lecture 10 Flashcards
early in vertebrate evolution, what dominated, the brainstem or the cerebellum?
brainstem - didn’t have much else in the brain
early in vertebrate evolution, what was the main visual and auditory region?
the tectum
as the brain evolved, what became more dominant?
cerebrum plugged into the sensory and motor systems, eventually taking on an executive role
what are the three main functions of the brainstem?
- its a conduit
- CNs III-XII enter and leave
- it has integrative functions
explain how the brainstem acts as a conduit
informations relayed between the periphery and the cerebrum/cerebellum
are the ascending pathways through the brainstem sensory or motor?
sensory pathways
what do the ascending pathways through the brainstem include?
- dorsal columns medial lemniscus
- spinothalamic tract
what are the functions of the dorsal columns medial lemniscus?
proprioception, touch and pressure sensation
what are the functions of the spinothalamic tract?
pain and temperature sensation
where do the ascending pathways relay?
in thalamus to cortex
do the ascending pathways crossover?
yes - near the level of input
describe the descending pathways through the brainstem
these are upper motor neuron axons destined to synapse on lower motor neurons in the ventral horn and intermediate horn of the spinal cord
what do upper motor neurons form?
the corticospinal tracts
are there upper motor neurons in the brainstem’s vestibular, red, tectal and reticular nuclei?
yes - also descend and synpase on lower motor neurons in the brainstem/sc
what are the oldest motor control areas?
where do they now work?
- upper motor neurons in the brainstem’s vestibular, red, tectal and reticular nuclei
- work with the newer motor and premotor cortex
why is upper motor neuron an imprecise term?
not necessarily above, just descending pathway
do the descending pathways cross over?
yes - 90% at the medulla, rest at the SC
where do the descending pathways origionate?
in the primary motor area of the cerebral cortex
what would be the result of a lesion to the cortiocospinal tract?
locked-in syndrome
what is locked-in syndrome?
paralysis, but full conciousness because most upper motor neuron axons are cut but cortical cognitive function is ok
when is locked-in syndrome common?
after stroke
diseases or lesions to the brain stem can lead to:
- visual disturbances
- pupil abnormalities
- muscle weakness
- hearing problems
- vertigo
- swallowing problems
- speech difficulty
- voice changes
- coordination problems
which cranial nerves are involved with each dysfunction?
- CN II
- CN III
- CN V
- CN VII
- CN VII
- CNs IX-XII
- CN IX, XII
- CN X
- CN VII
(guesses)
what are the integrative functions of the brainstem?
- cardiovascular control
- respiratory control
- pain sensitivity control
- influencing conciousness (awareness, alterness and the sleep cycle)
is brainstem damage lifethreatening? why or why not?
yes - bc of integrative functions
describe cardiovascular control with respect to the brainstem
- skeletal muscle ergoreceptors in the heart send afferents to cardiovascular areas of the brain via group III and IV muscle afferents
- parasympathetic (vagal) efferents slow down HR (Ach)
- sympathetic efferents speed up HR (adrenaline)
describe respiratory control with respect to the brainstem
- respiratory areas in the pons and medulla receive higher (cortical) and CN IX/X input from aorta and lungs
- output affects autonomic traffic to lungs and respiratory muscles
describe Brown-Sequard’s concept of rostral-caudal deterioration of brain function in response to global ischemia
cerebral cortical function is lost before brainstem (& hypothalamus) function (in respone to global ischemia)
what Is the persistent vegetative state (PVS)?
chronic neurological disorder of conciousness characterized by wakefullness without awareness
where is the damage with PVS?
- cerebral cortical neurons
- thalamic neurons
- their white matter connections
sparing of hypothalamus and brainstem
what does PVS result from?
extensive bilateral lesion to higher brain gray matter or white matter
in a PVS patient, how do we know the brainstem is working but the higher brain is not?
missing:
- awarness of self/environment
- language comprehension/expression
- sustained, purposeful, reproducible or voluntary behavioural responses
retained:
- intermitten wakefullness (have sleep/wake cycles)
- hypothalamic and brainstem autonomic functions
- cranial nerve reflexes (pupillary, corneal, vesibulo-ocular, gag)
what is coma?
deep state of unconciousness usually caused by severe head trauma
why does coma arise?
from bilareral lesions to the reticular network in the brainstem
what must function during coma to prevent the higher brain from shutting down?
reticular activating system (RAS)
how are coma and PVS different?
the higher brain is not neccessarily damaged
what is brain death?
if a patient does not wake up to at least a level of PVS then the RAS is damaged - need RAS for upper brain function
what does conciousness require? describe.
- upper brainstem function
- RAS must be intact for the content of conciousness to be expressed
conciousness is a function of:
the cerebral hemispheres
what is the most common cause of death for patients with brainstem injury?
apnea (patient can’t breathe without ventilator)
why does breathing stop before the heart in patients with brainstem injuries?
pressure on the brainstem from the free edge of the tentorial notch
describe “brain dead”
RAS is not functioning and the patient cannot breathe (patient fails apnea test)
is recovery possible with PVS?
no
is recovery possoble with coma?
yes
is recovery possible with brain death?
no
what may cause brain death?
severe head injuries or massive intracranial hemorrhages
how does head injury threaten brainstem function?
pooling blood and/or swelling causes a space-occupying lesion that forces the brain down due to the rigid cranium
what is a cingulate herniation?
brain swells from one hemisphere into other
what is an uncal herniation? what is the result?
- cortex pushes medially and down into cerebellum/brainstem
- result - midbrain/pons damage
what is a downward (transtentorial) herniation?
cortex pushes down into cerebellum/brainstem
what is the result of cingulate herniation, uncal herniation, or downward (transtentorial) herniation?
brainstem tissue is under pressure, which causes damage to brainstem function and often death
what is external herniation?
cortex swells out of the head if a fracture opens the cranium
what is cerebellar herniation through the formamen magnum? what is the result?
- cerebellum swells down in through foramen magnum
- medulla damage
the brainstem is also the origin of 6 ________ systems that send inputs to ______
what is the result?
- neurotransmitter
- entire higher brain
- cause different kinds of global brain activation
