Transcript Neuroanatomy , the nerve plexuses

Neuro-anatomy
Nerve Plexuses
By
Khaled Na3im
The C.N.S = Brain + Spinal Cord
• C.N.S tissue is enclosed within the skull
and vertebral column
• The C.N.S.is protected by bones,
meninges, and cerebrospinal fluid (CSF)
• Epidural space is the space between the
bones and the Dural sheath (dura mater)
THE MENINGES
• The meninges are a set of 3 connective
tissue layers that surround the brain and
spinal cord.
– The dura mater – toughest & outermost
– The arachnoid mater – middle layer
containing most major blood vessels and
cerebrospinal fluid.
– The pia mater – inner most layer with fine
blood vessels.
Meninges
Spinal Cord
• Cervical and lumbosacral
enlargements – sites
where nerves serving the
limbs emerge
• Conus medullaris –
terminal portion of the
spinal cord
• Cauda equina –
collection of nerve roots
at the inferior end of the
vertebral canal
• Spinal nerves – 31 pairs
Spinal Gray Matter
• Gray matter consists of neurons, unmyelinated
processes, and neuroglia
• Gray commissure – connects masses of gray
matter; encloses central canal
• Posterior (dorsal) horns – interneurons (sensory)
• Anterior (ventral) horns – some interneurons but
mostly somatic motor neurons
• Lateral horns – contain autonomic nerve fibers
Gray Matter and Spinal Roots
Cross Section of Spinal Cord
Reflex Arc
• Basic functional unit of nervous system and simplest
portion capable of receiving a stimulus and producing a
response
• Automatic response to stimulus, occurs without
conscious thought.
• Components
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–
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Action potentials produced in sensory receptors transmitted to
Sensory neuron. ToInterneurons. ToMotor neuron. ToEffector organ which responds with a reflex
Variety of Reflexes
• Some integrated within spinal cord; some
within brain
• Some involve excitatory neurons yielding a
response; some involve inhibitory neurons
that prevent an action
• Higher brain centers can influence,
suppress, or exaggerate reflex
responses
Spinal Nerve Organization
• Dorsal half – sensory roots
and ganglia
• Ventral half – motor roots
• Dorsal & ventral roots fuse
laterally to form spinal nerves
Cross-Sectional Anatomy of Spinal
Cord
Spinal Nerves
• 31 pairs of mixed nerves supply all parts of
body except head
• Named according to their point of issue
– 8 cervical (C1-C8)
– 12 thoracic (T1-T12)
– 5 Lumbar (L1-L5)
– 5 Sacral (S1-S5)
– 1 Coccygeal (C0)
Spinal Nerve
• Each spinal nerve connects to the spinal
cord via two medial roots
• Each root forms a series of rootlets that
attach to the spinal cord
• Ventral roots arise from the ventral horn
and contain motor (efferent) fibers
• Dorsal roots arise from sensory neurons
in the dorsal root ganglion and contain
sensory (afferent) fibers
Spinal Nerves: Roots
Nerve Plexuses
• All ventral rami except T2-T12 form interlacing
networks called plexuses
• Plexuses are found in the:
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cervical,
brachial,
lumbar,
and sacral regions
• Each resulting branch of a plexus contains fibers
from several spinal nerves
• Each muscle receives a nerve supply from more
than one spinal nerve
• Damage to one spinal segment cannot completely
paralyze a muscle
Cervical Plexus
• The cervical plexus is formed by ventral
rami of C1-C4
• Most branches are cutaneous nerves of
the neck, ear, back of head, and shoulders
• The most important nerve of this plexus is
the phrenic nerve - the major motor and
sensory nerve of the diaphragm
Cervical Plexus
Figure 13.8
Brachial Plexus
• Formed by ventral rami of C5-C8 and T1 (C4 and
T2 may also contribute to this plexus)
• It gives rise to the nerves that innervate the
upper limb ( except trapezes is supplied by
accessory nerve and skin of tip of shoulder )
• The major ones :
– Axillary n.
- Nerve to serratus ant.
– Radial n.
- Nerve to L.D.
– Musculocutaneous n.
– Ulnar n.
- Median n.
Brachial Plexus
• C4 from cervical plus C5-T1
• Five ventral rami form
• three trunks that separate into
six divisions then form
• three cords that give rise to:
• Branches/nerves
– Axillary
– Radial
– Musculocutaneous
– Ulnar
– Median
– Smaller nerves, too.
Brachial Plexus: Distribution of Nerves
Lumbosacral Plexus
(Lumbar and Sacral Plexuses)
• Arises from L1-L4 & L4-S4 and innervates the
thigh, abdominal wall, psoas muscle, the
buttock, lower limb, pelvic structures, and the
perineum
• The major nerves are the
– Femoral (Lumbar)
– Obturator (Lumbar)
– Sciatic (Sacral)
• Tibial
• Common fibular (peroneal)
Questions
Which of the following is NOT a nerve
plexus?
A. The thoracic rami
B. The lumbosacral plexus
C. The cervical plexus
D. The brachial plexus
Questions
Which of the following nerves does NOT
arise from the brachial plexus?
A. The musculocutaneous nerve
B. The radial nerve
C. The axillary nerve
D. The ulnar nerve
E. The phrenic nerve
Questions
The muscle fiber or gland cell that responds
to the efferent impulses is known as the
A. Effector
B. Motor neuron
C. Integration center
D. Sensory neuron
E. Receptor
Questions
The basic pattern of the CNS in the spinal
cord is a central cavity surrounded by a
gray matter core and a white matter layer
lying outside of that.
True
False
Questions
Although the pairs of spinal nerves
correspond to the number of vertebrae in
the each area, there are eight pairs of
cervical cranial nerves, but only seven
cervical vertebrae.
True
False
Questions
Each muscle in a limb receives its nerve
supply from one spinal nerve.
True
False
Questions
A sensory nerve transmits afferent impulses
to the CNS.
True
False