the nervous system is
a complex network of neurons that form the rapid control system of the body and carry electrical signals
emergent properties of the nervous system include
-consciousness
-intelligence
-emotion
the nervous system is divided into
-central nervous system (CNS)
-peripheral nervous system
central nervous system is composed of
-brain
-spinal cord
the types of neurons the peripheral nervous system has
-afferent (sensory) neurons
-efferent neurons
afferent (sensory) neurons
carry info to the central nervous system
efferent neurons
carry information away from the CNS back to various parts of the body
the efferent neurons include
-somatic motor neurons (control skeletal muscles)
-autonomic neurons (control smooth & cardiac muscles, glands, and some adipose tissue)
autonomic neurons are subdivided into
-sympathetic
-parasympathetic branches
neurons have
-Cell body : with nucleus & organelles to direct cellular activity
-Dentrites : receive incoming signals
-Axon : transmit electrical signals from the cell body to the axon terminal
Where are neurotransmitters released?
in the axon terminal
interneurons are
neurons that lie entirely within the CNS
the region where an axon terminal meets its target cell is called
synapse
the target cell is called
postsynaptic cell
the neuron that releases the chemical signal is known as
the presynaptic cell
the region between the postsynaptic cell and presynaptic cell is the
synaptic cleft
material (proteins & organelles) is transported between the cell body and axon terminal by
axonal transport
glial cells provide
physical support and direct the growth of neurons during repair and development
schwann cells and satellite cells are
glial cells associated with the peripheral nervous system
Microglia, oligodendrocytes, astrocytes, and ependymal cells are
glial cells found in the CNS
microglia are
modified immune cells that act as scavengers
schwann cells and oligodendrocytes form
insulating myelin sheaths around neurons.
the nodes of Ranvier are
secretions of uninsulated membrane occuring at intervals along the length of an axon.
Neural stem cells are
found in the ependymal layer
membrane potential is influenced by
the concentration gradients of ions across the membrane and by the permeability of the membrane to those ions
the Goldman-Hodgkin-Katz (GHR) equation
predicts membrane potential based on ion concentration gradients and membrane permeability
the permeability of a cell to ions changes when
ion channels in the membrane open and close. Movement of only a few ions significantly changes the membrane potential.
Gated ion channels in neurons open or close in response to
chemical or mechanical signals or in response to depolarization of the cell membrane.
graded potentials are
depolarizations or hyperpolarization whose strength is directly proportional to the strength of the triggering event.
*lose strength as they move through the cell
the wave of depolarization that moves through the cell with a graded potential is known as
local current flow
action potentials are
rapid electrical signals that travel undiminished in amplitude. form the cell body to the axon terminals
action potentials begin in the
trigger zone if either a single graded potential or the sum of multiple graded potentials exceeds a minimum depolarization known as the 'threshold'
depolarizing graded potentials makes a neuron
more likely to fire an action potential
hyperpolarizing graded potentials makes a neuron
less likely to fire an action potential
the all-or-none principle states
that all stimuli great enough to bring the membrane threshold will produce action potentials of identical magnitude. either occur as a maximal depolarization or do not occur at all.
the rising phase of the action potential is due to
increased Na+(sodium) flow into the cell.
the falling phase of the action potential
is due to K+(potassium) flow out of the cell
Overshoot is the point during
an action potential when the inside of the cell has become more positive than the outside.
the voltage-gated Na+ channels of the axon have a
-fast activation gate (entrance)
and
-a slower inactivation gate (exit)
once an action potential has begun, there is a brief period of time known as the
-absolute refractory period
*during which a second action potential cannot be triggered, no matter how large the stimulus.
*because of this, action potentials cannot be summed
During the relative refractory period
a higher-than-normal graded potential is required to trigger an action potential.
Excitatory postsynaptic potential (EPSP)
occurs when sodium channels are opened and depolarizes a neuron, making it easier to fire.
Inhibitory postsynaptic potential (IPSP)
results in local hyperpolarizations
information about the strength and duration of a stimulus is conveyed by
the frequency of action potential propagation.
very few ions cross the membrane during an action potential. The Na+ -K+ -ATPase eventually restores
NA+ and K+ to their original compartments.
the movement of an action potential through the axon at high speed is called
conduction
larger axon diameter and increased membrane resistance speed up action potential conduction by
increasing membrane resistance and decreasing current leakage.
the apparent jumping of an action potential from node to node is called
saltatory conduction
changes in blood K+ concentration affect
resting membrane potential and the conduction of potentials.
hyperkalemia
indicates too much potassium in the blood
in electrical synapses
an electrical signal passes directly from the cytoplasm of one cell to another through gap junctions.
chemical synapses
use neurotransmitters to carry information from one cell to the next, with neurotransmitters diffusing across the synaptic cleft.
neurotransmitters are synthesized in the cell body or in the axon terminal. They are stored in
-Synaptic vesicles
-released by exocytosis when an action potential reaches the axon terminal.
neurotransmitters combine with
receptors on target cells
Cholinergic neurons secrete
acetylcholine
*important neurotransmitter
adrenergic neurons secrete
norepinephrine
*important neurotransmitter
glutamate, GABA, serotonin, adenosine, and nitric oxide are
other major neurotransmitters
neurotransmitter receptors are either
*ligand-gated ion channels
or
*G protein-coupled receptors
ion channels create
fast synaptic potentials
G protein-coupled receptors either create
-slow synaptic potentials
or
-modify cell metabolism
neurotransmitter action is rapidly terminated by
-reuptake into cells
-diffusion away from the synapse
-enzymatic breakdown
if a presynaptic neuron synapses on a larger number of postsynaptic neurons, the pattern is known as
divergence
if several presynaptic neurons provide input to a smaller number of postsynaptic neurons, the pattern is known as
convergence
the summation of simultaneous graded potentials from different neurons is known as
spatial summation
*space
repeated graded potentials reaching the trigger zone one after the other is called
temporal summation
*time
presynaptic modulation of an axon terminal allows
selective modulation of collaterals and their targets
postsynaptic modulation
occurs when a modulatory neuron (usually inhibitory) synapses on a postsynaptic cell
long-term potentiation is
one mechanism by which neurons change the quality or quantity of their synaptic connections
developing neurons find their way to their targets by using
chemical signals.