Human Anatomy & Physiology I Supplemental · Exam Block 5
Week 13 · Ch. 12–13 · Neural Tissue & Spinal Cord
Slide 1 of 14
Week 13 · Chapters 12 & 13
Neural Tissue & the Spinal Cord
Exam Block 5 opens the nervous system: first, the microscopic building block — the neuron and its support cells (Ch. 12) — then how billions of those neurons organize into the spinal cord and its 31 pairs of spinal nerves (Ch. 13). Next week continues with the brain; this week lays the foundation everything else builds on.
By the end of this week, you will be able to:
1Identify the structural parts of a neuron and their function
2Distinguish sensory, motor, and interneurons by direction of signal flow
3Match each neuroglial cell type to its job
4Describe the spinal cord's gray matter/white matter organization
5Trace a spinal nerve from dorsal/ventral roots to the periphery
6Walk through the five components of a reflex arc
Part 1 — Big Picture
The neuron: built to receive, conduct, and transmit
A neuron's shape mirrors its job. Dendrites receive incoming signals; the cell body integrates them; the axon — often wrapped in a segmented myelin sheath with gaps called Nodes of Ranvier — conducts the signal at high speed over distance; and axon terminals pass it on to the next cell. Every neuron in the body follows this same basic plan.
Part 1 — Vocabulary & Word Parts
Neural tissue roots
neur/o-nerve, neuron
Neuron = the basic conducting cell of the nervous system.
dendr/o-tree, branching
Dendrites branch out from the cell body like a tree's limbs.
ax/o-axis, main stem
The axon is the single main conducting fiber of the neuron.
-glia / gli/o-glue
Neuroglia = the "glue" cells that support neurons without conducting signals themselves.
syn-together, joined
A synapse is the junction where two neurons communicate.
-algiapain
Neuralgia = nerve pain, covered again in this week's clinical correlation.
Part 1 — Structure & Function
Three neuron types, sorted by signal direction
Neurons are classified by which way they carry information. Sensory (afferent) neurons carry signals from receptors toward the central nervous system (CNS). Motor (efferent) neurons carry signals from the CNS out to muscles and glands. Interneurons never leave the CNS — they connect sensory input to motor output, often adding layers of processing in between.
Part 1 — Structure & Function
Neuroglia: five support cells, five jobs
Glial cells outnumber neurons but don't conduct signals — each type has a specific support role instead. The two myelin-producing types are easy to mix up: oligodendrocytes myelinate axons in the CNS, while Schwann cells do the same job in the peripheral nervous system (PNS). That CNS-vs-PNS distinction is a common exam trap.
Part 1 — Clinical Correlation
Multiple sclerosis: when myelin is the target
This condition shows exactly why the myelin sheath from the Big Picture diagram matters functionally, not just structurally.
🩺 In practice
Multiple sclerosis (MS) is an autoimmune condition in which the immune system attacks and damages myelin in the CNS — the territory of oligodendrocytes specifically. Without an intact myelin sheath, signal conduction along the axon slows or fails entirely, producing the varied neurological symptoms (vision changes, muscle weakness, coordination problems) associated with MS, depending on which CNS pathways are affected.
Part 2 — Big Picture
Spinal cord cross-section: an H inside a column
Cut across the spinal cord, and you'll always see the same two-region pattern: an inner, butterfly/H-shaped core of gray matter (neuron cell bodies, organized into dorsal and ventral horns), surrounded by an outer ring of white matter (myelinated axon tracts carrying signals up and down the cord). This is the reverse of the brain's organization, where gray matter is on the outside.
Part 2 — Vocabulary & Word Parts
Spinal cord & spinal nerve roots
myel/o-spinal cord (also: bone marrow)
Myelin and the spinal cord share this root — context tells you which meaning applies.
radic/o- / rhiz/o-root
Radiculopathy = a pinched or damaged nerve root.
plex/o-network, braid
A nerve plexus is a braided network where spinal nerve roots intermix and reorganize.
quadri-four
Quadriplegia = paralysis affecting all four limbs.
para-beside, two similar parts
Paraplegia = paralysis of the two lower limbs.
-plegiaparalysis
Combined with a prefix, this suffix tells you exactly which body regions are affected.
Part 2 — Structure & Function
How a spinal nerve is built from two roots
Each of the 31 spinal nerve pairs forms the same way: a dorsal root carrying only sensory (incoming) fibers, and a ventral root carrying only motor (outgoing) fibers, join together just outside the cord. Once joined, every spinal nerve is mixed — carrying both sensory and motor information — which is why damage to a spinal nerve itself (versus just one root) affects both sensation and movement.
Part 2 — Structure & Function
The reflex arc: five stops, no brain required
A reflex is the body's fastest, most automatic response, and it follows this same five-step path every time: a receptor detects a stimulus, a sensory neuron carries that signal to the spinal cord, an integration center (often a single synapse) processes it, a motor neuron carries the response back out, and an effector (usually a muscle) acts. Because the signal never has to travel to the brain and back, reflexes are dramatically faster than a conscious decision.
Part 2 — Clinical Correlation
Spinal cord injury: why the level matters most
This connects directly to the quadriplegia/paraplegia vocabulary above and the white-matter tracts from the Big Picture diagram.
🩺 In practice
Because ascending and descending tracts run the full length of the cord, the level of a spinal cord injury — not just its severity — determines its effect. A cervical injury can affect all four limbs (quadriplegia) because it interrupts signals before they ever reach the arms. A lumbar injury, much lower on the cord, generally spares the arms and affects only the legs (paraplegia), since arm-controlling tracts branch off well above that level.
Your Turn — Connecting Ch. 12 & 13
Apply both chapters before the quiz
A patient has a severe injury at the C4 level of the spinal cord (mid-neck).
Question 1 — Based on the level of injury, what is the most likely outcome?
A cervical injury sits above the point where arm-controlling tracts branch off the cord, so signals to and from all four limbs are disrupted — producing quadriplegia rather than the leg-only paraplegia seen with lower, lumbar-level injuries.
Question 2 — At the cellular level, which structure being disrupted explains the loss of signal conduction?
The white matter tracts are the myelinated axon highways carrying signals up and down the cord. Damage at any single level severs those tracts for everything below it — the actual mechanism behind why level of injury predicts which body regions lose function.
Practice Quiz
8 questions across Ch. 12–13
Question 1
Which part of a neuron receives incoming signals?
Dendrites receive incoming signals. The axon conducts the signal away from the cell body, and axon terminals pass it on to the next cell.
Question 2
A neuron carrying a signal from a receptor toward the CNS is classified as:
Sensory (afferent) neurons carry signals toward the CNS. Motor neurons carry signals away from the CNS, and interneurons stay entirely within it.
Question 3
Which glial cell myelinates axons in the peripheral nervous system?
Schwann cells myelinate PNS axons. Oligodendrocytes do the same job in the CNS, and astrocytes support neurons without producing myelin.
Question 4
In a spinal cord cross-section, gray matter is located:
Spinal cord gray matter forms an inner, H-shaped core, surrounded by white matter tracts. This is the reverse of the brain, where gray matter is on the outside.
Question 5
The dorsal root of a spinal nerve carries:
The dorsal root carries only sensory fibers. The ventral root carries only motor fibers; the two combine into one mixed spinal nerve only after they join outside the cord.
Question 6
In the reflex arc, the integration center is typically located in the:
The integration center is typically in the spinal cord itself — that's precisely why reflexes are so fast: the signal doesn't have to travel all the way to the brain and back.
Question 7
"Quadriplegia" refers to paralysis of:
Quadri- means four, so quadriplegia affects all four limbs. Paralysis of only the legs is paraplegia instead.
Question 8
A cervical-level spinal cord injury typically affects more of the body than a lumbar-level injury because:
A cervical injury sits above where arm-controlling tracts branch off, so it disrupts signals to both arms and legs. Vertebral size and white matter presence (which exists at every level) aren't the deciding factors.
Score: 0 / 8
Quick-Reference Recap
Chapters 12–13 One-Page Summary
Everything from this week, condensed onto one page.
Ch. 12 — Neuron Parts
Dendrites — receive
Cell body — integrate
Axon (+ myelin) — conduct
Terminals — transmit
Ch. 12 — Neuron Types
Sensory (afferent) — in
Motor (efferent) — out
Interneuron — CNS only
Ch. 12 — Neuroglia
Oligodendrocytes = CNS myelin. Schwann cells = PNS myelin. Astrocytes, microglia, ependymal cells each have distinct support roles.
Ch. 13 — Cord Cross-Section
Gray matter (H-shaped) inside, white matter tracts outside — opposite of the brain.
Chapters 12–13 complete. You now know the neuron, its support cells, and how the spinal cord organizes and routes signals — including the reflex arc that skips the brain entirely. Next week moves upward: the brain and cranial nerves.