Download Neurons, Synapses, and Signaling

Neurons, Synapses, and
Signaling
Chapter 48
YOU MUST KNOW
 The anatomy of a neuron.
 The role of active transport in establishing the membrane
potential of a neuron.
 How long-distance and short-distance signaling is done
in neurons.
 The mechanisms of impulse transmission in a neuron.
 The process that leads to release of neurotransmitter,
and what happens at the synapse.
Neuron organization and structure
reflect function in information transfer
 The Neuron is the functional unit of the nervous system.
 It is composed if a cell body, which contains the nucleus
and organelles.
 Dendrites which are cell extensions that receive
incoming messages from other cells.
 Axons which transmit messages to other cells.
 Many axons are covered by an insulating fatty myelin
sheath. This speeds the rate of impulse transmission.
 The synapse is a junction between two neurons (or a
neuron and a muscle fiber or gland).
Neurotransmitters
 Neurotransmitters are chemical messengers released
from vesicles in the synaptic terminals into the synapse.
 They will diffuse across the synapse and bind to
receptors in the neuron, muscle fiber, or gland across
the synapse, effecting a change in the second cell.
 Ex. Acetylcholine, dopamine, and serotonin.
 At the synapse, the transmitting neuron is the
presynaptic cell and the neuron, muscle or gland that
receives the signal is the postsynaptic cell.
Nervous System
 Central nervous system CNS consists of the brain and spinal cord.
 Peripheral nervous system (PNS) consists of the nerves that
communicate motor and sensory signals throughout the rest of the
body.
 Sensory receptors collect information about the world outside the
body as well as processes inside the body.
 Ex. The rods and cones of the eye; pressure receptors in the skin.
 Sensory neurons transmit information from the eyes and other
sensors that detect stimuli to the brain or spinal cord for processing.
 Interneurons connect sensory and motor neurons or make local
connections in the brain and spinal cord.
 Motor neurons transmit signals to effectors, such as muscle cells and
glands.
 Nerves are bundles of neurons. A nerve can contain all motor
neurons, all sensory neurons, or be mixed.
Ion Pumps and Ion Channels
 Membrane potential describes the difference in electrical charge
across a cell membrane.
 The membrane potential of a nerve cell at rest is called its resting
potential. It exists because of differences in the ionic composition of
the extracellular and intracellular fluids across the plasma
membrane.
 The concentration of Na+ is higher outside the cell, whereas the
concentration of K+ is higher inside the cell. This gradient is
maintained by sodium-potassium pumps.
 Changes in the membrane potential of a neuron are what give rise
to transmission of nerve impulses (action potentials).
 A stimulus changes the permeability of the membrane to Na+, so
the membrane depolarizes as Na+ enter the cell.
 This may result in an action potential.
Acton Potential
 An action potential (nerve impulse) is an all-or-none response to
depolarization of the membrane of the nerve cell.
 In order to generate an action potential, a certain level of
depolarization must be achieved, known as the threshold.
 Saltatory conduction which is the jumping of the nerve impulse
between nodes of Ranvier (areas on the axon not covered by the
myelin sheath), speeds up the conduction of the nerve impulse.
Neuron Communication
 The signal is conducted from the axon of a presynaptic cell to the
dendrite of a postsynaptic cell via the synapse.
 Neurotransmitters are released by the presynaptic membrane into
the synaptic cleft.
 They bind to receptors on the postsynaptic membrane and are
then broken down by enzymes or taken back up into surrounding
cells.
 There are two categories of neurotransmitters: excitatory and
inhibitory.
 Excitatory neurotransmitters cause depolarization of the
postsynaptic membrane, which brings the membrane potential
closer to the threshold.
 Inhibitory neurotransmitters cause hyperpolarization of the
postsynaptic membrane, which moves the membrane potential
further from the threshold.
Dopamine
https://www.youtube.com/watch?v=lIJW9XLDE-I
Nervous System 49.2
 The brainstem is made up of the medulla oblongata,
pons, and midbrain.
 The brainstem controls homeostatic functions, such as
breathing, swallowing, and digestion and conducts
sensory and motor signals between the spinal cord and
higher brain centers.
 The Cerebellum helps coordinate motor, perceptual,
and cognitive functions.
 The thalamus is the main center through which sensory
and motor information passes to and from the
cerebrum.
 The hypothalamus regulates homeostasis; basic survival
behaviors such as feeding, fighting, fleeing, and
reproducing; thermostat, thirst center, and circadian
rhythms.
 The cerebrum has two hemispheres, each with a
covering of gray matter over white matter. Information
processing is centered here, and this region is
particularly extensive in mammals.
 The cerebral cortex controls voluntary movement and
cognitive functions.
 The corpus callosum is a thick band of axons that
enables communication between the right and left
cortices.
Different regions….different functions