Transcript INTEGUMENTARY SYSTEM - Coast Colleges Home Page

NERVOUS SYSTEM
NERVOUS TISSUE
Nervous System - Overview
Control System; Regulator of Homeostasis
Electrical Impulses & Neurotransmitters
Rapid & Transient Effects
Comparison of Control Systems
Endocrine System
 Hormones
 Targets: cells with
receptors
 Changes metabolic activity
(enzymes, genes)
 Slower onset, more
persistent effects
 Widespread effects
 Slow recovery
Nervous System
 Neurotransmitters
 Targets: neurons, muscle
cells, gland cells
 Stimulates contraction or
glandular secretion
 Rapid onset, brief
duration
 Local effects
 Rapid recovery
18-3
Nervous System - Functions
Sensory - Monitors Internal & External
Environments
Integrative
- Analyzes Sensory Information
- Stores
- Makes Decisions Regarding Appropriate
Responses
Motor – Controls muscles & glands;
responds to sensory information
Structural Subdivisions
Central Nervous System (CNS)
- Brain, Spinal Cord
- Dorsal Body Cavity
- Integration & Command Center
Peripheral Nervous System (PNS)
-
All Neural Tissue outside CNS
Nerves (Cranial & Spinal)
Carries Info. Between CNS & Rest of Body
Sensory & Motor
Peripheral Nervous System (PNS)
Functional Subdivisions
 Sensory/Afferent (“carrying to/toward”)
- Conveys sensory information from receptors
to CNS
- Somatic afferent fibers (from skin, skeletal
muscles, joints)
- Visceral afferent fibers (from organs in
ventral body cavity)
 Motor/Efferent (“carrying away”)
- Conveys motor commands from CNS to
muscles & glands
Motor Divisions of PNS
Somatic Nervous System (SNS)
- Voluntary Control of Skeletal Muscles
Autonomic Nervous System (ANS)
- Involuntary Control of Smooth Muscle,
Cardiac Muscle & Glands
- Sympathetic Division
- Parasympathetic Division
Divisions of the ANS
Two Antagonistic Branches that Serve
same Organs:
- Parasympathetic
* “Housekeeping”
* Conserves Energy
* Craniosacral Origin
* Effects include: increased gastrointestinal
activity, increased healing rate, decreased
heart & resp. rates
Divisions of the ANS continued
- Sympathetic
* “Fight or Flight”
* Expends Energy
* Thoracolumbar Origin
* Effects Include: Increased heart & resp.
rates, constriction of blood vessels,
increased blood pressure, pupil dilation,
bronchiole dilation, inhibition of G.I.
activity
Fig. 8.39
Cells of Nervous System
 Neurons
- Basic Unit of Nervous System
- Most Specialized Cell in Body
- Conduct Impulses
 Neuroglia (“Nerve Glue”)
- Support, Framework (fill
spaces) & Phagocytes
- Most Numerous
- Can Divide & Multiply
Neurons - Structure
Cell Body (Soma)
- Nucleus
- Nissl Bodies (Rough
ER + polyribosomes)
- Neurofibrils
(Cytoskeletal)
Processes
- Dendrites
- Axon
Neuron Processes
 Dendrites
- Carry Impulse
Towards Cell Body
(Afferent)
- Numerous, Short,
Branched
- Receive Impulse
from other Neurons
or Receptors
Neuron Processes
 Axon
- Carries Impulse
Away from Cell
Body (Efferent)
- Carries Towards:
* Neuron
* Muscle Fiber
* Gland
- Long, Singular
Neuron Processes - Axon continued
-
Many Mitochondria, Neurofibrils
Axon Hillock (Joins Cell Body & Axon)
Collaterals (Axon Branches)
Axon/Synaptic Terminals
*Numerous, Fine Processes at end of
Axon & Axon Collaterals
*Some with Synaptic Knobs
Neurons – Axon continued
- Myelination
*Most Axons
*Enclosed in Schwann Cells
(Neurolemmocyte)
Myelin Sheath – Inner, Fatty,
Tight Layers of Membrane
Neurolemma – Outer Schwann
Cell Membrane & Cytoplasm
Myelination
 Addition of insulating
material
 Most Axons
 Provided by Schwann
Cells in PNS
 Myelin Sheath – inner,
fatty, tight layers of
membrane
 Neurolemma – outer,
Schwann Cell
membrane & cytoplasm
Neurons – Axon Myelination
continued
*Insulates & Increases Speed of
Conduction
*Nodes of Ranvier
Occur Along Axon Between
Schwann Cells
No Myelin
Fig. 8.6
Neurons – Functional
Classification
 Sensory
- Afferent
- Connect Receptors & CNS
 Motor
- Efferent
- Carry Commands from CNS to Effectors
 Interneurons (Association)
- CNS
- Integrate Sensory & Motor
- Most Numerous
Sensory Receptors
Receptors are sensitive only to specific
stimuli
Free nerve endings (pain, temp, itch,
tickle)
Encapsulated nerve endings
- Meissner’s & Pacinian corpuscles,
Stretch receptors
Complex, clusters of cells (sound, light,
taste, balance)
Sensory Cells
Neurons – Structural
Classification
 Unipolar
- One Process (Dendrites & Axon Fused)
- Sensory
 Bipolar
- Two Processes: One Dendrite, One Axon
- Rare (Special Senses)
 Multipolar
- Several Dendrites, One Axon
- Common
- Motor & Interneurons
Location of Neuron Cell Bodies
The cell bodies of most neurons are found
in the CNS
- Gray matter contains cell bodies and
unmyelinated fibers
- Nuclei are clusters of cell bodies within
white matter of CNS
Ganglia are groups of cell bodies in the
PNS
Neuron Terminology: PNS vs CNS
Bundle of
Fibers
(Axons)
Cluster of
Neuron Cell
Bodies
PNS
CNS
Nerve
Tract
Ganglion
(Ganglia)
Nucleus
(Nuclei)
Neuroglia – Supporting Cells in CNS
 Astrocytes
- Large, Star-shaped
- Link Neurons & Blood Vessels; Help form
Blood-brain Barrier
 Oligodendrocytes
- Form Myelin Sheath in CNS
 Microglia
- Derived from WBCs; Phagocytic
 Ependymal Cells
- Epithelium; Line Ventricles & Central Canal
- Produce & Help Circulate CSF
Neuroglia – Supporting Cells in PNS
Schwann Cells (Neurolemmocytes)
- Form Myelin Sheath
Satellite Cells
- Protect, Cushion Ganglia
Nerve Impulse Transmission
Two mechanisms involved
- Transmission along a neuron
*An electrical process
- Transmission between neurons
*A chemical process
*Occurs at synapse
Neuron Physiology
Transmission Requirements:
- Resting Membrane Potential (cell
membrane is polarized in neuron at rest)
- Delivery of Threshold Stimulus
*Neurotransmitter, light, sound, stretch,
pressure, etc…
- Ion Channels in Cell Membrane (allow
ions to diffuse when open)
Resting Membrane Potential
Conduction Along Neuron
Resting Membrane Potential (+/Na+
outside, -/K+ inside (polarized)
Appropriate Threshold Stimulus Opens
Na+ Channels
Na+ Diffuses into Neuron, Results in
Depolarization (+ inside/- outside)
Depolarization wave spreads from dendrite
to axon (Action Potential)
+
Na
Opening of
Channels
Causes Depolarization
Conduction Along Neuron
continued
Na+ Channels Close, K+ Channels Open &
K+ Diffuses Out of Neuron
Results In Repolarization (+ outside/- inside)
Repolarization Required before another
Action Potential
Sodium-Potassium Pump moves Na+ out &
K+ in (Requires Energy)
+
K
Opening of
Channels
Causes Repolarization
Action Potential: self-propagating reversal
of charge across plasma membrane
Conduction continued
All-or-None Principle
- Neurons respond to stimuli by generating an
impulse (action potential), or don’t respond at
all
Refractory Period
- Neurons must repolarize their cell membranes
before they respond to subsequent stimuli
- Occurs when K+ diffuses out of neuron
Types of Conduction
 Continuous
- Typical of Unmyelinated Neurons (Slower)
- Steps as Previously Described (“transmission
along a neuron”)
 Saltatory
- Occurs along Myelinated Neurons
- No Current where Myelin occurs
- Action Potential Leaps from Node of Ranvier
to Node
- Faster!
Fig. 8.12
Synaptic Transmission
 Arriving Action Potential Depolarizes Synaptic
Knob
 Ca++ Enters Cytoplasm of Presynaptic Neuron
 Exocytosis of Synaptic Vesicles, Releasing
Neurotransmitter
 Neurotransmitter Diffuses across Synaptic Cleft
& Binds to Receptors on Postsynaptic Membrane
 Na+ Channels Open, Postsynaptic Membrane
Depolarizes
Neurotransmitters
Excitatory – Cause Depolarization/Na+
ions channels open
Inhibitory – Raise the Threshold
- Hyperpolarize membrane/K+ or Cl- ion
channels open
Removed by specific enzymes, diffusion,
active transport back into neuron