Week 6 - Brainstem and Venous Drainage Flashcards
What are the 3 parts of the brainstem inferior to superior?
- Medulla Oblongata
- Pons
- Midbrain
What are the anatomical relations of the medulla oblongata?
What cranial nerves is it associated with?
What centres does it contain?
- most caudal portion of brainstem and brain, and below the pons
- associated with cranial nerves IX, X, XI, XII
- contains respiratory, cardiac and vasomotor centres
What are the anatomical relations of the pons?
What cranial nerves is it associated with?
What functions is it involved in?
- central portion of brainstem between midbrain and medulla oblongata (“pons” latin for: bridge)
- associated with cranial nerves V, VI, VII, VIII
- involved in control of sleep and respiration
What are the anatomical relations of the midbrain?
What cranial nerves is it associated with?
What functions is it involved in?
- between diencephalon and pons
- associated with cranial nerves III and IV
- composed of white matter tracts and grey matter nuclei; coordinates movements in response to visual and auditory stimuli. Conveys motor information from cerebral cortex to pons. Conveys sensory information from spinal cord to thalamus
What are prominent features of the midbrain?
superior and inferior colliculi (visual and auditory reflex centres) cerebral peduncle/crus cerebri substantia nigra red nucleus cerebral aqueduct interpeduncular fossa
What are prominent features of the pons?
rhomboid fossa - forming floor of 4th ventricle
bulbopontine sulcus
basilar sulcus
middle cerebellar peduncles
What are prominent features of the medulla oblongata?
olive pyramid decussation of pyramids nucleus gracilis and cuneatus anterior median fissure ventrolateral sulcus
At the level of the rostral medulla - what is the function of the inferior cerebellar peduncle/restiform body? Where is it located?
- most dorsolateral part
- consists of fibres passing between the medulla and cerebellum
- includes - olivocerebellar fibres (connects vestibular nuclei and cerebellum)
- includes - dorsal spinocerebellar tract (conveys proprioceptive information from lower limb)
At the level of the rostral medulla - what is the function of the nucleus solitarius? Where is it located?
- medial to inferior cerebellar peduncles and ventral to vestibular nuclei
- surrounds a small, dense fascicle of fibres called the solitary tract
- nucleus solitaris receives visceral afferent fibres entering the brainstem in the facial (CNVII), glossopharyngeal (CNIX) and vagus (CNX) nerves
At the level of the rostral medulla - what is the function of the nucleus ambiguus? Where is it located?
- deep to ventricular floor and ventral to nucleus solitarius. dorsal to inferior olivary nucleus
- sends motor fibres into glossopharyngeal (CNXI) and vagus (CNX) nerves, and cranial roots of the accessory (CNXI) nerve (therefore muscles of the pharynx and larynx)
At the level of the mid medulla - what is the function of the gracile and cuneate nuclei?
the termination point for ascending fibres (1st order neurons) of the dorsal columns
2nd order neurons continue on to medial lemniscus.
At the level of the mid medulla - what is the function of the medial lemniscus?
runs through the brainstem (rostral medulla, pons and midbrain) to terminate on 3rd order neurons in the ventral posterior nucleus of the thalamus
At the level of the caudal medulla - what is the function of the trigeminal sensory nucleus? Where is it located?
- dorsal medulla contains both nuclei and spinal tract of trigeminal. large nucleus extending the whole length of the brainstem and into the upper segments of the spinal cord
- regarded at brainstem homologue of dorsal horn
- receives primary afferent fibres conveying general sensation from head entering the brainstem as CNV
- caudal portion of the trigeminal nucleus particularly associated with modalities of pain and temperature
At the level of the mid medulla - what is the function of the decussation of the pyramids?
in the ventral medulla, majority of the pyramids undergo decussation - crossing over. They pass laterally and dorsally and caudally to form the lateral corticospinal tract
At the level of the rostral medulla - what is the function of the inferior olivary nucleus?
Dorsolaterally located
nucleus focus:
- control of movement
- afferent from motor and sensory cortices of cerebral hemisphere and red nucleus from midbrain
- main efferent fibres connect cerebellum via inferior cerebellar peduncle
At the level of the pons - what is the function of the pontine nuclei?
give off transversely oriented fascicles of pontocerebellar fibres that pass contralaterally via middle cerebellar peduncle to opposite cerebellar hemisphere.
At the level of the pons - what is the function of the trapezoid body?
consists of acoustic fibres that cross the brainstem from the cochlear nuclei
ascend into the midbrain at the lateral lemniscus, terminating in the inferior colliculus
What nuclei are found below the floor of the 4th ventricle in the pontine tegmentum?
Abducens - innervates lateral rectus muscle
Facial Motor - innervates muscles of facial expression
Trigeminal Motor - innervates muscles of mastication
Where is the superior cerebellar peduncle located?
What kind of fibres does it contain? What do they convey?
In the rostral half of the pons, forming the lateral walls of the 4th ventricle
ventral spinocerebellar tract - convey proprioceptive information from lower limb and efferent fibres ascending from the cerebellum which coordinate movement. They are destined for the red nucleus of the midbrain and ventral lateral nucleus of the thalamus
At the level of the midbrain - what is the function of the superior colliculus?
Is part of the visual reflex centre
corticotectal fibres from the visual cortex of the occipital lobe and the frontal eye field of the frontal lobe are involved in the accommodation reflex
inputs concerned with controlling movements of the eyes, e.g. when following a moving object with eyes (smooth pursuit) or altering direction of gaze (saccadic eye movement)
What is the function of the Edinger-Westphal Nucleus?
controls the smooth muscle of the eye and is part of the circuit mediating the pupillary light reflex
At the level of the midbrain - what is the function of the inferior colliculus?
Is part of the auditory reflex centre
At the level of the midbrain - what is the nuclei subdivisions of the substantia nigra? Where is it located?
Ventral-most part of the midbrain
2 types of subnuclei - pars compacta and pars reticulata
What is the function of pars compacta?
What pathology is degeneration associated with?
pigmented, melanin-containing neurons
synthesis dopamine
project neurons to caudate nucleus and putamen of basal ganglia - nigrostriatal pathway
controls voluntary movement, posture and muscle tone
degeneration associated with Parkinson’s
What is the function of pars reticulata?
non-pigmented subdivision
functional homologue of internal segment of globus pallidus
shares very similar connections as pars compacta
What is the function of the medial longitudinal fasciculus in the midbrain?
links oculomotor and Edinger-Westphal nuclei to abducens nucleus (in pons) and vestibular nucleus (in medulla)
functions to help control gaze
What is the function of the red nucleus in the midbrain?
motor control
major source of afferents from motor cortex in frontal lobe
efferent fibres from the red nucleus cross in the ventral tegmental decussation and descend into the spinal cord via the rubrospinal tract
projects to the inferior olivary nucleus of the medulla via the central tegmental tract
What is the function of crus cerebri in the midbrain?
made up entirely of descending cortical efferent fibres from cerebral hemisphere by traversing the internal capsule
around the middle 50% of the crus cerebri consists of corticobulbar and corticospinal fibres
either side of this corticopontine fibres originating in the cerebral cortex travel to the pontine nuclei of the ventral pons
Where is the dentate nucleus found? What is it’s function?
The dentate nuclei are located deep within the lateral hemispheres
They receive the majority of their input from the lateral hemispheres
(dentate - has a tooth-like/serrated edge)
Name the 4 deep cerebellar nuclei
dentate
emboliform
fastigial
globose
What are the inputs and outputs of the deep cerebellar nuclei?
They receive projections from mossy fibers and climbing fibers
The nuclei receive inhibitory GABAergic input from the Purkinje cells
The nuclei receive excitatory input from the mossy and climbing fibers
The majority of the output from the cerebellum arises from these nuclei
What are symptoms of cerebellar diseases?
- dysarthria - slurring of speech/inappropriate phrasing and/or articulating words correctly
- ataxia - unsteady gait
- asynergia - inability to combine motions into fluid movement
- nystagmus - involuntary and rhythmic to and fro motion of eyes
- dysdiadochokinesia - inability to perform rapid alternating movements
- dysmetria - inability to control range of movement
- hypotonia - decreased muscle tone
- scanning speech - slow enunciation with tendency to hesitate at beginning of a word/syllable
- tremor - oscillating movement, can be intention or postural tremor
What is the tectum? Where is it found?
The posterior region of the midbrain, dorsal to the cerebral aqueduct
The roof of the midbrain
Contains two pairs of sensory nuclei - superior and inferior colliculi
Collectively called - tectal place
What is the tegmentum? Where is it found?
sandwiched between substantia nigra and periaqueductal gray matter in the midbrain
contains red nuclei and reticular formation
What causes the red colour in the red nucleus?
blood vessel density
iron pigmentation in neuronal cell bodies
What is the rhomboid fossa?
forms the floor of the fourth ventricle of the brain
is formed by the dorsal surfaces of the pons and medulla oblongata
What is the difference between direct and indirect descending spinal pathways?
direct = conscious skilled movements indirect = unconscious movements
Name two direct descending spinal pathways
What are the functions they control? Give an example
Corticospinal tract - lateral and anterior
movements below the head, especially of the hands
lateral - neck, trunk and limbs, e.g. push-ups, moving with a hula hoop
anterior - neck and upper limb extremities, e.g. typing
Corticobulbar tract
movements of the head and face, e.g. facial expression, chewing
What is the origin of the direct descending spinal pathways?
cerebral cortex
What is the pathway of the lateral corticospinal tract?
- originates from cerebral cortex
- crossover at inferior end of medulla oblongata
- terminates in anterior horn of spinal cord
- innervates contralateral side of body
What is the pathway of the anterior corticospinal tract?
- originates from cerebral cortex
- crossover at level of lower motor neuron
- terminates in anterior horn of spinal cord
- innervates contralateral side of body
What is the pathway of the corticobulbar tract?
- originates from cerebral cortex
- crossover varies depending on the cranial nerve
- terminates in cranial nerve nuclei in brainstem (lower motor neuron)
- innervates contralateral side of body
Name four indirect descending spinal pathways
What are the functions they control? Give an example
Rubrospinal - movement coordination, e.g. positioning of digits and palm of hand when reaching out to grasp
Vestibulospinal - maintenance of upright posture and balance, e.g. extension of upper limbs when falling
Reticulospinal - posture adjustment, walking, e.g. maintenance of posture when standing on one foot
Tectospinal - movements of head and neck in response to visual and auditory reflexes, e.g. movement of head and neck away from a sudden flash of light