Ch.12-The Peripheral Nervous System Flashcards
Name the 12 cranial nerves.
I - olfactory II - optic III - oculomotor IV - trochlear V - trigeminal VI - abducens VII - facial VIII - vestibulocochlear IX - glossopharyngeal X - vagus XI - accessory XII - hypoglossal
Explain reflex activity and spinal reflexes.
Reflexes are either inborn(intrinsic) or learnt(acquired).
Inborn reflexes are rapid, predictable motor responses to stimuli.
Learnt reflexes developed from repetition over time.
The 5 essential components of a reflex arc are: A receptor A sensory neuron An integration centre A motor neuron An effector
Reflexes are functionally classified as somatic or autonomic(visceral).
Somatic reflexes activate skeletal muscle, whereas autonomic reflexes activate visceral effectors, which include smooth or cardiac muscle, or glands.
Spinal reflexes are somatic reflexes controlled by the spinal cord, often without direct involvement of higher brain centres.
The brain can intercede on spinal reflexes due to continuous monitoring.
Spinal shock may occur if the spinal cord is transected.
Tests of somatic reflexes are used to assess nervous system function.
Explain dual innervation of the autonomic nervous system.
Dual innervation of the autonomic nervous system helps to balance the sympathetic and parasympathetic divisions of the ANS.
Sympathetic-fight or flight, stresses-alert, energised, Rise in BP-HR-RR, elevation in muscle tone, slowing of non-essential functions(eg. GI tract)
Parasympathetic-rest and digest, stress subsides, decrease in BP-HR-RR, relaxing of muscle tone, non-essential functions stimulated.
Via dual innervation, the divisions counterbalance each other, keeping the systems of the body functioning normally.
Both of the divisions generally cause opposite effects on the same visceral organs(smooth muscle, cardiac muscle, glands).
Cooperative dual innervations involve the fibers of both systems working together to produce a response.
Dual innervations may also be antagonistic or complementary.
Describe the arrangement of sympathetic neurons and ganglia.
In the sympathetic division all preganglionic fibres arise from cell bodies of preganglionic neurons in the spinal cord, from level of T1 down to L2, hence it has another name ‘Thoracolumbar division’.
The many preganglionic sympathetic neurons in the spinal cord grey matter form the lateral horns, which are just posterolateral to the ventral horns that contain the somatic motor neurons.
After leaving the spinal cord via the ventral root preganglionic sympathetic fibres pass through a white Ramos communicans to enter an adjoining sympathetic trunk ganglion that forms part of the sympathetic trunk.
Sympathetic trunk consists of the sympathetic ganglia and fibers that run from one ganglion to another.
Sympathetic fibres arise only from the thoracic and lumbar spinal cord segments.
When a preganglionic axon reaches a trunk ganglion, it can synapse at the same level, or at higher and lower levels, or may synapse in a distant collateral ganglion.
Describe the arrangement of parasympathetic neurons and ganglia.
In the parasympathetic division, also called the ‘craniosacral division’, preganglionic fibres emerge from opposite ends of the CNS(brain stem and sacral spinal cord).
Preganglionic axons extend from the CNS to nearly reach the structures they innervate.
The axons then synapse with postganglionic neurons in the terminal ganglia.
Short postganglionic axons emerge from the terminal ganglia to synapse with nearby effector cells.
Distinguish between the sympathetic and parasympathetic divisions of the Autonomic Nervous System.
The Sympathetic division mobilises the body during activity.
The Parasympathetic division promotes ‘maintenance’ functions and conserves energy.
Commonly one division will stimulate a reaction while the other inhibits them.
Sympathetic can be thought of as ‘E’ division as its in charge of Emergencies, Excitement and Exercise.
Parasympathetic can be thought of as ‘D’ division as it’s in charge of Digestion, Defecation and Diureses
The 2 divisions maintain dynamic antagonism in order to balance homeostasis.
Sympathetic fibres are thoracolumbar in origin.
Parasympathetic fibres arecraniosacral in origin.
Sympathetic division has short preganglionic fibres and long postganglionic fibres.
Parasympathetic division is the opposite with long preganglionic and short postganglionic fibres.
Sympathetic ganglia lie close to spinal cord.
Parasympathetic ganglia are mostly located in the visceral effector organs.
Describe function of cranial nerves II, III, IX and X
II - Optic
- associated with the sense of vision, it is actually a brain tract, because it develops as an outgrowth of the brain.
III - Oculomotor
- motor fibres - raising eyelids, moving eyes, adjusting amount of entering light and focusing lenses.
This nerve supplies 4 out of the 6 extrinsic muscles that move the eyeball in its orbit, these are the inferior oblique, superior, inferior and medial recurs muscles.
The parasympathetic motor fibers reach the sphincter pupillary causing the pupils to constrict.
The ciliary muscle controls lens shape.
- some sensory fibres - associated with muscle condition.
IX - Glossopharyngeal
- motor fibres - transmit impulses to the pharynx muscles used in swallowing, and to the salivary glands. These nerves also innervate part of the tongue.
- sensory fibres - transmit impulses from the pharynx, tonsils, posterior tongue and carotid arteries.
X - Vagus
- somatic motor fibres - transmit impulses to muscles used for speech and swallowing.
- autonomic motor fibres - transmit impulses to the heart, smooth muscles, and thoracic and abdominal glands.
- sensory fibres - transmit impulses from the pharynx, larynx, oesophagus, and visceral of the thorax and abdomen.
