Neuronal communication

Question 1

how do cells communicate with another

Answer 1

• cell releases a chemical

- which has an effect on the target cell

Question 2

during cell signalling cells can:

Answer 2

• transfer signals locally, between neurones

- transfer signals across large distances using hormones

Question 3

describe the structure of a neurone

Answer 3

• cell body: large amounts of ER and mitochondria which are involved in the production of neurotransmitters
  these are chemicals which are used to pass signals from one neurone to the next
• axon: singular elongated nerve fibres that transmit impulses away from the cell body , the fibre is cylindrical in shape consisting of a very narrow region
• dendrons: short extensions which come from the cell body, these divide into smaller branches called dendrites
  responsible for transmitting electrical impulses towards the cell body

Question 4

describe sensory neurones?

Answer 4

• transmit impulse from a secondary receptor cell to a relay neurone, motor neurone or brain
• one dendron
• which carries the impulse to the cell body
• one axon
• which carries the impulse away from the cell body

Question 5

describe relay neurones?

Answer 5

• these neurons transmit impulses between neurons

- they have many short axons and dendrons

Question 6

describe motor neurones?

Answer 6

• these neurones transmit impulses from a relay neurone to an effector such as a muscle or gland
• one axon and many short dendrites

Question 7

describe myelinated neurones

Answer 7

• can transmit impulses at up to 100 metres per seconds
• Axon of a myelinated neurone is covered in myelin
• the sheath is formed by Schwann cells growing around the axon several times
• there
  are gaps in the myelin sheath known as nodes of Ranvier electrical impulse moves in a series of
  jumps’ from one node to the next/saltatory conduction impulse transmitted much faster than
  along an unmyelinated axon (1).

Question 8

difference between myelinated and unmyelinated neurons

Answer 8

• in myelinated neurons, the electric impulse jumps from one node to the next, making it transmit faster
• in unmyelinated neurons, electric impulses do not jump it transmits continuously alone the nerve fibre so is much slower

Question 9

describe the role of a sensory receptor in the body

Answer 9

• convert the stimulus they detect, into a nerve impulse

- the information is then passed through the nervous system and into the CNS

Question 10

describe the features of the sensory receptors

Answer 10

• they are specific to a single type of stimulus

- they act as a transducer- convert a stimulus into a nerve impulse

Question 11

what is the stimulus of a mechanoreceptor

Answer 11

• pressure and movement

- in skin

Question 12

what is the role of a transducer

Answer 12

• the receptor converts the stimulus into a nervous impulse called a generator potential

Question 13

what is the pacinian corpuscle

Answer 13

• specific sensory receptor that detect mechanical pressure

- located deep within your skin and are most abundant in the fingers

Question 14

explain how a pacinian corpuscle converts mechanical pressure into a nervous impulse?

Answer 14

1. ) in its resting state, the stretch-mediated sodium ion channels are too narrow to allow sodium ions to pass through
   - the neuron has a resting potential
2. ) when pressure is applied to the pacinian corpuscle, it changes shape causing the membrane surrounding its neurone to stretch
3. ) when the membrane stretches, the sodium ion channels present widen
   - sodium ions now diffuse into the neurone
4. ) the influx of the positive sodium ins changes the potential of the membrane- it becomes DEPOLIRISED
   - this results in a generator potential
5. ) generator potential creates an action potential then passes along sensory neurons
6. ) action potential will be transmitted along neurons to the CNS

Question 15

describe and explain the events in the creation of a resting potential

Answer 15

1. ) 3 sodium ions are actively pumped out of the axon
2. ) 2 potassium ions are actively pumped into the axon
3. ) this is done by a intrinsic proteins called, Potassium-sodium pump

4.) as a result there are more sodium ions outside the membrane than inside the axon, where as there are more potassium ions inside the cytoplasm than outside the axon
5.) therefore sodium ions are diffuse back into the axon down its electrochemical gradient
- where as potassium ions diffuse out of the axon
6.) more of the gated sodium ion channels are closed preventing the movement of sodium ions
however potassium ion channels are open allowing potassium ions to diffuse out of the axon
- therefore there are more positively charged ions outside the axon than inside
this creates a resting potential across the membrane of -70mV with the inside negative relative to the outside

Question 16

describe and explain the events of action potential?

Answer 16

1. ) energy of the stimulus triggers some sodium voltage-gated channels to open therefrom sodium ions diffuse into the axon down there electrochemical gradient making the inside of neurone less negative
2. ) this change causes more sodium ion channels to open allowing more sodium ions do diffuse into the axon, example of positive feedback
3. ) when potential difference reaches +40mV, sodium voltage-gated channels close and potassium voltage-gated channels ope membrane more permeable to potassium ions
4. ) potassium ions diffuse out of the axon down their elecrochemical gradient reducing the charge and inside of axon more negative than outside
5. ) lots of potassium ion diffuse out of the axon resulting the inside of the axon becoming more negative this is known as hyper-polarisation

6.) the voltage-gated potassium channels now close the sodium potassium pump causes sodium ions to move out of the cell and potassium ions to move in the axon returns to its resting potential
it is now repolarised

Question 17

describe the structure of a synapse

Answer 17

1. ) SYNAPTIC CLEFT:
   - the gap which seperates the axon of one neurone from the dendrite of the next neuron
   - gap is 20-30nm across
2. ) PRESYNAPTIC neurone:
   - neurone along which the impulse has arrived
3. ) POSTSYNAPTIC neurone:
   - neurone that receives the neurotransmitter
4. ) SYNAPTIC KNOB:
   - the swollen end of the presynaptic neurone
   - contains mitochondria and endoplasmic reticulum to enable it to manufacture neurotransmitters
5. ) SYNAPTIC VESICLES
   - vesicles containing neurotransmitters
   - vesicles fuse with the presynaptic membrane and release their contents into the synaptic cleft
6. ) Neurotransmitter receptors:
   - receptor molecules which the neurotransmitter binds to in the postsynaptic membrane

Question 18

what are the types of neurotransmitters?

Answer 18

1.) excitory - these result in the depolarisation of the postsynaptic neurone
if the threshold is reached in the postsynaptic membrane, an action potential is triggered
- acetycholine is an example of an excitatory neurotransmitter

2.) inhibitory - these result in the hyperpolarsation of the postsynaptic membrane
this prevents an action potential being triggered
- gamma- aminobutyric acid is an example

Question 19

what happens in order for the synaptic transmissions to occur?

Answer 19

• action potential reached the end of the presynaptic neurone
• depolarisation of the the presynaptic neurone cuases calcium ion channels to open
• calcium ions diffuse into the presynaptic knob
• this causes the synaptic vesicles to fuse with the presynaptic membrane
• ## it gets released into the synaptic cleft via exocytosis

Question 20

describe and explain the mechanism of transmission across a cholinergic synapse

Answer 20

• arrival of an action potential causes calcium ions channels to open and calcium ions enter the synaptic knob
• the influx of calcium ions into the presynaptic neurone causes synaptic vesicles to fuse with presynaptic membrane so releasing acetylcholine into the synaptic cleft
• acetylcholine molecules fuse with receptor sites on the sodium ion channel in the membrane of the postsynaptic neurone
• this causes the sodium ions channels to open allowing sodium ions to diffuse rapidly along a concentration gradient
• the influx of sodium ions generates a new action potential in the postynaptic neurone
• acetylcholinesterase hydrolyses acetycholine into choline and ethanoic acid, which diffuse back into the synaptic cleft and into the presynaptic neurone
• breakdown of acetyhcholine also prevents it from generating a nee action potential
• ATP released by mitochondria is used to combine choline and ethanoic acid into acetylcholine
• this is stored in synaptic vesicles for future use
• sodium ion channels close in the absence of acetylcholine in the receptor sites

Question 21

give three roles of the synapses

Answer 21

• they ensure impulses are unindirectional
  as impulses can only teavel from the presynaptic neurone to the postsynaptic neurone
• they can allow an impulse from one neureon to be transmitted to a number of nuerones at multiple synapses
• a number of nuerones may feed in to the same synapse with a single postsynaptic neurone

Question 22

explain both of the summation

Answer 22

• spatial summation:
  - this occurs when a number of presynaptic neurones connect to one postsynaptic neurone
• each releases neurotransmitter which builds up to a high enough level in the synapse to trigger an action potential in the single postsynaptic neurone
• temporal summation
  - occurs when a single presynaptic neurone releases neurotransmitter as a result of an action potential several times over a short period
• this builds up in the synapse until quantity is sufficient to trigger an action potential

Question 23

what are the 2 mammalian nervous systems?

Answer 23

• central nervous system (CNS) - consists of your brain and spinal cord
• Peripheral nervous system (PNS) - consists of all the neurones that connect CNS to the rest of the body
• sensory - carry nerve impulses- CNS
• motor - to effectors

Question 24

what are the 2 functional organisations

Answer 24

• somatic nervous system - under conscious control
  carries impulses to the bodies muscles
• autonomic nervous system - system works constantly
  it is under subconscious control and is use when your body does something automatic without you deciding to do it , it is involuntary
  carries nerve impulses to glands smooth muscle

Question 25

which nervous system is further divided?

Answer 25

• autonomic nervous system
• into sympathetic motor system
• into parasympathetic motor system

Question 26

what is the neurotransmitter at effector in a somatic nervous system and effector organ?

Answer 26

• acetylcholine

- skeletal muscle

Question 27

what is the neurotransmitter at effector in a sympathetic motor system and effector organ?

Answer 27

• NA none

- smooth muscle, cardiac muscle, glands

Question 28

what is the neurotransmitter at effector in a parasympathetic motor system and effector organ?

Answer 28

• acetylcholine

- smooth muscle, cardiac muscle

Question 29

what does the cerebrum do>

Answer 29

controls and coordinates all voluntary actions such as

learning, memory, personality and conscious thought) +some involuntary ones

Question 30

describe the cerebrum>

Answer 30

Receives sensory information, interprets it with respect to
that stored from previous experiences and then sends
impulses along motor neurones to effectors to produce
appropriate response

Highly convoluted to increase surface area and capacity for
complex activity

Left and right cerebral hemispheres. Outer layer known as
cerebral cortex - most sophisticated processes such as
reasoning and decision making occur in frontal and
prefrontal lobe of cerebral cortex

Each sensory area receives information from receptor cells
located in sense organs; size allocated proportional to
relative number of receptor cells in body part. Information
passed to association areas to be analysed and acted
upon. Impulses come into motor areas where motor
neurones send out impulses; size allocated proportional to
relative number of motor endings in it.

Base of brain impulses from each side of body cross – left
hemisphere receives impulses from ride hand-side of body