1 the nervous system the spinal cord & spinal nerves chapter 9
TRANSCRIPT
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Parts of the nervous system are grouped according to structure or function
Structural Divisions
1. Central Nervous System (CNS):• Brain• Spinal Cord
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Peripheral Nervous System (PNS):
Cranial Nerves – carry impulses to and from the BRAIN
Spinal Nerves – carry messages to and from the SPINAL CORD
**Together, the CNS & PNS include all of the nervous tissue in the body
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Functional Divisions
Functionally, the nervous system is divided according to whether control is voluntary or involuntary
A tissue or organ that carries out a command from the nervous system is called an EFFECTOR
Effectors are our muscles and glands
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The Somatic Nervous System
Controlled voluntarily (by conscious will) and all the effectors are skeletal muscles
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The Autonomic Nervous System
Is an involuntary system and controls:
Smooth muscleCardiac MuscleGlands
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Neuroglia Cells of the nervous system that serve to
support & protect. Types with specialized functions include:
1. Protection of nervous tissue2. Supporting nervous tissue & binding to other
structures3. Aiding in the repair of cells4. Acting as phagocytes to remove pathogens5. Regulating fluids in between & around cells**Neuroglia continue to multiply throughout life
(unlike typical nerve cells)**Disadvantage is the potential of tumor growth
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Neurons
Functional cells of the nervous system Highly specialized cells Main portion (cell body) contains typical
nucleus & other organelles Distinguishing feature NOT found in any other
cells:Long, threadlike fibers that extend out from the
cell body & carry impulses across the cell called AXONS & DENDRITES
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Types of Neurons
Sensory Neurons – conduct impulses TO the spinal cord and brain
Motor Neurons – carry impulses from the Central Nervous System to the muscles and glands
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The Synapse
Neurons do not work alone
Impulses must be transferred between neurons to convey information
The synapse becomes the “point of junction” or “gap” where impulses are transferred
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Neurotransmitters
Chemicals contained in the end of the axon
They are released into the synapse to stimulate the next cell
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The Reflex Arc A complete pathway through the nervous
system Basic parts include:
1. Receptor – detects a stimulus
2. Sensory neuron – transmits the impulse TO the CNS
3. CNS – impulses are coordinated & a response is organized
4. Motor neuron – carries the impulse AWAY from the CNS
5. Effector – a muscle or gland that carries out a response
**The Patellar Reflex or “Knee-Jerk” Reflex
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Disorders Involving the Spinal CordMultiple Sclerosis (MS) –
• Myelin sheath is damaged• Fibers degenerate• Although not fully understood, strong evidence
indicates a person’s own immune system attacks the myelin sheath:
Prior viral or bacterial infection Genetic make-up Environmental factors
• Different rate of progression• Episodes of relapse or remission
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Tumors
Commonly found in tissue in or around the spinal cord
Symptoms caused by pressure on the cord and spinal nerves
Symptoms include: pain, numbness, weakness and loss of function
Diagnosed through the use of MRI Treated by surgery and/or radiation (for
malignant tumors)
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Amyotrophic Lateral Sclerosis (ALS) Also known as “Lou Gherig’s Disease” Motor neurons are destroyed Progressive destruction that causes
muscle atrophy and loss of motor control Eventually, the person is unable to
swallow, talk or breathe Death follows soon after
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Poliomyelitis (Polio)
Viral disease of the nervous system Occurs commonly in children Gastrointestinal tract infection passes the virus into
the bloodstream – eventually spreading to the CNS Virus multiplies in motor neurons within the spinal
cord Leads to paralysis and death, if left untreated Vaccines have eliminated the disease in many
countries – Jonas Salk (1954)
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Spinal Cord Injuries
Occur when vertebrae are broken or dislocated (car accidents, diving accidents, etc.)
Because brain & spinal tissue cannot repair itself, severing of the spinal cord causes paralysis of all muscles supplied by nerves BELOW the level of the injury