Head and neck things to remember

what constitutes the brainstem?

the midbrain and the hindbrain (pons and medulla oblongata)

what constitutes the hindbrain?

the pons, medulla oblongata and the cerebellum

is the thalamus included in the brainstem?

typically no

what does the pons extend back into?

the 4th ventricle

what structure marks the limits of the midbrain?

the cerebral aqueduct - the channel that links the third ventricle above with teh fourth ventricle below and the two bumps at the back - colliculi

where is the open medulla?

above the closed medulla

what are the functions of the brainstem? 7

1. Conduit for ascending and descending pathways

2. Conduit for cerebellar connections - communicates with the cerebellum

3. Houses most cranial nerve nuclei

4. Chemoreception, salivation, mastication, swallowing and gag reflex

5. Reticular formation – arousal; cardiovascular and respiratory centres – vital life-supporting role

6. Raphe, locus coeruleus nuclei - mood, sleep

7. Substantia nigra – movement control

what is the raphe, locus coeruleus and substantia nigra?

• grey matter: monoaminergic centres

• the raphe is located on the midline of the brainstem and is the source of all the serotonergic centres in the body - mood and sleep

• the locus coeruleus has its nuclei in the pons and is the location for all the noradrenergic pathways - mood and sleep

• the substantia nigra is most of the dopaminergic pathways - important in movement - parkinson’s - the rest come from the tegmentum

what is this? and what is the dorsal side?

section through the closed medulla, dorsal is TOP

how would the image differ if it was the open medulla?

the dorsal side would be concave because of the floor of the FOURTH ventricle

red

closed medulla - fasciculus gracilis - ascending pathway , carrying fine touch, conscious proprioception and vibrational information - remember nerve fascicles

orange

closed medulla - nucleus gracilis - at this point the ascending fibres are synapsing with their target fibres

yellow

closed medulla - fasciculus cuneatus - also an ascending pathway carrying fine touch, conscious proprioception and vibrational information

green

closed medulla - nucleus cuneatus

sky blue

trigeminal sensory nucleus - closed medulla - the long one from the medulla to the midbrain

lilac

closed medulla - spinocerebellar fibres

pink

closed medulla - pyramid - contain axons of the cortiospinal tract - axons are named from their origin to where they are going - these axons are going from the cortex to the spinal cord - DECENDING PATHWAY

brown

closed medulla - decussation of the pyramids - this is where they cross over to the opposite side - they cross in swaves

what is the structure in the centre?

central canal of the medulla - continuous with the 4th ventricle above and the central canal of the spinal cord below

what is significant about this stain?

myelin is stained black

this is nuclei for the spinal accessory nerve

which side is ventral?

the bottom is ventral

what is this?

pons - notice the ventral bulge at the bottom

red

pons - medial longitudinal fasiculus

orange

pons - superior cerebellar peduncles

yellow

pons - pontocerebellar fibres

green

pons - lateral meniscus

blue

pons - spinothalamic tract

lilac

medial lemniscus

pink

pons - upper motor neurones corticospinal (from cortex to spine) and corticobulbar fibres (they terminate at cranial nerve motor nuclei)- these with gather into the medullary pyramids soon

start of the cerebral aqueduct - remember this is the pons - around this is grey matter, peri-aqueduct grey matter

dorsally - trochlear is the only cranial nerve that exits

what is this and what is the dorsal surface?

this is the midbrain, with the dorsal surface at the top

red

midbrain, inferior colliculi, along with the superior colliculi, they are responsible for reflex extraocular muscles, the superior are visual stimuli reflex and the inferior are the auditory reflex

orange

midbrain - trochlear nucleus

yellow

green

midbrain, temporopontine fibres

blue

cerebral peduncles - midbrain big white matter tract - large number of descending tracts - corticospinal and corticobulbar tracts

lilac

front pontine fibres - midbrain

navy

midbrain - substantia nigra - neuromelanin

purple

decussation of superior cerebellar peduncles - midbrain

grey

medial lemniscus- midbrain

what is the hole in the dorsal medial ?

start of the cerebral aqueduct- midbrain

what are the two bumps on the dorsal surface?

hills - inferior colliculus - midbrain

what is special about the trochlear nerve?

all cranial nerves exit the brain on the ventral surface except the trochlear, which exits dorsally and wraps back round

location of the cranial nerve exit points

cranial nerve columns

optic nerve vs tract

since the retina is part of the cns, anything coming from it is a tract but we call the axon between the retina and the optic chiasm the optic nerve, note that it doesn’t synapse at the optic chiasm

where do special sensory optic nerves synapse?

in the lateral geniculate nucleus of the thalamus - to visual cortex

what part of the pathway cross over?

nasal retinae, midline

as opposed to temporal - stay ipsilateral

complete blindness in left eye

half blind in both eyes

what happens at the edinger whesphal nuclei?

It receives input from the pretectal nucleus and sends parasympathetic fibers via cranial nerve III to the ciliary ganglion, controlling pupillary constriction. These fibers innervate the iris sphincter muscle, causing the pupil to constrict in response to light. 

list the trigeminal nuclei 4

1. Motor nucleus (muscles of mastication)

2. Spinal nucleus (sensory) – thermal/nociception from head and neck

3. Principal nucleus (sensory) –touch, proprioception

4. Mesencephalic nucleus –jaw reflexes

A

Trigeminal ganglion

B

trigeminal principle nucleus - sensory - proprioception and touch

C

thalamus - VPM

D

cerebral cortex

E

trigeminal spinal nucleus - thermal and nociception from the head and neck

F

trigeminal mesencephalic nucleus - jaw reflexes

G

trigeminal motor nucleus - muscles of mastication

1

spinal tract of trigeminal

2

ventral trigeminothalamic tract

3

dorsal trigeminothalamic tract

4

coronal radiata

what is the trigeminal ganglion?

where the cell bodies are of the sensory component - like DRG

how is the facial nerve general somatic sensory?

skin of the external auditory meatus and the tympanic membrane/eardrum

what are mimetic muscles?

muscles of facial expressions

where does the facial nerve innervate taste?

anterior 2/3rds of the tongue and the palate

what cranial nerve innervates the lacrimal gland?

facial - parasympathetic

lesion A

as both hemispheres contribute to the facial nuclei for upper face innervation, an upper motor lesion will not affect the upper face, but as the lower face is innervated only by the nerve on the contralateral, the lower opposite half of the face is paralysed

• Called CENTRAL FACIAL PALSY or CORTICOBULBAR PALSY

lesion B

there are no neurones from the contralateral that contribute to a side’s innervation after the nuclei in the pons

contralateral face is paralysed,

• Called PERIPHERAL FACIAL PALSY or BELL’S PALSY

glossopharyngeal motor component

upper pharynx

glossopharyngeal visceral sensory component

– blood pCO2 /[H+ ] monitoring (carotid body)

glossopharyngeal sensory component

post 1/3 of tongue; oropharynx

vagus somatic sensory

- mucous membranes of laryngopharynx, larynx and upper trachea

glossopharyngeal takes pharynx

vagus visceral sensory

- trachea, lungs, carotid sinus, abdominal veins, gut (to splenic flexure)

vagus somatic motor

- lower pharynx, upper oesophagus (swallowing and vomiting)

vagus parasympathetic motor

- cardiac muscle (control of heart beat), smooth muscle in GIT (GI motility), trachea and bronchi (airway diameter)

Note that there is probably only a spinal root of C.XI.

Earlier texts additionally refer to a cranial root but these are now thought to be aberrant fibres of C.X. but also has origins in cervical 1-4

what cranial nerves are in the nucleus ambiguous?

glossopharyngeal and vagus

what is the function of the nucleus ambiguous?

Motor: larynx, pharynx, upper oesophagus

-Vomiting, swallowing, modulation of phonation

what cranial nerves make up the nucleus tractus solitaris?

facial, glossopharyngeal, vagus

(Solitary Nucleus) Visceral Sensory: tongue, carotid body, carotid sinus, GIT, trachea, bronchi

- Chemoreception (inc taste, pCO2/[H+] monitoring, gut distension, blood pressure monitoring