Transcript Central nervous system

Lecture 14 – Ch. 48 & 49: Nervous Systems
I.
Overview
II. Neuron Structure
and Function
III. Relationship
between Stimuli
 Input
IV. Nervous System
Organization
V. Brains
VI. Preparation for
next lecture
Nervous System Overview
Sensory input
Integration
Sensor
Motor output
Effector
Peripheral nervous
system (PNS)
Central nervous
system (CNS)
Neurons
Dendrites
Stimulus
Specialized “excitable”
cells: receive input,
integrate, send output
Axon hillock
Nucleus
Presynaptic cell
Cell
body
Axon
Signal
direction
Synapse
Neurotransmitter
Synaptic terminals
Postsynaptic cell
Synaptic
terminals
Neurons
Neurons are electrical:
• At rest, neurons maintain
an electrical difference
across their membrane
Key
Na+ pumped out
K+ pumped in
but K+ can
leak out
• (-) inside cell; (+) outside cell
• charge = about -70 mV
Na
K
Sodiumpotassium
pump
Potassium
channel
Sodium
channel
Few Na+
channels open
INSIDE
OF CELL
OUTSIDE OF CELL
Action Potentials
Neurons Transmit Signals via Action Potentials:
Action Potential (AP): The electrical signal passed along
the length of a neuron
• Neuron membrane polarized
= charge difference
• During action potential,
Na+ channels open,
flows in
• Charge difference lost
= depolarized
(+) inside cell; (-) outside cell
Na+
action potential
(axon)
(extracellular fluid)
Na+
• Triggers K+ channels
to open, flows out
action potential
(axon)
• Repolarized
K+
(extracellular fluid)
Action Potentials
Membrane potential
(mV)
50
0
50
Action
potential
K+ channels
closed 3
Depolarization:
Na+ channels
open
2
Repolarization:
Some Na+ channels
close, K+ channels open
4
Undershoot: K+
channels stay open
1
5
Threshold
1
Resting potential
100
Time
Before K+ channels close, greater
charge difference = hyperpolarized
Action Potentials
Axon
Na+ and K+ channels
are voltage gated – as
first Na+ channels open,
more triggered to open
(i.e. positive feedback)
1
Na
K
Action potentials are
propagated down the
length of the neuron –
after the AP, neuron
resets itself (Na+ out,
K+ in)
Plasma
membrane
Action
potential
2
Cytosol
Action
potential
Na
K
K
3
Action
potential
Na
K
Action Potentials
Action potentials can be measured electrically:
• Stimulation from a neighbor neuron excites the cell
(brief increase in voltage = EPSP)
potential
(millivolts)
• Inhibition from another neuron causes a brief decrease
in voltage (IPSP)
threshold
resting
potential
EPSP
IPSP
time
(milliseconds)
Action Potentials
synaptic
vesicle
Pre-synaptic
terminal
IPSP = inhibitory postsynaptic potential
(-) Neurotransmitter
potential
(millivolts)
neurotransmitter
dendrite of
Post-synaptic
neuron
EPSP = excitatory
post-synaptic potential
(+) Neurotransmitter
Individual EPSP & IPSP weak
EPSP
IPSP
time
(milliseconds)
Action Potentials
Action Potentials
• Sum of all excitatory & inhibitory ‘blips’ = summation
potential
(millivolts)
• If threshold
voltage is reached,
an action potential
occurs
action potential
resting
potential
threshold
Less (-)
More (-)
time
(milliseconds)
Stimuli  Input
Information Coding in the Nervous System:
1) Determine stimulus type (e.g. light / sound / touch)
• All neurons use same basic signal
• Wiring pattern in brain distinguishes stimuli
2) Signal intensity of stimulus
• All signals similar in size (all-or-none response)
• Intensity coded by:
1) Frequency of action potentials
2) # of neurons responding
Stimuli  Input
Information Coding in the Nervous System:
1 fires slowly
1 fires rapidly
2 silent
2 fires slowly
1
fires moderately
2 silent
Stimuli  Input
Information Coding in the Nervous System:
3) Integrate/coordinate signals
4) Determine Output
Neural Pathways Direct Behavior:
1) Receptor: Detects stimulus
2) Sensory neuron: Sends stimulus message
3) Interneuron(s): Integrates stimuli
4) Motor neuron: Activates effector
5) Effectors: Performs function (muscle / gland)
Reflexes
Quadriceps
muscle
Cell body of
sensory neuron in
dorsal root
ganglion
Gray
matter
White
matter
Hamstring
muscle
Spinal cord
(cross section)
Sensory neuron
Motor neuron
Interneuron
Nervous System Organization
Nervous System Organization
The Brain:
Human Brain
meninges
skull
1) Cerebellum:
Coordinates movement &
balance
2) Brain Stem:
Automatic Behaviors
A) Medulla: Controls
breathing, heart rate,
blood pressure
B) Pons: Controls
wake/sleep transitions;
sleep stages
cerebellum
pons
medulla
spinal cord
The Brain:
Human Brain
pituitary
gland
pineal
gland
2) Brain Stem:
C) Midbrain: Relay /
“Screening” Center
midbrain
Filters sensory input from body
Visual / Auditory Reflex Centers
3) Diencephalon:
A) Thalamus
Input center for sensory information
B) Hypothalamus
Regulates homeostasis, thermostat, biological clock
The Brain:
Human Brain
cerebral
cortex
4) Forebrain (Cerebrum):
“Seat of Consciousness”
A) Cerebral Cortex
• Two hemispheres (Connection =
Corpus Callosum)
• Left hemisphere controls right side
of body (and vise versa)
corpus
callosum
The Brain:
Human Brain
Parietal
Lobe
Frontal
Lobe
Occipital
Lobe
Temporal
Lobe
4) Forebrain (Cerebrum)
A) Cerebral Cortex
Four regions:
1) Frontal: Primary motor area; complex reasoning
2) Parietal: Primary sensory area
3) Temporal: Primary auditory and olfactory areas
4) Occipital: Primary visual area
Human Brain
primary
sensory area
Frontal
Lobe
primary
motor area
premotor
area
higher
intellectual
functions
leg
trunk
arm
hand
Parietal
Lobe
sensory
association
area
face
speech
motor area
tongue
primary
auditory
auditory association
area
area: language
comprehension
memory
Temporal
Lobe
visual
association
area
primary
visual
area
Occipital
Lobe
Human Brain
Motor and
Sensory
areas
Human Brain
Cortical Regions Involved
in Different Tasks:
Hearing Words
Seeing Words
Reading Words
Generating Verbs
0
max
The Brain:
Human Brain
limbic region
of cortex
B) Limbic System
• Parts of thalamus:
Information relay
• Amygdala: Produces
sensations of pleasure,
fear, or sexual arousal
• Hippocampus:
Formation of long-term memory
cerebral cortex
corpus
callosum
thalamus
hypothalamus
hippocampus
amygdala
Things To Do After Lecture 14…
Reading and Preparation:
1.
Re-read today’s lecture, highlight all vocabulary you do not
understand, and look up terms.
2.
Self-Quiz: Ch. 48 #1-3, 5; Ch. 49 # 2, 4, 5, 6 (correct answers in
back of book)
3.
Read chapters 48 & 49, focus on material covered in lecture (terms,
concepts, and figures!)
4.
Skim next lecture.
“HOMEWORK” (NOT COLLECTED – but things to think about for studying):
1.
Explain the difference between the motor and autonomic nervous
systems.
2.
Diagram a basic neuron and describe how an action potential begins
and propagates. For sensory, motor, interneurons explain the location
of each region with respect to peripheral or central nervous system.
3.
Compare and contrast the embryonic vertebrate brain with that of adults.
4.
List the regions of the brain (with functions) from the “bottom” of the
brain, toward the “top”.