Chapter 48—Nervous

SystemsYour Brain—the most intricately

organized aggregate of matter on Earth

What characteristics does a

nervous system need?

• Fast

• Accurate

• Ability to reset quickly

I. Overview of Nervous Systems

3 overlapping functions:

� sensory input

� integration

� motor output

CNS vs. PNS?

Vertebrate Neuron (nerve cell)

Figure 48.2, pg. 1023!!!

Learn your vocab!!

Neuron—Functional unit of nervous

system

Most specialized form of cells in

animals

Structure fits function

� many entry points for signal (dendrites)

� one path out (axon)

� transmits signal to next cell

Incoming

signal

Outgoing

signal

Schwann Cells

� Glia (supporting cells) that form insulating myelin sheaths around axons

� lipids act as electrical insulators

Multiple Sclerosis (MS)—T cells destroy myelin of neurons

Structural Diversity of Neurons

3 main types of

neurons:

� sensory neurons

� interneurons

� motor neurons

Il. The Nature of Nerve Signals

� Membrane Potential = voltage

(charge difference) across a cell

membrane

� inside cell—more negative

charge

� outside cell—more positive

charge

Charge difference is a form of

stored energy (like a battery)

Resting potential (unstimulated

cell) = -70mV

How does a cell maintain a

membrane potential?

Differences in ion concentration inside vs. outside are maintained by sodium-

potassium pump (maintains electro-chemical gradient)

� uses ATP to actively transport Na+ out of cell and K+ into cell

Nerve Impulses

What is a nerve signal/impulse?

� a change in the voltage across the plasma membrane of a nerve cell

� voltage changes are caused by ion movement by way of ion channels

(chemical-gated/voltage-gated)

What types of cells are excitable?

� nerve, muscle (can do this)

Graded Potentials vs. Action PotentialsFigure 48.8, pg. 1029

Graded potential—change in voltage depends on strength of stimulus

(hyperpolarization or depolarization)

Action potential—all or nothing nerve impulse (once above threshold potential)

(depolarization)

Action Potential occurs due to

voltage-gated ion channels

K+ & Na+ channels are closed

Stimulus reaches

threshold potential due to

a few open Na+ channels

Na+ channels open; K+ channels closed

(inside of cell becomes more positive)

Na+ channels

close; K+

channels open

(inside of cell

more negative)

K+ channels close slowly

(can’t refire until returned to resting

potential)

Refractory period

Axons are one-way streets only

Propagation of Action Potential

Long-distance signals must “travel” along the

axon (A. P. regenerated repeatedly)

How is the transmission of a nerve

signal like dominoes?

Saltatory Conduction

Action potential jumps from node to node as it moves down the axon

ion channels are only found in nodes between Schwann cells

What happens at the end

of the axon?

Synapse—cell junction between a

neuron & another cell

Electrical signal (1st cell) → turns into

chemical signal (synapse)→ back into

electrical signal (2nd cell)

diffusion of neurotransmitters across

synapse conducts the chemical signal

from one cell to another

Chemical synapse:

• action potential

depolarizes presynaptic

membrane

• triggers influx of Ca+

(voltage gated channels)

• vesicles fuse with

membrane & release

neurotransmitter to

synaptic cleft

• neurotransmitters bind

with receptors on

postsynaptic membrane,

opens ion channels

(chemical gated)

• new action potential

starts in next neuron

EPSP vs. IPSP?

Neurotransmitters

How can the same neurotransmitter produce different effects on different cells?

How do neurotransmitters relate to nervous system diseases?

III. Diversity in Nervous Systems

IV. Vertebrate Nervous System

Hierarchy of PNS

Skeletal

muscles under

voluntary

control

Cardiac muscle, organs

under involuntary control

Parasympathetic vs. Sympathetic

Calming, self-

maintenence

Arousal,

energy

generation

Figure 48.18, pg. 1041

Human Brain

Cerebrum