lab 10

Superior Extent of Spinal Cord

Begins at the foramen magnum of the occipital bone as a continuation of the brainstem.

Inferior Extent of Spinal Cord

Ends at the conus medullaris (medullary cone) around the level of the L1

Cauda Equina Definition

Bundle of lumbar, sacral, and coccygeal spinal nerve roots located at the distal end of the vertebral canal, resembling a horse's tail.

Filum Terminale Structure and Function

Fibrous extension of the pia mater extending from the conus medullaris down to the posterior coccyx to anchor the spinal cord vertically.

Gray Matter Composition

Inner butterfly

Gray Commissure Function

Central bridge of gray matter surrounding the central canal that connects the left and right sides of the spinal cord.

Central Canal Function

Narrow central cavity of the spinal cord continuous with the brain's ventricular system containing cerebrospinal fluid (CSF).

White Matter Composition

Outer region of the spinal cord composed of myelinated axon tracts organized into posterior, lateral, and anterior funiculi (columns).

Ascending Tracts Function

White matter pathways that transmit sensory information superiorly up to the brain.

Descending Tracts Function

White matter pathways that transmit motor commands inferiorly from the brain down to peripheral effectors.

Dorsal Horn Classification and Content

Sensory; posterior gray matter region containing cell bodies of interneurons that process incoming sensory input.

Ventral Horn Classification and Content

Motor; anterior gray matter region containing cell bodies of somatic motor neurons supplying skeletal muscles.

Lateral Horn Location and Content

Found only in thoracic and upper lumbar regions (T1

Dorsal Root Content and Classification

Purely sensory; contains axon fibers of sensory neurons carrying input into the spinal cord.

Dorsal Root Ganglion Content and Classification

Purely sensory; enlarged region on the dorsal root containing cell bodies of sensory neurons outside the CNS.

Ventral Root Content and Classification

Purely motor; contains axon fibers of motor neurons carrying output away from the spinal cord.

Spinal Nerve Formation and Classification

Mixed (both sensory and motor); formed by the fusion of the dorsal and ventral roots as they exit through the intervertebral foramen.

Dorsal Ramus Functional Distribution

Mixed nerve branch that innervates the skin and deep muscles of the posterior trunk (back).

Ventral Ramus Functional Distribution

Mixed nerve branch that innervates the anterior/lateral trunk; T2

Nerve Plexus Definition

Complex interwoven network of ventral rami (formed by all spinal nerves except T2

Cervical Plexus Spinal Levels and Key Nerve

Formed by C1 through C5 (or C1

Phrenic Nerve Target and Function

Arises from C3

Brachial Plexus Spinal Levels

Formed by C5 through T1 ventral rami; innervates the upper limb and shoulder girdle.

Musculocutaneous Nerve Target

Brachial plexus nerve innervating anterior arm flexor muscles (biceps brachii, brachialis, coracobrachialis) and lateral forearm skin.

Axillary Nerve Target

Brachial plexus nerve innervating the deltoid and teres minor muscles of the shoulder joint.

Radial Nerve Target

Brachial plexus nerve innervating posterior arm and forearm extensor muscles (triceps brachii, brachioradialis, wrist extensors).

Median Nerve Target

Brachial plexus nerve innervating flexor muscles of the anterior forearm, lateral palm, and lateral 3.5 digits.

Ulnar Nerve Target

Brachial plexus nerve innervating flexor carpi ulnaris, medial flexor digitorum profundus, and intrinsic hand muscles.

Lumbar Plexus Spinal Levels

Formed by L1 through L4 ventral rami; innervates the anterior/medial thigh and lower abdominal wall.

Femoral Nerve Target

Lumbar plexus nerve innervating anterior thigh muscles (quadriceps femoris, rectus femoris, sartorius, iliacus) and anterior knee/thigh skin.

Obturator Nerve Target

Lumbar plexus nerve innervating medial thigh adductor muscles (adductor longus, brevis, magnus, gracilis).

Sacral Plexus Spinal Levels

Formed by L4 through S4 (or Co1) ventral rami; innervates the gluteal region, posterior thigh, leg, and foot.

Sciatic Nerve Structure and Significance

Largest nerve in the human body; encased in a sheath that splits into the tibial and common fibular (peroneal) nerves.

Superior Gluteal Nerve Target

Sacral plexus nerve innervating upper hip muscles (gluteus medius and gluteus minimus).

Inferior Gluteal Nerve Target

Sacral plexus nerve innervating the main buttock muscle (gluteus maximus).

Tibial Nerve Target

Sciatic nerve branch innervating posterior thigh hamstrings, calf muscles (gastrocnemius, soleus), and sole of foot.

Common Fibular (Peroneal) Nerve Target

Sciatic nerve branch innervating anterior and lateral leg muscles (tibialis anterior, fibularis longus) and dorsum of foot.

Definition of a Reflex

Rapid, predictable, involuntary motor response to a specific sensory stimulus.

Five Components of a Reflex Arc in Order

1. Receptor 2. Sensory Neuron (Afferent) 3. Integration Center (Interneuron in CNS) 4. Motor Neuron (Efferent) 5. Effector (Muscle or Gland).

Patellar Tendon Reflex Spinal Level and Nerve

Tested at spinal levels L2, L3, L4 via the Femoral nerve (quadriceps contraction).

Biceps Tendon Reflex Spinal Level and Nerve

Tested at spinal levels C5, C6 via the Musculocutaneous nerve (biceps brachii contraction).

Achilles Tendon Reflex Spinal Level and Nerve

Tested at spinal levels S1, S2 via the Tibial nerve (plantar flexion of foot).

Triceps Tendon Reflex Spinal Level and Nerve

Tested at spinal levels C7, C8 via the Radial nerve (triceps brachii extension).

Babinski (Plantar) Reflex Spinal Level and Terminal Nerve

Tested at spinal levels S1, S2 via the Sciatic/Tibial nerve.

Normal Adult Plantar Reflex Response

Negative Babinski sign; curling of the toes downward (plantar flexion).

Pathological Adult Babinski Sign Response and Significance

Positive Babinski sign; dorsiflexion of big toe and fanning of lateral toes, indicating an Upper Motor Neuron (UMN) lesion or corticospinal tract damage (normal only in infants).

Pupillary Reflex Classification and Nerves

Cranial reflex (NOT a spinal cord reflex); uses Cranial Nerve II (Optic) for sensory input and Cranial Nerve III (Oculomotor) for motor output.

Location and Function of Satellite Cells

Located in the Peripheral Nervous System (PNS) surrounding neuronal cell bodies in ganglia; they regulate the intercellular chemical environment (similar to astrocytes in the CNS).

Location and Function of Schwann Cells

Located in the Peripheral Nervous System (PNS); they wrap around outstretching neuronal axons to form the insulating myelin sheath, increase neurotransmission speed, and insulate the cell.

Nodes of Ranvier

Gaps within the myelin sheath between adjacent Schwann cells along a peripheral axon.

Saltatory Conduction

Rapid propagation of an action potential along a myelinated axon where the nerve impulse jumps from one Node of Ranvier to the next.

Neuroglia Essential for Peripheral Fiber Regeneration

Schwann cells; they are essential for the regeneration and guiding of damaged peripheral nerve fibers.

Endoneurium Layer and Target

Innermost connective tissue layer that directly covers an individual nerve axon.

Perineurium Layer and Target

Middle connective tissue layer that wraps around a group of axons to form bundles called fascicles.

Epineurium Layer and Target

Outermost dense connective tissue layer that wraps around all fascicles and binds them together to form a whole nerve.

Blood Vessels in Epineurium vs Perineurium/Endoneurium

Epineurium contains larger arteries and veins; perineurium and endoneurium contain smaller arterioles, venules, and capillaries supplying individual fascicles and axons.

Connection of the Spinal Cord

The spinal cord connects the brain and the peripheral nervous system (PNS).

Reason Spinal Cord is the Center for Reflex Activity

It contains interneurons (association neurons) that integrate incoming sensory information and directly trigger motor output locally without requiring brain involvement.

Protective Coverings of the Spinal Cord

The spinal cord is surrounded and protected by meninges (dura mater, arachnoid mater, and pia mater) and cerebrospinal fluid (CSF).

Landmark for Start of Spinal Cord

Begins at the foramen magnum of the occipital bone as a continuation of the brainstem.

Landmark for End of Spinal Cord

Terminates at the conus medullaris (medullary cone) around the level of the L1

Cauda Equina Meaning and Contents

Latin for "horse's tail"; a tail

Filum Terminale Structure and Function

A fibrous thread

Total Number of Spinal Nerves

31 pairs of mixed spinal nerves.

Number of Spinal Nerves at Each Level

8 Cervical (C1

Special Feature of C8 Spinal Nerve

There are 8 pairs of cervical spinal nerves (C1

Dermatome Definition

A specific region or area of skin innervated by sensory nerve fibers from a single pair of spinal nerves.

Myotome Definition

A group or collection of skeletal muscles innervated by motor nerve fibers from a single spinal nerve.

General Dermatome and Myotome Regions

T2

Loss of Feeling with Good Motor Function Diagnosis

A dermatome issue, indicating damage to sensory pathways or dorsal roots rather than motor pathways (myotomes).

Mechanism of the Reflex Arc

A sensory receptor detects a stimulus

Patellar Tendon Reflex Test Details

Tests spinal nerve levels L2, L3, L4 via the Femoral nerve, causing quadriceps contraction and extension of the knee.

Biceps Tendon Reflex Test Details

Tests biceps brachii contraction and flexor function; mediated by spinal nerve levels C5 and C6 via the Musculocutaneous nerve.

Achilles Tendon Reflex Test Details

Tests plantar flexion of the foot; mediated by spinal nerve levels S1 and S2 via the Tibial nerve.

Triceps Tendon Reflex Test Details

Tests triceps brachii extension; mediated by spinal nerve levels C7 and C8 via the Radial nerve.

Babinski Reflex Test Details

Tested at spinal levels S1 and S2 via the Sciatic nerve (Tibial branch); normal adult response is plantar flexion (curling toes down), while a positive Babinski sign (dorsiflexion of big toe and fanning of toes) in adults indicates an Upper Motor Neuron (UMN) lesion.

Pupillary Reflex Classification and Nerves

A Cranial Reflex (NOT a spinal cord reflex); uses Cranial Nerve II (Optic) for sensory input and Cranial Nerve III (Oculomotor) for motor output.