Brainstem Flashcards
What is the organisation of the brainstem?
Midbrain
Pons
Medulla
What is contained within the midbrain?
Midbrain – associated with hearing, vision, motor control, sleep and wakefulness, alertness, temp regulation.
Blood supply: PCA, Superior Cerebellar & Basilar
CN’s III & IV
What is contained within the Pons?
Pons – Contains nuclei that deal with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, expressions, facial sensation, and posture.
CN’s V-VIII
Blood supply – Pontine arteries
What is contained within the Medulla?
Medulla – Contains cardiac, respiratory, vomiting, and vasomotor centres.
CN’s IX - XII
(Bulbar – nerves/tracts associated with medulla)
Blood supply – Anterior & posterior spinal artery, PICA, Vertebral.
Connects pons superiorly with spinal cord inferiorly
Junction of Medulla and Spinal Cord
level of foramen magnum and pyramidal decussation
Junction of Medulla and Pons
Anteriorly: Inferior edge of basilar pons
Posteriorly: Inferior edge of middle and inferior cerebellar peduncles
Conical shape with its broad extremity directed superiorly
Central canal of spinal cord continues upward into lower half of medulla
In upper half of medulla central canal expands as the cavity of 4th ventricle
Dorsal horn of spinal cord is replaced by caudal part of trigeminal sensory nucleus, which is homologous to dorsal horn of spinal cord
What are the cerebral peduncles of midbrain?
Comprised of many motor tracts to the body and face
What are the superior and inferior colliculus of midbrain involved with?
Involved in visual and auditory processing and associated reflexes
What is the midbrain (Mesencepahlon) comprised of?
Composed of tectum and tegmentum.
Serves important functions in motor activity, particularly eye movements (MLF), and in auditory and visual processing.
CN’s III and IV Nuclei located within midbrain.
Midbrain tegmentum – Red nucleus/periaqueductal grey/substantia nigra
Tectum - Inferior and superior colliculi
Crus Cerebrii /cerebral peduncle – Corticospinal, corticobulbar, conticopontine
Substangia nigra – interactions with basal ganglia>thalamus>cortex motor coordination
Portion of reticular formation – concerned with arousal and alertness
In the midbrain, what is the tectum?
Roof of midbrain posterior to cerebral aqueduct
Consists largely of inferior and superior colliculi
In the midbrain, what is the Tegmentum?
Mid part of midbrain anterior to cerebral aqueduct (aqueduct of silvus) and posterior to crus cerebri (Cerebral peduncles)
in the midbrain, where is the Crus Cerebri?
Separated from tegmentum by substantia nigra
What is the superior colliculi’s functions?
Main efferents are corticotectal fibres originating from visual cortex of occipital lobe and from frontal eye field of frontal lobe
Concerned with controlling movements of eyes, such as following a moving object (smooth pursuit) or altered direction of gaze (saccadic eye movements)
Just anterior to superior colliculus is pretectal nucleus, part of pathway mediating the pupillary light reflex
Corticotectal fibers from visual cortex are involved in accommodation reflex.
What is the inferior colliculi’s functions?
Involved in auditory reflexes and in determining the side on which a sound originates
Receive input from both ears and project to medial geniculate nucleus of thalamus
What is the pretectal nuclei’s role?
the pretectal nuclei receive afferents from the retina and the optic tectum, and they are involved in modulating motor responses to visual input
What are the Descending & Ascending Tracts of the brainstem?
All descending tracts terminating in spinal cord pass through brainstem
All ascending tracts that reach brainstem or cerebral cortex pass through part or all of this region
Other ascending tracts originate in brainstem
Important conduit or relay station for many longitudinal pathways
What are the Descending Autonomic System Pathways?
Pass to spinal cord via brain stem
What are the cranial nerve nuclei?
Almost all the cranial nerve nuclei are located in the brain stem.
Exceptions are CN1 and 2, which are invaginations of the brain itself
What is the Reticular Formation?
Complex matrix of neurones extending throughout tegmentum of brain stem
Controls respiration, cardiovascular system functions and states of consciousness, sleep and alertness
Descending reticulospinal tracts influence muscle tone and posture
Interconnected nuclei located throughout the brainstem.
Includes descending pathways to the spinal cord via the reticulospinal tracts of the descending reticular formation and ascending pathways to the cortex in the ascending reticular activating system (ARAS) (wakefulness and wake-sleep transition).
Reticulospinal tracts of the spinal cord = function in maintaining tone, balance, and posture—especially during body movements. Reticulospinal - Act on Alpha and gamma motor neurons – proximal limbs
Pontine reticular formation – involved in horizontal eye movements – saccades.
Raphe nuclei –within – serotonin – mood production.
Cardiovascular control – The reticular formation includes the cardiac and vasomotor centers of the medulla oblongata.
Pain modulation - origin of the descending analgesic pathways.
Sleep and consciousness
What is the relationship with Tegmentum and Nuclei?
The tegmentum is the location of several cranial nerve (CN) nuclei. The nuclei of CN III and IV are located in the tegmentum portion of the midbrain. The nuclei of CN V to VIII are located in the tegmentum at the level of the pons. The nuclei of CN IX, X, and XII are located in that of the medulla
Where is the pons located?
Between midbrain and medulla
Ventral portion is basis pontis
Dorsal portion is tegmentum
Where is the junction of pons and midbrain?
Imaginary line drawn from exit of trochlear nerve posteriorly to superior edge of basis pontis anteriorly commissure posteriorly to caudal edge of mammillary bodies
in the pons, What is the basis pontis?
Contains corticospinal tracts
Pontine nuclei receive input from cerebral cortex via corticopontine pathway
Pontine nuclei project pontocerebellar fibres to cerebellum via middle cerebellar peduncle
In the pons, what does the tegmentum house?
Contains cranial nerve nuclei for abducens (CN VI), facial (CN VII) and trigeminal (CN V)
What is the anterior median fissure of the medulla?
Continuous inferiorly with anterior median fissure of spinal cord (Anterior spinal artery)
What is the posterior median sulcus of the medulla?
Continuous inferiorly with posterior median sulcus of spinal cord
