Central nervous system (CNS)
Brain and spinal cord -Integration and command center
nervous system is the master controlling and communicating system of the body. Name the 3 main functions
Sensory input-external stimuli occuring outside the body.
Integration-interpretation of sensory input
Motor output- response to stimuli
afferent signals travel towards (sensory)
efferent travels away (motor)
Peripheral nervous system (PNS)
Paired spinal and cranial nerves -Carries messages to and from the spinal cord and brain
Peripheral Nervous System (PNS): Two Functional Division
Sensory (afferent) division +
Motor (efferent) division
sensory (afferent) division has these 2 fibers
sensory afferent fibers +
Visceral afferent fibers
sensory afferent fibers do what
carry impulses from the skin, skeletal muscles, and joints to the brain
Visceral afferent fibers
transmit impulses from visceral organs to the brain
Motor (efferent) division has two main parts, name them
somatic nervous system +
autonomic nervous system
somatic nervous system
conscious control of skeletal muscles
autonomic nervous system does what
regulates smooth muscle, cardiac & glands
2 divisions of ANS
sympathetic & parasympathetic
two principal cell types of the nervous system are
1) Neurons - excitable cells that transmit electrical signals
2) Supporting cells - cells that surround and wrap neurons
analogys
CNS: TRACT PNS: NERVE
CNS: NUCLEUS PNS: GANGLION
CNS: ASTROCYTE PNS: SATELLITE
CNS: OLIGODENDROCYTE PNS: SCHWANN
somatic structures
spinal nerves, motor + sensory fibers, sensory ganglia.
enteric nervous system includes
nervous tissue within the organs of the digestive tract
nerve cell body (soma or perikaryon)
functional cells of the CNS. Is the major biosynthetic center and focal point for the outgrowth of neruonal processes.
contains: axon hillock, axons, dendrites, nucleus, nucleolus.
processes are arm like extentions from the soma. name two:
axons + dendrites
Dendrites
Short, tapering, and diffusely branched processes
-They are the receptive, or input, regions of the neuron. electrical signals are conveyed as graded potentials.
axons
arise from hillock. long axons are called nerve fibers.
contain axonal terminal, axon collaterals.
function of axon
generate and transmit action potentials
secrete neurotransmitters from axonal terminals.
movement along axons occur in two ways
anterograde-towards axonal terminal
retrograde-away from axonal terminal
What is the myelin sheath
Formed by schwann cells in PNS,
Whitish, fatty (protein-lipoid), segmented sheath around most long axons
It functions to: -Protect the axon -Electrically insulate fibers from one another -Increase the speed of nerve impulse transmission
Schwann cell:(PNS) is
Envelopes an axon in a trough
-Encloses the axon with its plasma membrane
-Has concentric layers of membrane that make up the myelin sheath Neurilemma - remaining nucleus and cytoplasm of a Schwann cell
Nodes of Ranvier (Neurofibral Nodes)
Gaps in the myelin sheath between adjacent Schwann cells They are the sites where axon collaterals can emerge
Myelin sheaths CNS are formed by oligodendrocytes, t/f
true
unmyelinated axons
a schwann cell surrounds nerve fibers but coiling does not take place
Schwann cells partially enclose 15 or more axons
axons of the CNS
Both myelinated and unmyelinated fibers are present
Myelin sheaths are formed by oligodendrocytes
Nodes of Ranvier are widely spaced
There is no neurilemma
Axons are arranged in bundles to form nerves; much like muscle cells form muscle fibers in the musc
Regions of the Brain and Spinal Cord, name two
White matter - dense collections of myelinated fibers
Gray matter - mostly soma and unmyelinated fibers
neuron classification
Multipolar � three or more processes
Bipolar � two processes (axon and dendrite)
Unipolar � single, short process
functional classification of neurons, name 3
sensory (afferent) motor ( efferent) interneurons (association neurons).
Sensory (afferent) � transmit impulses toward the CNS
Motor (efferent) � carry impulses away from the CNS & Interneurons (association neurons) � shuttle signals through CNS pathways
Astrocytes-star shaped.
Most numerous of glial cells
Support neurons, linking to surrounding tissues
Direct neuron growth direction and attachment (synapse formation)
Recycle neurotransmitters �maintaining the blood brain barrier- a wrapping around capillaries in the brain, affe
Microglia-
nervous system "cootie catchers".(immune cells) �Surveyors of damaged cells and infectious agents.
These become functional macrophages
Ependymal cells
Line the cavities (ventricles and spinal column) of the brain
�Squamous?columnar
�Some ciliated �Help form and circulate the cerebrospinal fluid
Oligodendrocytes
myelin producing cells; Cell extensions wrap nerve fibers in a myelin sheath. CNS cells. One cell may have many extensions that wrap myelin around many neuron Axons.
Glial cells of the CNS
The CNS has astrocytes, oligodendrocytes, microglia, and ependymal cells that support the neurons of the CNS in several ways.
schwann cell
myelin producing cells. cell extensions wrap nerve fibers in a myelin sheath and help to regenerate damanged neurons
satellilte cells are like astrocyte, but in the pNS
satellilte cells are like astrocyte, but in the pNS
depolarization means
the difference between 2 sides or regions has become less
Glial Cells of the PNS
Schwann Cells : myelin producing cells
Cell extensions wrap nerve fibers in a myelin sheath �Help to regenerate damaged neurons
Satellite cells: like astrocytes, but in PNS
Voltage (V)
- measure of potential energy generated by separated charge
Potential difference
- voltage measured between two points
Current (I)
the flow of electrical charge between two point
Resistance (R
hindrance to charge flow
Insulator
substance with high electrical resistanc
Conductor
substance with low electrical resistance
Electrical Current and the Body Reflects the flow of ions rather than ______
electrons
Role of 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
for ions to flow through a membrane, there must be a way through. how could this happen?
some channels leak:
na/k pumps bail the leakage
Depolarization
the inside of the membrane becomes less negative
Repolarization -
the membrane returns to its resting membrane potential
Hyperpolarization -
the inside of the membrane becomes more negative than the resting potential
Graded Potentials
Short-lived, local changes in membrane potential Decrease in intensity with distance
Their magnitude varies directly with the strength of the stimulus
Sufficiently strong graded potentials can initiate action potentials
Voltage changes in graded potential
Action Potentials (APs)
A brief reversal of membrane potential with a total amplitude of 100 mV
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 An action potentia
Action Potential: Resting State
Na+ and K+ channels are closed(Na high outside cell; K higher inside cell) Leakage accounts for small movements of Na+ and K+ Each Na+ channel has two voltage-regulated gates -Activation gates - closed in the resting state -Inactivation gates - open in th
Graded potentials are
temporary changes in the membrane voltage, the characteristics of which depend on the size of the stimulus. Some types of stimuli cause depolarization of the membrane, whereas others cause hyperpolarization. It depends on the specific ion channels that ar
Synapses
A junction that mediates information transfer from one neuron: -To another neuron -To an effector cell Presynaptic neuron - conducts impulses toward the synapse Postsynaptic neuron - transmits impulses away from the synapse
resting membrane potential
the potential difference across the membrane of a resting neuron
generated by diff concentrations of na,k,cl-,a-
membrane potential changes: signals
used to integrate, send and recieve information
membrane potential changes are produced by
changes in a membrane permeability to ions
alterations of ion concentrations across the membrane
types of signales-graded potentials and action potentials
changes in a membrane potential caused by 3 events
depolorization- inside becomes less negative
repolarization- membrane returns to resting membrane potential
hyperpolarization- inside of the membrane becomes more negative then resting potential
graded potentials are
short lived changed in membrane potential.
decrease in intensity with distance.
magniture varies with stregnth of stimulus
can initiate action potentials
dissipates due to leaky plasma membrane
action potentials
breif reversal of membrane potential
only generated by muscle cells + neurons
do not decrease in strength over distance
principle means of neural communication
action potential resting state
na+ and k+ channels are closed
activation gates- closed in resting state
inactivation gates- open in resting state
propagation of an action potential
na_ influx causes a patch of the axonal membrane to depolarize
threshold and action potentials
established by the total amount o fcurrent flowing through the membrane
absolute refractory period
time from the opening of the na+ activation gates until the closing of inactivation gates
relative refractory period
the interval following when sodium gates are closed and potassium gates are open and repolarization is occuring
conduction velocities of axons
conduction velocities vary widely among neurons. rate of impulse is determined bye axon diamter and presecne of a myelin sheath.
action potentials are an all or none event.
if strong enough, chain reaction happens
refractory period
absolute the nerve cannot be stimulated. relative a stronger stimulus is needed
hyperpolarization
difference across teh membrane increases and becomes more negative inside.
synapses
junction that mediates information transfer from one neuron to another or effector cell
electrical synapses
are less common then chemical synampses
corrospond to gap junctions found in other cell types
important to cns in arousal from sleep, mental attention and emotions and memory, ion h20 balance
chemical synapses
release and reception of neurotransmitters composed of two parts; axonal terminal and receptor region
synaptic cleft
fulid filled space seperating neurons
prevents nerve impulses from directly passing fromone neuron to the next
transmission across the synaptic cleft: chemical event.
2 types of post synaptic potentials are
epsp and ipsp
chemical neurotransmitters
ach
biogenic amines
amino acids
peptides
novel messengers: atp and dissolved gases NO & CO
neurotransmitters are
chemicals used to neuronal communications with the body and the brain