Download The Nervous System The Nervous System Functions of the Nervous

1/1/2016
The Nervous System
The nervous system is responsible for all of our
behaviors, memories, & movements
The Nervous System
Neurons
Chapter 11
The nervous system…
• Cooperates with endocrine system
• Senses environment
• Responds to changes in environment
• Maintains homeostasis
Functions of the Nervous System
Sensory input
1. Sensory input
–
Information gathered by sensory receptors about
internal and external changes
2. Integration
–
Interpretation of sensory input
3. Motor output
–
Activation of effector organs (muscles and glands)
produces a response
Integration
Motor output
Works through rapid and specific
electrical and chemical signals
to produce immediate responses
Organization
• Central Nervous System
– Brain
– Spinal Cord
Organization
• Peripheral Nervous System
– Afferent (sensory)
– Efferent (motor)
• Somatic
• Autonomic
– Sympathetic
– Parasympathetic
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Peripheral nervous system (PNS)
Cranial nerves and spinal nerves
Communication lines between the
CNS and the rest of the body
Central nervous system (CNS)
Brain and spinal cord
Integrative and control centers
Major Structures of the Nervous System
Sensory (afferent) division
Somatic and visceral sensory
nerve fibers
Conducts impulses from
receptors to the CNS
Somatic sensory
fiber
Skin
Motor (efferent) division
Motor nerve fibers
Conducts impulses from the CNS
to effectors (muscles and glands)
Somatic nervous
system
Somatic motor
(voluntary)
Conducts impulses
from the CNS to
skeletal muscles
Visceral sensory fiber
Stomach
Skeletal
muscle
Autonomic nervous
system (ANS)
Visceral motor
(involuntary)
Conducts impulses
from the CNS to
cardiac muscles,
smooth muscles,
and glands
Motor fiber of somatic nervous system
Sympathetic division
Mobilizes body
systems during activity
Sympathetic motor fiber of ANS
Structure
Function
Sensory (afferent)
division of PNS
Motor (efferent)
division of PNS
Copyright 2009 John Wiley & Sons, Inc.
Two principal cell types
1. Neurons
•
Excitable cells that transmit electrical signals
2. Accessory cells (neuroglia)
•
Non-excitable supporting cells
Heart
Parasympathetic motor fiber of ANS
Bladder
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Histology of Nervous Tissue
•
Parasympathetic
division
Conserves energy
Promotes housekeeping functions
during rest
Neurons and Nerves
• Neurons
– Individual nerve cells
• Nerves
– Parallel bundles of neurons carrying
impulses in the PNS (called tracts in the CNS)
• Types
– Sensory (afferent)
– Motor (efferent)
– Association (interneurons)
Only about 20% empty space!
Nerves
Neurons
• Special characteristics of neurons
– Long lived
– Amitotic
– High metabolic rate
– Excitable
Endo = within
Peri = next to; around
Epi = above
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Figure 11.4 Structure of a motor neuron.
The Structure of a Neuron
Dendrites
(receptive
regions)
Cell body
(biosynthetic center
and receptive region)
• Body
• Dendrites
• Axon (only one)
Neuron cell body
Nucleolus
Axon
(a)
(impulse
Impulse
generating
direction
and conducting
region)
Nucleus
Nissl bodies
Axon hillock
Neurilemma
(b)
Schwann cell
(one internode)
Dendritic
spine
Node of Ranvier
Axon terminals
(secretory
region)
Terminal
branches
Copyright © 2010 Pearson Education, Inc.
The Structure of a Neuron
• Unipolar neurons
– Found mostly in ANS, although some in CNS
The Structure of a Neuron
• Bipolar neurons
– Rare, but found in the special sense organs (retina, olfactory mucosa)
The Structure of a Neuron
• Pseudounipolar neurons
– Found chiefly in PNS as sensory neurons
The Structure of a Neuron
• Multipolar neurons
– Most common type in humans (>99%)
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Accessory Cells
Accessory Cells
•
•
•
•
•
Neuroglia
About 50% of cellular mass in nervous tissue
Do not conduct impulses
Most retain capacity to divide
Different types found in PNS and CNS
Accessory Cells
• Neuroglia of the CNS
1.
2.
3.
4.
Astrocytes - support
Oligodendrocytes - myelin
Microglial cells - defense
Ependymal cells - CSF
Capillary
• Astrocytes
– Most abundant of CNS neuroglia
– Contact blood vessels
– Blood Brain Barrier (BBB) regulates passage of
molecules
Neuron
Astrocyte
Astrocytes are the most abundant of
CNS neuroglia. Provide most structural support
Figure 11.3a
Accessory Cells
• Oligodendrocytes
– Branched cells
– Processes wrap around CNS neurons
• Form insulating myelin sheaths
Myelin sheath
Process of
oligodendrocyte
Nerve
fibers
Oligodendrocytes have processes that form
myelin sheaths around CNS nerve fibers.
Figure 11.3d
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Accessory Cells
– Ependymal cells
•
•
•
•
•
Vary in shape from squamous to columnar
Many are ciliated
Line the central cavities of the brain and spinal column
Form cerebrospinal fluid
Separate the CNS interstitial fluid from the cerebrospinal fluid
in the cavities
Myelin insulates neuronal axons, much the way
insulation protects wires.
Accessory Cells
• Microglia
Fluid-filled cavity
Ependymal
cells
Brain or
spinal cord
tissue
– Small, ovoid cells with thorny processes
– Migrate toward injured neurons
– Phagocytize microorganisms and neuronal debris
• Why do you think this would be so important?
Ependymal cells line cerebrospinal
fluid-filled cavities.
Add these to your list!
Figure 11.3c
Accessory Cells
• Neuroglia of PNS
1. Satellite cells
Neuron
Microglial
cell
• Surround neuron cell bodies in the PNS
2. Schwann cells
• Surround peripheral nerve fibers and form myelin sheaths
– Axon + myelin = nerve fiber
• Vital to regeneration of damaged peripheral nerve fibers
(b) Microglial cells are defensive cells in
the CNS.
Figure 11.3b
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Accessory Cells
Satellite
cells
• Schwann cells cont.
Cell body of neuron
Schwann cells
(forming myelin sheath)
Nerve fiber
– Myelin sheath
– Neurilemma
– Nodes of Ranvier
Satellite cells and Schwann cells (which
form myelin) surround neurons in the PNS.
Figure 11.3e
Schwann cell
plasma membrane
Schwann cell
cytoplasm
Axon
1 A Schwann cell
envelopes an axon.
Schwann cell
nucleus
2 The Schwann cell then
rotates around the axon,
wrapping its plasma
membrane loosely around
it in successive layers.
Neurilemma
Myelin sheath
(a) Myelination of a nerve
fiber (axon)
3 The Schwann cell
cytoplasm is forced from
between the membranes.
The tight membrane
wrappings surrounding
the axon form the myelin
sheath.
Figure 11.5a
Multiple Sclerosis
• Autoimmune disease of young adults
• Variety of clinical signs
• No known cure
Antibodies produced in multiple sclerosis attack
myelin made by oligodendrocytes, and lead to
demyleination in the CNS.
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