learning outcomes

Question 1

Describe the anatomical organisation of the nervous system

Answer 1

CNS- brain and spinal cord
PNS- all the neurones which connect the CNS to the rest of the body. 
Autonomic- involuntary
Somatic-voluntary
enteric-Surrounds the gut

Comprises neurones and Glia.
Glia- Astrocytes, microglia, oligodendricites, ependymal cells

Question 2

Describe the general structure of a neurone

Answer 2

cell body/soma- contains nucleus and organelles- essential for protein synthesis
Dendrites- carry info to the cell body
Axons- carry info away from the cell body- white matter due to myelin sheath.
axon compromised of :
-initial segment/hillock which contains many sodium/potassium pumps and is where the initial action potential is generated
-axon terminal: where neurotransmitter is released into synapse.

Question 3

describe the ionic basis for resting membrane potential

Answer 3

More K+ inside the cell, more Na+ outside the cell.
Maintained by:
-leaky potassium channels- potassium can flow out of the cell along its concentration gradient by facilitated diffusion. as this happens an electrical gradient is set up which draws the potassium back into the cell until equilibrium potential is reached: the electrical gradient and the contraction gradient are the same but opposite.
-sodium-potassium pump
-large negative cells which cannot diffuse out of cell ( Cl-).

Question 4

describe the ionic basis of an action potential?

Answer 4

Action potentials are generated when generator potentials reach threshold (-55mv). This causes a sudden influx of sodium ions and the membrane becomes depolarised (+30mv). At this stage the sodium channels close and the potassium channels open which causes the cell to become hyper polarised. The RMP is then re-established through the sodium-potassium pump.

Action potentials are

• all or nothing- the graded potential has to reach threshold. If the stimulus is stronger it will increase the frequency of the action potential.
• self- propagating NOT decremental.

Question 5

Describe the classification of nerve fibres

Answer 5

Afferent- sensory. Enter dorsal root ganglion-dorsal- dorsal trunk
Efferent- motor. central ventral root
Interneurons- connect sensory and motor neurons

Question 6

Define conduction velocities and their relationship with different fibre types

Answer 6

Depends on

• myelination: contained in folds of membrane in schwann cells in PNS and oligodendricites in CNS. prevents ions from leaking out along axon membrane. Sodium channels only present at gaps between schwann cells- nodes of ranvier so electrical impulse jumps between these- saltatory conduction.
• Axon diameter: the greater the diameter the lower the axial resistance so charge can spread more evenly.

Question 7

Describe the consequences of de-myelinating diseases?

Answer 7

Eats hole in Schwann cells. Prevents action potential from reaching next node- conduction fails.

Question 8

Describe the structure of the neuromuscular junction,

Answer 8

At neuromuscular junction the Motor-end plate comes to synapse onto the muscle.
The muscle side of the synapse shows the sarcolemma with folds which contain Ach receptors which allow the muscle contraction to be deeper.

Question 9

describe the process of synaptic transmission at the NMJ

Answer 9

1-Action potential reaches the pre-syanptic terminal and causes the voltage-gated channels to open.
2- Vesicles containing Ach bind to pre-synpatic membrane and are released into synapse
3- Ach diffuses across synapse and binds to receptors on the sarcolemma. This causes the ligand-gated Na+ channels to open.
4- A end-plate potential is formed which reaches threshold causing Ligand-gated Na+ channels to open in the adjacent section of membrane and an action potential to form which leads to contraction
5- Ach is broken down by acyl-cholinesterase.

Question 10

Ultra-structure and function of synapses between neurones?

Answer 10

Structure very similar to NMJ.
Significant differences include:
- many neurotransmitters not just Ach
- Variety of different potentials not just end-plate potential
- neurotransmitter can be released onto different points on the neurone
- synaptic connectivity i.e. convergence and divergence.

Question 11

Describe what is meant by EPSP and IPSP

Answer 11

EPSP- excitatory- neurone is depolarised.
Fast- receptors bind to membrane causing a non-specific +1 channel to be open. Na+ flows in at a greater rate of K+ flowing out
Slow- receptor binds to membrane causing G-protein to ?K+ channel to close

IPSP- inhibitory- more negative
Fast- receptor binding causes Cl- channels to open
Slow- G-protein causes K+ channels to open

Question 12

common excitatory and inhibitory neurotransmitters?

Answer 12

Ach, GABA, NA, dopamine, serotonin, ATP, peptides

Question 13

Explain the role of synapses in integration of neuronal function.

Answer 13

convergence/ divergence/ feedback-inhibition
Feedback inhibition- sends an impulse when A.P. fired which prevents another A.P. from being fired so that separate electrical impulses can be fired.