Nerve Plexuses & Reflex Actions

Nerve Plexuses:

• A nerve plexus is a complex network of intersecting nerves that combine and redistribute nerve fibers from multiple spinal nerves.

• These networks enable the sharing of sensory input and motor output across several spinal nerves, providing redundancy and diversification of functions.

• There are four major nerve plexuses in the human body:

  

  illustration of nerve plexuses, showing the complex network of intersecting nerves and their sensory and motor functions

1. Cervical Plexus (C1-C4):

• Located in the neck, supplies muscles and skin of the neck and head.

• Includes the phrenic nerve, crucial for diaphragm function and breathing

2. Brachial Plexus (C5-T1):

• Located in the shoulder; innervates the upper limbs (shoulder, arm, forearm, hand).

• Major nerves: median, ulnar, radial, axillary, and musculocutaneous nerves.

3. Lumbar Plexus (L1-L4):

• Located in the lower back; supplies the lower abdomen, groin, and anterior thigh.

• Major nerves: femoral and obturator nerves.

4. Sacral Plexus (L4-S4):

• Located in the pelvis; innervates the buttocks, posterior thigh, leg, and foot.

• Major nerve: sciatic nerve, the largest in the body.

Reflex Actions:

• A reflex action is a fast, involuntary response to stimuli that bypasses the brain and follows a reflex arc. It involves:

  1. Receptor: Detects stimulus (pain, pressure, etc.).

  2. Sensory Neuron: Carries the signal to the spinal cord.

  3. Integration Center: Processes information in the spinal cord.

  4. Motor Neuron: Sends the response to the effector.

  5. Effector: Carries out the response (muscle contraction or gland secretion).