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Human Physiology > Nervous System > Flashcards

Nervous System Flashcards

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1
Q

Neuron

A
  • Communication, information processing, control functions
  • Work together with the endocrine system to maintain homeostasis
  • Converts information to an electrical signal
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2
Q

Cell Body (soma)

A

Contains large nucleus and other organelles

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3
Q

Dendrites

A
  • Key role: intercellular communication

- Site of vesicular/axonal transport

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4
Q

Synaptic Terminals

A

The end of an axon

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5
Q

Synapse

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Site of communication between cells

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6
Q

Anatomical Divisions of the Nervous System: CNS

A
  • Spinal cord and brain

- Integrates, processes and coordinates sensory data and motor commands

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7
Q

Anatomical Divisions of the Nervous System: PNS

A
  • All neural tissue outside CNS (nerves, ganglia, sensory)

- Delivers sensory information to CNS and carries motor commands to peripheral tissues and systems

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8
Q

Functional Divisions of the Nervous System (PNS): Afferent

A
  • Carries sensory information from PNS sensory receptors to CNS
    > incoming division
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9
Q

Functional Divisions of the Nervous System (PNS): Efferent

A
  • Carries motor commands from CNS to PNS muscles and glands
    > outgoing division
    > has somatic and autonomic components
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10
Q

Efferent: SNS (somatic nervous system)

A
  • controls skeletal muscle contractions (voluntary response)

- reflexes (involuntary)

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11
Q

Efferent: ANS (autonomic nervous system)

A
  • regulates smooth muscle, cardiac muscle, glandular secretion and adipose tissue
  • sympathetic division: increased rate and force of contraction
  • parasympathetic division: decreased rate and force of contraction
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12
Q

Neuroglia

A
  • Preserve physical and biochemical structure of neural tissue
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13
Q

Neuroglia of the CNS: Ependymal Cells

A
  • Line central canal of spinal cord and ventricles of brain

- Produce, secrete and monitor Cerebrospinal Fluid (CSF)

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14
Q

Neuroglia of the CNS: Astrocytes

A
  • Maintain blood-barrier (isolates CNS)
  • Create three-dimensional framework for CNS
  • Repair damaged neural tissue
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15
Q

Neuroglia of the CNS: Oligodendrocytes

A
  • Smaller cell bodies with fewer processes
  • Processes contract other neuron cell bodies
  • Wrap around axons to form myelin sheaths
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16
Q

Neuroglia of the CNS: Microglia

A
  • Conduct phagocytosis to remove cellular debris, waste products and pathogens
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17
Q

Neuroglia of the PNS: Satellite cells

A
  • Regulate environment around neurons like astrocytes in the CNS
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18
Q

Neuroglia of the PNS: Schwann Cells

A
  • Form myelin sheaths around peripheral axons
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19
Q

Types of Neurons (Functional Classification): Sensory Neurons - form afferent division of PNS

A

Deliver information received from interoceptors, exteroceptors and proprioceptors to CNS

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20
Q

Types of Neurons (Functional Classification): Motor Neurons - form efferent division of PNS

A

Stimulate or modify the activity of a peripheral tissue, organ or organ system

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21
Q

Types of Neurons (Functional Classification): Interneurons - Located in CNS - situated between sensory and motor neurons

A

Distribute sensory inputs, coordinate motor inpute

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22
Q

Structural Classification of Neurons: Anaxonic

A

Have more than two processes but axons cannot be distinguished from dendrites

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23
Q

Structural Classification of Neurons: Bipolar

A

Two processes separated by the cell body

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24
Q

Structural Classification of Neurons: Unipolar neurons

A

Single elongate process, with the cell body situated off the side

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25
Structural Classification of Neurons: Multipolar neurons
More than two processes, single axon and multiple dendrites
26
Resting Potential
- Transmembrane potential of a resting cell - All neural activities begin with a change in the resting potential of a neuron - A charge difference is maintained across the cell membrane > -70mV (sodium-potassium exchange pump stabilises)
27
What is the transmembrane potential?
Results from the unequal distribution of ions across the plasma membrane
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Resting Potential: Extracellular
High concentrations of sodium ions and chloride ions
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Resting Potential: Intracellular
High concentrations of potassium ions and negatively charged proteins
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Electrochemical Gradients for Potassium and Sodium Ions: Potassium Ion Gradients
- At normal resting potential, an electrical gradient opposes the chemical gradient for potassium ions (K+). The net electrochemical gradient tends to force potassium ions out of the cell - If the plasma membrane were freely permeable to potassium ions, the outflow of K+ would continue until the equilibrium potential (-90mV) was reached
31
Electrochemical Gradients for Potassium and Sodium Ions: Sodium Ion Gradients
- At the normal resting potential, chemical and electrical gradients combine to drive sodium ions (Na+) into the cell - If the plasma membrane were freely permeable to sodium ions, the influx of Na+ would continue until the equilibrium potential (+66mV) was reached
32
Electrochemical Gradients for Potassium and Sodium Ions: Electrochemical gradient
Sum of all chemical and electrical forces acting across the plasma membrane
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Changes in Transmembrane Potential
In response to temporary changes in membrane permeability. Results from opening or closing of specific membrane channels
34
Changes in Transmembrane Potential: Passive Channels
- Always open - leak channel | - Membrane permeability changes in shape in response to the environment
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Changes in Transmembrane Potential: Active Channels
- Open and close in response to specific stimuli | - At resting potential, most gated channels are closed
36
Changes in Transmembrane Potential: Active Channels: Chemically Gated Channels
- Open and closed when they bind to specific chemicals e.g. acetylcholine - Found on the dendrites and cell body of a neuron
37
Changes in Transmembrane Potential: Active Channels: Voltage-Gated Channels
- Open or close in response to changes in the membrane potential - Have activation gates (open) and inactivation gates (closes) - Characteristic of areas of excitable membrane - Found in neural axons, skeletal muscle sarcolemma, cardiac muscle
38
Changes in Transmembrane Potential: Active Channels: Mechanically Gated Channels
- Open or close in response to membrane distortion | - Found in sensory receptors (touch, pressure, vibration)
39
Graded Potential: Summary
Changes in the transmembrane potential that cannot spread far from the site of stimulation. Any stimulus that opens a gated channel produces a graded potential
40
Graded Potential
1) Sodium ions enter cell and are attracted to negative charges along the inner surface of the membrane. Transmembrane potential shifts toward 0mV (Depolarisation) 2) As the plasma membrane depolarises, sodium ions are released from its outer surface. These ions, along with other extracellular sodium ions, then move toward the open channels, replacing ions that have already entered the cell
41
Depolarisation
Any shift from the resting potential toward a more positive potential
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Local Current
Movement of positive charges parallel to the inner and outer surfaces of a membrane
43
Action Potential
- Propagated changes in the transmembrane potential, that once initiated, affect an entire excitable membrane - Arises when a region of excitable membrane depolarises to its threshold - Rate of an action potential is dependent on the diameter of the axon and degree of myelination
44
Why does an action potential relate to "all or none"
Because a given stimulus either triggers a typical action potential, or none at all
45
Generation of Action Potential
1) A graded depolarization brings an area of excitable membrane to threshold (-60mV) 2) Voltage-gated sodium channels open and sodium ions move into the cell. Transmembrane potential rises to +30mV 3) Sodium channels close, voltage-gated potassium channels open, and potassium ions move out of the cell. Repolarisation begins 4) Potassium channels close, and both sodium and potassium channels return to their normal states
46
Absolute Refractory Period
Membrane cannot respond to further stimulation
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Relative Refractory Period
Membrane can respond to only a larger than normal stimulus
48
Propagation of Action Potentials
Mechanism to move the action potential along the axon - Continuous Propagation - Saltatory Propagation
49
Propagation of Action Potentials: Continous Propagation
- Action potential spreads across the entire excitable membrane surface in a series of small steps - Unmyelinated axons - 1 segment at a time - Action potential arrives in 1 direction
50
Propagation of Action Potentials: Saltatory Propagation
- Action potential appears to lead from node to node, skipping the intervening membrane surface - Myelinated axons - Faster and uses less energy than continuous propagation - Depolarisation occurs only at nodes
51
Rate of Signal Propagation
Myelin and Axon diameter affect the speed of action potentials - Type A fibres - Type B fibres - Type C fibres
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Type A fibres
- Myelinated, large diameter, conduction velocity 12-130m/s - urgent information
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Type B fibres
- Myelinated, small diameter, conduction velocity 15m/s - | less urgent information
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Type C fibres
- Unmyelinated, small diameter, conduction velocity 1m/s - less urgent information
55
Neurotransmission
Nerve impulse passes from one neuron to a second neuron at a synapse via neurotransmitters
56
Synapses
- Communication occurs among neurons or between neurons and other cells - Action potential travels along axon: Nerve Impulse
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Types of Synapses: Electrical
- Located in CNS (and PNS but rare) - Direct physical contact at gap junctions - Ions move between cells through gap junctions - Held in position by binding between integral membrane proteins: connexons - Action potential is propagated quickly and efficiently
58
Types of Synapses: Chemical
- Most abundant type of synapse - Communication between neuron-neuron and neuron-tissue - Message transferred by neurotransmitters
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Events at Chemical Synapse: Presynaptic Neuron
- Message transfer beings here - Presence of neurotransmitter-filled synaptic vesicles - Neurotransmitters are stored in synaptic vesicles - Synaptic vesicles deliver their content into the synaptic cleft by exocytosis - Synaptic vesicles rapidly reform by endocytosis and recycling
60
Events at Chemical Synapse: Postsynaptic Neuron
- Can receive signal from multiple presynaptic neurons | - Many receptors present in membrane
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Neurotransmitters: Excitatory Neurotransmitters
Cause depolarisation and promote the generation of action potentials
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Neurotransmitters: Inhibitory Neurotransmitters
Cause hyperpolarisation and suppress the generation of action potentials
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Cholinergic Synapses
Synapses that release ACh e.g. neuromuscular junction
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Events at cholinergic synapse
1) an action potential arrives and depolarises the synaptic terminal 2) extracellular calcium ions enter the synaptic terminal, triggering the exocytosis of ACh 3) ACh binds to receptors and depolarises the postsynaptic membrane 4) ACh is removed by AChE
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Common Neurotransmitters: Dopamine
CNS neurotransmitter, excitatory or inhibitory, involved in Parkinson disease and cocaine use
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Common Neurotransmitters: Seotonin
CNS neurotransmitter that affects attention and emotional state
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Common Neurotransmitters: Gamma Aminobutyric Acid (GABA)
Inhibitory, functions in CNS
68
Neuromodulators
- Chemicals released at synaptic knob that have similar function to neurotransmitters - Long term effects - Can affect presynaptic or postsynaptic membrane or both
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How to neuromodulators affect presynaptic or postsynaptic membrane or both?
Neuropeptides: Bind to receptors and activate enzymes Opioids: In CNS, bind to same receptors as opium or morphine, relieve pain
70
Neurotransmitters and Neuromodulators: How do they work?
- Direct effects on membrane channels e.g. ACh, glutamate - Indirect effect via G proteins e.g. E, NE, dopamine, histamine, GABA - Indirect effects via intracellular enzymes e.g. lipid-soluble gases (Nitric Oxide (NO), Carbon Monoxide)
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Information Processing
The postsynaptic responses dictate whether the message is passed on or not. This ultimately depends on the post-synaptic potential (inhibitory or excitatory)
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Information Processing: Modified by a number of factors
- Type of neurotransmitter - Response of the post-synaptic receptors - Pharmacology
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What does the effect of a neurotransmitter on postsynaptic membrane depend on?
The receptor not the type of neurotransmitter
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Postsynaptic Potentials
Graded potentials developed in postsynaptic cell in response to neurotransmitters
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Postsynaptic Potentials: Excitatory Post Synaptic Potential (EPSP)
Depolarises postsynaptic membrane bringing closer to firing threshold e.g. -60mV
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Postsynaptic Potentials: Inhibitory Post Synaptic Potential (IPSP)
Hyperpolarises postsynaptic membrane moving further away from firing threshold e.g. -90mV
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Summation
Processes where the effects of all graded potentials are integrated at one region of the plasma membrane e.g. combination of individual EPSP Combination of graded potentials can either be all excitatory all inhibitory or both
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Summation: Temporal Summation
- Occurs on a membrane that receives two depolarising stimuli from the same source in rapid succession - Effects of the second stimulus are added to those of first
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Summation: Spatial Summation
- Occurs when sources of stimulation arrive simultaneously, but at different locations - Local currents spread the depolarising effects and areas of overlap experience the combined effects
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Information Processing: Presynaptic Modulation
The ability of passing on a signal might be affected before the release of neurotransmitter
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Information Processing: Presynaptic Excitation
Increased neurotransmitter release
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Information Processing: Presynaptic Inhibition
Decreased neurotransmitter release

Human Physiology (8 decks)

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