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Chapter 13
The Spinal Cord, Spinal Nerves, and Spinal Reflexes
58
Anatomy
Undergraduate 2
11/25/2017

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Term
Where does the spinal cord end?
Definition
Between L1 and L2
Term
Posterior median sulcus
Definition
A shallow longitudinal groove on the dorsal surface of the spinal cord
Term
Anterior median fissure
Definition
A deep groove along the anterior surface of the spinal cord.
Term
What does the cervical enlargement do?
Definition
It supplies nerves to the shoulders and upper limbs.
Term
What does the lumbar enlargement do?
Definition
It innervates the structures of the pelvis and the lower limbs.
Term
Conus medullaris
Definition
inferior to the lumbar enlargement, tapered and conical
Term
filum terminale
Definition
A slender strand of fibrous tissue, extends from the inferior tip of the conus medullaris and continues as far as the 2nd sacral vertebra where it supports the spinal cord as part of the coccygeal ligament.
Term
dorsal roots
Definition
Axons of the neurons which bring sensory information into the spinal cord.
Term
Ventral roots
Definition
Contain the axons of motor neurons that extend into the periphery to control somatic and visceral effectors.
Term
Spinal meninges
Definition
Provide physical stability and shock absorption
Term
Dura mater
Definition
The tough fibrous layer that forms the outermost covering of the spinal cord.
Term
Meningitis
Definition
Inflammation of the meningeal membranes caused by a bacterial or viral infection
Term
Epidural space
Definition
Between the dura mater and the vertebral canal
-Contains areolar tissue, blood vessels, and adipose tissue
Term
coccygeal ligament
Definition
A dense cord of collagen fibers blended with components of the filum terminale.
-Continues along the sacral canal blending into the periosteum of the coccyx.
Term
Arachnoid mater
Definition
The middle meningeal layer.
-the inner surface of the dura mater is in contact with the outer surface of the arachnoid mater.
Term
Subarachnoid space
Definition
The region between the arachnoid membrane and the pia mater, contains the cerebrospinal fluid (CSF).
Term
Cerebrospinal fluid
Definition
Acts as shock absorber and a diffusion medium for dissolved gases, nutrients, chemical messengers, and wastes.
-Found in the subarachnoid space.
Term
Pia mater
Definition
The innermost meningeal layer.
-consists of a meshwork of elastic and collagen fibers
Term
Denticulate ligaments
Definition
Prevent side to side and superior-inferior movement of the spinal cord.
-Extend from the pia mater to the dura mater
Term
Horns
Definition
The areas of gray matter on each side of the spinal cord.
Term
Posterior gray horns
Definition
Contain somatic and visceral sensory nuclei
Term
Anterior gray horns
Definition
Contain somatic motor nuclei
Term
Lateral gray horns
Definition
-only found in the thoracic and lumbar segments
-Contain visceral motor nuclei
Term
Organization of white matter
Definition
-Posterior white columns: between the posterior gray horns and the posterior mediun sulcus
-Anterior white columns: between anterior gray horns and the anterior median fissure
-Anterior white commisure: where axons cross from one side of the spinal cord to the other; interconnects the anterior white columns
-Lateral white columns: between the anterior and posterior white columns on each side
Term
epineurium
Definition
outermost layer of the spinal nerve
-dense network of collagen fibers
Term
perineurium
Definition
middle layer of the spinal nerve cover
-fibers extend inward from the epineurium
-fascicles (bundles of axons)
Term
endoneurium
Definition
delicate connective tissue fibers, extend from the perineurium, surround individual axons
Term
peripheral neuropathy
Definition
Regional losses of sensory and motor function resulting from nerve trauma or compression
Term
4 major plexuses
Definition
1.Cervical plexus
2.Brachial plexus
3.lumbar plexus
4.sacral plexus
Term
nerve plexus
Definition
complex, interwoven network of nerves
Only the ventral rami form plexuses
Term
Cervical plexus
Definition
-Consists of the ventral rami of spinal nerves C1-C5; innervate the muscles of the neck and extend into the thoracic cavity, control the diaphragmatic muscles.
Term
Phrenic nerve
Definition
major nerve of the cervical plexus.
Left and right phrenic nerves supply the diaphragm
Term
Brachial plexus
Definition
innervates the pectoral girdle and upper limb, with contributions from the ventral rami of spinal nerves C5-T1.
Term
Trunks
Definition
Large bundles of axons from several spinal nerves.
Term
Cords
Definition
Small branches of axons that originate at trunks.
Term
Lumbar plexus
Definition
Formed by the ventral rami of T12-L4.
Term
Sacral plexus
Definition
Formed by a branch from L4 and the ventral rami of L5-S4
Term
5 steps in a simple neural reflex
Definition
1.The arrival of a stimulus and the activation of a receptor
2.The activation of a sensory neuron
3.Information processing in the CNS
4.The activation of a motor neuron
5.The response of a peripheral effector
Term
Reflexes
Definition
Rapid, automatic responses to specific stimuli
Term
Divergence
Definition
A mechanism for spreading stimulation to multiple neurons or neuronal pools in the CNS.
-The spread of information from one neuron to several neurons.
Term
Convergence
Definition
A mechanism for providing input to a single neuron from multiple sources.
Several neurons synapse on a single post-synaptic neuron.
Term
Serial processing
Definition
Information is relayed in a step-wise fashion,from one neuron or neuron pool to another.
Term
Parallel processing
Definition
When several neurons or neuronal pools process the same information simultaneously
Term
Reverberation
Definition
Collateral branches of axons somewhere along the circuit extend back toward the source of an impulse and further stimulate the presynaptic neurons.
Term
Events in a reflex arc
Definition
1.Arrival of stimulus and activation of receptor.
2.Activation of a sensory neuron.
3.Information processing in the CNS.
4.Activation of a motor neuron.
5.Response by a peripheral effector.
Term
Stretch reflex
Definition
A monosynaptic reflex.
Provides automatic regulation of skeletal muscle length.
Term
Patellar reflex
Definition
An example of a stretch reflex. The stimulus is a tap on the patellar tendon that stretches receptors within the quadriceps muscles. The response is a brief contraction of those muscles which produces a noticeable kick.
Term
Polysynaptic reflexes
Definition
The interneurons can control motor neurons that activate several muscle groups simultaneously.
Term
Withdrawal reflex
Definition
Moves affected parts of the body away from a stimulus
Term
Flexor reflex
Definition
An example of a withdrawal reflex, affects the muscles of a limb.
Term
Crossed extensor reflex
Definition
A motor response to the stimulus also occurs on a side opposite the stimulus.
Term
Innate reflexes
Definition
result from the connections that form between neurons during development. (withdrawal from pain, chewing, suckling)
-genetically programmed
Term
Acquired reflexes
Definition
Learned motor patterns
Term
Somatic reflexes
Definition
Provide a mechanism for the involuntary control of the muscular system.
-Superficial reflexes: triggered by stimuli at the skin or mucous membranes
-Stretch reflexes: triggered by the sudden elongation of a tendon, and thus of the muscle to which it attaches.(ex. knee-jerk reflex)
Term
Muscle spindles
Definition
Each consists of a bundle of small specialized muscle fibers called intrafusal muscle fibers
The muscle spindle is surrounded by larger skeletal muscle fibers called extrafusal muscle fibers.
-Responsible for resting muscle tone, and at greater levels of stimulation, for the contraction of the entire muscle.
Term
Intrafusal fiber
Definition
-has one set of myofibrils at each end
Term
Postural reflexes
Definition
Help us maintain a normal upright posture
Term
Tendon reflex
Definition
Monitors the external tension produced during a muscular contraction and prevents tearing or breaking of the tendon.
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