5.3.2 structure & function of neurones

Question 1

motor neurones

Answer 1

neurones which carry an action potential from CNS to effector

Question 2

myelinated neurone

Answer 2

has individual layer of myelin around it

Question 3

non-myelinated neurone

Answer 3

no individual layer of myelin

Question 4

relay neurones

Answer 4

join sensory neurones to motor neurones

Question 5

sensory neurones

Answer 5

neurones which carry action potential from sensory receptor to CNS

Question 6

effector

Answer 6

eg. muscle or gland

Question 7

basic structure of neurones

Answer 7

• many are long so can transmit action potentials over long distance
• cell surface membrane has gated ion channels to control entry/exit of sodium, potassium or calcium
• sodium/potassium pumps use ATP to actively transport sodium ions out/potassium ions into cell
• neurones maintain potential difference across cell surface membrane
• cell body = nucleus, mitochondria & ribosomes
• numerous dendrites connect to other neurones & carry impulses towards cell body
• axon carries impulse away from cell body
• surrounded by fatty layer which insulates cell = composed of schwann cells (myelin sheath)

Question 8

structure of motor neurone

Answer 8

• cell body in CNS
• long axon which carries action potential to effector

Question 9

structure of sensory neurone

Answer 9

• long dendron carrying action potential from sensory receptor to cell body
• cell body positioned just outside CNS
• short axon carrying action potential into CNS

Question 10

structure of relay neurone

Answer 10

• connect sensory/motor neurones
• many short dendrites
• short axon
• number of dendrites/divisions is variable

Question 11

describe myelinated neurones

Answer 11

• most sensory/motor neurones
• schwann cells make up fatty sheath = myelin sheath
• schwann cells wrapped tightly around neurone so sheath consists of several layers of membrane & thin cytoplasm of schwann cell
• intervals 1-3mm along neurone = gaps called ‘nodes of ranvier’
• myelin sheath prevents movement of ions across membrane (only occur at nodes of ranvier)
• impulse ‘jumps’ one node to the next
• rapid conduction

Question 12

describe non-myelinated neurones

Answer 12

• several neurones may be enshrouded in one loosely wrapped schwann cell
• action potential moves along neurone in wave (not ‘jumping’)

Question 13

advantages of myelination

Answer 13

• transmit action potential quicker
• myelinated neurones carry action potentials from sensory receptors –> CNS –> effectors
• carry action potentials over long distances & increased speed of transmission means action potential reaches end of neurone quicker
• enables more rapid response to stimulus

Question 14

non-myelinated neurones role

Answer 14

• shorter
• carry action potentials over shorter distance
• often used in coordinating body functions eg. breathing, action of digestive system
• increased speed of transmission isn’t important