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33 Cards in this Set
- Front
- Back
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How many spinal cord segments are there?
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31
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What are the different sections of the spinal cord?
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Cervical (C1-C8)
Thoracic (T1-T12) Lumbar (L1-L5) Sacral (S1-S5) Plus 1 coccygeal segment |
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What is an easy way to tell the difference between dorsal and ventral spinal cord?
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Ventral has a larger separation (fissure) between left and right ventral white matter
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What are the 2 types of matter in the spinal cord?
What makes them up? |
White matter: Mylinated fiber (axon) tracts
Grey matter: Neuronal cell bodies/small processes |
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The dorsal cord carries and processes what type of information?
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Sensory information
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The intermediate zone (sensorimotor) does what?
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Integrates sensory information and directs motor output
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The ventral cord contain what?
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Contains motor neurons
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What do afferent and efferent apply to in terms of sensory and motor?
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Afferent: Sensory. Signaling coming into the CNS.
Efferent: Motor. Signals taking information out of CNS to muscles |
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The dorsal columns carry exclusively what information?
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Ascending sensory information
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The ventral columns carry primarily what?
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Descending motor commands
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The lateral columns in the SC contain what?
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A mixture of ascending sensory and descending motor pathways
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Where are all the sensory neuron cell bodies located?
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OUTSIDE the CNS in the Dorsal Root Ganglion
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Sensory neurons are classified on the basis of what?
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Their Axon Diameters
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Group I axons contain what neurons?
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Largest diameter, fastest conducting axons: Muscle Sensory Neurons
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Group III/IV axons contain what neurons?
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Sensory neurons for pain/temp
Recall: Do not use the dorsal columns, but rather comprise anterolateral system |
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What are the 2 types of motor neurons?
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1. Alpha motor neurons
2. Gamma motor neurons |
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What is the function of an alpha motor neuron?
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- Large Diameter
- Make excitatory synapses on skeletal muscle fibers and directly control skeletal muscle contraction |
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What is the function of a gamma motor neuron?
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Small Diameter
- Synapse on specialized, small muscle fibers withing sensory structures called muscle spindles - Controls spindle SENSITIVITY |
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What are the 2 muscle sensory receptors?
Their Functions? |
1. Muscle Spindles - sense STRETCH of muscles
2. Golgi Tendon Organs - sense CONTRACTION of muscles |
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Where are muscle spindles and golgi tendon organs found?
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Muscle spindles - found throughout the muscle. Set up in parallel with extrafusal fibers (so they experience same length changes)
Golgi Tendon Organs - Located at tip of each muscle at muscle-tendon junction |
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Muscle spindles are innervated by what 2 types of sensory neurons?
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1. a single group Ia sensory neuron
2. A single group II sensory neuron |
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Where are intrafusal fibers contractile?
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Only at their tips
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How do the sensory neurons detect stretch within the muscle spindle?
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Local membrane stretch activates stretch-sensitive ion channels in the sensory neurons, causing a depolarization
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Golgi Tendon Organs are innervated by what?
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Dendrites of a single group of Ib Afferent neurons
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What provides compensatory regulator of spindle sensitivity?
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Gamma motor neurons
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What is the purpose of alpha/gamma MN co activation?
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Enables the spindles to remain stretch sensitive regardless of the amount of contraction in the parent muscle
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What is reciprocal innervation?
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Common theme in spinal reflexes where sensory input will excite MN's that innervate a particular muscle and inhibit MN's that innervate the antagonist
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What is the simplest and fastest somatic reflex?
Why? |
Myotactic (stretch) reflex
Because Only reflex involving just one synapse within the SC and associated sensory/motor neurons are both the largest diameter |
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What is the function of the Golgi Tendon Organ reflex?
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Opposes excessive contraction of the muscle in which it is located
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Does the GTO reflex contain interneurons?
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YES, has interneurons for both extensor (inhibitory) and flexor (excitatory) muscles
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What are the 2 movement components of the withdrawal reflex?
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1. Ipsilateral Flexion
2. Contralateral Extension |
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What is the effect of stimulus strength on the withdrawal reflex?
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The stronger (more painful) the stimulus, the larger number of sensory neurons activated.
Strengthens reflex and EXTENDS the reflex circuit action to additional SC segments, recruiting other parts of the body. |
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Are reflex responses static?
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NO, extensively regulated by descending projections and local spinal cord circuits.
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