Transcript Action Potentials

Nervous Tissue
Chapter 12
12-1
Nervous Tissue
• Overview of the nervous
system
• Nerve cells (neurons)
• Supportive cells
(neuroglia)
• Electrophysiology of
neurons
• Synapses
• Neural integration
12-2
Overview of Nervous System
• Master Control of the Body
– Endocrine and nervous system maintain
internal coordination
• endocrine = _____________________________
• nervous
– _______________________ receive information
– brain and spinal cord determine responses
– brain and spinal cord __________________________
_____________________________________________
12-3
Subdivisions of Nervous System
Two major subdivisions
• _________________________
– brain and spinal cord
enclosed in bony coverings
• _________________________
– nerve = _________________
_______________________
– _____________ = swelling
of ____________ in a nerve
12-4
Functional Divisions of PNS
• Sensory (____________) divisions
(receptors to CNS)
– visceral sensory and somatic
sensory division
• Motor (_______________) division
(CNS to effectors)
– visceral motor division (ANS)
effectors: cardiac, smooth
muscle, glands
• sympathetic division
(action)
• parasympathetic division
(digestion)
– somatic motor division
effectors: skeletal muscle
12-5
Fundamental Types of Neurons
• Sensory (afferent) neurons
– _________________________
_________________________
– Transmit info to brain/spinal
cord
• ___________________________
– In between sensory and
motor pathways in CNS
– 90% of neurons are
interneurons
– _________________________
_________________________
• ___________________________
– send signals to muscles and
glands
– organs respond called
effectors
12-6
Properties of Neurons
• ____________________________
– ability to respond to changes (stimuli)
in/out of body
• Conductivity
– _______________________________
• ____________________________
– ____________________________________
12-7
Structure of a
Neuron
• _________________________
_________________________
– single, central nucleus
– cytoskeleton
• microtubules and
neurofibrils (bundles of
actin filaments)
• RER  Nissl bodies
• _________________________
– ______________________
• Singe axon (nerve fiber)
arising from axon hillock for
rapid conduction
– _______________________
_______________________
12-8
Variation in
Neural Structure
• ____________________
– most common
– many dendrites/one axon
• Bipolar neuron
– ______________________
– ______________________
• ____________________
– sensory from skin and
organs to spinal cord
• Anaxonic neuron
– many dendrites/no axon
– help in visual processes
12-9
Types of Neuroglial Cells
• ___________________________________________
– wraps around nerve fibers
• ___________________________________________
• ___________________________________________
– in areas of infection, trauma or stroke
12-10
Types of Neuroglial Cells
• ________________________________
–
–
–
–
–
–
_________________________________________________
regulate composition of brain tissue fluid
convert glucose to lactate to feed neurons
secrete nerve growth factor promoting synapse formation
electrical influence on synaptic signaling
sclerosis – damaged neurons replace by hardened mass of
astrocytes
• ________________________________________
12-11
Myelin
• ________________________________________
– formed from wrappings of plasma membrane
• 20% protein and 80 % lipid (looks white)
– all myelination completed by late adolescence
• In PNS, hundreds of layers wrap axon
– ____________________________________________
– covered by basal lamina and endoneurium
12-12
• Gaps between myelin segments = _________________
Speed of Nerve Signal
• Diameter of fiber and presence of myelin
• ______________________________________________
• Speeds
– small, unmyelinated fibers = 0.5 - 2.0 m/sec
– small, myelinated fibers = 3 - 15.0 m/sec
– large, myelinated fibers = up to 120 m/sec
• Functions
– slow signals supply the stomach and dilate pupil
– fast signals supply skeletal muscles and transport
sensory signals for vision and balance
12-13
Regeneration of Peripheral Nerves
• Soma and neurilemmal tube intact
• Stranded end of axon and myelin
sheath degenerate
– cell soma swells, ER breaks up
and some cells die
• Axon stump puts out several
sprouts
• _____________________________
_____________________________
– schwann cells produce nerve
growth factors
12-14
Local Potentials
• Local disturbances in
membrane potential
– ___________________
___________________
– depolarization (opens
gated Na+ channels)
decreases potential
across cell membrane
• Na+ rushes in
• Na+ diffuses for
short distance
inside membrane
producing a
change in voltage
called a local
potential
12-15
Local Potentials 2
• ___________________________
– vary in magnitude with stimulus strength
– get weaker the farther they spread
– are reversible as K+ diffuses out of cell
– ____________________________________
____________________________________
12-16
Action Potentials
• __________________________________________
__________________________________________
• If threshold potential (-55mV) is reached voltagegated Na+ channels open (Na+ enters causing
depolarization)
• Slow K+ gates fully open
• K+ exits repolarizing the cell
• __________________________________________
12-17
– excessive exiting of K+
The Refractory Period
• Resists stimulation
• ________________________
– as long as Na+ gates are open
– _________________________
• ________________________
– as long as K+ gates are open
– __________________________
__________________________
• Refractory period occurs to a
small patch of membrane at
one time (quickly recovers)
12-19
Impulse Conduction - Unmyelinated
Fibers
12-20
_______________________________
• Voltage-gated channels needed for APs
– fewer than 25 per m2 in myelin-covered regions
– up to 12,000 per m2 in nodes of Ranvier
• Fast Na+ diffusion occurs between nodes
12-21
Saltatory Conduction
• Notice how the action potentials jump from
node of Ranvier to node of Ranvier.
12-22
Chemical Synapse Structure
• ______________________ have synaptic
vesicles with neurotransmitter and
____________________ have receptors
12-26
Types of Neurotransmitters
•
_______________________________
–
•
•
Amino acid neurotransmitters
_______________________________
–
–
–
•
formed from acetic acid and choline
replace –COOH in amino acids with another
functional group
______________________ (epi, NE and dopamine)
indolamines (serotonin and histamine)
________________
12-27
Synaptic Transmission
3 kinds of synapses with different actions
• _______________________________ = ACh
• Inhibitory GABA-ergic synapse = GABA
• ________________________________ = NE
Synaptic delay (.5 msec)
– time from arrival of nerve signal at synapse to
start of AP in postsynaptic cell
12-29
Neural Integration
• More synapses a neuron has the greater its
information-processing capability
– cerebral cortex  40,000 synapses
• estimated to contain 100 trillion synapses
• Chemical synapses are decision-making
components
– ______________________________________
12-30
Postsynaptic Potentials- EPSP
• __________________________________
_____________________
– a positive voltage change causing
postsynaptic cell _____________________
• result from Na+ flowing into the cell
– glutamate and aspartate are excitatory
neurotransmitters
• ACh and norepinephrine may excite or
inhibit depending on cell
12-31
Postsynaptic Potentials- IPSP
• ___________________________________
postsynaptic cell to be less likely to fire
(hyperpolarize)
• result of Cl- flowing into the cell or K+ leaving the
cell
– glycine and GABA are inhibitory
neurotransmitters
• ACh and norepinephrine may excite or
inhibit depending upon cell
12-32