ME01 - Nerve & Synaptic Physiology Flashcards
Communications and control network that allows an organism to interact in appropriate ways with its environment
Nervous System
Involved in Myelin formation around axons in the peripheral nervous system
Schwann Cell
Each Schwann cell myelinates only one axon
Myelinating Cells
C-O-P-S CNS Oligodendrocytes PNS Schwann cells
Importance of Myelination
Increases speed of AP conduction
Restricts flow of ionic current to small myelinated portions of the axon between adjacent sheath cells (Nodes of Ranvier) – Saltatory conduction
Encapsulate dorsal root and cranial nerve ganglion cells
Regulate their microenvironment in a fashion similar to that used by the astrocytes
Satellite Cells
PARTS OF NEURON
CELL BODY - metabolic and integrative center of the neuron
DENDRITES - processes extend outward (arbor vitae)
AXON - long fibrous process that originates from axon hillock; divides into presynaptic terminals ending in synaptic knobs (terminal button)
Contain granules or vesicles which contain neurotransmitter
Divisions of NS
CNS -
PNS -
CNS - central hub, all info is being processes, Brain and Spinal Cord
PNS - Interface between Env’t and CNS, Sensory neurons, somatic motor neurons and autonomic motor neurons
Process whereby neurons transduce env’t energy into neural signals
Accomplished by sensory receptors
Ex. Mechanical, Light, Sound, Chemical, Thermal
Sensory Detection
Information and Processing, which is a function of NS, includes:
Transmission of information via neural networks
Transformation of information by recombination with other information
Perception of sensory information
Storage and retrieval of information
Planning and implementation of motor commands
Thought processes and conscious awareness
Learning
Emotion and motivation
Totality of na organism’s response to its environment
Expression of Behavior
Function of NS which plays a role in processing and storage of information
Language
Special forms of information processing that permit behavior to change appropriately in response to previously experience env’t challenges
Learning and Memory
Major Cell Types in the NS
Neurons -
Neuroglia -
Neurons - nerve cells; for communication and signaling
Neuroglia - nerve glue; sustain neurons both metabolically and physically: MAINTAIN internal milieu of the nervous system
Types of Neuroglia:
Microglia -
Macroglia -
Ependymal cells -
Types of Neuroglia:
Microglia - macrophage in the brain; removes injury or disease
Macroglia - supportive matrix of CNS; protects neurons
Ependymal cells - epithelial lining in ventricular spaces of brain
Special Ependymal cell: CHOROID PLEXUS - prod. of CSF
Types of Macroglia
In the CNS
In the PNS
In the CNS: Astrocytes and Oligodendroglia
In the PNS: Schwann Cell and Satellite Cells
Star-shaped
Regulate CNS microenvironment
Foot processes form the BLOOD-BRAIN BARRIER
ASTROCYTES
TYPES OF ASTROCYTES
Fibrous -
Protoplasmic -
Fibrous - many intermediate filaments, in white matter
Protoplasmic - granular cytoplasm, in gray matter
involved in myelin formation around axons of CNS
Many central axons can be myelinated by single ________
OLIGODENDROCYTE
TYPES OF NERVE FIBERS
FIBER TYPE FUNCTION DIAMETER VELOCITY MYELINATION
A a
ß
y
∫ (s)
B
C dorsal root
sympathetic
FIBER TYPE FUNCTION DIAMETER VELOCITY MYELINATION
A a Proprioception 12-20 70-120 Myelinated
ß Touch, pressure 5-12 30-70 Myelinated
y Motor to musc. spindle 3-6 15-30 Myelinated
∫ (s) Pain, Cold, Touch 2-5 12-30 Myelinated
B Preganglionic autonomic
Type of Fibers Unmyelinated
Type C
Classification of Sensory Neurons Ia Ib II III IV
Ia - Annulospiral endings of muscle spindle (A alpha)
Ib - Golgi tendon organs (A alpha)
II - Flower-spray endings of muscle spindle (Aß, Ay)
discrete cutaneous tactile receptors -pressure and touch
III - Temperature, Crude touch, Pricking pain (A∫ (s)
IV - Unmyelinated fibers carrying pain, itch, temp, crude touch (C)
Ability to respond to env’t changes called STIMULI
Highest degree of development of this property seen in neurons
Excitability
Any change in the env’t that will influence an organism and cause a response
Stimulus Mechanical - pinching, pricking Chemical - acid, alkali Thermal - Change in temp Electrical - electrical stimulation
Elementary Attributes of Stimulus Modality - Location Intensity Duration (An effective stimulus is MILD)
Modality - type of energy; Adequate stimulus is most sensitive
Location - site on body where stimulus originated
Intensity - Response amplitude or frequency of action potential
Duration - Time from start to end of response in receptors
What is a sensory unit
Sensory unit = single sensory axon and all its peripheral branches
Spatial distribution from which stimulus produces response
Receptive field
Sensation from receptors of peripheral edge of stimulus is inhibited compared to sensation from central receptors
Lateral inhibition
Magnitude of sensation felt is proportional to the intensity of the stimuli
Weber-Fechner Law
Frequency of action potentials in sensory nerves decline over time
Desensitization/Adaptation
Receptors can be classified as
Rapidly adapting - Phasic receptors
Slowly adapting - Tonic receptors
Graph of threshold stimulus vs stimulus duration
Strength-Duration Curve
Stimulus strength required to reach threshold should __________ during prolonged stimulation
DECREASE
An asymptote wherein the curve flattens out with long stimulus durations
Rheobase
When stimulus is below the rheobase, stimulation is ineffective even when stimulus duration is very long
Stimulus duration equal to twice the rheobase
Chronaxie
Chronaxie and Excitability
LOWER the Chronaxie, the MORE excitable a nerve is
Strength-Duration and Conduction Velocity
Curve shifted to the _______ for slower nerve fibers
RIGHT
Longer stimulus duration would be needed to bring SLOWER NERVE FIBERS to threshold
Once threshold is reached, full fledged AP is produced
Further increase produce no change or increment
AP fails to occur if stimulus is subthreshold in magnitude
All-Or-None Principle
Junction that permits neurons to pass electrical or chemical signal to other cells
Synapse
Types of Synapse Parameter NERVE CONDUCTION SYNAPTIC TRANSMISSION type of event continuity of neurons directionality conduction delay neurotransmitters speed of propagation
Parameter NERVE CONDUCTION SYNAPTIC TRANSMISSION
type of event Electrical Chemical
continuity of neurons Continuous Non-continuous (cleft)
directionality Multi directional Unidirectional
conduction delay Absent Present
neurotransmitters Absent Present
speed of propagation +++ ++
Plaque like structures in which plasma membranes of coupled cells become closely apposed
Gap Junction
Time required for multiple steps in chemical neurotransmission
Synaptic delays
ARRANGEMENT OF SYNAPSES
One-to-One
One-to-Many
Many-to-One
Presynaptic neurons»_space; Postsynaptic neurons
One-to-One - neuromuscular junction
One-to-Many - motoneurons on renshaw cells
Many-to-One - widespread in CNS/PNS
EVENTS IN SYNAPTIC TRANSMISSION
1 - Synthesis and Storage of Neurotransmitter (formation of Ach)
2 - Depolarization and Calcium Influx (depolarization opens Ca chann)
3 - Release of Neurotransmitters
4 - Binding of Neurotransmitter to Postsynaptic Membrane (binding of Ach to Ach receptor cause increase Na+ and K+ conductance)
5 - Generation of Postsynaptic Potential - MEPP
6 - Depolarization of Effectors - AP in adjacent muscle tissure
7 - Terminaiton of Neurotransmitter Action - ACh is degraded by AChE
Small molecules endogenous chemicals transmit signals from neuron to target cell across synapse
Neurotransmitter
Essential Characteristics of Neurotransmitters
Precursors/Synthesis enzymes located in presynaptic neuron
Available in sufficient quantity affect postsynaptic cells
Capable of binding to postsynaptic receptors
Biochemical mechanism for inactivation
Where is ACh secreted
Large pyramidal cells in motor cortex
Basal Ganglia (Nucleus basilis of Meynart)
Skeletal Muscles
All preganglionic of ANS
Postganglionic of Parasympathetic and Sympa NS
Where is Norepi and Epi secreted
Brain stem
Hypothalamus
Locus ceruleus in the pons
Postganglionic neurons of sympathetic NS
Function of Norepi and Epi
Control overall activity and mood of mind,
Increasing level of waefulness
Where is Dopamine secreted
Substantia Nigra
Action terminated by DAR
Where is Glycine secreted and function
Spinal cord (Renshaw cells) Inhibitory transmitter
Where is GABA secreted and function
Spinal cord, cerebellum, basal ganglia
Inhibitory transmitter
Where is GLUTAMATE secreted and function
Presynaptic terminals of sensory pathways
PREVALENT EXCITATORY neurotransmitter
Where is SEROTONIN secreted and function
Median raphe of brainstem
Inhibitory
Mood and Sleep
Where is NO secreted and function
areas responsible for long-term behavior and memory
Short-acting inhibitory
Not preformed and stored in vesicles, it is synthesizes almost instantly as needed
Neurotransmitter ORIGIN FUNCTION Acetylcholine Norepinephrine Dopamine Serotonin
Neurotransmitter ORIGIN FUNCTION
Acetylcholine basal forebrain learning, memory
Norepinephrine locus ceruleus of pons arousal, wakefulness
Dopamine substantia nigra of basal ganglia fine tuning movement
Serotonin median raphe of brain stem mood, sleep
NT purely excitatory
Glutamate
NT purely inhibitory
Glycine, GABA, Serotonin
NT may be inhibitory or excitatory
ACh, NorEpi and Epi, Dopamine,
Synaptic Information
EPSP
IPSP
EPSP - inputs that depolarize bring it CLOSER to threshold, Na+K+
IPSP - inputs that hyperpolarize move it away from threshold, Cl-
Process of adding up post synaptic potentials and respond to their net effect
Summation
Types of Summation
SPATIAL
TEMPORAL
SPATIAL - when two EPSPs arrive at PSN simultaneoulsy, produce greater depolarization
TEMPORAL - when EPSPs arrive at PSN rapid succession, overlap in tume adding in stepwise fashion
Process where one neuron enhances the effect of another neuron
EPSPs bring membrane potential nearer to threshold
Presynaptic Facilitation
Opposite of facilitation
One presynaptic neuron suppresses another one
IPSPs bring MP farther from threshold
Presynaptic Inhibition
Bringing additional neurons into play as stimulus becomes stronger
Enables Nervous System to judge stimulus strength by which neurons, how many of them are firing
RECRUITMENT
Neurons function in larger ensembles
Neuronal Pool
Ex. Neuronal Pool for Rhythm of breathing
Zones of Neuronal Circuits
Discharge Zone
Facilitated Zone
Discharge Zone - input neuron acting alone can make PS cells fire
Facilitated Zone - presynaptic input neuron synapse with other neurons in the pool, can stimulate to fire only with assistance of other input neurons
Subliminal Fringe
If they are not discharged by afferent volley
They have excitability increased
Decrease in expected respons
Occurs due to presynaptic fibers SHARING postsynaptic neurons
Occlusion
Signals from multiple inputs unite to excite single neuron
Convergence
Types of Convergence
Convergence from
Single Source
Multiple separate sources
Input from just one neuron may produce output through dozens of neurons
Divergence
Types of Divergence
Amplifying - input signal spreads to INC no of neurons as it passes through successive orders of neurons in its path,
Ex. CST
Divergence into Multiple Tracts - signal is transmitted in two directions from neuronal pool
Ex. Dorsal columns, thalamic pathways
Known as Close chain Circuit
Send prolonged or repetitious signals until one neuron fail to fire or inhibitory signals stops one of neurons from firing
Reverberation
One input neuron diverges to stimulate several circuit of neurons
OUTPUT CEASE once all neurons in the circuit have fired
Continued firing after the stimulus stop is called AFTERDISCHARGE
PARALLEL-AFTER-DISCHARGE
Classification of Neurons based on
NUMBER OF PROCESSES
UNIPOLAR - one process, different segments that serve as receptives
BIPOLAR - two specialized processes (dendrites and axon)
PSEUDO-UNIPOLAR - single process splits into two, both of which function as PDF,
MULTIPOLAR - more than 2 specialized processes
