Diseases of muscle and peripheral nerve: review of the CNS blood supply Flashcards
Cerebrum CNS
Right and left cerebral hemispheres Frontal lobe: cognition, motor activity Parietal lobe: sensory input Temporal lobe: memory storage Occipital lobe: visual perception Hypothalamus: vital center for regulation of body temperature and blood circulation.
Cerebellum CNS
right and left hemispheres
equilibrium and coordination
Brainstem CNS
midbrain, pons, medulla
vital centers: respiration, heart rate, blood pressure
Spinal cord CNS
traversed by nearly all of the nerves carrying information to and from the body.
cervical: arms, diaphragm (respiration)
thoracic: chest, abdomen
lumbo-sacral: legs, urinary bladder, rectum, reproductive organs.
Cranial (sensory and motor nerves) Nervs PNS
eye muscles, ear, face, tongue, mouth and viscera.
Spinal (Sensory and motor nerves) Nerves PNS
limbs and trunk, kin, musculoskeletal and viscera.
Meninges
fibrous tissue covering the brain
- Dura: tough outer alter, separates cranial cavity into compartments.
- Pia-arachnoid: thin inner layer containing many blood vessels.
Ventricular System
- Cerebrospinal Fluid (CSF): produced by the choroid plexus, flows through the ventricles and is reabsorbed by the special cells of the pia-arachnoid (arachnoid villi).
- Lateral ventricle with inter ventricular foramen (Monroe).
- Third ventricle with cerebral (Sylvian) aqueduct
- Fourth ventricle with a median aperture (Magendie) and two lateral foramina (Luschka).
Neurons (Nerve cell)
components:
cell body-resins in gray matter
axon- may be extremely long, mainly contained in white matter.
myelin sheath- multiple lamellae to specialized cell membrane surround and isolate axon (speeds up conduction).
Metabolic activity:
very high, requires high demand for glucose and oxygen and very susceptible to a lack of them.
Upper motor neuron:
cell body resides in grey matter of frontal lobe
axon travels great distance to brainstem and spinal cord to synapse with corresponding lower motor neuron (efferent motor-out signal to the body).
Lower motor neuron:
cell body in spinal cord grey matter; axon exits in the anterior nerve root to become peripheral motor nerve (efferent motor), innervates skeletal muscles.
Glia
astrocytes: supporting cell; proliferate in area of injury to form a “scar.”
oligodendrocytes: produce and maintain myelin sheaths int he CNS.
microglia: function not well understood; may be macrophages of the CNS.
Schwann cell: produce and maintain myelin sheathing the PNS.
Muscle Fiber Review
Uniform size and polygonal shape.
Muscle fibers are mosaic and randomly distributed.
Myofibers, endomysium (connective tissue around each muscle fiber which contains many myofibrils), perimysium (tissue that maps multiple muscle fibers in fascicles).
Type 1 Muscle Fibers: used in a sustained cotraction; red fibers, have many mitochondria and lipid droplets for energy; if ATPase is reactive in acidic domain (pH 4.3), the Type 1 fibers are darker.
Type 2 Muscle Fibers: white; loaded with glycogen and use for quick actions; if ATPase is reactive in basic domain (pH 9.4), the Type 2 fibers become dark.
The classification depends on the innervating nerves, not the fiber itself.
Most muscles have more Type 2 than Type 1 fibers.
Neurogenic Atrophy
Results in a patter of atrophy referred to as GROUP ATROPHY.
Small fibers with angular outlines occur together in groups in fascicles that may also have fibers of normal size and morphology or hypertrophies fibers.
Eventually, adipose and fibrous tissue replaces lost muscle fibers, late occurrence.
As soon as a muscle fiber is deinnervated, them muscle expresses receptors on the surface to attract neighboring axons for innervation; this can change the muscle fiber type with new innervation.
Atrophic and grouped=deinnervation atrophy.
Progression of deinervation and reinervation results in grouping of the same muscle fiber types.
Seen in anterior horn cell diseases such as poliomyelitis, amyotrophic lateral sclerosis (ALS), disorders of the peripheral nerve such has polyarteritis nodosa, diabetes, trauma, and other peripheral neuropathies that result in degeneration of peripheral nerves which in turn may all lead to atrophy of skeletal muscles.
Myopathies- Muscular Dystrophy; problem with muscles themselves.
Genetically determined and often start in childhood.
Progressive weakness and muscle loss.
Subdivision is based on: pattern of inheritance, severity of weakness, and distribution.
Inherent (genetic) loss or abnormality of the contractile proteins in the muscle resulting in weakness.
Progressive (Duchenne) muscular dystrophy:
Sex-linked, recessive disorder affecting male children and produces progressive course with proximal muscle weakness and atrophy and sometimes pseudo hypertrophy of the calf muscles.
There is a loss of an important contractile protein; DYSTROPHIN: anchors actin to the cell membrane and is a cell membrane protein; with no connection the cell membrane and actin multiple contractions, the cell membrane breaks down and there is an influx of calcium, which kills cells=necrosis.
Serum enzymes elevated, Progressive with a uniformly fatal outcome around age 20.
Earliest and more distinctive histological sign consists of SMALL GROUPS/CLUSTERS OF MUSCLE FIBERS UNDERGOING NECROSIS OR REGENERATION OF MUSCLE FIBERS IN THE AROUP AT A SIMILAR STAGE OF REACTION.
There is a futile attempt at muscle regeneration, but there is still no dystrophin, so this fails.
Fibrosis and adipose replacement of muscle fibers occurs during course of disease and may progress to a final stage with non-specific histological characteristics; increased connective tissue and fibrosis.
Necrotic muscle fibers have associated macrophage infiltrates.
Muscle necrosis and fiber loss
Variable inflammatory cell infiltration
Fibrosis and adipocyte infiltration
PNS anatomy
The thicker the axon, the thicker the myelin sheath, and the more rapid conduction velocity.
The perineurium surrounds the fascicles within each nerve.
The epinerurium is the connective tissue connecting all of the fascicles and blood vessels together in the nerve.
The endonerurium is the connective tissue between axons.
Not all neurons have myeline sheaths, some have thick ones and some have thing ones.
Trauma is the most common cause of disorders of the peripheral nerve.
Not including trauma, the most frequent cause is metabolic disease (diabetes); hereditary and infectious causes used to be the most common (leprosy).
Axonal degeneration
Following peripheral nerve injury from compression or transection, first degenerative changes are seen in the afflicted nerve. Later on, nerve regeneration may be observed.
In a severed nerve soon after injury, the axon detail to point of injury undergoes degeneration and fragmentation; the myelin sheath surrounding this axon also breaks down, but the Schwann cells remain (Wallerian degeneration).
Macrophages phagocytize the axon and myelin debris by entering the basal lamina and surrounding each nerve fiber.
As debris is removed, the proximal axon produces new sprouts, which may grow distally into the remaining basal lamina tunnel; it could ultimately reach the original destination and synapse on the end organ and the Schwann cells that have remained form new myelin around the new axon.
Traumatic neuroma: when the axonal sprouts are growing, they cannot find the basal lamina tunnel; without treatment of the severed nerve and alignment of the trunk through surgery this happens. It is a cluster of nerves that could never find the basal lamina tunnel; scar tissue buildup.
Axonopathy: Axon dies, myelin breaks down to form myelin ovoids, less myelinated axons.
Schwann cells increase=shorter, thinner myelin segments=decreased conduction velocity.
Remyelination=can get large axons with thin myelin.
Multiple axonal sprouts regrow through one basal lamina=axonopathy=axon clusters.
Review of CNS blood supply
2 internal carotid arteries anterior
2 vertebral arteries posterior
These fuse to form the basilar artery.
Most of the cerebrum is supplied by the anterior circulation, some by the posterior.
Arterial Circle
Interna Carotid branches:
Arterial Cerebral Artery (ACA); one on each side; supplies the medial surface of brain, frontal and parietal lobes.
Middle cerebral artery (MCA): one on each side; supplies most of the lateral surface of the cerebrum; frontal, parietal, temporal, and a small part of occipital lobe; all lobes on lateral surface are receiving blood from MCA.
Vertebral branches:
Posterior cerebral artery (PCA); one on each side; also supplies the medial surface of the brain, the temporal and occipital lobes.
As the PCA and ACA approach the edge of the medial surface of the brain, they spill over and supply the lateral surface of the brain a little bit.
Posterior communicating artery connected the internal carotid artery with the PCA.
THIS IS THE ARTERIAL CIRCLE; partly anterior circulation and partly posterior circulation.
Border zone: when vessel meet and supply that part of the brain with 2 vessels; ACA + MCA, PCA + MCA; makes a C shape pattern; part of brain that receives a dual supply; does not mean that it receives to much or to little blood; receives right amount; ON THE LATERAL SURFACE OF THE BRAIN.
Coronal Section of the brain (like cutting the brain like a loaf of bread from front to back): can see 4 parts of the border zone.
