BIO 004 · Human Anatomy
Gross Anatomy & Neuronal Integration
Block 5 · Module 2: Gross Anatomy and Neuronal Integration
A reference for the neuronal integration video and lab. This page covers gray and white matter, the names for bundles of fibers and clusters of cell bodies, the reflex arc, types of reflexes, and neuronal pools.
How to use this sheet Toggle the toolbar above. Notes prints the full reference for review. Study prints as a fill-in-the-blank worksheet. Print it, then write each definition while you watch the video or read your book. Quiz me is on-screen typing practice: type the term, click Reveal to check yourself. The comparison grids respond to Study and Quiz too, with a Reveal button on each row.
The Foundations video gives you a complete foundational understanding of this topic, enough on its own for a foundational course. Learn it first, then move on to the Deep dive, which adds the majors-level material: the reflex arc, types of reflexes, and neuronal pools.
- Distinguish gray matter from white matter.
- Define the terms tract, nerve, nucleus, and ganglion.
- Name the five components of a reflex arc in order.
- Compare the types of reflexes and describe a neuronal pool.
Your pre-work
Work through these the evening before class. None of it is turned in. It is how you learn the material and build your spaced recall.
This is more than a checklist. Ticking these boxes is the start, not the finish. Committing this material to memory and being able to apply it takes considerable time and repeated effort. You are not done when the boxes are checked. Put in the real hours, and keep coming back for frequent recall and review until the material is genuinely yours.
Gray and white matter
Add a labeled section of the spinal cord showing the gray matter core and white matter.
The reflex arc
Add a labeled diagram of a reflex arc from receptor to effector.
Neuronal pool circuits
Add labeled diagrams of convergence, divergence, and serial and parallel circuits.
An Overview
This page covers two things: how nervous tissue is organized into the larger structures of the system, and how neurons work together in groups to process information.
- Gross organizationhow nervous tissue is arranged into the brain, cord, and nerves
- Neuronal integrationhow neurons work together in groups to receive, combine, and respond to information
- Gray matterregions made mostly of neuron cell bodies, dendrites, and synapses
- White matterregions made mostly of myelinated axons
- Reflexa fast, automatic, predictable response to a stimulus
Gray Matter and White Matter
Nervous tissue sorts into two looks. Where cell bodies gather, the tissue looks gray; where myelinated axons run, it looks white. Compare them.
| Type | What it is made of | Where it is |
|---|---|---|
| Gray matter | neuron cell bodies, dendrites, and unmyelinated fibers | the cortex of the brain and cerebellum, and the inner core of the spinal cord |
| White matter | myelinated axons running in bundles | beneath the cortex of the brain, and the outer part of the spinal cord |
Bundles of Fibers and Clusters of Cell Bodies
The same structure has a different name in the CNS and the PNS. Learn the four terms as two pairs: bundles of axons, and clusters of cell bodies.
| Term | Where | What it is |
|---|---|---|
| Tract | CNS | a bundle of axons within the central nervous system |
| Nerve | PNS | a bundle of axons within the peripheral nervous system |
| Nucleus | CNS | a cluster of neuron cell bodies within the central nervous system |
| Ganglion | PNS | a cluster of neuron cell bodies within the peripheral nervous system |
The Reflex Arc
A reflex is fast because it runs a short, fixed pathway. Every reflex arc has the same five components, in order.
- Receptordetects the stimulus
- Sensory neuroncarries the signal from the receptor to the CNS
- Integration centerone or more synapses in the CNS where the signal is processed
- Motor neuroncarries the command from the CNS to the effector
- Effectorthe muscle or gland that carries out the response
Types of Reflexes
Reflexes are sorted several ways: by the effector, by the number of synapses, and by whether they are inborn. Compare them.
| Reflex type | Basis of the name | Example |
|---|---|---|
| Somatic reflex | the effector is skeletal muscle | the patellar, or knee-jerk, reflex |
| Autonomic reflex | the effector is smooth muscle, cardiac muscle, or a gland | the pupillary light reflex |
| Monosynaptic reflex | just one synapse in the integration center | the stretch reflex |
| Polysynaptic reflex | two or more synapses, with interneurons | the withdrawal reflex |
| Innate reflex | present from birth, not learned | the blink reflex |
| Learned reflex | built through practice and repetition | catching a suddenly dropped object |
Neuronal Pools and Circuits
Neurons rarely act alone. They are wired into groups, the neuronal pools, and the wiring pattern shapes how a signal is handled.
- Neuronal poola functional group of interconnected neurons in the CNS that processes information together
- Convergencea circuit in which many neurons feed their signals onto one neuron
- Divergencea circuit in which one neuron spreads its signal to many neurons
- Serial processinga signal passing along a single straight chain of neurons, as in a reflex arc
- Parallel processinga signal sent along several pathways at the same time
- Integrationthe combining of all the incoming signals so that a neuron produces a single response
Sensory and Motor Pathways
Information travels the CNS on long tracts: sensory signals climb upward, motor commands descend, and most pathways cross to the opposite side.
- Sensory receptora structure that detects a stimulus and triggers a signal in a sensory neuron
- Types of receptorsnamed for what they detect: mechanoreceptors, thermoreceptors, photoreceptors, chemoreceptors, and nociceptors for pain
- Ascending pathwaysthe tracts that carry sensory information up the spinal cord to the brain
- Descending pathwaysthe tracts that carry motor commands down from the brain to the body
- Decussationthe crossing of a pathway to the opposite side, so each half of the brain serves the opposite half of the body
See also: Functional Organization and Nervous Tissue for the neuron and glia, and The Brain, the next page in this block.
Study questions
Work on answering these in writing, in your own words. They are the questions to bring to class, and good practice for the reasoning the exams ask for.
- Compare gray matter and white matter by what each one is made of.
- Define a nucleus, a ganglion, a tract, and a nerve, and state whether each is in the CNS or the PNS.
- Trace the structures of a reflex arc in order, from stimulus to response.
- Explain why a reflex can happen without involving the brain.
Step 2 . Retrieval check
Now explain it back, in your own words.
In 60 words or more, pull together what the video just taught you. Include the key concepts. This is the point where the learning actually sticks. After you submit, your spaced-recall cards for this topic unlock.