Download 11 Func[ons of the Nervous System Divisions of the Nervous System

1/28/15 Func?ons of the Nervous System 1.  Sensory input –  Informa?on gathered by sensory receptors about internal and external changes 11 2.  Integra?on –  Interpreta?on of sensory input Fundamentals of the Nervous System and Nervous Tissue: Part A 3.  Motor output –  Ac?va?on of effector organs (muscles and glands) produces a response Divisions of the Nervous System Sensory input
•  Central nervous system (CNS) –  Brain and spinal cord –  Integra?on and command center •  Peripheral nervous system (PNS) Integration
–  Paired spinal and cranial nerves carry messages to and from the CNS Motor output
Figure 11.1
Peripheral Nervous System (PNS) •  Two func?onal divisions 1.  Sensory (afferent) division • 
• 
Soma?c afferent fibers—convey impulses from skin, skeletal muscles, and joints Visceral afferent fibers—convey impulses from visceral organs Motor Division of PNS 1.  Soma?c (voluntary) nervous system –  Conscious control of skeletal muscles 2.  Motor (efferent) division • 
Transmits impulses from the CNS to effector organs 1 1/28/15 Cranial nerves and spinal nerves
Communication lines between the
CNS and the rest of the body
Brain and spinal cord
Integrative and control centers
Sensory (afferent) division
Somatic and visceral sensory
nerve fibers
Conducts impulses from
receptors to the CNS
2.  Autonomic (involuntary) nervous system (ANS) Somatic sensory
fiber
–  Visceral motor nerve fibers –  Regulates smooth muscle, cardiac muscle, and glands –  Two func?onal subdivisions • 
• 
Peripheral nervous system (PNS)
Central nervous system (CNS)
Motor Division of PNS 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
Skin
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
Sympathe?c Parasympathe?c Sympathetic motor fiber of ANS
Structure
Function
Sensory (afferent)
division of PNS
Motor (efferent)
division of PNS
Parasympathetic motor fiber of ANS
Parasympathetic
division
Conserves energy
Promotes housekeeping functions
during rest
Heart
Bladder
Figure 11.2
Histology of Nervous Tissue •  Two principal cell types Histology of Nervous Tissue 2.  ______________________ (glial cells)—suppor?ng cells: 1.  ______________________—excitable cells that transmit electrical signals • 
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______________________ •  Most abundant, versa?le, and highly branched glial cells •  Cling to neurons, synap?c endings, and capillaries •  ______________________ and brace neurons Astrocytes (CNS) Microglia (CNS) Ependymal cells (CNS) Oligodendrocytes (CNS) Satellite cells (PNS) Schwann cells (PNS) Astrocytes • 
• 
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Help determine capillary permeability Guide migra?on of young neurons Control the chemical environment Par?cipate in informa?on processing in the brain 2 1/28/15 ______________________ Capillary
Neuron
•  Small, ovoid cells with thorny processes •  Migrate toward injured neurons •  Phagocy?ze microorganisms and neuronal debris Astrocyte
(a) Astrocytes are the most abundant
CNS neuroglia.
Figure 11.3a
______________________ Cells Neuron
Microglial
cell
•  Range in shape from squamous to columnar •  May be ______________________ •  Line the central cavi?es of the brain and spinal column –  Separate the CNS inters??al fluid from the cerebrospinal fluid in the cavi?es (b) Microglial cells are defensive cells in
the CNS.
Figure 11.3b
______________________ Fluid-filled cavity
Ependymal
cells
•  Branched cells •  Processes wrap CNS nerve fibers, forming insula?ng myelin sheaths Brain or
spinal cord
tissue
(c) Ependymal cells line cerebrospinal
fluid-filled cavities.
Figure 11.3c
3 1/28/15 ______________________ Cells and ______________________ Cells Myelin sheath
Process of
oligodendrocyte
Nerve
fibers
•  Satellite cells –  Surround neuron cell bodies in the PNS •  Schwann cells (neurolemmocytes) (d) Oligodendrocytes have processes that form
myelin sheaths around CNS nerve fibers.
–  Surround peripheral nerve fibers and form myelin sheaths –  Vital to regenera?on of damaged peripheral nerve fibers Figure 11.3d
______________________ (Nerve Cells) Satellite
cells
•  Special characteris?cs: Cell body of neuron
Schwann cells
(forming myelin sheath)
Nerve fiber
(e) Satellite cells and Schwann cells (which
form myelin) surround neurons in the PNS.
–  Long-­‐lived (→ 100 years or more) –  Amito?c—with few excep?ons –  High metabolic rate—depends on con?nuous supply of oxygen and glucose –  Plasma membrane func?ons in: •  Electrical signaling •  Cell-­‐to-­‐cell interac?ons during development Figure 11.3e
Cell Body (Perikaryon or Soma) Cell Body (Perikaryon or Soma) •  Biosynthe?c ______________________ of a neuron •  Spherical nucleus with nucleolus •  Well-­‐developed ______________________ •  Rough ER called Nissl bodies (chromatophilic substance) •  Network of neurofibrils (neurofilaments) •  _________ _____________—cone-­‐shaped area from which axon arises •  Clusters of cell bodies are called nuclei in the CNS, ganglia in the PNS 4 1/28/15 Dendrites
(receptive regions)
Cell body
(biosynthetic center
and receptive region)
Processes •  ______________________ and axons •  Bundles of processes are called Nucleolus
–  Tracts in the CNS –  Nerves in the PNS Axon
(impulse generating
and conducting region)
Nucleus
Nissl bodies
Axon hillock
(b)
Impulse
direction
Node of Ranvier
Schwann cell
Neurilemma (one interTerminal
node)
branches
Axon
terminals
(secretory
region)
Figure 11.4b
Dendrites •  Short, tapering, and diffusely branched •  ______________________ (input) region of a neuron •  Convey electrical signals toward the cell body as graded poten?als The Axon •  Numerous ______________________ branches (telodendria) •  Knoblike axon terminals (synap?c knobs or boutons) The Axon •  One axon per cell arising from the axon hillock •  Long axons (nerve fibers) Axons: Func?on •  ______________________ region of a neuron •  Generates and transmits nerve impulses (ac?on poten?als) away from the cell body –  ______________________ region of neuron –  Release neurotransmiders to excite or inhibit other cells 5 1/28/15 Axons: Func?on Dendrites
(receptive regions)
Cell body
(biosynthetic center
and receptive region)
•  Molecules and organelles are moved along axons by motor molecules in two direc?ons: Nucleolus
–  ______________________—toward axonal terminal Axon
(impulse generating
and conducting region)
•  Examples: mitochondria, membrane components, enzymes –  ______________________—toward the cell body •  Examples: organelles to be degraded, signal molecules, viruses, and bacterial toxins Impulse
direction
Nucleus
Nissl bodies
Axon hillock
(b)
Node of Ranvier
Schwann cell
Neurilemma (one interTerminal
node)
branches
Axon
terminals
(secretory
region)
Figure 11.4b
Myelin Sheath •  Segmented protein-­‐lipoid sheath around most long or large-­‐diameter axons •  It func?ons to: –  Protect and electrically ______________________ the axon –  Increase ______________________ of nerve impulse transmission Myelin Sheaths in the PNS •  ______________________ of Ranvier Myelin Sheaths in the PNS •  ______________________ cells wraps many ?mes around the axon –  Myelin sheath—concentric layers of Schwann cell membrane •  Neurilemma—peripheral bulge of Schwann cell cytoplasm Schwann cell
plasma membrane
Schwann cell
cytoplasm
Axon
–  Myelin sheath gaps between adjacent Schwann cells –  Sites where axon collaterals can emerge 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
6 1/28/15 Unmyelinated Axons Myelin Sheaths in the CNS •  Thin nerve fibers are ______________________ •  One Schwann cell may incompletely enclose 15 or more unmyelinated axons •  Formed by processes of ______________________, not the whole cells •  Nodes of Ranvier are present •  No neurilemma •  Thinnest fibers are ______________________ White Mader and Gray Mader •  ______________________ mader Myelin sheath
Process of
oligodendrocyte
–  Dense collec?ons of myelinated fibers •  ______________________ mader –  Mostly neuron cell bodies and unmyelinated fibers Nerve
fibers
(d) Oligodendrocytes have processes that form
myelin sheaths around CNS nerve fibers.
Figure 11.3d
Structural Classifica?on of Neurons •  Three types: 1.  ______________________—1 axon and several dendrites • 
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Most abundant Motor neurons and interneurons Structural Classifica?on of Neurons 3.  ______________________ (pseudounipolar)—
single, short process that has two branches: • 
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Peripheral process—more distal branch, ohen associated with a sensory receptor Central process—branch entering the CNS 2.  ______________________—1 axon and 1 dendrite • 
Rare, e.g., re?nal neurons 7 1/28/15 Table 11.1 (1 of 3)
Func?onal Classifica?on of Neurons Func?onal Classifica?on of Neurons 3.  ______________________ (associa?on neurons) •  Three types: • 
1.  ______________________ (afferent) • 
Table 11.1 (2 of 3)
Transmit impulses from sensory receptors toward the CNS Shudle signals through CNS pathways; most are en?rely within the CNS 2.  ______________________ (efferent) • 
Carry impulses from the CNS to effectors Table 11.1 (3 of 3)
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