1. Ch. 11 The Nervous System Part 3: Peripheral nervous system (interactive notes 417-439)

2. Peripheral Nervous System
Peripheral Nervous System (P N S):
Consists of nerves that connect C N S to other body parts; P N S includes:
Cranial nerves arising from the brain.
Spinal nerves arising from the spinal cord.
P N S can also be divided into:
Somatic nervous system: cranial & spinal nerves that connect C N S to the skin and skeletal muscles (conscious activities).
Autonomic nervous system: cranial & spinal nerves that connect C N S to viscera (subconscious activities).

3. Subdivisions of the Nervous System
Table 11.8 Subdivisions of the Nervous System
1. Central nervous system (C N S)
a. Brain
b. Spinal cord
2. Peripheral nervous system (P N S)
a. Cranial nerves arising from the brain
(1) Somatic afferent and efferent fibers connecting to the skin and skeletal muscles
(2) Autonomic efferent fibers connecting to viscera
b. Spinal nerves arising from the spinal cord
(1) Somatic afferent and efferent fibers connecting to the skin and skeletal muscles

4. Nerve and Nerve Fiber Classification
Sensory nerves:
Conduct impulses into brain or spinal cord
Motor nerves:
Conduct impulses to muscles or glands
Mixed nerves:
Contain both sensory and motor nerve fibers.
Most nerves are mixed nerves.
All spinal nerves are mixed nerves (except the first pair).

5. Nerve Fiber Classification
Cranial and spinal nerves are subdivided into these types:
General somatic efferent fibers: Carry motor impulses from C N S to skeletal muscles
General visceral efferent fibers: Carry motor impulses from C N S to smooth muscles and glands
General somatic afferent fibers: Carry sensory impulses to C N S from skin and skeletal muscles
General visceral afferent fibers: Carry sensory impulses to C N S from blood vessels and internal organs
“General” indicates that fibers are associated with general structures, as opposed to those of the special senses.

6. Nerve Fiber Classification
“Special” fibers are associated with specialized structures, and are found only in cranial nerves:
Special somatic efferent fibers: Carry motor impulses from brain to muscles used in chewing, swallowing, speaking and forming facial expressions
Special visceral afferent fibers: Carry sensory impulses to brain from olfactory and taste receptors
Special somatic afferent fibers: Carry sensory impulses to brain from receptors of sight, hearing and equilibrium

7. 12 pairs of cranial nerves on the inferior side of the brain that are either sensory, motor, or mixed.

8. Cranial Nerves I and II Olfactory nerve (I): Optic nerve (II): Sensory
Smell
Bipolar neurons; pass through cribriform plate of ethmoid bone, and enter olfactory bulbs
Optic nerve (II):
Sensory
Vision
Neuron cell bodies form ganglion layers of retina, and pass through optic foramina of the orbits.

9. Cranial Nerves III and IV
Oculomotor nerve (III):
Motor
raise eyelids & move the eyes.
Motor impulses to involuntary muscles that focus lens, adjust light entering eye (part of autonomic nervous system)
Small sensory component (proprioceptive fibers)
Trochlear nerve (IV):
Smallest pair of cranial nerves
Motor
Motor impulses to one pair of muscles that move the eyes
Small sensory component (proprioceptive fibers)

10. Cranial Nerve V Trigeminal nerve (V): Mixed nerve.
Largest pair of cranial nerves.
3 large sensory branches:
Ophthalmic division: Sensory from surface of eyes, tear glands, scalp, forehead, and upper eyelids.
Maxillary division: Sensory from upper teeth, upper gum, upper lip, palate, and skin of face.
Mandibular division: Sensory from scalp, skin of jaw, lower teeth, lower gum, and lower lip.
Motor to muscles of mastication.

11. Cranial Nerves VI and VII
Abducens nerve (VI):
Motor
Motor impulses to one pair of muscles that move the eyes
Some sensory (proprioceptive fibers)
Facial nerve (VII):
Mixed
Sensory from taste receptors
Motor to muscles of facial expression, tear glands, and salivary glands

12. Cranial Nerves VIII and IX
Vestibulocochlear nerve (VIII):
Acoustic or auditory nerve
Sensory
2 branches:
Vestibular branch:
Sensory from equilibrium receptors of ear.
Cochlear branch:
Sensory from hearing receptors.
Glossopharyngeal nerve (IX):
Mixed Sensory from pharynx, tonsils, part of tongue (the region posterior to the nasal cavity, the oral cavity and the larynx).
Motor to salivary glands and muscles of pharynx (for swallowing).

13. Cranial Nerve X Vagus nerve (X): Mixed
Somatic motor to muscles of speech and swallowing
Autonomic motor to heart, other viscera of thorax and abdomen
Sensory from pharynx, larynx, esophagus, and viscera of thorax and abdomen

14. Cranial Nerves XI and XII
Accessory nerve (XI):
Motor
Contain cranial and spinal branches:
Cranial branch:
Join Vagus N.; motor to muscles of soft palate, pharynx and larynx
Spinal branch:
Motor to muscles of neck and back
Small sensory component (proprioceptive fibers)
Hypoglossal nerve (XII):
Motor
Motor to muscles of the tongue for speaking, chewing, swallowing
Small sensory component (proprioceptive fibers)

16. Spinal Nerves
All are mixed nerves, except the first pair (the first pair is purely motor) Originate from spinal cord
31 pairs of spinal nerves:
8 cervical nerves, (C1 to C8).
12 thoracic nerves (T1 to T12).
5 lumbar nerves (L1 to L5).
5 sacral nerves (S1 to S5).
1 coccygeal nerve (Co).
Cauda equina: Formed by descending roots of lumbar, sacral, and coccygeal nerves

17. Spinal Nerves Posterior (dorsal) root: Sensory
Each spinal nerve splits into a dorsal and ventral root inside the vertebral column:
Posterior (dorsal) root:
Sensory
Posterior root ganglion: Contains cell bodies of sensory neurons whose axons conduct impulses from peripheral body parts into the spinal cord.

18. Dermatome:
An area of skin innervated by the sensory nerve fibers of a particular spinal nerve

19. Spinal Nerves Anterior (ventral) root: Spinal nerve: Motor root.
Axons of motor neurons whose cell bodies are in the spinal cord.
Spinal nerve:
Union of anterior root and posterior roots.
Anterior + Posterior = “mixed” nerve.
Branches of spinal nerves outside the spinal cord:
Meningeal branch.
Posterior branch/ramus.
Anterior branch/ramus.
Visceral branch (only in thoracic and lumbar).

20. Nerve Plexuses Nerve plexus:
Complex network formed by anterior rami (branches) of spinal nerves.
Not in T2 through T12(become intercostal nerves)
There are 3 nerve plexuses: Cervical, Brachial, Lumbosacral.
Cervical plexus:
Formed by anterior rami (branches) of C1-C4 spinal nerves.
Lies deep in the neck.
Supply muscles and skin of the neck.
C3-C4-C5 nerve roots contribute to phrenic nerves, which transmit motor impulses to the diaphragm.
The fibers of various spinal nerves are sorted and recombined, so all fibers heading to same peripheral body part reach it in the same nerve.

22. Brachial Plexus 5 branches: Formed by anterior branches C5- T1.
Lies deep within shoulders.
5 branches:
Musculocutaneous nerve: Supply muscles of anterior arms & skin of forearms.
Ulnar and Median nerves: Supply muscles of forearms & hands, skin of hands.
Radial nerve: Supply posterior muscles of arms and skin of forearms & hands.
Axillary nerve: Supply muscles and skin of anterior, lateral, & posterior arms.

23. Lumbosacral Plexus Lumbosacral plexus:
Formed by the anterior branches of L1-S4 roots.
Lumbar portions are in lumbar regions of the abdomen, and the sacral portions are in pelvic cavity.
Obturator nerve: Supply motor impulses to adductors of thighs Femoral nerve: Supply motor impulses to muscles of anterior thigh and sensory impulses from skin of thighs and legs
Sciatic nerve: Supply muscles and skin of thighs, legs and feet; largest and longest nerve in the body

24. Clinical Application 11.7 Spinal Nerve Injuries
Caused by birth injuries, dislocations, vertebral fractures, stabs, gunshot wounds, pressure from tumors
Whiplash: sudden bending of the neck, compression of cervical plexus nerves; leads to persistent headache, pain in neck
Broken or dislocated vertebra in neck can sever or damage axons leading to the phrenic nerves can result in paralysis of diaphragm
Thoracic outlet syndrome: pressure on brachial plexus, due to continuous flexion of arm (as in painting or typing); results in pain in neck, shoulder, upper limb
Sciatica: compression of intervertebral disc in lumbar region; results in pain in lower back, gluteal region, and perhaps thigh, calf, foot
Carpal tunnel syndrome: repeated movements of hand inflame tendons that pass through carpal tunnel (space between bones in wrist); swelling in tendons compresses median nerve, resulting in pain in the arm, wrist

25. Autonomic Nervous System
Autonomic Nervous System (A N S):
Peripheral nervous system (P N S)
Involuntary
Controls visceral activities
Regulates smooth muscle, cardiac muscle, and glands
Homeostasis
Helps body respond to stress
Prepares body for exercise, intense physical activity

26. General Characteristics of the A N S
Sensory (afferent) nerve fibers transmit signals from the viscera and skin to neural centers in C N S.
Motor (efferent) impulses travel along 2 efferent nerve fibers which synapse in ganglia outside C N S.
Muscles or glands respond to nerve impulses by contracting, secreting, or being inhibited.
2 divisions of the autonomic nervous system:
Sympathetic division:
Prepares body for ‘fight or flight’ situations; speeds body up.
Most active under energy-requiring, stressful, emergency situations.
Parasympathetic division:
Prepares body for ‘resting and digesting’ activities; slows body down.
Most active under resting, non-stressful conditions.
***Most organs receive input from both divisions.

28. Autonomic Nerve Fibers
All of the neurons are motor (efferent) Somatic motor pathways link the C N S and a skeletal muscle fiber via 1 neuron Autonomic motor pathways contain 2 neurons:
Preganglionic fibers:
Axons of preganglionic neurons.
Neuron cell bodies are in C N S.
Postganglionic fibers:
Axons of postganglionic neurons.
Neuron cell bodies in ganglia.
Extend to visceral effector.

29. Sympathetic Division Thoracolumbar division (T1 – L2).
Preganglionic fibers originate in spinal cord, leave via ventral roots, leave spinal nerves through white rami and enter sympathetic chain (paravertebral) ganglia.
Sympathetic chain ganglia + fibers that connect them make up the sympathetic trunks.

30. Sympathetic Division
Sympathetic chain ganglia lie some distance from viscera they regulate.
Other sympathetic ganglia are close to viscera.
Example: collateral ganglia in abdomen lie close to some large blood vessels.

31. Sympathetic Division Preganglionic fibers may do any of the following:
Synapse with a postganglionic neuron in a paravertebral ganglion.
Continue through a paravertebral ganglion, and synapse at another sympathetic ganglion.
Pass through to collateral ganglia to synapse there.
Postganglionic fibers:
Extend from sympathetic ganglia to visceral effector organs.
Postganglionic fibers that originate at paravertebral ganglia usually pass through gray rami and return to a spinal nerve before proceeding to an effector.
Exception: preganglionic fibers pass through sympathetic ganglia and extend to adrenal medulla; these terminate on hormone-secreting cells that release epinephrine and norepinephrine.

32. Sympathetic Division

33. Parasympathetic Division
Craniosacral division.
Preganglionic neurons originate in brainstem and S2 – S4 spinal levels.
Preganglionic fibers extend out on cranial or sacral nerves to terminal ganglia (near or in visceral organs).
Short postganglionic fibers continue to specific muscles or glands.
Preganglionic fibers of the head are included in oculomotor (III), facial (VII), and glossopharyngeal (IX) nerves.
Preganglionic fibers of thorax and abdomen are parts of vagus (X) nerve, which contains
of all parasympathetic fibers.
Preganglionic fibers of sacral (S2 – S4) region of spinal cord carry impulses to pelvic viscera.

34. Parasympathetic Division

35. Autonomic Neurotransmitters
Cholinergic neurons:
Release acetylcholine
All preganglionic sympathetic and parasympathetic fibers
Postganglionic parasympathetic fibers
Adrenergic neurons:
Release norepinephrine (noradrenaline)
Most postganglionic sympathetic fibers

36. Actions of Autonomic Neurotransmitters
Actions result from binding to protein receptors in the membrane of effector cells in synapses or neuromuscular junctions:
Cholinergic receptors:
Bind to acetylcholine; 2 types:
Muscarinic receptors: Excitatory, slow, also activated by fungal toxin, muscarine.
Nicotinic receptors: Excitatory, rapid, also activated by tobacco toxin, nicotine.
Adrenergic receptors:
Bind to epinephrine and norepinephrine; 2 types:
Alpha and beta receptors: Elicit different responses on various effectors.

37. Terminating Autonomic Neurotransmitter Actions
After acting at a synapse or neuromuscular junction, neurotransmitters must be removed/inactivated, to prevent continued stimulation of the postsynaptic cell:
The enzyme acetylcholinesterase (A C h E) rapidly decomposes the acetylcholine that cholinergic fibers release
Norepinephrine from adrenergic fibers is removed from synapse by active transport, and then inactivated by the enzyme monoamine oxidase (M A O)

38. Control of Autonomic Activity
Controlled by hypothalamus.
Involuntary
Medulla oblongata regulates cardiac, vasomotor and respiratory activities.
Hypothalamus regulates visceral functions, such as body temperature, hunger, thirst, and water and electrolyte balance.
Autonomic reflex centers occur in medulla oblongata and spinal cord.
Reflex centers in medulla oblongata control cardiac, vasomotor, respiratory activities.
Limbic system and cerebral cortex control emotional responses.

39. Life-Span Changes
Brain cells begin to die before birth, due to apoptosis, a form of normal programmed cell death.
Over average lifetime, brain shrinks 10%
More gray matter than white matter is lost with aging
Many cells die in temporal lobes, but few in brainstem
By age 90, frontal cortex has lost half its neurons
Number of dendritic branches in cerebral cortex decreases
Decreased levels of neurotransmitters
Action potentials propagation rate declines by 5-10%
Fading memory
Slowed responses and reflexes
Increased risk of fainting, falling
Changes in sleep patterns that result in fewer sleeping hours