spinal cord

Created by krlindsay 

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Anatomy of Spinal Cord:

- less than 1" in diameter
- covered in pia matter
- divided into 5 regions
- enlarged in cervical & lumbosacral regions
- ends at L2, tapers and is called conus medullaris

5 Regions of the Spinal Cord:

- Cervical (7 vertebrae; 8 spinal nerves)
- Thoracic (12 vertebrae; 12 spinal nerves)
- Sacral (5 vertebrae; 5 sacral nerves)
- Coccygeal (1 fused vertebrae, 1 coccygeal nerve)

Spinal nerves formed by union of:

- Dorsal root (sensory) &
- Ventral root (motor)

Spinal nerves leave the __________________ through the _____________________ on each side of the vertebrae and fuse to form ________________.

vertebral canal; intervertebral foramina; peripheral nerves

Cross section of SC reveals butterfly shaped area of grey matter which is divided into:

- ventral (anterior) horns &
- dorsal (posterior) horns

The Ventral Horn:

cell bodies that innervate skeletal muscle (motor- MEV)

The Dorsal Horn:

recieves exteroceptive info from PNS (sensory- SAD)

Cross section of SC reveals surrounding area of white matter that contains:

nerve fibers and tracts of the spinal cord

S-A-D

Sensory-Afferent- Dorsal

M-E-V

Motor-Efferent-Ventral

Functional Components of the Spinal Nerves

- General Afferent Fibers (sensory fibers)
- general somatic afferent (info from skeletal mm)
- general visceral afferent (info from viscera)
- General Efferent Fibers (motor fibers)
- general somatic efferent (skletal mm)
- general visceral efferent (smooth & cardiac mm)

General Afferent Fibers:

- general somatic afferent (info from skeletal mm)
- general visceral afferent (info from viscera)

General Efferent Fibers:

- general somatic efferent (skletal mm)
- general visceral efferent (smooth & cardiac mm)

Nerve fibers are categorized by:

- diameter
- thickness of myelin sheath
- speed of nerve impulse conduction

Classification of Nerve Fibers

- A fibers
- B fibers
-C fibers

A fibers:

- myelinated
- fastest conducting
- afferent & efferent
- subdivided into: alpha, beta, gamma

B fibers:

- myelinated
- 2 fastest conduction
- sensory & motor for viscera

C fibers:

- unmyelinated
- slowest conduction
- sensory for pain & temp

Alpha Motorneuron:

- largest of anterior horn cell
- axon synapes directly with skeletal muscle
- LMN of voluntary systen to extremities
- innervates extrafusal (striated skeletal) mm fibers with a specific mm

Beta Motor Neuron:

innervetes both intra & extrafusal muscle fibers

Gamma Motorneuron

- located in the anterior horn cell
- smaller than alpha motorneuron
- NOT under direct voluntary control
- axons synapse with mm fibers that belong to the muscle spindle system (intrafusal fibers)
- functions to change "sensitivity" of spindle
- influenced from higher levels, play inhibitory role to decrease sensitivity to stretch of muscle spindle

Intrafusal fibers:

play a role in adjusting sensitivity of muscle spindle, rather than generating overall tension in the muscle

Muscle Spindle (proprioceptor):

- located between large fibers of skeletal muscles
- detects degree of stretch to muscles
- when mm is stretched: sends message to alpha MN which sends message to the muscle to relax
- when mm contracts: muscle spindle is no longer stretched

Muscle Spindle Function:

specialized sensory receptors which provide infor to the CNS about muscle length & velocity of stretch

Gamma Motor Neuron Function:

- to change sensitivity of muscle spindle:
- acts inhibitory to the muscle spindle to decrease the spindle's sensitivity to stretch

Gama MN is controlled by:

- extra pyramidal input from the CNS:
if the input is lost, the gamma MN fires more and the muscle spindle reacts more to the muscle stretch (basis for DTRs)

Golgi Tendon Organ (GTO)

proproceptor which provides info to CNS about tension in muscle & tendon
- encapsulated structures attached with large collagenous fibers of tendons at insertion point of muscle
- sensitive to muscle contraction
- stimulated by strong muscle contraction
- sends message inhibiting alpha MN
- facilitates contraction of antagonist muscle

GTO Function:

prevent excessive, strong contractions which could damage the muscle by inhibiting the agonist and facilitating the antagonist

Abarognosis

inability to recognize weight

Allesthesia

sensation experienced at a site remote from point of stimulation

Allodynia

Pain produced by a non-noxious (not normally painful) stimulus (i.e. touch)

Asterognosis

inability to recognize the form and shape of objects by touch (aka tactile agnosia)

Causalgia

painful, burning sensation usually along the distribution of a nerve

Dyesthesia

normal toch sensation experienced as pain

Hypalgesia

decreased sensitivity to pain

Hyperalgesia

increased sensitivity to pain

Hyperesthesia

increased sensitivity to sensory stimuli (i.e. touch)

Parathesia

abnormal sensation such as numbeness, prickling, burning, or tingling without apparent cause

Thalamic Syndrome

vascular lesion of the thalamus resulting in sensory disturbances and partial or complete paralysis of one side of the body, associated wtih severe, boring-type pain;sensory stimuli may produce an exaggerated, prolonged or painful response

Cutaneous Receptors (Mechanoreceptors)

- free nerve endings
- hair follicle endings
- Merkel's Discs
- Ruffini's Endings
- Krauses's End Bulb
- Meissner's Corpuscles

Deep Tendon Reflex (DTR):

basic neural mechanism for maintenance of tone
- alpha MN causes contraction of muscle to PREVENT OVERSTRETCH
(important in the maintenance of posture)

Asymetrical Tonic Neck Relex (ATNR):

Stimulus: rotation of head to one side
Repsonse:
- UE & LE on same side extend
- UE & LE on opposite side flex

Symetrical Tonic Neck Reflex (STNR)

Stimulus: flex head
Response: UEs flex, LEs extend

Stimulus: extend head
Response: UEs extend, LEs flex

Flexor Withdrawl Reflex:

Stimulus: with LE in flexed position, lightly touch sole of foot
Repsonse: LE withdrawls from stimulus

Symmetrical Tonic Labynrinthine (TLR or STLR)

Stimulus: position in prone or supine
Response:
- prone: increases flexor tone
- supine: increases extensor tone
- sidelying: increases extensor tone on sidelying limbs; increases flexor tone on non-weight bearing limbs

Protective Extension:

Stimulus: push patient forward, backward, or sideways
Response: patient reaches out with arms to catch self

Equilibrium Response:

Stimulus: tip or tilt surface of patient causing COG to move outside of BOS
Response: body & head move in whatever direection neccessary to maintain balance

Positive Supporting:

Stimulus: contact to the ball of the foot in upright standing position
Response: rigid extension (co-contraction) of the LEs

Righting Reaction

Stimulus: move patient by pushing forward, backward, or to the side
Response: head will try to orient self & maintain balance

Associated Reaction:

Stimulus: resisted voluntary mvmt in any part of the body
Response: involuntary mvmt in a resting extremity

Muscle Tone Assessment should be done with:

passive mvmt

Hypotonia

decreased resistance to passive mvmt

Hypertonia

increased resistance to passive mvmt

2 types of hypertonia:

- rigidity
- spasticity

Rigidity:

cogwheel type ratchety giving & catching to passive mvmt
- Not rate dependent (i.e. doesnt change in relation to speed of passibve mvmt)
- Does NOT have clasp knife phenomenon

Spasticity:

increase in tone (UMNL) occuring due to loss of inhibition of reflex arc from decsending pathways
- worse with increased speed of passive mvmt
- clasp knife phenomenon present

Clasp Knife Phenomenon

initial resistance to passive mvmt followed by relaxation

Cervical Plexus

- formed by spinal roots C1-C4
- phrenic (diaphram) nerve arises from C3-C4

Brachial Plexus

- formed by spinal roots C5-T1
- peripheral nerves of UE

Peripheral Nerves formed by the Brachial Plexus:

-

Lumbar Plexus

- formed by spinal roots L1-L4
- peripheral nerves of LE

Peripheral Nerves formed by the Lumbar Plexus:

-

Sacral Plexus

- formed by the spinal roots L5-S3 & small branches from L4 and S4
-

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