W12 L9
Lecture 9 – The peripheral nervous system,
lower limb plexuses, terminal branches and
compartmentalisation
CHI108 W12 L9 flashcards
Learning objectives
1. Identify the neural make up (spinal nerve root levels) and the structural arrangement of the
identified plexus
2. Describe the anatomical courses and pathways of the terminal branches
3. Review the muscles that reside in each compartment and the nerve supply to each compartment
__________________________________________________________________________________
Putting the PNS into perspective
• Sensory: input, afferent cutaneous innervation and proprioceptive information
• All the nervous system does is sense information from the internal and external environment and
inform the CNS that change has occurred
• Motor: output, efferent motor innervation
• The CNS then responds to the stimulus at either the cord level (reflex) or alternatively at higher
levels, the brainstem, cerebellum, basal ganglia, thalamus or cerebrum
Spinal enlargements
Spinal enlargements
• Spinal cord enlargements are the direct consequence of increased quantities of grey matter
(lower motor neurons, interneurons and afferent input) at those specific segmental levels
• The enlargements of the spinal cord supply the quantity of neural machinery necessary to
operate the limbs
• Distally the second enlargement is the lumbar enlargement from (T11) L2 to S2, which controls
and coordinates bilaterally the upper limb muscles (maximum circumference 33 mm)
• The reason behind the enlargement of the lumbar region is because of the increased neural input
and output to the lower limbs
The lumbar plexus
• It forms the proximal (superior) part of the larger lumbosacral plexus
• It is formed by the first four lumbar nerves L1 to L4 and from contributions of T12
• Additionally, L4 spinal nerve supplies communicating branches known as the lumbosacral trunk
to the sacral plexus
• The plexus forms lateral to the intervertebral foramina and passes through psoas major
• Its smaller motor branches are distributed directly to psoas major, while the larger branches leave
the psoas major at various sites to run obliquely down through the pelvis
• These branches leave under the inguinal ligament with the exception of the obturator nerve which
exits the pelvis through the obturator foramen
• The nerves of the lumbar plexus pass in front of the hip joint and mainly support the anterior and
medial compartments of the thigh
• The lumbar plexus has both and anterior division - obturator n. L2 to 4 and posterior division -
femoral n. L2 to 4
Femoral nerve / posterior division
Lumbar plexus
• The largest and longest nerve of the lumbar plexus supplying skin on the upper thigh and inner
leg, and the muscles that extend the knee
• Femoral nerve (L2, L3, and L4) is the major nerve supplying the anterior compartment of thigh
• In the thigh it divides into numerous sensory and muscular branches and the saphenous nerve,
its long sensory terminal branch which continues down to the foot
• In the pelvis it runs in between psoas major and iliacus giving off branches to both muscles
• The nerve enters the anterior compartment by passing beneath the inguinal ligament, just lateral
to the femoral artery
• In the thigh, the nerve lies in a groove between iliacus muscle and psoas major muscles and after
a short course of about 4 cm, the nerve divides
• Branches of the femoral n. innervate
○ Pectineus
○ Sartorius
○ Rectus femoris
○ Vastus medialis, vastus lateralis and the vastus intermedius
Obturator nerve / anterior division
• The obturator nerve (L2, L3, and L4) arises from the lumbar plexus, the branch derived from the
L3 spinal nerve is the largest, while that from L2 is often very small
• The obturator nerve is responsible for the sensory innervation of the skin of the medial aspect of Femoral nerve and obturator nerve
the thigh via its cutaneous branch
• It descends through the fibres of the psoas major, and emerges from its medial border near the
superior pelvic aperture (brim) of the pelvis
• It then passes behind the common iliac arteries, and runs along the lateral wall of the lesser
pelvis to the upper part of the obturator foramen
• Here it enters the thigh, through the obturator canal, within the obturator membrane and
innervates the muscles of the medial compartment of the thigh
• Branches of the obturator n. innervate
CHI108 Page 1
Lecture 9 – The peripheral nervous system,
lower limb plexuses, terminal branches and
compartmentalisation
CHI108 W12 L9 flashcards
Learning objectives
1. Identify the neural make up (spinal nerve root levels) and the structural arrangement of the
identified plexus
2. Describe the anatomical courses and pathways of the terminal branches
3. Review the muscles that reside in each compartment and the nerve supply to each compartment
__________________________________________________________________________________
Putting the PNS into perspective
• Sensory: input, afferent cutaneous innervation and proprioceptive information
• All the nervous system does is sense information from the internal and external environment and
inform the CNS that change has occurred
• Motor: output, efferent motor innervation
• The CNS then responds to the stimulus at either the cord level (reflex) or alternatively at higher
levels, the brainstem, cerebellum, basal ganglia, thalamus or cerebrum
Spinal enlargements
Spinal enlargements
• Spinal cord enlargements are the direct consequence of increased quantities of grey matter
(lower motor neurons, interneurons and afferent input) at those specific segmental levels
• The enlargements of the spinal cord supply the quantity of neural machinery necessary to
operate the limbs
• Distally the second enlargement is the lumbar enlargement from (T11) L2 to S2, which controls
and coordinates bilaterally the upper limb muscles (maximum circumference 33 mm)
• The reason behind the enlargement of the lumbar region is because of the increased neural input
and output to the lower limbs
The lumbar plexus
• It forms the proximal (superior) part of the larger lumbosacral plexus
• It is formed by the first four lumbar nerves L1 to L4 and from contributions of T12
• Additionally, L4 spinal nerve supplies communicating branches known as the lumbosacral trunk
to the sacral plexus
• The plexus forms lateral to the intervertebral foramina and passes through psoas major
• Its smaller motor branches are distributed directly to psoas major, while the larger branches leave
the psoas major at various sites to run obliquely down through the pelvis
• These branches leave under the inguinal ligament with the exception of the obturator nerve which
exits the pelvis through the obturator foramen
• The nerves of the lumbar plexus pass in front of the hip joint and mainly support the anterior and
medial compartments of the thigh
• The lumbar plexus has both and anterior division - obturator n. L2 to 4 and posterior division -
femoral n. L2 to 4
Femoral nerve / posterior division
Lumbar plexus
• The largest and longest nerve of the lumbar plexus supplying skin on the upper thigh and inner
leg, and the muscles that extend the knee
• Femoral nerve (L2, L3, and L4) is the major nerve supplying the anterior compartment of thigh
• In the thigh it divides into numerous sensory and muscular branches and the saphenous nerve,
its long sensory terminal branch which continues down to the foot
• In the pelvis it runs in between psoas major and iliacus giving off branches to both muscles
• The nerve enters the anterior compartment by passing beneath the inguinal ligament, just lateral
to the femoral artery
• In the thigh, the nerve lies in a groove between iliacus muscle and psoas major muscles and after
a short course of about 4 cm, the nerve divides
• Branches of the femoral n. innervate
○ Pectineus
○ Sartorius
○ Rectus femoris
○ Vastus medialis, vastus lateralis and the vastus intermedius
Obturator nerve / anterior division
• The obturator nerve (L2, L3, and L4) arises from the lumbar plexus, the branch derived from the
L3 spinal nerve is the largest, while that from L2 is often very small
• The obturator nerve is responsible for the sensory innervation of the skin of the medial aspect of Femoral nerve and obturator nerve
the thigh via its cutaneous branch
• It descends through the fibres of the psoas major, and emerges from its medial border near the
superior pelvic aperture (brim) of the pelvis
• It then passes behind the common iliac arteries, and runs along the lateral wall of the lesser
pelvis to the upper part of the obturator foramen
• Here it enters the thigh, through the obturator canal, within the obturator membrane and
innervates the muscles of the medial compartment of the thigh
• Branches of the obturator n. innervate
CHI108 Page 1
