Download Part 1 - Kirkwood Community College

Fundamentals of
the Nervous
System and
Nervous Tissue
(The Three Pound
Universe)
Nervous System
• The master controlling and communicating
system of the body
• Functions
Nervous System
• What are the three most
basic three functions the
brain performs?
• Functions
– Sensory input – monitoring
stimuli occurring inside and
outside the body
– Integration – interpretation of
sensory input
– Motor output – response to
stimuli by activating effector
organs (muscles/glands/etc.)
Simply put…
• Learning without
thought is labor lost;
thought without
learning is perilous. -Confucious
• Take some time in the
next week to analyze
what your brain is doing
as you drive, read, sit,
think, etc…
• Transition
Basic
Setup of the Nervous
System
Nervous Tissue
Peripheral Nervous
System
Spinal and Cranial
Nerves
Central Nervous
System: Integration
and Command
Brain
Spinal Cord
Sensory
Sensory
Skin, skeletal
muscle and joints
Motor
Visceral
Visceral Organs
Somatic:
Control of skeletal
muscles
Autonomic:
Regulates smooth
muscle, cardiac
muscle and glands
Sympathetic:
Fight or Flight
Parasympathetic
Rest and Digest
Basic
Setup of
the
Nervous
System
Organization of the Nervous
System
• Central nervous system (CNS)
– Brain and spinal cord
– Integration and command center
• Peripheral nervous system (PNS)
– Paired spinal and cranial nerves
– Carries messages to and from the spinal cord
and brain
Peripheral Nervous System
(PNS): Two Functional Divisions
• Sensory (afferent) division
– Sensory afferent fibers – carry impulses from
skin, skeletal muscles, and joints to the brain
– Visceral afferent fibers – transmit impulses from
visceral organs to the brain
• Motor (efferent) division
– Transmits impulses from the CNS to effector
organs
Motor Division: Two Main Parts
• Somatic nervous system
– Conscious control of skeletal muscles
• Autonomic nervous system (ANS)
– Regulates smooth muscle, cardiac muscle,
and glands
– Divisions – sympathetic and parasympathetic
Transition
Histology of Nerve Tissue
• The two principal cell types of the nervous
system are:
– Neurons – excitable cells
that transmit electrical signals
– Glia: supporting cells that
surround and wrap neurons
Starting with the easiest: Glia
Einstein’s brain was
unusual in having
more glial cells than
most humans, not
more neurons!
There are Six Types of Glia; Four
in the CNS and Two in the PNS
• CNS
• PNS
– Astrocytes
– Schwann
Cells
– Microglia
– Satellite
– Ependymal Cells
Cells
– Oligodendrocytes
Four Types of Glia in CNS
• Astrocytes
• Microglia
• Ependymal Cells
• Oligodendrocytes
Astrocytes
Astrocytes
• Most abundant, versatile,
and highly branched glial
cells
• Functionally, they:
– Support neurons like a
scaffold
– Are the bridge between neurons and blood
vessels.
– Control the chemical environment. There are
ions/neurotransmitters “flying” around and
astrocytes clean this up.
– Guide migration of young neurons
Microglia
• Microglia – small, ovoid cells
with spiny processes that are
the brain’s immune system
– Phagocytes that monitor the health of neurons
– Engulf bacteria, viruses, debris
Neuron
Astroctye
Microglia
Ependymal Cells
• Ependymal cells –They line
the ventricles of the brain
and spinal column
Oligodendrocytes,
• Oligodendrocytes –
branched cells that
wrap CNS nerve
fibers
Axons
Oligodendrocytes
Glia of the PNS: Schwann Cells,
and Satellite Cells
• Schwann cells –
surround fibers of the
PNS
• Satellite cells surround
neuron cell bodies with
ganglia
Neurons (Nerve Cells): Cellular
Properties
• Structural units of the nervous system
– Long-lived, amitotic, and have a high
metabolic rate
– They communicate
– Composed of four
parts
Neuron (Nerve Cell): Parts
1.Soma (cell body)
2.Dendrite
3.Axon
4.Synapse
The Soma (Cell Body)
• Is the same as other cells in that it…
– Contains the nucleus and a nucleolus
– Is the major biosynthetic center
– Has well-developed RER (Nissle
bodies)
• Is different from other cells in that it…
– Is the focal point for the outgrowth of
neuronal processes
– Has no centrioles
• (hence its amitotic nature)
– Contains an axon hillock – coneshaped area from which axons arise
Dendrites of Motor Neurons
• Short, tapering, and diffusely
branched processes
• They are the receptive, or
input, regions of the neuron
• Electrical signals are
conveyed as graded
potentials (not action
potentials)
Axons: Structure
• Slender processes of uniform diameter arising
from the hillock
• Long axons are called nerve fibers
• Usually there is only one unbranched axon
per neuron
• Rare branches, if present, are
called axon collaterals
• Axonal terminal – branched
terminus of an axon
Myelin Sheath
• Whitish, fatty (protein-lipoid),
segmented sheath around most
axons
• It functions to:
long
– Protect the axon
– Electrically insulate fibers from one another
– Increase the speed of nerve impulse transmission
Nodes of Ranvier
• Gaps in the myelin sheath
between adjacent myelinating
glia
• The gaps will make more sense
when we study the action
potential and “saltatory
conduction”
Axons
• Both myelinated and unmyelinated fibers
are present in the CNS and PNS
Myelinated
Unmyelinated
Regions of the Brain and Spinal
Cord: myelin = white
• White matter – dense collections of
myelinated fibers (axons)
• Gray matter – mostly soma and
unmyelinated fibers
Synapse
• A junction that
mediates
information
transfer from
one neuron:
– To another
neuron
– To an effector
cell
We will return to the synapse when talking about the
specific mechanisms, called synaptic transmission.
• Before talking too much more about how
neurons work, we will first discuss the
different types of neurons.
Neuron Classification: Structural
• Structural (Anatomical)
– Multipolar — three or
more processes
– Unipolar — single, short
process
– Bipolar — two processes
(axon and dendrite)
Comparison of Structural
Classes of Neurons
Comparison of Structural
Classes of Neurons
Neuron Classification: Functional
• Functional
(Physiological)
– Motor (efferent) — carry
impulses away from the
CNS
– Interneurons (association
neurons) — shuttle
signals through CNS
pathways
– Sensory (afferent) —
transmit impulses toward
the CNS. Smell and sight
use bipolor neurons.
Comparison of Structural
Classes of Neurons
Comparison of Structural
Classes of Neurons: Review
• Structural (Anatomical)
– Multipolar — three or
more processes
– Unipolar — single,
short process
– Bipolar — two
processes (axon and
dendrite)
• Functional (Physiological)
– Motor (efferent) — carry
impulses away from the
CNS
– Interneurons (association
neurons) — shuttle signals
through CNS pathways
– Sensory (afferent) —
transmit impulses toward
the CNS. Smell and sight
use bipolar neurons.
Neurons Make
Decisions
• Whether reading or
deciding to take an
umbrella, what
neurons do is
make decisions.
• Weigh the pros and
cons, note that the
pros and cons
have various
strengths, and
make a decision.
Umbrella Metaphor
• Think about all the thoughts that go into
whether you brought an umbrella today.
• We are going to use this metaphor to try to
understand many of the other
thoughts/decisions you make.
• We will look at the parts of the neurons,
their functions, and how neurons interact.
• The story will cycle up in complexity and
we will draw it on an 11x17 piece of paper.
Questions we need to understand
1. What makes the electricity flow in the
axon?
•
Action potentials
2. What happens at the end so you get
different outcomes?
•
Synaptic Transmission
3. How do dendrites govern whether an
axon will fire?
– Integration of signals.
• The rest of these slides are for reference. The
information on them will be presented in the
form of drawings on the board. If you
understand the drawings, you can disregard the
remainder of these slides.