Brainstem and Cranial Nerves Part 1 Flashcards
What are the constituents of the brainstem/lower brain?
Medulla Pons Midbrain Hypothalamus Thalamus Cerebellum
What shape is the brainstem (from a mid-sagittal view)?
Woody Woodpecker
Where is the brainstem located and what are its three main components? What is not included in the brainstem?
- 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
What does each component of the brainstem do?
See picture in lecture notes
What are the functions of the brainstem?
- 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
In what way is the brainstem a continuation of the spinal cord?
- 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
What is the dorso-ventral organisation of the brainstem? How is this knowledge helpful?
- 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
What is the tegmentum? And the peduncle?
- Tegmentum- covering over the ventral part of the brainstem- generally central grey matter
- Peduncle– stalk or stem
What is another name for the mid-brain? What are its different parts and their functions?
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)
Which nerves originate in the midbrain?
- 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
What is another name for the pons? What are its different parts and their functions?
Pons (metencephalon)
- Ascending and descending tracts pass through, also connects with cerebellum
o Cerebellar peduncles
Which nerves originate in the pons?
- 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
What is another name for the medulla? What are its different parts and their functions?
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
-
Which nerves originate in the medulla?
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
What are the main functions of the midbrain?
Associated with auditory, visual and pupillary reflexes and with eye movements
What are the main functions of the pons?
Its main functions are mastication (V), eye movement (VI), facial expression, taste, blinking, salivation, lacrimation (VII), and equilibrium and audition (VIII)
What are the main functions of the medulla?
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)
What is special about cranial nerve V?
- 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)
Where do cranial nerves enter/exit the brainstem? How are they organised? What are their functions?
- 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)
Which afferents do cranial nerves have?
- 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
What are the three types of motor nuclei and what do they do?
- 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)
What are the orders of the nuclei from the midline (they are bilateral)?
- 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)
What are branchiomotor nuclei sometimes called? Which cranial nerves have branchiomotor nuclei?
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
Where are cranial nerve nuclei located in the brainstem?
- Cranial nerve nuclei: columns of neurons associated with cranial nerves
- The nuclei follow the rostral-caudal organisation of the structures innervated
