module 5.1.3

Question 1

outline the importance of the junction between neurones in the functioning of the nervous system

Answer 1

ensures movement of action potential in one direction only
one neurone can receive impulses from many neurones
allows summation
filters out low level stimuli

Question 2

outline how the first neurone communicates with the second neurone across the gap

Answer 2

neurotransmitters are released from the pre - synaptic membrane
diffuses across synaptic cleft
acetylcholine broken down in cleft

Question 3

describe the function of structure A (Scwhann cells)

Answer 3

produces myelin
electrical insulation
prevents depolarisation
speeds up transmission of impulses
action potential also occurs at Nodes of Ranvier
saltatory conduction - impilses jump from node to node

Question 4

what are sensory receptors

Answer 4

are groups of specialised cells that detect changes in the surroundings and convert them to neuronal signals by initiating or changing the frequency of action potentials

Question 5

what some examples of sensory receptors

Answer 5

rods and cones in the eye, which are photoreceptors, chemoreceptors, such as the olfactory receptors in the nose, thermoreceptors in the end-bulbs of Krause in the tongue, and vibration receptors in the cochlea of the ear

Question 6

what are tranducers

Answer 6

converting one type of energy, or a change in the magnitude of frequency of a type of energy, and converting it to chemical, and then electrical, energy

Question 7

what is the Pacinian corpuscle

Answer 7

a mechanoreceptor—detecting pressure and movement—found in the epidermis of the skin. It comprises a neuron with concentric layers of connective tissue
when pressure is placed on the skin, this deforms the layers of connective tissue, and because the membrane of the neuron contains stretch-mediated sodium ion channel, the neuron is depolarised when the connective tissue is deformed, generating a generator potential, which, by positive feedback, will generate an action potential which is transmitted along neurones to the central nervous system

Question 8

what do sensory neurones do

Answer 8

carry the action potential from a sensory receptor to the central nervous system

Question 9

describe the structure of sensory neurones

Answer 9

have a long dendron carrying the action potential from a sensory receptor to the cell body, which is position just outside the CNS
they have a short axon carrying the action potential into the CNS

Question 10

what do relay neurones do

Answer 10

connect sensory and motor neurons, mainly in the central nervous system

Question 11

describe the structure of relay neurones

Answer 11

they have many short dendrites to receive impulse transmissions from a number of sensory receptors and a short axon with variable numbers of synaptic endings to carry the action potential to the cell bodies of motor neurones in the CNS

Question 12

what do motor neurones do

Answer 12

carry an action potential from the central nervous system to an effector such as cells in a muscle or gland

Question 13

describe the structure of the motor neurones

Answer 13

have their cell body in the CNS and have a long axon that carries the action potential to effector cells

Question 14

describe the structure and function of the cell body

Answer 14

contains the nucleus, surrounded by cytoplasm containing large amounts of endoplasmic reticulum and mitochondria to produce neurotransmitters used at the synapses of all three neurones

Question 15

describe the structure and role of the dendron

Answer 15

are short extensions which carry action potentials toward the cell body where dendrites of relay neurons synapse with sensory receptors, or relay neurons synapse with motor neurones

Question 16

describe the structure and role of the axon

Answer 16

are singular, elongated nerve fibres that carry action potential potentially long distances away from the cell body the plasma membranes of the latter two structures include gated ion channels and sodium-potassium pumps

Question 17

the peripheral neurones in vertebrates are

Answer 17

myelinated

Question 18

which neurones are myelinated

Answer 18

sensory and motor neurones

Question 19

what are most sensory and motor neurones wrapped in and what does it do

Answer 19

many Schwann cells
insulates the neurone from adjacent ones and preventing the membrane from depolarising

Question 20

what are the gaps between the myelin sheath called

Answer 20

nodes of Ranvier

Question 21

what happens at the nodes of Ranvier

Answer 21

membrane can be depolarised

Question 22

what happens to speed of unmyelinated cells

Answer 22

speed is less imperative with unmyelinated neurones carrying action potentials over small distances, or coordinating bodily functions, such as breathing and the action of the digestive system

Question 23

what is the membrane polarised at

Answer 23

-70mV

Question 24

why does the resting potential occur

Answer 24

as a result of the movement of sodium and potassium ions across the axonal membrane, the sodium-potassium pump actively transports three sodium ions out of the axon for every two potassium ions that are pumped in

Question 25

what do both ions have a tendency of doing

Answer 25

diffuse down their electrochemical gradient

Question 26

what happens to the gated ion channels while at rest

Answer 26

gated sodium ion channels are closed when the neuron is at rest, but gated potassium ion channels are open

Question 27

what does the gated potassium ion channels being open at rest result in

Answer 27

allowing cations to diffuse out of the axon, increase the polarization caused by the action of the sodium-potassium pump

Question 28

what happens when a stimulus is detected by a sensory receptor

Answer 28

the energy of the stimulus is used to temporarily depolarise the axonal membrane, generating an action potential

Question 29

what does the energy of the simulus trigger

Answer 29

triggers some voltage-gated sodium ion channels to open, causing sodium ions to diffuse into the axon down their electrochemical gradient
this reduces the polarisation of the membrane and causes more voltage-gated sodium ion channels to open, allowing more sodium ions to diffuse into the axon
this creates a positive feedback loop which further depolarises the membrane until the potential difference reaches +40mV

Question 30

what happens after the potential difference reaches +40mV

Answer 30

the voltage-gated sodium ion channels close, and voltage-gated potassium ion channels open, allowing potassium ions to diffuse out of the axon down their electrochemical gradient, resulting in the inside of the cell repolarising
the efflux of sodium ions causes the axon to hyperpolarise, before some potassium ion channels close, and the sodium-potassium pump sodium ions to move out of the cell, and potassium ions to move in

Question 31

what happens when the threshold of +40mV is reached

Answer 31

an initial action potential is generated at a synaptic junction or sensory receptor, the depolarisation of the membrane acts as a stimulus for the depolarisation of the membrane further down the axon, propagating the action potential