Chapter 2: Neuroanatomy
Module 2.1: Cells of the Nervous System
Every living thing made up of cells.
What makes human a higher-functioning organism is fact that humans have
aggregates of specialized cells that perform specialized functions.
Brain composed of many parts, which have multiple functions, larger components
of brain are made up of individual cells.
Neurons and glia are specialized cells of nervous system; they are specialized in
both structure and function.
Glia provide support and functions, and neurons are communicators.
Neurons react and respond to stimuli, they are basis of behaviors.
Neurons also learn and store information about their external environment.
Neurons and Glia: Structure and Function
Gross Anatomy of the Neuron
Most distinctive structural feature of neuron is its shape.
Neurons shape is closely related to its function: to receive, conduct, and transmit
signals to collect information and send it on (or not).
Neurons consists of three main components:
1. Dentrites: Which receive incoming information from other neurons.
2. Soma or cell body: Which contain the genetic machinery and most of the
metabolic machinery needed for common cellular functions.
3. Axon: Which sends neural information to other neurons.
Information is passed from axon to dendrite across a gap called synapse.
Basis of their positions relative to synapse, events that occur in the axon referred to
as presynaptic and events that happened in dendrite referred as postsynaptic.
Dendrites essentially increase surface area available for reception of signals from
axons of other neurons.
Extent of branching of dendrites gives indication of number of connections or
synapses it makes w/ incoming axon.
All of this information is sent to rest of neuron in form of electrical charge or action
Dendrites often covered w/ tiny spines, which grow and retract in response to
Spines themselves can form synapses w/ other neurons.
Axon is commonly thought of as information sender.
Neuron has only one axon, although axon can divide at its far end into many
branches (increasing number of synapses it can form).
Axon essentially long thin fibre or wire that can pass its message along many
different cells simultaneously.
Many axons in mammalian nervous system are covered w/ insulation, called
myelin. It helps speed rate of information transfer and ensure message gets to end
of axon. End of axon is terminal button. Information send from terminal button across
synapse to dendrite.
Information that passes from axon across synapse is in form of neurochemical
message (by substances referred to as neurotransmitters), which may be
transformed into electrical message w/in dendrite.
Internal Anatomy of the Neuron
Neuron is covered w/ a membrane.
Nothing obvious sets neural cell membranes apart from other animal cell
Plasma Membrane consists of bilayer of continuous sheets of phospholipids that
separate two fluid environments inside (cytoplasm) and outside the cell.
W/in membrane are proteins and channels that allow passage of materials into and
out of neuron.
Inside main cell body, small components of the cell (called organelles) form
complex environment which organelles perform various genetic (nucleus),
synthetic (ribosomes, endoplasmic reticulum), and metabolic (mitochondria)
processes that keep neuron functioning.
Nucleus packages and controls genetic information contained in DNA
(Deoxyribonucleic acid). Nucleus processes genetic information needed to
complete series of events that form path from the recipe that genetic information
provides to form proteins that neuron needs. Nucleus also contains all genetic
information needed to code proteins such as for eye or hair color, as well as those
thought to underlie complex processes such as linguistic ability
Structure and Functions of Neurons
Neurons can be classified according to structure and function.
In nervous system, structure and function are related.
Some common neurons are labelled as unipolar, bipolar, and multipolar (most
common). Unipolar neurons have only one process emanating from cell body;
bipolar neurons have two processes; and multipolar have numerous processes
extending from cell body. Neurons w/ no axons or only very short axons are called
interneurons and they tend integrate information w/in a structure rather than
sending information between structures.
Functionally, neurons can be classified by type of signals they process. For
example, signals motor neurons convey muscle contraction. Sensory neurons
process information elicited from sensory-type stimuli, interneurons make
connections between cells, enabling sort of convergence and combination of
behavioural responses. Type of information that represented by neural activity
related to function of neuron.
Neurons can be classified as being afferent (bringing information to central
nervous system or structure) or efferent (sending information from brain or away
Neurons vary in size, shape, and function and that neuron can change shape as
result of experience.
Glia performs an essential role in functioning of central nervous system. Glia performs support functions, different types of glia providing different types of
Support cells outside of brain and spinal cord called satellite cells.
At least three diff. types of glia: astrocytes, oligodendocrytes, and microglia.
Astrocytes are largest glia cells and named astrocytes because tend to be star-
Astrocytes involved in blood-brain barrier, protective system that keeps brain
separate from rest of body. Astrocytes also perform nutritive and metabolic
functions for neurons. Astrocytes also essential for regulation of chemical content
of extracellular space because the envelope synapse and can regulate how far
neurotransmitters and other substances released by terminal button can spread.
Astrocytes important in storage of neurotransmitters. Clear we do not know all of
the functions of astrocytes.
Oligodendrocytes one very clear function: to make myelin. Oligodendrocytes
wrap their processes around most axons in brain and spinal cord. These processes
made of myelin, which fatty substance that acts to insulate axon.
Axons outside brain and spinal cord frequently myelinated, w/ myelin provided by
Schwann cells provide only one segment of myelin to an axon, oligodendrocytes
can contribute many segments to many axon.
Microglia named w/ reference to their size smallest of the glia.
Microglia is phagocytes remove debris from nervous system. Debris can
accumulate in brain as result of injury, disease, infection or aging. Microglia very
different from other cells of nervous system: made outside of brain and spinal cord