Lecture 11 Neurons and Neural signals

Question 1

Functions of the Nervous system

Answer 1

sensation
communication
integration
control

Question 2

Neurons

Answer 2

functional cells of the nervous system
excitable cells- generate electrical signals (changes in membrane potentials)
communicate information in the form of electrical and chemical signals

Question 3

Cell body of a neuron

Answer 3

contains the nucleus and most organelles

Question 4

dendrites

Answer 4

branch from the cell body

receive signals from other cells through synapse

Question 5

axon

Answer 5

extends from the cell body, conducts action potentials

Question 6

axon hillock

Answer 6

region where axon joins the cell body

Question 7

Trigger zone

Answer 7

initial segment adjacent to the axon hillock is the trigger zone for AP

Question 8

axon terminals

Answer 8

contain vesicles with neurotransmitter, form synapses with other cells

Question 9

Central Nervous system

Answer 9

brain and spinal cord

where most neurons are located

Question 10

Peripheral Nervous System

Answer 10

Nerves, ganglia and sensory receptors
Afferent Division
Efferent Division

Question 11

Afferent Division

Answer 11

Sensory neurons, input to CNS from sensory receptors
somatic sensory- from skin, muscles, bones & joints
Visceral sensory- from internal organs
Special senses- vision, hearing, equilibrium, olfaction, taste

Question 12

Efferent Division

Answer 12

Motor neurons, output from CNS to effectors
Somatic Motor- to skeletal muscles (voluntary)
Autonomic (ANS) - to heart, smooth muscle, gland, adipose tissue (involuntary)
a.sympathetic
b. parasympathetic

Question 13

Enteric Nervous System

Answer 13

Nerve network of the GI tract

Question 14

Functional Types of Neurons

Answer 14

Sensory neurons
Motor neurons
Interneurons

Question 15

Sensory Neurons

Answer 15

afferent
Input to CNS from sensory receptors; dendrites located at receptors, axon in nerves, cell bodies in ganglia outside the CNS

Question 16

Motor Neurons

Answer 16

efferent
Output from CNS to effectors
cells bodies and dendrites located in the CNS, axons in nerves

Question 17

Interneurons

Answer 17

communicate and integrate information within the CNS
located entirely within the CNS
Most common

Question 18

Astrocytes

Answer 18

CNS

structural and chemical support, blood-brain barrier

Question 19

Oligodendrocytes

Answer 19

CNS

Myelin in CNS

Question 20

Microglia

Answer 20

CNS

Phagocytes

Question 21

Ependymal cells

Answer 21

CNS

produce CSF

Question 22

Schwann cell

Answer 22

myelin in PNS

Question 23

satellite cells

Answer 23

in PNS ganglia

Question 24

Graded Potentials

Answer 24

small, localized changes in membrane potential
formed at the cell body and dendrites
can be depolarization or hyperpolarization
spread passively and weaken with distance
size depends on stimulus strength
seen at cell bodies and sensory receptors
Stimulates action potentials
caused by opening of chemically gated channels
must exceed threshold to start AP

Question 25

Action Potentials (nerve impulses)

Answer 25

large change in membrane potential formed along the axon rapid depolarization followed by repolarization actively conducted along the axon all or none- size is not dependent on stimulus strength Doesn't weaken with distance

Question 26

Phase 1 of action potentials

Answer 26

Rising (Depolarization) phase - initial depolarization stimulus must be above threshold to form an AP - voltage gated Na+ channels open - activation gate opens in response to initial depolarization - > rapid Na+ inflow -> rapid depolarization

Question 27

Phase 2 of action potentials

Answer 27

``` Falling (repolarization) Phase -Voltage gated Na+ channels close inactivation gate - closes when depolarization reaches peak -voltage gated K+ channels open ->rapid K+ outflow-> repolarization ```

Question 28

Phase 3 of action potentials

Answer 28

Undershoot voltage gated K+ channels remain open, high K+ permeability results in hyperpolarization resting states of channels and resting potential restored at end of undershoot phase -both voltage gates closed only the leak channels open when RP is restored

Question 29

Name the properties of action potentials

Answer 29

threshold all or more regenerative refractory period

Question 30

Threshold

Answer 30

stimulus must be greater than a certain strength to evoke an AP (subthreshold - cant start AP below threshold) enough activation gates must open -55mV

Question 31

"All or None"

Answer 31

once threshold is reached size of the AP is constant regardless of stimulus

Question 32

regenerative

Answer 32

AP is regenerated and does not decrease in strength along the axon

Question 33

Refractory period

Answer 33

short delay following an AP before another AP can be formed

Question 34

absolute refractory period

Answer 34

ARP | period in which another AP can not be formed

Question 35

relative refractory period

Answer 35

RRP | period in which a larger stimulus is required to form another AP

Question 36

Main importance of refractory period

Answer 36

ARP sets an upper limit on frequency of AP During RRP, a stronger stimulus can result in increased frequency of APs -stimulus intensity is coded by the frequency of APs Refractory period prevents AP from traveling backward along the axon

Question 37

Are concentration gradients affected during an AP

Answer 37

No they are not, Na+/K+ pump still maintains gradients

Question 38

How are stimulus intensity coded

Answer 38

by the frequency of AP

Question 39

Unmyelinated Axons

Answer 39

AP depolarization spreads a short distance down the axon depolarization stimulates formation of AP farther down the axon axons are leaky to Na+ and K+; need to regenerate AP often along the axon -> slow conduction speed increasing axon diameter increases conduction speed

Question 40

Myelinated Axons

Answer 40

myelin sheath formed by membrane of schwann cells in PNS and oligodendrocytes in CNS insulates axon, reduced leakage of Na+ and K+ nodes of ranvier- gaps in myelin sheath are sites of AP regeneration AP "jumps" from node to node (saltatory conduction) faster conduction speeds (up to 120 m/s)