Spinal Cord

Unit 5

What does the decussation of the fiber tracts allow the left brain to do?

control the right body

what matter is found in the outer portion of the spinal cord

white matter

what matter is found in the core of the spinal cord

gray matter

function of the spinal cord

* interface of CNS and PNS
* receives **somatosensory** information from the limbs/body
* contains all the **motor neurons** that supply muscles
* major populations of the autonomic efferents

What is the extent of the spinal cord

medulla to L1

How much does the spinal cord weigh?

35g

Diameter of spine at widest point

1cm

cauda equina

spinal root fibers

inferior extension of the pia mater

filum terminale

what anchors the cord to the coccyx

filum terminale

What spinal nerve has a rudimentary dorsal root? What nerve has a single dermatome?

1. C1
2. all others innervate single dermatome

C5 spinal cord levels

dense sensory and motor innervation to the upper extremities

T8 spinal cord level

chest and back area

L1 spinal cord level

denser sensory and motor innervation to the upper extremities - feet

S3 spinal cord level

cauda equina

2 columnar enlargements

1. cervical
2. lumbar

What level is the conus medullaris

approximately level of kidneys

cauda equina syndrome

pressure on cauda equina causing bladder retention/incontinence and bowel incontinency and paralysis-surgical emergency

What are symptoms of cauda equina syndrome

* low back pain
* “saddle” anesthesia
* bilateral sciatica
* sexual dysfunction

What can cause cauda equina syndrome?

central lumbar disc herniation, but can also be cause by a hematoma or mass lesion

Meninges and spaces of vertebrae (superficial to deep)

* epidural space
* dura mater
* subdural space
* arachnoid mater
* subarachnoid space
* pia mater

gray commissure

connects masses of gray matter, encloses the central canal

posterior (dorsal) horns

interneurons

anterior (ventral) horns

interneurons and somatic motor neurons

lateral horns

contain sympathetic fibers

gray matter

consists of soma, unmyelinated process, and neuroglia

WHat indicates the borders of the spinal segment?

dorsal and ventral roots

What form the spinal nerve in the intervertebral foramen

dorsal and ventral rootlets

What joins distally to the dorsal root ganglion

dorsal and ventral rootlets

What type of fibers does the anterior white commissure contain?

decussating fibers

What horn of gray matter does NOT reach its side?

dorsal horn reaches dorsal side, but **ventral horn does not reach ventral side**

dorsal half of gray matter

sensory roots and ganglia

ventral half of gray matter

motor roots

4 zones that can be found in the gray matter

* somatic sensory
* visceral sensory
* visceral motor
* somatic motor

Lissauer’s tract

* fine dorsal root fibers at the dorsolateral fasciculus
* receive exteroreceptive input
* pain, temperature, tactile info

Rexed laminae

* 10 layers of spinal cells
* layers 1-5 in dorsal horn
* regions of sensory and motor functions

What are the sensory functions of rexed laminae layers 1-6

* pain and temperature afferents 1 & 2
* tactile afferents 3
* muscle spindle afferents 6, 7, 9

What is above rexed laminae 1? what does it carry?

* lissauer’s tract


* carries nociceptive fibers, also carries potential damaging impulses

what is rexed laminae 2? what does it do?

* substansia gelatinosa
* forms spinothalamic tract

what is rexed laminae 3-6? what does it carry?

* nucleus proprius
* contains synapses from the mechanoreceptors

rexed laminae 7 and 10

intermediate zone

rexed laminae 8-9

motor neuron columns

rexed laminae 9

motor neurons innervation limb muscles

intermediate zone

* all spinal roots are sensory afferents
* all ventral roots are motor efferents

dorsal nucleus of clark AKA….

dorsal thoracic nucleus

Where is the dorsal nucleus of clark located?

laminae 7 of the intermediate zone

What spinal levels is the dorsal nucleus of clark

C7/C8/T1 to L2/L3

When stained, how does the dorsal nucleus of clark appear?

oval shaped

Axons of the dorsal nucleus of clarke

axons may scene uncrossed, or crossed at the spinal border cells

Where does the lateral horn occur

C7/C8/T1 to L2/L3

What does the lateral horn contian

contains a column of preganglionic sympathetic neurons AKA intermediolateral cell column

What does the lateral horn exit with?

ventral roots

sympathetic chain if synapse occurs **on the SAME level**

* sympathetic preganglionic neuron leaves via the ventral root to the spinal nerve
* travels via the white ramus communicans to the sympathetic paravertebral ganglion
* **synapse occurs on the same level in the sympathetic paravertebral ganglion**
* **post-ganglion if neuron innervates effector organ**

sympathetic chain if the synapse occurs **on DIFFERENT level**

* sympathetic preganglionic neuron leaves via the ventral root to the spinal nerve
* travels via the white ramus communicans to the sympathetic paravertebral ganglion
* **preganglionic neuron travels up or down the sympathetic chain**
* **synapses in the ganglion and sends a postganglionic fascicle into the spinal nerve via the gray ramus communicans**
* **nerve via gray ramus communicans**

What are the basic sensations from the periphery

1. touch
2. vibration
3. proprioception
4. pain
5. itch
6. heat vs cold
7. visceral sensations

Touch

* deep pressure
* fine touch
* supplied by myelinated alpha-beta fibers

Vibration

* single sensory receptors
* pacinian receptors encode the rate and force of **repeated** stimuli

Proprioception

* proprioception - sensory endings in muscle spindles detect joint position
* kinesthesia - sensory endings also detect small changes in limb position, direction, force and speed

Pain

mediated by specific **nociceptors**

Itch

* triggered by **chemical irritation** of the skin
* particularly in response to tissue inflammatory agents

Heat vs Cold

thermal sensory provide information that allows us to maintain our body temperature

Visceral sensation

* provides information for regulating body functions (IE: BP and breathing)
* conscious: nausea and fullness
* unconscious: arterial pressure

What are the 3 types of Nerve fibers in the spinal white matter

1. long ascending
2. long descending
3. shorter propriospinal interconnections

What are the 3 major (specific) pathways of the white spinal cord matter?

1. DCML system
2. Spinothalamic tract (anterolateral system)
3. Corticospinal tract (pyramidal tract)

Parts of the DCML system and where they originate

1. gracile fasciculus
2. cuneate fasciculus
3. spinocerebellar tracts

Gracile fasciculus

originate in lower limbs and lower trunk

Cuneate fasciculus

originate in upper limbs, upper trunk, neck

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unconscious proprioceptive information from upper limbs

spinocerebellar tracts

carrie’s unconscious proprioceptive information about the location of the body

3 neuron chain in the sensory pathway of DCML tract

1. primary afferent neuron
2. second order target neuron
3. third order neurons in the ventro-posteromedial

Where do the first order neuron of the DCML synapse?

in the spinal cord for **reflex action**, ascend to ipsilateral synapse with 2nd order neuronal cells in the medulla

How many neurons are in a reflex action? What type of reflexes can we observe?

monosynaptic reflex (sensory neuron, motor neuron)

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knee-jerk reflex, deep tendon reflex

What 2 nuclei synapse in the medulla?

gracile nucleus, cuneate nucleus

Where do second order neurons of the DCML tract travel? where do they project their axons to?

1. medial lemniscus
2. ventral posterior nucleus of the thalamus

Where do 3rd order neurons of the DCML project their axons to?

primary somatic sensory cortex in the post central gyrus

Ventral areas of sensory cortex

recognizing objects by touch and grasp alone, ***WHAT?***

Dorsal areas and **area 5** of the primary sensory cortex

spatial localization, ***WHERE?***

Spinocerebellar tract division

anterior and posterior

DCML system

* fine tactile input
* two point discrimination
* vibration
* proprioception

Spinothalamic tract

mechanical and thermal nociceptive inputs

Corticospinal tract (pyramidal tract)

activation of motor neurons in the ventral horn

Homunculus

mapping of the somatosensory system, showing us the innervation of our body and their relative areas in the brain

Ataxia

total loss of proprioception and kinesthesia

symptoms when theres damage to the DCML

* complex discrimination severely affected
* simple touch, pressure, and vibration minimally affected
* ataxia

Examples of damage to the DCML:

* tabes dorsalis
* late stages of neuro-syphilis

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Romberg test

* patient stands upright and is asked to close his eyes
* this, removes visual function
* a loss of balance is interpreted as **positive Romberg sign**

What does a positive romberg test imply about the patient?

a patient who has a problem with **somatosensory proprioception** can still maintain balance by compensating with their **vestibular function and vision**

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romberg test takes this **vestibular function** away, and if pt loses balance theres damage to **somatosensory proprioception**

What are the 3 unconscious proprioceptive pathways

Ipsilateral


1. cuneo-cerebellar pathway - axons from upper limbs and trunk to thalamus via DCML
2. dorso-spinocerebellar - tract to cerebellum

Contralateral


3. ventral-spinocerebellar - tract to cerebellum

Spinocerebellar Atrophy examples

* friedrich’s ataxia - affects the cerebellum and DC of spine
* inherited (recessive disorder)
* scoliosis
* hypertrophic cardiomyopathy

Symptoms of friedrich’s ataxia

poor gait and loss of coordination

disrupted tactile sensation and proprioception

loss of reflexes

dysarthia

nystagmus

type 1 DM

Where does sensory information from the arm/leg enter the **spintothalamic tract**?

lissauer’s tract

After entering the thalamus, where does the information go? (spinothalamic tract)

severe subcortical and cortical centers

(interpretation of pain, emotional and cognitive effects of pain)

What are the smaller tracts that are added as the spinothalamic tract ascends?

1. spinoreticular tract
2. spinomesencephalic tract


1. spinohypothalamic tract

What is the function of the lateral corticospinal tract (pyramidal tracts)

controls distal limb muscles, controls circuits through their direct spinal projections, principal motor control pathway in humans

Where does the lateral corticospinal tract travel?

originates from the frontal lobe in primary motor cortex and supplementary motor area

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occupies the lateral funiculus

medial corticospinal tract

occupies the **anterior funiculus**

**controls axial limb muscles**

Extrapyramidal tracts

originate outside the cortex from the brainstem nuclei

do NOT travel through the pyramids

responsible for **autonomic functions**

4 extra pyramidal tracts

1. rubrospinal tract
2. reticulospinal tract
3. tectospinal tract
4. vestibulospinal tract

rubrospinal tract

* originates in red nucleus
* function is autonomic upper limb control

reticulospinal tract

* originates in the pontine and medullary reticular formation
* functions in autonomic control of proximal muscles and locomotion

tectospinal tract

* originates deeper in superior colliculus
* functions to control neck, shoulder, and upper trunk muscles and coordinates head and eye movements