Structural Organisation Of The Brainstem And Spinal Cord Flashcards
The brainstem consists of…
Medulla oblongata
Pons
Midbrain
What are the 3 brad functions of the brainstem
Connects the tracts to higher centres
Contains reflex centres
Houses nuclei of CNS 3-12
Describe the structure of the brainstem
Occupies the posterior cranial fossa of the skull
Stalk like shape
Connects the spinal cord with the cerebral hemispheres and cerebellum and has long tracts of fibres present at all levels
In transverse section can be divided into 4 areas from posterior to anterior:
Tectum (roof over the ventricular system)
Ventricular system
Tegmentum (core of brainstem)
Basal portion (situated most anteriorly)
What are the 4 areas of the brainstem in transverse section
Tectum (roof over the ventricular system)
Ventricular system
Tegmentum (core of brainstem)
Basal portion (situated most anteriorly)
Where s the midbrain/mesencephalon
Between the Diencephalon and pons
What links the brainstem to the thalami and the cerebrum
2 lateral half’s on the anterior side of the cerebral peduncles which are the part of the midbrain that links these
What connects the 3rd and 4th ventricles of the brain
The hollow cerebral aqueduct running through the midbrain
What nerves emerge from the midbrain
Oculomotor 3
Trochlear 4
What is the function of the red nucleus
Relay station and integrator of info
Describe the corpa quadrigemina
Contains 4 rounded bodies
2 superior colliculi - control reflex movements of the eyes, neck and head in response to visual stimuli movements
2 inferior colliculi - control reflex movements of the head, neck and trunk in response to auditory stimuli
Describe what th red nucleus contains
Numerous blood vessels and receives info form the cerebrum and cerebellum and issues subconscious motor commands concerned with muscle tone and posture
What is lateral to the red nucleus and what is its function?
Melanin-containing substantia nigra
Secretes dopamine to inhibit the excitatory neurons of the basal nuclei
Depigmentation of substantia nigra can be indicative of…
Parkinson’s disease
Describe the Pons
Found between the midbrain and medulla oblongata
Anterior surface - large bulge , basilar pons
Posterior surface cerebral peduncles - Tegmentum
What is the Locus ceruleus
Located within the dorsal wall of the upper pons, under the cerebellum in the caudal midbrain, surrounded by the 4th ventricle
Main source of noradrenaline in the brain
Melanin granules contribute to its blue colour
Motor root lies ….. to sensory root
Medially
What nerves emerge from the groove between the medulla and pons
6 7 8
What nuceli are involved with respiration
Apneustic centre - apneusis sustained gasping inhalation followed by a short inefficient exhalation
Pneumotaxic centres - prevents apneusis by promoting coordinated respiration
The pons contains…
Sensory and motor nuclei of CNs 5,6,7,8
Nuclei involved with respiration
Nuclei and tracts that process and relay information to and from the cerebellum
Ascending, descending and transverse tracts
Describe the function of the medulla oblongata
Connects the pons superiority with the spinal cord inferiority
Contains long ascending and descending fibres to higher centres
Allows brain and spinal cord to communicate
Coordinates complex autonomic reflexes
Controls visceral functions
Describe the anterior surface of the medulla oblongata
Pyramids - contains corticospinal tracts
Decussation of pyramids
Olives - underlying olivary nuceli
Describe the posterior surface of the medulla oblongata
Gracile tubercle
Cuneate tubercle
What is the function of autonomic nuclei
Regulate/control a range of visceral activities
Describe respiration control by medulla
Subset of neurons in the medulla , respiratory pattern generator that sends signals to the cranial and spinal motor nerves that directly innervate the respiratory muscles
Medulla can generate respiratory pattern fine tuned by higher centres
Describe the cardiovascular centre of the medulla
• Vasomotor area rostral ventrolateral medulla and the inferior olivary complex
• Most afferent fibres from the baroreceptors project to the nucleus tractus solitarii (NTS)
• Inhibitory neurons from the NTS project to the vasomotor area and when stimulated and uninhibited by interneurons produces a vasoconstrictor response
• Therefore an increase in pressure stimulates baroreceptor firing which causes inhibition by vasomotor interneurons causing vasodilation.
•cardioinhibitory area includes the nucleus ambiguus and the dorsal motor nucleus of the vagus nerve
• Excitatory neurons project from the NTS into the cardioinhibitory area
• Neurons in the dorsal motor nucleus of the vagus account for the cardiac component of the baroreceptor reflex (bradycardia). Inhibitory interneurons project from the NTS onto a cardioacceleratory area and stimulation of these causes heart rate and cardiac contractility to increase
Describe sensory and relay nuclei
• The fasciculus gracilis contains ascending fibres from sacral, lumbar and lower thoracic segments T6-T12 (the lower body). synapse with the ipsilateral gracile nucleus in the medulla.
• It is involved in the mediation of conscious proprioception including kinaesthesia and discriminative touch sensations from the lower body.
• The fasciculus cuneatus exists in thoracic segments above T6 and cervical segments and contains long ascending fibres from the upper body.
Describe the reticular formation
Extends through brainstem, loose and far-flung neurons, into the cerebral cortex
Reticular activating system-alertness
Filters out repetitive or familiar stimuli
Inhibited by sleep, alcohol, drugs
Severe injury = coma
Where does the spinal cord extend from
Foramen magnum L1-2
How many spinal nerves in SC
31 pairs mixed spinal nerves
8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal
Signal nerved C1-7 exit…. To corresponding vertebra
Rostrally
C8-S5 exit ….. to corresponding vertebra
Caudally
….. and ….. enlargements in SC
Cervical C1-T1 and lumbosacral L1-S3
Where do adult cord end
L1-L2
Where do children’s spinal cord end
Caudal end of L3
Distal end of the cord …. Emerges ….
Conus medullaris
Emerges cauda equina l2-c1
What anchors the cord
Denticulate ligaments anchors the cord within the dural sac
What is the lumbar cistern
Caudal end of spinal cord
Suitable for lumbar puncture
Adults - between L3-L4
Children - between L4-L5
Describe the internal structure of the spinal cord
Gray matter is shaped like a butterfly or an H
At every level the gray matter is capped by a zone of closely packed small neurones, the substantia gelatinosa.
The white matter surrounds the gray butterfly
Consists of the ascending and descending tracts / fasciculi)
The neurons comprising these tracts have similar origins and sites of termination.
A bundle containing one or more tracts or fasciculi is called a funiculus.
Two sides of gray matter connected by gray commissure
Name and describe the 3 funiculi in each half of the spinal cord
The dorsal (posterior) funiculus, located between the dorsal (posterior) horn and the dorsal (posterior) median septum.
The lateral funiculus which is located between where the dorsal roots enter and the ventral (anterior) roots exit the spinal cord.
The anterior (ventral) funiculus located between the anterior (ventral) median fissure and the site where the ventral roots exit.
