Download Notes to Introduction

2401 : Anatomy/Physiology
Dr. Chris Doumen
Week 5
Neural Tissue
Introduction
TextBook Readings
♦ Pages 388 through 397.
♦ Make use of the figures
in your textbook ; a
picture is worth a
thousand words !
♦ Work the Problems and
Questions at the end of
the Chapter
The process of homeostasis makes sure
that the processes that occur in the
body are maintained within normal
physiological limits. In addition, our
body constantly reacts to a multitude
of signals, be it external or internal
signals.
Two body systems are responsible for
dealing with these signals and
controlling the state of homeostasis
•
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Endocrine
system
:
releases
hormones into the blood stream,
with a slow action response
Nervous system : communicates by
means
of
electrical
signals,
resulting in an immediate response
The nervous
functions:
♦
♦
♦
system
has
3
overlapping
Sensory : uses sensory receptors to
detect internal and external changes
(stimuli)
Integrative:
analyzes
the
sensory
information, stores it and makes decision
Motor : responds to stimuli by initiating
muscular contractions or glandular
secretions
The branch of Neurology is the study of the
normal and disordered nervous system
Over view of the N.S.
The nervous system can be divided into
2 principal parts :
1.
♦
♦
The Central Nervous system (CNS)
consists out of the Brain and
Spinal Cord
(integrating and
command center )
it is connected to the sensory
receptors, muscles and glands in
the Peripheral Nervous system
♦
•
Collin County
Community
College District
2. The Peripheral Nervous system
(PNS)
♦
consists out of cranial ( arise from
the brain) and spinal ( from the
spinal cord) nerves
♦
they carry impulses in and out of
the CNS
the input component of the PNS ( from
sensory receptors to the CNS) = sensory
division (afferent nerves)
• somatic afferent part : input from
skin, skeletal muscle and joints
• visceral afferent part: input from
the organs and glands
the output component ( from CNS to the
muscles, glands) = motor division
(efferent nerves)
2401 : Anatomy/Physiology
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This motor division of the PNS has an additional two functional subdivisions
A. The Somatic Nervous system
• also called voluntary nervous system
• composed of somatic motor nerve fibers that conduct impulses from CNS to skeletal
muscles
B. The Autonomic Nervous System
• called involuntary nervous system
• consist of visceral motor nerve fibers that regulate the activity of smooth muscles,
cardiac muscles and glands.
Two branches exist in the ANS
• Sympathetic : usually involves expenditure of body energy, stimulates
• Parasympathetic : restores and conserves body energy, contra acts on the activities
of the Sympathetic Nervous system
.
Histology of the Nervous System
The tissue making up the nervous system contains highly packed cells. But notwithstanding the
complexity of the nervous system, nervous tissue is made up of two principle types of cells
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Neurons : the excitable nerve cells that conduct the electrical signals
Supporting cells or neuro-glial cells : support, nurture and protect the neurons
A. Neurons
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they relay the electrical signals
can be short or extremely long
functional contact between 2 neurons = synapse
in mature individuals, neuron do not grow or repair themselves ( can't divide anymore)
they have a long longevity and have an extremely high metabolic rate
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1.
Anat om y
•
Cell B ody or Soma
•
contains the nucleus, mitochondria, ER
• Rough ER plus ribosomes = Nis sl bodies)
; the provide a gray texture to neuron
bodies
• Lacks centrioles ; thus neurons can not
divide
Dendrite s
• short highly branched processes, always
unmyelinated
Ax on
• long cylindrical projection with terminal
bulbs (synap tic t e rminals ) containing
the neurotransmitters
• surrounded by an ax olem ma, contains
ax oplasm a and neurofibrils,
mitochondria, lysosomes
• Area where axon connects with cell
body is called the axon hilloc k
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Dendrites specialize in receiving the stimulus
from other neurons or receptors to the cell
body.
Axons conduct the nerve impulse from the cell
body to the cell body or dendrites of other
neurons.
Important Terminology
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A ne rve fiber is the terminology for a
single axon.
A ne rve is a bundle of nerve fibers running
in the same path in the PNS, surrounded by
connective tissue.
Ne rve c ell bodi es clustered together in
the PNS are called Ganglia
Bundl e of nerve fi be rs in the CNS are
termed Tracts.
2401 : Anatomy/Physiology
2401 : Anatomy/Physiology
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The Synapse
This is the special site where two neurons
communicate with each other. The axon will in
most cases ‘meet’ up with a dendrite from
another neuron and a s ynp as e is formed.
♦
The neuron with the axon ( passing on the
electrical information) is called the presynap tic neu ron
• The neuron with the dendrite (receiving the
electrical information) is referred to as the
post- s ynaptic ne uron.
At a synpase, no direct cell to cell contact
occurs. Instead, a small space exists between
the axon and the dendrite. This is called the
synap tic cle ft.
Axonal Transport
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a mechanism that transports material up and
down
the
axon,
using
microtubules,
neurofillamants and actin fillaments
the axon contains all cell organelles but no
nucleus or Nissl bodies. Therefore, transport
is needed for new protein and other material
to be delivered to remote areas away from
the cell body.
2 types of transport
• "slow" axonal transport: goes only one
way ( body to axon)
• "fast" axonal transport : goes both ways
and uses "molecular" motors ( ATP
dependent "motor" proteins called
kine sin )
Since there is no direct contact, the electrical
information cannot be passed on directly.
Instead, the information is now passed on via
specific molecules called N eu rot ransmit te rs .
Neurotransmitters are packed in s ynap tic
ve sicles in the synaptic terminals of an axon.
Specific receptors on the post synaptic
membrane ( the membrane of the dendrite) bind
these neurotansmitters and turn that signal
back into an electrical signal.
The
details of these processes will become
clear at the end of these discussions.
Keep in mind that the presynaptic neuron is
always a neuron. The postsynaptic entity
receiving the information can be another neuron,
or it can be a muscle ( the synapse area is then
called a neu ro-m uscul ar ju nc tion) or it can
be a gland ( with a neuro-glandular junction)
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Classification
Struct ural
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of Neurons
Classific ation
Multipolar neurons
• Typical neuron displays numerous
branching dendrites and a single axon.
• Most common in human and major type
in CNS
Bipolar neurons
• Have typically one dendrite and one
axon
• Rare in adult human, only found in
special sense organs
Unipolar neurons
• Have a single process that emerges
form the cell body, and divides T-like
into a proximal and distal branch.
• Collective length of both branches are
considered to be an axon
Func ti onal
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Afferent or sensory neurons: transmit
nerve impulses from receptors to the
brain, spinal cord. There are somatic
sensory neurons and visceral sensory
neurons
Efferent or motor neurons: convey motor
nerve impulses from CNS to effectors
(muscles, glands). Somatic motor neurons
activate your skeletal muscles and visceral
motor neurons activate effectors other
than the skeletal muscles.
Association or inter-neurons : carry signals
from one neuron to another
Pre-synaptic and post-synaptic neurons.
B. Neuroglial C ells
There are 4 types of neuroglial cells that are
only found i n th e CNS !
Epe ndymal Cells
These are specialized epithelial cells that line
the ventricles of the brain and the central canal
within the spanl cord.
In the ventricles these are ciliated. They are
instrumental
in
the
production
of
the
cerebrospinal fluid and in circulating this fluid
around.
Olig ode ndroc yt es
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These cells are only found in the CNS
They wrap themselves around axons and
insulate them with the many wrappings of
their cell membrane
This is the myelin sh eath
Ast rocyte s
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These cells are only found in the CNS and have
a variety of functions.
Microglia
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Maintain blood-brain barrier by wrapping
around CNS capillaries.
Repair damaged neural tissues
Control the interstitial fluid environment
(control electrolyte balance, absorb/recycle
neurotransmitters,… )
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These cells are only found in the CNS
They function like macrophages
They are tiny and move along neural tissue
removing debris and pathogens membrane
2401 : Anatomy/Physiology
The other neuroglia are found
Pe riphe ral Ne rvous S ys tem
only
in
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the
Schwann Cell or N eu rilemm oc yt es
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These are similar to oligodendrocytes in that
they wrap themselves around axons and form
myelin sheats
Amphic yt es
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or Satellit e c ells
These cells are similar in function as
Astrocytes. They are specifically found in the
Ganglia of the PNS.