The nervous system (C3)

Question 1

Two parts of the human nervous system

Answer 1

1. Central Nervous System (CNS); brain and spinal cord

2. Peripheral Nervous System (PNS); nerves and ganglia on the outside of the CNS

Question 2

Components of a nervous response (3 elements)

Answer 2

STIMULI -> RECEPTOR -> EFFECTOR (muscle or glad; via the nervous system or as hormones via the blood

Question 3

Stimuli definition and example

Answer 3

detectable change in internal or external environment of an organism
e.g. light, heat, mechanical pressure, sound, osmotic pressure

Question 4

Receptor definition and example

Answer 4

detects stimuli and converts it to electrical energy to send an electrical impulse to the CNS via nerves
e.g photoreceptor, thermoreceptor, chemoreceptor, mechanoreceptor

Question 5

An effector is usually a…

Answer 5

muscle or glad

Question 6

Three types of neurons and roles

Answer 6

1. SENSORY: carries impulse from sense to receptor in CNS
2. RELAY: carries impulse from sensory neuron (or other relays) to motor neuron found in spinal cord
3. MOTOR: carries impulse from CNS to effector organ (muscle or gland)

Question 7

What does grey matter consist of?

Answer 7

mainly nerve cell bodies

Question 8

What does white matter consist of?

Answer 8

nerve fibers surrounded by myelin sheath (axons)

Question 9

What are meninges?

Answer 9

membranes surrounding the spinal cord

Question 10

What is a reflex arc and its stages? plus example

Answer 10

a simple reflex is a rapid inborn, involuntary response to a stimulus.
transmission along a three-neurone reflex arc involves: STIMULUS -> RECEPTOR-> sensory neurone
-> relay neurone (in CNS) -> motor neurone -> EFFECTOR
-> RESPONSE.
e.g knee jerk

Question 11

features nerve nets in cnidaria e.g hydra

Answer 11

• the sense receptors respond to a LIMITED number of stimuli, so the number of effectors is small.
• their nerve net system consists of SIMPLE nerve cells with short extensions joined to each other and BRANCHING in a number of DIFFERENT directions
• ability to REGENERATE neurons

Question 12

TS of spinal cord diagram

Answer 12

includes. ..
- grey matter
- white matter
- central canal
- dorsal root ganglia
- dorsal root
- ventral root
- s. neu, r. neu, m. neu

Question 13

How can potential difference be measured?

Answer 13

Inserting microelectrodes into axons, measuring changes in electrical potential which can be read on a CATHODE RAY OSCILLOSCOPE

Question 14

What is resting potential?

Answer 14

• 70mV

* no nerve impulse being recorded

Question 15

Maintaining resting potential across membrane

Answer 15

to maintain the resting potential, sodium-potassium
pumps ACTIVLEY transport sodium/Na ions OUT of the neurone and potassium/K ions INTO the neurone
(3Na+ out for each 2K+ in, per ATP hydrolysed)

*large protein anions and organic phosphates (e.g.
ATP4-) remain in the cytoplasm thus producing a
NEGATIVE potential difference across the membrane
at around -70mV relative to the exterior of the
axon;

Question 16

Voltage gated Na+ and K+ channels during resting potential along membrane

Answer 16

voltage-gated Na+ channels are CLOSED but some

K+ channels (of which SOME are OPEN most closed) allow K+ to ‘LEAK’ out of the axon

Question 17

How is an action potential created?

Answer 17

a STIMULUS (a change in the voltage across the axon membrane) OPENS the Na+ channels so that Na+
FLOOD IN and DEPOLARISES the axon to about **+40mV**   – this is the action potential and will only occur if the THRESHOLD VOLTAGE is reached

Question 18

After depolarisation occurs the membrane is repolarised, explain how?

Answer 18

REPOLARISATION occurs as the Na+ channels CLOSE
and K+ channels OPEN resulting in K+ FLOODING OUT/RAPIDLY DIFFUSE of the axon and REDUCING the potential difference
across the axon membrane – an OVERSHOOT results
in the membrane being HYPERPOLARISED

Question 19

What happens during the refractory period and when?

Answer 19

(AFTER hyperpolarisation) during the REFRACTORY PERIOD the concentrations of
K+ and Na+ ions are RESTORED to that of the resting
potential – during this time the axon CANNOT
TRANSMIT another action potential and this
ensures that transmission is in ONE DIRECTION only

Question 20

What is the all or nothing law, and the relationship between action potential and size of stimuli?

Answer 20

The size of the action potential is INDEPENDENT of the size of the stimulus, as long as the stimulus EXCEEDS the value of the threshold potential an action potential is generated; this is called the ‘ALL OR NOTHING’ LAW

*no matter the size of the stimulus the same action potential is always generated if exceeding the threshold, however, the LARGER the stimulus the more FREQUENT the action potentials

Question 21

What is a myelinated neuron?

Answer 21

the axon is surrounded by SCHWANN CELLS that form a myelin sheath to act as an ELECTRICAL INSULATOR

*only vertebrates have a myelin sheath surrounding their neurones

Question 22

Advantages of myelinated neuron and what its known as

Answer 22

action potentials can only take place at the nodes of ranvier, where voltage gated ion channels are found, because myelin is a LIPID type substance thus IMPERMEABLE to IONS as a result impulses JUMP from one node to another - speed of transmission is INCREASED

** this is called SALTATORY PROPAGATION

Question 23

Factors affecting speed of conduction of an impulse

Answer 23

• TEMP - the higher the temperature, the faster
the speed; ions have more KE at higher temp thus move faster (hence warm blooded animals transmit impulses quicker and have faster responses)
• AXON DIAMETER - the larger the diameter, the faster
the speed; more na+ can flow along axon so impulse travels faster
• MYELIN SHEAT - electrical insulation of axon increasing speed of transmission , saltatory propagation, while nerve impulses
in unmyelinated neurones have a maximum speed
of around 1 m/s, in myelinated neurones they travel
at 100 m/s

Question 24

Features of the synapse and roles x7

Answer 24

• PRE synaptic KNOB and MEMBRANE
• SYNAPTIC VESICLES
• NEUROTRANSMITTERS (e.g. acetylcholine)
• POST synaptic MEMBRANE
• SYNAPTIC CLEFT
• voltage gated Ca2+ CALCIUM CHANNELS
• RECEPTORS on post-synaptic membrane

Question 25

The process of synaptic transmission

Answer 25

• action potential arrives at axon TERMINAL, causing voltage gated CALCIUM ion channels OPEN, calcium ions DIFFUSE rapidly into pre synaptic KNOB
• causes synaptic VESICLES containing neurotransmitters (acetylcholine) to FUSE with pre synaptic membrane
• acetylcholine released into synaptic CLEFT by EXOCYTOSIS, diffusing over and binding to SPECIFIC RECEPTOR on POST synaptic membrane
• causes SODIUM ion channels to OPEN in POST s.m., sodium ions FLOOD in DEPOLORISING post s.m, if threshold is exceeded an a.p is generated is post neuron
• acetylcholine in receptors is broken down by cholinease into ETHANOIC ACID and CHOLINE, diffusing back into axon terminal via PRE s.m
• ATP to re-synthesis and PACKAGE into VESICLES
• CALCIUM ions ACTIVLEY transported back into synaptic KNOB resetting electrochemical gradient

Question 26

Effect of organophosphorus

Answer 26

EXCITATORY / AGONIST

• INCREASEING number of action potentials
• prevent breakdown of neurotransmitter by INHIBITING acetylcholinesterase (acetylcholine remains bound to post synaptic specific receptors, action potential continues to be produced)