Biological- Neurons And The Action Potential

Question 1

The nervous system

Answer 1

Central Nervous- brain and spinal chord
Peripheral nervous system

Question 2

Neurons

Answer 2

-receive and transmit information
-100 billion neurons in the adult brain- combine to form consciousness sensory experience and controlled behaviours (william and Herrup 1988)
-vary in size and shape- all have the same basic structure

Question 3

Types of neurons

Answer 3

Sensory- carry sensory signals from the skin, eyes,ears ect to the central nervous system (CNS)

Motor- carry signals from the cns to the muscles

Sensory neuron -Afferent- carry info towards the CNS

Motor neuron-Efferent- carry information away from the cns

Interneurons receive/carry info from/to other neurons

Question 5

The anatomy of a neuron

Answer 5

Cell body (Soma)- contains the nucleus,and much of the machinery that maintains the neuron

Dendrites- information receiving part of the neuron. Receive information across a tiny gap called a synapse. Surface lined with synaptic receptors. Greater the surface are of the dentrite the more info can be received

Axon- the information sender. Transfers information from the cell body to the terminal buttons

Myelin sheath- protective, insulating substance, not continuous but consists of segments. The unmyelinated area between the segments is known as the Node of Ranvier

Presynaptic terminals- also known as terminal button/synaptic bulb or knob. When an action pote tial reaches the presynaptic terminal they secrete a transmitter substance which travels across the synapse to the next neuron

Always travels from the dendrites to the presynaptic terminal

Question 6

Supporting cells

Answer 6

-neurons are not the only cells that exist in the nervous system
-most prominent is Glial cells
-provide the cells with nutrition, clear waste products and hold the neurons in place
-neurons need constant supply of oxygen and nutrients to survive
-different types- Oligodendrocytes ,Schwann cells, astryocytes, microglia

Question 7

Oligodendrocytes and Schwann cells

Answer 7

-main function is to support neuron axions and produce the myelin sheath which surrounds axons
- oligodendrocytes- cns
Schwann cells- PNS

Question 8

Astrocytes and microglia

Answer 8

Astrocytes- star shaped, provide physical support to neurons and clear debris
Some astrocyte extensions cover blood vessels - receive nutrients and release them to neurons
Microglia- smallest, protect cells in the brain from disease

Question 9

Transmitting information

Answer 9

Neuron receives chemical message
Triggers and electrical response
Causes release of chemicals at presynaptic terminals

Question 10

Inside the neuron

Answer 10

The fluid inside (intracellular) and outside (extracellular) the neuron contains electrically charged particles called ions
Sodium Na +
Potassium K+
Chloride Cl -
Organic A-
Membrane potential - difference in electrical charge inside as compared to outside the neuron

Question 11

Resting potential

Answer 11

• when the neuron is completely a rest it shows membrane potential of -70mV

-This membrane potential of -70mV is called the neurons resting potential

Voltmeter measures volt, glass microelectode filled with liquid that conducts electricity, wire electrode placed in seawater connected to a giant squid axon

Question 12

Ion distribution

Answer 12

Inside membrane
150 K+
15 Na+
10 Cl-
385 A-
Negative charge

Outside membrane
5 K +
150 Na +
110 Cl -
0 A -
Positive charge

Question 13

Forces

Answer 13

• the outside layer of the neuron, the plasma membrane, made up to a double layer of lipid molecules
• allows small uncharged particles,water,oxygen,carbon dioxide to move through it
  -Charged ions must pass through special openings called ion channels
• organic ions cannot pass through (A-)

Question 14

Diffusion and electrostatic pressure

Answer 14

Diffusion - particles are in constant motion. An array of particles in a solution will therefore tend to become evenly distributed

Electrostatic pressure- particles with the same charge repel one another while particles with different charges attract one another

Question 15

Sodium- potassium pump

Answer 15

• when the neuron is at rest sodium and potassium can pass across the plasma membrane
• A so called ‘sodium potassium pump’ however expels sodium ions out and draws potassium ions in at a ratio of 3 sodium ions out to 2 potassium ions in

Question 16

The action potential

Answer 16

• if we apply an electrical charge to a neuron this produces a brief period of depolarisation ie the inside becomes briefly positive then returns to negative
• if we apply a strong enough charge to reach a neurons so called ‘level of excitation’ teh neuron will produce an action potential
• action potential- membrane potential is rapidly reversed and becomes strongly positive (up to 40mV) compared to the outside
• then briefly overshoots and drops to -75mV (hyper polarisation)

Question 17

The action potential

Answer 17

• ‘all or none law’- an action potential occurs or doesn’t. If it occurs its the same size regardless of the level of excitation
• rate law’- the strength of a stimulus is represented by the firing rate of an axon
• absolute refractory period - following an action potential the sodium gates are close for approx. 1ms - no further action potentials, regardless of simulation can be triggered during this time
• relative refractory period- after sodium gates open potassium gates remain open for a further 2-4 ms and flow out of the cell at a faster than usual rate, making an action potential less likely, a greater stimulus would be needed

Question 18

Speed of nerve impulses

Answer 18

• in an unmyelinated axon- each point along the axon generates the action potential- passes down the axon like a wave
• in a myelinated axon- the sodium potassium exchange can only occur at the nodes of Ranvier the action potential therefore jumps from one node to another. This jumping is called saltatory conduction

Question 19

Synaptic transmission

Answer 19

Process of communication between neurons,chemical

Question 20

Stage 1 - synthesis

Answer 20

-Neurotransmitters
-Synthesised from modules derived from the diet
- small neurotransmitters- synthesised in pre synaptic terminals
- neuropeptides- synthesised in cell body

Question 21

Stage 2 and 3- storage and transport

Answer 21

• stored in spherical packets called synaptic vesicles
• travel down the axon to the terminal buttons
  -Collect next to the pre synaptic membrane

Question 22

Closer look

Answer 22

Presynaptic neuron
Vesicle
Neurotransmiters
Synaptic cleft
Receptors
Postsynaptic activity

Question 23

Stage 4- release

Answer 23

• Action potential reaches terminal button
• voltage dependent calcium channels open
  -Calcium (Ca2+) ions enter terminal button
  -Vesicles fuse with pre synaptic membrane
• neurotransmitters released into synaptic cleft
  -Whole process is called exocytosis

Question 24

Exocytosis

Answer 24

Look at photo

Question 26

Stage 5- Attachment

Answer 26

-Diffuse across the pre synaptic cleft to the post synaptic membrane - neurotransmitter binds to the receptors in the postsynaptic membrane - receptors can only work with a specific neurotransmitter 'Key in lock' - any chemical that attaches to a receptor is called a ligand

Question 27

Stage 6- Activation

Answer 27

- once binding occurs postsynaptic receptors open ion channels in the neurons membrane which allow particular ions to pass into the neuron Ionotropic effects -Rapid but short lived -Open ion channels directly Metabotropic effects -Slower and long lasting -Activates second messenger Excitatory post synaptic potentials (EPSPs) - receptors open sodium channels (Na +) channels -Depolarisation- neuron becomes more positive -Makes an action potential more likely to occur Inhibitory post synaptic potentials (IPSPs) -Receptors open either potassium (K+) channels or the Chloride channels (Cl-) -Hyperpolarisation - neuron becomes less positive -Makes an action potential less likely to occur

Question 28

sta

Question 29

Neural integration

Answer 29

Spatial summation- summation over space -Inputs from separate locations can have combined effects Temporal summation- summation over time -Repeated stimulating in a brief period of time can have a cumulative effect

Question 30

Stage 7- removal

Answer 30

Deactivation -Special enzymes breakdown the neurotransmitter -Eg- acetylcholine (chlorine and acetate) -The parts are drawn back to pre synaptic membrane -Recombined to form more Reuptake -Detach from receptors and drawn back to the pre synaptic membrane -Recycled

Question 31

Neurotransmitters

Answer 31

-Inhibitory or excitatory effects -Dopamine- implicated in movement,attention and learning. Degradation of dopaminergic neurons responsible for Parkinson's disease. Linked to schizophrenia Serotonin- implicated in the regulation of mood,eating,pain,sleep dreaming and arousal. Implicated in depression and eating disorders

Question 32

Drug effects

Answer 32

-Psychopharmacology- the influence of drugs on neurotransmitter action -Agonists- facilitate neurotransmitter effects Antagonists- inhibit neurotransmitter effects

Question 33

Ahonistic drug effects

Answer 33

-Drug increases the syntheses of neurotransmitter molecules (eg increasing the amount of precursor) -Drug increases the number of neurotransmitter molecules by destroying degrading enzymes -Drug increases the release of neurotransmitter molecules from terminal buttons -Drug binds to auto receptors and blocks their inhibitory effect on neurotransmitter release - drug binds to postsynaptic receptors and either activates them or increases the effect on them of neurotransmitter - drug blocks the deactivation of neurotransmitter molecules by blocking degradation or reuptake

Question 34

Antagonistic drug effects

Answer 34

- drug blocks the synthesis of neurotransmitter molecules (eg by destroying synthesizing enzymes) - drug causes the neurotransmitter molecules to leak from the vesicles and be destroyed by degrading enzymes -Drug blocks the release of the neurotransmitter molecules from terminal buttons - drug activates auto receptors and inhibits neurotransmitter release - drug is a receptor blocker it binds to the postsynaptic receptors and blocks the effect of the neurotransmitter

Question 35

What makes drugs addictive?

Answer 35

- avoidance of unpleasant symptoms of withdrawal - relative strength of the pleasant physiological effects of the drug - the same thing that makes other behaviours 'rewarding' Adapting behaviours -Anticipating financial reward Attractive mates (Ie sex) Feeding Drinking when thirsty Orgasm and sexual activity Flight from danger Hoarding (for rats?) They all activated the 'reward circuitry' in the brain. Ie the nucleus accumbens

Question 37

Something about rat brains

Answer 37

Location of the human and rat reinforcement system Medial forebrain bundle Approx 60 bundles of neurons

Question 38

Dopamine levels in the nucleus accumbens are increased by?

Answer 38

-Amphetamine -Cocaine -Nicotine -Morphine -Alcohol -Cannabis -3,4-methylenedioxymethamphetamine (MDMA)

Question 39

Negative reinforcement

Answer 39

-Taking some drugs provides negative reinforcement (Ie they make the aversive 'withdrawal symptoms stimuli cease). This must be a factor in maintinence of the habit but not in addiction -Eg- the strength of withdrawal effects is not related to addictiveness -Eg- some medical drugs that don't hit the nucleus accumbens have withdrawal effects but are not addictive

Question 40

Speed of action

Answer 40

-Operant conditioning theory suggests that the sooner the reward is experienced after the stimuli the stronger will be the reinforcement -This is seen quite clearly in the addictiveness of drugs. Note that addictiveness is not directly related to the strength of the effect -Alcohol- slow onset- low addictiveness -Morphine -Heroin- smoked and injected - cocaine -Crack cocaine -Cigarettes- not nicotine patches, injections ect