Peripheral nervous system (PNS) Consists of: 12 pairs of cranial nerves 31 pairs of spinal nerves The autonomic nervous system

Transcription

1 Peripheral nervous system (PNS) Consists of: 12 pairs of cranial nerves 31 pairs of spinal nerves The autonomic nervous system

2 Nerves and neurons

3 Cranial nerves There are 12 pairs They are numbered according to the order in which they arise from the brain. The names are descriptive of their function Many of the cranial nerves are mixed nerves they have both sensory and motor functions Cranial nerves are nerves that emerge directly from the brain stem, in contrast to spinal nerves which emerge from segments of the spinal cord.

4 Cranial Nerves AAAAAAAAD3Q/qagLJp_bJkw/s400/cranial_nerves.jpg

5 Cranial nerves 1 st (I) olfactory nerve sense of smell 2 nd (II) optic nerve sense of sight 3 rd (III) oculomotor nerve motor function of four extraocular muscles, the intraocular muscles, and the levator palpebrae 4 th (IV) Trochlear motor fiber to eye muscles 5 th (V) Trigeminal nerve sensory for the face; motor fibers to chewing muscles 6 th (VI) Abducens nerve motor fibers to eye muscles

6 Cranial nerves 7 th (VII) facial nerve is a mixed nerve that gives rise to our facial expression, and the sense of taste 8 th (VIII) vestibulocochlear nerve sense of balance (vestibular nerve) and hearing (cochlear nerve) 9 th (IX) Glossopharyngeal nerve sensory for taste; motor fibers to the pharynx 10 th (X) vagus nerve is a mixed nerve that gives rise to sensation and motor function of many organs (heart, stomach, intestines) 11 th (XI) Accessory nerve motor fibers to neck and upper back 12 th (XII) Hypoglossal nerve motor fibers to tongue

7 Distribution of Cranial Nerves Figure 7.21

8 The nerves of the PNS Sensory nerves carrying nerve impulses to the central nervous system Motor nerves carrying nerve impulses from the central nervous system to muscles, glands or organs in the periphery Mixed a combination of sensory and motor nerves within the nerve fibres

9 Spinal nerves 31 pairs Named according to the vertebrae from which they originate Cervical 8 pairs Thoracic 12 pairs Lumbar 5 pairs Sacral 5 pairs Coccygeal 1 pair

10 Each spinal nerve is formed by the union of a motor and a sensory nerve Spinal nerves (cont)

11 Plexus is an intersecting of many nerves Each plexus supplies a specific area of the body with sensory, motor and autonomic fibres There are four plexuses Cervical Brachial Lumbar Sacral Spinal nerves (cont)

12 Reflex arc A reflex arc are actions that occur in response to sensory information without conscious or voluntary initiation The sensory impulse is received in the spinal cord and is perceived as an emergency (potential for injury or damage to the organism) In response to this perceived danger, the nerve impulse short-circuits across the spinal cord and initiates a rapid motor response At the same time the usual message is sent to the brain for interpretation The action occurs before the brain is consciously aware of the situation.

13 Reflex arc

14 Reflex arc

15 Autonomic nervous system (ANS) Controls the body's internal environment in a coordinated manner (homeostasis) The ANS helps control the heart rate, blood pressure, digestion, respiration, blood ph and other bodily functions through a series of complex reflex actions These controls are done automatically, below the conscious level To exert this control the activities of many different organs must be coordinated so they work to accomplish the same goal

16 The sympathetic nerves come from the thoracic and lumbar regions of the spinal cord. The preganglionic nerves are short and synapse in paired ganglia adjacent to the spinal cord Parasympathetic nerves come from the cranial and sacral regions of the CNS. They have long preganglionic nerves which synapse at ganglia near or on the organ innervated.

17 The 2 branches use the same neurotransmitter, acetylcholine (ACh), in the ganglia. At the organ quite different neurotransmitters are used: Parasympathetic = ACh Sympathetic = norepinephrine (NE) also known as noradrenaline (NA).

18 Sympathetic The Sympathetic is the "Fight or Flight" Branch of the ANS Emergency situations, where the body needs a sudden burst of energy, are handled by the sympathetic system The sympathetic system increases cardiac output and pulmonary ventilation, routes blood to the muscles, raises blood glucose and slows down digestion, kidney filtration and other functions not needed during emergencies Whole sympathetic system tends to "go off" together In a controlled environment the sympathetic system is not required for life, but it is essential for any stressful situation.

19 Parasympathetic The Parasympathetic is the "Rest and Digest" Branch of the ANS The parasympathetic system promotes normal maintenance of the body- acquiring building blocks and energy from food and getting rid of the wastes It promotes secretions and mobility of different parts of the digestive tract. Also involved in urination, defecation. Does not "go off" together; activities initiated when appropriate The vagus nerve is the chief parasympathetic nerve Other cranial parasympathetic nerves are: III (oculomotor), VII (facial) and IX (glossopharyngeal)

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21 Occasionally the 2 systems work together: Sexual intercourse: the parasympathetic promotes erection and the sympathetic produces ejaculation Eye: the sympathetic response is dilation and relaxation of the ciliary muscle for far vision (parasympathetic does the opposite) Urination: the parasympathetic system relaxes the sphincter muscle and promotes contraction of muscles of the bladder wall urination (sympathetic blocks urination) Defecation: the parasympathetic system causes relaxation of the anal sphincter and stimulates colon and rectum to contract defecation (sympathetic blocks defecation)

22 Reference list & diagrams MARIEB, E Human Anatomy and Physiology, 6 th edition. Pearson Education Australia. WAUGH, A. & GRANT, A Ross and Wilson Anatomy and Physiology in Health and Illness. Churchill Livingston Elsevier. Sydney Australia. 22 HLTEN507A Session 14