Nervous system Flashcards by Phoebe Mountain

What is the role of somatic nervous system?

Control voluntary muscular system and voluntary reflex arcs

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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

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Describe why peripheral nerve have segmental organisation

Caudal half of each somite contains inhibitory molecules preventing nerve fibre outgrowth

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What are the 2 elements of somatic nervous system?

Somatic alpha motor neurones

Somatosensory neurones

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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

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Where are motor neurone cell bodes?

In ventral horns of gray matter in spinal cord

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Describe somatic innervation of muscles of tongue and extraocular muscles

Cranial nerves supply their own somatic efferent neurones

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What causes paralysis/weakness in muscle?

Loss of motor fibres

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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

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Where are cell bodies of sensory nerves?

Dorsal root ganglia

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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

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Describe pathologies of sensory nerve fibres

Pain from irritation of sensory fibres

Loss of sensation from damage to sensory fibres

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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)

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What do mixed nerves divide into?

Dorsal ramus and ventral ramus

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Can motor and sensory neurones travel in rami?

Yes

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Describe typical fibres of somatic nervous system

Usually myelinated (esp motor ones) with fast to medium velocity

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Describe C type fibres

Unmyelinated and slow conducting afferent fibres

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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

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What nerves does LA target, why?

Fibres carrying nociceptive impulse, are unmyelinated, smaller diameter, fire rapidly (unmyelinated C fibres)

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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)

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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

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What happens in a reflex?

Stimulate sensory receptor

AP along sensory neurone which synapses with interneurone

Interneurone synapses with motor neurone

Stimulates reflex contraction

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What is unique about some refelxes e.g. muscle stretch reflex (knee jerk)?

Sensory neurone synapses onto motor neurone directly (no interneurone)

What is the autonomic nervous system?

Efferent system for involuntary control of body functions

Describe structure innervated by only either symp/para

Blood vessels innervated by symp system only

Describe course of autonomic system fibres

Cell bodies in CNS send preganglionic fibres to synapse on post ganglion cells outside CNS Preganglionic neurotransmitter Ach

Describe features of most autonomic preganglionic fibres

Myelinated and slow to medium velocity

Describe differneces between pre and post ganglionic neurones

Pre: cell body in brain, axon is myelinated, synapses in ganglion Symp: cell body in autonomic ganglia, unmyelinated, synapses on visceral effector

Describe course of autonomic fibres as they approach white and gray ramus (at paravertebral ganglia)

Exits the spinal cord via the ventral root, it then forms the mixed nerve before exiting into the sympathetic chain via the white ramus Then can synapse at same segment Above/below in paravertebral sympathetic ganglion Descend to prevertebral ganglion and synapse with post synaptic cell.

What are the two divisions of the ANS?

Sympathetic and parasympathetic

What are paravertebral ganglia?

Along the length of the sympathetic trunks are ganglia known as paravertebral ganglia.

What are prevertebral ganglia?

Prevertebral ganglia are sympathetic ganglia which lie between the paravertebral ganglia and the target organ.

Describe sympathetic output origin of ANS?

Thoracic and lumbar spinal cord (T1-L2) preganglionic output to all visceral (no cervical outflow)

Describe 2 types of sympathetic ganglia

Paravertebral: located on each side of vertebrae and connected to form sympathetic chain. Prevertebral ganglia

Describe post ganglionic fibres in ANS

Originate in ganglion cells, which send out post ganglionic fibres which are unmyelinated and innervate effector e.g. cardiac muscle, glands etc

Compare pre and post ganglionic fibre length in sympathetic ANS

Short preganglionic | Long post ganglionic

Describe autonomic innervation of adrenal glands

Adrenal medullary cells are modified ganglion cells secreteing adrenaline into blood (Muscarinic receptors) Innervated by preganglionic autonomic fibres for CNS (nerves pass through symp chain)

Describe examples of prevertebral ganglia

Preganglionic neurones from spinal cord come togehter in 3 midline ganglia, these nerves then synapse with post ganglionic nerve Nerves that innervate gut/abdomen/pelvic organs are supplied by greater, lesser and least splanchnic nerves which reach coeliac superior mesenteric and inferior mesenteric ganglia before sending fibres to viscera

What is the role of the 3 midline ganglia and what are the 3 midline ganglia?

Coeliac ganglion: foregut Superior mesenteric ganglion: midgut Inferior mesenteric ganglion: hindgut and pelvic organs

What do most midline ganglia release?

Noradrenaline

What do para sympathetic ganglion cells release?

Ach (in end organ)

What is preganglionic transmitter?

Ach

What is Horner's syndrome caused by?

Lesion of superior cervical ganglion e.g. Pancoast tumour at apex of lung block superior cervical ganglion

What are symptoms of Horner's syndrome?

Loss of sympathetic action - Pupil constriction (para system not opposed) - Drooping eye lid - Dry face (sweat glands don't work) - Flushed face

Describe parasympathetic division output of ANS

Cranial nerves from 4 nerves in brain and sacral spinal nerves (s2-s4)

Describe ganglia in parasympathetic division

No segmental chain ganglia Ganglia close to target organ

Describe neurone length in parasympathetic division of ANS

Long pre-ganglionic and short post ganglionic nerves | para ganglionic cells close to target organ

What do sacral nerves innervate?

Lower gut and urogenital tract

What do cranial nerves provide to face and head?

Motor, sensory and autonomic supply

What are 4 parasympathetic nerves emerging from sympathetic nerves?

Oculomotor - innervate eye Facial nerve - innervate ganglia supplying tears and salivary glands Glossopharyngeal nerve - supply ganglia regulated parotid salviary gland Vagus nerve - supplies parasympathetic nerves to thorax and abdomen

What are the different routes of preganglionic nerve?

Terminate in ganglia Pass along chain then terminate in ganglia Pass to prevertebral/midline ganglia via splanchnic nerves

What are the cotransmitters for sympathetic and parasympathetic system

Symp: ATP and neuropeptide Y Para: NO and VIP

What is the role and course of of visceral afferents in ANS?

Visceral afferents primarily chemoreceptors, mechanoreceptors and stretch receptors and often run with autonomic nerves -monitor changes in viscera and conduct sensory impulses to CNS

What might visceral afferents elicit?

Involuntary autonomic reflex (baroreceptor reflex)

What causes visceral referred pain?

Convergence of visceral afferent (sensory) nerve fiber entering the spinal cord at the same level as the superficial, somatic structures experiencing the pain.

The main neurotransmitter used by peripheral sensory neurons

Glutamate