Transcript The Nervous System

The Nervous System
Three functions of the nervous
system
Sensory Input
Receipt of information (sensory receptors) &
movement of information to integration center
Integration
Interpretation of input
Motor Output
Conduction of signals from integration center
to effector cells (muscles or glands, i. e.)
Two divisions of the nervous
system
Central Nervous System (CNS)
Brain & Spinal Cord
Peripheral Nervous System (PNS)
Nerves that conduct impulses from the
CNS and the rest of the body
Nerves—Ropelike bundles of extensions
of neurons wrapped in connective tissue
Functional Unit of the Nervous
System—The NEURON
Cell body—contains nucleus &
organelles
Dendrites—short, highly branched
processes (extensions) that receive
incoming messages from other cells
Axons—usually much longer than
dendrites, convey outgoing messages
from neurons to other cells
Also important in signal
conduction. . .
Synapse—the site of contact between
an axon and a target cell
Neurotransmitter—chemical
messengers that relay messages
across the synapse
The simplest nerve circuit—the
reflex arc
The Nature of Nerve Signals
Galvani (18th century)—discovered
that frog muscle cells produce
electricity
Helmholtz (19th century)—found
electrical activity of nerve cells
carries signals from one end of a cell
to the other end and from cell to cell
The Nature of Nerve Signals
All nerve signals are changes in the
voltage across the plasma membrane
of cells
Voltage changes are caused by
movement of ions across the plasma
membrane via specialized ion channels
The membrane potential of cells
Cations ++
--Anions
Cations ++
Anions --Anions ----Anions
Cations ++
Anions ----Anions
Negative charge inside
Anions --cell is greater than
Anions ----Anions
positive charge outside
--Anions
cell. Membrane is
polarized.
Cations ++
Cations ++
Cations ++
Cations ++
Resting potential
The membrane potential of an
unstimulated neuron
It is about –70 mV
The inside of the cell is more
negative than the outside
The basis of membrane potential
The Ability to Conduct an
Impulse
Excitable Cells—Neurons & muscle cells
that can generate large changes in
membrane potential
Resting potential—the voltage of an
excitable cell in unexcited state
Gated ion channels—allow ions to pass only
under certain conditions
Chemically-gated ion channels
Voltage-gated ion channels
The Ability to Conduct an
Impulse
Hyperpolarization—Increase in voltage
across a membrane
Depolarization—Reduction in the voltage
across a membrane
Threshold potential—A particular voltage
that triggers a particular response
Action potential—The response triggered
by the threshold potential. The nerve
impulse
Generating Action Potential
Figure 48.9
A Nerve Impulse
The Resting Potential
The Action Potential
Propogation of
the Action
Potential
Communication between cells
Types of synapses
Excitatory synapses—neurotransmitter
causes Na+ to enter and K+ to exit, which
depolarizes the cell. If enough “excitation”
occurs action potential is the result.
Inhibitory synapses—causes membrane to
be more permeable to K+ and Cl-,
hyperpolarizing the cell. If enough
“inhibition” occurs, it is more difficult for
an action potential to occur.
Neurotransmitters
Acetylcholine—usually stimulates
muscle cells
Dopamine & serotonin—affect sleep,
mood, attention, and learning—LSD
binds to serotonin receptors in brain
Endorphins—decrease perception of
pain by CNS. Opium binds to
endorphin receptors
Vertebrate Nervous Systems
Major Components
Brain—provides integrative power for
complex behavior
Spinal Cord—Integrates simple
responses (such as knee jerk) and
conveys information to & from brain
Peripheral Nervous System (PNS)—
transmits info to & from CNS &
regulates internal environment
Divisions of the Peripheral
Nervous System
The Autonomic Nervous System
The human brain
The Brainstem
Medulla oblongata—controls breathing,
heart & vessel activity, swallowing,
vomiting, & digestion. Axons carrying
instructions about movement cross in
medulla. Left side of brain controls
movement of the right side of body.
Pons—Regulate breathing centers in
medulla
Midbrain—Contains centers for receipt &
integration of sensory information.
Sleep & Arousal
Reticular Formation—neurons that
regulates sleep & arousal
It filters or selects which information
reaches the cerebrum
The more information we receive, the more
alert we are
Parts of pons & medulla contain nuclei that
cause sleep when stimulated
Milk contains a lot of trytophan, the amino
acid from which serotonin is synthesized
Cerebellum
Functions in coordination and errorchecking during motor, perceptual and
cognitive performances
Controls movement & balance such as
hand-eye coordination
Thalamus & Hypothalamus
Major integrating centers
Thalamus—main input center for sensory
information going to the cerebrum & main
output center for motor information
leaving cerebrum
Hypothalamus—source of posterior
pituitary hormoness & releasing hormones
for anterior pituitary; contains the body’s
thermostat; regulates hunger, thirst &
survival mechanisms
The real “biological clock”
Circadian rhythms—daily patterns
Biological clock—the internal
component of circadian rhythms
Suprachiasmatic nuclei (SCN) in
hypothalamus serves as human
biological clock
Responds to light/dark
The Cerebrum
Divided into right & left cerebral
hemispheres
The largest & most complex part of the
mammalian brain
Left hemisphere receives info from and
controls movement of the right side of the
body and vice versa
Corpus callosum—communicates between
left & right cerebral hemispheres
Regions of the cerebrum
Motor & Somatosensory Areas
Lateralization of Brain Function
Left hemisphere becomes adept at
language, math, logic operations, and
processing serial sequences.
Right hemisphere is stronger at
pattern recognition, face recognition,
spatial relations, nonverbal ideation,
and emotional processing
The Limbic System
Form a ring around the brainstem
Generates feelings and emotions
Mediates behaviors such as laughing &
crying