14 - Overview of Brainstem Organisation Flashcards
Proportion of CNS represented by the brainstem in lower animals
~90%
How can anencephalic babies survive for a few days?
Brainstem is intact
Broad functions of brainstem
Reflexive and unconscious behaviour. Modulation of various arousal and conscious states
Three regions of brainstem
Mid-brain (most rostral) Pons Medulla oblongata
Where in the skull is the brainstem located?
Posterior cranial fossa
Extension of the brainstem
(Rostral) Mammillary bodies to (caudally) pyramidal decussation
Pyramidal decussation
Where white fibre tracts involved in motor function cross over.
Gross physical characteristics of midbrain (dorsal)
Has two pairs of bumps called the superior and inferior colliculi.
Gross physical characteristics of pon (dorsal)
1) Linked with cerebellum 2) Limited by the 4th ventricle 3) Along floor of 4th ventricle are the facial colliculi formed by the abducens nucleus and fibres of SN VII
Role of superior colliculi
Eye movements
Role of inferior colliculi
Relay station for hearing
Location of 4th ventricle
Between pons and cerebellum
Gross physical characteristics of medulla (dorsal)
Caudally: dorsal columns and nuclei (gracile and cuneate tubercle).
Gross physical characteristics of midbrain (ventral)
Cerebral peduncles (between interpeduncular fossa)
Gross physical characteristics of pons (ventral)
Attached to cerebellum dorsolaterally by cerebellar peduncles (superior, middle, inferior)
Gross physical characteristics of medulla (ventral)
Rostral: Two bulges - inferior olivary nuclei Pyramids descending to the pyramidal decussation
Role of inferior olivary nuclei
Location of a sound in space
Four important brainstem structures
1) Cranial nerve nuclei and related structures 2) Reticular formation and related structures 3) Long fibre tracts 4) Cerebellar circuitary
Role of reticular formation
Important in complex reflexes (eg: sneezing, vomiting)
Tectum
‘Roof’ Roof of the 4th ventricle.
Tegmentum
‘Covering’ Region of the brainstem that is continuous with the spinal cord.
Three broad regions of mid-brain
Tectum, tegmentum and basis
Broad regions of pons
Tegmentum (dorsally) and a lot of basis (ventrally)
Generalised role of basis
Descending motor control
Generalised role of tegmentum
Like the spinal cord. Cranial nerves. Reticular formation.
General types of nerves emerging from the spinal cord
General somatic nerves (innervate skeletal muscle, skin) General visceral nerves (innervate viscera)
Where do spinal nerves end?
C2
Role of cranial nerves 1 2
1) Supply somatic and visceral motor and sensory information to head. 2) NIX & X-also supply visceral sensory and motor innervation to neck, chest and most abdominal organs.
Number of pairs of cranial nerves
12
Order in which cranial nerves exit brainstem
In numerical order (rostral to caudal)
Orientation in which cranial nerves exit brainstem
Most exit ventral surface except IV
Exclusively motor cranial nerves
III, IV, VI control eye movements. XI, XII
Exclusively sensory cranial nerves
I, II, VIII
Mixed sensory and motor cranial nerves
V, VII, IX, X
Rule of 4 for cranial nerves 1 2 3
1) 4 cranial nerves exit the medulla * CNIX-XII 2) 4 exit the pons * CNV, VI, VII, VIII 3) 4 exit above the pons * CNIII, IV
Organisation of motor and sensory parts of brainstem
Similar to spinal cord. Dorsal part is sensory. Ventral part is motor.
Effect of motor nuclei developing from basal plate
Located at the midline
Broad locations of motor and sensory cranial nerves
Sensory are lateral. Motor and in midline.
*Columns within which cranial nerves sit in brainstem
Role of general somatic efferent motor nerves
Innervate muscle of the face
Role of general visceral efferent cranial nerves
For visceral smooth muscle
General and special visceral afferent cranial nerves
EG: taste
Role of general somatic sensory cranial nerves
Sensory information from face
Location of all cranial nerve cell bodies
Dorsal half of brainstem, near 4th ventricle
What is in the ventral half of brainstem?
White matter dorsal tracts of sensory nerves
Location of reticular formation
Continuous rostrally with certain nuclei in the thalamus. Continuous caudally with intermediate grey of the spinal cord. Within the tegmentum of the brainstem
Broad divisions of the reticular formation
Rostral and caudal halves
Rostral reticular formation broad roles
Maintain alert and conscious state.
Parts of midbrain in rostral reticular formation
Midbrain, upper pons
Rostral reticular formation broad roles
Work together with cranial nerve nuclei and spinal cord to carry out a variety of important motor reflex and autonomic functions. Modulation of forebrain activity
What dominates caudal reticular formation activity?
Long projection systems Defined by neurotransmitters
Examples of neurotransmitters of long projection system in caudal reticular formation 1 2 3 4
1) Noradrenergic (locus ceruleus) 2) Dopaminergic (eg substantia nigra) 3) Serotonergic (dorsal raphe nucleus) 4) Cholinergic
Examples of caudal reticular formation functions 1 2 3 4 5 6
Ventrolateral medullary reticular formation 1) Regulate visceral functions of X (Vagus). 2) GI responses (swallowing, vomiting) 3) Respiratory activities: *Rhythm, coughing, hiccupping, sneezing. *Cardiovascular responses Other regions: 4) Lateral medullary, pontine RF 5) Important for chewing 6) Region surrounding facial nucleus: crying, smiling
Three major pathways traversing brainstem
Ascending pathways: (ie touch and pain) 1. Dorsal column - medial lemniscus system * Fine touch-tactile, vibration * Crosses in medulla (medial lemniscus) 2. Anterolateral system (pain) * Crosses in spinal cord * Three pathways each terminating in different region. * Thalamus, midbrain, reticular formation 3. Descending pathway: corticospinal tract * Controls motor function * Crosses at pyramidal decussation (most-caudal part of brainstem) * Descends through ventral brainstem
