19-09-23 - Brain stem overview and cranial nerve nuclei Flashcards
Learning outcomes
- Specify the importance of the brainstem’s location
- Identify three main anatomical parts making up the brainstem
- Provide an overview of how cranial nerve nuclei are organized
- Describe how this information is used in diagnosing a brainstem lesion
Where is the brainstem orientated in the brain?
How is it orientated and linked?
What does rostral mean?
What 3 structures is the brainstem attached to?
What are the 3 types of functions of the brainstem?
What does the brainstem exert influence over?
What is a nucleus?
- The brainstem is located in the central portion of the brain, it is orientated rostro-caudally and links rostrally
- Rostral - situated or occurring near the front end of the body, especially in the region of the nose and mouth or (in an embryo) near the hypophyseal region.
- 3 structures the brainstem is attached to:
1) Diencephalon superiorly (group of subcortical structures)
2) Cerebellum posteriorly
3) Spinal cord inferiorly
- 3 types of functions of the brainstem:
1) A Conduit – longitudinal tracts to and from the brain and cerebellum and spinal cord
2) Cranial nerve functions via brainstem nuclei
3) Integrative & modulatory functions through the reticulum
- The brainstem exerts neuronal influence over a wide array of vital and non-vital processes
- A nucleus is a collection of cell bodies which function to help relay/generate information
What 11 factors does the brainstem exert neuronal influence over?
- 11 factors the brainstem exerts neuronal influence over:
1) Heart rate
2) Respiration (Pre-Bötzinger complex)
3) Antigravity and postural muscles
4) Eye movement
5) Head tracking
6) Lower motor neuron excitation
7) Autonomic activation
8) Pain perception modulation
9) Arousal
10) Sleep
11) Vomiting
What structure is the brainstem located in?
What structures are located anterior, posterior, inferior, and superior to the brainstem?
- The brainstem is located within the posterior cranial fossa
- Structures located around the brainstem:
1) Anterior
* Clivus
* Nerves & vessels
2) Posterior:
* Cerebellum & attachments
3) Inferiorly
* Foramen magnum & spinal cord
4) Superiorly:
* Tentorium cerebelli & diencephalon
Label the external features of the brainstem (in picture)
Label the internal features of the brainstem (in picture)
Descending Tracts.
Where does the corticospinal tract originate?
Where does the corticospinal tract carry motor information to and from?
What % of fibres do/do not decussate in the corticospinal tract?
What will a brainstem lesion of the lateral corticospinal tract in the brainstem cause?
- Descending Tracts
- The corticospinal tract is a descending pathway
- Most of the neurons of the corticospinal tract originate in either the primary motor cortex (precentral gyrus, Brodmann area 4) or the premotor frontal areas.
- The corticospinal descending pathway carries motor information from the cortex to lower motor neurons in the spinal cord.
- 85-90% of fibres decussate in the medullary pyramids
- 10-15% of fibres remain ipsilateral until bilaterally innervating LMNs in the spinal cord
- A brainstem lesion of the lateral corticospinal tract in the brainstem will produce contralateral UMN signs
Descending Tracts.
Where does the corticobulbar descending pathway originate?
Where does it carry information to and from?
Is information from this pathway bilateral or contralateral?
Where does decussation occur?
What does a brainstem lesion of these tracts cause?
How can we tell what side the lesion is on with this tract?
How does this compare to lesions on cranial nerves?
- Descending Tracts
- The corticobulbar tract originates in the precentral gyrus (primary motor cortex)
- It carries motor information from the motor cortex to motor nuclei of the brainstem.
- Innervation from the corticobulbar pathway is mostly bilateral (see CN VII) with the fibre decussation occurring at the level of the nucleus
- A brainstem lesion of these tracts will produce effects dependant on where the lesion is
- If we have loss of function on one side, a brainstem lesion in the corticobulbar tract will be on the same side as the loss of function
- With cranial nerves, the loss of function is always ipsilateral to the side the lesion is on
What are the 4 descending tracts that originate in the brainstem?
Where do they each originate and go to? What do they each link?
What is their purpose?
Rubrospinal and tectospinal pathways in picture
- 4 descending tracts that originate in the brainstem:
1) Rubrospinal tract
* Originates in the red nucleus and goes to the flexors of the upper limb
* Primarily linked to effecting changes directed by the cerebellum in upper limb flexation – don’t overrun on the movements we make
2) Tectospinal pathway
* Originates in the superior colliculus and goes to the neck musculature
* Links visual stimuli with head and neck movements allowing visual stability and a focus on a given target
* Contralateral pathway
3) Vestibulospinal pathways
* Originates in the lateral and medial vestibular nuclei and goes bilaterally to the neck muscles (medial vestibulospinal tract) and ipsilaterally to excite extensors and to inhibit flexors (lateral vestibulospinal tract)
* Provides control over antigravity muscles and processes to protect the head during unexpected posture changes
4) Reticulospinal pathway
* Originates in the pontine and medullary reticular formation and goes to the cervical spinal cord
* Ipsilateral descending pathway with bilateral innervation in the cervical spinal cord.
* This pathway can link emotion to posture and enhance the response to stimulation (primes the upper body for attack or defence amongst other things)
- Rubrospinal and tectospinal pathways in picture
Vestibulospinal pathways and Reticulospinal pathway (in picture)
Ascending Tracts.
What are the 3 ascending tracts that involve the brainstem?
Where do each of these tracts originate and terminate?
What information do these pathways carry?
Where do they decussate?
What are the effects of brainstem lesions in these tracts?
- 3 ascending tracts that involve the brainstem:
1) Medical lemniscal pathway
* The medial lemniscus (second-order neuron of DCML - Dorsal column–medial lemniscus pathway) commences at the nucleus gracilis and nucleus cuneatus at the caudal medulla
* This pathway terminates in the sensory cortex
* The medial lemniscal pathway carries JPS and mechanical information (discriminating touch vibration & pressure etc) from the dorsal columns
* This pathway decussates after the gracile/cuneate nuclei and ascends medially to the thalamus
* Brainstem lesion of this tract produces contralateral loss of JPS and discriminating touch – this is not the same as a lesion in the spinal cord, as decussation occurs high up
2) Spinal lemniscal pathway
* Spinal lemniscal pathway is the extension of the spinothalamic tract through the Brainstem
* This pathway pathway terminates in the sensory cortex
* It carries pain and temperature sensation
* The spinal lemniscal pathway decussates quickly in the spinal cord and ascends laterally to the thalamus
* Brainstem lesion of this tract produces a contralateral loss of pain and temperature sensation.
3) Spinocerebellar tract
* Carries proprioceptive information
* The spinocerebellar tract ascends ipsilaterally in the lateral portion of the brainstem to the pons, where it enters the brainstem.
* Brainstem lesion of this tract produces an ipsilateral defect.
Medial lemniscal pathway (in picture)
Spinal lemniscal pathway (in picture)
Spinocerebellar tract (in picture)
Summary of tracts (in picture).
What are the 6 tracts associated with the brainstem?
Which 3 are medial and lateral?
What is the function of each?
What is the reticulum of the brainstem?
Where is it located in the brainstem?
What are 3 functions of the reticulum of the brainstem?
- The reticulum of the brainstem is a Diffuse network of neurons without detectable nuclei but which work predominantly in groups of neurotransmitter related networks.
- It is found throughout the brainstem, located in the central tegmentum
- 3 functions of the reticulum of the brainstem:
1) Regulation of pain sensation
2) Arousal of the cortex
3) Modulation of descending motor output
How are motor and sensory nuclei arranged in the spinal cord?
How does this change as the medulla is ascended?
What does somatic and visceral sensory mean?
- In the spinal cord the motor and sensory nuclei are arranged across the horns in a ventral-dorsal order
- As medulla is ascended, the tectum increases, ‘pushing’ the nuclei into a more medial-lateral arrangement
- Note that this rotation does not affect the positions of the general motor or sensory areas with respect to each other.
- Somatic sensory signals are conscious sensory signals
- Visceral sensory signals are unconscious sensory signals
Describe the organization of the cranial nuclei in the brainstem
- Organization of the cranial nuclei in the brainstem:
- Three lateral sensory columns of nuclei on each side
- Three medial motor columns of nuclei on each side
- In reality there is some overlap between the columns however in general this diagram holds true
Name each cranial nerve and the nuclei that supply each (in picture)
What is the rule of 4 regarding cranial nerves?
How many different types of cranial nerves are there?
Why is it important to know what connectivity of cranial nerves?
Overview of the Anatomy and Physiology of the Cranial Nerves (CN) (in picture)
- Cranial nerves follow the rule of 4, i.e.
- There are 4 cranial nerves in or above the midbrain
- There are 4 cranial nerves in the Pons
- There are 4 cranial nerves in the medulla
- There are pure motor, pure sensory and mixed nerves. A single nerve can therefore map to more than one nucleus
- Knowing which nerves map onto what nuclei, and where they are located in the brainstem is vital for brainstem diagnosis
- Overview of the Anatomy and Physiology of the Cranial Nerves (CN) (in picture)
Nuclei controlling somatic motor output to the eye and tongue.
What type of nuclei are in the most medial column of the brainstem?
What are the 4 nuclei in the most medial column of the brain stem?
What cranial nerve do they each serve? What is their function?
- Nuclei controlling somatic motor output to the eye and tongue
- There are somatic motor nuclei in the most medial column of the brainstem
- 4 nuclei in the most medial column of the brain stem and the cranial nerve they serve:
1) Oculomotor nucleus (Oculomotor N. 3)
* Function: control of extraocular eye muscles except superior oblique and lateral rectus
2) Trochlear nucleus (Trochlear N. 4)
* Function: control of superior oblique muscle of the eye
3) Abducens nucleus (Abducens N. 6)
* Function: control of lateral rectus muscle of the eye – Note the above three are all linked through the Medial Longitudinal Fasciculus (MLF) Nuclei controlling somatic motor output to the eye and tongue
4) Hypoglossal nucleus (Hypoglossal N. 12)
* Function: control of tongue muscles
* Tongue deviates to one side when stuck
Nuclei controlling Special visceral (pharyngeal derived) motor output.
What type of nuclei are in the 2nd most medial column of the brainstem?
Why do these nuclei not follow the medial rule of brainstem nuclei?
What are the 4 nuclei in the 2nd most medial column of the brain stem?
What cranial nerve do they each serve?
What is their function?
What are 5 important controls to remember about these cranial nerves?
- Nuclei controlling Special visceral (pharyngeal derived) motor output
- There are pharyngeal motor nuclei in the 2nd most medial column of the brainstem
- Note these more ‘lateral’ motor nuclei are ‘special’ so doesn’t follow the medial rule
- 4 nuclei in the 2nd most medial column of the brain stem and the cranial nerve they serve:
1) Trigeminal motor nucleus (Trigeminal N. 5)
* Function: Controls muscles of mastication Nuclei controlling Special visceral (pharyngeal derived) motor output
2) Facial nucleus (Facial N. 7)
* Function: control of muscles of facial expression (NB ventral to the Vestibulocochlear nucleus)
3) Nucleus ambiguus
* Function: Motor to pharynx and larynx (Glossopharyngeal N. 9 and Vagus N. 10)
4) Accessory nucleus
* Function: Motor to sternocleidomastoid and trapezius muscles (Accessory nerve 11)
- 5 important controls to remember about these cranial nerves:
1) Chewing (5)
2) Grimace (7)
3) Swallow (9-10)
4) Speak (9-10)
5) Shrug (11)
Nuclei with Autonomic (general visceral / autonomic) control.
What are the 4 nuclei with Autonomic (general visceral / autonomic) control in the brainstem?
What cranial nerve do they each serve?
What is their function?
- Nuclei with Autonomic (general visceral / autonomic) control.
- 4 nuclei with Autonomic (general visceral / autonomic) control in the brainstem and the cranial nerve they serve :
1) Edinger-Westphal nucleus (Occulomotor N. 3)
* Function: control of pupillary constriction and lens accommodation
2) Superior Salivatory nucleus (Facial N. 7)
* Function: control of lacrimal sublingual and submandibular glands, salivary glands (Facial N. 7 & Glossopharyngeal N. 9) NB Nucleus Ambiguus also supplies N. 9 Inferior
3) Salivatory nucleus (Glossopharyngeal N. 9)
* Function: control of parotid gland
4) Dorsal motor nucleus of the Vagus (Vagus N. 10)
* Function: secretomotor to lungs and gut; control of heart rate
Nuclei receiving sensory information.
What are the 5 Nuclei in the brainstem receiving sensory information?
What cranial nerve do they each serve?
What is their function?
- Nuclei receiving sensory information
- 5 Nuclei in the brainstem receiving sensory information and the cranial nerve they serve:
1) Trigeminal mesencephalic – somatic sensory (Trigeminal N. 5)
* Function: Proprioception from the mouth
2) Trigeminal pontine (principal) – somatic sensory nucleus (Trigeminal N. 5)
* Function: Discriminating touch from face
3) Vestibulocochlear nucleus (Occulomotor N. 8) - Special somatic sensory
* Function: Balance and hearing
4) Solitary nucleus - Visceral sensory
* Function: Taste (Facial N. 7, Glossopharyngeal N. 9, Vagus N. 10), carotid baroceptors (Glossopharyngeal N. 9) & visceral afferent from pharynx, larynx lungs, gut (Vagus N. 10)
5) Trigeminal spinal nucleus (Trigeminal N. 5) – somatic sensory
* Function: pain and temperature sensation from face, back of tongue, pharynx larynx and ear
Summary of cranial nerve linkages to brainstem nuclei Dorsal view (in picture)
Summary of cranial nerve linkages to brainstem nuclei Lateral view (in picture)
Describe the Non-cranial nerve nuclei (and networks) & their function (in picture):
* Midbrain – 6
* Pons – 2
* Medulla - 4
What is an initial clue during examination that there is a brainstem lesion present?
What 3 questions can we ask to determine the location of the brainstem lesion?
What other information should we recall?
- During examination, signs on both sides of the body (above and below the neck) but asymmetrical distribution suggests there may be a brainstem lesion present
- 3 questions can we ask to determine the location of the brainstem lesion:
1) Which cranial nuclei are involved? This gives the level in the brainstem.
2) Which tracts are involved? This indicates if the lesion is medial, lateral or bilateral
3) Which side is affected:
* Ipsilateral: Sympathetic; LMN cranial nerve, limb ataxia
* Contralateral: limb/body UMN & loss of pain /temperature sensation & fine touch/ proprioception
- Recall from the summary table (in picture) the:
- 3 structures which lie to the midline of the brainstem and begin with the letter “M”
- 3 structures which lie to the side of the brainstem and begin with the letter “S”
How do cerebellum issues normally present?
When should we consider that there may be a medullary problem present?
What should we look at to determine the side of the lesion?
What is Lateral medullary or Wallenberg syndrome?
Describe how Lateral medullary or Wallenberg syndrome typically presents with a right-side lesion (in picture)
- Cerebellum issues will be ipsilateral to the lesion
- Above the neck and below the neck with different syndromes, we should immediately start thinking about a medullary problem
- We should look at what is wrong with the face, as this will tell us the side of the lesion
- This is because cranial nerve lesions are ipsilateral e.g loss of pain and sensation via the trigeminal nerve on the right side of the face, the lesion is on the right side
- Lateral medullary or Wallenberg syndrome is an infarct affecting the lateral tegmentum of the brainstem
- How Lateral medullary or Wallenberg syndrome typically presents with a right-side lesion (in picture):
1) Ptosis & Small pupil (right side - same side as lesion)
2) Loss of pain & temp sensation in the face via trigeminal nerve (right side - same side as lesion)
3) Ataxia from infarct of cerebella peduncle – (right side - same side as lesion, as cerebellum issues are ipsilateral to side of lesion)
4) Loss of pain & temperature
* Loss of pain and temperature on the left side - if the lesion is in the brainstem, it will be on the opposite side from this loss of pain and temperature
5) Dysphagia (cant tell what side this is on usually)
