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Topic 10: The Spinal Cord

Terms in this set (65)

CNS
Central nervous system; consists of the brain and the spinal cord
Cortex and Nucleus
What is the gray matter of the CNS made of?
Tract
What is the white matter of the CNS made of?
PNS
Peripheral nervous system; consists of nerves and ganglia
Ganglia
What is the gray matter of the PNS made of?
Nerves
What is the white matter of the PNS made of?
Sensory (Afferent)
Carries sensory signals to CNS from receptors
Motor (Efferent)
Carries motor signals from CNS to effectors
Visceral (Autonomic)
PNS; Innervates viscera
Somatic
PNS; Innervates skeletal muscles
Gray Matter
~Contains somas, dendrites, and synapses
~Little myelin: gray in color
~Site of information processing: neural integration
~Found in the nuclei, ganglia, and cortex
White Matter
~Contains axons (nerve fibers) that can be sensory
or motor
~Abundance of myelin: white in color
~Carries signals form one part of the CNS to
another: conduction/communication
~Found in columns and tracts
Enlargement
A thickening in the width which is located in the inferior cervical region, this is the place where branches for the spinal cord
Cervical Enlargement
The upper limbs originate, C4-T1
Lumbar Enlargement
Found in the lumbosacral (lower back) region, this is the place where branches for the lower limbs originate, T9-T12
Medullary Cone
The tapered-conical end of the spinal cord, around L2
Cauda Equine
A bundle of nerve roots that occupies the vertebral canal below L2, looks like a horse's tail
Filum Terminale
below L2, anchors the spinal cord to the coccyx of the vertebral column
Posterior Median Sulcus
longitudinal shallow groove on the posterior side of the spinal cord
Anterior Median Fissure
a deeper longitudinal grove on the anterior part of the spinal cord
Central Canal
opening found in the middle of the gray commissure. It is lined with ependymal cells, continuous with the 4 th ventricle rostral and filled with CSF.
Gray Matter
Forms the posterior horn, gray commissure, lateral horn, and anterior horn. Its appearance is
similar to a butterfly with open wings
Dorsal (Posterior) Horn
this is a section of gray matter that extends toward the posterior part of the spinal cord, has sensory neurons. Associated with dorsal root ganglion
Anterior (Ventral) Horn
a section of gray matter that extends towards the anterior part of spinal cord, has motor neurons. Associated with ventral root
Gray Commissure
a section of gray matter that connects the right and left halves of the spinal cord gray matter around the central canal
White Matter
made of axons, myelin is present=white. Forms the posterior, lateral, and anterior columns
Columns (Funiculi)
bundles of axons travelling up and down the spinal cord. They provide
avenues of communication between different levels of the CNS
Posterior (Funiculus) Column
the column between the dorsal horn and the posterior
median sulcus
Lateral (funiculus) column
the column between the dorsal horn and the lateral horn
Anterior (funiculus) column
the column between the anterior horn and the anterior
median fissure
Tracts
a collection of axons in CNS that have similar origin, destination, and function. Found in the
columns. Ascending and descending tracts
Ascending Tracts
always SENSORY - carry sensory information up the spinal cord from receptors towards the brain. Ex: fasciculus gracilis and cuneatus, spino thalamic, spino cerebellar (names generally start with "spino"). Have three neurons in a chain
Descending Tracts
always MOTOR - conduct motor impulses down the spinal cord from the brain towards effectors. Ex: corticospinal, rubrospinal, tectospinal (names end in -"spinal"). Have two neurons in a chain
Decussate
The axons will cross to the opposite side, right to left
and left to right. As a result, right side of brain controls movement on left side of body and sensory
perception on left side of body; left side of the brain controls movement on the right side of the body and
sensory perception on the right side
First-Order Neurons
found in the dorsal root ganglion (unipolar): they detect stimuli and forward it to the spinal cord or brainstem
Second-Order Neurons
mostly found in the dorsal horns: they forward the signal on to the thalamus of diencephalon
Third-Order Neurons
found in the thalamus: they carry the signal the rest of the way to the cerebral cortex's sensory region (ex: post-central gyrus/sensory homunculus for touch, pressure, pain, etc.)
Parethesia
Loss of sensory function (can be partial or complete)
Upper Motor Neurons
the starting place of efferent (motor) signals, like the neurons of the corticospinal tract. Most are located in the cerebral cortex (precentral gyrus) and have a long axon that synapses on a lower motor neuron
Lower Motor Neurons
the starting place of axons that synapse on the effector (skeletal muscle). Most are located in ventral horns of spinal cord
Paralysis
Loss of motor function (can be partial or complete)
Reflex
Quick, involuntary, stereotyped reaction of effectors (muscles and glands) to stimulation. This means that ALL of them will require a stimulus, will happen quickly, will be involuntary and happen in the same manner every time (predictable)
Receptor
a specialized structure able to detect a stimulus/signal (can be dendrites of sensory neurons)
Sensory (Afferent) Neuron
its axons carry sensory input thru the dorsal root to the dorsal horn of the spinal cord. Usually are the unipolar neurons of the dorsal root ganglion. In PNS
Integration Center
always located in the CNS (brain or spinal cord). Integrates the information/makes decisions
Motor (Efferent) Neuron
its axons carry the motor output from ventral horn through the ventral root to effectors. Mostly in ventral horns. In PNS
Intrinsic (Inborn) Reflexes
reflexes we are born with for primitive protection
Acquired (Learned) Reflexes
Reflexes that are learned over time
Somatic Reflexes
involve skeletal muscles (stretch reflex)
Visceral Reflexes
deal with internal organs (blood pressure regulation through baroreceptors)
Monosynaptic Reflexes
have one neural synapse in the reflex arc
(stretch reflex). This is commonly between a primary sensory neuron and a motor neuron. No interneurons
are involved, which makes them faster than polysynaptic
Polysynaptic Reflexes
have two or more synapses in the CNS between three or more neurons in a pathway. Interneurons are involved, so it is slower than the monosynaptic reflex (Golgi tendon reflexes)
Ipsilateral Reflexes
those where the sensory input and the motor
output are on the same side of the body (the withdrawal reflex)
Contralateral Reflexes
those that have a sensory input on one side of the body and the motor output is sent to the opposite side of the body (the crossed extensor reflex)
Spinal Reflexes
the decision (neural integration) is made in spinal cord, involves spinal nerves (stretch reflex)
Cranial Reflexes
decision (neural integration) is made in the brain, involves cranial nerves (blinking)
Muscle spindles
stretch receptors that belong to a group of receptors called proprioceptors; found within the muscle (in the belly of the muscle); will detect stretch of muscle and send signals to the CNS to maintain/adjust posture
Golgi Tendon Organs
stretch receptors that belong to a group of receptors called proprioceptors; found in the tendons; will detect stretch of muscle and send signals to the CNS to maintain/adjust posture
Monosynaptic Reflex
~helps maintain equilibrium and posture.
~Is ipsilateral.
~Depends on muscle spindles to send the sensory
signal about the stretch of the muscle.
~As the muscle gets stretched, it contracts in
response and resists stretch.
~Maintains increased tonus and feeling stiffer than
an un-stretched muscle.
~Maintains length of muscle
Polysynaptic Reflex (Golgi Tendon Organ Reflex)
~Helps prevent overstretch of tendon and damage
to it.
~Is ipsilateral
~depends on Golgi tendon organs that send
sensory signal about muscle tension.
~As the tendon stretches, the muscle relaxes in
response to prevent rupture of tendon
Flexor (Withdrawal) Reflex
~This is a quick contraction of flexor muscles which
results in retracting or withdrawing the limb from
a possibly dangerous stimulus (stepping on glass). ~Is polysynaptic and ipsilateral
Crossed-extensor reflex
~contraction of extensor muscles in the opposite
limb from the one being withdrawn.
~Is polysynaptic and contralateral
Patellar Reflex
~commonly known as a knee-jerk reflex and is an
example of a stretch reflex.
~When a physician strikes the patellar ligament (it
connects the patella to the tibia and is the
continuation of the patellar tendon, which
attaches the quad muscle to the patella) with a
hammer, it stretches the quad muscle.
~Stretch is detected by muscle spindles and is
carried by the sensory axons in the femoral nerve
to the dorsal horn of spinal cord (L4).
~In the spinal cord, the sensory axon synapses with
a motor neuron directly (monosynaptic reflex). ~The motor neuron then sends the motor output to
the quadriceps muscle on the same
side (ipsilateral), which contracts in response and
extends the knee (jerks the knee upward; the
quad muscle is an extensor muscle)
Hypoactive (Absent)
in peripheral nerve damage, chronic diabetes mellitus, coma, neurosyphilis
Hyperactive
in lesions of corticospinal tract
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