Transcript Peripheral Nervous System

I. Overview of Nervous System
NERVOUS SYSTEM
Central Nervous
System (CNS)
Peripheral Nervous
System (PNS)
Somatic Nervous
System
Autonomic Nervous
System (ANS)
SYMPHATHETIC
NERVOUS SYSTEM
PARASYMPHATHETIC
NERVOUS SYSTEM
CNS- brain and spinal cord
PNS- cranial nerves and spinal nerves
SNS- Controls skeletal/voluntary muscles and
transmits sensory information to the CNS
ANS- Controls automatic/involuntary body
functions
Sympathetic Division - Arouses body to expend
energy – Fight or flight
Parasympathetic Division- Peacekeeping or
housekeeping system. Calms body to conserve
and maintain energy.
II. General functions
A. Sensory, integration, and motor – needed to
maintain homeostasis.
Ex.
Seeing a red light - sensory
Red = Stop – integration
Foot pressing brake - motor
1. Sensory – using sensory receptors to monitor
changes inside and outside your body.
2. Integration – processes and interprets
sensory and how to proceed/decide what to do.
3. Motor – effects a response by activating
muscles or glands – called effectors.
III. Nervous Tissue
A. Histology
– Neurons – nerve cell component –
conducts impulses; neuron = one, nerve
= a bundle.
– Neuroglia or glia, – Latin for “nerve glue”
– supportive cells – do not conduct
impulses used for vascular support.
B. Structure of neurons,– 3 basic parts
– Cell body or soma – contains structures like a
common cell – cytoplasm, mitochondria,
lysosomes, Golgi bodies, microtubules
(structural support), Nissl bodies (ER), large
nucleus that includes a nucleolus.
– Dendrites – Latin for “tree” – look like branch
structures. Highly branched structures that
provide receptive surfaces for communication
(basically they receive impulses and conduct
impulses to the soma).
-
Axon – long, slender, cylinder shaped
process that has a smooth surface. It
carries impulses away from the soma to
other structures (axons or dendrites).
Axon has several different structures.
– Axon collateral – a branching axon.
– Axon terminals or telodendria – fine
extensions at the end of the axon. (book uses
terminal branches- we are using telodendria or axon terminals)
– Synaptic knob or synaptic bulb –
swollen end of an axon. (book uses axon terminals (secretory
region- don’t use this)
• Myelin sheath – insulating, lipid material
wrapped around an axon. It helps to
speed up reactions. Myelinated tissues
are called white matter and unmyelinated
tissue is called gray material.
• Nodes of Ranvier – the spaces between
myelin sheaths.
C. Neuroglia or glia – specialized cells
• Oligodendrocytes – in central nervous
system – forms myelin sheaths in central
nervous system.
• Schwann cells – peripheral nervous
system – forms myelin sheaths in the
peripheral nervous system
• Astrocytes – looks like star shaped
structures – forms blood brain barrier and
provides active transport of blood used for
nourishment.
• Microglia- phagocytic cells used for
defense in the Central Nervous System
• Ependymal cells -lines fluid-filled cavities
in the brain and spinal cord. It has cilia to
keep fluid circulating within the cavities
IV. Classifications of neurons
A. Structural divisions
– Multipolar – most common type, they have
cell body with many nerve fibers/dendrites,
and one axon.
– Bipolar – has cell body with one dendrite and
one axon. Are found in sensory tracts, retina,
inner ear, olfactory cells (smell).
– Unipolar- has a cell body, one axon extension
branching into two axon type structures ,
central process and a peripheral process,
one acts as the axon and one as the dendrite
B. Functional divisions/classifications,
• Sensory neurons/afferent neurons – carry
conducting impulses from receptor to the brain and
spinal cord/central nervous system.
• Interneurons/association neurons – transports
impulses between neurons with brain and spinal
cord/central nervous system.
• Motor neurons/efferent neurons – conducts impulses
from brain and spinal cord/central nervous system to
effectors (muscles or glands).
V. Neurophysiology OverviewA. Neurophysiology – the functions of
neurons – Nerve Impulses
1. Neurons are highly irritable (they
respond to stimuli).
2. When a neuron is adequately
stimulated, an electrical impulse can be
generated.
3. Impulse is generated along the axon
and the plasma membrane (neurilemma).
4. Ion differences allow the cell membrane to be
more permeable using a sodium/potassium
pump where two K+ are pumped in and three
Na+ are ejected from the cell. (solute pumpactive transport)
5. Membrane potential – the difference in
electrical charge between inside and outside of
the plasma membrane due to the various
concentrations of ions that normally exist in the
ECF and ICF.
Measuring Membrane Potential
Figure 11.7
B. Role of Ion Channels
1. Types of plasma membrane ion
channels:
– Passive or leakage channels – always open
– Chemically gated channels – open with
binding of a specific neurotransmitter
– Voltage-gated channels – open and close in
response to membrane potential
– Mechanically gated channels – open and close
in response to physical changes of receptors
Operation of a Gated Channel
Figure 11.6a
Operation of a Voltage-Gated
Channel
VI. Conduction of Nerve Impulses
A. Resting Membrane Potential (RMP) –
when a neuron is not conducting electrical
signals, it is said to be “resting”. At rest, a
neuron’s resting membrane potential is
typically maintained at about -70 mV. This is
due to differences in the ions inside and
outside of the cell
Resting Membrane Potential
Figure 11.8
B. Changes in Membrane Potential
1. Changes are caused by three events
– Depolarization – the inside of the membrane
becomes less negative as Na+ rushes into the cell
– Repolarization – the membrane returns to its resting
membrane potential, Na+ gates close, K+ gates open
– Hyperpolarization – the inside of the membrane
becomes more negative than the resting potential due
to too much K+ leaving the cell
These 3 events generate an Action Potential (AP)principle method neurons use to send signals
over long distances (nerve impulse)
Changes in Membrane Potential
Figure 11.9
C. Action Potentials (APs)
• A brief reversal of membrane potential
• Action potentials are only generated by muscle
cells and neurons
• They do not decrease in strength over distance
• They are the principal means of neural
communication
• This is an electrical fluctuation that travels along
the surface of a neuron’s plasma membrane.
• Action potential is typically maintained at
+30mV.
Propagation of an Action Potential
(Time = 2ms)
Figure 11.13b
Phases of the Action Potential
• 1 – resting state
• 2 – depolarization
phase
• 3 – repolarization
phase
• 4–
hyperpolarization
Figure 11.12
Action Potential Graph
a. Resting membrane potential – -70 mV due to
ion differences.
b. Depolarization – moves up to zero and higher
to +35 mV. Also called AP
c. Repolarization – going back to resting
membrane potential. Na+ gates close and K+
gates open .K+ rush out of the cell. High K+
outside of the cell and high Na+ inside the
cell.
d. Hyperpolarization – causes change away from 0 mV. More K+
moved out than was necessary. Neuron cannot be stimulated due
to too much K+ in the cell.
e. Refractory period – a brief period during which a local area of
an axon’s membrane resists stimulation – no stimulus can occur.
Na+ /K+ pump moves Na+ out of the cell and K+ into the cell.
Reestablishes or balances out the original distribution of ions.
VII. Difference in Conduction
A. Unmyelinated fibers – impulse or action
potential are produced along the length of the
axon – the impulse travels slower.
B. Myelinated fibers – impulses or action
potentials are generated at the nodes of Ranvier
called saltatory conduction – impulses travel
faster.
1. Saltatory conduction –process in which a nerve
impulse travels along a myelinated fiber by jumping or
leaping from one node of Ranvier to the next.
Saltatory Conduction
Figure 11.16
VIII. Synaptic Transmission
A. Synapse – the location or place where signals
are transmitted from neuron to neuron.
• 1. There are two types:
– Electrical synapse – occurs where two cells are joined
end to end by gap junctions (found in cardiac muscle
and some smooth muscles…are part of the cardiac
conduction system). Are important in the CNS in
arousal from sleep, mental attention, emotions and
memory, ion and water homeostasis
– Chemical synapse – chemical transmitter also called
a neurotransmitter. Used to send a signal from the
pre-synaptic cell to the post-synaptic cell.
Synapses
Figure 11.17
Synaptic Cleft
Ca2+
1
Neurotransmitter
Axon terminal of
presynaptic neuron
Postsynaptic
membrane
Mitochondrion
Axon of
presynaptic
neuron
Na+
Receptor
Postsynaptic
membrane
Ion channel open
Synaptic vesicles
containing
neurotransmitter
molecules
5
Degraded
neurotransmitter
2
Synaptic
cleft
Ion channel
(closed)
3
4
Ion channel closed
Ion channel (open)
Figure 11.18
Structures to Know-synapse
A.
B.
C.
D.
E.
F.
G.
Pre-synaptic membrane – the semi-permeable
membrane of the synaptic bulb.
Synaptic knob – end of an axon.
Synaptic vesicles – in the synaptic knob, houses
neurotransmitters.
Neurotransmitters – located inside the synaptic
vesicles.
Synaptic cleft – space between pre-synaptic
membrane and post-synaptic membrane.
Post-synaptic membrane – the semi-permeable
membrane of the receptor site.
Ion channels (protein receptors) – located on the postsynaptic membrane, where neurotransmitter binds
What Happens in Synaptic transmission?
1. Impulse reaches synaptic bulb
2. Presynaptic membrane depolarizes
3. Ca+2 channels/gates open
4. Ca+2 enters synaptic bulb
5. Vesicles migrate to presynaptic membrane
6. Vesicle fuse with membrane
7. Neurotransmitter release into cleft by
exocytosis
8. Neurotransmitters binds to receptor on post
synaptic membrane
9. Postsynaptic neuron depolarizes
10.Passes impulse to next postsynaptic
membrane
IX. Neurotransmitters
A.
Neurotransmitters- chemical messengers used in
neuron impulse transmission.
1. stored in synaptic vesicles in synaptic bulb.
2. 50 different neurotransmitters have been
identified
3. classified as either inhibitory or excitatory based
on function
4. classified as Acetylcholine (ACh), amines, amino
acids, peptides, purines, dissolved gases
5. common examplesAcetylcholine (ACh), epinephrine, norepinephrine,
dopamine, serotonin, endorphins