Nervous System: Spinal Cord and Spinal Nerves Vocabulary

Comprehensive vocabulary terms and definitions covering spinal nerve plexuses, specific nerves, clinical injuries, reflex classifications, and spinal cord development based on the lecture.

Nerve plexus

A network of interweaving anterior rami of spinal nerves, grouped into four main pairs: cervical, brachial, lumbar, and sacral.

Intercostal nerves

Nerves located between the ribs, formed by the anterior rami of spinal nerves $T1–T11$.

Subcostal nerve

The $T12$ spinal nerve, located inferior to the ribs.

Cervical plexus

A network formed by the anterior rami of spinal nerves $C1–C4$, with some contribution from $C5$, innervating the neck, head, and shoulders.

Phrenic nerve

A nerve arising from the $C3–C5$ rami of the cervical plexus that innervates the diaphragm.

Brachial plexus

A network formed by the anterior rami of $C5–T1$ that extends from the neck into the axilla to innervate the upper limbs.

Axillary nerve

A terminal branch of the brachial plexus that innervates the deltoid and teres major muscles and receives sensory input from the superolateral arm.

Median nerve

A terminal branch of the brachial plexus that innervates most anterior forearm muscles, thenar muscles, and lateral lumbricals.

Musculocutaneous nerve

A terminal branch of the brachial plexus that innervates anterior arm muscles, such as the biceps brachii.

Radial nerve

A terminal branch of the brachial plexus that innervates posterior arm and forearm muscles and receives sensory input from the posterior arm, forearm, and dorsolateral hand.

Ulnar nerve

A terminal branch of the brachial plexus that innervates anterior forearm muscles, most intrinsic hand muscles, and provides sensory input for the two medial fingers.

Crutch palsy

An injury to the posterior cord, affecting the axillary and radial nerves, which may be caused by the improper use of crutches.

Lumbar plexus

A network formed by the anterior rami of spinal nerves $L1–L4$.

Femoral nerve

The main nerve in the posterior division of the lumbar plexus that innervates the anterior thigh muscles and the sartorius.

Obturator nerve

The main nerve in the anterior division of the lumbar plexus that innervates the medial thigh muscles.

Sacral plexus

A network formed by the anterior rami of spinal nerves $L4–S4$.

Sciatic nerve

The largest and longest nerve in the body, composed of the tibial division and the common fibular division.

Tibial nerve

A division of the sciatic nerve that innervates the hamstrings and splits into the lateral and medial plantar nerves.

Common fibular nerve

A division of the sciatic nerve that innervates the short head of the biceps femoris and splits into the deep and superficial fibular nerves.

Sciatica

An injury to the sciatic nerve characterized by extreme pain down the posterior thigh and leg, often caused by a herniated intervertebral disc.

Reflexes

Rapid, preprogrammed, involuntary responses of muscles or glands to a stimulus.

Reflex arc

The neural pathway responsible for generating a reflex response, typically involving a sensory receptor, sensory neuron, integration center, motor neuron, and effector.

Monosynaptic reflex

A reflex involving direct communication between a sensory neuron and a motor neuron with only one synapse.

Polysynaptic reflex

A reflex that utilizes one or more interneurons between the sensory and motor neurons.

Ipsilateral reflex

A reflex where the sensory receptor and the effector organ are on the same side of the body.

Contralateral reflex

A reflex where the sensory receptor and the effector organ are on opposite sides of the body.

Muscle spindle

A proprioceptor that detects stretch in a muscle, containing intrafusal muscle fibers innervated by gamma motor neurons.

Stretch reflex

A monosynaptic, somatic reflex that causes reflexive contraction of a muscle after it is stretched.

Tendon reflex (Golgi tendon reflex)

A polysynaptic reflex that prevents muscles from contracting excessively by causing the muscle to relax when tension is too high.

Withdrawal (flexor) reflex

A polysynaptic reflex that pulls a body part away from a painful stimulus by contracting flexor muscles.

Crossed-extensor reflex

A reflex occurring with the withdrawal reflex where interneurons excite extensor motor neurons on the opposite side to support body weight.

Clonus

Rhythmic oscillating movements observed during reflex testing that may indicate damage to the brain or spinal cord.

Sulcus limitans

A horizontal groove in the lateral walls of the neural canal that serves as the dividing point between the basal and alar plates.

Basal plates

Structures anterior to the sulcus limitans that develop into the anterior and lateral horns and the anterior gray commissure.

Alar plates

Structures posterior to the sulcus limitans that develop into the posterior horns and the posterior gray commissure.