8. Nervous system short

2007-2008

http://www.youtube.com/watch?v=jN99Kx_ghC8&NR=1

Information Processing

• _{Nervous systems process information in three stages:}

sensory input, integration, and motor output

Sensor

Sensory input

Motor output

Integration

Effector

Peripheral nervous

system (PNS) Central nervoussystem (CNS)

Sensory

neurons _interneurons

Neuron Structure

• _{Most organelles are in the cell body}

• _{Most have dendrites that receive signals from}

other neurons

• _{The axon transmits signals to other cells at}

synapses; often covered with a myelin sheath

dendrites

cell body

axon

synaptic terminal signal direction

signal direction

Supporting Cells (Glia)

• _{Essential for structural integrity of the nervous}

system and for functioning of neurons

– _{Astrocytes: structural support for neurons; regulate}

extracellular concentrations of ions and neurotransmitters

– _{Oligodendrocytes (in the CNS) and Schwann cells (in the}

PNS) form the myelin sheaths around axons of many vertebrate neurons

Axon Nodes of Ranvier Schwann

cell

Myelin sheath Schwann cellNucleus of Schwann

cell

Nodes of Ranvier

Layers of myelin Axon

Transmission of a signal

• _{Think dominoes!}

– _{start the signal}

• _{knock down line of dominoes by tipping 1}st _one – _{propagate the signal}

• _{do dominoes move down the line?}

– _{re-set the system}

• _{before you can do it again,}

Transmission of a nerve signal

• _{Neuron has similar system to those dominoes}

– _{protein channels for ions are set up}

• _{(why do ions need channels to cross the membrane?)}

– _{once first one is opened, the rest open in succession}

• _{all or nothing response}

– _{a “wave” action travels along neuron}

Cells: surrounded by charged ions

• _{Cells live in a sea of charged ions}

– _{anions (negative)}

• _{more concentrated within the cell} • _Cl-_{, charged amino acids (aa}-₎

– _{cations (positive)}

• _{more concentrated in the extracellular fluid}

• _Na+

Na+ Na+ Na Na+ Na+ Na+ Na+ Na+ + _Na+ _K+ _Na+ _Na+

Cl

-K+ Cl- Cl- Cl

-K+

aa

-K+ Cl- Cl

-aa- aa

-aa

-aa- aa

-K+ K+

Ion channels in the membrane

leaks K+._{. write that down!!!}

Ion channels in the membrane

leaks K+._{. write that down!!!}

+

Neurons at rest have a net negative charge

• _{Opposite charges on opposite sides of cell}

membrane: membrane is polarized

• _{This is called “resting potential”} • _{negative inside; positive outside}

• _{charge gradient}

• _{stored energy (like a battery)}

+ + + + + + + + + + + + + + +

+ + + + + + + + + + + + + + +

– – – – – – – – – – – – – –

– – – – – – – – – – – – – –

http://bcs.whfreeman.com/thelifewire/content/chp44/4402 001.html

How does a nerve impulse travel?

• _{Stimulus: nerve is stimulated}

– _{reaches threshold potential} (critical amount of stimulation)

• This causes Na+ _{channels in cell membrane to OPEN}

• Na+ _{ions diffuse into cell}

– _{charges reverse at that point on neuron}

• positive inside; negative outside: cell becomes depolarized

– + + + + + + + + + + + + + +

– + + + + + + + + + + + + + +

+ – – – – – – – – – – – – – –

Gate

+ –

+ +

channel

closed channel open

How does a nerve impulse travel?

• _{Wave: nerve impulse travels down neuron}

– _{change in charge opens}

next Na+ _{gates down the line}

• _{These sodium channels are called “voltage-gated” channels}

– _Na+ _{ions continue to diffuse into cell through these newly} opened gates, triggered gates a little farther to open

– _{“Wave” moves down neuron = action potential}

– – – + + + + + + + + + + + +

– – – + + + + + + + + + + + +

+ + + – – – – – – – – – – – –

+ + + – – – – – – – – – – – – Na+

How does a nerve impulse travel?

• _{Re-set: 2nd wave travels down neuron behind the first}

– _K+ _{channels open}

• _K+ _{channels open up more slowly than Na}+ _channels

– _K+ _{ions diffuse out of cell}

– _{charges returns to starting point} • _{negative inside; positive outside}

+ – – – – + + + + + + + + + +

+ – – – – + + + + + + + + + +

– + + + + – – – – – – – – – –

– + + + + – – – – – – – – – –

Na+

K+

How does a nerve impulse travel?

• _{Combined waves travel down neuron}

– _{signal moves in one direction}     

• _{flow of K}+ _{out of cell stops activation of Na}+ _{channels in}

wrong direction

• _{How is this transmission NOT like a simple row of dominoes?}

+ + + – – – – + + + + + + + +

+ + + – – – – + + + + + + + +

– – – + + + + – – – – – – – –

– – – + + + + – – – – – – – –

Na+

wave 

K+

• _{http://www.blackwellpublishing.com/matthe}

ws/channel.html

• _{Show 2}nd _first

• _{http://highered.mcgraw-hill.com/sites/007249}

How does the nerve re-set itself?

• _{After firing a neuron has to re-set itself}

– _Na+ _{needs to move back out} – _K+ _{needs to move back in}

– _{both are moving against concentration gradients} • _{needs a pump!!}

+ + + + + + + + + + – – – – + + + + + + + + + + + – – – – + – – – – – – – – – – + + + + – – – – – – – – – – – + + + + – Na+ Na+ Na+

Na+ Na+

Na+

K+ K+

K+

K+ Na+ Na+

Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ K+ K+

K+K

+

K+ K+

K+ K+

wave 

K+

Build a neuron!

• _{Sodium…blue beads}

• _{Potassium….red beads}

• _{You will need:}

– _{Multiple voltage gated sodium channels and}

potassium channels

• _toothpicks

– _{At least one sodium potassium pump}

• _{Develop an animated model of an action}

How does the nerve re-set itself?

• _{Sodium-Potassium pump}

– _{active transport protein in membrane}

• _{requires ATP}

– _{3 Na}+ _{pumped out}

– _{2 K}+ _{pumped in}

– _{re-sets charge}

across

membrane

Cell body Axon Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ K+ K+ K+

K+ K+ K+

-1. Resting potential

2. Stimulus reaches threshold potential

3. Depolarization

Na+ _{channels open;}

K+ _{channels closed}

4. Na+ _{channels close;}

K+ _{channels open}

5. Repolarization

reset charge gradient

6. Undershoot

K+ _{channels close slowly, so}

gets TOO neg. inside!

Action potential graph

–70 mV –60 mV –80 mV –50 mV –40 mV –30 mV –20 mV –10 mV 0 mV

10 mV Depolarization Na+ _{flows in} 20 mV

30 mV 40 mV

Repolarization

K+_{flows out}

Threshold Hyperpolarization(undershoot)

Review!

•

Myelin sheath



 _{insulates axon}

 _{speeds signal}

 _{signal hops from node to node}  _{saltatory conduction}

 _{150 m/sec vs. 5 m/sec}

(330 mph vs. 11 mph) signal

direction

myelin sheath

Synapse

Impulse has to jump the synapse!

– _{junction between neurons}

– _{has to jump quickly from one cell to next}

axon terminal

synaptic vesicles

muscle cell (fiber) neurotransmitter acetylcholine (ACh) receptor protein Ca++ synapse action potential

Chemical synapse



 action potential

depolarizes membrane

 opens Ca++ channels

 neurotransmitter vesicles

fuse with membrane

 release neurotransmitter

to synapse  diffusion

 neurotransmitter binds

with protein receptor

 _{ion-gated channels open}

 neurotransmitter

degraded or reabsorbed

Nerve impulse in next neuron

• _{Post-synaptic neuron}

– _{triggers nerve impulse in next nerve cell}

• _{chemical signal opens ligand-gated channels} • _Na+ _{diffuses into cell}

• _K+ _{diffuses out of cell}

– + + + + + + + + + + + + + +

– + + + + + + + + + + + + + +

+ – – – – – – – – – – – – – –

+ – – – – – – – – – – – – – – Na+

K+ K

+

Na+ Na+

Na+

ion channel

Neurotransmitters

•_{Glutamate –excitatory} •_{GABA - inhibitory}

• _{Acetylcholine}

– transmit signal to skeletal muscle

• Epinephrine (adrenaline) & norepinephrine (noradrenaline)

– _{fight-or-flight response}

• _{Dopamine & serotonin}

– _{widespread in brain}

Neurotransmitters

• _{Weak point of nervous system}

– _{any substance that affects neurotransmitters or}

mimics them affects nerve function

• _{gases: nitrous oxide, carbon monoxide} • _{mood altering drugs:}

– _stimulants

» _{amphetamines, caffeine, nicotine} – _depressants

» quaaludes, barbiturates

• _{hallucinogenic drugs: LSD, peyote} • _{SSRIs: Prozac, Zoloft, Paxil}

Go up to receptors

LE 48-19

• _Vertebrate

nervous systems show a high

degree of

• _{The brain : integrative power that underlies the}

complex behavior of vertebrates

• _{The spinal cord integrates simple responses to}

certain kinds of stimuli and conveys information to and from the brain

• White matter: bundles of axons within the CNS

• Gray matter: dendrites, unmyelinated axons, and

neuron cell bodies

Gray matter

White matter

The Peripheral Nervous System

Peripheral nervous system

Somatic nervous system

Autonomic nervous

system

Sympathetic

division Parasympatheticdivision divisionEnteric

• _{The PNS has two functional components:}

– _{The somatic nervous system carries signals to skeletal}

muscles

– _{The autonomic nervous system regulates the internal}

environment (involuntary)

The Autonomic Nervous System

• _{The sympathetic division correlates with the}

“fight-or-flight” response

• _{The parasympathetic division promotes a}

return to self-maintenance functions

• _{The enteric division controls activity of the}

The Brainstem

1. The medulla oblongata: centers that control breathing, digestion, heart and blood vessel activity

2. The pons : participates in the same visceral functions

All info to and from higher brain passes through this region

3. The midbrain contains centers for receipt and integration of sensory information

The Cerebellum

• _{Important for coordination and error checking}

during motor, perceptual, and cognitive functions

• _{Involved in learning and remembering motor}

The Diencephalon

• _{Three regions: the epithalamus, thalamus, and}

hypothalamus

1. The epithalamus: pineal gland and choroid plexus (capillaries where CSF is made)

2. The thalamus: main input center for sensory

information to the cerebrum and the main output center for motor information

The Cerebrum

• _{The cerebrum has right and left hemispheres}

• _{Each cerebral hemisphere consists of a}

cerebral cortex of gray matter overlying white matter and basal nuclei (which plan movement sequences)

• _{A thick band of axons called the corpus}

• _{In mammals, the cerebral cortex has a}

convoluted surface called the neocortex

Left cerebral hemisphere

Corpus callosum

Neocortex

Right cerebral hemisphere

Frontal lobe Frontal association area Smell Speech Temporal lobe Auditory association area Hearing Visual association area Vision Occipital lobe Reading Somatosensory association area Taste Speech Parietal lobe

• _{Each side of the cerebral cortex has four lobes:}

frontal, parietal, temporal, and occipital

• _{Each lobe contains primary sensory areas and}

• _{http://faculty.washington.edu/chudler/flash/}

Mole-Ratunculus

• _{The incisors are an amazing adaptation with over}

Lateralization of Cortical Function

• _{The left hemisphere is more adept at language,}

math, logic, and processing of serial sequences

• _{The right hemisphere is stronger at pattern}

Language and Speech

• _{Studies of brain activity have mapped areas}

responsible for language and speech

• _{Portions of the frontal lobe, Broca’s area and}

Emotions

• _{The limbic system is a ring of structures around the}

brainstem

• _{It includes three parts of the cerebral cortex: the}

amygdala, hippocampus, and olfactory bulb which interact with the neocortex to mediate primary

emotions

HypothalamusThalamus

Hippocampus Amygdala

Olfactory bulb Prefrontal

Memory and Learning

• _{The frontal lobes are a site of short-term}

memory

• _{They interact with the hippocampus and}

amygdala to consolidate long-term memory

• _{http://robotic.media.mit.edu/projects/robots/le}