Lecture 6- Brain Stem and Cranial Nerves Flashcards
What are the three major parts of the brain stem?
midbrain, pons and medulla
What does the brain stem provide/ what is it’s major purpose?
Provides a pathway for axonal tracts running between the forebrain, cerebellum and spinal cord
How many pairs of cranial nerves is the brain stem associated with?
10
Are the cranial nerve considered part of the central nervous system or peripheral nervous system?
PNS
What are the Cerebral Peduncles (Crus Cerebri) associated with and what are their function?
- Mid brain of the brain stem
- Includes axons that descend from the cerebral cortex to the brainstem and spinal cord (passing longitudinally on the ventral surface of the midbrain)
- help to anchor the cerebrum to the brainstem
How many cranial nerves are associated with the mid brain and where are they located?
- III cranial nerves anteriorly
- IV cranial nerves posteriorly
What are colliculi?
- 2 pairs of mounds associated with the midbrain of the brain stem
- There is the superior colliculus (higher hill) and the inferior colliculus (lower hill)
Label the different elements of the brain stem including the peduncles (both cerebral and cerebellar) and colliculus on a posterior view of the brain stem and then on a midsagittal section… (OneNote)
Answers there
What is the role of the superior colliculi?
Visual relay + reflex center:
- receive inputs from the retina/visual cortex & project to vision-related areas in cortex
- concerned with the detection of movement of objects in the visual field
- relay vision information to neurons innervating the muscles that control eye movement
What is the role of the inferior colliculi?
Auditory relay & reflex nuclei:
- relaying auditory information from hearing receptors of the ear to the sensory cortex
- act in reflexive responses to sound (e.g., startle reflex)
What is the substantia nigra?
- located deep to the cerebral peduncle
- contains melanin pigment (precursor of dopamine) which makes it black in appearance
- functionally linked to the basal nuclei/ganglia
What does dopamine degeneration in the substantia nigra cause?
Parkinson’s disease
What are the two parts of the Substantia Nigra? Which is more ventral?
- pars compacta (SNpc)= cells are close together and where the dopamine neurons are found.
- pars reticulata (SNpr)= cells are more spread out like a network
Pars reticulata (SNpr)= more ventral. Actually can’t be seen in a standard picture showing the Substania Nigra
What connections does the pars reticular have?
SNpr has connections similar to the internal division of the globus pallidus (GPi) = inhibitory input to the thalamus
What is the red nucleus/ what is it’s function?
- lies deep to the substantia nigra
- rich blood supply & contains iron pigment
- relay nucleus in some descending motor pathways
To summarize what structures are found within the midbrain of the brainstem?
- Cerebral peduncles
- Colliculi: superior colliculi, inferior colliculi
- Substantia nigra
- Red nucleus
- Cranial nerves: oculomotor (III), trochlear (IV)
- Cerebral aqueduct
- Superior cerebellar peduncle
- Mammillary bodies
What cranial nerves are associated with the pons?
- trigeminal (V)
- abducens (VI)
- facial (VII)
- vestibulocochlear (VIII)
What is either side of the mamillary bodies and what view can they be seen in?
Mamillary bodies sit in the mid brain and can be seen in a ventral view. The cerebral peduncles are the lines either side.
Other than cranial nerves what else is associated with the pons?
- 4th ventricle
- Middle cerebellar peduncle
What is the pons composed of + How does this relate to it’s function?
- Composed of conduction tracts - both ascending sensory & descending motor tracts
- Composed of pontine nuclei (collection of neurons within the pons) e.g. Pneumotaxic Centre (respiratory center). Helps to maintain normal rhythm of breathing (together with medullary center)
How does the function of the pons illustrate how a stroke in the brain stem could be fatal?
Control of breathing is occurring therefore brain stem stroke could disrupt breathing.
What does the medulla consist of?
• Pyramids • Olives • Cranial nerves - glossopharyngeal (IX) - vagus (X) - accessory (XI) - hypoglossal (XII) • 4th ventricle • Inferior cerebellar peduncle (connecting the medulla to the cerebellum)
What are the pyramids in the medulla?
formed by the large pyramidal (corticospinal) tracts descending from the motor cortex
What is the Pyramidal Decussation?
Axons of pyramidal tracts cross over to the opposite side at the level just above the medulla spinal junction (at the level of the foramen magnum)