Chapter 11 Part 2 Introduction to the Nervous System

Neurophysiology

is the study of how the nervous system works

Neurons are

the functional units of the nervous system

Neurons use

electrical signals and chemicals to communicate

Electrical signals are produced when

ions move across membranes

Ions can cross membranes through

ion channels

Ligand-gated ion channel

responds to a chemical stimulus (neurotransmitter)

Mechanically gated ion channel

responds to physical force

Voltage-gated ion channel

responds to changes in the membrane potential

Membrane potential

is the charge difference (voltage) across a membrane

The membrane potential of a resting cell is about

-70 millivolts

The resting membrane potential is due to

the Na+K+ pump

The Na+K+ pump

pumps about 3 Na+ ions out of cell for every 2 K+ ions pumped into cell

The Resting membrane potential means

NO ELECTRICAL SIGNAL

Graded potentials are

short-distance signals

Action potentials are

long-distance signals

Graded potentials occur when

either a ligand-gated or mechanically-gated ion channel opens

Graded potentials decrease with

distance

Action Potentials Transient reversal is of

the membrane potential

Action Potentials occur when

voltage-gated ion channels open

Action Potentials occur along

axolemma and sarcolemma

Action Potentials are All or none events caused by

the diffusion of Na+ and K+ ions

All or none means that

APs either operate at 100% (all) or nothing happens (none)

The membrane potential that must be reached for the AP to begin is

Threshold (about -55 millivolts)

1st phase of AP

Depolarization

2nd phase of AP

Repolarization

3rd phase of AP

Hyperpolarization

Depolarization is Caused by

Na+ channel opens then, Na+ ions enter cell

Depolarization membrane potential

becomes more positive

Repolarization is Caused by

K+ channel opens then, K+ leaves the cell

Repolarization membrane potential

becomes more negative

Hyperpolarization is Caused by

K+ channels close slowly

Hyperpolarization membrane potential

becomes more negative than resting

The Action Potential starts at

the Axon Hillock

In order for the AP to travel along the axolemma, it uses either

Continuous conduction or Saltatory conduction

Continuous conduction occurs on

unmyelinated axons

Saltatory conduction occurs on

myelinated axons

How fast APs are conducted depends on

Diameter of the axon and Amount of myelination

A Synapse

is a junction between 2 neurons or between a neuron and an effector cell

Electrical synapses

gap junctions connecting 2 neurons together

chemical synapses

releases neurotransmitters

Pre-synaptic neurons

send the signal

Post-synaptic neurons

receive the signal

Neurotransmitters (NTs)

are chemical messengers released by the nervous system

2 NTs in the CNS

Dopamine and Serotonin

Dopamine

motor control

Parkinson's disease is due to

the lack of dopamine in brain

Serotonin maintains

moods, sensory perception

The 2 main NTs in the PNS

Acetylcholine and Norepinephrine

Acetylcholine stimulates

skeletal muscle contraction, released by the ANS

Norepinephrine is produced by

the autonomic nervous system