Download 04. internal feature..

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The cord is composed
of:
Inner core of Gray
matter.
On cross section
It is H- shaped Pillar or
Butter Fly.
Outer core of White
matter.
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It is correlated to:
Amount of Muscle
Innervated.
Greatest in:
Cervical and
Lumbosacral Segments.
They innervate the
muscles of the Upper
and Lower limbs.
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Anterior and Posterior
Gray Columns or Horns.
They are united by:
A thin Gray
Commissure.
It contains the small
Central Canal.
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It Receives
Most of the
Termination of the
Dorsal Nerve Roots
entering the spinal
cord.
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Contains:
Lower Motor Neurons.
Their axons exit through
Ventral Nerve Roots to
innervate the skeletal
muscles.
The Neurons
receive Input from:
Descending pathways for
the motor control.
Some dorsal root afferents.
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A small
Intermediolateral Horn
is present in:
Thoracic and Upper
Lumbar Segments.
It contains the cell
bodies of Preganglionic
Sympathetic Neurons.
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A similar place is found
in:
2nd 3rd and 4th Sacral
Segments.
It gives rise to
Preganglionic
Parasympathetic
Neurons.
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The Gay Matter can
be divided into (10)
Zones.
They are Numbered
Sequentially from
Dorsal to Ventral.
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Superficial Laminae
Receive:
Cutaneous Afferents.
Deeper Laminae Receive:
Proprioceptive and
Muscle Afferents.
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At the Tip of the Dorsal
Horn (Laminae 1-111)
It Extends:
Throughout the Length of
the spinal cord .
It receives:
1. Nerve Fibers associated
with Nociception
Temperature and Touch.
2. Input from Supraspinal
Levels.
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Large Nerve Cells.
Position:
Anterior to Substantia
Gelatinosa.
Extension:
Throughout the spinal cord.
It receives:
Fibers from the Posterior
White Column associated
with the senses of Position
and Movement.
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Composed of:
Thoracic Nucleus.
Nucleus Dorsalis.
Occupies:
Base of the Dorsal Horn (Lamina
V11): Segments C8- L3
It receives afferents from:
Muscle Spindle.
Golgi Tendon Organs.
Tactile and Pressure Receptors.
These form the ascending fibers of
the Dorsal Spinocerebellar Tract.
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(1) Alpha Neurons :
Innervate Extrafusal
muscle fibers.
(2) Gamma Neurons:
Innervate Intrafusal
muscle fibers within the
muscle.
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Neurons innervating
Muscles of the Neck
and Trunk :
Medial .
Neurons innervating
Muscles of the Limbs :
Lateral.
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Phrenic Nucleus
Centrally Located (C3C5).
Gives rise to: Phrenic
Nerve.
Essential for Breathing.
Acessory Nucleus
Located in the Upper
Cervical Segments.
Its Axons form the
Spinal Part of the
Acessory Nerve.
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Completely Surrounds the
Gray Matter.
More Abundant in the
Upper Levels of the cord
The Ascending Tracts gain
More Fibers at each
successive level.
The Descending fibers have
the opposite.
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Dorsal.
Lateral.
Ventral
It is Dorsolateral
Fasciculus.
Located
Superficial to the Tip of the
Dorsal Horn.
Formed of
Ascending and Descending
branches of the Dorsal
Roots which Don’t
Terminate at their Point of
Entry.
Fibers within the Tract
Run Varying Distances in
Either Direction
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Fasciculus Proprius
Occupies:
A Narrow band
immediately Peripheral
to the Gray Matter.
Functions:
Interconnects Adjacent
or Distant Cord
Segments.
Permit Intersegmental
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Between the Posterior
Median Sulcus and the
Posterior Horn.
Composed of:
Fasciculus Gracilis :
Medial throughout the
Length of the Spinal
Cord .
Contains
Ascending fibers from
Sacral, Lumbar and
Lower Thoracic.
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Fasciculus Cuneatus
Lateral.
Receives fibers from:
Upper Thoracic and
Cervical regions.
The Fasciculi (Gracilis &
Cuneatus)are concerned
with
Proprioceptive Information
(Awareness of Posture and
Discriminitive Touch).
CONTAIN:
 (1) Ascending Tracts
 Dorsal Spinocerebellar:
 Carries information from:
Muscles, joints and ligaments.
 For the Control of Posture and
Coordination of Movement.
Lateral Spinothalamic :
 Carries impulses of
 Pain, Temperature, Pressure and
Coarse Touch (Extroceptive).
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(2) Descending Tracts:
Lateral Corticospinal:
Controls
Voluntary, Discrete and
Skilled Movements.
Rubrospinal:
Has a control over the Tone
of Limb Flexor Muscles.
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CONTAIN:
(1) Descending Tracts
1. Ventral
Corticospinal
2.Tectospinal.
Mediates reflex
movements in
response to Visual
Stimuli.
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3.Vestibulospinal
Has an Influence
upon Extensor Motor
neurons.
4. Reticulospinal
It influences
Voluntary movement,
Reflex activity and
Muscle Tone.
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(2) Ascending Tracts
1. Ventral
Spinocerebellar.
2. Ventral
Spinothalamic.
3. Medial Longitudinal
Fasciculus.
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(1) Poliomyelitis
Acute Viral Infection of the
Lower Motor neurons .
Rapid Paralysis and
Wasting of the Limb.
Can Affect the Diaphragm.
Recovery is Incomplete.
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Chronic Degenerative
Disease.
A Progressive Muscular
Atrophy with Hypotonia
and Wasting of the limb
muscles.
Affect both the Lower
Motor Neurons and the
Descending Tracts.
Degeneration of the
Descending Tracts cause
Spasticity and Weakness of
the muscles.
SPINAL REFLEXS
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Involuntary
stereotyped response
that is initiated by a
sensory stimulus.
The pathway is formed
of afferent neurones
conveying impulses
from sensory receptors
in the CNS ( spinal cord
or brain stem) and
efferent neurones
coming out from the
CNS to the effector
organ (muscle or
SPINAL REFLEXS
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Interneurons
within the CNS
exist between the
afferent and
efferent
components.
Reflexes are
qualitatively the
same but
quantitatively they
differ.
FUNCTIONS OF STRETCH
REFLEXES
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(1) control of muscle
tone which in turn
determine the
proportion of motor
units that are active
at any one time.
(2) control of posture
by keeping the anti
gravity muscles at a
constant length in
opposition to imposed
stretch.
STRETCH RECEPTORS
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Neuromuscular
spindles (muscular
spindles) are most
numerous in the
central non contractile
part toward the
tendinous attachment
of skeletal
muscles.They provide
sensory information
that is used by the CNS
in the control of muscle
activity. Each spindle
has a fusiform capsule
STRETCH RECEPTORS
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The nuclear bag
fibers are concerned
with dynamic
responses and are
associated more
with velocity and
position of
contraction.the
nuclear chain fibers
are associated with
slow static
contractions.
STRETCH RECEPTORS
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The intrafusal
fibers are of two
types : the nuclear
bag and the
nuclear chain.
There are two
types of sensory
ending of muscle
spindles : the
(primary)
annulospiral and
the (secondary)
STRETCH RECEPTORS
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There are two types
of sensory ending of
muscle spindles :
the (primary)
annulospiral and
the (secondary)
flower spray.
The ordinary muscle
fibers outside the
spindles are the
extrafusal fibers.
STRETCH (MONOSYNAPTIC )
REFLEX
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Stretching(elongationo
f the intrafusal fibers
results in stimulation
of the annulospiral and
flower spray endings.
Nerve impulses pass to
the spinal cord in the
afferent neurons.In
the spinal cord, they
stimulate the large
alpha motor
neurons.the efferent
motor neurons
STRETCH (MONOSYNAPTIC )
REFLEX
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The muscle spindle
afferent neurons inhibit
the alpha motor
neurons supplying the
antagonist muscles
(reciprocal inhibition).
GAMMA REFLEX LOOP
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Centers in the brain and
spinal cord( reticular
formation, basal ganglia
and cerebellum)give rise
to tracts that synapse
with the gamma motor
neurons.
Gamma efferent motor
fibers cause shortening
of the intrafusal fibers
and stimulate the
sensory nerve endings
FLEXOR REFLEX
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It is a polysynaptic
reflex in which one or
more interneurons are
interposed between
afferent and efferent
neurons. Cutaneous
stimulation of the
limbs causes
withdrawal from the
stimulus.
All forms of cutaneous
stimulation can initiate
flexor reflex but
CROSSED EXTENSOR REFLEX
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Activation of the
flexor reflex in a
weight bearing
limb
simultaneously
causes reflex
extension of the
contralateral limb
so as to carry the
weight of the body.