anatomy and physiology Flashcards
what is Syringomyelia?
Cystic cavity (syrinx) within central canal of spinal cord. associated with chiari malformations,trauma,tumors
Tract affected in syringomyelia and result
Fibers crossing in anterior white commissure (spinothalamic tract) are typically damaged first. Results in a “cape-like,” bilateral loss of pain and temperature sensation in upper extremities (fine touch sensation is preserved).
Chiari 1 malformation
cerebellar tonsillar ectopia > 3–5 mm; congenital, usually asymptomatic in childhood, manifests with headaches and cerebellar symptoms.
Anencephaly
Malformation of anterior neural tube no forebrain, open calvarium. Clinical findings: AFP, polyhydramnios (no swallowing center in brain). Associated with maternal type 1 diabetes. Maternal folate supplementation risk.
holoprosencephaly
Failure of left and right hemispheres to separate; usually occurs during weeks 5–6. May be related to mutations in sonic hedgehog signaling pathway. Moderate form has cleft lip/palate, most severe form results in cyclopia. Seen in Patau syndrome and fetal alcohol syndrome.
chiari 2 malformations
Herniation of low-lying cerebellar vermis through foramen magnum with aqueductal stenosis hydrocephalus. Usually associated with lumbosacral meningomyelocele (paralysis/sensory loss at and below the level of the lesion).
Dandy Walker syndrome
Agenesis of cerebellar vermis with cystic enlargement of 4th ventricle (fills the enlarged posterior fossa A). Associated with noncommunicating hydrocephalus, spina bifida.
Neurons
1.Signal-transmitting cells of the nervous system. 2.Permanent cells(do not divide in adulthood).
3.Signal-relaying cells with dendrites (receive input), cell bodies, and axons (send output).
4.Cell bodies and dendrites can be seen on Nissl staining (stains RER).
RER is not present in the axon.
Injury to axon Wallerian degeneration—degeneration distal to injury and axonal retraction proximally; allows for potential regeneration of axon (if in PNS).
astrocytes
Physical support, repair, K+ metabolism, removal of excess neurotransmitter, component of bloodbrain barrier, glycogen fuel reserve buffer. Reactive gliosis in response to neural injury. Astrocyte marker: GFAP. Derived from neuroectoderm.
microglia
Phagocytic scavenger cells of CNS (mesodermal, mononuclear origin). Activated in response to tissue damage. Not readily discernible by Nissl stain.
HIV-infected microglia fuse to form multinucleated giant cells in CNS.
myelin
conduction velocity of signals transmitted down axons saltatory conduction of action potential at the nodes of Ranvier, where there are high concentrations of Na+ channels. CNS—oligodendrocytes; PNS—Schwann cells.
Wraps and insulates axons A: space constant and conduction velocity.
schwann cell
Each Schwann cell myelinates only 1 PNS axon. Also promote axonal regeneration. Derived from neural crest. conduction velocity via saltatory conduction at the nodes of Ranvier, where there is a high concentration of Na+ channels.
May be injured in Guillain-Barré syndrome. Vestibular schwannoma—typically located on CN VIII in internal acoustic meatus, may extend to cerebellopontine angle
oligodendroglia
Myelinates axons of neurons in CNS. Each oligodendrocyte can myelinate many axons (∼ 30). Predominant type of glial cell in white matter.
Derived from neuroectoderm. “Fried egg” appearance histologically. Injured in multiple sclerosis, progressive multifocal leukoencephalopathy (PML), leukodystrophies.
functions of hypothalmus
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 (found in medulla, responds to emetics). Supraoptic nucleus primarily makes ADH. Paraventricular nucleus primarily makes oxytocin. Hypothalamus makes ADH and oxytocin. They are carried by neurophysins down axons to posterior pituitary, where they are stored and released.
lateral hypothalmus
hunger,Destruction anorexia, failure to thrive (infants). Stimulated by ghrelin, inhibited by leptin.
ventromedial hypothalmus
Satiety. Destruction (eg, craniopharyngioma) hyperphagia. Stimulated by leptin.
anterior hypothalmus
cooling, parasympathetic
posterior hypothalmus
heating symathetic
suprachiasmatic nucleus
circadian rhythm
BBB structures
- Tight junctions between nonfenestrated capillary endothelial cells
- Basement membrane
- Astrocyte foot processes
Poliomyelitis and Werdnig-Hoffmann disease
Congenital degeneration of anterior horns of spinal cord. LMN lesions only. “Floppy baby” with marked hypotonia and tongue fasciculations. Infantile type has median age of death of 7 months. Autosomal recessive inheritance. Poliomyelitis asymmetric weakness. Werdnig-Hoffmann disease symmetric weakness
Amyotrophic lateral sclerosis
Combined UMN and LMN deficits with no sensory or bowel/bladder deficits (due to loss of cortical and spinal cord motor neurons, respectively). Can be caused by defect in superoxide dismutase 1. Commonly presents with asymmetric limb weakness (hands/feet), fasciculations, eventual atrophy. Fatal. Commonly known as Lou Gehrig disease. Treatment: riluzole.
Complete occlusion of anterior spinal artery
Spares dorsal columns and Lissauer tract; upper thoracic ASA territory is watershed area, as artery of Adamkiewicz supplies ASA below ∼ T8.
tabes dorsalis
Caused by 3° syphilis. Results from degeneration (demyelination) of dorsal columns and roots progressive sensory ataxia (impaired proprioception poor coordination). Associated with Charcot joints, shooting pain, Argyll Robertson pupils. Exam will demonstrate absence of DTRs and ⊕Romberg sign.
syringomyelia
Syrinx expands and damages anterior white commissure of spinothalamic tract (2nd-order neurons) bilateral loss of pain and temperature sensation in cape-like distribution; seen with Chiari I malformation; can expand and affect other tracts.
b12 deficiency
Subacute combined degeneration (SCD)— demyelination of Spinocerebellar tracts, lateral Corticospinal tracts, and Dorsal columns. Ataxic gait, paresthesia, impaired position/vibration sense.
