Neurone structure and function

Question 1

Number of neurones in human brain

Answer 1

100 (or more) billion neurones

Question 2

if all neurones are connected brain would be

Answer 2

12.5 miles in diameter

Question 3

Structure of nervous system

Answer 3

NS
PNS or CNS
The PNS = somatic nervous system and automotive nervous system

The CNS = spinal cord and brain

Question 4

Two types of cells other than neurons in the CNS

Answer 4

supporting cells. Neurons only half the volume of the CNS. Neurones have a very high rate of metabolism no means of storing nutrients as must be supplied with nutrients and oxygen of they will die quickly

Question 5

types of Glia cells

Answer 5

Astrocytes,
Oligodendrocyte
Schwann (PNS)

Question 6

Astrocytes

Answer 6

hold neurons in place so insulating them from other neurons, deliver food from blood supply to neuron

Astrocytes surround and isolate the synapses, limiting the dispersion of neurotransmitters released by the terminal buttons

Centre, thin tendrils go our of the Astrocytes and attached to the soma

Question 7

oligodendrocyte

Answer 7

provides support for neurons and forms the myelin sheath

Oligodendrocyte has a soma, similar to structure of a neuron. Many tendrils go out of it merge with the myelin sheaths of surrounding axons

Question 8

schwann cells

Answer 8

Schwann cell a large circular structure that engulf the axon, the Schwann cell beginning to wrap itself around the axon. The third step shows the Schwann cells wrapped around the axon ointment many layers forming the myelin sheath

In the peripheral nervous system

Question 9

blood brain barrier

Answer 9

semi-permeable barrier between the blood and the brain produced by the cells in the walls of the brains capillaries

Paul Ehrlich discovered if a blue dye is injected into an animals bloodstream, all tissues except the brain and spinal cord will be tinted blue

Capillary in all of body except brain. Gaps that permit the free flow of substances into and out of the blood. Capillary in the brain

Question 10

blood-brain barrier semi-permeable barrier

Answer 10

Some substances such as water molecules, can pass through the cells of the capillaries passively. Other molecules require active transport to move between tightly packed cells of the capillaries

Tight gap junction - Water-soluble agents pass from the blood to the brain through tight gap junctions between the blood cells.

Question 11

Neurons outside the brain

Answer 11

sensory neuron, motor neuron and inter neuron

Question 12

Sensory neuron

Answer 12

a neuron that detects changes in the external or internal environment and sends information about these changes to the CNS

Question 13

motor neuron

Answer 13

a neuron located in the CNS that controls the contraction of a muscle or the secretion of a gland

Question 14

interneuron

Answer 14

a neuron located entirely within the CNS

Question 15

Reflex arc

Answer 15

stimuli - sensory neuron - interneuron - spinal cord - motor neuron

Question 16

Inhibition

Answer 16

inhibitory signal arising form the brain can prevent the withdrawl reflex from causing the person to drop a hot object

Question 17

Structure of the cell body of a neuron

Answer 17

membrane - lipid molecules that define the outer boundaries of a cell constitutes many of the cell organelle

Mitochondria - extracting energy from nutrients

Cytoplasm - viscous, semiliquid substance that contained the interior of a cell

Nucleus - contains the chromosomes and genetic information

Microtubule - long strand of bundles of protein filaments arranged around a hollow core, cytoskeleton and transportation

Question 18

movement of material by microtubules

Answer 18

transport neurotransmitters and proteins from the soma to the terminal buttons (Anterograde axoplasmic transport) and also move materials from the terminal buttons to the soma, recycled neurotransmitters retrograde

Question 19

how do we measure activity in the neuron?

Answer 19

electrode - conductive medium that can be used to apply electrical stimulation or to record electrical potentials

Micro electrode - a very fine electrode generally used to record activity of individual neurons

Membrane potential - the electrical charge across a cell membrane, the difference in electrical potential inside and outside the cell

Question 20

Resting potential inside the neuron

Answer 20

-70mV

Question 21

How do messages travel along the neuron?

Answer 21

resting potential is inside the neuron -70mv

3 pressures act on the ions in and outside the neuron membrane

Diffusion concentration gradient

Electrostatic forces

Active transport by the Na+/K+ pump

Na+ is driven by electrostatic forces and the concentration gradient

K+ is driven by electrostatic forces and out by its concentration gradient

Cl- is at equilibrium

Sodium potassium pump - active force that exchanges 3 Na+ inside from 2 K+ outside

Question 22

forces of electrostatic pressure

Answer 22

ions evenly distribute themselves throughout a medium

+ and - = attract
- and - = repel
+ and + = repel

Question 23

Maintaining the resting potential inside

Answer 23

sodium-potassium system maintains the distribution of ions needed for the resting state and normal functioning of the cell

Question 24

Action potential

Answer 24

brief electrical impulse that provides the basis for conduction of information along an axon

Threshold of excitation - the value of the membrane potential that must be reached to produce an action potential

Question 25

triggering an action potential §

Answer 25

a) activation by a previous neuron B) activation by previous action potential When sodium ions enter the axon at the stat of the AP some will diffuse along axon because the next bit along is still negative and doesn’t contain many sodium ions This will increase the axon membrane potential and though depolarisation decreases as it spreads down the axon, it is still enough to trigger a new AP at the next node of ranvier Decrease in size as it passes down the axon is known as decremental conduction The action potential get retriggered or repeated at each node of ranvier, but decreases along the myelinated area to the next node

Question 26

jumping down the axon

Answer 26

action potentials slow down the transmission of message. The myelin sheath speeds up the process by limiting the action potential Ions enter and leave the membrane of a myelinated axon ONLY AT THE NODES OF RANVIER Saltatory conduction speeds up the velocity at which an axon can conduct an action potential as it does not have to depolarised every bit of the axon The maximum velociraptor of conduction in motor neuron is 60 metres per second

Question 27

if decremental conduction of message is faster than action potentials

Answer 27

depolarisation decreases as it spreads down the axon but it is still enough to trigger a new AP at the next node of ranvier but would peter our before getting to end of axon (decremental conduction)

Question 28

all or none law of conduction of action potential

Answer 28

the principe that once an action potential is triggered in an axon, it is propagated, without decrement, to the end of the fibre Rate law The principle that variations in the intensity of a stimulus or other information being transmitted in an axon are represented by variations on the rate at which axons fire

Question 29

communication between neurons

Answer 29

From the synapses to dendrites and soma then along axon to the terminal buttons and the synapse

Question 30

how neurones communicate with each other?

Answer 30

presynaptic membrane - the membrane of a terminal button that lies adjacent to the postsynaptic membrane and through which the neurotransmitter is released Postsynaptic membrane - the cell membrane opposite the terminal button in a synapse, the membrane of the cell that receives the message Synaptic cleft- space between the presynaptic membrane and the postsynaptic membrane

Question 31

communication between two neurons at the synapse

Answer 31

transmitter are released into synaptic cleft, molecules can then bind with receptors on post-synaptic neuron Lifecycles of the neurotransmitter: synthesis, release, bind in and inactivation Example: acetylcholine, dopamine noradrenaline, GABA

Question 32

two types of receptors:

Answer 32

ionotropic receptors Metabotropic receptors

Question 33

ionotropic receptors

Answer 33

ligand gated ion channels respond to the presence of neurotransmitter and cause post synaptic potentials, inhibitory or excitatory depending on the ion. Voltage ion channels open and loose naked on the cell membrane potential, When Na+ enters the cell it polarises When the K+ levels rhe cell it hyperpolarises moving away from the thresholds Opening of the Cl channels can also cause to inux rather than eux

Question 34

Metabotropic receptors

Answer 34

they have a slower and less direct mode of action An auto receptor is a type of Metabotropic receptor located on the pre-synaptic membrane and is sensitive to neurotransmitter released Auto receptors are a type of Metabotropic re ports located on the pre-synaptic neuron, they allow a neuron to monitor and respond to release if its own transmitter

Question 35

inactivation

Answer 35

The two mechanisms for terminating the neurotransmitter action in the synapse: usually through reuptake but also through enzymatic degradation AChE breaks down Ach Reuptake - dopamine

Question 36

inhibit excitatory reflexes

Answer 36

the brain can prevent the withdrawl reflex from causing the person to drop something or get hurt..

Question 37

neural integration

Answer 37

If Na+ channels are opened (excitatory occurs) If K+ channels are opened (inhibitory occurs) The voltage gated ions channels open and closed according to the cell’s membrane potential, When Na+ enters the cell, it polarises When K+ enters the cell it hyperpolarises moving away from the thresholds If several excitatory synapse are active at the same time the excitations summate as they travel towards the axon and the axon fires If several inhibitory synapses are active at the same time, the IPSP’s diminish the size of the EPSPs preventing the axon from firing