Unit 4 Part 1 Flashcards
The master controlling and communication system of the body
Nervous System
Controls and integrates all body activities within limits that maintain life
Nervous System
Three basic functions of nervous system
- Sensory Function
- Integrative function
- Motor function
▪ Monitors internal and external stimuli (changes)
▪ Afferent pathway to the brain
▪ Receptors
Sensory Function
▪ Process and interprets information
▪ Decides appropriate response
Integrative Function
▪ Efferent pathway to effector organs (muscles or glands), effects a response
Motor Function
Basic divisions of the nervous system
Central Nervous System
Peripheral Nervous System
Central Nervous System includes
brain and spinal cord
Peripheral Nervous System includes
cranial nerves, spinal nerves, ganglia, enteric plexuses, sensory receptors
Functional Classification of the PNS
Sensory (afferent) division
Motor (efferent) division
- carrying toward a center (usually integrating center, the CNS)
-Nerve fibers that carry information to the central nervous system
-Somatic sensory
-Visceral sensory
Sensory (afferent) division
Somatic sensory includes
(skin, skeletal muscle)
Visceral sensory includes
(visceral organs)
-Nerve fibers that carry impulses away from the central nervous system
-Activate (effect) muscles or glands to bring about a response.
Motor (efferent) division
Motor (efferent) = 2 divisions
Somatic nervous system
Autonomic nervous system
voluntary (skeletal muscles)
Somatic nervous system
involuntary (smooth and cardiac muscles, glands)
Autonomic nervous system
-basic structural units of the nervous system
-highly specialized cells
-conduct electrical signals from one part of the
body to another
-signals are transmitted along the plasma membrane in the form of nerve impulses or action potentials
Neuron
Characteristics of Neurons
-They have extreme longevity.
-They do not divide
-They have an exceptionally high metabolic
rate
-Neurons cannot survive for more than a few
minutes without oxygen
– metabolic center
Cell body
info for protein synthesis
Nucleus
Nissl bodies location
in ER
maintain structure
Neurofilaments
Cell processes
a) Dendrites
b) Axons
-Conducts impulses towards
the cell body (from other neurons or sensory receptors)
- short, highly branched & unmyelinated
- Surfaces specialized for contact with other neurons
-Most are extensions from the neuron cell body; others project from the peripheral ends of some axons
-Contains neurofibrils & Nissl bodies
Dendrites
-Conduct impulses away from cell body
-Long, thin cylindrical process of cell, branched or unbranched
-Arises at axon hillock
- Impulses arise from initial segment (trigger zone)
-Side branches (collaterals) end in fine processes called axon terminals
-Swollen tips called synaptic end bulbs contain vesicles filled with neurotransmitters
Axons
Neurons can be classified ___ or ____
structurally, functionally
Neurons are grouped ____ according to
the number of ___ that extend from the
cell body
structurally, processes
Structural Classification of Neurons
-Multipolar
-Bipolar
-Unipolar
-several dendrites & one axon
-most common cell type
multipolar
-one main dendrite & one axon
-found in retina, inner ear & olfactory
bipolar neurons
-one process only (develops from a bipolar)
-are always sensory
neurons
unipolar neurons
The ___ classification scheme groups neurons
according to the ___ in which the nerve impulse ___ relative to the CNS
functional; direction; travels
Functional Classification
▪ Sensory neurons
▪ Motor neurons
▪ Interneurons
-afferent neurons
-They transmit impulses toward the CNS from
sensory receptors in the PNS
-The single (unipolar) process is divided into the
central process and the peripherial process
Sensory Neurons
Sensory neurons have their cell bodies in __
outside of the ____
ganglia; cns
specialized to respond to changes in environment
Sensory receptors
Three ways to classify receptors:
- type of stimulus
- body location
- structural complexity
Classification by Stimulus Type
▪ Mechanoreceptors
▪ Thermoreceptors
▪ Photoreceptors
▪ Chemoreceptors
▪ Nociceptors
respond to touch, pressure, vibration, and stretch
Mechanoreceptors
sensitive to changes in temperature
Thermoreceptors
respond to light energy (example: retina)
Photoreceptors
respond to chemicals (examples: smell, taste, changes in blood chemistry)
Chemoreceptors
sensitive to pain-causing stimuli
(examples: extreme heat or cold, excessive pressure, inflammatory chemicals)
Nociceptors
Classification by Location
Exteroceptors
Interoceptors (visceroceptors)
Proprioceptors
-Respond to stimuli arising outside body
-Receptors in skin for touch, pressure, pain, and
temperature
-Most special sense organs
Exteroceptors
-Respond to stimuli arising in internal viscera and
blood vessels
-Sensitive to chemical changes, tissue stretch, and
temperature changes
-Sometimes cause discomfort but usually person is
unaware of their workings
Interoceptors (visceroceptors)
▪ Respond to stretch in skeletal muscles, tendons,
joints, ligaments, and connective tissue coverings of bones and muscles
▪ Inform brain of one’s movements
Proprioceptors
Majority of sensory receptors belong to one of two
categories:
▪ Simple receptors of the general senses
▪ Receptors for special senses
▪ Modified dendritic endings of sensory neurons
▪ Are found throughout body and monitor most
types of general sensory information
Simple receptors of the general senses
▪ Vision, hearing, equilibrium, smell, and taste
▪ All are housed in complex sense organs
Receptors for special senses
▪ Neurons that carry impulses away from the CNS to effector organs (muscles and glands) are called motor or efferent neurons
▪ Upper motor neurons are in the brain
▪ Lower motor neurons are in PNS
▪ multipolar and their cell bodies are located in the CNS (except autonomic)
▪ form junctions with effector cells, signaling muscle to contract or glands to secrete
Motor Neurons
▪ lie between the motor and sensory neurons
▪ Form complex neural pathways
▪ Confined to CNS
▪ Make up 99.98% of the neurons of the body and are the principle neuron of the CNS
▪ Almost all are multipolar
▪ show great diversity in the size and branching patterns of their processes
Interneuron or Association Neurons
is the large neuron found in the primary motor cortex of the cerebrum
Pyramidal cell
interneuron from the cerebellum
Purkinje cell
-Supporting Cells
-Half of the volume of the CNS
-Smaller cells than neurons
-50X more numerous
-Not conduct impulses
-Cells can divide
Neuroglial Cells
▪ Star-shaped
▪ Most abundant
▪ Form blood-brain barrier
▪ Metabolize neurotransmitters (glutamate)
▪ Recapture and Recycle K+ ions
▪ Provide structural support
▪ Play a role in exchanges of ions between capillaries and neurons
▪ Involved with synapse formation in developing
neural tissue
▪ Produce molecules necessary for neural growth (brain-derived trophic factor BDTF)
▪ Propagate calcium signals that may be involved in memory
Astrocytes
Metabolize neurotransmitters
(glutamate)
Produce molecules necessary for neural growth
(brain-derived trophic factor BDTF)
Propagate ___ signals that may be involved in
memory
calcium
▪ Most common glial cell type
▪ Each forms myelin sheath around more than one axons in CNS
▪ Analogous to Schwann cells of PNS
Oligodendrocytes
▪ Smallest and least abundant cells found near
blood vessels
▪ Phagocytic role
▪ Derived from cells that also gave rise to macrophages & monocytes; migrate to the CNS during embryonic and fetal development
Microglia
clear away dead cells
Phagocytic role
▪ Form epithelial membrane lining cerebral cavities & central canal
▪ Produce cerebrospinal fluid (CSF)
▪ Cilia aid circulation of CSF
Ependymal cells
▪ These cells are similar in type and differ mainly in location
Neuroglia in the PNS
There are two supporting cells in the PNS
▪ Satellite cells
▪ Schwann cells
▪ Flat cells surrounding neuronal cell bodies in peripheral ganglia
▪ controlling the chemical environment of neurons
▪ Support neurons in the PNS ganglia; ACT AS
PROTECTIVE CUSHIONING
Satellite Cells
▪ produces part of the myelin sheath in the PNS
▪ protective role: aid in maintaining the integrity of normally functioning nerve fibers
▪ vital to peripheral nerve fiber regeneration – PNS only,
Schwann Cell
▪ Insulation of axon
▪ Increase speed of nerve impulse
▪ Makes impulse propagation more energy efficient
▪ White lipid protein substance
Myelination
▪ Prevents the leakage of electrical current from the axon
▪ Increases the speed of impulse conduction
Insulation of axon
All axons surrounded by a lipid & protein covering (myelin sheath) produced by
Schwann cells
cytoplasm & nucleus of Schwann cell
Neurilemma
gaps that occur at regular intervals about 1mm apart
nodes of ranvier
-found in portions of the autonomic nervous system as well as in some sensory fibers
-Thin, slowly conducting axons lack a myelin sheath
Unmyelinated fibers
▪ Neurilemma is found
▪ nodes of ranvier
▪ Only thick, rapidly conducting axons are sheathed in myelin
▪ nerve impulses do not travel along the myelin-covered regions of the axonal membrane, but instead jumps from the membrane of one Node of Ranvier to the next greatly increasing impulse conduction
Myelination: PNS
myelinated axons in PNS, nerve impulses do not travel along the myelin-covered regions of the axonal membrane, but instead____
jumps from the membrane of one Node of Ranvier
Myelinated axons transmit nerve impulses rapidly at what speed
150 meters/second
Unmyelinated axons transmit quite slowly at what speed
1 meter/second
▪ Oligodendrocytes myelinate axons
▪ Broad, flat cell processes wrap about ___ axons, but the cell bodies do not surround the axons
▪ No neurilemma is formed
▪ Little regrowth after injury is possible
Myelination: CNS
Little regrowth in CNS after injury is possible due to the
lack of a distinct tube or neurilemma
▪ Structure that contain a number of cell bodies in the
PNS
▪ Occurs in the PNS
▪ Form the plexuses
▪ Dorsal root ganglia, autonomic ganglia, cranial nerve ganglia
GANGLIA
▪ Structure that contain a number of cell bodies in the CNS
▪ Occur in the CNS
▪ Occur in the gray matter of the brain
▪ Caudate, putamen, dentate, emboliform, pallidum, substantia nigra, subthalamic nuclei
NUCLEI
Bundles of nerve fibers running through CNS
Tracts
Bundles of nerve fibers running through PNS
Nerves
Nerve Fibers
Tracts
Nerves
myelinated processes
White matter
nerve cell bodies, dendrites, axon terminals,
bundles of unmyelinated axons and neuroglia
Gray matter
Neurons are electrically excitable due to the
voltage difference across their membrane
Excitable cells communicate with 2 types of electric signals
Action potentials
Graded potentials
electric signal that can travel long distances
Action potentials
electric signal that are local membrane changes only
Graded potentials
In living cells, production of action potential or graded potential depends upon
upon the existence of resting membrane
potentials and existence of certain ions
Leakage (nongated)
channels are always
open
Gated channels can
open and close
gated channels can be:
a. Chemically (ligand)-gated
b. Mechanically-gated
c. Voltage-gated
-Leakage channels alternate between open
and closed
-K+ channels are more numerous than Na+ channels
Ion Channels in Neurons - Leakage
-Ligand-gated channels respond to chemical
stimuli (ligand binds to receptor)\
-Mechanically-gated channels respond to
mechanical vibration or pressure stimuli
-Voltage-gated channels respond to direct
changes in membrane potential
Ion Channels in Neurons - Gated
Nerve & Muscle cells are
“excitable”
Capable of self-generating electrical impulses
at their membranes
“excitable”
- Electrical potentials exist across the
membranes of essentially all cells of the
body - Nerve & Muscle cells are “excitable” - -
Capable of self-generating electrical impulses
at their membranes - Concentration difference of ions across a
selectively permeable membrane can
produce a membrane potential.
Membrane Potentials
difference in potential ( voltage ) between
the inner side & outer side of the membrane
- Inside cell more negative and more K+
- Outside cell more positive and more Na+
– Must exist for action
potential to occur
– The value for Vm in
inactive muscle cells is
typically btwn –80 and
–90 millivolts.
– Cells that exhibit a Vm
are said to be
polarized.
– Vm can be changed by
influx or efflux of
charge.
Membrane Potentials
It ranges between -70 and -90 mV in different
excitable tissue cells
Resting Membrane Potential ( RMP)
MP in a stimulated cell that is producing a local, non-propagated potential;
-an electrical change which is measurable only in the immediate vicinity of the cell but not far
from it.
Graded Potential (Local Response )
Small deviations in
resting membrane
potential of
-70mV
(more negative
inside)
occurs in response to the
opening of a mechanically-gated or ligand-
gated ion channel
Graded Potentials
The amplitude of a graded potential
depends on the
stimulus strength
Graded potentials can be add together to
become larger
amplitude
MP in case of a
nerve/muscle that is generating a propagated
electrical potential after stimulation by effective
stimulus
Action potential ( AP)
– Large changes in cell membrane potential (charge)
– Inside of the cell becomes more positive relative
to the outside of the cell
– Function to transmit information over long
distances
– Electrical signal that travels along the nerve axon
and ends at the synaptic terminal
– All-or-none principle - Like camera flash system
– RESULTS IN: Releases neurotransmitter
(acetylcholine or ACh)
Action Potentials
level of depolarization
needed to trigger an action potential. Action
potential does not occur until
threshold potential has been reached.
Threshold potential
state membrane
suddenly becomes permeable to Na+ ions;
Allows tremendous numbers of (+) charged
Na+ ions to flow to the interior of the axon;
Potential rises rapidly in the (+) direction
Depolarization stage
Na channels begin to close; K
channels open more than they normally
do; Rapid diffusion of K+ ions to the exterior
re-establishes the normal negative resting
membrane potential
Repolarization
Membrane potential may
briefly become over negative; due to opened
voltage-gated K channels
Hyperpolarization
Ion channels open:
1. Na+ rushes ___
(__polarization)
2. K+ rushes ___
(__polarization)
in; de
out; re
Action potentials can only occur if the
membrane potential reaches
threshold
Period of time during which neuron can
not generate another action potential
Refractory Period of Action Potential
▪ even very strong stimulus will
not begin another AP
▪ From beginning of action potential
until near end of repolarization
▪ Na+ channels are open or
recovering
Absolute refractory period
▪ a suprathreshold stimulus will be
able to start an AP
▪ Occurs when the membrane is
hyperpolarised (-80mV), where the
K+ channels are open
▪ Relative refractory period
Resting membrane
potential is at
-70mV
Depolarization is the
change from
-70mV to
+30 mV
Repolarization is the
reversal from
+30 mV
back to -70 mV)
▪ nerve is -70mV
▪ skeletal & cardiac muscle is closer to -90mV
Resting membrane potential
Duration of nerve impulse is
1/2 to 2 msec
Duration muscle action potential
skeletal
cardiac & smooth
1-5 msec
10-300msec
Fastest nerve conduction velocity is ___ times faster than velocity over skeletal muscle fiber
18
Propagation of An Action Potential
▪ as Na+ flows into the cell
during depolarization, the
voltage of adjacent areas
is effected and their
voltage-gated Na+
channels open
▪ self-propagating along the
membrane
nerve
impulse
traveling action
potential
Nerve impulse conduction
in which the impulse jumps
(Salta) from node to node
Saltatory Conduction
The propagation speed of a nerve impulse is not related to__
stimulus strength.
the___, myelinated fibers conduct impulses __ due to size & saltatory conduction
larger; faster
myelinated somatic sensory & motor to skeletal muscle
largest
A fibers
a fibers speed
(5-20 microns & 130 m/sec)
myelinated visceral sensory & autonomic preganglionic
medium
B fibers
B fibers speed
(2-3 microns & 15 m/sec)
▪ unmyelinated sensory & autonomic motor
smallest
C fibers
C fibers speed
.5-1.5 microns & 2 m/sec
Action potentials can travel along axons at speeds of
of 0.1-100m/s.
Action potentials can travel along axons at speeds of
of 0.1-100m/s.
The speed is affected by 3 factors:
Temperature
Axon diameter
Myelin sheath
increases the speed
of propagation dramatically,
saltatory propagation
Application : Local Anesthetics
▪ Prevent opening of voltage-gated Na+ channels
▪ Nerve impulses cannot pass the anesthetized region
▪ Novocaine and lidocaine
(1)May be blocked in its transmission from one neuron
to the next
(2)May be changed from a single impulse into
repetitive impulses
(3)May be integrated with impulses from other
neurons to cause highly intricate patterns of
impulses in successive neurons.
Fate of Action Potentials
*A connection between a neuron and a second cell
*In the CNS, this other cell is also a neuron.
*In the PNS, the other cell may be either a neuron or an effector cell e.g. gland or muscle
Synapse
from axon to dendrite
axodendritic
from axon to cell body
axosomatic
from axon to axon
axoaxonic
from dendrite to dendrite
dendrodenritic
from dendrite to cell body
dendrosomatic
2 Types of synapses
electrical
chemical
▪ ionic current spreads to next cell through gap
junctions
▪ faster, two-way transmission & capable of
synchronizing groups of neurons
electrical
one-way information transfer from a presynaptic
neuron to a postsynaptic neuron
chemical
both electrical and chemical,
e.g. neurons in lateral vestibular nucleus
CONJOINT SYNAPSE
- Have direct open fluid channels that conduct electricity from one cell to the next without interruption
- Have gap junctions which allow the movement of ions
- Very few in the CNS (brain and glial cells) but are the
predominant type in the periphery of the body (i.e.
skeletal, cardiac and smooth muscle contraction) - The bidirectional transmission of electrical synapses
permits them to help coordinate the activities of large
groups of interconnected neurons. - Promotes synchronous firing of a group of interconnected
neurons - For example, in Mental attention, Emotions and
Memory, Arousal from sleep
Electrical Synapse
- Almost all of the synapses in the CNS
- First neuron secretes a neurotransmitter
- Neurotransmitter binds to receptors on the second neuron
(excites, inhibits, or modifies its sensitivity) - Always transmit signals in one direction (from the pre-synaptic neuron (releases neurotransmitter) to the post-
synaptic neuron - Called the principle of one way conduction
Chemical Synapse
Factors Affecting Synaptic Transmission
- pH of the interstitial fluid
- Hypoxia – depresses neurons
- Drugs, toxins and diseases
neuronal excitability; causes cerebral epileptic seizures (Increased excitability cerebral neurons) e. g. overbreating in person with
epilepsy
Alkalosis
–decreased neuronal activity; pH around 7.0 usually causes a coma
(e.g.severe diabetic or uremic acidosis)
Acidosis
depresses neurons
Hypoxia
caffeine found in coffee, tea,
strychnine, theophylline, theobromine increases neuronal
excitability by decreasing the threshold for excitation of neurons
Drugs, toxins and diseases
▪ More than 50 chemical substances have been proven
▪ Two groups: small molecule (rapidly acting) and neuropeptides (slowly acting)
Neurotransmitters
▪ Synthesized in the cytosol of the presynaptic
terminal
▪ Absorbed by means of active transport intro
transmitter vehicles
▪ Continuous recycling of vesicles
Small-Molecule Transmitters
▪ Typical small-molecule
transmitter
▪ released by many PNS neurons & some CNS
▪ Excitatory in the central nervous system
▪ Excitatory on NMJ but inhibitory at others – mixed action depending on receptor
▪ inactivated by acetylcholinesterase
Acetylcholine (ACh)
- modified
amino acids (tyrosine)
Biogenic Amines
regulates mood,
dreaming, awakening
from deep sleep
norepinephrine
regulating skeletal muscle tone
dopamine
control of mood, temperature regulation, & induction of sleep
serotonin
removed from synapse &
recycled or destroyed by
enzymes (monoamine
oxidase or catechol-0-
methyltransferase)
Biogenic Amines
secreted at the
synapses of spinal cord,
inhibitory
Glycine
released by nearly
all excitatory neurons in the
brain – sensory pathways
entering the CNS and spinal
cortex
Glutamate
inhibitory
neurotransmitter for 1/3 of all
brain synapses and spinal
cord
GABA Gamma Amino Butyric
Acid
Gamma Amino Butyric
Acid
Valium
▪ excitatory in both CNS & PNS
▪ released with other neurotransmitters (ACh & NE)
ATP and other purines (ADP, AMP & adenosine)
▪ formed from amino acid arginine by an enzyme
▪ formed on demand and acts immediately
▪ diffuses out of cell that produced it to affect
neighboring cells
▪ may play a role in memory & learning
▪ first recognized as vasodilator that helps lower blood pressure (cerebral and peripheral)
Gases (nitric oxide or NO)
▪ 3-40 amino acids linked by peptide bonds
▪ Slow acting→more prolonged actions
▪ Synthesized as integral parts of large-protein
molecules by ribosomes in the cell body
▪ Substance P
▪ Pain relief
Neuropeptides
enhances our
perception of pain
Substance P
pain-relieving effect by blocking the release of
substance P
enkephalins
___ may produce loss of pain sensation
because of release of ____ substances
such as ___ or ___
acupuncture, opioids-like, endorphins, dynorphins
Action potential travels from
axon
Action potential reaches
end bulb and voltage-gated Ca+ 2
channels open
Ca+2 flows___ the
concentration gradient
inward down
causes triggers
rapid fusion of synaptic
vesicles triggering release of
neurotransmitter
Inward diffusion
crosses synaptic cleft & binding to
ligand-gated receptors in the
post-synaptic membrane
Neurotransmitter
Quantity of transmitter
released is directly related to
the amount of Ca that enters
The effect of a
neurotransmitter can be either
excitatory or inhibitory
a depolarizing postsynaptic
potential is called
an EPSP
an inhibitory postsynaptic
potential is called
an IPSP
Diffusion out of synaptic
cleft into surrounding fluid
move down
concentration gradient
Enzymatic degradation
acetylcholinesterase
Uptake by neurons or glia
cells – active transport back
into pre-synaptic terminal
(norepinephrine)
neurotransmitter
transporters
