BIO 304 · Human Anatomy & Physiology · Week 4 · Day 3

Nervous Tissue, Organization & Anatomy

The cells of the nervous system and how the brain and spinal cord are built. We cover the structure now; the physiology comes next week.

Use the arrow keys, or the buttons below, to move through the slides.

Dr. Sharilyn Rennie

These slides Study guide

What you will be able to do

Today’s objectives

  • 1Map the divisions of the nervous system: CNS and PNS, sensory and motor, somatic and autonomic.
  • 2Identify the parts of a neuron and classify neurons by structure and function.
  • 3Name the CNS and PNS neuroglia and one job for each.
  • 4Name the four brain regions and the lobes, and locate the major functional areas.
  • 5Describe the spinal cord, the meninges, and the flow of cerebrospinal fluid.

The organizational map

How the nervous system is divided

  • Central (CNS)Brain and spinal cord. Integration and command.
  • Peripheral (PNS)All nerves outside the CNS. Cranial and spinal nerves and ganglia.
  • Sensory (afferent)Carries information toward the CNS.
  • Motor (efferent)Carries commands out to muscles and glands.
  • SomaticVoluntary motor control of skeletal muscle.
  • AutonomicInvoluntary control of organs; sympathetic (fight or flight) and parasympathetic (rest and digest).
OpenStax overview of the nervous system: CNS, PNS, and ENS with somatic and autonomic functions.
Divisions of the nervous system. OpenStax Anatomy & Physiology, CC BY 4.0

The working cell

Parts of a neuron

  • DendritesBranching receivers; carry signals toward the soma.
  • Soma (cell body)Nucleus and organelles; the integration center.
  • AxonCarries the signal away from the soma; can be over a meter long.
  • Axon terminalReleases neurotransmitter at the synapse.
  • Myelin sheathFatty insulation that speeds conduction.
  • Nodes of RanvierGaps in myelin; the signal jumps between them (saltatory conduction).
OpenStax diagram of a neuron: dendrites, soma, axon, myelin sheath, nodes of Ranvier, and synapse.
Structure of a neuron. OpenStax Anatomy & Physiology, CC BY 4.0

Sorted two ways

Classes of neurons

  • MultipolarMany dendrites, one axon. Most neurons, including motor neurons.
  • BipolarOne dendrite, one axon. Special senses such as the retina.
  • PseudounipolarOne process that splits. Most sensory neurons.
  • Sensory (afferent)Carries signals toward the CNS.
  • Motor (efferent)Carries signals from the CNS to an effector.
  • InterneuronConnects neurons within the CNS; about 99 percent of all neurons.
OpenStax figure of unipolar, bipolar, and multipolar neurons.
Neuron types. OpenStax Anatomy & Physiology, CC BY 4.0

Support cells, part 1

Neuroglia of the CNS

Glia outnumber neurons and do the housekeeping. The CNS has four types.

  • AstrocyteMost numerous; forms the blood-brain barrier and buffers potassium.
  • OligodendrocyteMyelinates CNS axons; one cell wraps several axons.
  • MicrogliaThe CNS immune cells; clear debris and pathogens.
  • EpendymalLine the ventricles; make and circulate cerebrospinal fluid.
OpenStax figure of CNS neuroglia: astrocyte, microglia, ependymal cells, and oligodendrocytes.
Neuroglia of the CNS. OpenStax Anatomy & Physiology, CC BY 4.0

Support cells, part 2

PNS glia, and gray vs white matter

  • Schwann cellMyelinates PNS axons; one cell wraps one segment of one axon. Supports nerve regeneration.
  • Satellite cellSurrounds and supports cell bodies in ganglia.
  • Gray matterCell bodies, dendrites, and synapses. Cortex and nuclei.
  • White matterMyelinated axons in tracts; the white color comes from myelin.
OpenStax figure of myelinated axons and the nodes of Ranvier with an electron micrograph.
Myelin and nodes of Ranvier. OpenStax Anatomy & Physiology, CC BY 4.0

The big four

Major brain regions

  • CerebrumLargest region. Cognition, sensation, and voluntary movement.
  • DiencephalonThalamus, hypothalamus, and epithalamus.
  • BrainstemMidbrain, pons, and medulla. Vital reflexes.
  • CerebellumCoordination, balance, and motor learning.
OpenStax figure of the cerebellum with arbor vitae and a sagittal brain image.
The cerebellum. OpenStax Anatomy & Physiology, CC BY 4.0

Map of the cortex

Cerebral lobes

  • FrontalVoluntary motor (precentral gyrus), executive function, personality, Broca speech.
  • ParietalSomatosensation (postcentral gyrus) and spatial orientation.
  • TemporalHearing, language comprehension (Wernicke), and memory.
  • OccipitalVision.
  • InsulaDeep lobe; taste and interoception.

Relay, regulate, survive

Diencephalon and brainstem

  • ThalamusSensory relay station for everything except smell.
  • HypothalamusHomeostasis: temperature, hunger, thirst, hormones via the pituitary.
  • Pineal glandEpithalamus; melatonin and circadian rhythm.
  • MidbrainVisual and auditory reflexes; the substantia nigra.
  • PonsBridge to the cerebellum; helps control breathing.
  • MedullaCardiac, vasomotor, and respiratory centers; where motor tracts cross.
OpenStax sagittal brain showing the brainstem: midbrain, pons, and medulla.
The brainstem. OpenStax Anatomy & Physiology, CC BY 4.0

The cable and its cross-section

Spinal cord

  • ExtentFrom the medulla to L1 or L2 in adults.
  • 31 nerve pairsExit through the intervertebral foramina.
  • EnlargementsCervical and lumbar, where limb nerves arise.
  • Conus and cauda equinaThe tapered end, then the nerve roots that hang below it.
  • Dorsal vs ventral hornDorsal takes sensory input; ventral holds motor neuron cell bodies.
  • White matter columnsAscending and descending tracts; the central canal carries CSF.
OpenStax spinal cord cross-section: gray and white matter, dorsal and ventral horns, central canal, with a micrograph.
Spinal cord cross-section. OpenStax Anatomy & Physiology, CC BY 4.0

Protection and plumbing

Meninges and cerebrospinal fluid

  • Dura materTough outer layer.
  • Arachnoid materWeb-like middle; the subarachnoid space holds CSF.
  • Pia materThin inner layer that follows every contour.
  • CSFMade by the choroid plexus; cushions, gives buoyancy, and stabilizes the chemistry.
  • CSF flowLateral ventricles, third ventricle, cerebral aqueduct, fourth ventricle, subarachnoid space, arachnoid villi, venous blood.
OpenStax figure of the cranial meninges: dura, arachnoid, and pia mater with the subarachnoid space.
The meninges. OpenStax Anatomy & Physiology, CC BY 4.0
OpenStax figure of the ventricles and cerebrospinal fluid flow through the brain.
Ventricles and CSF. OpenStax Anatomy & Physiology, CC BY 4.0

A selective wall

The blood-brain barrier

  • Built byTight junctions between brain capillary cells, supported by astrocyte end-feet.
  • Lets throughLipid-soluble molecules, oxygen, carbon dioxide, and glucose (by transporter).
  • Keeps outMost drugs, toxins, and pathogens, which protects neurons but complicates treating brain disease.
OpenStax figure of the arteries supplying the brain, including the circle of Willis.
Blood supply to the brain. OpenStax Anatomy & Physiology, CC BY 4.0

When the structure is damaged

Clinical tie-in

  • Multiple sclerosisImmune attack on CNS myelin; conduction slows and fails.
  • Stroke localizationSymptoms point to the region damaged: speech (frontal or temporal), vision (occipital), movement (frontal).
  • HydrocephalusBlocked CSF flow raises pressure inside the skull.
  • MeningitisInflammation of the meninges; tested by sampling CSF.

Pull it together

Recap, then go practice

You now have the cells and the architecture: neurons and glia, the divisions, the four brain regions and lobes, the cord, the coverings, and the barrier. Print the workbook, label it by hand, then open your recall cards.

Next week: Nervous Physiology, the resting membrane potential, action potentials, and synaptic transmission.

Open Week 4 pre-work Print the workbook

BIO 304 Human Anatomy & Physiology · American River College · Summer 2026 · Dr. Sharilyn Rennie