Cranial Nerves and the Brainstem Flashcards
How can the brain be divided into different parts?
The diencephalon is composed of the thalamus and hypothalamus
What does is the brainstem composed of, what does it contain and what does it control?
Midbrain, pons and medulla
Contains many of the CNs’ nuclei
Contains centres that control heart rate, breathing rate etc.
What passes through the brainstem?
All ascending and descending pathways - many of these pathways synapse in brainstem nuclei before going off up to the brain / down to the rest of the body, or some pathways start within the nuclei in the brainstem
How is the cerebellum connected to the pons (in the brainstem)?
By 3 white fibre tracts called the 3 cerebellar peduncles
How many of the cranial nerves (CNs) have their cell bodies in the brainstem?
Why not CN XI?
What is the role of the Accessory nerve (AKA CN XI)?
9 of them - CN III TO CN XII (except CN XI)
Is called the Accessory Nerve - many say there isn’t a cranial part of the Accessory Nerve, as the nerve comes from the spinal cord, to the brain and exits via the vagus nerve (CN X), so it is really a spinal accessory nerve, found in the spinal cord and not the brainstem
Supplies motor fibres to 2 muscles: the sternocleidomastoid (neck) and the trapezius
Through which part of the brainstem is this a section of (the black line)?
What is this type of section / plane?
Through the midbrain:
Sagittal
Label this diagram (taken from a cross section of the midbrain, as shown in the previous card) and describe the 4 parts of this internal structure:
[4 parts relate to the entirety of the brainstem - midbrain, pons and medulla]
Tectum roof - back of the brainstem, behind the ventricular system e.g. the cerebral aquiduct etc.
Tegmentum - large part of the brainstem
Base - towards the front
What is this an image of?
What is the single cranial nerve that comes out of the dorsal aspect?
The back of the brainstem - posterior view, cerebellum has been removed
CN IV - trochlear nerve
What is the diamond shaped part of the brainstem that rests under the cut away cerebellum?
The diamond is the base of the 4th ventricle, CSF would be there (in the oval shape)
The roof of the 4th ventricle would be towards the right of the diamond, where the other structure sticks out
What are the 4 structures that are ascending / occupying the posterior aspect of the medulla?
What is the slight enlargements towards the top of the dorsal columns?
Dorsal columns - gracile and cuneate pathways
The point at which the cuneate and gracile pathways are synapsing onto their nuclei, which contain the cell bodies of the 2nd order sensory neurons
These 2nd order neurons are crossing over to the other side before going up to the brain
This image is the anterior aspect of the brain stem
What would be seen if the top part of the image had continued to be drawn?
The cerebral hemisphere
What are those structures?
The olfactory bulbs, the left olfactory bulb is on the right side of the image, and vice versa
What is the structure beneath the olfactory bulbs?
Optic tract
What structure hangs from that region?
Pituitary gland
What are these structures and which system are they a part of?
Mammillary bodies - part of the limbic system
Label all the CNs you can see on this diagram:
What is that large area on the diagram?
Cerebral peduncle - white fibre tract bringing information down from the cerebral hemispheres to the spinal cord
What occurs in that area (at the bottom) and what is it called?
And the enlarged / bulging area above?
Where 85 - 90% of the motor neurones cross from one side to the another to innervate the limbs - this point is called the decussation of the pyramids
Pyramids / pyramidal tract - contain corticospinal axons
Fill in the labels in this diagram (this is the posterior aspect of the brainstem):
Pineal gland - important for melatonin, circadian rhythms i.e. sleep-wake cycles
Superior and inferior colliculi - small bumps seen on the back of the midbrain, involved in visual and auditory pathways respectively
What is the pineal gland and why is it important?
Sleep-wake cycle / circadian rhythms
Controls the release of melatonin
What is meant by colliculi?
What are they responsible for?
Little hills
Superior colliculus = Visual pathways
Inferior colliculus = Auditory pathway
Fill in the labels and describe the diagram (the anterior aspect of the brainstem):
What is this structure coming out from the optic chiasm?
What is the anatomical difference betwee the optic nerve and the optic tract?
Optic tract
Optic nerve - fibres that come from one eye to the chiasm, contains axons from one eye
Optic tract - axons that have come from both eyes
Where do CN III and CN IV emerge from?
Re-label the structures on this cross-section of the midbrain:
Explain each of the structures (i.e. what they are responsible for):
The midbrain
Posterior - there are hills sticking out, which are the superior (vision) and inferior (auditory) colliculi
Aqueduct - part of the ventricular system
CN nuclei in the tegmentum - CN III (occulomotor, emerges from the anterior aspect) and CN IV (trochlear, emerges from the posterior aspect)
Cerebral peduncles - white fibre tracts
What descending tracts are carried in the huge white fibre tracts (cerebral peduncles)?
Corticospinal and corticobulbar
Which section of the brainstem is this cross-section from (the black line)?
Pons
Label this diagram of the pons and describe the labels:
4th ventricle - ventricular system much larger in the pons than in the midbrain
3 pairs of peduncles that connect the cerebellum to the pons
Major descending fibres found towards the anterior aspect of this diagram - continuous from the cerebral peduncles found in the midbrain cross-section diagram
Tranverse fibres found in the centre of this diagram - fibres travelling from one side to the other
What is seen further down the aqueduct in the pons? How does it compare to the same structure in the midbrain?
Where does the cerebellum sit in comparison to the pons? And how are these 2 connected?
Which cranial nerves emerge from the pons? And where do they bring the information?
4th ventricle - much larger than in the midbrain where the ventricular system is a small hole
Behind / back - connected via the middle cerebelluar peduncle
CN V (trigenimal), VI (abducens), VII (facial) and VIII (vestibulocochlear) - all bring info back to the pontine nuclei
What forms the roof of the 4th ventricle?
The cerebellum
What is medulla?
What is meant by the terms rostral and caudal?
What are the 2 parts of the medulla?
Continuation of the spinal cord going up (rostral)
Rostral = head end
Caudal = tail end
Open (rostral) and closed (caudal)
The anterior aspect contains the pyramids - they are the descending voluntary movement pathway tracts
Posterior aspect contains dorsal columns - disappear at the open medulla as they are made of the primary sensory neurons which synapse at the nuclei and become secondary neurons
Which part of the brainstem is this cross-section from?
Open / Upper medulla
Label this diagram and describe the features:
Why is called the ‘open’ medulla?
Theoretically, the part of the medulla from which the cerebellum can be removed / detached, the 4th ventricle is shaped like a ‘v’ and will be exposed if the cerebellum is removed
It is not surrounded by neural tissue, unlike the aqueduct and spinal cord
Contain many nuclei - CN nuclei and specialised sensory nuclei (receiving senses and providing outflow of info to the cardiovascular, respiratory and vasomotor areas)
What surrounds the aqueduct and spinal cord that does not surround the 4th ventricle?
Which cranial nerves emerge from the open medulla?
Neural tissue
CN IX (glossopharyngeal), X (vagus), and XII (hypoglossal)
Which part of the brainstem is this cross-section from?
Closed (lower) medulla
Label this diagram and describe the features:
Why is it called the ‘closed’ medulla?
4th ventricle is completely enclosed by neural tissue. it continues as the ‘central canal’ in the closed medulla, unlike in the open medulla where it is placed more posterior and the roof is the cerebellum
Dessucation of the pyramids - crossing of the motor neurons
Dorsal columns - innervation from all 4 limbs
Why are the medulla closed or open?
Closed has more neural tissue
Medulla at the cerebellum level = open, medulla below the cerebellum level = closed as neural tissue covers the 4th ventricle
What do the dorsal columns in the closed medulla contain?
Fibres coming from all 4 limbs - gracile = lower limbs, cuneate = upper limbs
What does the anterior surface of the medulla have?
What does the posterior surface of the meulla have?
What are the 2 divisions of the posterior surface of the medulla?
Pyramids
Dorsal columns
Open and closed
Which motor pathway crosses at the medulla?
Corticospinal tract - involved in voluntary movement
What are the 2 blood arterial systems that supply the CNS and which parts of the CNS do they supply?
Anterior supply is derived from the internal carotid system (pair of arteries), feeds most of the forebrain and cerebral hemispheres
Posterior supply is derived from the vertebrobasilar (vertebral arteries that join to form the basilar), feeds the brainstem
Label this diagram of the brainstem blood supply:
Vertebrobasilar system supplies the brainstem, carotid system supplies the circle of willis
Carotid arteries are at right angles of the other artery, all on the same plane
Label the CNs on this brainstem diagram:
CN IX, X AND XII are in the medulla
CN VI, VII and VIII are associated with the junction between medulla and pons (called the pontomedullary junction)
CN III and IV are in the midbrain
1st cervical segment = ventral root of the first spinal nerve (C1) - cervical nerve 1
Both are equally on both sides, but label the nuclei of the CNs - motor and sensory nuclei:
What are the functions of the nuclei that do not have a specific CN number next to them e.g. the salivatory nuclei?
The nuclei such as the salivatory nuclei and the ambiguus nuclei are part of the CN nuclei, however, they send out motor neurons to multiple cranial nerves e.g. salvation = CN IX (parotid salivary gland) and CN VII (facial - submandibular and sublingual salivary glands)
Other nuclei in the diagram with CN numbers next to them supply a single CN
Are CNs motor or sensory?
Can be either or both
Why does the Trigeminal nerve (CN V) have 3 different sensory nuclei?
Where is the trigeminal ganglion? What do they bring back?
The different branches of the trigenimal nerve have different functions - nerves bringing information back go to different nuclei depending on what function they are serving
Information from the head, neck and various parts of the face - then split to go to different nuclei
Carrying different modalities of sensation and so end up at different nuclei e.g. sensory information from mastication VS sensory information from the face
Another diagram:
[Sagittal view]
.
In terms of modalities, what do the GSE, GSA, GVE, SVE … etc. stand for?
Fill in the rest of this table:
General Somatic Efferent, General Somatic Afferent, General Visceral Efferent, Special Visceral Efferent
What are the 2 functions of the occulomotor functions?
CN III
Provide motor neurones to the skeletal muscle fibres that move the eye
Reflexes - e.g. pupillary light reflex + accomodation reflex
What is the function of the trochlear? (Only 1 function)
CN IV
Supplies fibres to the superior oblique muscle
What are the functions of the trigeminal nerve? (3 sensory nuclei = 3 sensory functions, 1 motor nuclei = 1 motor function)
CN V
Sensory - bring back sensations from the face, including: propioception from muscles of mastication (e.g. opening the jaw), discriminative touch from the head, pain and temperature from the head
Motor - innervates the muscles involved in mastication
What is the function of the Abducens nerve? (Only 1 function)
CN VI
Supplies the lateral rectus muscle (that moves the eye out)
4 functions
What are the functions of the facial nerve?
CN VII
Facial expression; some sensation around the ear; parasympathetic motor to lacrimal, submandibular, sublingual and muscosal glands of the mouth and nose e.g. salvation, tears, muscles of mastication; and taste on 2/3 of the tongue
What are the functions of the vestibulocochlear nerve?
CN VIII
Balance and hearing
What are the functions of the glossopharyngeal nerve?
CN IX
Sensation from the posterior 1/3 of the tongue, tonsils, pharynx, chemoreceptors and baroreceptors in the carotid body, gag reflex
Parasympathetic motor to parotid gland
What are the functions of the vagus nerve?
CN X
Many functions
Sensory from around the ear, trachea, larynx stretch receptors from aortic arch, taste buds from the epiglottis (flap that covers windpipe when swallowing)
Motor to pharyngeal muscles, intrinsic muscles of the larynx, smooth muscle and glands of the larynx, pharynx and abdominal viscera, cardiac muscle
What are the functions of the hypoglossal muscles?
CN XII
All intrinsic muscles of the tongue
What are the names of the nuclei each CN connects to / goes through?
