brainstem Flashcards
brainstem
mesencephalon (midbrain) + pons + medulla oblongata
Functions
Conduit for ascending (sensory) & descending (motor) tracts
• Contains nuclei of cranial nerves III to XII (head’s equivalent of spinal nerves + special sensory)
• Reticular formation reticula = network
• Visceral reflex centres (respiratory & cardiovascular CPG’s)
• Muscle tone & postural reflexes
• Level of arousal / consciousness
• Modulation of pain transmission
BLOOD SUPPLY
vertebrobasilar system
Mesencephalon
Cerebral peduncles •Crus cerebri •Interpeduncular fossa •CN III •Superiorcolliculi (littlehills) •Inferior colliculi •CN IV
Pons
- Transverse fibres
- CN V
- CN VI
- CN VII & VIII
- Superior cerebellar peduncles
- Superior medullary velum
- Middle cerebellar peduncles
- Rostral floor of the 4th ventricle
- Median sulcus
- Medial eminence
- Sulcus limitans
- Facial colliculus
- Vestibular area
Medulla oblongata:
- Anterior median fissure
- Pyramids
- Decussation of pyramids
- Anterolateral sulci
- Olives
- CN IX, X, XI
- CN XII
- Open medulla
- Inferior cerebellar peduncles
- Closed medulla
- Gracile tubercle
- Cuneate tubercle
The internal structure of the brainstem can be divided anteroposteriorly into 3 longitudinal layers:
- Base = descending projection fibres (motor pathways)
- Tegmentum = ascending sensory pathways & descending extrapyramidal pathways;
cranial nerve nuclei; reticular formation neurons 3. 3. Tectum (roof) = superior & inferior colliculi in the midbrain
Reticular formation
- Network of neurons located in the tegmentum of the brainstem
- Large fields of dendrites allow them to receive inputs from multiple sources
- Extensive connections
- Spinal cord
- Throughout brainstem
- Diencephalon
- Basal nuclei
- Cerebral cortex
Reticular formation FUNCTIONS
- Control of movement (connections with cerebellum; CPG’s)
- Cranial nerve reflexes
- Visceral reflexes
- Modulation of pain
- Control of arousal and consciousness
Location of sensory & motor cranial nerve nuclei in the brainstem: Spinal cord
Sulcus limitans separates dorsal sensory from ventral motor
Location of sensory & motor cranial nerve nuclei in the brainstem: rostral medulla / caudal pons
Sulcus limitans separates
lateral sensory from
medial motor cranial nerve nuclei
Mesencephalon
•Cerebral peduncles
•Crus cerebri
•Substantia nigra
•Level of superior colliculus = oculomotor N & red nucleus* - *processes information
going from cerebellum to thalamus
•Level of inferior colliculus = trochlea N
Features of a lower cervical spinal cord cross section
- oval shape
- large amount of white matter
- fasciculus cuneatus & fasciculus gracilis
wide base of the ventral horn
Features of a thoracic spinal cord cross section
- lateral horn present
- narrow ventral horn
- Clarke’s nucleus present
- fasciculus cuneatus present in levels above T6, absent below
Clarke’s nucleus
extends from C8 to L3. It is formed by cell bodies of sensory neurons transmitting nonconscious proprioceptive information.
lateral horn
is present in levels T1 - L2 & contains the cell bodies of preganglionic sympathetic neurons
Features of a lumbar spinal cord cross section
- only 1 fasciculus present in each dorsal column
- relatively wide ventral horn due to increased number of motor neurons required to innervate the lower limb muscles
no lateral horn below L2
Features of a sacral spinal cord cross section
- minimal white matter present
- small fasciculus gracilis & no fasciculus cuneatus
predominantly grey matter
adult brainstem subdivision - midbrain
secondary vesicle- mesencephalon
associated adult ventricle - cerebral aqueduct
adult brainstem subdivision - pons
secondary vesicle- mesencephalon
associated adult ventrice - 4th ventrical
adult brainstem subdivision - medulla
secondary vesicle- mylencephalon
associated adult ventrice - 4th ventrical and central canal
