Spinal Cord Physiology

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Physiology

Spinal Cord Physiology


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Introductiony A thin column of nerve tissue that extends downward from

the brain through the vertebral column to the level of thesecond lumbar vertebra.

y

Transmits pain signals and other nerve impulses to and fromthe brain and controls reflexes actions.


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Three Main Components1 . Spinal nerves2. Nerve Tissue3. Meninges


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N erve TissueThe spinal cord consists of two types of nerve tissue.1 . Gray matter2. White matter


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G ray Mattery Makes up the centre of the spinal cord.y Consists primarily of dendrites.

Dendrites- short fiber that conducts toward the cell body of theneuron


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W hite Mattery Surrounds the gray matter.y Consists of bundles of nerve fibers that form conduction

paths called spinal tracts.


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G ray Matter and W hite Matter


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G ray Matter and W hite Matter


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Sensory (Ascending) Pathways1 . Lateral spinothalamic tract

-pain and temperature (warm & coolness)2. Ventral spinothalamic tract

-crude touch, pressure

3. Posterior column-conscious proprioception, discriminative touch, pressure,vibration

-consists 2 tracts: gracile fasciculus and cuneate fasciculus.4. A nterior & posterior spinocerebellar tracts

-muscle toneProprioception: the ability to sense the position and location and orientation and

movement of the body and its partsDiscriminative: capable of making fine distinctions


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Sensory (Ascending) Pathways


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Motor (Descending) Pathways1 . Direct pathways

(a) Lateral corticospinal tract(b) A nterior corticospinal tract

(c) Corticobulbar tract-Caused voluntary movements at skeletal muscles


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Motor (Descending) Pathways2. Indirect pathways

(a) Tectospinal tract(b) Vestibulospinal tract

(c) Rubrospinal tract(d) Lateral reticulospinal tract(e) Media reticulospinal tract-regulate muscle tone, posture, balance, orientation of thehead and body.


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Motor (Descending) Pathways


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R eflexes are y inborny unlearnedy unconscious


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R eflexesy A reflex is a predictable involuntary response to a stimulus.y A reflex involving the skeletal muscles is called asomatic

reflex .y

A reflex involving responses of smooth muscle, cardiacmuscle, or a gland is av isc er a l reflex.


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R eflex ArcsDefinition: highly specific neural pathway through which a

reflex occurs.


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5 Essential Componentsof the R eflex Arc1 . Receptor2. Sensory Neuron3. integrating center

4. motor neuron5. Effector


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2. 5 Essential Componentsof the R eflex Arc

Figure 7.11a

Stimulus at distal

end of neuron

Skin Spinal cord(in cross section)

Interneuron

Receptor

Effector

Sensory neuron

Motor neuron

Integrationcenter

(a)


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The R eflex Arc

Figure 7.11a, step 1

Stimulus at distal

end of neuron

Skin

Receptor

(a)


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The R eflex Arc


Stimulus at distal

end of neuron

Skin

Receptor Sensory neuron

(a)


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The R eflex Arc


Stimulus at distal

end of neuron


Interneuron


Integrationcenter

(a)


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The R eflex Arc


Stimulus at distal

end of neuron


Interneuron


Motor neuron

Integrationcenter

(a)


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The R eflex Arc


Stimulus at distal

end of neuron


Interneuron

Receptor

Effector

Sensory neuron

Motor neuron

Integrationcenter

(a)


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y Somatic reflex A ny reflex (relatively rapid and predictablemotor response to a stimulus) in which the effectors areskeletal muscles

y A

utonomic reflex -A

ny of a large number of normal reflexesgoverning and regulating the functions of the viscera.

Viscera - internal organs collectively (especially those in theabdominal cavity)


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Somatic Spinal R eflexes1 . The stretch reflexes2. The tendon reflexes3. The flexor reflexes

4. The crossed extensor reflexes


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Stretch R eflexy A lso called myotatic reflexy Causes contraction of a skeletal muscle in response to

stretching of the muscle.y

Three components:(a) Muscle spindles(b) Sensory neuron(c) Motor neuron


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Stretch R eflex

Figure 7.11bc

Spinal cord

Sensory (afferent)neuron

Inter-neuron

Motor (efferent)neuron


Sensory receptors

(stretch receptorsin the quadricepsmuscle)


Sensory receptors(pain receptors inthe skin)

Effector (quadricepsmuscle of thigh)

Effector (bicepsbrachiimuscle)

Synapse inventral horngray matter

(c)

(b)


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3 . W hy test your reflexes?

Reflexes determine the general health of themotor portion of the nervous system.

Whenever reflexes are exaggerated, distorted, or

absent, nervous system disorders are indicated.

Reflex changes often occur before the pathologicalcondition has become obvious


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Stretch R eflex

Figure 7.11b, step 1

Spinal cord

Sensory receptors


(b)


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Stretch R eflex


Spinal cord


Sensory receptors


(b)


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Stretch R eflex


Spinal cord


Sensory receptors



(b)


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Stretch R eflex


Spinal cord



Sensory receptors



(b)


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Stretch R eflex

Figure 7.11c, step 1

Spinal cord


(c)


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Stretch R eflex


Spinal cord



(c)


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Stretch R eflex


Spinal cord

Inter-neuron



(c)


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Stretch R eflex

Figure 7.11c, step 4a

Spinal cord

Inter-neuron




(c)


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Stretch R eflex

Figure 7.11c, step 4b

Spinal cord

Inter-neuron





(c)


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Stretch R eflex

Figure 7.11bc

Spinal cord


Inter-neuron



Sensory receptors




Effector (quadricepsmuscle of thigh)



(c)

(b)

Spinal Cord Physiology

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