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BB1 > Brainstem and Cranial Nerves Part 1 > Flashcards

Brainstem and Cranial Nerves Part 1 Flashcards

1
Q

What are the constituents of the brainstem/lower brain?

A 
Medulla
Pons
Midbrain
Hypothalamus Thalamus
Cerebellum
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2
Q

What shape is the brainstem (from a mid-sagittal view)?

A

Woody Woodpecker

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3
Q

Where is the brainstem located and what are its three main components? What is not included in the brainstem?

A 
-	Located between forebrain and spinal cord
o	Midbrain
	CN III-IV 
o	Pons
	CN V - VIII
o	Medulla 
	CN IX – XII
-	Does not include the cerebellum although the brainstem communicates with the cerebellum
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4
Q

What does each component of the brainstem do?

A

See picture in lecture notes

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5
Q

What are the functions of the brainstem?

A
  • Conduit
    o Long tracts to / from spinal cord pass through the brainstem
  • Cranial nerve functions
    o Sensory input and motor output for the head and neck plus parasympathetic output; special senses, and the reflexes involving them
  • Integrative centres in the brainstem:
    o Sensorimotor integration - connectivity with cerebellum (coordination); reflex centres
  • Brainstem core (reticular formation) mediates:
    o Autonomic control of respiratory and cardiovascular reflexes & other behaviours e.g., swallowing, sneezing
    o Somatic/ autonomic modulation via descending pathways (reticulospinal tract, descending autonomic axons from hypothalamus)
    o Diffuse neuromodulatory systems that regulate consciousness, and that affect sensory, motor and cognitive functions
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6
Q

In what way is the brainstem a continuation of the spinal cord?

A
  • Starts around C2 vertebrae with spinal cord changing gradually into the brainstem
  • General rule
  • Sensory nuclei / tracts that were dorsal in the spinal cord move laterally
  • Motor nuclei / tracts move medially
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7
Q

What is the dorso-ventral organisation of the brainstem? How is this knowledge helpful?

A
  • Dorsal part (tectum)
    o Cranial nerve nuclei and sensory reflex centers
  • Middle part (tegmentum)
    o Ascending pathways & reticular formation (looser, less defined) (with integrating nuclei; descending sympathetic axons
  • Ventral part
    o Descending motor pathways e.g. CST (corticospinal tract), CBT (corticobulbar tract), rubrospinal, reticulospinal and vestibulospinal tracts
  • Conduit functions of brainstem are important
    o Allow integration of information at subconscious, reflexive levels by connectivity with brainstem
  • Knowledge of dorso-ventral and medio-lateral organisation aids in the deduction of location of pathology occurring with deficits
  • Descending sympathetic control from hypothalamus— to preganglionic in T1-L2/3– projecting to ganglia where postganglionic fibres arise
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8
Q

What is the tegmentum? And the peduncle?

A
  • Tegmentum- covering over the ventral part of the brainstem- generally central grey matter
  • Peduncle– stalk or stem
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9
Q

What is another name for the mid-brain? What are its different parts and their functions?

A

Midbrain (mesencephalon)
- Superior posterior portion = tectum
o Means “roof”
o Structures such as pineal gland control sleep and circadian cycle
- Surface of tectum covered with 4 bumps (2 paired structures)
o Superior and inferior colliculi
- Superior colliculi
o Involved in eye movements and visual processing
o Sends information to lateral geniculate nucleus
- Inferior colliculi
o Involved with auditory processing (e.g. startle reflex)
o Send information to medial geniculate nucleus
- Anterior side = cerebral peduncles
o Tracts descending from thalamus
 CST and CBT
- Superior colliculi = movement of eyes head and neck in response to visual stimuli (tracking)
- Inferior colliculi = movement of head and truck in response to sound stimuli (startle reflex)
- Substantia nigra is located in midbrain
o Rich in dopamine neurons
o Part of basal ganglia
- Cerebral aqueduct
o Links 3rd ventricle to 4th ventricle
o Surrounded by periaqueductal grey
 Role in analgesia, quiescence and bonding
o Dorsal raphe nucleus (largest serotonin nucleus) ventral side of periaqueductal grey
o Role in depression and sleep wake cycle

(See diagram in notes)

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10
Q

Which nerves originate in the midbrain?

A 
-	Cranial nerves
o	Oculomotor (CN III)
	Controls eyelid, eye movements 
	Pupil and lens
-	Trochlear (CN IV)
o	Only CN to leave from posterior (dorsal) side
o	Eye movement
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11
Q

What is another name for the pons? What are its different parts and their functions?

A

Pons (metencephalon)
- Ascending and descending tracts pass through, also connects with cerebellum
o Cerebellar peduncles

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12
Q

Which nerves originate in the pons?

A 
-	Cranial nerves
o	Trigeminal (CN V)
	Sensation to face
	Motor to muscles of mastication
-	Abducens (CN VI)
o	Eye movements
-	Facial (CN VII)
o	Movements of face
o	Special sense of taste
o	Parasympathetic to lacrimal and some salivary glands)
-	Vestibulocochlear (CN VIII)
o	Hearing and balance
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13
Q

What is another name for the medulla? What are its different parts and their functions?

A

Medulla (myelencephalon)
- Continuation (connects) spinal cord
- Contains nucleus of solitary tract
o Receives information about blood flow and levels of oxygen and carbon dioxide
o When information suggest problem reflexive actions to restore back to desired range
-

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14
Q

Which nerves originate in the medulla?

A 
Cranial nerves
o	Glossopharyngeal (CN IX)
	Sensory to back of throat
•	Afferent for Gag reflex
o	Motor to soft palate
o	Parasympathetic to salivary glands
-	Vagus (CN X)
o	Motor for Gag reflex
o	Most of parasympathetic to body (about 95%)
-	Spinal accessory (CN XI)
o	Motor to muscles on neck (trapezius and sternocleidomastoid) 
-	Hypoglossal (CN XII)
-	Motor to tongue
-	Nucleus of solitary tract not only communicates with vagus nerve, but also sympathetic outflow to allow for homeostasis
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15
Q

What are the main functions of the midbrain?

A

Associated with auditory, visual and pupillary reflexes and with eye movements

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16
Q

What are the main functions of the pons?

A

Its main functions are mastication (V), eye movement (VI), facial expression, taste, blinking, salivation, lacrimation (VII), and equilibrium and audition (VIII)

17
Q

What are the main functions of the medulla?

A

Associated with equilibrium, audition (VIII), deglutition, salivation, taste (IX), respiration & circulation, GI function (X), neck & shoulder movments (XI) tongue movements (XII), coughing and vomiting (RF)

18
Q

What is special about cranial nerve V?

A
  • V carries postganglionic parasympathetic efferents– from otic ganglion (to parotid– inf salivatory nucleus via IX to ganglion), submandibular ganglion, pterygopalatine ganglion (assoc with VII- innervated by greater petrosal nerve– superior salivatory nucleus and lacrimal nucleus), and ciliary (III)
19
Q

Where do cranial nerves enter/exit the brainstem? How are they organised? What are their functions?

A
  • Cranial nerves enter / exit at specific rostral-caudal locations in brainstem
  • In general II-IV are associated with the midbrain, V-VIII pons and IX-XII medulla
  • There is a lateral (sensory)– medial (motor) organisation
  • There are pure sensory nerves (I, II, VIII), pure motor nerves (III, IV, VI, XI, XII) and mixed sensory & motor nerves (V, VII, IX, X)
20
Q

Which afferents do cranial nerves have?

A
  • Cranial nerves have general somatic sensory and visceral sensory afferents like spinal nerves
    o There are also special sensory afferents
     i.e. vision, hearing, smell, taste
21
Q

What are the three types of motor nuclei and what do they do?

A
  • There are 3 types of motor nuclei:
    o Somatic motor nuclei project to skeletal muscle (eye muscles and tongue)
    o Branchial motor nuclei project to muscles derived from branchial arches (craniofacial structures)– movement of jaws (V), facial expression (VII), motor to larynx and pharynx (X) and neck and shoulder muscles (XI)
    o Visceral motor nuclei: pre-ganglionic parasympathetic fibres
  • (Branchial – relating to gills. In fish bony structures supporting gills – in other vertebrates structures derived from the same embryologic precursors)
22
Q

What are the orders of the nuclei from the midline (they are bilateral)?

A
  • From midline (nuclei are bilateral):
    o 1. Somatic motor: lower motor neurons (LMNs- somatic and branchial)
    o 2. Visceral motor i.e. preganglionic parasympathetic
    o 3. Visceral sensory i.e. from gut, blood vessels, mucosa incl. taste
    o 4. Somatic sensory – general (V) and special (VIII)
23
Q

What are branchiomotor nuclei sometimes called? Which cranial nerves have branchiomotor nuclei?

A

Special visceral efferent

  • V,VII,IX,X,XI– refers to efferent nerves that provide motor innervations to the muscles of the pharyngeal arches in humans
  • Spinal accessory are from C1- C5 so not here
24
Q

Where are cranial nerve nuclei located in the brainstem?

A
    1. Cranial nerve nuclei: columns of neurons associated with cranial nerves
    1. The nuclei follow the rostral-caudal organisation of the structures innervated
25
Q

Which part of the brainstem are each type of cranial nerve nuclei located in? What do each of these nuclei do?

A

See table in lecture notes

26
Q

What are the important brainstem reflexes? Which nerves do the afferent and efferent arcs involve? Which area of the brainstem is involved?

A

See table in lecture notes

27
Q

What are the afferent and efferent nerves involved in the pupillary light reflex? What is the parasympathetic reaction for this reflex? What happens when there are lesions in the afferent or efferent nerves?

A
  • Afferent CN II
    o To both pretectal areas
    o To both Edinger-Westphal nuclei (CN III)
  • Efferent CN III
    o Direct and indirect pupil closure
  • Parasympathetic reflex
    o Light- sensory input- axons of retinal ganglion cells in CNII- optic nerve
    o Synapse in pretectal nucleus (midbrain)
    o Bilateral innervation of Edinger-Westphal nucleus (E-W; parasympathetic div of CNIII)
    o E-W nuclei send output to both ciliary ganglia which cause constriction of pupils via sphincter pupillae muscles
    Normal = both pupils constrict
    CN III lesion = loss of consensual pupillary light reflex
    CN II lesion = loss of direct pupillary light reflex

See lecture notes for useful diagram

28
Q

What happens in the accommodation reflex?

A
  • Eyes move from focusing on far to near object
  • 3 reactions happen
    o Constriction of pupils
    o Thickening of lens
     Constriction of ciliary muscles
    o Convergence of both eye balls

See lecture notes for useful diagrams

29
Q

What are the afferent and efferent nerves in the doll’s eye reflex (oculocephalic or vestibulocular reflex)? How is it tested? What is a normal result, and what is a positive (abnormal) result?

A
  • Afferent = CN VIII
  • Efferent = CN III, CN IV and CN Vi
  • New-born babies passive turning of head leaves eyes behind (stationary)
    o Disappears within a week or two
  • Tested by turning patients head from side to side
  • Normal = as head moves in one direction eyes move in opposite to maintain gaze
  • Positive test (Abnormal) = eyes do not turn with the head
    o Suppressed in alert patients but surfaces in comatose patients

See lecture notes for useful diagrams

30
Q

What is the medial longitudinal fasciculus (MLF)? What does it become in the spinal cord? What is internuclear ophthalmoplegia and when might it be seen?

A
  • MLF heavily myelinated composite tract
    o Extends length of brainstem in paramedian plane
    o Signals from vestibular nuclei to keep eyes balanced in space despite head movements
  • MLF becomes the medial vestibulospinal tract (mVST) in the spinal cord
    o Acts on motoneurons for neck muscles
    o mVST coordinates reflexive head and neck movements to keep eyes stable in space
  • Internuclear ophthalmoplegia
    o Lesion in superior pons between abducent and oculomotor nuclei
    o Seen in MS
     Isolates paralysis of medial rectus on side of lesion on attempted lateral gaze
     Mononuclear horizontal nystagmus in adducting eye contralateral to side of lesion
  • The medial longitudinal fasciculus (MLF) connects cranial nerve nuclei controlling eye movement and the vestibular nuclei

See lecture notes for useful diagrams

31
Q

When might MLF damage occur? What are its symptoms?

A
  • MLF damage can occur with stroke (unilateral) or multiple sclerosis lesion (often bilateral)
  • Leading eye nystagmus and failure of adduction of the eye
  • Internuclear ophthalmoplegia occurs with damage to the medial longitudinal fasciculus (MLF).
  • Normally when looking left, the left abducens nucleus (VI) fires to contract the left lateral rectus and via its connection to contralateral oculomotor nucleus causes contraction of right medial rectus. BOTH EYES LOOK THE SAME DIRECTION. With MLF lesion, this does not occur however convergence is intact (all CN III).
  • III, IV and VI– MOTOR- extra-ocular eye muscles
  • Left internuclear opthalmoplegia
  • Internuclear ophthalmoplegia (damage to MLF, which connects CN III and CN VI) unilateral condition probably due to stroke.
  • ***bilateral condition a/w multiple sclerosis
  • Normally when looking to the left, the left nucleus of CN VI fires, which contracts the left lateral rectus and stimulates the contralateral (right) nucleus of CN III via the right MLF to contract the right medial rectus
  • Paramedian pontine reticular formation
32
Q

What are the afferent and efferent nerves involved in the blink reflex?

A
  • Afferent CN V1
  • Also bright light (CN II), loud noise (CN VIII)
  • Efferent CN VII

See lecture notes for useful diagrams

33
Q

What are the afferent and efferent nerves involved in the gag reflex? What do these cause?

A
  • Afferent CN IX
    o Evoked by touching roof of the mouth, back of the tongue and back of the throat
  • Efferent CN X
    o Contraction of the muscles at the back of the throat soft palate and pharynx
  • May lead to actual vomiting plus
    o Excessive lacrimation, salivation and sweating
    o Healthy defence preventing entry of foreign bodies into larynx / pharynx

See lecture notes for useful diagram

BB1 (28 decks)

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