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1INNERVATION Brain Spinal CordPeripheral nerves
Locations of nerve tissue
Anatomical Divisions of the Nervous System: Central Nervous System (CNS)
brain and spinal cordcontained within bone (skull, vertebral column)
Peripheral Nervous System (PNS) all nerve tissue outside CNSsensory & motor divisions
Every skeletal muscle fiber is supplied (INNERVATED) by a motor neuron
Skeletal Muscle is voluntaryfibers will not contract unless a neuron tells them to
(all movements are initiated by the nervous system)
junction Neuromuscular
Muscle
Neuromuscular Junction
fibers
muscle
neurons (2)
BIO223: Human Anatomy L11: Spinal Cord and Innervation UNC-Asheville, f2011
2Muscle contraction is a biochemical rxn each fiber always contracts with the maximum force it can.Strength of contraction of an entire muscle (ex. Deltoid) is determined by % of fibers within the muscle firing at the same time.
How do muscles control force?Nerves and Neurons a nerve is an organ
a neuron is a cell of nerve tissue
Neuron
neuroglia
NERVE
200x
NERVE TISSUE
NeuronsNeurons
Neurons: impulse-conducting nerve cells Neuroglia: supporting cells
NeurogliaNeuroglia
Direction
Axon HillockTrigger Zone
AXON
Axon (only 1, but branches) conducts impulse release neurotransmitters into synapse (junction bet. cells) NT alters the activity of cells
[excitatory / inhibitory]
Neuron basic structure
Cell Body(soma)
Cell body (soma)Dendrites
Direction of impulse
Synaptic knobs
Schwann cell(neuroglia)
Dendrites
Functional Classification of Neurons1. Sensory (input) PNS 2. Motor (output) PNS 3. Interneurons (processing) CNS
sensory
motor
interneurons
motor (= efferent) neurons produce effects on body structures (ex. muscle; glands) travel from CNS motor organ
sensory (= afferent) neurons provide info about intl & extl conditions travel from sensory organ CNS
Motor & Sensory Innervation
interneurons Connect neuronneuron Involved with thought, processing, memory, etc.
BIO223: Human Anatomy L11: Spinal Cord and Innervation UNC-Asheville, f2011
3Sensory Neuron(unipolar)
axon
Interneurons(multipolar)
dendrites
Motor Neuron(multipolar)
axon
dendrite
cell body
axonaxon axon
muscle
nervegross structure of PNS containing the axons of
several neurons
Axon
Spinal Cord
Vertebrae
NERVE 100s+ of axons wrapped together supporting cells (neuroglia) blood supply connective tissue
NeuronVertebrae
IntervertebralForamen
Spinal Nerve
Neuroglia
axons
RRadial Nerve
TricepsTriceps
Nerves are distinct gross anatomical structures(ultimately originate from brain or spinal cord)
TricepsTriceps
TricepsTriceps
Nerves can be entirely sensory, entirely motor, or mixedA neuron can only be sensory (afferent) or motor (efferent)
Spinal cord
Afferent neuron(ex. from skin)
Efferent neuron(to muscle)
Nerve Sensory neurons Motor neurons
Nerve
BIO223: Human Anatomy L11: Spinal Cord and Innervation UNC-Asheville, f2011
4StimulusSensory neuron
Sensory and motor neurons often travel within the same nerve.
Effector response
Processing Motor neuron
SPINAL NERVE
formed in the intervertebral foramen from branches off
spinal cord
Originate between each pair of vertebrae
spinal cord
spinal cord
spinal nerve
cord cord
Posterior view
Spinal Nerves (PNS)Spinal Cord (CNS)
SPINAL NERVESemerge along vertebral column
Spinal nerves are named by the vertebrae they emerge
between.
Spinal nerves organs of PNS exit between each pair of vertebrae (intervertebral foramina) carry both sensory & motor fibers
SKULLbrain
C1
C2
C3
C4
C1
C2
C3
C4
C5
Spinal CordSpinal Nerves(emerge at each vertebral level)
Segmentation of spinal cord; numbering of spinal nerves
C5
C6
C7
T1
T3
T2
C5
C6
C7
C8
T2
T1
T3
Formed in intervertebral foramen by junction of dorsal and ventral roots
from spinal cord.
SPINAL NERVE
Denticulate Ligament (pia)Separates dorsal/ventral roots
Ventral RootDorsal Root
Form a spinal nerve here(on other side of dura)
BIO223: Human Anatomy L11: Spinal Cord and Innervation UNC-Asheville, f2011
5Spinal cord cross sections
Anterior median fissure Ventral (anterior)gray horns
Ventral root
Spinal nerve
Orientation of spinal cord cross-section
Dorsal (posterior)gray horns
Dorsal Root
Dorsal root ganglion
Fibers of Dorsal Root are entirely sensoryFibers of Ventral Root are entirely motor
cross-section
Ventral root only contains axons of motor neurons(cell bodies in anterior gray horn of spinal cord)
Dorsal root ganglionContains cell bodies of sensory neurons
Ventral Ramus(mixed sensory + motor)
to limbs & anterior body wall
Each Spinal Nerve branches into dorsal and ventral ramus
Spinal Nerve
Ventral Root(motor only)
Dorsal Ramus(mixed sensory + motor)
to intrinsic back muscles[ex. erector spinae]
Dorsal Root ganglion
Dorsal Root(sensory only)
BIO223: Human Anatomy L11: Spinal Cord and Innervation UNC-Asheville, f2011
6Dorsal RootVentral Root
Dorsal Root Ganglion
Spinal Nerve
Dorsal Ramus
Ventral Ramus
Ventral Ramus supplies muscles anterior to spinal cord, including all muscles of limbs
Dorsal Ramus supplies intrinsic back muscles(erector spinae is only muscle we will dissect)
All other back muscles are actually muscles of the limbs, which are supplied by ventral rami
Muscles supplied by Ventral ramus
Muscles supplied by Dorsal ramus
Anterior median fissure Anterior
median fissure
GRAY MATTER contains unmyelinated nerve tissue (ex. cell bodies) WHITE MATTER contains myelinated axons
Somatic motor
Gray versus White Matter
White matterGray matter White matter
Gray matter
Visceral motorVisceral sensorySomatic sensory
One neuron can be in both gray and white matter.
Dendrites
Cell Body(soma)
Nodes of Ranvier
Myelin is produced by neuroglia: PNS = Schwann cells CNS = oligodendrocytes
Fatty substance that wraps around & insulates axonsincreases speed impulse travels:
without myelin ~2 mphw/ myelin ~300 mph
MYELIN
Direction of impulse
Schwann cells
Ranvier
Myelin sheathaxon
Schwann cell
BIO223: Human Anatomy L11: Spinal Cord and Innervation UNC-Asheville, f2011
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