Brainstem Part 1 Flashcards
where is the brainstem located
Located between the forebrain and spinal cord
what makes up the brainstem
Comprised of the midbrain, pons and medulla
what is the oldest part of the brain
brainstem
what does the pons do
- it relays sensory information to the cerebellum and thalamus
- subconscious somatic and visceral motor centres
what does the midbrain do
- it processes visual and auditory data
- generation of reflexive somatic and motor responses
- maintenance of consciousness
what does the medulla do
- relays sensory information to the thalamus and other parts of the brainstem
- autonomic centres for regulation of visceral function such as cardiovascular, respiration and digestive system
what are the 3 functions of the brainstem
- conduits
- Cranial nerve functions
- integrative centres in the brainstem
what is the conduit function of the brainstem
long tracts to or from the spinal cord pass through the brainstem
what are the cranial nerve functions of the brainstem
- there is the sensory input and motor output for the head plus parasympathetic motor output;
- cranial nerves also carry special senses
- the brainstem coordinates reflexes involving them.
what are the integrative centres in the brainstem
sensoriomotor integration
brainstem core
- autonomic control
- somatic and autonomic modulation
what is sensorimotor integration
- this is connectivity with the cerebellum and where the reflex centres are
what is the brainstem core mediating
- autonomic control of important respiratory and cardiovascular reflexes & other behaviours e.g., swallowing, sneezing.
- Somatic/ autonomic modulation via descending pathways (reticulospinal tract, descending premotor sympathetic axons from hypothalamus)
different neuromodulatory systems are….
important in regulation of conscious states as well as affecting sensory, motor and cognitive functions.
where dot he sensory nucleic that were dorsal in the spaniel cord move when they enter the brainstem
they move laterally and ventrally(towards the front and down )
where do the motor nuclei that were ventral in the spinal cord move when they enter the brainstem
- the move more medially
how is the brainstem organised
It is divided into..
- Dorsal part
- middle part
- ventral part
what does the dorsal part(tectum) of the brainstem have in it
- cranial nerve nuclei and sensory reflex centres
what does the middle part (tegmentum) of the brainstem have in it
- it contains the ascending pathways and reticular formation (with integrating nuclei; descending sympathetic axons
what does the ventral part of the brain stem have in it
descending motor pathways e.g., corticospinal & corticobulbar tracts; rubrospinal, reticulospinal and vestibulospinal tracts arising in brainstem
what do conduit functions of the brainstem allow
- they allow integration of information at subconscious, reflexive level by connectivity with brainstem
how many Paris of cranial nerves are there
12 pairs
what do cranial nerves do
- Provide sensorimotor innervation of the skin, muscles and joints of the head & neck.
- Mediate vision, hearing, taste and olfaction (special senses)
- Carry autonomic fibres that control visceral functions e.g. gut, breathing, heart rate, and blood pressure regulation.
what are the origin of cranial nerves
Cranial nerve nuclei are one origin of preganglionic parasympathetic neurons
what surface of the brainstem can cranial nerves be seen from
Cranial nerves can be seen from the ventral surface
where do afferent cranial nerves arise form
- cranial nerves have afferents which arise from ganglia
where do 2nd order sensory nuclei arise from
they are located in cranial nuclei
where do motor efferents arise from
Motor efferents arise from cranial nerve nuclei. Such nuclei control parasympathetic and somatic motor functions
name the cranial nerves and whether they are sensory or motor or both
CNI - Sensory CNII - sensory CNIII - motor CNIV- motor CN V - sensory and motor CN VI - motor CN VII - sensory and motor CN VIII - sensory CN IX - sensory and motor CN X - sensory and motor CN XI - motor CN XII - motor
what cranial nerves is the midbrain associated with
II - IV
- Associated with auditory, visual and pupillary reflexes and with eye movements.
what cranial nerves is the pons associated with
V-VIII
- Its main functions are mastication (V), eye movement (VI), facial expression, taste, blinking, salivation, lacrimation (VII), and equilibrium and audition (VIII).
what cranial nerves is the medulla associated with
VIII-XII
- 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).
where are the sensory nerves located
laterally
where are the motor nerves located
medially
describe the general breakdown of cranial nerves in parts of the brainstem
In general II-IV are associated with the midbrain, V-VIII pons and IX-XII medulla
what are the three types of motor nucleic
- somatic motor nuclei
- branchial motor nucleic
- visceral motor nuclei
describe the three types o motor nuclei
Somatic motor nuclei project to skeletal muscle (eye muscles and tongue)
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)
Visceral motor nuclei: pre-ganglionic parasympathetic fibres
describe the nuclei from the midline
- Somatic motor: lower motor neurons (LMNs- somatic and branchial)
- Visceral motor i.e. preganglionic parasympathetic
- Visceral sensory i.e. from gut, blood vessels, mucosa incl. taste
- Somatic sensory – general (V) and special (VIII)
what are cranial nerve nuclei
- these are columns of neurones that are associated with cranial nerves
what organisation do the cranial nuclei follow
- they follow the rostral-caudal organisation of the structures innervated
where does the spinal accessory nerve arise from and describe its pathway
- Arises from branchial motor neurons in the spinal cord.
- Enters cranial cavity via foramen magnum and exits via the jugular foramen.
what does the spinal nerve innervated
Innervates sternocleidomastoid
&trapezius muscles.
where do the motor neurones that give rise to the accessory nerve come from
The motor neurons giving rise to the accessory nerve are actually a separated fragment of the long column of the nucleus ambiguus. They arise from C3-C5
what are the three nuclei that the vagus can arise from
Can arise from 3 nuclei
- dorsal motor nucleus of vagus
- nucelus ambiguus
- nucleus of the solitary tract
what does the vagus from - dorsal motor nucleus of vagus - nucelus ambiguus - nucleus of the solitary tract arise from and innervate
- The dorsal motor nucleus of the vagus gives rise to Parasympathetic outflow to the heart and digestive system (and parasympathetic part of n. ambiguous
- the nucleus ambiguus - this is where the brachial motor innervation arises which innervates the palate, pharynx and larynx
The nucleus of the solitary tract gives rise to Afferents from the lungs and gut travel in the vagus nerve mediating parasympathetic reflexes, swallowing, coughing, retching etc… Visceral afferent information is processed in the caudal nucleus of the solitary tract (NTS)
what is the role of the glossopharygneal
- Its main function is to detect the taste of things in the back of the mouth and secrete saliva into the mouth.
- It also contains touch fibres from the back of the mouth and these trigger the gag reflex.
what nucleus is involved in the glossopharyngeal
- Taste from posterior part of tongue is detected and conveyed to the rostral nucleus of the solitary tract & stimulates saliva secretion.
- There are also sensory mechanoreceptors in pharynx for touch travelling in it.
what does damage to the vagus lead to
- difficulty swallowing and vocalising due to paralysis of vocal cords on affected site
- poor secretion of various gut fluids, saliva, stomach acid, etc due to lost vagal parasympathetic control
what does damage to the glossophargenal lead to
Loss of Gag reflex on affected side.
what does the Vestibulocochlear nerve do
Cochlear portion: conveys the special senses of audition (hearing)
Vestibular portion: our perception of self motion, head position and spatial orientation relative to gravity
describe the pathway of the Vestibulocochlear nerve
- there is vestibular and cochlear nuclei that form a complex that spans from the pons into the rostral medulla
- the nerve enters the brainstem at the medulla and pons junction
where does the facial nerve enter the skull
- via the internal auditory meatus - it can be damaged by an caustic neuroma as it travels with the vestibulocochlear nerve
what is the main action of the facial nerve
Main action is to provide motor supply to muscles of facial expression
what are the 3 jobs of the facial nerve
1- motor supply to muscles of facial expression
2 - parasympathetic secretomtoor - controls nasal and lacrimal secretion
3. Taste afferents
describe the 3 jobs of the facial nerve
Five somatic divisions– mainly branchial motor (some sensory fibres carry touch, pain, temperature sensations via posterior auricular nerve)
Parasympathetic secretomotor– superior petrosal nerve controls nasal secretion and lacrimation
Taste afferents from the anterior 2/3 of the tongue travel from the chorda tympani (with parasympathetic fibres to submandibular and sublingual salivary glands) via the geniculate ganglion to the rostral nucleus of the solitary tract (→ventromedial thalamus → insular cortex)
what are the 4 roles of the trigeminal
Motor to muscles of mastication in V3
Touch sensation of face
Pain, temperature, crude touch of face
Proprioceptive input-
describe the nuclei that are involved in each of the roles of the trigeminal
- Motor to muscles of mastication in V3
- Touch sensation of face
- Pain, temperature, crude touch of face
- Proprioceptive input
Motor to muscles of mastication in V3 : Motor nucleus of trigeminal - upper motor neuron (cortical) innervation is bilateral, so supratentorial stroke will not alter mastication
Touch sensation of face (+ dura…) → this is controlled by the Trigeminal ganglion→ Principal trigeminal nucleus
Pain, temperature, crude touch of face (+) → Trigeminal ganglion → spinal trigeminal nucleus
Proprioceptive input- muscles of mastication– mesencephalic trigeminal nucleus
what does the medial longitudinal fascicles do
this connects cranial nerve nuclei controlling eye movement and the vestibular nuclei
what does damage to the medial longtudinal fascicles do
Internuclear ophthalmoplegia occurs with damage to the medial longitudinal fasciculus (MLF).
- with a MLF lesion when asked to look left normally both eyes look left but with MLF lesion one eye stays central
- both eyes can still do convergence
how can damage to the MLF occur
- can occur due to a stroke - unilateral
- multiple sclerosis - bilateral
where is the MLF in the brainstem
The MLF extends the length of the brainstem
what does the MLF become in the spinal cord
The MLF becomes the medial vestibulospinal tract (mVST) in the spinal cord
what does the medial vestibulospinal tract (mVST) do
Acting on motoneurons for neck muscles, the mVST coordinates reflexive head and neck movements to keep eyes stable in space.
what is the input and output for the pupillary light reflex
CNII (in) and III (out)
describe how the pupillary light reflex works
- Light- sensory input- axons of retinal ganglion cells in CNII- optic nerve
- Synapse in pretectal nucleus (midbrain)
Bilateral innervation of - Edinger- Westphal nucleus (E-W; parasympathetic div of CNIII)
- E-W nuclei send output to both ciliary ganglia which cause constriction of pupils via sphincter pupillae muscles
what is information sent to the superior colliculus involved in
Information sent to the superior colliculus is important in visual fixation and tracking
