ME01 - Nerve & Synaptic Physiology Flashcards by Kate Alyssa Caton

Communications and control network that allows an organism to interact in appropriate ways with its environment

Nervous System

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Involved in Myelin formation around axons in the peripheral nervous system

Schwann Cell

Each Schwann cell myelinates only one axon

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Myelinating Cells

C-O-P-S
CNS
Oligodendrocytes
PNS
Schwann cells

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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

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Encapsulate dorsal root and cranial nerve ganglion cells

Regulate their microenvironment in a fashion similar to that used by the astrocytes

Satellite Cells

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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

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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

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Process whereby neurons transduce env’t energy into neural signals
Accomplished by sensory receptors
Ex. Mechanical, Light, Sound, Chemical, Thermal

Sensory Detection

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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

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Totality of na organism’s response to its environment

Expression of Behavior

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Function of NS which plays a role in processing and storage of information

Language

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Special forms of information processing that permit behavior to change appropriately in response to previously experience env’t challenges

Learning and Memory

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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

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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

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Types of Macroglia
In the CNS
In the PNS

In the CNS: Astrocytes and Oligodendroglia

In the PNS: Schwann Cell and Satellite Cells

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Star-shaped
Regulate CNS microenvironment
Foot processes form the BLOOD-BRAIN BARRIER

ASTROCYTES

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TYPES OF ASTROCYTES
Fibrous -
Protoplasmic -

Fibrous - many intermediate filaments, in white matter

Protoplasmic - granular cytoplasm, in gray matter

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involved in myelin formation around axons of CNS

Many central axons can be myelinated by single ________

OLIGODENDROCYTE

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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

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Type of Fibers Unmyelinated

Type C

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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)

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Ability to respond to env’t changes called STIMULI

Highest degree of development of this property seen in neurons

Excitability

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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

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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

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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 >> 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