Spinal Cord — Revision Notes

⚡ 30-Second Revision

Location: — Medulla oblongata to L1/L2.
Protection: — Vertebral column, Meninges (Dura, Arachnoid, Pia), CSF in subarachnoid space.
Internal Structure: — Central Grey Matter ('H'-shaped, cell bodies), Peripheral White Matter (myelinated axons, tracts).
Grey Matter Horns: — Anterior (motor), Posterior (sensory), Lateral (autonomic, T1-L2).
White Matter Tracts: — Ascending (sensory to brain), Descending (motor from brain).
Spinal Nerves: — 31 pairs, mixed (sensory + motor).
Roots: — Dorsal (sensory, DRG), Ventral (motor).
Functions: — Conduction pathway, Reflex center.
Reflex Arc: — Receptor $\rightarrow$ Afferent neuron $\rightarrow$ Integration center $\rightarrow$ Efferent neuron $\rightarrow$ Effector.
Monosynaptic Reflex: — Direct synapse between sensory and motor neuron (e.g., stretch reflex).
Polysynaptic Reflex: — Involves interneurons (e.g., withdrawal reflex).

2-Minute Revision

The spinal cord is the vital link between your brain and body, extending from the brainstem to the lumbar region, protected by the vertebral column, meninges, and cerebrospinal fluid (CSF). Its internal structure features a central 'H'-shaped grey matter, rich in neuron cell bodies, responsible for processing and integration.

This grey matter is surrounded by white matter, composed of myelinated axons organized into ascending (sensory) tracts carrying information to the brain, and descending (motor) tracts relaying commands from the brain.

Thirty-one pairs of mixed spinal nerves emerge, each with a sensory dorsal root and a motor ventral root. Beyond being a mere conduit, the spinal cord is a crucial reflex center, mediating rapid, involuntary responses via reflex arcs.

These arcs can be monosynaptic (direct sensory-motor connection, like the knee-jerk) or polysynaptic (involving interneurons, like the withdrawal reflex). Key concepts for NEET include identifying structures in a cross-section, understanding the functions of different tracts and horns, and knowing the components and types of reflex arcs.

5-Minute Revision

Let's consolidate the crucial aspects of the spinal cord for NEET. This cylindrical nervous tissue, roughly 45 cm long, is the central communication hub. It's meticulously protected by the bony vertebral column, three meningeal layers (dura, arachnoid, pia mater), and the cushioning cerebrospinal fluid (CSF) found in the subarachnoid space. Remember the spinal cord terminates as the conus medullaris, from which the filum terminale anchors it, and below which lies the cauda equina (nerve roots).

In cross-section, the spinal cord reveals a distinct internal organization. The central 'H'-shaped region is the grey matter, packed with neuron cell bodies, dendrites, and unmyelinated axons. Its subdivisions are critical: the anterior (ventral) horns house somatic motor neuron cell bodies, the posterior (dorsal) horns receive sensory input and contain interneurons, and the lateral horns (T1-L2/L3) contain autonomic (sympathetic) neuron cell bodies.

The surrounding white matter consists of myelinated axons bundled into tracts or columns. Ascending tracts (e.g., spinothalamic, dorsal columns) carry sensory information up to the brain, while descending tracts (e.

g., corticospinal) relay motor commands from the brain down to muscles.

Thirty-one pairs of spinal nerves emerge, each a mixed nerve formed by the union of a dorsal (sensory) root (with its dorsal root ganglion containing sensory neuron cell bodies) and a ventral (motor) root. These nerves form plexuses (cervical, brachial, lumbar, sacral) for limb innervation.

Crucially, the spinal cord is a reflex center. A reflex arc is the neural pathway for involuntary, rapid responses. It involves a receptor, afferent neuron, integration center (spinal cord), efferent neuron, and effector.

Differentiate between monosynaptic reflexes (one synapse, sensory directly to motor, e.g., stretch reflex) and polysynaptic reflexes (involving one or more interneurons, e.g., withdrawal reflex).

For NEET, be prepared for diagram identification, functional questions on tract damage, and detailed questions on reflex arc components.

Prelims Revision Notes

The spinal cord is a vital part of the CNS, extending from the medulla oblongata to L1/L2. It has two enlargements: cervical (for upper limbs) and lumbar (for lower limbs). The conus medullaris is its tapering end, from which the filum terminale (pia mater extension) anchors it to the coccyx. Below L2, the nerve roots form the cauda equina.

Protection:

1
Vertebral Column: — Bony encasement.
2
Meninges: — Dura mater (outer, tough), Arachnoid mater (middle, web-like), Pia mater (inner, adheres to cord).
3
Spaces: — Epidural space (fat, blood vessels), Subdural space (potential), Subarachnoid space (CSF).
4
Cerebrospinal Fluid (CSF): — Cushions, nourishes, removes waste; found in subarachnoid space and central canal.

Internal Structure (Cross-section):

Grey Matter (Central, 'H'-shaped): — Contains neuron cell bodies, dendrites, unmyelinated axons.

* Anterior (Ventral) Horns: Somatic motor neuron cell bodies. * Posterior (Dorsal) Horns: Sensory neuron terminals, interneurons. * Lateral Horns: Autonomic (sympathetic) neuron cell bodies (T1-L2/L3). * Grey Commissure: Connects halves of grey matter, surrounds central canal. * Central Canal: CSF-filled, runs longitudinally.

White Matter (Peripheral): — Myelinated axons organized into tracts/columns.

* Ascending Tracts: Carry sensory info to brain (e.g., spinothalamic for pain/temp, dorsal columns for touch/proprioception). * Descending Tracts: Carry motor commands from brain (e.g., corticospinal for voluntary movement).

Spinal Nerves:

31 pairs: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal.
Mixed Nerves: — Each contains both sensory (afferent) and motor (efferent) fibers.
Dorsal Root: — Sensory fibers; cell bodies in Dorsal Root Ganglion (DRG).
Ventral Root: — Motor fibers; cell bodies in anterior horn.
Plexuses: — Networks of spinal nerves (cervical, brachial, lumbar, sacral) for limb innervation.

Functions:

1
Conduction Pathway: — Bidirectional transmission of sensory and motor signals.
2
Reflex Center: — Mediates rapid, involuntary responses (reflexes).

Reflex Arc:

Components: — Receptor $\rightarrow$ Afferent neuron $\rightarrow$ Integration center (spinal cord) $\rightarrow$ Efferent neuron $\rightarrow$ Effector.
Monosynaptic: — One synapse (sensory $\rightarrow$ motor); e.g., stretch reflex (knee-jerk).
Polysynaptic: — Involves interneurons; e.g., withdrawal reflex.

Vyyuha Quick Recall

Super Protected Inside Nerve Architecture Located Centrally Organizes Reflexes Diligently.

Sensory (Dorsal) Motor (Ventral) - 'SAME DAVE' (Sensory Afferent Motor Efferent, Dorsal Afferent Ventral Efferent) for nerve roots.