ANAT20006 Lecture Notes - Lecture 7: Peripheral Nervous System, Dorsal Root Ganglion, List Of Lumbar Nerves
12 Jun 2018
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LECTURE 7
NEUROANATOMY (2)
TODAY
•Organisation of the peripheral nervous system
•Efferents, afferents and nerves
•Somatic versus Autonomic divisions
•Segmental innervation
PNS
•(1) Axons in the periphery cluster together to form
nerves - collections of thousands of individual
axons within a common external connective tissue
sheath (epineurium). Within the nerve axons are
sub-grouped into fascicles, surrounded by a
perineurial sheath.
•(2)
•(3) cranial nerves are from brain stem,
spinal nerves are from spinal
cord.
SPINAL CORD & NERVES
•(4) There are 31 pairs of spinal
nerves. Named according to what
region they belong to. Cervical
nerves are named C1-C8 etc.
There are 7 cervical vertebra and
yet 8 cervical nerves? This is
because the first one comes out
above the C1 and the rest come out below the respective
vertebra. Generally the nerves originate beneath the respective
vertebra except C1 which comes out of the top.
•31 pairs of spinal nerves:
•8 pairs of cervical nerves (C1-C8)
•12 pairs of thoracic nerves (T1 – T12)
•5 pairs of lumbar nerves (L1-L5)
•5 pairs of sacral nerves (S1-S5)
•1 pair of coccygeal nerves (Co1)
•(5) Complex.
In the lumbar
regions it is
complex again.
Lecture 7 - Monday 7 August 2017
ANAT20006 - HUMAN STRUCTURE & FUNCTION
4
5
•(6) spinal nerve = mixture of sensory and
motor fibres. The nerve is comprised
of both types of fibres. But at the
level of the spinal cord there is
separation of the motor and sensory
information. Peripheral nerve axons
can be either efferent (motor)
carrying signals from the CNS or
afferent (sensory) carrying signals to
the CNS.
•Separate spinal roots connect efferent
and afferent to the CNS.
EFFERENTS, AFFERENTS &
NERVES
•(7) dorsal roots with dorsal root ganglion.
•Efferent (blue) and afferent (red) axons segregate at
the point just before they contact the CNS (spinal
cord or brainstem): sensory axons join the CNS via a
dorsal (posterior) root, motor axons join at a ventral
(anterior) root.
•(9) can see the roots. This is a cervical level.
Can also see the dura mater folded back near
the forceps.
Lecture 7 - Monday 7 August 2017
ANAT20006 - HUMAN STRUCTURE & FUNCTION
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SPINAL CORD RAMI
•(11) anatomically what happens is the mixed spinal nerve branches again. It re splits into what is
called two rami, two branches, a ventral ramus and a posterior/dorsal ramus. Each spinal nerve
comes out and then splits to wrap around and supply the tissues in the front or back of your
body. This is different to the roots of the spinal cord which is separated; these are still mixed
nerves.
•(14) each section of the spinal cord innervates a
very specific section of the body. It is said to
innervate a dermatome; the area of skin
supplied by that segment. Derma = skin, tome
= slice. This is bc the body appears to be
made up of slices.
•A dermatome is an area of skin that is mainly
supplied by a single spinal nerve.
•A myotome is the group of muscles that a
single spinal nerve innervates.
•(15) can see C2 C3 C4 C5 and work your way
down.
•(16) Important clinically because if you damage a spinal nerve, Eg. T1, we would expect a loss of
sensation in the T1 dermatome.
Lecture 7 - Monday 7 August 2017
ANAT20006 - HUMAN STRUCTURE & FUNCTION
12
Document Summary
Today: organisation of the peripheral nervous system, efferents, afferents and nerves, somatic versus autonomic divisions, segmental innervation. Pns: (1) axons in the periphery cluster together to form nerves - collections of thousands of individual axons within a common external connective tissue sheath (epineurium). Within the nerve axons are sub-grouped into fascicles, surrounded by a perineurial sheath: (2, (3) cranial nerves are from brain stem, spinal nerves are from spinal cord. Spinal cord & nerves: (4) there are 31 pairs of spinal nerves. Named according to what region they belong to. This is because the first one comes out above the c1 and the rest come out below the respective vertebra. In the lumbar regions it is complex again. Lecture 7 - monday 7 august 2017: (6) spinal nerve = mixture of sensory and motor fibres. The nerve is comprised of both types of fibres.
