Transcript neurons

Lecture Outline – Ch. 44: Nervous System
I.
Neurons
II. Action Potentials
III. Relationship between Stimuli  Input
IV. Nervous System Organization
The Nervous System
Includes all nerve cells (neurons) and support cells
Neurons
Specialized “excitable” cells: receive input, integrate, send output
1 Synaptic terminals:
Bring signals from
other neurons.
2 Dendrites:
Receive signals
from other neurons.
3 Cell body:
Integrates signals;
Coordinates.
synaptic
terminal
4 Action potential
starts here.
5 Axon: Conducts
the action potential.
dendrite
synapse
6 Synaptic terminals:
Transmit signals to
other neurons.
7 Dendrites
(of other neurons).
5
Neurons
Synapse: Region connecting two neurons or neuron and muscle
• Electrical signal converted to chemical cue (neurotransmitter);
then back to electrical impulse
• Neurotransmitter may excite or inhibit the next neuron
Neurons
synaptic
terminal
synaptic
vesicle
Signal reaches
end of axon.
Synaptic vesicles
release neurotransmitter.
gap
neurotransmitter
Receptor binds
neurotransmitter.
dendrite of
postsynaptic
neuron
Neurotransmitter
signals next
neuron.
Neurons
Neurons are electrical:
• At rest, neurons maintain an electrical difference across
their membrane
• (-) inside cell; (+) outside cell
• charge = about -70 mV
Neurons
Neurons
Neurons
Chemically-gated or
ligand-gated
channels
Ligands: hormones or
neurotransmitters
Open channels &
cause changes in
cell membrane
permeability
Neurons
Common Neurotransmitters:
1) Acetylcholine: Activates skeletal muscle (muscle)
• Curare blocks Ach receptor
2) Dopamine: Controls movement (brain)
• Parkinson’s Disease
3) Epinephrine: Activates fight-or-flight response (body)
• a.k.a. Adrenaline
4) Serotonin: Influences mood (brain)
• Anti-anxiety / anti-depressants
5) Endorphins: Influences mood; reduces pain sensation
• Runner’s high
Neurons
Neurons Transmit Signals via Action Potentials:
Action Potential (AP): The electrical signal passed along
the length of a neuron
(+) inside cell; (-) outside cell
• During action
potential, charges flip
Na+
action potential
(axon)
(extracellular fluid)
• Action potential
propagated down axon
Na+
action potential
(axon)
K+
(extracellular fluid)
Action Potentials
Action Potentials are fast:
axon
• Long axons are
wrapped with myelin
node
axon
• Speeds up signal
myelin nucleus
myelin-forming
cell
myelin sheath
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
Action potentials can be measured electrically:
potential
(millivolts)
• Sum of all
excitatory &
inhibitory ‘blips’ =
summation
• If threshold
voltage is
reached, an
action potential
occurs (highly +
voltage, briefly)
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 APs are similar in structure
• Wiring pattern in brain distinguishes stimuli
2) Signal intensity of stimulus
• All APs are 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:
• Reflex: Involuntary movement in response to stimulus
• Simplest behavior:
1) Receptor: Detects stimulus
2) Sensory neuron: Sends stimulus message
3) Association neuron: Integrates stimuli
4) Motor neuron: Activates effector
5) Effectors: Performs function (muscle / gland)
1 A painful
stimulus activates
a pain receptor.
2 Signal transmitted
by a pain sensory neuron.
stimulus
receptor
dorsal
root
sensation
relayed
to the brain
REFLEX
ARC
5 Effector muscle
causes withdrawal effector
response.
ventral
root
4 Motor neuron
stimulates the
effector muscle.
3 Signal transmitted
to a motor neuron by an
interneuron within the
spinal cord.
Stimuli  Input
Increased Complexity in Nervous System = Increased centralization
Nerve Net: Nervous tissue woven throughout body (no head)
Cephalization: Nervous tissue centralized in “head” region
ring of ganglia
brain
nerve cords
diffuse network
of neurons
(a) Hydra
Nerve Net
(b) Flatworm
cerebral
ganglia
(brain)
(c) Octopus
Cephalization
Nervous System Organization
Brain and spinal cord
1) Bone (Skull; Spinal Cord = vertebrae)
2) Meninges (Triple-layer of connective tissue)
• Contains cerebrospinal fluid
(cushioning / nourishment)
3) Blood-brain Barrier
• Selective barrier in blood vessels
Spinal Cord:
Nervous System Organization
Myelin = Insulation around axons
• Increases AP conduction rate
Nervous System Organization
Spinal Cord:
CNS
Nervous System Organization
Brain and Spinal Cord
Motor Pathways
PNS
Sensory Pathways
Sensory neurons
registering external
stimuli
Sensory neurons
registering external
stimuli
Somatic nervous
system
(voluntary)
Sympathetic nervous
system
"fight or flight"
Autonomic nervous
system
(involuntary)
Parasympathetic nervous
system
"rest and repose"
Nervous System Organization
Thought Question:
How far can you safely drive behind the
car in front if you are travelling at 60 mph?
Think about: Your reaction time
(what has to happen for you to stop if the car in front of you stops?)
How far you go per second
(at what speed are you traveling?)
Lecture Outline – Ch. 45 Sensory Input
I.
Brains
II. Sensory Input
A. Sound
B. Sight
C. Odor/Taste
D. Pain
E. “Spidey Senses”
The Brain:
(a)
Vertebrate Brains
(c)
optic lobe
thalamus
cerebrum
cerebellum
cerebrum
midbrain
cerebellum
medulla
forebrain midbrain hindbrain
EMBRYONIC VERTEBRATE BRAIN
cerebrum midbrain
cerebellum
(b)
GOOSE BRAIN
(d)
cerebrum
SHARK BRAIN
midbrain
(inside)
cerebellum
HUMAN BRAIN
Brains: What are the major differences?
The Brain:
Human Brain
meninges
skull
1) Hindbrain:
Automatic
Behaviors
A) Medulla: Controls
breathing, heart rate,
blood pressure
B) Pons: Controls
wake/sleep transitions;
sleep stages
C) Cerebellum:
Coordinates movement
hindbrain
cerebellum
pons
medulla
spinal cord
Human Brain
The Brain:
(Figure 38.12)
pituitary
gland
pineal
gland
midbrain
- Reticular
Formation
2) Midbrain: Relay /
“Screening” Center
A) Reticular Formation:
Controls arousal of brain
• Filters sensory input from body
B) Visual / Auditory Reflex Centers
The Brain:
Human Brain
(Figure 38.12)
cerebral
cortex
3) 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
3) 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
hypothalamus
thalamus
3) Forebrain (Cerebrum)
B) Limbic System
• Produce emotions; form memories
C) Thalamus
• Relays information from body to limbic system / cerebral cortex
The Brain:
Human Brain
limbic region
of cortex
B) Limbic System
• Hypothalamus:
Homeostatic control center
• Amygdala: Produces
sensations of pleasure,
fear, or sexual arousal
• Hippocampus:
Formation of long-term memory
C) Thalamus
• Relays to limbic system /
cerebral cortex
cerebral cortex
corpus
callosum
thalamus
hypothalamus
hippocampus
amygdala
Sensory Input
What is a Sensory Receptor?
Specialized cells that signals when stimulated
Receptors named after stimuli they respond to:
1) Thermoreceptors: Heat / Cold
2) Mechanoreceptors: Motion; pressure; gravity
3) Photoreceptors: Light (photons)
4) Chemoreceptors: airborne/waterborne molecules
5) Nociceptors: Pain (chemical release)
Sensory Input
Pressure:
Skin: Pressure  Electrical Signal
free nerve endings
(touch, pain, or
temperature)
Merkel’s disc
(steady touch)
hair endorgan (hair
movement)
Pacinian
corpuscle
(rapid movement)
Ruffini’s endorgan (pressure)
Meissner’s corpuscle
(light touch, rapid movement)
Sound:
Sensory Input
Sound waves are vibrations in fluid (air, water)
Sound:
Sensory Input
Ear: Sound  Electrical Signal
1) Sound wave enters
ear (auditory canal)
Outer ear
Middle ear
bones of
middle ear
2) Tympanic
membrane vibrates
Inner ear
vestibular system
(detects head
movement
and gravity)
auditory nerve
to brain
3) Vibration passes
to inner ear bones
4) Inner ear
(cochlea) converts
vibrations to
electrical signal
cochlea
auditory
canal
tympanic
membrane
auditory tube
(Eustachian tube)
to
pharynx
Sensory Input
Vision:
Eye: Light  Electrical Signal
Some animals only sense light/dark
Many arthropods
have a
compound eye,
where many
images are
pieced together
into a visual
mosaic
Compound eyes
Vision:
Sensory Input
Eye placement changes vision:
• Forward-facing: many carnivores that need depth perception
• Widely spaced: herbivores - allows better predator detection
Vision:
Sensory Input
Eye: Light  Electrical Signal
Mammals: collects &
focuses light waves;
transmits signal to brain
1) Light enters via cornea (transparent covering),
through the pupil (opening in center of iris)
2) The iris is a pigmented ring of muscle that
controls light entry
3) Light is focused on the retina (sheet of
photoreceptors) by the lens (transparent surface)
Vision:
Sensory Input
4) Muscles attached to lens contract to change the lens shape and focus
image on the fovea for any visual distance
retina
Distant object,
lens thins to
focus on retina.
Close object, lens
fattens to focus
on retina.
Vision:
Sensory Input
Abnormally long eyeball:
the image is focused in front of the retina: nearsightedness
Abnormally short eyeball:
the image is focused behind the retina: farsightedness
Vision:
Sensory Input
Eye: Light  Electrical Signal
5) Light on the retina triggers
receptors; optic nerve excited
Rods: Dim-light vision
(many but scattered)
Cones: Color vision
(Red/green/blue)
The blind spot is where the
optic nerve connects to
eyeball
No photoreceptors, so
images disappear
blind
spot
fovea
Sensory Input
Odor/Taste:
Nose / Tongue: Chemical  Electrical Signal
olfactory
epithelium
olfactory structure of brain
nasal
cavity
bone
air with
odor molecules
nasal cavity
1) Chemicals enter nasal cavity;
bind to receptors (olfactory epithelium)
olfactory
receptors
mucus layer
olfactory
dendrites
2) Olfactory bulb
(in brain) excited
Sensory Input
Odor/Taste:
Nose / Tongue: Chemical  Electrical Signal
The human tongue
1) Dissolved chemicals enter taste buds
on tongue (via taste pore)
2) Chemicals bind with receptors;
papillae
stimulate nerves
• Five primary tastes:
• Sweet / Salt / Bitter / Sour / Umami
• Olfaction enhances taste
Taste bud
taste pore
microvilli
taste
receptor
cells
nerve
fibers
to brain
Sensory Input
Pain is a specialized Chemical Sense:
1) Damaged cells spill
chemicals
2) Nociceptors detect
tissue damage
Self-Check
Sensation
Type(s) of receptor; Description of sense
Touch
Sound
Sight
Taste
Smell
Pain
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Some senses are unfamiliar to humans
Other Senses:
Sensory Input
Electrolocation:
Animal
produces
electrical field;
interpret
distortion
in field
Magnetic
Field
Detection:
Echolocation:
Animal emits pulse interprets returning signal
Animals
detect and
orient based
on earth’s
magnetic field
Lecture 10 Summary
1. Neurons (Ch. 44)
Structure
Types
2. Action Potentials (Ch. 44)
How electrical charge is set up
AP stimulus, propagation, transfer to next cell
3. Stimuli (Ch. 44)
Coding of stimuli
Route in NS
Nervous System Organization
4. Brain Regions and Function (Ch. 44,45)
5. Sensations (Ch. 45)
Types of receptors
Touch, sound, vision, taste, smell, pain
Other senses