached along the spinal cord?
31 pairs
These include 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves, and 1 coccygeal nerve.
What are the anterior and posterior roots of spinal nerves responsible for?
Anterior roots are motor roots and posterior roots are sensory roots.
What is the significance of the cervical and lumbosacral enlargements?
They accommodate the many motor neurons required for the upper and lower limbs, respectively.
What are the denticulate ligaments?
Pial tissue sheets that anchor the spinal cord within the dural sac.
What are the main components of the spinal cord’s arterial supply?
1 anterior spinal artery and 2 posterior spinal arteries
The anterior spinal artery originates from the vertebral artery.
What is the artery of Adamkiewicz?
The largest medullary artery that usually arises on the left side in the lower thoracic upper lumbar region (T9-L1).
How many anterior and posterior spinal veins are there typically?
3 anterior and 3 posterior spinal veins.
What is the shape of the spinal cord gray matter when transversely sectioned?
Shaped like a butterfly or an H.
What is the role of the substantia gelatinosa?
It modulates the activity of pain and temperature afferent fibers.
What are the three funiculi in each half of the spinal cord?
- Dorsal (posterior) funiculus
- Lateral funiculus
- Anterior (ventral) funiculus
What do laminae I-IV in the spinal cord gray matter primarily receive?
Exteroceptive inputs such as pain, temperature, and tactile touch.
What is the function of lamina VI in the spinal cord?
Involved in the integration of somatic motor processes
Present only in cervical and lumbar segments.
What type of neurons are found in lamina VIII and IX?
Alpha and gamma motor neurons.
True or False: The ventral horn of the gray matter reaches the ventral surface.
False.
What does the gray commissure connect?
The two sides of the gray matter.
What is the role of neurons in the medial aspect of the ventral horn?
They receive afferents from the vestibulospinal and reticulospinal systems and innervate axial musculature.
Fill in the blank: The gray matter of the spinal cord consists primarily of _______.
[neuronal cell bodies, dendrites, and myelinated and unmyelinated axons]
What is the somatotopic arrangement of neurons in the ventral horn of the spinal cord?
Neurons are located according to the muscles they innervate:
* Extensor muscles - ventral
* Flexor muscles - dorsal
* Axial and limb girdle muscles - medial
* Distal extremity muscles - lateral
This arrangement allows descending pathways to preferentially influence distal musculature activity.
Where are the motor phrenic neurons located in the spinal cord?
Lamina IX of the cervical spinal cord (C3-C5)
These neurons provide innervation to the diaphragm.
What type of neurons are located in lamina IX of the thoracic segments?
Thoracic respiratory motor neurons
They innervate the intercostal, rib cage, and other back muscles.
What is the function of lamina X in the spinal cord?
It surrounds the central canal and is a site for the convergence of somatic and visceral afferents
About 10%-15% of preganglionic sympathetic neurons are located in laminae VII and X.
True or False: Neurons that innervate flexor muscles are located ventral to those innervating extensor muscles.
False
Neurons innervating flexor muscles are located dorsal to those innervating extensor muscles.
Fill in the blank: Lamina X is primarily involved in the convergence of _______ and _______ afferents.
somatic, visceral
This convergence plays a role in integrating sensory information.
What are the three main components of the brainstem?
Medulla oblongata, pons, midbrain
What shape does the brainstem have?
Stalk-like shape
Which cranial nerves nuclei are contained in the brainstem?
CN III to XII
What is the tectum and where is it located?
Roof over the ventricular system, mostly in the midbrain
What does the tegmentum contain?
Descending and ascending tracts, many relay nuclei, reticular formation, cranial nerve nuclei
What is the basal portion of the brainstem?
Most anterior part containing basilar structures like crus cerebri, basilar pons, and pyramids of the medulla
What is the approximate length of the medulla oblongata?
Approximately 3 cm long
What marks the junction of the medulla and the spinal cord?
Origin of the anterior and posterior roots of cervical spinal nerve 1
What structure is continuous with the anterior median fissure of the spinal cord?
Anterior median fissure of the medulla oblongata
What are the pyramids in the medulla oblongata?
Swelling on each side of the anterior median fissure consisting of corticospinal tracts
What occurs at the decussation of the pyramids?
Majority of descending tracts cross over to the opposite side
Where do the rootlets of the hypoglossal nerve (CN XII) emerge?
In the groove between the pyramids and olives
What connects the medulla to the cerebellum?
Inferior cerebellar peduncles
What is the obex?
Apex of the V-shaped boundary of the 4th ventricle
True or False: The floor of the 4th ventricle is found in both the medulla oblongata and the pons.
True
What structures are observed at the level of decussation of the pyramids?
Corticospinal tract, nucleus gracilis, nucleus cuneatus
Fill in the blank: The _______ is the great sensory decussation.
Decussation of lemnisci
What does the internal arcuate fibres do?
Travel anteriorly and laterally around the central grey matter and curve medially toward the midline
What nuclei are present at the level of the olives?
Vestibulocochlear, glossopharyngeal, vagus, accessory, hypoglossal nuclei
What is the function of the dorsal longitudinal fasciculus?
Contains autonomic fibres descending from the hypothalamus to the spinal cord
What are the two triangles marked in the inferior part of the rhomboid fossa?
Vagal triangle (ala cinerea) and hypoglossal triangle
What are the main components of the internal structure of the medulla oblongata considered at?
Decussation of pyramids, decussation of lemnisci, level of the olives, pontomedullary junction
What is the function of the olivary nuclei?
Associated with voluntary muscle movement
The inferior olivary nucleus is the largest and responsible for the elevation of the olives on the surface of the medulla oblongata.
What is the largest nucleus of the Olivary Nuclear Complex?
Inferior olivary nucleus
What is the role of the vestibulocochlear nuclear complex?
Receives afferent fibres from the inner ear and sends efferent fibres to the cerebellum and spinal cord
This coordination allows for balance and eye movement during head motion.
Fill in the blank: The _______ is an auditory fibre bundle ascending to the inferior colliculus.
lateral lemniscus
List the nuclei of the glossopharyngeal nerve.
- Main motor nucleus
- Inferior salivatory nucleus
- Sensory nucleus
What are the three nuclei of the vagus nerve?
- Main motor nucleus
- Parasympathetic nucleus
- Sensory nucleus
True or False: The hypoglossal nerve supplies all intrinsic muscles of the tongue.
True
What is the main function of the reticular formation?
Control of skeletal muscle, somatic and visceral sensations, autonomic nervous system, and consciousness
It also influences sleep and wakefulness.
What are the three functional zones of the reticular formation?
- Median column/zone
- Medial column/zone
- Lateral column/zone
Fill in the blank: The _______ nucleus is responsible for the constrictor muscles of the pharynx.
nucleus ambiguus
What is the role of the medial vestibulospinal tract?
Reflex balance pathways
What type of information do the cranial nerve nuclei process?
Motor and sensory information
What is the primary function of the medial column/zone of the reticular formation?
Processes efferent motor information
True or False: The pons connects the medulla oblongata to the cerebellum.
False
What structures are observed at the pontomedullary junction?
- Medial and spinal lemnisci
- Spinal tract of trigeminal nerve
- Lateral and trigeminal lemnisci
What are the cranial nerves emerging from the groove between the medulla oblongata and the pons?
- Abducent (CN VI)
- Facial (CN VII)
- Vestibulocochlear (CN VIII)
Fill in the blank: The _______ tract contains descending autonomic fibres.
dorsal longitudinal fasciculus
What does the hypoglossal nucleus control?
Intrinsic and extrinsic muscles of the tongue
What is the primary role of the dorsal nucleus of the vagus?
Parasympathetic control of involuntary muscles
Describe the structure of the pons.
Approximately 2.5cm long, anterior to the cerebellum, connects the medulla oblongata to the midbrain
What are the ascending and descending projections of the reticular formation responsible for?
Motor control and sensory processing
What is the role of the arcuate nuclei?
Receive nerve fibres from the cerebral cortex and send efferent fibres to the cerebellum
What is the shape of the posterior surface of the 4th ventricle?
Triangular in shape
The posterior surface is limited laterally by the superior cerebellar peduncles
What divides the posterior surface of the pons into medial and lateral areas?
Sulcus limitans
The sulcus limitans bounds the median eminence laterally
What is the area known as lateral to the median sulcus?
Area vestibuli (vestibular area)
The vestibular nuclei lie beneath this area
What is the facial colliculus produced by?
Facial nerve root winding around the nucleus of the abducent nerve
It is located at the inferior end of the median eminence
What are the components of the nervus intermedius?
Gustatory fibres for the supply of the taste buds
These fibres terminate centrally in the solitary nucleus
What is the function of the pontine gaze center?
Activates contraction of the lateral rectus muscle
Located beside the abducens nerve in the pontine structure
Where does the sensory root of the trigeminal nerve terminate?
Pontine sensory nucleus
It is located lateral to the motor nucleus
What does the motor root of the trigeminal nerve supply?
Muscles of mastication
The motor nuclei of the trigeminal nerve are located within the reticular formation
What connects the inferior colliculus with the medial geniculate nucleus?
Inferior brachium
The superior brachium connects the superior colliculus to the lateral geniculate body
What is the main function of the superior colliculi?
Centers for visual reflexes
The inferior colliculi house lower auditory centers
What is the only cranial nerve to decussate?
Trochlear nerve (CN IV)
It emerges from the dorsal surface of the brainstem
What do the tectospinal tracts operate?
Visuospinal reflexes
These reflexes turn the head, neck, and trunk in response to light
What is the function of the Edinger-Westphal nucleus?
Sends parasympathetic fibres to activate the ciliary ganglion
This causes contraction of the pupillary sphincter and ciliary muscle
What are the three lemnisci present at the midbrain-thalamic junction?
Medial, spinal, and trigeminal lemnisci
They ascend to the ventral posterior nucleus of the thalamus
What is located in the dorsal tegmentum of the midbrain?
Pretectal nucleus
It participates in visual reflex pathways and pupil constriction
What is the primary role of the habenular nuclei?
Participate in the sleep-wake cycle
They connect across the midline and project to the interpeduncular nucleus
