The Nervous System

Question 1

Basic principle of the nervous system?

Answer 1

Master controlling and communicating system of the body - via electrical impulses.
Sensory imput at the sensory receptors travel to the brain where integration takes place (comparison of incoming info with memory of previous events) these impulses are then sent to the muscular system (motor output, hormone production and smooth muscle contraction

Question 2

Classification of the NS.

Answer 2

CNS: brain and spinal cord.
PNS: nerves extending from the CNS (cranial nerves and spinal nerves)

Question 3

Functional classification of the PNS.

Answer 3

Neurones carrying info TO the CNS = afferent/sensory neurones (affect CNS)
Neurones carrying info FROM the CNS = efferent/motor neurones (carry effects from CNS)

Question 4

Brain cells.

Answer 4

During growth, the NS makes connections. Some of which are reinforced/lost. We only use one third of our brain cells, when the brain is damaged dormant cells take over the role (neuroplasticity).

Question 5

Myelination of neurones.

Answer 5

Rolled cell electrically insulates axons.
Increasing speed of nerve impulse.
Formed by Schwann cells in PNS.
Formed by oligodendrocytes in the CNS.

Question 6

Repair of CNS axons.

Answer 6

Very limited ability.

Heal by scar tissue and release chemicals which block axonal regrowth.

Question 7

Damage of PNS neurones.

Answer 7

Chromatolysis - chromatophilic substance (cluster of rough endoplasmic reticulum in the cell bodies of a neurone) breaks down and the cell body swells.
*Wallerian degeneration - distal portion degrades, axon and myelin sheath degraded.

Question 8

PNS neurone repair.

Answer 8

Myelinated cells are able - but only if cell body and Schwann cells intact.
Regeration:
Intact neurolemma cells (cells wrapping myelin sheath) divide.
Formation of regeneration tube.
New axon will reform, eventually myelin too.

Question 9

Physiology of a nervous impulse.

Answer 9

Neurones have a negative resting membrane potential (-70mV)

1) Stimuli cause ion channels to open.
2) Na+ channels open > Na+ ions rush into cell.
3) Depolarisation occurs.
4) K+ channels open > K+ ions move out of cell.
5) Repolarisation

Question 10

Threshold.

Answer 10

At approx -55mV threshold reached an action potential is generated (large, fast influx of Na+ to +35mV. AP caused, then K+ channels open).

Question 11

Hyperpolarisation.

Answer 11

Occurs to ensure Na+ and K+ return to normal to ensure same AP isnt generated again.

Question 12

Types of synaptic transmission.

Answer 12

Chemical
Mechanical
Electrical

Question 13

Type of synaptic transmission between NS and muscular system.

Answer 13

Chemical

Question 14

Neuromuscular Junction.

Answer 14

1 - arriving AP depolarises synaptic knob
2 - Ca+ enters synaptic knob cytoplasm. ACh released through exocytosis of neurotransmitter vesicles
3 - ACh diffuses across synaptic cleft, binding to receptors on postsynaptic membrane. Na+ channels on post synaptic surface are activated, producing a graded depolarisation. ACh release stops because Ca ions are removed from cytoplasm of synaptic knob.
4 - Depolarisation ends as ACh is broken down by acetylcholinesterase. (Choline reabsorbed for resynthesis of ACh)
Muscle Contraction