Download Nervous System - Mrs. Riggs Online

Nervous System
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Only people have the ability to use language, exercise judgment, solve difficult
problems, produce creative objects and ideas, and transmit abstract notions from one
person to another
neurobiologist: biologist who studies the nervous system
neurologist: physician who specializes in disorders of the nervous system
Central Nervous System
• brain: principal organ; adult brains weighs around 3lb; receives messages from
sensory organs, blood and other body fluids
• spinal cord: thick bundle of nerve fibers located within spinal cavity; merges with brain
stem at upper end where nerve fibers continue upward into the brain
• 31 spinal nerves: pairs of nerves that branch out from the cord and extend out of
spinal cavity; ten pairs continue past end of spinal cord and exit spinal cavity through
gaps in lumbar vertebrae and sacrum
• 12 cranial nerves: pairs of nerves that branch directly from the brain stem and transmit
nerve signals to and from eyes, ears, mouth, face, scalp
• spinal cord does not extend all the way down the spine but tapers just below first
lumbar vertebra
• meninges: layer of protective tissues covering spinal cord and brain; dura mater –
arachnoid – pia mater
• cerebrospinal fluid circulates through fibers of arachnoid; cushions brain
• glial cells: support and insulate nerve tissue
• neurons: actual nerve cells; long fibers branch out from cell bodies
• cell body: contains nucleus and most of nerve cell's cytoplasm; found only in brain,
spinal cord or in a ganglion (mass of cell bodies)
• dendrite: branched extension of cell that receives nerve impulses from other neurons
and conducts them toward cell body
• axon: long extension which relays nerve impulses from the cell body to other neurons;
in most sensory neurons dendrites bypass cell body and conduct directly to axon →
spinal cord; nerve impulses travel in one direction from dendrites toward cell body to
axon
• gray matter: consists largely of cell bodies which lack white myelin; white matter
composed of axons and glial cells
• some ganglia grouped together to form a large nerve called a plexus; brachial plexus
at back of neck and shoulder is congregation of nerve cells which help connect
median nerve and other arm nerves;
• nerve center: group of cell bodies in brain or spinal cord that help control body
function
• 1) sensory neurons: neurons that transmit information to CNS from senses as well as
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pain signals
2) motor neurons: neurons that relay from CNS to other parts of body
3) interneurons: only in CNS; relay signals between neurons/groups of neurons
blood-brain barrier: capillaries of CNS tightly sealed to prevent bacteria from entering
brain and spinal cord; brain contains own wbc called microglia
meningitis: infection of the meninges; more often affects children b/c blood-brain
barrier not fully developed
poliomyelitis (polio): virus enters motor neurons of spinal cord and destroys them;
connecting skeletal muscles become paralyzed;
Peripheral Nervous System
• nerves branching from the brain and spinal cord and connecting the CNS to the
extremities of the body; can be several feet long - sciatic nerve connects leg
extremities with spinal cord in lower back
• each of 31 pairs of spinal nerves supplies a particular body part; mixed nerves –
contain both sensory and motor fibers
• [Fig. 8.8 p.126]
sensory nerve fibers
located in ganglia outside spinal cord
carry impulses from sense-receiving
body parts TO brain/spinal cord
connect to spinal cord through rear
nerve root
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motor nerve fibers
found in gray matter of spinal cord
carry impulses FROM CNS to
muscles/organs
connect to spinal cord through front
nerve root
autonomic nervous system: controls involuntary functions (heart, digestive system,
glands, etc.)
-sympathetic: respond's to body's needs during increased activity, emergency
situations by causing heartbeat and breathing rates to increase, supplying more blood
to body for quick response
-parasympathetic: counteracts sympathetic division by blocking action of sympathetic
fibers
Nerve Structure
• [Fig. 8.10 p.127]
• median nerve: bundles of nerve fibers imbedded in connective tissues; axons within
bundles imbedded among glial cells protected by myelin sheath; blood, lymph
vessels, fatty tissue help nourish and protect nerve fibers
• neurons rarely reproduce
• Schwann cells: peripheral nerves only; produce layers of myelin sheathing around
axons; myelinated axons transmit nerve impulses much faster than non-covered
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multiple sclerosis (MS): body's immune system attacks glial cells; myelin sheaths
deteriorate and are replaced by scar tissue which slows nerve impulses
action potential [Fig 8.11 p.128]: wave of electrical activity in which a brief (+) charge
sweeps through neuron and races down axon; propagated by fast-acting, voltagesensing ion gates that quickly open and close, allowing Na and K ions to briefly flow
into and out of cell; after action potential passes, cell membrane's ion pumps restore
cell's original ion balance to be ready in as little as 1/2000 second
synapse: enclosed junction between axon of one neuron and dendrites or cell body of
another; when action potential reaches synapse → neurotransmitter released into
synapse → sensors in receiving neuron detect neurotransmitter → trigger neuron to
fire
some substances can inhibit transmission of nerve impulses
-Novocaine (anesthetic) blocks nerve impulses in sensory nerves
-botulinum B toxin inhibits impulse transmission in motor nerves
Parkinson's disease: lack of neurotransmitter dopamine in the motor-control areas of
brain caused by damage to a region of the midbrain that produces dopamine; affects
patient's control of movement characterized by tremors and limb stiffness
reflex action: quick, automatic response; simplest act of the nervous system
reflex arc: short circuit allows nerve impulses to bypass brain
Homework
Section 8.1 (p.126) #1-6
Section 8.2 (p.129) #1-6 (#5 can be written as a flow chart)