Brain stem and cranial nerves Flashcards
Define brain stem
The part of the CNS, exclusive of the cerebellum that lies between the cerebrum and the spinal cord
What are the major divisions of the brain stem from top to bottom?
midbrain, pons and medulla oblongata
What is the superior and inferior colliculus?
The roof of the midbrain.
Superior colliculus - controls the coordination of the eye and head
Inferior colliculus - Auditory reflexes
What structure lies in the midline of the brain stem?
The pineal gland - secretes melatonin required for management of the circadian rhythm
What cranial never emerges from the anterior surface of the brain stem?
Trochlear nerve (CN IV) emerges from the back of the brain stem. Only cranial nerve of dorsal origin.
What does CN IV supply?
It supplies the superior oblique
What are the two main sensory pathways in the dorsal column?
Touch
Proprioception
How can the pons be identified?
It has transverse fibres going across it
Describe the layout of the midbrain and the structures around it
See diagram and notes
What cranial nerve emerges just emerges just above the transverse fibres of the pons?
CN III - oculomotor nerve
- Medial rectus
- Superior rectus
- Inferior rectus
- Inferior oblique
It emerges between the cerebral peduncles.
What does the midbrain have that has a structural and functional role?
Cerebral peduncle - the main motor nerve fibres coming from the motor cortex to the spinal cord. Sensory fibres as well. It also holds the cerebrum to the brainstem. It travels behind the Pons and remerges below as pyramids. The fibres cross over at the base of the medulla called the pyramidal decussation. 90-95% of the fibres cross here.
What cranial nerves emerge from the pons?
Lateral part of pons - Trigeminal (CN V)
Three cranial nerves emerge from the ponto-medullary junction. Going from most medial to lateral. Abducens (CN VI), Facial (CN VII) and Vestibulocohlear (CNVIII)
The emerge at the level of the pyramids before the decussation
What is Bell’s Palsy?
Dysfunction of the facial nerve causing a loss of facial muscle tone
What are the three CN that arise from the lateral part of the medulla?
Glossopharyngeal (CN IX) - Sensory and motor innervation to the tongue and pharynx
Vagus (CN X) - main parasympathetic nerve that projects down to the viscera
Accessory (CN XI) - supplies the sternocleidomastoid (allows turning of the head) and the trapezius
What CN emerges separately from the other three cranial nerves of the medulla?
Hypoglossal Nerve (CN XII) - supplies the musculature of the tongue
What are the functional subtypes of the cranial nerves?
GSA - sensation from the skin and mucous membranes
GVA - sensation from the GI tract, heart, vessels and lungs
GVE - preganglionic parasympathetic
GSE - muscles for eye and tongue movements
This order is also the order of the fibres from dorsal to ventral in an embryonic spinal cord
What are also functional subtypes of the cranial nerves (S)?
SSA - Vision, hearing and equlibrium
SVA - Smell (CN I) and Taste (2 cranial nerves that go to the nucleus solitarius. Anterior 2/3 CN VII, posterior 1/3 CN IX)
SVE - Muscles involved in chewing, facial expressions, swallowing, vocal sounds and turning the head
What is the sulcus limitans?
Separates the sensory nuclei from the motor nuclei
Draw the arrangement of the nuclei of the cranial nerves
See diagram. Nucleus ambiguus - involved in laryngeal movements
What appearance does the midbrain typically have?
Mickey mouse appearance
What are the signs that you’re in the midbrain?
Inferior colliculus - low down in the midbrain
Cerebral aqueduct
Substantia nigra - Dopminergic neurones produce neuromelanin which gives it the distinct black colour
(cerebral peduncle)
Where is the 4th ventricle in the region of?
The Pons
The are the signs that you’re in the pons?
Transverse fibres
Cerebellar peduncles (main one is middle cerebellar peduncle)
Cerebral peduncles
4th ventricle
Signs you are at the top of medulla?
Inferior olivary nucleus - connected to the cerebellum involved in fine tuning motor movements
4th Ventricle
Pyramids
