nervous system

Question 1

what does the sensory neurone do

Answer 1

brings impulses from sense organs/receptors into the central nervous system

Question 2

what does relay neurone do

Answer 2

receives impulse from sensory neurone and relays it to motor neurone.
also known as a connector neurone
is unmyelinated so it appears grey

Question 3

What does the motor neurone do

Answer 3

it carries impulses from the central nervous system to the effector (e.g muscles/organs)

Question 4

what are dendrites

Answer 4

thin extensions that carries the impulses towards the cell body

Question 5

what are axons

Answer 5

long membrane-covered cytoplasmic extensions that transmits impulses away from cell body.

Question 6

what are schwann cells

Answer 6

cells which surround and support peripheral neurones

Question 7

what is the myelin sheath

Answer 7

multi-layered fatty sheath surrounding axons made by schwann cells. acts as an electrical insulator, speeds up transmission along axon.

Question 8

what is a node of ranvier

Answer 8

areas along the axon where there is no schwann cells meaning it is not electrically insulated

Question 9

what is the cell body

Answer 9

the area of a neurone which contains the nucleus, rer, numerous mitochondria and other organelles

Question 10

what is a reflex

Answer 10

an automatic, rapid response to an adverse stimulus

Question 11

describe the pathway of the electrical impulse from receptor to effector

Answer 11

• stimulus is detected by receptors in the skin
• a nerve impulse is passed along the sensory neurone
• sensory neurone enters the spinal cord via dorsal branch of the spinal nerve
• the sensory neurone synapses with a relay neurone in the grey matter.
• then synapses to a motor neurone
• the motor neurone leaves via the ventral root
• it carries the impulse to an effector (muscle/organ)
• action (muscle contracts etc)
• action is a response.

Question 12

experiment with ‘giant squid’ axons

Answer 12

microelectrodes are used to stimulate the axon and the cathode ray oscilloscopes are used to measure the potential difference across the membrane

Question 13

what is a resting potential

Answer 13

the potential difference between the inside and outside of a membrane when a nerve impulse is NOT being conducted

Question 14

what is the typical voltage for a resting potential and what is it said to be

Answer 14

-70mV (inside is negative with respect to outside) and it is said to be polarised.

Question 15

how are resting potentials achieved?

Answer 15

Sodium-potassium pump is a transmembrane protein, they maintain the concentration of an uneven distribution of Na+ and K+ across the membrane
the membrane is more permeable to K+ than Na+.
K+ diffuses out of nuerone due to concentration gradient caused by the Na+K+ pump.
Anion concentrations are higher inside the nuerone.

Question 16

what is the all or nothing law

Answer 16

where the size of the impulse is independent of the size of the stimulus.
if the intensity of stimulus is below a certain threshold intensity, an action potential will not be initiated
if the intensity of a stimulus is exceeds the threshold value, and action potential is initiated.
HOWEVER, any further increase in intensity does not give a greater action potential.

Question 17

What is an action potential

Answer 17

• stimulation of an axon results in a change in the potential difference across the membrane from -70mV to +40mV
• this depolarization is due to a sudden increase in the permeability of the membrane to Na+ (Voltage-gated Na+ channels open)
• Na+ diffuse into axon down a concentration gradient
• A fraction of a second later, voltage-gated k+ channels open and the membrane becomes more permeable to K+ which diffuses out of the axon which repolarises the membrane.
• There is an overshoot (hyperpolarisation) of k+ leaving, but the Na/K pump restores the ionic balance. This is called the refractory period.

Question 18

what does an action potential cause

Answer 18

they cause a small electric current across the membrane and as a portion of the membrane is depolarised, depolarisation of the next portion is initiated.

Question 19

what allows another impulse to be initiated after one

Answer 19

resting potential

Question 20

how to action potentials travel along an unmyelinated axon

Answer 20

• influx of Na+ ions and depolarisation of membrane causes a local flow of electrical current.
• these local currents trigger the adjacent region of the plasma membrane to become more permeable to Na+ ions (by opening voltage gated Na+ channels) causing a depolarisation in the next region.

Question 21

How is myelination a factor that affects the speed of conduction of the nerve impulse?

Answer 21

Myelin is lipid rich, makes axons impermeable to ions (and acts as insulators) this makes ions unable to diffuse between tissue fluid and nuerone so action potentials cannot be generated in myelinated regions.
Action potentials are only generated at nodes of ranvier
Thus causing the action potentials to ‘jump’ from node to node (called a saltatory conduction)

Question 22

how is the diameter of an axon a factor that affects the speed of conduction of the nerve impulse

Answer 22

the greater the diameter of axon, the greater the velocity of transmission. Less resistance from cytoplasm to the flow of ions

Question 23

how is temperature of an axon a factor that affects the speed of conduction of the nerve impulse

Answer 23

increased temperature increases the rate of aerobic respiration therefore the production of ATP which is needed for the sodium-potassium pumps

Question 24

there are many neurotransmitter substances - give exmaples

Answer 24

dopamine and serotonin - active in brain
acetylcholine released at synapses contacting with motor neurone - cholinergic synapses
noradrenaline released at synpases involved in the sympathetic Neurone systen - adrenergic synapses

Question 25

steps of a transmission of an impulse across a synpase

Answer 25

• nerve impulses arrive and depolarises the pre-synaptic membrane.
• voltage gated ca+ channels open and calcium enters the presynaptic knob down a concentration gradient (via diffusion)
• influx of calcium causes vesicles of neurotransmitter to move towards the presynaptic membrane
• vesicles fuse with presynaptic membrane and releases its contents by exocytosis into the presynaptic cleft
• neurotransmitter molecules diffuse across the cleft
• and then binds to complementary receptors on the post-synaptic membrane
• sodium gate channels open.

Question 26

what are the roles of synapses

Answer 26

makes sure the flow of impulses are one direction only. vesicles containing transmitter in presynpatic membrane, receptors on postsynaptic membrane
allows integration - synapses has many post synaptic neurones going to different locations
several pre-synaptic neurones may converge to go to one post-synaptic neurone which will then create the same response
acclimatisation - neurone may run out of neurotransmitter due to repeated stimulation.

Question 27

what does organophosphorus insecticides do

Answer 27

inhibits acetylcholinesterase
prolongs the effect of acetylcholine which remains in the synaptic cleft and causes repeated firing of the post-synaptic neurones
resulting to a repeated firing of neurones at neuromuscular junction resulting in repeated contractions of muscle which can cause paralysis and breathing will stop

Question 28

how does psychoactive drugs such as cocaine work

Answer 28

they attach to the dopamine transporter and blocks the recycling process causing a build up of dompamine in synapse which is the cause of the pleasurable effects of cocaine.

Question 29

what is the motor neurone disease

Answer 29

it is the degeneration of motor nerve cells in spinal cord and brain that controls voluntary muscles e.g skeletal muscles.
usually death within 5 years after diagnosis
develops at different speeds and ways for different people

Question 30

what are the symptoms of the motor neurone disease

Answer 30

gradual impairment of legs and arms
muscle twitch, pain, stiffness around joints
difficulty in swallowing and speech if throat muscles affected
difficulty in breathing if thoracic muscles affected.

Question 31

what is the diagnosis for motor neuron disease

Answer 31

difficult to find

a needle is injected to various muscles to measure electrical activity.

Question 32

what is the cause and treatment for motor neurone disease

Answer 32

cause is unknown

there is no treatment but people can use the pill (riluzole) to slow down progression.

Question 33

what is parkinsons disease

Answer 33

progressive disease caused by death of brain cells that produce dopamine
dopamine are important neurotransmitters that carries signals between neurones and brain
dopamine enables smooth-co-ordinated movements

Question 34

what are the symptoms of parkinsons

Answer 34

temors, slowness of movement, affects talking, walking, swallowing

Question 35

cure/treatments for dopamine

Answer 35

no cure
treatments
early treatments = levadopa (replaces missing dopamine
long term treatments = physiotherapy

Question 36

what is a stroke

Answer 36

blood clots in the blood vessels in the brain where neurones surrounding blood vessels becomes starved of oxygen and die.
stroke on right side affects movement on left side
stroke on left side affects speech
memory is often impaired

Question 37

symptoms of stroke

Answer 37

numbness
weakness/paralysis on one side of body
slurred speech
blurred vision
confusion
unsteadiness
severe headache

Question 38

treatment of stroke

Answer 38

immediate - clotbusting drugs e.g streptokinase
longer term- aspirin, reduces recurrence
rehabilitation therapy

Question 39

risk factors of stroke

Answer 39

hypertension
obesity
smoking
lack of exercise