Neurotransmission

Question 1

what is the function of dendrites in relation to membrane potential.

Answer 1

aka cell body
receive in-put signals
lead to depolarisation
hyperpolarisation of plasma membrane

Question 2

what are axons responsible for in relation to membrane potential

Answer 2

responsible for out-put signal

Question 3

ways to classify neurons

Answer 3

morphology/shape
afferent/efferent nerves
neurotransmitter

Question 4

how are neurons classified by shape

Answer 4

Bi-polar neurons vs multi-polar neurones

number of projections from cell body

Question 5

how are neurons classified by afferent/efferent

Answer 5

Neurones that transmit information towards the CNS are afferent (arriving)
Neurones that transmit information from the CNS are efferent (exiting, effector organ)

Question 6

how are neurons classified by neurotransmitter

Answer 6

Substance / chemical they release (e.g. dopamine, acetylcholine)

Question 7

name the function ways to classify nerves

Answer 7

sensory and motor nerves

Question 8

function of sensory nerves

Answer 8

send information to the central nervous system about the internal and external environment

Question 9

function of motor nerves

Answer 9

control the activity of the body by controlling muscle and gland functions (contraction, relaxation, secretion

Question 10

synapse

Answer 10

Synapse is the junction between one neurone & the next cell

converts electrical impulse -> chemical signal for communication between cells (electro-chemical coupling)

Question 11

type of communication of the synapse

Answer 11

Nerve-Nerve
Nerve-Organ / Organ-Nerve
Nerve-Muscle
Nerve-Gland

Question 12

Synapses between nerve and muscle cells are also called …

Answer 12

neuromuscular junctions or motor end plates

Question 13

the process of the chemical synapse

Answer 13

neurotransmitter is released from presynaptic neuron
neurotransmitter crosses synaptic cleft
neurotransmitter binds to receptor of specific plasma membrane protein changing the membrane potential

Question 14

how are synapses categorised

Answer 14

either excitatory or inhibitory

Question 15

what do neurotransmitters at excitatory synapses do and name example

Answer 15

depolarises the postsynaptic membrane.
e.g. acetylcholine binds to receptors of post synaptic cell and opens ligand-gated sodium channels - depolarises - reduce membrane potential and increase Na+ ions

Question 16

types of potential

Answer 16

graded potentials

action potential

Question 17

difference between graded and action potential

Answer 17

gp - local changes in membrane potential but do NOT threshold of -50
die out over short distances

Question 18

how does the magnitude of the graded potential vary

Answer 18

Magnitude of graded potential varies directly with the magnitude of the triggering event

Question 19

action potentials of VGSC (Voltage Gated Sodium Channels)

Answer 19

If depolarisation at a certain spot on the neurone reaches a threshold voltage of approx. – 50 mV, the reduced voltage opens up several voltage-gated Na+ channels in that portion of the plasma membrane as well as adjacent portions of the membrane causing a wave of depolarisation along the cell. Strength does not decrease as it travels

Question 20

process of membrane potentials

Answer 20

action potential reaches -50 - depolarisation and VGSC open influx of Na+ ions ( Na+ ions move to cell)
reach membrane potential of +50 - closing of VGSC and opening of VGPC (Voltage Gated Potassium Channels)
hyperpolarisation - efflux of K- ions (K+ ions leave cell)
Opening of VGSC let some Na+ ions but not as intense
returns to resting membrane potential

Question 21

refractory period

Answer 21

the period when a further stimulus applied to the neurone (or muscle fiber) will not trigger another action potential

Question 22

what causes refractory period

Answer 22

Due to inactivation of sodium channels (absolute refractory period) and repolarisation brought about by opening of potassium channels and potassium ions (K+) movement out of cell (relative refractory period).

Question 23

what happens when a neurotransmitter reaches an inhibitory synapse and name example

Answer 23

hyperpolarises the postsynaptic membrane.
GABA binds to receptor of post synaptic neuron and opens ligand gated chloride (Cl-) channel
from -70 to -90
counteracts excitatory signals that may arrive at that neuron

Question 24

myelin sheath

Answer 24

a fatty sheath many neurons are encased in

Question 25

what is the function of the myelin sheath and what cells produce it

Answer 25

Myelin functions as an “electrical insulator” - restricts current flow It is the expanded plasma membrane of a neighboring cell called the Schwann cell (or oligodendrocyte in the CNS action potential moves to next ligand gated or voltage gated channel without having to start another action potential across myelin

Question 26

conditions that interfere with nerve conduction

Answer 26

``` Cold, ischaemia (reduction in blood flow) Demyelinating diseases (Multiple sclerosi ```

Question 27

how does local anaesthetics inhibit voltage gated action Na+

Answer 27

Local anaesthetics inhibit voltage-gated Na+ channels. This leads to an inhibition of the formation and propagation of action potentials along nerve fibres. Examples: “benzocaine”, “lidocaine