Moto Neuron
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Transcript of Moto Neuron
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The pyramidal motor systemcontrols all of our voluntary
movements.
The pyramidal system is a two neuron system
- upper motor neurons in the PrimaryMotor Cortex
- lower motor neurons in the anterior
horn of the spinal cord
consisting of
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The upper motor neurons reside in theprecentral gyrus of the frontal lobe also
called the "motor strip".
Upper motor neurons (UMN) are a type of
first order neuron
They are unable to leave the centralnervous system
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The axons of these lower motor
neurons then exit the spinal cord viathe Ventral root
The upper motor neuron axons thensynapse on lower motor neurons in the
Anterior horn of the spinal cord
The ventral root then joins the dorsalroot to form the spinal nerve, which
finally innervates the skeletal muscle.
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This group of fibers carries messages for voluntary motormovement to the lower motor neurons in the brain stem
and spinal cord.
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are the motor neuronsconnecting thebrainstemand spinal cordto muscle fibers,
bringing the nerve impulsesfrom theupper motor neuronsout to the muscles. A
lower motor neuron's axon terminates onan effector (muscle).
Lower motor neurons (LMNs)
The lower motor neurons relay the movementinstructions provided by the upper motor neurons,to the muscles. When the lower motor neurons aredamaged the result is muscle weakness, twitching
and atrophy.
http://en.wikipedia.org/wiki/Motor_neuronhttp://en.wikipedia.org/wiki/Brainstemhttp://en.wikipedia.org/wiki/Spinal_cordhttp://en.wikipedia.org/wiki/Muscle_fibershttp://en.wikipedia.org/wiki/Action_potentialhttp://en.wikipedia.org/wiki/Upper_motor_neuronhttp://en.wikipedia.org/wiki/Musclehttp://backandneck.about.com/od/m/g/uppermotorneuro.htmhttp://backandneck.about.com/od/m/g/muscstrength.htmhttp://backandneck.about.com/od/m/g/muscstrength.htmhttp://backandneck.about.com/od/m/g/uppermotorneuro.htmhttp://en.wikipedia.org/wiki/Musclehttp://en.wikipedia.org/wiki/Upper_motor_neuronhttp://en.wikipedia.org/wiki/Action_potentialhttp://en.wikipedia.org/wiki/Muscle_fibershttp://en.wikipedia.org/wiki/Spinal_cordhttp://en.wikipedia.org/wiki/Brainstemhttp://en.wikipedia.org/wiki/Motor_neuron -
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Lower motor neurons are classifiedbased on the type of muscle fiber they
innervate:
Alpha motor neurons(-MNs) innervate extrafusal
muscle fibers, the most numerous type of musclefiber and the one involved in muscle contraction.
Gamma motor neurons(-MNs) innervateintrafusal muscle fibers, which together with
sensory afferents compose muscle spindles. Theseare part of the system for sensing body position(proprioception).
http://en.wikipedia.org/wiki/Alpha_motor_neuronhttp://en.wikipedia.org/wiki/Extrafusal_muscle_fiberhttp://en.wikipedia.org/wiki/Extrafusal_muscle_fiberhttp://en.wikipedia.org/wiki/Muscle_contractionhttp://en.wikipedia.org/wiki/Gamma_motor_neuronhttp://en.wikipedia.org/wiki/Intrafusal_muscle_fiberhttp://en.wikipedia.org/wiki/Muscle_spindlehttp://en.wikipedia.org/wiki/Proprioceptionhttp://en.wikipedia.org/wiki/Proprioceptionhttp://en.wikipedia.org/wiki/Muscle_spindlehttp://en.wikipedia.org/wiki/Intrafusal_muscle_fiberhttp://en.wikipedia.org/wiki/Gamma_motor_neuronhttp://en.wikipedia.org/wiki/Muscle_contractionhttp://en.wikipedia.org/wiki/Extrafusal_muscle_fiberhttp://en.wikipedia.org/wiki/Extrafusal_muscle_fiberhttp://en.wikipedia.org/wiki/Alpha_motor_neuron -
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Glutamatereleased from the upper motorneurons triggers depolarizationin the
lower motor neurons in the ventral hornwhich in turn causes an action potential to
propagate the length of the axonto theneuromuscular junctionwhere
acetylcholineis released to carry the signal
across the synaptic cleftto thepostsynaptic receptors of the muscle cellmembrane, signaling the muscle to
contract
Physiology
http://en.wikipedia.org/wiki/Glutamatehttp://en.wikipedia.org/wiki/Depolarizationhttp://en.wikipedia.org/wiki/Axonhttp://en.wikipedia.org/wiki/Neuromuscular_junctionhttp://en.wikipedia.org/wiki/Acetylcholinehttp://en.wikipedia.org/wiki/Synaptic_clefthttp://en.wikipedia.org/wiki/Muscle_cellhttp://en.wikipedia.org/wiki/Muscle_cellhttp://en.wikipedia.org/wiki/Synaptic_clefthttp://en.wikipedia.org/wiki/Acetylcholinehttp://en.wikipedia.org/wiki/Neuromuscular_junctionhttp://en.wikipedia.org/wiki/Axonhttp://en.wikipedia.org/wiki/Depolarizationhttp://en.wikipedia.org/wiki/Glutamate -
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not all cranial nerves have lowermotor neuron components.
Some of the cranial nerves containonly sensory fibers and therefore
cannot be classified as lower motorneurons
CN I, the olfactory nerve, CN II the opticnerve, and CN VIII, the auditory nerve
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Peripheral Nervous System
Cranial nervesarising from the brain
Somatic fibers connecting to the skin and skeletal muscles
Autonomic fibers connecting to viscera
Spinal nervesarising from the spinal cord
Somatic fibers connecting to the skin and skeletal musclesAutonomic fibers connecting to viscera
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Nervous System Subdivisions
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Structure of a PeripheralNerve
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Nerve Fiber Classification
Sensory Nervesconduct impulses into brain or spinal
cord
Motor Nervesconduct impulses to muscles or glands
Mixed Nervescontain both sensory nerve fibers and
motor nerve fibers; most nerves
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Nerve Fiber Classification
General somatic efferentfibers
carry motor impulses from
CNS to skeletal muscles
General visceral efferentfibers
carry motor impulses away from
CNS to smooth muscles and
glands
General somatic afferentfibers
carry sensory impulses to
CNS from skin and skeletal
muscles
General visceral afferentfibers
carry sensory impulses to CNS
from blood vessels and internal
organs
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Nerve Fiber Classification
Special somatic efferent fibers
carry motor impulses from brain to muscles
used in chewing, swallowing, speaking, and
forming facial expressions
Special visceral afferent fibers
carry sensory impulses to brain from olfactory and
taste receptors
Special somatic afferent fibers
carry sensory impulses to brain from receptors of
sight, hearing, and equilibrium
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Cranial Nerves
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Cranial Nerves I and II
Olfactory (I)
sensory
fibers transmit
impulses associated
with smell
Optic (II)
sensory
fibers transmit
impulses associated
with vision
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Cranial Nerves III and IV
Trochlear (IV)
some sensory
proprioreceptorsprimarily motor
motor impulses to
muscles that move the
eyes
Oculomotor (III)
some sensory
proprioreceptorsprimarily motor
motor impulses to
muscles thatraise eyelids
move the eyes
focus lens
adjust light entering
eye
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Cranial Nerve V
Trigeminal (V)
mixed
opthalmic divisionsensory from surface of eyes,
tear glands, scalp, forehead, and
upper eyelidsmaxillary division
sensory from upper teeth,
upper gum, upper lip, palate,
and skin of face
mandibular divisionsensory from scalp, skin of jaw,lower teeth, lower gum, and
lower lip
motor to muscles of mastication
and muscles in floor of mouth
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Cranial Nerves VI and VII
Abducens (VI)
primarily motor
motor impulses to
muscles that move
the eyes
some sensory withproprioreceptors
Facial (VII)
mixed
sensory from tastereceptors
motor to muscles of
facial expression,
tear glands, and
salivary glands
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Cranial Nerves VIII and IX
Vestibulocochlear (VIII)
sensory
vestibular branch
sensory from
equilibrium receptors of
ear
cochlear branch
sensory from hearing
receptors
Glossopharyngeal (IX)
mixed
sensory from pharynx,tonsils, tongue, and carotid
arteries
motor to salivary glands
and muscles of pharynx
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Cranial Nerve X
Vagus (X)
mixed
somatic motor to
muscles of speech
and swallowing
autonomic motor to
viscera of thorax and
abdomen
sensory from
pharynx, larynx,esophagus, and
viscera of thorax and
abdomen
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Cranial Nerves XI and XII
Accessory (XI)
primarily motor
cranial branchmotor to muscles of
soft palate, pharynx,
and larynx
spinal branch
motor to muscles ofneck, and back; some
proprioreceptor
Hypoglossal (XII)
primarily motor
motor to muscles ofthe tongue; some
proprioreceptor
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Functions of Cranial Nerves
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Spinal Nerves
mixed nerves
31 pairs
8 cervical
(C1 to C8)
12 thoracic
(T1 to T12)
5 lumbar
(L1 to L5)
5 sacral(S1 to S5)
1 coccygeal
(Co)
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Spinal Nerves
Dorsal root (posterior
or sensory root)
axons of sensory
neurons in the
dorsal root
ganglion
Dorsal root ganglion
cell bodies of sensory
neurons whose axonsconduct impulses inward
from peripheral body
parts
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Dermatome
an area of skin that the sensory nerve fibers of a particular
spinal nerve innervate
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Spinal Nerves
Ventral root (anterior or
motor root)
axons of motor
neurons whose cell
bodies are in spinal
cord
Spinal nerve
union of ventral root
and dorsal root
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Cervical Plexuses
Nerve plexuscomplex networks formed by anterior branches
of spinal nerves; fibers of various spinal nerves are sorted and
recombined
Cervical Plexusformed by anterior
branches of C1-C4
lies deep in the neck
supply muscles and
skin of the neck
C3C5 contribute to
phrenic nerves
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Brachial Plexuses
C5-T1
lies deep within shoulders
musculocutaneous nervessupply muscles of anterior arms
and skin of forearms
ulnar and median nerves
supply muscles of forearms andhands
supply skin of hands
radial nerves
supply posterior muscles ofarms and skin of forearms and
hands
axillary nervessupply muscles and skin of
anterior, lateral, and posterior
arms
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Lumbosacral Plexuses
T12S5
extend from lumbar
region into pelvic cavity
obturator nervessupply motor impulses
to adductors of thighs
femoral nervessupply motor impulses
to muscles of anterior
thigh and sensory
impulses from skin of
thighs and legs
sciatic nervessupply muscles and skin
of thighs, legs, and feet
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Plexuses
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Autonomic Nervous System
functions without conscious effort
controls visceral activities
regulates smooth muscle, cardiac muscle, and glandsefferent fibers typically lead to ganglia outside CNS
Two Divisions
sympatheticprepares body for fight or flight
situationsparasympatheticprepares body for resting
and digesting activities
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Autonomic Nerve Fibers
all are neurons are
motor (efferent)
preganglionicfibersaxons of preganglionic
neurons
neuron cell bodies in
CNS
postganglionicfibersaxons of postganglionic
neurons
neuron cell bodies in
ganglia
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Sympathetic Division
thoracolumbardivison
location of preganglionic
neurons
preganglionic fibers leavespinal nerves through white
ramiand enter
paravertebral ganglia
paraverterbral ganglia
and fibers that connect
them make up the
sympathetic trunk
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Sympathetic Division
postganglionic fibers
extend from sympathetic
ganglia to visceral organs
postganglionic fibersusually pass through gray
ramiand return to a spinal
nerve before proceeding to
an effector
Exception: preganglionic
fibers to adrenal medulla do
not synapse with
postganglionic neurons
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Sympathetic Division
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Parasympathetic Division
craniosacraldivision
location of preganglionic
neurons
ganglia are near or
within various organs
terminal ganglia
short postganglionicfibers
continue to
specific muscles or
glands
preganglionic fibers of the
head are included in nerves
III, VII, and IX
preganglionic fibers of
thorax and abdomen are
parts of nerve X
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Parasympathetic Division
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Autonomic Neurotransmitters
CholinergicFibers
release acetylcholine
preganglionic
sympathetic and
parasympathetic
fiberspostganglionic
parasympathetic
fibers
AdrenergicFibersrelease
norepinephrine
most
postganglionic
sympatheticfibers
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Actions of AutonomicNeurotransmitters
depend on receptors in the membrane
Cholinergic receptors
bind to acetlycholinemuscarinic
excitatory
slow
nicotinicexcitatory
rapid
Adrenergic Receptors
bind to epinephrineand norepinephrine
alpha and betaboth elicit different
responses on various
effectors
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Insert figure 11.39Actions of Autonomic
Neurotransmitters
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Control of Autonomic
ActivityControlled largely by CNS
Medulla oblongata regulates cardiac, vasomotor andrespiratory activities
Hypothalamus regulates visceral functions, such as body
temperature, hunger, thirst, and water and electrolytebalance
Limbic system and cerebral cortex control emotional
responses
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