Neuroanatomy/physiology - Nervous Systems

Question 1

What structures does the CNS contain?

Answer 1

• brain
• spinal cord (to L2)

Question 2

What structures does the PNS contain?

Answer 2

Autonomic NS:
- sympathetic
- parasympathetic
- enteric (gastrointestinal)

Somatic NS:
- afferent & efferent nerves
- spinal
- cranial (12 pairs)

Question 3

Describe each type of sensory receptor and give some examples

Answer 3

Proprioceptors detect joint/limb position in space:
- golgi tendon organ
- muscle spindle
- joint/skin receptors

Thermoreceptors/nociceptors detect heat/nociceptive stimuli:
- free nerve endings

Mechanoreceptors detect crude/discriminative touch, pressure, vibration:
- Pacinian/Meissner’s corpuscles
- Ruffini endings
- Merkel’s discs

Question 4

Describe structure of a neuron

Answer 4

• Cell Body (Soma) contains nucleus & organelles to provide energy and synthesise organic materials (esp. neurotransmitters)
• Dendrites receive info form other neurons
• Axon propagates action potential
• Myelin sheath speeds up conduction
• Nodes of Ranvier are gaps in myelin sheath that allow saltatory conduction of APs

Question 5

What cells produce myelin?

Answer 5

• CNS = oligodendrocyte
• PNS = Schwann cell

Question 6

Describe neuroglia (inc. function) and give examples

Answer 6

separate and protect neurons, provide supporting framework, act as phagocytes

• ependymal produce CSF
• astrocytes maintain BBB
• oligodendrocytes produce myelin in CNS
• microglia produce monocytes and macrophages

Question 7

What factors affect the speed of nerve conduction?

Answer 7

• axon diameter (greater = faster)
• temperature (lower = slower)
• presence of myelin (more = faster)

Question 8

Describe propagation of action potential

Answer 8

• resting state of excitable membrane is -70mV
• stimulus detected and impulses sent
• membrane is depolarised and when threshold is reached (-55mV), AP generated
• sodium channels open and Na+ ions move across membrane into cell
• cell becomes positively charged
• when AP stops, sodium channels close and potassium channels open
• K+ ions move across membrane out of cell
• cell repolarises and becomes negatively charged (more than resting state)
• refractory period occurs: until cell charge returns to resting state, cell is unable to generate another AP

Question 9

Describe the different types of conduction

Answer 9

Continuous conduction:
- depolarisation continuous
- occurs in unmyelinated axons (CNS)

Saltatory conduction:
- depolarisation occurs at nodes of Ranvier (impulse ‘jumps’ btw nodes)
- occurs in myelinated axons