Chapter 11

Seite 1

Chapter 11

I. Organization of the Nervous

System

A. The central nervous system consists of …

·

CNS = brain and spinal cord

·

Nuclei and tracts in CNS

B. The peripheral nervous system consists of… PNS- ganglia

and nerves in PNS

1. The sensory, or afferent, division

·

Signals toward CNS

2. The motor, or efferent, division (sends signals

away from CNS)

a. The somatic nervous

system

·

voluntary control of skeletal muscle

b. The autonomic nervous system

·

involuntary control of cardiac muscle, smooth

muscles, glands

·

sympathetic and parasympathetic division

II. Histology of Nervous Tissue

A. Neuroglia, or glial cells

·

astrocytes- (star shape cells) chemical houses

keeping in CNS

·

microglia- defense cells of CNS

·

oligodendrocytes-

provide myelinate CNS axons of neurons

·

Schwann cells- myelinate PNS axons

B. Neurons are specialized cells that conduct messages in the form of

electrical impulses

1. Neuron traits

·

longevity

·

high metabolic rate

·

amitotic (built to live a lifetime)

2. Neuron parts

·

a.) dendrites- receive chemical signals

·

b.) soma- also can receives chemical signals,

synthesizes large molecules

·

c.) axon- long fibers-sends impulse (AP)

o myelinated

axons have gaps in myelin (gaps known as Nodes of Ranvier)

·

d.) axon terminals- knobs secrete transmitter when

AP

3. Classes of neurons

·

a.) structurally:

o unipolar: axon only

o bipolar: 1 dendrite, 1

axon

o multipolar: many

dendrites, 1 axon

§ (depending on

how many fibers are coming off the soma)

·

b.) functionally:

o sensory

neurons- from periphery (within the brain and spinal cord)

o interneurons-

within CNS

o motorneurons-

efferents to muscles, glands

III. Neurophysiology

A. Basic Principles of Electricity and Membrane Potential

1. Voltage is…

·

separation of opposite charge = potential

·

current = voltage/ resistance

B. Role of Membrane Ion Channels

1. leakage

channels

·

always open pore (all over parts of the cell)

·

determines resting membrane potential

·

many for potassium

2. gated channels

a)

chemically

gated channels

· open up when a

neurotransmitter is present and binds to it

o slide says, “open

in response to binding of the appropriate neurotransmitter”

b)

voltage

gated channels

· open up when

the cells membrane potential changes and get to a certain level

o slide says, “open

in response to changes in membrane potential”

c)

mechanically gated channels

· opens when

membrane is stretched

C. The Resting Membrane Potential

· size wise

about -70mV

· because

potassium leaks out of leakage channels due to it having been pumped in

· negatively

charged internal proteins

D. Membrane Potentials That Act as Signals

1. Neurons use changes in membrane potential as communication signals

2. A change in membrane potential from rest can either be

depolarization: the membrane

potential moves towards 0mV, the inside becoming less negative (more positive)

·

cell becomes less negative

o e.g. when a

cation enters cell

hyperpolarization: the membrane

potential increases, the inside becoming more negative

·

cell becomes more negative

o e.g. when an

anion enters cell or when a cation leaves cell

3. Graded potentials are …

·

changes in voltage that vary with stimulus strength

o decremental-

fade with distance

o e.g. end plate

potential; post synaptic potential in neurons

4. Action potentials

·

draw graph

o i.) rest- all

volt gates closed

o ii.)

depolarization- rise

§ Na gate open;

Na+ enters

o iii.) repolarization-

fall

§ Na+ gate

closes- inactive; K+ gate opens; K+ exits (leaves)

o iv.)

hyperpolarization- Na+ still closed; K+ still leaving

o GOES BACK TO

REST, STARTS OVER

·

refractory period- cell less responsive

o absolute

refractory period- impossible to fire

o relative

refractory- means it is difficult but not impossible; elevated threshold to

fire

·

AP’s: all-or-none; non-decrmental; on axon (the part

of the cell we are talking about)

E. Influence of

Axon Diameter and Myelin on Conduction Velocity

·

Myelinated axons are faster

o AP occurs at

nodes

·

Fatter axons are faster (signal spreads faster on

fatter axons)

F. The Synapse

1. A synapse is…

·

a junction between two neurons, where information is

transferred

2. Electrical synapses (rare)

·

gap junctions couple the cells

o fast

communication

3. Chemical synapses and their parts

·

a.) presynaptic terminal – AP arrives, it’s going to

open up calcium channels, causing the calcium to enter terminal thru volt-gated

channels; exocytosis of neurotransmitter

·

b.) cleft- neurotransmitter diffuses

·

c.) postsynaptic cells dendrite or soma catches the

transmitter

o has PSP=

post-synaptic potential

4. Neurotransmitter clearance

·

a.) degrade by enzyme

·

b.) reuptake by presynaptic cell

·

c.) diffuses away from cleft

G. Postsynaptic Potentials and Synaptic Integration

1. Neurotransmitters trigger graded potentials at synapses…

·

a.) EPSPs (excitatory postsynaptic potential) –

depolarization (thing become less negative)

o makes cell

more likely to fire AP (brings it closer to threshold)

·

b.) IPSP (inhibitory postsynaptic potential)-

hyperpolarization

o makes

postsynaptic cell less likely to fire AP

2. Summation by the postsynaptic neuron

·

spatial summation: simultaneous inputs from multiple

presynaptic terminals

o PSP added

across space

·

temporal summation- successive in puts from same

terminal close together in time

3. Presynaptic inhibition results when another neuron inhibits the

release of excitatory neurotransmitter from a presynaptic cell.

·

One axon terminal inhibits another

o Draw picture

H. Neurotransmitters and Their Receptors

1. Neurotransmitters are categorized in several chemical classes.

·

a.) amino acids

o GABA- common,

inhibitor in brain

o Glutamate-

common, excitatory in brain

·

b.) acetylcholine (Ach)

o motoneurons to

muscle cells

·

c.) biogenic amines

o norepinephrine-

brainstem; alertness

o dopamine-

motor control; basal nuclei

·

d.) neuropeptide

o endorphins-

pain relief in brain spinal cord

2. Two main types of neurotransmitter receptors:

·

a.) ionotropic receptors- direct (fast passing)

“channel linked”

o the receptors

is a ligand (chemical transmitter) gated channel

·

b.) metabotropic receptor- indirect

o work through G

proteins and (often times generate second messagers) 2nd messagers

in order to cause EPSP or IPSP

IV. Basic Concepts of Neural Integration

A. Types of Circuits

1. diverging

vs. converging circuits

·

diverging

circuits: a few presynaptic cells talk to many post synaptic cells

o e.g. alertness

system- norepinephrine released of many different brain synapses

·

converging

circuits: many presynaptic cells talk to few postsynaptic cells

o e.g. many rods

talk to moderate number of interneurons that talk to fewer ganglion cells of

optic nerve

B. Patterns of Neural

Processing

1. serial vs. parallel processing

·

serial

processing: in sequence

o e.g. retina

detects light, sends signal to thalamus, thalamus sends signal to cortex, etc.

·

parallel

processing: simultaneous processing in different places of

neurons system

o e.g. visual

system can figure out where a stimulus is (parietal lobe) while figuring out

what a stimulus is (temporal lobe)