Biol-102: Nervous System: Neurons And Synapses

Front 1

What is the general organization of the Nervous System?

Back 1

Central Nervous System and Peripheral Nervous System

Front 2

What does the Central Nervous System consist of and its function?

Back 2

consists of: brain and spinal cord
function: control and integration

Front 3

What does the Peripheral Nervous System consist of and its function?

Back 3

consists of: cranial nerves and spinal nerves
function: communication
• connects the CNS to sensory receptors, muscles and glands

Front 4

What is the function of neurons?

Back 4

conduct electrical signals

Front 5

What is the function of Neuroglia?

Back 5

• majority of all nerve tissue cells
• supports neurons

Front 6

What is the function of Cell Body?

Back 6

nucleus and typical organelles

Front 7

What is the function of Dendrites?

Back 7

receive stimulation

Front 8

What is the function of the Axon?

Back 8

• conducts electrical signals (action potentials)
• Often insulated with a myelin sheath

Front 9

What is the function of the Axon Hillock?

Back 9

the site where action potentials originate

Front 10

What is the function of the Axon Terminals?

Back 10

the site where signals are released

Front 11

Sensory (Afferent) Neurons

Back 11

• part of the PNS
• transmit electrical signals from tissues to CNS
• detect changes in environments and relay info to controller

Front 12

Motor (Efferent) Neurons

Back 12

• part of the PNS
• transmit signals from CNS to effector tissues (muscle, gland cells)

Front 13

What are the two basic types of motor neurons?

Back 13

Somatic motor neurons and Autonomic motor neurons

Front 14

Somatic Motor Neurons

Back 14

• Innervate skeletal muscles
• Voluntary control

Front 15

Autonomic Motor Neurons

Back 15

• Innervate smooth muscle, cardiac muscle and glands
• under involuntary control
• divided into sympathetic and parasympathetic divisions

Front 16

Associated Neurons (Interneurons)

Back 16

• located within the CNS
• Receive sensory information
• Analyze, modulate modify and integrate signals
• Stimulate motor neurons
• Responsible for cognition, memory, etc.

Front 17

Structural Types of Neurons are based on ___.

Back 17

the number of processes (extensions)

Front 18

What are the three basic structural types of neurons?

Back 18

1. bipolar
2. pseudounipolar
3. multipolar

Front 19

Bipolar Neurons

Back 19

(sensory neurons in eyes and ears)
• two processes originate from cell body
• dendritic and axonal

Front 20

Pseudounipolar

Back 20

(mostly sensory neurons)
• one process that splits into two away from the cell body

Front 21

Multipolar Neurons

Back 21

(motor and association neurons)
• many processes extend from cell body
• many dendrite and a single axon

Front 22

What at two types of Neuroglia in the Peripheral Nervous System?

Back 22

Schwann Cells and Satellite Cells

Front 23

Schwann Cells

Back 23

• surround all PNS axons
• forms neurilemma
• guide regeneration of damaged axons
• form myeline sheaths around many axons

Front 24

Satellite Cells

Back 24

• form capsules around cell neuron cell bodies and ganglia

Front 25

What are the types of Neuroglia in the Central Nervous System?

Back 25

1. Oligodendrocytes
2. Astrocytes
3. Microglia
4. Ependymal Cells

Front 26

Oligodendrocytes

Back 26

function: form myelin sheath around axons

Front 27

Astrocytes

Back 27

function:
• control permeability of capillaries in the CNS (blood brain barrier)
• support neuronal activity
*most common type of neuroglial cells

Front 28

Microglia

Back 28

function: engulf foreign/degenerated material

Front 29

Ependymal Cells

Back 29

function: form epithelial lining of brain and spinal cord cavities

Front 30

Myelin Sheath

Back 30

• Formed by wrapping plasma membrane of certain neuroglia repeatedly around axon
• Insulates axon with multiple lipid bilayers
- Prevents exchange of hydrophilic materials between axon and adjacent extracellular fluid
- Accelerates electric signal transmission

Front 31

Schwann Cells

Back 31

• single flat cells wrapped repeatedly around axon segment
• gaps between (where axon plasma membrane is in direct contact with the extracellular fluid) are the Nodes of Ranvier

Front 32

Oligodendrocytes

Back 32

form myeline sheath by wrapping processes around multiple individual axons

Front 33

depolarization

Back 33

decrease difference in charge between the ICF and ECF

Front 34

hyperpolarization

Back 34

increase difference in charge between intracellular and extracellular fluids

Front 35

Non-gated (leak) ion channels

Back 35

• "always" open
• specific for a particular ion

Front 36

Gated ion channels

Back 36

open only in response to a specific stimuli

Front 37

Ligand-gated (-regulated)

Back 37

• binding of a chemical signal (ligand) causes channel to open
• found on dendrites and cell body

Front 38

Voltage-gated (-regulated)

Back 38

• changes in membrane potential (depolarization) cause channel to open
• found in axons
• requires membrane to be depolarized to a certain degree from the resting potential (threshold membrane potential)
• If membrane depolarized to threshold, a cycle of activation (channel opening) followed by inactivation (closing) ensues

Front 39

Membrane Proteins Involved in Electrical Signals

Back 39

Na+/K+ pump

Front 40

Na+/K+ Pump

Back 40

• used to maintain electrochemical gradients for Na+ and K+ across the plasma membrane
• maintains resting potential
• active (requires ATP)
• Three Na+ pumped out, two K+ pumped in per ATP

Front 41

"All or None" response

Back 41

• axon hillock must by depolarized to the threshold potential for voltage-gated channels to open
• if depolarized to (or beyond) threshold, voltage-gated channels will open and action potential will depolarize as much as possible
• if threshold not reached, voltage-gated channels do not open and no action potential will occur
- signal will quickly lose strength as it travels down axon

Front 42

___ is driven by the flow of Na+ into the cell.

Back 42

Depolarization

Front 43

___ is driven by the flow of K+ out of the cell.

Back 43

Repolarization

Front 44

Refractory Period

Back 44

• Interval that must pass before the neuron segment can undergo a second action potential
• Membrane potential and ion concentration gradates must be restore

Front 45

Absolute refractory period

Back 45

• Neuron segment is in the process of undergoing an action potential
• Na+ channels are either fully open (depolarization) or in an inactive state (repolarization)
• cannot respond to a second stimulus

Front 46

Relative Refractory Period

Back 46

• Na+ channels can be activated again, but K+ still flowing out of the cell at a high rate
• action potential may be produced if a stronger stimulus is applied

Front 47

Saltatory conduction

Back 47

• action potential "jump" from one node to the next
• increased action potential speed (↑ 50x)

Front 48

Synapse

Back 48

• communication junction between a neuron and either another neuron or a muscle or gland cell
• chemical signals (neurotransmitters) released from axon terminal and bind to receptors on adjacent cell
• stimulates physiological change (usually change in membrane potential) in the recipient cell

Front 49

Presynaptic neuron

Back 49

• axon terminals
• contains synaptic vesicles filled with neurotransmitters

Front 50

synaptic cleft

Back 50

narrow space between cells

Front 51

postsynaptic cell

Back 51

contains receptor proteins that will bind to neurotransmitter

Front 52

What are two possible types of synaptic potential?

Back 52

Excitatory postsynaptic potential (EPSP) and Inhibitory postsynaptic potential (IPSP)

Front 53

Excitatory Postsynaptic potential

Back 53

postsynaptic cell membrane depolarizes

Front 54

Inhibitory Postsynaptic Potential

Back 54

postsynaptic cell membrane hyperpolarizes

Front 55

Characteristics of Synaptic Potentials

Back 55

1. Decrease in amplitude with distance
• The change in membrane potential decreases the further the distance from the chemical synapse
2. Graded responses
• More neurotransmitter causes greater changes in membrane potential
3. Can summate
• No refractory period for synaptic potentials
• EPSPs and IPSPs generated in close succession can have an additive effect on the membrane potential of the postsynaptic cell
• Aspects of summation
- Spatial summation – summation due to release of neurotransmitter from multiple presynaptic neurons
- Temporal summation – summation due to high rate of neurotransmitter release from presynaptic neurons

Front 56

spatial summation

Back 56

summation due to release of neurotransmitter from multiple presynaptic neurons

Front 57

temporal summation

Back 57

summation due to high rate of neurotransmitter release from presynaptic neurons

Front 58

Acetylcholine (ACh)

Back 58

• Used by many diverse neurons
• Generates ESPSs or IPSPs depending on the particular mechanism activated by the binding of ACh

Front 59

Nicotinic ACh Receptors

Back 59

- Found in certain brain regions, skeletal muscle cells, and cell bodies of autonomic motor neurons in ganglia
- Receptor is a ligand-gated ion channel activated by the direct binding of ACh
- Channel opens, Na+ flows into cell quickly, K+ flows out slowly
- (A little K+ is able to flow out)
- Induces EPSPs
- ACh quickly broken down by acetylcholinesterase embedded in post-synaptic cell membrane
- Short term effect of acetylcholine on receptors

Front 60

Muscarinic ACh Receptors

Back 60

• Found in some CNS neurons, smooth muscle, glands, and cardiac muscle
• Receptor for ACh (G-protein linked receptor) is separate from the ion channel
- ACh binding induces activation of G-proteins in the plasma membrane
- G-protein dissociates into α and βγ subunits
- Soon become inactivated (subunits link back together)
- G-proteins activate enzymes and channels specific to the cell
- E.g., generates EPSPs in smooth muscle in digestive tract
- E.g., generates IPSPs in cardiac muscle

Front 61

GABA (gamma-aminobutyric acid)

Back 61

- Important CNS neurotransmitter
- Binds directly to ligand-gated Cl- channels
- Cl- flows into cell
- Induces IPSPs

Front 62

Monoamines

Back 62

• Dopamine, norepinephrine, epinephrine (catecholamines)
• Serotonin
• Function through G-Protein linked receptors
• Leads to activation of enzymes and production of second messengers (e.g., cAMP) inside cell
• Second messengers activate additional enzymes (e.g., protein kinases), that induce metabolic changes or changes in membrane potential
• Monoamines generally taken back up by the presynaptic cell