S3C2 (2.0) Flashcards
What is a dermatome?
an area of skin that is mainly supplied by afferent nerve fibers from a single dorsal root of spinal nerve which forms a part of a spinal nerve
What innervates muscles?
Myotomes - a single ventral root
What are most muscles innervated by?
Axons from two spinal segments
What muscles are unsegmentally innervated?
Intrinsic muscles of the hand
When do muscles share innervation by the same spinal segment?
When they have a common primary action
What is the innervation for muscles with opposing action? Example?
They are supplied in sequence
i.e. C5/C6 bicep flexors
C7/C8 triceps extensors
What does complete sensory loss mean?
More than one spinal root must be damaged as there are functional overlap at boundaries between dermatomes/myotomes
When does the notochord appear in the medoserm?
3rd week
When are dermatomes formed?
3rd week - the tri-laminar disc has been established and the middle layer (mesoderm) has differentiated into its different types
What is directly adjacent to the neural tube?
Paraxial mesoderm
What does the paraxial mesoderm differentiate into?
44 somites
How many somites are formed? How many break down? How many are left?
44 formed
13 broken down
31 somites left
What does the ventral portion of somites contain?
Sclerotome, the precursor to the ribs and vertebral column.
What does the dorsal portion of somites contain?
Dermomyotome
How can spinal cord cells be classified?
Interneurons
Projection neurons
What % of spinal cord cells are interneurons?
97%
What is the role of interneurons?
Involved in modulating sensory input and motor output and make local connections with other cells in the spinal cord
What can interneurons be subdivided into?
Inhibitory and excitatory
What is the role of inhibitory neurones?
Limit receptive field size or activity of other neurones
What neurotransmitters do inhibitory neurones use?
GABA
glycine
enkephalin
{others}
What neurotransmitters do excitatory neurones use?
Glutamate
various neuropeptides
What is the role of excitatory neurones?
Their stimulation evokes action potentials in other cells
What % of spinal cord cells are projection neurons?
3%
What can projection neurons be subdivided into?
Axons of the ascending pathways (1%) Motor neurones (2%) - project from the spinal cord to innervate skeletal muscle and others