1. Brachial Plexus Formed by ventral rami of C5–C8 and T1
It gives rise to the nerves that innervate the upper limb
Skin, Shoulder Joint, Muscles

2. (a) Roots (rami C5 – T1), trunks, divisions, and cords
Roots (ventral rami): C4
Dorsal scapular C5
Nerve to
subclavius C6
Suprascapular
Upper
Posterior
divisions C7
Middle
Trunks
Lateral C8
Lower
Cords
Posterior T1
Long thoracic
Medial
Medial pectoral
Lateral pectoral
Axillary
Upper subscapular
Musculo-
cutaneous
Lower subscapular
Thoracodorsal
Radial
Medial cutaneous
nerves of the arm
and forearm
Median
Ulnar
(a) Roots (rami C5 – T1), trunks, divisions, and cords
Anterior
divisions
Posterior
divisions
Trunks
Roots
Figure 13.9 (a)

3. Musculocutaneous nerve Ulna Radius Ulnar nerve Median nerve
Axillary
nerve
Anterior
divisions
Posterior
divisions
Trunks
Roots
Humerus
Radial nerve
Musculocutaneous nerve
Ulna
Radius
Ulnar nerve
Median nerve
Radial nerve (superficial branch)
Dorsal branch of ulnar nerve
Superficial branch of ulnar nerve
Digital branch of ulnar nerve
Muscular branch
Median nerve
Digital branch
(c) The major nerves of the upper limb
Figure 13.9 (c)

4. Lumbar Plexus Arises from L1–L4
Innervates the thigh, abdominal wall, and psoas muscle
Femoral Nerve- Quadriceps
Obturator Nerve- adductor muscles

5. Ventral rami: Iliohypogastric L1 Ilioinguinal Femoral L2
Lateral femoral
cutaneous
Iliohypogastric
Ilioinguinal
Obturator L3
Genitofemoral
Anterior femoral
cutaneous
Lateral femoral
cutaneous
Saphenous L4
Obturator
Femoral L5
Lumbosacral
trunk
(a) Ventral rami and major branches
of the lumbar plexus
(b) Distribution of the major nerves from
the lumbar plexus to the lower limb
Figure 13.10

6. Sacral Plexus Arises from L4–S4
Serves the buttock, lower limb, pelvic structures, and perineum
Sciatic nerve
Longest and thickest nerve of the body
Innervates the hamstring muscles, adductor magnus, and most muscles in the leg and foot
Composed of two nerves: tibial and common fibular

7. Ventral rami and major branches of the sacral plexus
Superior
gluteal L5
Lumbosacral
trunk S1
Inferior
gluteal
Common
fibular S2
Tibial S3
Posterior
femoral
cutaneous S4
Pudendal S5
Sciatic
Co1
Ventral rami and major branches
of the sacral plexus
Figure (a)

8. (b) Distribution of the major nerves from
Superior gluteal
Inferior gluteal
Pudendal
Sciatic
Posterior femoral
cutaneous
Common fibular
Tibial
Sural (cut)
Deep fibular
Superficial fibular
Plantar branches
(b) Distribution of the major nerves from
the sacral plexus to the lower limb
Figure (b)

9. Reflexes
Inborn (intrinsic) reflex: a rapid, involuntary, predictable motor response to a stimulus
Learned (acquired) reflexes result from practice or repetition,
Example: driving skills

10. 1 2 3 4 5 Stimulus Skin Interneuron Receptor Sensory neuron
Integration center 4
Motor neuron 5
Effector
Spinal cord
(in cross section)
Figure 13.14

11. endings (type II fiber) Efferent (motor) fiber to muscle spindle
Secondary sensory
endings (type II fiber)
Efferent (motor)
fiber to muscle spindle
 Efferent (motor)
fiber to extrafusal
muscle fibers
Primary sensory
endings (type Ia
fiber)
Extrafusal muscle
fiber
Muscle spindle
Intrafusal muscle
fibers
Connective
tissue capsule
Sensory fiber
Golgi tendon
organ
Tendon
Figure 13.15

12. Muscle
spindle
Intrafusal
muscle fiber
Primary
sensory (la)
nerve fiber
Extrafusal
muscle fiber
Time
Time
(a) Unstretched
muscle. Action
potentials (APs)
are generated at
a constant rate in
the associated
sensory (la) fiber.
(b) Stretched
muscle. Stretching
activates the muscle
spindle, increasing
the rate of APs.
Figure 13.16a, b

13. The patellar (knee-jerk) reflex—a specific example of a stretch reflex2
Quadriceps (extensors) 3a 3b 3b 1
Patella
Muscle spindle
Spinal cord (L2–L4) 1
Tapping the patellar ligament excites muscle spindles in the quadriceps.
Hamstrings (flexors)
Patellar ligament 2
Afferent impulses (blue) travel to the spinal cord, where synapses occur with motor neurons and interneurons.
The motor neurons (red) send activating impulses to the quadriceps causing it to contract, extending the knee. 3a
+ –
Excitatory synapse Inhibitory synapse
The interneurons (green) make inhibitory synapses with ventral horn
neurons (purple) that prevent the antagonist muscles (hamstrings) from resisting the contraction of the quadriceps. 3b
Figure (2 of 2)

14. Superficial Reflexes Plantar reflex
Stimulus: stroking lateral aspect of the sole of the foot
Response: downward flexion of the toes
Tests for function of corticospinal tracts

15. Superficial Reflexes Babinski’s sign Stimulus: as above
Response: dorsiflexion of hallux and fanning of toes
Present in infants due to incomplete myelination
In adults, indicates corticospinal or motor cortex damage