Download Function of the spinal cord, cerebellum and brain stem

Function of the spinal cord,
cerebellum and brain stem
Romana Šlamberová, MD PhD
Department of Normal,
Pathological and Clinical
Physiology
Spinal cord (1)
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The spinal cord is an extension of the brain and is
enclosed in and protected by the bony vertebral
column.
Main function = transmission of neural inputs
between the periphery and the brain.
The peripheral regions of the spinal cord contains
neuronal white matter tracts containing sensory and
motor neurons.
The central region is gray matter that contains nerve
cell bodies.
The central canal is an anatomic extension of the
fourth ventricle.
Rexed’s zones
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Cells of grey matter of the spinal cord
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10 layers (laminae) based of the functione – Rexed’s
zones
dorsal horns – neurons of the zones I – VI – sensoric
function
lateral horns – neurons of the zone VII – autonomic
function
ventral horns – neurones of the zones VIII – IX - motoric
function
Zone X - around central canal – integration of all functions
White matter of the spinal cord is made from
ascending and descending tracts that connect
structures of the brain and spinal cord.
Spinal cord (2)
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Three meninges cover the spinal cord - the outer dura mater,
the arachnoid membrane, and the innermost pia mater
(continuation of the brainstem)
Cerebrospinal fluid - in the
subarachnoid space
Generally:
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Ventral roots – motor nerves
Dorsal roots – sensory nerves
The ventral and dorsal
roots later join to form
paired spinal nerves, one on
each side of the spinal cord.
Spinal cord (3)
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The spinal cord is divided into 31 different segments:
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8 cervical segments
12 thoracic segments
5 lumbar segments
5 sacral segments
1 coccygeal segment
Because the vertebral column grows longer than the spinal cord,
spinal cord segments become higher than the corresponding
vertebra, especially in the lower spinal cord segments in adults.
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In a fetus, the vertebral levels originally correspond with the spinal
cord segments.
In the adult, the cord ends around the L1/L2 vertebral level at the
conus medullaris, with all of the spinal cord segments located superiorly
to this.
After segments pass the end of the spinal cord, they are considered to
be part of the cauda equina.
Cauda equina
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The cauda equina is a
structure within the lower end
of the spinal column, that
consists of nerve roots and
rootlets from above.
Reminds a horse's tail.
Clinical relevance: possible
to inject or collect the cerebral
spinal fluid without a danger.
Lumbar puncture
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Is a diagnostic and at
times therapeutic
(decreases CSF
pressure, brain
oedema) procedure that
is performed in order to
collect a sample of
cerebrospinal fluid.
Also used to give spinal
anesthesia.
Between the lumbar
vertebrae L3/L4 or
L4/L5.
Connections between brain
and spinal cord
Pyramidal tract
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The corticospinal or pyramidal tract is a massive collection
of axons that travel between the cerebral cortex of the brain
and the spinal cord.
Mostly contains motor axons.
Consists of two separate tracts in the spinal cord: the lateral
corticospinal tract and the medial (anterior) corticospinal tract.
Originates from cells in layer V of the motor cortex.
The lateral corticospinal tract: Most of the cortico-spinal fibers
(about 85%) cross over to the contralateral side in the medulla
oblongata (pyramidal decussation).
The medial (anterior) corticospinal tract: The remainder of
them (15%) cross over at the level that they exit the spinal
cord.
End as a synapse with another neuron in the ventral horn.
Extrapyramidal motor
pathways
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The extrapyramidal system is a neural network
located in the brain that is part of the motor system
involved in the coordination of movement.
Parts of extrapyramidal system:
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Reticulospinal tract – proprioception, voluntary
movements, autonomic functions.
Vestibulospinal tract – posture in space, righting reflexes,
voluntary and unvoluntary movements.
Tectospinal tract – head movements based of the eye and
ear inputs.
Olivospinal tract – from cerebellum, striatum and cortex.
Coordination of movements.
Rubrospinal tract – from cerebellum and motor cortex.
Spinal shock
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is the phenomena surrounding injury of the spinal cord that
leads to temporary loss or depression of all or most spinal
reflex activity below the level of a spinal trauma.
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When lesion above C3-C5 = no breathing
the period of spinal shock can last from hours to 6 weeks.
In the acute stage, there will be hypotone paralysis,
areflexia, loss of sensory function and dysautonomia. Patient
shows retention of the bladder due to the impaired reflex of
emptying the bladder.
In post acute stage, first autonomic reflexes come to normal.
Patient shows autonomic dysreflexia if the trauma level is
above T6.
In the chronic stage, there will be hypertone paralysis,
hyper-reflexia, spastic-reflex. Patient at this stage shows
incontinence.
Brown-Sequard syndrome
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It was first described in 1850 by the British neurologist Charles Édouard
Brown-Sequard (1817-1896), who studied the anatomy and physiology of
the spinal cord.
A loss of motor abilities (paralysis and ataxia) and sensation caused by the
lateral hemisection of the spinal cord.
The hemisection of the cord results in a lesion of each of the three main
neural systems:
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The corticospinal lesion produces ipsilateral spastic paralysis.
The lesion to fasciculus gracilis or fasciculus cuneus results in ipsilateral loss of
vibration and proprioception (position sense).
The loss of the spinothalamic tract leads to pain and temperature sensation
being lost from the contralateral side beginning one or two segments below the
lesion.
Tactile sensation not affected much (both crossed and uncrossed pathways).
Above the level of lesion – hyperesthesia (increased sensation) – irritation of
dorsal horns.
Dermatomic area (dermatome)
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Is an area of skin that is supplied by a single pair of dorsal roots.
The body can be divided into regions that are mainly supplied by a
single spinal nerve.
There are 8 cervical (one for the head, and one for each cervical
vertebra), 12 thoracic, 5 lumbar and 5 sacral spinal nerves.
This innervates the body in a patterned form. Along the thorax and
abdomen it is simply like a stack of discs forming a human, each
supplied by a different spinal nerve.
Along the arms and the legs, the pattern is different: the
dermatomes run longitudinally along the limbs.
Clinical significance:
 Dermatomes are useful in neurology for finding the site of
damage to the spine.
 Herpes zoster infections (shingles) can reveal dermatomic areas.
Dermatomes
Brain stem
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The brain stem is
the lower part of the
brain, adjoining and
structurally
continuous with the
spinal cord.
Parts of brain stem:
the pons, medulla
oblongata, and
sometimes midbrain.
Medulla oblongata
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Located in rostral to the spinal cord, caudal to the pons and ventral to the
cerebellum.
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relays nerve signals between the brain and spinal cord
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Cranial nerve nuclei: the hypoglossal nerve, glossopharyngeal and vagus nerves.
Function:
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Respiration – central chemoreceptors – centers for inspiration (dorsal) and
exspiration (ventral)
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Cardiac center – cardioexcitatory and cardioinhibitory centers
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Vasomotor center – baroreceptors – vasoconstriction and vasodilatation centers
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Digestion – Chewing and swallowing
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Reflex centers of vomiting, coughing, sneezing, and apnoe.
 These reflexes can be classified as "bulbar reflexes“
 Vomiting reflex – ncl. tractus solitarii (affected by central emetics)
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Motor centers – control of muscle tone and postural reflexes
Ondine's curse
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also called:
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congenital central hypoventilation syndrome (CCHS)
primary alveolar hypoventilation
congenital or developed due to severe neurological
trauma to the brainstem
Episodes of apnea occur in sleep
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Other symptoms include darkening of skin color
from inadequate am ounts of ox ygen ,
drowsiness, fatigue, headaches, and an inability
to sleep at night.
Most people with Ondine's curse do not survive
infancy, unless they receive ventilatory assistance
during sleep.
Treatment: tracheotomies and lifetime mechanical
ventilation
Ondine by John William Waterhouse
(1849–1917)
Pons Varolii
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Located in rostral to the medulla oblongata, caudal to the
midbrain, and ventral to the cerebellum.
Function:
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relays sensory information between the cerebellum and cerebrum.
Some theories posit that it has a role in dreaming.
Control of respiration:
 the apneustic center - lower pons – activates dorsal respiratory
center in m edulla – inspiration
 the pneumotaxic center - upper pons - activates ventral
respiratory center in m edulla – exspiration
A number of cranial nerve nuclei are present in the pons (from top to
bottom):
 the trigeminal nerve, abducens nucleus, vestibulocochlear nuclei,
facial nerve nucleus
Reticular formation
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It is absolutely essential for the basic functions of life (stereotypical actions, such as
walking, sleeping, and lying down)
phylogenetically one of the oldest portions of the brain
It is a poorly-differentiated area of the brain stem.
Parts:
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the ascending part reticular activating system connects to areas in the
thalamus, hypothalamus, and cortex
 By stim ulation – Arousal reaction from sleeping (desynchronizing on the
EEG)
 P athology – problems with learning and memory
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the descending inhibitory part - connects to cortex, BG, spinal cerebellum
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Inhibits voluntary movements – spinal cord reflexes (tonus of extensors)
the descending facilitatory part – connects to thalamus, statokinetic sensor,
vestibular cerebellum and cortex
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Holds the standing posture and body position
When functional dominance – decerebrate rigidity (dominance of extensors)
Decerebrate rigidity
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involuntary extension of the upper extremities in response to external stimuli
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the head is arched back
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the arms are extended by the sides
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the legs are extended
The patient is rigid, with the teeth clenched
Indicates brain stem damage, specifically damage below the level of the red nucleus
(e.g. mid-collicular lesion).
It is exhibited by people with lesions or compression in the midbrain and lesions in
the cerebellum.
are in a coma and have poor prognoses
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risks for cardiac arrythmia or arrest
respiratory failure
Function of the Reticular
formation
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The RF appears to not only control physical behaviors
such as sleep, but also has been shown to play a
major role in alertness, fatigue, and motivation to
perform various activities.
Some researchers have speculated that the RF
controls approximately 25 specific and mutuallyexclusive behaviors, including sleeping, walking,
eating, urination, defecation, and sexual activity.
RF has also been traced as one of the sources for the
introversion (easily stimulated RF) and extroversion
(less easily stimulated RF) character traits.
Cerebellum (1)
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The cerebellum
(Latin: "little brain") plays an important role in the integration
of sensory perception and motor output.
Many neural pathways link the cerebellum with the motor
cortex—which sends information to the muscles causing them
to move—and the spinocerebellar tract—which provides
feedback on the position of the body in space (proprioception).
The cerebellum integrates these pathways, using the constant
feedback on body position to fine-tune motor movements.
Also, recent brain imaging studies using functional magnetic
resonance imaging (fMRI) show that the cerebellum is
important for language processing and selective attention.
Cerebellum (2)
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The cerebellum contains similar gray and white matter
divisions as the cerebrum.
 The white matter is known as the arbor vitae (Tree of Life)
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due to its branched.
The grey matter – cortex – 3 layers
The cerebellum is divided into two large hemispheres,
much like the cerebrum, and contains ten smaller lobules.
There are three phylogenetic divisions within the
cerebellum: archicerebellum (the flocculonodular lobe),
paleocerebellum (anterior lobe), and neocerebellum
(posterior lobe).
The cerebellum can also be divided by function: The
midline division is the cerebellar vermis (“worm”) and
lateral hemispheres.
Cerebellum (3)
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A: Midbrain
B: Pons
C: Medulla
D: Spinal cord
E: Fourth ventricle
F: Arbor vitae
G: archicerebellum
H: paleocerebellum
I: neocerebellum
Archicerebellum
(Vestibulocerebellum)
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associated with the flocculonodular lobe
mainly involved in balance (vestibular system)
and eye movement functions
receives input from the inferior and medial
vestibular nuclei
sends fibers back to the vestibular nuclei,
creating a feedback loop
Function: constant maintenance of balance
Paleocerebellum
(Spinocerebellum)
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associated with the anterior lobe
receives its inputs from the dorsal and ventral
spinocerebellar tracts, which carry information
about the position and forces acting on the legs
sends axonal projections to the deep cerebellar
nuclei
Function: controls proprioception related to
muscle tone (maintenance of posture)
Neocerebellum
(Cerebrocerebellum)
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associated with the posterior lobe
receives input from the pontocerebellar tract
projects to the deep cerebellar nuclei
Function: motor control
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the coordination of fine finger movements (fine
movements)
feedback correction of motor activity
operates in conjunction with the cortical motor
centres to plan movement
The functional organization (1)
The functional organization (2)
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Vermis
 receives its inputs mainly from the spinocerebellar tracts from the trunk
of the body
 information on the position and balance
 sends projections to the fastigial nucleus of the cerebellum, which then
sends output to the vestibular nuclei
Intermediate zone (paravermis)
 receives input from the corticopontocerebellar fibers that originate from
the motor cortex
 also receives sensory feedback from the muscles
 Control of muscles
Lateral zone
 receives input from the parietal cortex via pontocerebellar mossy fibers
 Information regarding the location of the body in the world
 The large numbers of feedback circuits allow for the integration of this
body position information with indications of muscle position, strength,
and speed.
Cerebellar nuclei (1)
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The 4 deep cerebellar nuclei are in the center of the
cerebellum, embedded in the white matter.
receive
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inhibitory (GABAergic) inputs from Purkinje cells in the
cerebellar cortex
excitatory (glutamatergic) inputs from mossy fiber pathways
Most output fibers of the cerebellum originate from
these nuclei.
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One exception is that fibers from the flocculonodular lobe
synapse directly on vestibular nuclei without first passing
through the deep cerebellar nuclei.
Cerebellar nuclei (2)
Cerebellar nuclei (3)
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From lateral to medial, the four deep cerebellar
nuclei are:
The Dentate, Emboliform, Globose, Fastigial
easy mnemonic device: "Don't Eat Greasy Food“
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The Dentate nuclei are deep within the lateral
hemispheres, Emboliform and Globose nuclei are
located in the paravermal (intermediate) zone, and
the Fastigial nuclei are in the vermis.
In general, each pair of deep nuclei is associated with
a corresponding region of cerebellar surface anatomy.
Dysfunction of the cerebellum
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Problems in walking, balance, and accurate hand and arm movement (ataxia).
Neuropsychiatric disorders such as dyslexia, schizophrenia and autism appear to
be associated with a deficiency in the cerebellum.
Patients with cerebellar lesions (injuries) typically exhibit "intention tremors"—a
tremor occurring during movement rather than at rest (as seen in Parkinson's
disease).
Patients may also show dysmetria, i.e., an overestimation or underestimation of
force, resulting in overshoot or undershoot when reaching for a target.
Inability to perform rapid alternating movements.
In case of intoxication: uncoordinated movements, swaying, unstable walking,
and a wide gait.
Chronic alcohol abuse is also a common cause of cerebellar lesions. Alcohol
abuse can lead to thiamine deficiency, which in the cerebellum will cause
degeneration of the anterior lobe. This degeneration leads to a wide, staggering
gait but does not affect arm movement or speech.
Patients with a cerebellar lesion may have nystagmus with the fast stroke
pointing towards the side of the lesion.
Nystagmus
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is a form of involuntary eye movement that is part of
the vestibulo-ocular reflex.
characterized by alternating smooth pursuit in one
direction and saccadic movement in the other
direction.
Physiologic nystagmus: postrotatory n.,
opticokinetic n. (watching moving visual stimuli)
Pathologic nystagmus: disorders in vestibular
apparatus, cerebellum, drug and alcohol abuse etc.
Spinal reflexes (1)
Spinal reflexes (2)
Spinal reflexes (3)