the nervous system - physiology

Question 1

two types of cell in nervous tissue

Answer 1

-neurones
-neuroglia

Question 2

neurones

Answer 2

-generate and transmit nerve impulses
-10^11 neurones (100billion)
-unable to replicate

Question 3

neuroglia

Answer 3

-provide a supportive connective tissue
-10^12 (1trillion) glial cells
-able to replicate (i.e. can repair)

Question 4

types of glial cells

Answer 4

the excitable neurones in the CNS are supported by non-excitable glial cells
-astrocytes: blood brain barrier (BBB)
-oligodendrocytes: myelin
-ependymal cells : CSF
-microglia: phagocytes

Question 5

neurone structure

Answer 5

-cell body
-1 axon
-many dendrites
-axon hillock

Question 6

neurones: cell body

Answer 6

-forms GREY matter of the nervous system
=periphery of brain
=centre of spinal cord

Question 7

neurones: axons

Answer 7

-carry impulses away from cell body
-forms WHITE matter of nervous system
=centre of brain
=periphery of spinal cord
-tracts: bundles of axons in CNS
-nerves: bundles of axons in PNS

Question 8

fast signal adaptations ?

Answer 8

-invertebrates: giant axons (1mm thick)
-vertebrates: myelin sheaths (electrical insulation)

Question 9

myelin sheaths

Answer 9

-oligodendrocytes (CNS) or Schwann cells (PNS) produce fatty myelin to insulate electrical conduction
-fast conduction from node to node

Question 10

neurones: dendrites

Answer 10

-numerous (1-10,000) short processes for incoming impulses
-often branching
-in sensory neurones form sensory receptors
-in motor neurones form part of synapses

Question 11

function of neurones

Answer 11

-rapid transmission of nervous impulses
-transmission of impulses is both ELECTRICAL and CHEMICAL

Question 12

rapid transmission of nervous impulses

Answer 12

-some neurones initiate nerve impulses
-other neurones relay impulses

Question 13

transmission of impulses is both electrical and chemical

Answer 13

-electrical: (impulses called action potentials) down the nerve axon
-chemical: between adjacent neurones (synapse)

Question 14

electrical conduction (action potential)

Answer 14

-transmission of impulses along an axon is ELECTRICAL
-an impulse is a wave of movement of ions across the nerve cell membrane
-requires co-ordinated opening/closing of ion channels to change the electrical potential across the membrane
=sodium (3Na+ out)
=potassium (2K+ in)

Question 15

initiation of action potential

Answer 15

-initiated at the axon hillock
-threshold
=if exceeded an AP is triggered
=if not, no AP
=i.e. ‘all or nothing’ principle
-single AP is fast (<1ms)

Question 16

saltatory conduction

Answer 16

-in myelinated neurones, the fatty myelin insulates the neurone and prevents movement of ions
-ion movement and therefore electrical changes can only occur at the gaps (nodes of ranvier)
-wave of depolarisation passes along myelin sheath and seemingly jumps from node to node (saltatory conduction)