class 7 (brainstem) Flashcards
Medulla oblongata
-starts at the foramen magnum and goes to pons
-made up of sensory (ascending) tracts and motor
(descending) tracts
pyramids of Medulla oblongata
bulges of white matter on the anterior part
of the medulla
-formed by the corticospinal tracts
decussation of pyramids:
crossing of axons in pyramids
- 90% of axons cross here -explains why each side of brain controls the opposite side of body
decussation etymology
“The word “decussation” comes from the Latin word decussare, which means “to divide crosswise” or “to arrange crosswise”. Decussare comes from the Latin word decussis, which means “the figure ‘ten’”. The Roman numeral for ten is X, which is an intersection of two lines. “
olive (olives of medulla)
-just lateral to each pyramid
-oval-shaped swelling
-inferior olivary nucleus
nucleus = cluster of cell bodies (CNS)
- within the olive
receives input from:
-cerebral cortex
-red nucleus (midbrain)
-spinal cord
neurons of inferior olivary nucleus —> where do they go?
- its neurons extend into cerebellum, where
they regulate the activity of cerebellar
neurons - it provides instructions that the cerebellum uses to make adjustments to muscle activity as you learn new motor skills
medulla other nuclei
Medulla also contains several nuclei
Many of these nuclei control vital body functions
—> nuclei control vital body function
E.g.
= swallowing
= breathing
= vomiting
= bp control
= heartrate
CV centre of medulla oblongata (nucleus)
-regulates the rate and force of the
heartbeat & the diameter of blood
vessels
Medullary rhythmicity area of the respiratory center (medulla)
-adjusts the basic rhythm of breathing
(along with areas in the pons)
Other nuclei control reflexes for vomiting, swallowing,
sneezing, coughing, hiccupping. Example:
Vomiting center —> -causes vomiting
Deglutition center —> -causes swallowing
deglutition define
deglutire =
swallow down
Gracile nucleus & cuneate nucleus (MEDULLA)
-are associated with sensations of touch, pressure,
vibration and conscious proprioception
Gustatory nucleus
-from tongue to brain
-receives gustatory input from taste buds of tongue
Cochlear nucleus
-part of the auditory pathway from inner ear to brain
-receives auditory input from cochlea of the inner ear
Vestibular nucleus
-equilibrium pathway from inner ear to brain
ALSO NUCLEI ASSOCIATED WITH CRANIAL NERVES
nuclei of CN 8,9,10,11,12
—> ALL HAVE NUCLEI @/FROM MEDULLA
(8) vestibulocochlear n
(9) glossopharyngeal
(10) vagus n
(11) accessory n
(12) hypoglossal
bottom of brain
vital functions (keeps us alive)
top of brain
more complex “human” functions
E.g.
—> abstract thought, making music, theorizing, scientific thought
Injury to medulla
-by hard blow to back of head/upper neck
-can be fatal
-damage to medullary rhythmicity area is really bad
alcohol poisoning and medulla
-alcohol overdose also suppresses the medullary
rhythmicity area (of respiratory centre) and may result in death
pons consist of
consists of nuclei and tracts
pons
“bridge”
(mpm)
-is a bridge that connects parts of the brain with
each other
pons CN
CN 5,6,7,8
5 = trigeminal
6 = abducens
7 = facial
8 = vestibulocochlear (SHARED w/ MEDULLA)
pontine nucleus
-relays signals for VOLUNTARY MOVEMENTS from
cerebral cortex to cerebellum
pontine PNEUMOTAXIC AREA
Rhythm of breathing
pontine APNEUSTIC AREA
inhale/exhale
therefore, breathing =
1) pneumotaxic area (PONS)
2) & apneustic area (PONS)
+
3) medullary rhythmicity area
(of respiratory centre)
moving on to midbrain (mesencephalon)
…
cerebral peduncles
-paired bundles of axons
-axons from corticoSPINAL tracts
—-> -motor area in cerebral
cortex to the SC (spinal cord)
-axons from corticoBULBAR tracts
—-> -motor areas in cerebral
cortex to MEDULLA
-axons from corticoPONTINE tracts
—-> -motor areas in cerebral
cortex to PONS
tectum of midbrain
-posterior part
pillrolling
pathognomonic sign of parkinson’s disease
“Pill rolling is a type of tremor that involves rubbing the thumb and forefinger together in a rhythmic back-and-forth motion. It’s often a symptom of Parkinson’s disease (PD). “
tectum of midbrain contains 4 rounded elevations:
i) superior colliculi
ii) inferior colliculi
iii) Substantia nigra
iv) Red nuclei (of midbrain)
i) superior colliculi
- nuclei in 2 superior elevations
- coordinates mvts of head, eyes, trunk in response to visual stim
ii) inferior colliculi
- nuclei in 2 inferior elevations
- coordinates mvts of head, eyes, trunk in response to auditory stim
iii) Substantia nigra
-neurons release dopamine and help control subconscious muscle activities
-loss of these neurons is associated with Parkinson’s disease
iv) Red nuclei
-involved in voluntary muscle movements
-rich blood supply
-iron-containing pigment
CN in midbrain
3,4
3 = oculomotor
4 = trochlear
RETICULAR FORMATION
PART OF ENTIRE BRAINSTEM
not specific to midbrain
reticular formation ..
-is found throughout the brain stem
reticular formation sttructure
-it’s a net-like arrangement of grey and white matter
—> grey matter – clusters of cell bodies
—> white matter – small bundles of myelinated axons
Reticular activating system is part of
PART OF SENSORY PORTION (AXONS) OF RETICULAR FORMATION
what does reticular activating system consist of
- consists of sensory axons that project to the cerebral cortex
RAS can be activated via
visual stimuli
auditory stimuli
mental activities
pain, touch, pressure stimuli
proprioceptive receptors
rest in acivity of RAS?
= sleep
active RAS?
awake
even less active?
coma
sleep analogous to?
partial coma (??)
RAS is therefore involved in
- involved in consciousness
consciousness define
consciousness – state of wakefulness in which an individual is fully alert, aware and oriented
again, RAS is active during
- active during arousal (awakening from sleep)
RAS also helps maintain ____
- helps maintain attention and alertness
RAS also prevents
- prevents sensory overload by filtering out insignificant information so that it does not reach consciousness
again, inactivation of RAS =
- inactivation of the RAS produces sleep
sleep define
a state of partial consciousness from which an individual can be aroused
damage to RAS =
- damage to the RAS results in coma
coma define
coma: a state of unconsciousness from which an individual cannot be aroused
light vs deep coma?
-in the lightest stages of coma, people still have brain stem and spinal cord reflexes
-in deepest states, those reflexes are lost
melatonin & RAS
-drugs such as melatonin affect RAS by helping to induce sleep
anasthetic vs RAS
-anesthetics turn off consciousness via the RAS
WHY IS SMELL INDEPENDENT OF WAKING UP (RAS)
or in other words, why is smell independent from the brainstem?
because centres related to smelling are not within the brainstem – and have no connection to the brainstem (I.e. the RAS)
RAS other function
is also gatekeeper of sensory feedback
—-> e.g. anasthesia
—> decides whether is reaches higher centres of brain or not
anasthesia vs RAS
filters signal from pain receptors (nociceptor)
Note:
“The pain signal is also sent to the brain. Only when the brain processes the signal and interprets it as pain do people become aware of the pain.”
theory for certain types of autism/adhd
linked to RAS
—> RAS not filtering sensory feedback effectively –> making some individuals hyperaware of things that are usually filtered
RAS also consists of (motor component)
-consists of motor axons that connect to the cerebellum and spinal cord to help regulate muscle tone
define muscle tone
muscle tone: the slight degree of involuntary
contraction in normal resting skeletal muscles
RAS motor component also involved in ____
-also involved in regulation of heart rate, BP, respiratory rate
again, RAS & olfaction
-RAS does not receive input from olfaction so even strong odors won’t wake people up
