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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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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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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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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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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