the nervous system: nerve plexuses, reflexes, and sensory and motor pathways
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The Nervous System: Nerve Plexuses, Reflexes, and Sensory and Motor Pathways. . By: Avi Asraf Roger Yee Santiago Roybal Sasha Buz Valeria Muňoz Vincent Cottrill. Nerve Plexuses. - PowerPoint PPT PresentationTRANSCRIPT
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The Nervous System: Nerve Plexuses, Reflexes, and Sensory and Motor Pathways.
By:Avi Asraf
Roger YeeSantiago Roybal
Sasha BuzValeria Muňoz
Vincent Cottrill
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Nerve Plexuses• Cervical plexus – innervates the muscles of the neck and extends into
the thoracic cavity to control the diaphragm. • Brachial plexus – innervates the shoulder girdle and upper limb• Lumbar plexus & Sacral plexus – supply the pelvic girdle and lower
limb.▫*all designate the lumbosacral plexus.
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Reflexes • A reflex is an automatic motor response to a specific stimulus.• A reflex response usually removes or opposes the original stimulus.• Reflexes help maintain homeostasis by making
rapid adjustments to the functions of organs/ organ systems.• Reflex arcs are an example of negative • feedback.
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Simple Reflex•The “wiring” of a single reflex is called a reflex arc.
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Simple Reflex• In the simplest reflex arc, a sensory neuron synapses directly on a
motor neuron, which performs information processing function. This is also known as a monosynaptic reflex.
• The sensory receptors in the stretch reflex are called muscle spindles.
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Simple Reflex• Stretch reflexes are important in maintaining normal posture and
balance and in making automatic adjustments in muscle tone. • Doctors can use the sensitivity of the stretch reflex to test general
conditions of the spinal cord, peripheral nerves, and muscles. • Example: knee jerk reflex
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Complex Reflexes• Polysyanptic reflexes include a longer delay between stimulus and
response. • They can produce more involved responses because the interneurons
can control several muscle groups simultaneously.• Withdrawal reflexes move stimulated parts of the body away from a
source of stimulation.• The strongest withdrawal reflexes are caused by pain stimuli. • A flexor reflex is a withdrawal reflex affecting the muscles of a limb.
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Complex Reflexes• When a specific muscle contracts, opposing muscles are stretched. • Contraction of a flexor muscles should trigger in the extensors a
stretch reflex that would cause them to contract, opposing the movement that is underway.
• Interneurons in the spinal cord prevent such competitions through reciprocal inhibition.
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Integration and Control of Spinal Reflexes
• Although reflexes are automatic, higher centers in the brain influence these response by stimulating or inhibiting the interneurons and motor neurons involved.
• Stroking the side of an infants sole produces a fanning of toes known as the Babinski sign/positive Babinski reflex.
• In adults, the toes curl, which is called Plantar reflex/negative Babinski reflex.
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Sensory and Motor Pathways
• A sensation, the information gathered by a sensory receptor, arrives in the form of action potentials in an afferent (sensory) fiber.▫Posterior Column Pathway is an example of an ascending sensory
pathway.
Sensory Pathways
The pathway of messages sent from the brain to the phalanges.
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Sensory and Motor Pathways
• The corticospinal pathway/pyramidal system provides conscious, voluntary control of skeletal muscles.
• The medial and lateral pathways provide subconscious, involuntary control of muscle tone and movements of the neck, trunk, and limbs. ▫These pathways were known as the extrapyramidal system because
it was thought that they operated independently of and parallel to the pyramidal system.
▫The corticospinal pathway begins at pyramidal cells of the cerebral cortex.
Motor Pathways
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Quick Review• 1) What is another name for the simplest reflex arc?
• 2) Why are stretch reflexes important?
• 3) What is the difference between the positive Babinski reflex and the negative Babinski reflex?
• 4) What is a sensation?
• 5) Where do corticospinal pathways begin?