Download Nervous System

 Master
controlling and communicating system
of the body.
 Electrical impulses are rapid, specific and
cause almost immediate response.
 Three
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overlapping functions:
Uses millions of sensory receptors to monitor
changes occurring both inside and outside the
body. (changes are stimuli/ gathered info is
sensory input)
Processes/interprets sensory input and make
decisions about what should be done
(integration)
Effects a response by activating muscles or
glands (motor output)
 Divided
in terms of structures (structural
classification) or
 In terms of activities (functional
classification)
 Structural
Classifiction
 Two subdivisions – central nervous systems
(CNS) and peripheral nervous systems (PNS).
 CNS – brain and spinal cord in dorsal body
cavity
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integrating and command centers of the nervous
system.
Interpret incoming sensory information
Issues instructions based on past experience and
current conditions.
 PNS
– part of the nervous system outside the
CNS that serve as communication lines.
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Nerves that extend from the brain and spinal
cord
Spinal nerves carry impulses to and from the
spinal cord.
Cranial nerves carry impulses to and from the
brain
 Functional
classification
 Two principle divisions – sensory (afferent)
division and motor (efferent) divisions
 Sensory
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Keeps the CNS constantly informed of events
going on both inside and outside the body
Nerve fibers convey impulses to the CNS from
sensory receptors located in various parts of the
body.
Somatic sensory – delivers impulses from the
skin, skeletal muscles, and joints.
Visceral sensory – transmits impulses from
visceral organs.
 Motor
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Carries impulses from the CNS to effector organs,
muslces, and glands.
Impulses activate muscles/glands to cause their
motor response.
Has two subdivisions
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Somatic nervous system – voluntarily control our
skeletal muscles.
Autonomic nervous system – regulates involuntary
events ( smooth/cardiac muscles, glands) (two
systems, sympathetic and parasympathetic)
 Draw
picture of CNS and PNS and explain
both.
 Then
copy chart of nervous system onto back
of paper and explain all parts.
 Nervous
tissue is made up of two principle
types of cells
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Supporting cells
neurons
 Supporting
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Cells
Collectively called neuroglia
Includes many types of cells for support,
insulation, and protection
Not able to transmit nerve impulses
Never lose their ability to divide
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astrocytes
 Star-shaped, abundant, nearly ½ the neural
tissue
 Cling to neurons
 Braces/anchors neurons to nutrient supply lines
(blood capillaries)
 Forms a living barrier between capillaries and
nuerons
 Protect the neurons from harmful substances
 Help control the chemical environment in the
brain (picks up excess ions and recaptures
released neurotransmitters)
 Microglia
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Spiderlike
Phagocytic on dead brain cells, bacteria, etc.
 Ependymal
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cells
Line the cavities of the brain and spinal cord
Beating cilia helps to circulate the cerebrospinal
fluid
 Oligodendrocytes
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Wrap flat extensions tightly aroudn the nerve
fibers
Produces fatty insulating coverings called myelin
sheaths
Two major varieties in the PNS – Schwann cells
and satellite cells
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Schwann cells form myelin sheaths around nerve fibers
that extend from the CNS
Satellite cells act as protective/ cushioning cells
 Draw
a picture and write a sentence for each
of the members of the neuroglia family:
astrocyte, ependymal, microglia,
oligodendrocyte, schwann cell, and satellite
cell.
 The
picture should be anything that can help
you remember what each thing does or looks
like. For example microglia could be a spider.
 Neurons
 Highly
specialized to transmit messages
(nerve impuleses) from one part of the body
to another.
 Many common features
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Neurons never actually tough other neurons
Cell body that contains the nucleus and is the
metabolic center of the cell. ( if it is damaged
the cell dies and is not replaced)
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1+ slender processes (fibers) extending from cell
body ( vary in length from microscopic to four
feet long – lumbar region of the spine to the big
toe)
Processes that conduct electrical currents toward
the cell body are dendrites (depending on type, a
neuron may have hundreds of dendrites)
Processes that generate nerve impulses and
conduct them away from the cell body are axons
(only one axon)
(some have a collateral branch along its length)
(all branch to form hundreds to thousands of
axonal terminals)
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Tiny vesicles store neurotransmitters within each
axonal terminal.
Axonal terminal is seperated from the next
neuron by a tiny gap (synaptic cleft)
When impulses reach the axonal terminals they
stimulate the release of neurotransmitters.
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Most long nerve fibers are covered with a
whitish, fatty material (myelin)
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Protects and insulates the fibers
Increases the transmission rate of nerve impulses
Formed by many individual cells (oligodendrocytes or
Schwann)
Gaps or indentations at regular intervals (nodes of
Ranvier)
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Bundles of nerve fibers (neuron processes)
running through the CNS are tracts, in the PNS
they are called nerves.
White matter are myelinated processes and gray
matter is unmyelinated.
 Functional
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classification
Groups neurons according to the direction the
nerve impulse is traveling relative to the CNS.
Sensory (afferent neurons)
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Carry impulses from sensory receptors (internal organs
or the skin) to the CNS area
Dendrite endings associated with specialized receptors
that are activated by specific changes
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Skin ( cutaneous sense organs)
 Pain receptors (bare dendrite endings) are the least
specialized.
 Most numerous (warning us of some type of body
damage is occurring)
Muscles and tendons (proprioceptors)
 Detect the stretch/tension in skeletal muscles,
tendons and joints.
 Information sent to the brain for proper adjustments
to balance and posture.
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Motor (efferent) neurons
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Carry impulses from the CNS to the viscera and/or
muscles and glands
Cell bodies always located in the CNS
Interneurons (association neurons)
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Connect the motor and sensory neurons in a neural
pathways.
Cell bodies are always located in the CNS
 Structural
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Based on number of processes extending from
the cell body.
Several processes – multipolar neuron
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classification
All motor and association neurons
Most common structural type
Two processes (axon and a dendrite) – bipolar
neurons.
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Rare in adults – only in the eye and ear where they act
as sensory receptor cells
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Single process emerging from cell body – unipolar
neurons.
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Very short and divides almost immediatley into
proximal (central) and distal (peripheral) fibers
Only the small branches at the end of the peripheral
process are dendrites.
Remainder of peripheral processes and the central
process function as axons. (in this case, the axon
conducts impulses both toward and away from the cell
body)
 Class
work: Draw, label and explain a neuron
and its interaction with another neuron.
 Home
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work:
Compare
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1: sensory, motor and interneurons
2: uni, bi and multipolar neurons
 Cylindrical,
17 inches long, continuation of
brain stem from foramen magnum to L1 or
L2.
 Two-way conduction pathway to and from
the brain.
 A major reflex center.
 Cushioned and protected by meninges
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Meningal coverings do not end at L2
Extend well beyond the end of the spinal cord
4
major regions – cerebral hemispheres,
diencephalon, brain stem, cerebellum
 Cerebral
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hemispheres
Most superior part of the brain
Obscure most of the brain stem
Elevated ridges of tissue called gyri seperated by
shallow grooves called sulci
Deeper grooves called fissures which separate
large regions
Other fissures divide each cerebral hemisphere
into a number of lobes (named for cranial bones
over them)
 Diencephalon
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Interbrain
Sits anterior to the brain stem
Enclosed by the cerebral hemispheres
Major structures are thalamus, hypothalamus,
epithalamus,
Hypothalamus
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Plays a role in the regulation of body temperature,
water balance, and metabolism.
Center for many drives and emotions (thirst, appetite,
sex, pain, and pleasure centers)
Epithalamus
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Forms cerebrospinal fluid
 Brain
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stem
Control vital activities (breathing and blood
pressure)
Midbrain, pons and medulla oblongata
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Midbrain – reflex centers involved with vision and
hearing.
Pons – control breathing
Medulla oblongata – regulate vital visceral activities
(control heart rate, blood pressure, breathing,
swallowing, vomiting, etc.)
 Cerebellum
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Precise timing for skeletal muscle activity
Controls balance so movements are smooth and
coordinated.
 Draw,
label and explain the parts of the brain
we have covered: 4 major regions – cerebral
hemispheres, diencephalon (hypothalamus,
epithalamus), brain stem (midbrain, pons,
and medulla oblongata), cerebellum
 Nervous
tissue is very soft and delicate
 Irreplaceable neurons can be injured by
slightest pressure
 Protected by bone, membranes, cushion,
blood-brain barrier
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Bone- skull and vertebral column
Meninges – connective tissue membranes
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Outermost layer – durra mater
 Double-layered membrane surrounding the brain
 One layer attached to the inner surface of the skull
 Other layer forms the outermost covering of the
brain (becomes spinal cord durra mater)
Middle layer – web-like arachnoid mater
 Filled with cerebrospinal fluid
Inner most layer – pia mater
 Clings tightly/follows folds of the surface of the
brain and spinal cord
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Cerebrospinal fluid – watery cushion
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Similar to plasma
Continually formed from blood by the choroid plexus
(clusters of capillaries hanging from the “roof” in each
of the brain’s ventricles)
Protects the fragile nervous tissue from blows/trauma
continually moving (thru sc, subarachnoid, cerebral
hemispheres, diencephalon, midbrain, pons, medulla)
Forms and drains at a constant rate to maintain
normal pressure and volume (solutes include glucose,
proteins, NaCl)
 Blood
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Brain barrier
Neurons kept separated from blood-borne
substances
Barrier made of least permeable capillaries in
the body
Only water, glucose, and essential amino acids
(water-soluble substances) pass easily
Nonessential amino acids and potassium ions are
prevented and actively soluble molecules diffuse
easily (why blood-borne alcohol, nicotine, and
anesthetics affect the brain)
 Autonomic
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nervous system
Also called the involuntary nervous system
Motor subdivisions of the PNS
Controls body activities automatically
Regulate cardiac muscle smooth muscles and
glands
Two divisions – the sympathetic and
parasympathetic
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Both serve the same organs but cause essentially
opposite effects
Counterbalancing each others activities to keep body
systems running smoothly
 Sympathetic
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Mobilizes the body during extreme situations
(fear, exercise, or rage)
Often reffered to as the “fight or flight” system
Brings about efffects that help the individual
cope with the stressor.
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Increases heartrate, blood pressure, blood glucose
Dilates bronchioles of the of the lungs and blood
vessels in skeletal muscle.
Withdrawal of blood from the digestive organs.
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Effects continue for several minutes until
hormones are destroyed by the liver.
Gradually becomes less and less efficient
particularly in vasoconstriction
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Elderly often become light-headed or faint
System is not able to react quickly enough to
counteract the pull of gravity.
 Parasympathetic
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Allows us to “unwind” and conserve energy
Most active when the body is at rest and not
threatened in any way
Promoting normal digestion and elimination
Decreases demands on the cardiovascular system
Blood pressure, heart and respiratory rates are
regulated at low-normal levels
Digestive tract is actively digesting food
Skin is warm
Eye pupils are constricted to protect retinas from
excessive damaging light