Nervous system Flashcards
What is the role of somatic nervous system?
Control voluntary muscular system and voluntary reflex arcs
Describe how segmental organisation of somatic nerves arises
Somatic nerves arise with somites (arranged segmentally along neural tube)
Developing nerve cells in neural tube extend processes into diff dermomyotome of each sclerotome (these form motor neurones).
At same time neural crest derivatives form neurons either side of neural tube (these form sensory neurons)
Sensory and motor neurones organised segmentally along neural tube
Describe why peripheral nerve have segmental organisation
Caudal half of each somite contains inhibitory molecules preventing nerve fibre outgrowth
What are the 2 elements of somatic nervous system?
Somatic alpha motor neurones
Somatosensory neurones
Describe the course of somatic motor neurones
Motor neurone cell bodies in ventral horns of gray matter in spinal cord
Exit spinal cord via ventral roots, terminate on muscle cells at motor end plate
Where are motor neurone cell bodes?
In ventral horns of gray matter in spinal cord
Describe somatic innervation of muscles of tongue and extraocular muscles
Cranial nerves supply their own somatic efferent neurones
What causes paralysis/weakness in muscle?
Loss of motor fibres
Describe course of somatosensory neurones
Sensory nerve endings in tissue (e.g. Pacinian corpuscle)
Cell bodies in dorsal root ganglia
Dorsal root ganglia have peripheral and central axon
Synapse to other neurones in CNS
Where are cell bodies of sensory nerves?
Dorsal root ganglia
What do somatosensory neurones do?
Convey info from receptors in skin (e.g. pain, temp) and joints (e.g. position, sense pain) and muscle and tendon (reflex control of movement) stretch to spinal cord
Describe pathologies of sensory nerve fibres
Pain from irritation of sensory fibres
Loss of sensation from damage to sensory fibres
What are mixed nerves?
Contain both motor and sensory axons in same bundle/periphery nerve with fibres separating near attachment of nerve to spinal cord - dorsal root (sensory fibre) and ventral root (motor fibres)
What do mixed nerves divide into?
Dorsal ramus and ventral ramus
Can motor and sensory neurones travel in rami?
Yes
Describe typical fibres of somatic nervous system
Usually myelinated (esp motor ones) with fast to medium velocity
Describe C type fibres
Unmyelinated and slow conducting afferent fibres
What is the sequential response to pain in terms of A and C fibres?
A delta fibres respond to quick shallow pain
C fibres respond to stronger intensity pain which are slower but more widespread
What nerves does LA target, why?
Fibres carrying nociceptive impulse, are unmyelinated, smaller diameter, fire rapidly (unmyelinated C fibres)
Describe course of visceral afferents
Conduct sensory impulses to CNS with cell bodies in dorsal root ganglia
Often run with autonomic ganglia (considered part of ANS sometimes)
What are differernces between somatic and autonomic neurones?
Somatic neurone spans spinal cord to muscle (no intervening synapse)
Neurotransmitter at NMJ solely ACh
Post synaptic receptor at NMJ solely nAchR
What happens in a reflex?
Stimulate sensory receptor
AP along sensory neurone which synapses with interneurone
Interneurone synapses with motor neurone
Stimulates reflex contraction