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Main components of CNS
1. Spinal cord 2. Brain [cerebral hemispheres, cerebellum, & brainstem]
Spinal Cord
- continuous w. brainstem & exits from cranial cavity through FORAMEN MAGNUM. - gray matter is centrally located in an H shape & surrounded by white matter
Gray Matter
- contains cell bodies of voluntary motor neurons & preganglionic autonomic motor neurons, as well as cell bodies of association neurons [interneurons]
White Matter
- contains axons of ascending sensory & descending [suprasegmental] motor fibers - myelin surrounding these fibers gives them their white appearance
Spinal Cord: Ascending Tracks
- carry specific sensory info to higher levels of CNS - this info comes from special sensory endings [receptors] in the skin, muscles & joints, viscera, & blood vessels & enters the spinal cord by way of the dorsal roots of the spinal nerves
Spinal Cord: Ascending Tracks: Spinocerebellar Tracts
- carry subconscious info about muscle tension & body position to cerebellum for coordination of movement - this info is not consciously perceived
Spinal Cord: Ascending Tracks: Spinothalamic Tracts
- carry pain & temperature sensations
Spinal Cord: Descending Tracts
- carry impulses that are responsible for muscle movement - most important descending tracts are CORTICOBULBAR & CORTICOSPINAL TRACTS = collectively termed PYRAMIDAL TRACT - these tracts carry volitional [voluntary] impulses from cortex to cranial & peripheral nerves
Spinal Cord: Lower Motor Neurons
- final common pathway through which descending motor tracts influence skeletal muscle, the effector organ for movement.
Spinal Cord: Lower Motor Neurons
Cell bodies of LMNs, which send axons to innervate the skeletal muscles of the arms, trunk, & legs, are located in the ANTERIOR HORN of the corresponding segments of the spinal cord
Spinal Cord: Lower Motor Neurons
LMNs for skeletal muscles of the eyes, face, mouth, & throat are located in the corresponding segments of the brainstem
Spinal Cord: Lower Motor Neurons
LMN lesions generally cause weakness or paralysis, denervation atrophy, hyporeflexia or areflexia, & decreased muscle tone [flaccidity]
Spinal Cord: Upper Motor Neurons
- originates in cerebral cortex & project downward - corticobulbar tract ends in brainstem & corticospinal tract descends into spinal cord - these neurons influence skeletal muscle movement
Spinal Cord: Upper Motor Neurons
- UMN lesions generally cause weakness or paralysis, disuse atrophy, hyperreflexia, & increased muscle tone [spasticity]
Spinal Cord: Reflex Arc
- in the spinal cord, reflex arcs play an important role in maintaining muscle tone, which is essential for body posture - reflex is an involuntary response to stimulus - components of a monosynaptic reflex arc: receptor organ, an afferent neuron, an effector neuron, & an effector organ
Brain
divided into: 1. cerebrum 2. brainstem 3. cerebellum
Cerebrum
- right & left hemispheres - can be further divided into 4 major lobes: 1. frontal 2. temporal 3. parietal 4. occipital *these divisions are useful to delineate portions of the neocortex [gray matter], which makes up the outer layer of the cerebral hemispheres*
Frontal Lobe
controls higher cognitive function, memory retention, voluntary eye movements, voluntary motor movement, & expressive speech in Broca's area
Temporal Lobe
- behind frontal lobe - contains Wernicke's area, which is responsible for receptive speech & for integration of somatic, visual, & auditory data
Parietal Lobe
composted of the sensory cortex, controlling & interpreting spatial info
Occipital Lobe
Processing of sight takes place
Cerebrum
Also contains: 1. basal ganglia 2. thalamus 3. hypothalamus 4. limbic system
Basal Ganglia
- function is to modulate the initiation, execution, & completion of voluntary movements & automatic movements associated w. skeletal muscle activity, such as swinging of the arms while walking, swallowing saliva, & blinking - a group of paired structures located centrally in cerebrum & midbrain; most of them are on both sides of thalamus
Thalamus [Part of the Diencephalon]
- lies directly above brainstem & is the major relay center for sensory & other afferent inputs to cerebral cortex
Hypothalamus
- located inferior to thalamus & slightly in front of midbrain - regulates ANS & endocrine system
Limbic System
- phylogenetically, an old part of human cerebrum - located near inner surfaces of cerebral hemispheres & is concerned w. emotion, aggression, feeding behavior, & sexual response
Ventricles Of Brain
- 4 fluid-filled cavities w.in brain that connect w. one another & w. spinal canal - lower portion of 4th ventricle becomes central canal in lower part of brainstem - spinal canal located in center & extends full length of spinal cord
Cerebrospinal Fluid [CSF]
- circulates w.in subarachnoid space that surrounds brain, brainstem, & spinal cord. - provides cushioning, allows fluis shifts from cranial to spinal cavity, & carries nutrients - formation is in CHOROID PLEXUS in ventricles, involves passive diffusion & active transport of substances
Cerebrospinal Fluid [CSF]
- resembles an ultrafiltrate of blood - ventricles & central canal normally filled w. ave. of 135 mL of CSF - absorbed primarily through arachnoid villi into intradural venous sinuses & eventually into venous system
Vitamins Essential For Maintenance Of CNS
- thiamine [B1], niacin, & pyridoxine [B6] - deficiencies in 1 or more of these vitamins could result in such nonspecific complaints as depression, apathy, neuritis, weakness, mental confusion, & irritability - Cobalamin [vitamin B12] deficiency may be from vitamin absorption from natural food sources: meat, fish, & poultry = mental function decline
Elimination Pattern
- incontinence of urine & feces & urinary retention are the most common elimination problems associated w. a neurologic problem - IE: nerve root compression in cauda equina leads to sudden onset of incontinence
Delirium
- acute confusional state; an acute d/o of cognition - in elderly, delirium may be seen post-op. - often an early indicator of various illnesses
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