Neurology - Anatomy and Physiology (1) Flashcards
1
Q
Neurons
- Characteristics
- Functions
- Pathology
A
- Characteristics
- Permanent cells—do not divide in adulthood (and, as a general rule, have no progenitor stem cell population)
- Signal-relaying cells with dendrites (receive input), cell bodies, and axons (send output).
- Cell bodies and dendrites can be stained via the Nissl substance (stains RER).
- RER is not present in the axon.
- Functions
- Signal-transmitting cells of the nervous system.
- Pathology
- If an axon is injured, it undergoes Wallerian degeneration
- Degeneration distal to the injury and axonal retraction proximally
- Allows for potential regeneration of axon (if in PNS).
- If an axon is injured, it undergoes Wallerian degeneration
2
Q
Astrocytes
- Characteristics
- Functions
A
- Characteristics
- Derived from neuroectoderm
- Astrocyte marker—GFAP
- Functions
- Physical support, repair, K+ metabolism, removal of excess neurotransmitter, component of blood-brain barrier, glycogen fuel reserve buffer.
- Reactive gliosis in response to neural injury.
3
Q
Microglia
- Characteristics
- Functions
- Pathology
A
- Characteristics
- Mesodermal origin
- Not readily discernible in Nissl stains
- Have small irregular nuclei and relatively little cytoplasm
- Functions
- CNS phagocytes
- Scavenger cells of the CNS
- Respond to tissue damage by differentiating into large phagocytic cells
- Part of the mononuclear phagocyte system.
- Pathology
- HIV-infected microglia fuse to form multinucleated giant cells in the CNS
4
Q
Myelin
- Characteristics
- Functions
A
- Characteristics
- CNS—oligodendrocytes
- PNS—Schwann cells
- Functions
- Increase conduction velocity of signals transmitted down axons
- Results in saltatory conduction of action potential between nodes of Ranvier, where there are high concentrations of Na+ channels
- Wraps and insulates axons
- Increases space constant and increases conduction velocity.
5
Q
Oligodendroglia
- Characteristics
- Functions
- Pathology
A
- Characteristics
- Each oligodendrocyte can myelinate many axons (~30)
- Predominant type of glial cell in white matter.
- Derived from neuroectoderm
- “Fried egg” appearance on H&E stain
- Functions
- Myelinates the axons of neurons in the CNS
- Pathology
- Injured in multiple sclerosis, progressive multifocal leukoencephalopathy (PML), and leukodystrophies.
6
Q
Schwann cells
- Characteristics
- Functions
- Pathology
A
- Characteristics
- Each Schwann cell myelinates only 1 PNS axon
- Derived from neural crest.
- Functions
- Increase conduction velocity via saltatory conduction between nodes of Ranvier, where there are high concentrations of Na+ channels
- Also promote axonal regeneration
- Pathology
- Destroyed in Guillain-Barré syndrome
-
Acoustic neuroma
- Type of schwannoma.
- Typically located in internal acoustic meatus (CN VIII).
- If bilateral, strongly associated with neurofibromatosis type 2.
7
Q
Sensory corpuscles
- For each
- Description
- Location
- Senses
- Free nerve endings
- Meissner corpuscles
- Pacinian corpuscles
- Merkel discs
A
- Free nerve endings
-
Description:
- C—slow, unmyelinated fibers
- Aδ—fast, myelinated fibers
- Location: All skin, epidermis, some viscera
- Senses: Pain and temperature
-
Description:
- Meissner corpuscles
-
Description:
- Large, myelinated fibers
- Adapt quickly
- Location: Glabrous (hairless) skin
- Senses: Dynamic, fine/light touch; position sense
-
Description:
- Pacinian corpuscles
-
Description:
- Large, myelinated fibers
- Adapt quickly
- Location: Deep skin layers, ligaments, and joints
- Senses: Vibration, pressure
-
Description:
- Merkel discs
-
Description:
- Large, myelinated fibers
- Adapt slowly
- Location: Basal epidermal layer, hair follicles
- Senses: Pressure, deep static touch (e.g., shapes, edges), position sense
-
Description:
8
Q
Peripheral nerve
- Endoneurium
- Perineurium
- Epineurium
A
- Endoneurium
- Invests single nerve fiber layers
- Inflammatory infiltrate in Guillain-Barré syndrome
- Endo = inner.
-
Perineurium
- Permeability barrier
- Surrounds a fascicle of nerve fibers.
- Must be rejoined in microsurgery for limb reattachment.
- Peri = around.
- Epineurium
- Dense connective tissue that surrounds entire nerve
- Fascicles and blood vessels
- Epi = outer.
9
Q
Neurotransmitters
- For each
- Change in disease
- Locations of synthesis
- Norepinephrine
- Dopamine
- 5-HT
- ACh
- GABA
A
- Norepinephrine
-
Change in disease:
- Increased in anxiety
- Decreased in depression
-
Locations of synthesis: Locus ceruleus (pons)
- Locus ceruleus— stress and panic.
-
Change in disease:
- Dopamine
-
Change in disease:
- Increased in Huntington disease
- Decreased in Parkinson disease
- Decreased in depression
- Locations of synthesis: Ventral tegmentum and SNc (midbrain)
-
Change in disease:
- 5-HT
-
Change in disease:
- Increased in Parkinson disease
- Decreased in anxiety
- Decreased in depression
- Locations of synthesis: Raphe nucleus (pons, medulla, midbrain)
-
Change in disease:
- ACh
-
Change in disease:
- Increased in Parkinson disease
- Decreased in Alzheimer disease
- Decreased in Huntington disease
- Locations of synthesis: Basal nucleus of Meynert
-
Change in disease:
- GABA
-
Change in disease:
- Decreased in anxiety
- Decreased in Huntington disease
-
Locations of synthesis: Nucleus accumbens
- Nucleus accumbens and septal nucleus—reward center, pleasure, addiction, fear.
-
Change in disease:
10
Q
Blood-brain barrier
- Functions
- Formed by 3 structures:
- Substances
- A few specialized brain regions allow…
- Other notable barriers
- Pathology
A
- Functions
- Prevents circulating blood substances from reaching the CSF/CNS.
- Helps prevent bacterial infection from spreading into the CNS
- Also restricts drug delivery to brain
- Formed by 3 structures:
- Tight junctions between nonfenestrated capillary endothelial cells
- Basement membrane
- Astrocyte foot processes
- Substances
- Glucose and amino acids cross slowly by carrier-mediated transport mechanism.
- Nonpolar/lipid-soluble substances cross rapidly via diffusion.
- Hypothalamic inputs and outputs permeate the blood-brain barrier
- A few specialized brain regions with fenestrated capillaries and no blood-brain barrier allow…
- Molecules in the blood to affect brain function
- Area postrema—vomiting after chemo
- OVLT—osmotic sensing
- Neurosecretory products to enter circulation
- Neurohypophysis—ADH release
- Molecules in the blood to affect brain function
- Other notable barriers
- Blood-testis barrier
- Maternal-fetal blood barrier of placenta
- Pathology
- Infarction and/or neoplasm destroys endothelial cell tight junctions –> vasogenic edema.
11
Q
Hypothalamus
- Functions
- Inputs
- Nuclei
- ADH
- Oxytocin
A
- Functions (The hypothalamus wears TAN HATS)
- Thirst and water balance
- Adenohypophysis control (regulates anterior pituitary)
- Neurohypophysis releases hormones produced in the hypothalamus
- Hunger
- Autonomic regulation
- Temperature regulation
- Sexual urges.
- Inputs
- Areas not protected by blood-brain barrier
- OVLT
- Organum vasculosum of the lamina terminalis
- Senses change in osmolarity
- Area postrema (responds to emetics).
- Nuclei
- Supraoptic nucleus makes ADH.
- Made by hypothalamus
- Paraventricular nucleus makes oxytocin.
- Stored and released by posterior pituitary
- Supraoptic nucleus makes ADH.
12
Q
Hypothalamus
- Lateral area
- Function(s)
- Destruction –>
- Inhibited by…
- Ventromedial area
- Function(s)
- Destruction –>
- Stimulated by…
- Anterior hypothalamus
- Function(s)
- Posterior hypothalamus
- Function(s)
- Suprachiasmatic nucleus
- Function(s)
A
- Lateral area
- Hunger.
- Destruction –> anorexia, failure to thrive (infants).
- Inhibited by leptin.
- If you zap your lateral nucleus, you shrink laterally.
- Ventromedial area
- Satiety.
- Destruction (e.g., craniopharyngioma) –> hyperphagia.
- Stimulated by leptin.
- If you zap your ventromedial nucleus, you grow ventrally and medially.
- Anterior hypothalamus
- Cooling, parasympathetic.
- Anterior nucleus = cool off (cooling, pArasympathetic).
- A/C = Anterior Cooling.
- Posterior hypothalamus
- Heating, sympathetic.
-
Posterior nucleus = get fired up (heating, sympathetic).
- If you zap your Posterior hypothalamus, you become a Poikilotherm (cold-blooded, like a snake).
- Suprachiasmatic nucleus
- Circadian rhythm.
- You need sleep to be charismatic (chiasmatic).
13
Q
Sleep physiology
- Circadian rhythm
- REM sleep
- Alcohol, benzodiazepines, and barbiturates
- Benzodiazepines
- Norepinephrine
- Oral desmopressin acetate (DDAVP)
A
- Circadian rhythm
- Sleep cycle is regulated by the circadian rhythm, which is driven by SCN of hypothalamus.
- Circadian rhythm controls nocturnal release of ACTH, prolactin, melatonin, and norepinephrine
- Suprachiasmatic nucleus (SCN) –> norepinephrine release –> pineal gland –> melatonin.
- SCN is regulated by environment (e.g., light).
- Two stages: rapid-eye movement (REM) and non-REM.
- REM sleep
- Extraocular movements during REM sleep due to activity of PPRF (paramedian pontine reticular formation/conjugate gaze center).
- REM sleep occurs every 90 minutes, and duration increases through the night.
- Alcohol, benzodiazepines, and barbiturates
- Associated with decreased REM sleep and delta wave sleep
- Benzodiazepines
- Useful for night terrors and sleepwalking
- Norepinephrine
- Also decreases REM sleep.
- Oral desmopressin acetate (DDAVP)
- Treast bedwetting (sleep enuresis)
- Mimics ADH
- Preferred over imipramine because of the latter’s adverse effects.
14
Q
Sleep physiology
- For each
- % of total sleep time in young adults
- Description
- EEG waveform
- Awake (eyes open)
- Awake (eyes closed)
- Non-REM sleep
- Stage N1
- Stage N2
- Stage N3
- REM sleep
A
- Awake (eyes open)
- %: 0%
- Description: Alert, active mental concentration
-
EEG waveform: Beta
- Highest frequency, lowest amplitude
- Awake (eyes closed)
- %: 0%
- Description: N/A
- EEG waveform: Alpha
- Non-REM sleep
- Stage N1
- %: 5%
- Description: Light sleep
- EEG waveform: Theta
- Stage N2
- %: 45%
- Description: Deeper sleep; when bruxism occurs
- EEG waveform: Sleep spindles and K complexes
- Stage N3
- %: 25%
-
Description: Deepest non-REM sleep (slow-wave sleep)
- When sleepwalking, night terrors, and bedwetting occur
-
EEG waveform: Delta
- Lowest frequency, highest amplitude
- Stage N1
- REM sleep
- %: 25%
-
Description: Loss of motor tone, increased brain O2 use, increased and variable pulse and blood pressure
- When dreaming and penile/clitoral tumescence occur
- May serve a memory processing function
- EEG waveform: Beta
- At night, BATS Drink Blood
15
Q
Posterior pituitary (neurohypophysis)
A
- Function
- Receives hypothalamic axonal projections from supraoptic (ADH) and paraventricular (oxytocin) nuclei.
- Oxytocin
- Oxys = quick
- Tocos = birth.
- Adenohypophysis = Anterior pituitary.
19
Q
Basal ganglia
- Functions
- Structures
- Striatum
- Lentiform
- Pathways
- Excitatory pathway
- Inhibitory pathway
- Dopamine binds to…
- D1
- D2
A
- Functions
- Important in voluntary movements and making postural adjustments.
- Receives cortical input, provides negative feedback to cortex to modulate movement.
- Structures
- Striatum = putamen (motor) + caudate (cognitive).
- Lentiform = putamen + globus pallidus.
- Pathways
- Excitatory pathway
- Cortical inputs stimulate the striatum, stimulating the release of GABA, which disinhibits the thalamus via the GPi/SNr (increases motion).
- Inhibitory pathway
- Cortical inputs stimulate the striatum, which disinhibits STN via GPe, and STN stimulates GPi/SNr to inhibit the thalamus (decreases motion).
- Excitatory pathway
- Dopamine binds to…
- D1, stimulating the excitatory pathway
- _D1-R_eceptor = D1Rect pathway.
- D2, inhibiting the inhibitory pathway –> increases motion.
- Indirect = Inhibitory.
- D1, stimulating the excitatory pathway
24
Q
Cerebral cortex functions
A
25
Q
Homunculus
A
- Topographical representation of motor (shown) and sensory areas in the cerebral cortex.
- Distorted appearance is due to certain body regions that are more richly innervated and thus have increased cortical representation.
29
Q
Central pontine myelinolysis
- Definition
- Findings
- Correcting too fast:
- CPM
- Cerebral edema/herniation
A
- Definition
- A variant of the osmotic demyelination syndrome.
- Commonly iatrogenic, caused by overly rapid correction of hyponatremia
- Findings
- Acute paralysis, dysarthria, dysphagia, diplopia, and loss of consciousness.
- Can cause “locked-in syndrome.”
- Massive axonal demyelination in pontine white matter tracts [A] 2° to osmotic forces and edema.
- Correcting serum Na+ too fast:
- CPM: “From low to high, your pons will die”
- Cerebral edema/herniation: “From high to low, your brain will blow”
32
Q
Circle of Willis (458)
A
- System of anastomoses between anterior and posterior blood supplies to brain.
