6 - Spinal Cord + Nerves Grays

7/28/2019 6 - Spinal Cord + Nerves Grays

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Spinal Cord and Nerves


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The Nervous System

Coordinates the activity of muscles, organs,

senses, and actions

Made up of nervous tissue

Has 3 main functions:

1. Receives sensory Input

2. Integration

3. Dictates motor output

http://www.nationmaster.com/wikimir/images/upload.wikimedia.org/wikipedia/en/f/f0/ReflexArc1.jpg


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Structural Divisions of the

Nervous System

Central Nervous System (CNS)

Brain and spinal cord

Interprets incoming sensory signals

Dictates motor responses Peripheral Nervous System (PNS)

Nerves

Cranial nerves and spinal nerves

Nerve plexuses Enteric system

Communication between regions of

body and CNS

pg 34


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Review of Nervous Tissue

Features of Nervous Tissue

Neuron

Cell body

Dendrite

Axon

Myelin Sheath

Surrounds thicker axons

Forms insulating layer

Prevents leakage of electrical current Speeds up the impulse conduction

www.morphonix.com


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Review of Nervous Tissue

Neuroglia

Reflex Arc

Interneurons

Rapid, automatic motor response

Synapse

Action potential


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Organization of a Nerve

Endoneurium

Surrounds each axon (nerve fiber)

Myelinated and Unmyelinatedaxons

Motor and Sensory nerve fibers

Loose CT Perineurium

Bundles axons into fascicles

CT

Epineurium Bundles fascicles into a nerve

Fibrous CT

CT layers contain blood vessels

www.web-books.com


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Types of Nerve Signals/Fibers

Sensory (afferent)

Picked up by sensory receptors thru body

Carried by nerve fibers of PNS into CNS

Motor (efferent)

Carried away from the CNS by nerve fibers

into PNS

Innervate muscles and glands Causes these organs to contract or secrete

Remember: SAME


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Sensory and Motor Signals/Fibers

Somatic sensory Body senses

touch, pressure, temperature, vibration of body, musclesstretching, balance

Visceral sensory

Organ senses

Stretch, pain, temperature in organs

(eg) nausea, hunger, cramps

Somatic motor

Body movement Voluntary contraction of skeletal muscles

Visceral motor

Organ movement

Contraction of smooth muscle, glands

= Autonomic Nervous System (involuntary)


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CNSBrain

Spinal cord

PNSCranial nerves and

spinal nerves

Sensory (afferent)

division

Motor (efferent)

division

Somatic sensory

General: Touch,

pain, pressure,

vibration

Special: hearing,

equilibrium, vision,

smell

Visceral sensory

General: Stretch,

pain, temperature,

nausea, hunger

Special: Taste

Somatic motor

General: Motor

innervation of all

skeletal muscles

Visceral motor

General: Motor

innervation of smooth

muscle, cardiac

muscle, and glands;= ANS

Parasympatheticdivision Sympatheticdivision


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CNSSpinal Cord

Runs through vertebral canal of the vertebral column

Protected by bone, meninges, and cerebrospinal fluid

Spinal cord made of a core ofgray mattersurrounded by white

matter

31 pairs of spinal nerves branch off spinal cord throughintervertebral foramen

Functions in many ways:

Involved in sensory and motor innervation of body

inferior to the head (through spinal nerves)

Provides a 2-way conduction pathway for signals

between body and brain

Major center for reflexes

pg 101


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Meninges of Spinal Cord

Membranes surrounding the spinal cord

3 Layers of connective tissue

Functions

Protect spinal cord

Contains cerebrospinal fluid (CSF)

Protect blood vessels serving spinal cord


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Dura mater (superficial)

Spinal dural sheath

Does not attach to bone

Merges w/epineurium of spinal roots & nerves Epidural space

Loose CT, fat and veins

Between dura mater and vertebra

Not present around brain

Subdural space

Between dura mater and arachnoid

pg 105


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Arachnoid mater (middle)

Impermeable layer = barrier

Raised off pia mater by rootlets

Subarachnoid space

Between arachnoid and pia mater

Contains cerebrospinal fluid

Contains large blood vessels

*Runs to level of S2

Pia mater(deep)

Highly vascular

Adheres to brain/spinal cord tissue

Creates denticulate ligaments pg 105


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Regions of Spinal Cord

Cervical

Thoracic

Lumbar

Sacral Coccygeal

Cervical + Lumbosacral enlargements

Cauda equina

Conus medullaris Filum terminale

CT & pia mater

Attaches to coccyxpg 101, 109


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Gray Matter

Consists of neuron cell bodies, unmyelinated axons,

dendrites, and neuroglia

Shaped like an H

Gray commissure (crossbar)

Central canal

Posterior horns

Anterior horns

pg 102


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Gray Matter

Posterior horns

Consist of interneurons that transmit in from outside spinal cord into it

Dorsal root contain sensory fibers Somatic Sensory (SS)

Visceral Sensory (VS) Dorsal root gangliaclusters of cell bodies outside of CNS

Anterior horns

Cell bodies of motor neurons send info out of spinal cord to muscles and glands

Ventral Root contains Motor Fibers Visceral Motor

Somatic Motor

pg 102


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White Matter

Surrounds gray matter

Composed of myelinated and unmyelinated axons

Divided into white columns (funiculi) that create tracts

Tracts = bundles of axons traveling to similar destination

Posterior funiculus

Anterior funiculus

Lateral funiculus

Allow for communication between

Parts of the spinal cord

Spinal cord and brain

pg 102


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White Matter

3 types of nerve fibers:

Ascending

Carry sensory info from sensory neurons of body to brain

touch, pressure, pain, temperature

Descending Carry motor instructions from brain to spinal cord

Contraction of muscles and secretion of glands

controlling precise, skilled movement (e.g. writing, maintain

balance, create movement)

Commissural

Cross from one side of cord to the other

www.octc.kctcs.edu


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Spinal Nerves (31 Pairs)

Part of the PNS

Lie in intervertebral foramina

Send lateral branches to body

Named according to their point of attachment to spinal cord

segment

8 pairs of cervical spinal nerves; C1-C8

12 pairs of thoracic spinal nerves; T1-T12

5 pairs of lumbar spinal nerves; L1-L5

5 pairs of sacral spinal nerves; S1-S5 1 pair of coccygeal spinal nerves; C01

pg 110


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Spinal Nerves

Each spinal nerve connects to spinal cord via

posterior root (sensory) and anterior root (motor)

Each spinal nerve branches into a posterior ramus

and an anterior ramus

Anterior rami

Supply anterior and lateral regions of the neck,

trunk, and limbs Posterior rami

Supply the dorsum of the neck and trunk (back)

pg 42


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Recurrent Meningeal Nerves

Recurrent meningeal nerves branch from spinal nervesto supply intervertebral discs, dura mater, ligaments andblood vessels.

They access the vertebral canal via intervertebralforamina.

pg 105


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The Big Picture

Just lateral to the intervertebral foramen, each spinal

nerve then splits in 2

Dorsal Ramus

Ventral Ramus

RAMI contain BOTH Sensory and Motor fibers!!

Remember: Roots have sensory OR motor fibers, not both

pg 62


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Dermatomes

Area of skin innervated by cutaneous branches

of single spinal nerve

Clinical application for testing neurological

function

pg 40

CNS


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CNSBrain

Spinal cord

PNSCranial nerves andspinal nerves

Sensory (afferent)

division

Motor (efferent)

division

Somatic sensory

General: Touch,

pain, pressure,

vibration

Special: hearing,

equilibrium, vision,

smell

Visceral sensory

General: Stretch,

pain, temperature,

nausea, hunger

Special: Taste

Somatic motor

General: Motor

innervation of all

skeletal muscles

Visceral motor

General: Motor

innervation of smooth

muscle, cardiac

muscle, and glands;= ANS

Parasympathetic

division

Sympathetic

division

Autonomic

Nervous

System =

Visceral Motor


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Autonomic Nervous System

Visceral MotorFunction

Not controlled voluntarily

e.g. get nervous and sweat

Innervates smooth muscle, cardiac muscle, glands Regulates visceral function

Heart rate, blood pressure, digestion, urination

Has 2 divisions:

Parasympathetic

Sympathetic

i


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Autonomic Nervous System

Parasympathetic

rest and digest

Enables body to unwindand calm down

Most active when body atrest, normal activities

Routine maintenancefunctions

Most releaseacetylcholine

Axons branch less Craniosacral division

Fibers arise from brainand sacral spinal cord

Sympathetic

fight or flight

Mobilizes the body duringextreme situations

Becomes active when

extra metabolic effortneeded

Most releasenorepinephrine

Axons branch widely

Thoracolumbar division Fibers arise from

thoracic and lumbarparts of spinal cord

pg 42, 48


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Sympathetic Innervation

Comes from thoracolumbar regions (T1-L2)

Travels through anterior root and rami

Communicates with the sympathetic trunk

(via a connection called a ramus communicans)

Back to anterior rami (via another ramus

communicans) to spinal nerve to reach target

structures Can operate at same level of spinal cord (T1-L2)

or above a different level


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Parasympathetic Innvervation

Parasympathetic innervation comes fromcranio-sacral region of central nervous system

Cranial nerves III, VII and IX provide

parasympathetic innervation to structures of

head and neck CN X (Vagus) provides parasympathetic

innervation below neck to organs of thoracic &

abdominal cavities

Spinal nerves S2-S4 provide parasympathetic

innervation to inferior abdominal organs, pelvic

organs and tissue of perineum

Nerve fibers exit spinal cord through anterior roots

and then anterior rami into plexuses to serve organs


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Nervous System Overview

Sensory information (visceral and somatic)

travels along sensory nerves to the posterior

root into the spinal cord

The information is then processed by brain ora response is determined within the spinal

cord (e.g. in a reflex arc)

Motor information (visceral and somatic) goes

out of the spinal cord through the anterior root

along motor nerves to the body to make

muscles contract or glands secretepg 107


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Sympathetic Innervation at Same

Level of Spinal Cord

Sympathetic fibers providing innervation through spinal nerves at same

level of spinal cord (T1-L2)

Sympathetic fibers runs through anterior root into anterior ramus

It then connects to a whiteramus communicans, which leads to the

sympathetic chain ganglia and sympathetic trunk

Fibers then pass through the gray ramus communicans back out the

anterior ramus into a spinal nerve to body

pg 44

S th ti I ti t


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Sympathetic Innervation at

Different Level of Spinal Cord

Only from level T1-L2, so

Fibers may travel out anterior root and anterior

ramus

Through white ramus communicans up or downsympathetic trunk to different level of cord

Then through gray ramus communicans out

anterior root along spinal nerve to the body

pg 45

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6 - Spinal Cord + Nerves Grays