Download Nervous System Part 1

Nervous
System
Honors Biology
Powerpoint #3
Unit 8 – Chapter 35 pg. 897-904
The Senses Activities
Function of Nervous System:
Coordinates the body’s response
to changes in its internal and
external environments.
12-3
Overview of the Nervous System
Nervous system carries out task in 3 basic steps:
1. Sense organs receive information about changes
in the body and the external environment, and
transmit coded messages to the spinal cord and
the brain
2. Brain and spinal cord process this information,
relate it to past experiences, and determine what
response is appropriate to the circumstances
3. Brain and spinal cord issue commands to
muscles and gland cells to carry out such a
response
2 subdivisions of the Nervous System:
1.
Central Nervous System
(CNS)
Brain & Spinal chord
2.
Peripheral Nervous system
(PNS)
 All the nervous system except the
brain and spinal cord; made of
nerves and ganglia
Fig 9.2
7
Neurons
Pyramidal neurons
forming a network in
the brain
Neuron: main functional units
Nerve- bundle of neurons
Individual nerve fibers
(neurons)
Neuron
Neurons
Neurons = cells that transmit the electrical
impulses throughout the body
3 types of neurons:
1. Sensory: carry impulse from sense organ
to spinal chord and brain
2. Interneurons: connect sensory and motor
and carry impulses in between (found in
spinal chord and brain)
3. Motor: carry impulse from brain and spinal
chord to muscles and glands
3 types of Neurons
Neurons: Structure
• Cell Body (Soma): Cell’s “life support” center,
contains organelles (mitochondria, golgi, lysosomes)
• Dendrites - Receives signal from sensory cell or
neighboring neuron and conducts “signal” toward the
cell body -- [input zone]
Myelin Sheath
Myelin sheath—an insulating layer around a nerve
fiber (neuron)
 Formed by oligodendrocytes in CNS and Schwann cells
in PNS
 Schwann cells form Neurilemma: thick, outermost coil of
myelin sheath, contains nucleus and most of its cytoplasm
(helps regenerate nerve if damaged)
 No Neurilemma in CNS, can’t regenerate
Myelination in CNS
12-20
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Oligodendrocyte
Myelin
Nerve fiber
Figure 12.7b
(b)
Myelination in PNS
12-21
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Schwann cell
Axon
Basal lamina
Endoneurium
Nucleus
(a)
Neurilemma
Figure 12.7a
Myelin sheath
Fig 9.4
22
Fig 9.5
23
Axon - [conducting zone]
conducts signal away from axon hillock of cell body
to another neuron or effector cell
Axon Ending- a cluster of branches (100’s to
1000’s) that relays signal to next neuron / effector cell
Fig 9.17
25
Fig 9.8
26
Synapse
Narrow gaps in the myelin sheath between
Schwann cells are called nodes of Ranvier.
Allows signal to “jumps” from node of Ranvier
to node of Ranvier, increasing speed of
impulse (with myelin sheath (225 mph /
without 11 mph)
Schwann
Cell
Nucleus of Schwann cell
Myelin sheath
Myelinated axon
Nodes of Ranvier
Schwann cell
Cytoplasm of
Schwann cell
S
C
H
W
A
N
N
Myelinated axon
Myelin sheath
C
E
L
L
Nucleus of
Schwann cell
Multiple Sclerosis (MS)
• Immune System attacks Myelin in brain and spinal
chord, as well as fibers themselves (autoimmune
disorder)
Multiple Sclerosis (MS)
• Loss of motor functions
Classification of Neurons
Classification of Neurons
Structural classification
1. Multipolar neurons: many dendrites and 1 axon
arising from cell bodies, commonly found in the
CNS.
2. Bipolar neurons have a single axon and a single
dendrite extending from opposite sides of the cell
body, found only in eyes, nose, and ears
3. Unipolar neurons are found in ganglia outside the
CNS and have one axon that divides; the
peripheral process has dendrites near a
peripheral body part and a central process that
runs into the CNS.
36
Multipolar Neuron
Soma
Dendrites
Axon
Supportive Cells (Neuroglia)
12-38
About 1 trillion (1012) neurons in the nervous system
outnumber the neurons by as much as 50 : 1
Neuroglia or glial cells
 Support and protect the neurons
 Bind neurons together and form framework for nervous
tissue
 In fetus, guide migrating neurons to their destination
 If mature neuron is not in synaptic contact with another
neuron it is covered by glial cells
 Prevents neurons from touching each other
 Gives precision to conduction pathways
Neuroglial Cells of CNS
12-39
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Capillary
Neurons
Astrocyte
Oligodendrocyte
Perivascular feet
Myelinated axon
Ependymal cell
Myelin (cut)
Cerebrospinal fluid
Microglia
Figure 12.6
Types of Neuroglia
Four types occur only in
CNS
1. Oligodendrocytes
 Form myelin sheaths in
CNS
 Each armlike process
wraps around a nerve
fiber forming an
insulating layer that
speeds up signal
conduction
12-40
Types of Neuroglia
2. Ependymal cells
Line internal cavities of
the brain
Made of Cuboidal
epithelium with cilia on
apical surface
Secretes cerebrospinal
fluid (CSF)
 Clear liquid that bathes the
CNS
Types of Neuroglia
12-42
3. Microglia
 Small, wandering macrophages formed white blood cell
called monocytes
 Thought to perform a complete checkup on the brain tissue
several times a day
 Wander in search of cellular debris to phagocytize
Types of Neuroglia
4. Astrocytes
Most abundant glial cell in CNS
Cover entire brain surface and most nonsynaptic
regions of the neurons in the gray matter of the CNS
Diverse functions
 Form a supportive framework
 Have extensions that contact blood capillaries that stimulate
them to form a tight seal called the blood–brain barrier
 Convert blood glucose to lactate and supply this to the neurons
for nourishment
 Nerve growth factors secreted by astrocytes promote neuron
growth and synapse formation
Types of Neuroglia
12-45
Two types occur only in PNS
Schwann cells
 Envelope nerve fibers in PNS
 Produce a myelin sheath similar to the ones produced by
oligodendrocytes in CNS
 Assist in the regeneration of damaged fibers
Satellite cells
 Surround the neurosomas in ganglia of the PNS
 Provide electrical insulation around the soma
 Regulate the chemical environment of the neurons