Features of the Spinal Cord Flashcards
How can neurons be classified according to their structure?
Bipolar: 1 dendrite and 1 axon attached to the cell
Multipolar: Many dendrites and 1 axon
Pseudo-unipolar: Has 1 process forming the cell body which divides into an axon (connecting to the spinal cord/brain) & dendrites (connecting to receptors)
What is the extent of the spinal cord?
Beginning: Continuation of the medulla along the upper border of the atlas (C1)
Ending: Conus medullaris (at lower border of L1 vertebra or at the level of L1 & L2 intervertebral disc)
Where are the enlargements of the spinal cord?
The Cervical Enlargement: Neurons for the muscles of upper limb
The Lumbo-Sacral Enlargement: Neurons for the muscles of lower limb
What is the cauda equina?
The lowermost spinal nerves (lumbar, sacral and coccygeal) run downwards towards the corresponding intervertebral foramina
Classify the 31 pairs of spinal nerves
8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal
Spinal cord is shorter than vertebral column
Coverings of the spinal cord (meningeal layers)
Outside to inside:
1. Dura mater
2. Arachnoid mater
3. Pia mater
Name the meningeal spaces
Extradural (Epidural) Space: Between the bone & the dura
Subdural Space: Between the dura outside & the arachnoid
Subarachnoid Space: Between the arachnoid & pia mater
What is the dura mater?
Forms loose envelope around the spinal cord
Extends from foramen magnum to S2 vertebra
What is the arachnoid mater?
Covers the spinal cord loosely
Extends to lower border of S2 vertebra
The subdural & subarachnoid spaces extend up to S2
What is the lumbar cistern?
Wide part of the subarachnoid space, distal to the caudal end of spinal cord
Extends from L2 to S2
Contains CSF, cauda equina, and filum terminale
Describe the procedure of the lumbar puncture/spinal tap
The needle is introduced either above or below the tip of L4 spine
What is the purpose of the lumbar puncture?
Obtaining CSF samples
CSF withdrawal to decrease intra-cranial pressure
Injecting local anaesthetics and antibiotics
What is epidural block?
Anesthetic agent is injected into the epidural (extra – dural) space
How does epidural block work?
Diffuses through the dura and arachnoid and enters the subarachnoid space containing CSF
Acts on the nerve roots and the sensation is lost inferior to the level of the block
Most commonly recommended during parturition to relieve pain
What is pia mater?
Thicker & less vascular than cerebral pia
Invests the entire spinal cord
What is the filum terminale?
Non-nervous filamentous thread
Attached to tip of conus medullaris above & pierces the dura & arachnoid at S2 & blends with periosteum of 1st Coccygeal vertebra below
What are the features of the denticulate ligament?
Thickening of pia mater
One on either side of the spinal cord
Lateral margin gives off 21 pairs of processes, which attach to the dura mater to support the spinal cord
What are the two main internal components of the spinal cord?
Grey matter (centre)
White matter (periphery)
Shape of grey matter
Grey matter of right & left halves connect across in the midline by grey commissure & traversed by central canal
Organization of grey matter
A pair of anterior grey column (ventral horns)
Posterior grey column (dorsal horns)
Lateral grey column (lateral or intermediate horns) in thoracic and lumbar regions and middle sacral segments only
What types of motor neurons are present in the anterior gray column?
Alpha (α) neurons
Gamma (ϒ) neurons
Features of the α neurons
Large in size, thickly myelinated with high conduction velocity
Supply the extra-fusal fibers of striated muscle
Extrafusal muscle fibers comprise the bulk of muscle and form the major force-generating structure
Features of the ϒ neurons
Small in size, thinly myelinated less conducting velocity
Supply intra-fusal fibers
Intrafusal muscle fibers are buried in the muscle, and they contain afferent receptors for stretch, but they also contain contractile elements
Describe the formation of the nerve trunk
The 2 nerve roots united together to form the nerve trunk
How do the nerves split after the nerve trunk?
Each nerve will divide into 2 rami (anterior & posterior) which have mixed fibers (sensory & motor)
Describe how the reflex hammer stimulates contraction
Tapping by the hammer → stretch → stimulation of muscle spindle → sensations will be transferred to spinal cord through sensory fibers which are in turn synapsing with alpha and gamma motor neurons in the anterior grey → contraction of the muscle to prevent its tear
Fiber arrangement in the dorsal funiculi
Only ascending tracts
Includes fasciculus gracilis and funiculus cuneatus
Fiber arrangement in the ventral faniculus
Ascending (sensory): Anterior spino-thalamic
Descending (motor): Anterior cortico-spinal, tectospinal, vestibulo-spinal, olivo-spinal and medial and lateral reticulospinal
Fiber arrangement in the lateral faniculi
Ascending (sensory): Lateral spino-thalamic, anterior and posterior spino-cerebellar
Descending (motor): Lateral cortico-spinal, rubro-spinal
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