5/6) - Nerves and muscle Flashcards
(10 cards)
What are myelin sheaths
Insulators. Formed by tightly spiralled, very thin layers of oligodendrocytes (or Schwann cells in the PNS) around the axon
What is the principle glial cell
The Schwann cell- produces one myelin sheath per cell or wraps itself around unmyelinated nerve extensions
What are anatomical nerves
Bundles of nerve extensions (axons, dendrites), held together by epineurium, perineurium and endoneurium
What are nerve cell bodies (perikarya)
Situated in peripheral nervous system ganglia are covered by satellite cells. This is- for example the case for the pseudounipolar sensory neurons of a reflex arch
Describe the resting K+ channels
They leak K+ ions at resting membrane potential and are also known as tandem pore domain K+ channels.
Voltage gated K+ channels can be blocked by tetraammonium chloride or 4-aminopyridine
What do alpha spinal motor neurons innervate
Extrafusal muscle fibres - responsible for contraction of small Y spinal motor neurons innervate intrafusal muscle fibres in muscle spindles
What’s the point of reflexes
Escape / avoidance / withdrawal from a noxious stimulus
Postural control
Locomotion- smooth movement
Classification of reflexes
Superficial:
- corneal (blink)
- nasal (sneeze)
- plantar (toes curl)
Deep (myotactic)
- patellar (knee jerk)
Visceral (autonomic)
- pupillary (dilatation / constriction)
- micturition (voiding bladder)
What can assessment of reflexes tell us
Assessing reflexes are a key part of neurological examinations and significantly aid in the detection of damage or disease in the CNS
What is babinskis reflex
Flexor response (toes curl down toward plantar surface) seen in normal healthy adults
Extensor response (toes curl up and fan out) a sign of pathology or damage in adults
Extensor response is seen in babies or when adults are asleep
Abnormal babinski indicative of upper motor neurone damage or brain disease that impacts on the corticospinal tract
