Reticular formation/sleep/wakefulness and Cortex1 Flashcards
what is special about the reticular formation?
it is the oldest part of our nervous system phylogenetically
- It is present throughout the midbrain, pons, and medulla
where can the reticular formation be found? What does it look like?
regions of the brainstem between clearly defined nuclei and tracts
- It is groups of neurons embedded in a seemingly disorganized mesh of axons and dendrites
how many groups of neurons related by function and connections are identified in the reticular formation?
over 100
what brain regions does the reticular formation send information to and get information from?
the reticular formation receives input from all parts of the nervous system ⇒ every sensory system
- locus coeruleus
- cortex
- spinal cord
- motor nuclei
- hippocampus
- periaqueductal gray
- thalamus
- hypothalamus
- cerebellum
- superior colliculus
- amygdala
what do many of the neurons look like in there reticular formation
large, highly branches dendrites to receive diverse information
what regulation roles does the reticular formation play? (5)
- Motor control
- Sensory attention
- Autonomic nervous system
- Eye movements
- Sleep and wakefulness
Reticular formation (RF)
in the lower pons and medulla receives motor information from premotor cortex, motor cortex and cerebellum as well as proprioceptive and vestibular sensory information
- RF sends axons to cranial nerve motor nuclei and to ventral horn of the spinal cord via the reticulospinal tracts
- RF initiates accompanying movements
Accompanying movements
subconscious and are needed in support of a consciously initiated movement ⇒ these movements are often needed to maintain balance
what precedes conscious movement? What is required for this type of movement?
accompanying movements; reticular formation is required
connections to the RF are mono, bi, multi lateral?
bilateral
how does RF influence motor neuron activity?
through interneurons
how does RF influence somatic motor neuron activity?
integrates visceral sensory information to influence somatic motor neuron activity
- Ex: breathing is regulated by axons from RF to cervical spinal cord
what other roles does RF play? through what connections?
essential roles in regulating blood pressure and heart rate largely through connections with brainstem and spinal cord autonomic preganglionic neurons
Reticulo-thalamic neurons
helps in filtering sensory information
- Can help to reduce irrelevant stimuli
what senses do reticule-thalamic neurons involve?
Touch, temp, pain, auditory, and visual stimuli
which autonomic functions doe the RF affect? (3)
- Breathing
- Heart rate and blood pressure
- Vomiting, gagging, and coughing
what are efferents of the RF to help with autonomic functions? (2)
- glossopharyngeal nerve (9)
- vagus nerve (10)
how does vomiting work?
- Vomiting center in medulla
- Activated by different stimuli
- Chemical ⇒ no blood brain barrier (area postrema)
- Vestibular
- Cortical ⇒ emotions, smells, visual stimuli
- Visceral ⇒ pharynx, GI tract
- Increased intracranial pressure - efferents are nucleus of solitary tract and dorsal nucleus of X
- Complex series of coordinated actions
how does RF affect eye movements?
it influences horizontal eye movements because PPRF gets input from the frontal eye fields or cortex and sends information to the abducens and oculomotor pathways to contract the eye muscles
- The medial longitudinal pathway sends things to oculomotor
- The abducens nucleus contracts the abducens related muscles
T/F sleep and wakefulness are active processes? How are these influenced by RF?
True
- Sleep and wakefulness are controlled by areas of the reticular formation in the midbrain and upper pons
Reticular activating system (+ 2 parts)
from midbrain and pons is required for wakefulness
- locus coeruleus => NE
- raphe nucleus => SER
how does wakefulness work?
Noradrenergic neurons in the locus coeruleus and serotonergic neurons in the raphe nucleus of the reticular formation project to cortex and are required for wakefulness
what wakefulness network molecules make you awake? (5)
- Acetylcholine
- histamine
- norepinephrine
- orexin
- serotonin
for sleep and wakefulness where does the RF project? (3)
- Nonspecific thalamic nuclei ⇒ cortex
- Specific thalamic nuclei ⇒ cortex
- Norepinephrine and serotonin ⇒ cortex
what 2 molecules take turns having high/low doses for circadian rhythm?
cortisol and melatonin
- Melatonin peaks in dark
- Cortisol peaks in light
suprachiasmatic nucleus
an intrinsic pacemaker
- Synchronizes rhythms to the light/dark cycle
- Sends output to many brain regions (including pineal)
what is the suprachiasmatic nucleus projection pathway to release melatonin?
suprachiasmatic => paraventricular nucleus => IML => SCG => pineal gland releasing melatonin
what is light from the eyeball as a pathway via the suprachiasmatic nucleus?
input from the retinal ganglion cells (primary visual pathway from optic nerve ⇒ chiasm ⇒ LGN ⇒ visual cortex)
melatonin
first released at about 3 months of age, which correlates with the onset of a regular sleep/wake cycle
- Released at night, so some people take melatonin to help induce sleep
- Melatonin sometimes taken to help treat jet lag, particularly when flying eat
where does the suprachiasmatic nucleus project to (2) aside from the paraventricular nucleus?
- pre optic area
- reticular formation
5 stages of sleep
- Non rem sleep: first 4 stages are characterized by progressively decreasing frequency and increasing amplitude of EEG cortical activity
- Rapid eye movement (REM): 5th stage characterized by high frequency and low amplitude EEG cortical activity, similar to the awake state
how long do stages 1-4 of sleep take? What about REM?
about 1 hour and REM lasts about 10 minutes before the cycle repeats
what processes are slowed during non REM sleep? What about REM?
- physiological processes slowed in non REM but increased during REM
- Somatic muscle activity is reduced during REM sleep
- Most dreaming takes place during REM sleep
when does tossing and turning occur?
during non-REM sleep
- tend to have deeper sleep the longer we go and then become closer to awake as you get toward morning
characteristics of non REM sleep (5)
slow wave sleep) ⇒ SWS
- Muscle activity
- Little dreaming
- Few eye movements
- Slowing of breathing
- Reduced BP
what is non REM sleep characterized by?
inactive brain in an active body
characteristics of REM sleep (5)
- Reduced muscle activity
- Frequent dreaming
- Increased eye movements
- Enhanced breathing
- Increased BP
how is age and REM sleep related?
the amount of REM sleep a person gets per night decreases with age
- 8 hours at birth
- 2 hours at 20
- 45 minutes at 70
what inhibits thalamocortical axons during REM sleep?
cholinergic axons from the reticular formation to thalamus activate GABAergic neurons in thalamus
what inhibits the activity of spinal motor neurons during REM sleep?
Pontine reticulospinal axons
what does the pontine RF project to? What is this required for? (non nerve proj.)
projections to the superior colliculus and is required for the rapid eye movements during REM sleep
what does lack of sleep result in?
mental and physical fatigue, poor decision making, impaired learning, emotional irritability, and an increased risk of migraine and epileptic seizures
- Chronic insomnia results in death
T/F the mechanisms for understanding restorative sleep is well understood?
False => poorly defined
what happens to extracellular space in the brain for awake mammals vs sleep?
extracellular space in the brain of an awake mouse accounts for 14% of the brain volume ⇒ during sleep this increases to 23%
- the brain shrinks
how much does CSF increase/decrease during sleep?
increases 95%
what neurotransmitter is responsible for the loss of extracellular space when awake?
noradrenaline
- Lack of sleep makes your brain look older
beta amyloid
peptide linked to Alzheimer’s disease, is cleared from the extracellular space during sleep
narcolepsy
disabling form of sleepiness where sleep occurs in abnormal situations
- such as when driving
- May also involve loss of muscle tone with high emotion
what molecule promotes wakefulness related to narcolepsy?
orexin/hypocretin => 30 amino acid peptide
- decreased in some forms of narcolepsy and is likely autoimmune
somnambulism
sleep walking
- occurs early in non-REM sleep ⇒ more common in children than adults
night terrors
person appears to be awake and terrified, but remembers nothing in the morning
- Involves non-REM sleep
- More common in children than adults
restless leg syndrome
pain or tingling in legs that is relieved by movement
- Occurs during non REM sleep
- Cause is unknown, but may be related to amnesia
- Variety of drugs have been tried, mostly antidepressants
sleep apnea
interruption of breathing ⇒ decline in oxygen
- Can be central or obstructive
- More common in people who snore or who are obese
- Causes awakening from sleep and sleep is less restful and restorative
- Treated with oral device or CPAP (continuous positive airway pressure)
Rem behavioral disorder
tremor, rigidity, and gait problems
- Can occur in parkinson’s disease ⇒ typically thought of as disease of motor systems
- Degenerative disease
symptoms of REM behavioral disorder that can show up prior to Parkinson’s disease?
- Very vivid dreams
- Acting out dreams
- Inhibition of spinal motor neurons during REM sleep doesn’t occur
where does the cerebral cortex develop from?
the embryonic telencephalon
how many neurons are estimated in the human cortex?
15 billion neurons
- phylogenetically new
what are defining features of the cerebral cortex?
size and complexity
Neocortex
most of the human cerebral cortex is neocortex
- has 6 layers
allocortex
has less than 6 layers and is made of the piriform cortex, olfactory tubercle, anterior olfactory nucleus, hippocampus, olfactory bulb, and some others
what does more layers of cortex represent?
supposedly more complex processing
cell types in gray matter? (3)
- pyramidal neurons
- granule cells
- local circuit interneurons
pyramidal neuron characteristics
- Large
- Long dendrites
- Primary source of axons that leave the cortex
granule cell characteristics
- Small and star shaped
- No apical dendrites
T/F most of the cortex can be seen form the outside of the brain?
False most of it cannot
- Different regions of the cortex have different anatomy
afferent
coming into
efferent
going out
molecular layer
contains mainly axon and dendrites from deeper layers as well as horizontal cells being the only type of cell in the layer
- most superficial
external granule cell layer
contains primarily granule cells and receives input from primarily other cortical areas ⇒ such as info from association cortices
external pyramidal cell layer
contains primarily pyramidal cells and sends axons primarily to other cortical areas
internal granule cell layer
composed of primarily granule cells and receives afferent input primarily from the thalamus (LGN, MGN, VPL depending on area in the brain)
internal pyramidal cell layer
composed primarily of large pyramidal cells with a large apical dendrite and sends efferent output to subcortical regions ⇒ can get input from layer ⅔ with the large dendrites
multiform layer
contains a variety of cell types and is less well understood
- May receive input from and output to the thalamus
- most internal
excitation in one cell layer can result in what?
interconnections between all cell layers means excitation of any layer can result in excitation of the other layers
- This allows for the functional columns of the cerebellar cortex
- These functional columns are most clearly understood for the visual cortex
what do the functional columns respond to? (3)
- The angle a shape is presented ⇒ orientation columns
- The input from the one eye vs the other eye ⇒ ocular dominance columns
- Color columns ⇒ blobs
what layer and how large is the primary motor cortex?
large and layer 5
what layer and how large is the primary somatosensory cortex?
large and layer 4
what layer and how large is the associate areas?
somewhat large and layers 2 and 3
what are Brodmann’s areas?
Defined 52 different areas based on the cytoarchitecture of the layers of the cortex
- Based on anatomy and the anatomy was surprisingly good at demonstrating regions of functional similarities
layer 5 output goes to where?
lower cortical areas
- spinal cord and brainstem, reticular formation, red nucleus, caudate and putamen and pons, etc.
layer 3 outputs go to where?
other cortical region
layer 1, 2, and 3 get input from what via the reticular activating system?
monoamines
what do layer 2 and 3 get input from?
other cortical layers
what does layer 4 get input from?
the thalamus
Corpus callosum and anterior commissure
are the two primary white matter bundles connecting the two hemispheres
Uncinate fasciculus
connects the frontal and temporal lobes
Cingulum bundle and longitudinal fasciculi
run rostral-caudal and connect the frontal, parietal, and occipital lobes
Internal capsule
connects cortical regions with thalamus, subthalamic nucleus, and brainstem
what does layer 6 project to?
thalamus
what borders the occipital lobe?
the parieto-occipital line
what sensory areas does the occipital lobe include? (2)
primary visual area and visual association areas
what does the occipital lobe have thalamic input from?
lateral geniculate nucleus
what happens with injury to the occipital lobe?
- Difficulty perceiving more than one object at the same time
- Trouble recognizing objects by sight
- Color blindness
- Hallucinations involving vision
- Total blindness
where is the parietal lobe located?
Bordered by the lateral fissure, central sulcus, parieto-occipital line
what sensory areas does the parietal lobe include?
primary somatosensory area and somatosensory association areas
what does the parietal lobe have thalamic input from?
ventral posterior nucleus
what happens with injury to the parietal lobe? (9)
- Memory generation ⇒ other areas for this too
- Agraphia
- Difficulties with math
- Numbness
- Disorientation
- Poor hand-eye coordination
- Astereognosis
- Aphasia
- Apraxia
what borders the temporal lobe?
the lateral fissure and parieto-occipital line
what sensory areas does the temporal lobe include?
primary auditory area and auditory association areas
what does the temporal lobe have thalamic input from?
medial geniculate nucleus
what happens with injury to the temporal lobe?
- Hearing difficulties
- Memory issues ⇒ b/c they are close by
- Difficulty recognizing faces and objects
- Language impairments such as Wernicke’s (producing words but dont make sense) aphasia and difficulties understanding languag
what borders the frontal lobe?
the lateral fissure and central sulcus
what sensory areas does the frontal lobe include?
- Primary motor area: just in front of the central sulcus
- Other motor areas: premotor, supplementary motor, frontal eye fields, Broca’s (cannot put together sentences and may have difficulty understanding) area
- Prefrontal cortex
what does the frontal lobe have thalamic input from?
- mediodorsal nucleus
- ventroanterior nucleus
- ventrolateral nucleus
what happens with injury to the frontal lobe?
- Memory issues ⇒ such as frontotemporal dimensia
- Personality changes
- Problem solving, decision making issues
- Attention problems
- Emotional deficit, socially inappropriate behavior, behavior changes
- Aphasia
- Apraxia
- Flaccid hemiplegia
where is the limbic lobe located?
on the medial surface of the cerebral cortex
what areas are included in the limbic lobe
hippocampus and amygdala
where does the limbic lobe get thalamic input from?
anterior thalamic nuclei
what does injury to the limbic lobe result in?
- Mood changes
- Memory issues
- Sleep difficulties
- Behavioral changes
the limbic lobe is involved in what circuit?
Papez
T/F functions of the cerebral cortex are equal on each side of the brain?
False
- For any given function, one side of the brain may play a more dominant role than the other ⇒ particularly true for association areas
what layers does the majority of information come from on one side of the cortex and what layers does it go to?
comes from layers 2 and 3 and goes to layers 1-3
what are exceptions to the passing of information in layers of the cortex across hemispheres? (3 associated with?)
- Some parts of visual cortex
- Some parts of somatosensory cortex (fingers and toes)
- Some parts of motor cortex (fingers and toes)
- These parts of sensory and motor cortex are associated with the distal parts of the limbs
what is the theory for exceptions to cortex information crossing?
- Distal parts function somewhat independently
- More proximal parts like neck and trunk need to act together
- some functions appear to be localized to one side of the brain
split brain patients
patients who had corpus callosum severed, usually as treatment for severe epilepsy
- Function is mostly normal
- Specific testing can sometimes show deficits
