Peripheral Nervous System

somatic nerves types

• spinal nerves and cranial nerves

• voluntary control of muscles

spinal nerves

• arise from the spinal cord

• emerge from vertebrae

• mixed nerve - sensory and motor

• dorsal root

• ventral root

• convergence of doral branch and a ventral branch

• supply innervation to structures dorsal and ventral to the transverse processes of the vertebrae

• supply sensory and motor fibers to the region of the body in the area where they emerge from the spinal cord

dorsal root vs ventral root

• dorsal root

  • carries afferent (sensory) impulses from the periphery toward the spinal cord

  • the nerve cell bodies of the neurons composing the dorsal root are located in the dorsal root ganglion

• ventral root

  • carries efferent (motor) impulses from the spinal cord to striated muscle

cranial nerves

• 12 pairs

• supply innervation to the head and neck

  • except vagus nerve

• no dorsal or ventral roots

• can be strictly sensory, strictly motor, or a mix

• some have parasympathetic function

  • so not all are sympathetic

1 olfactory nerve

• sensory

• nasal mucous membrane - olfaction

• suits above nasal epithelium

• sends signal through sinus

2 optic nerve

• sensory

• retina of the eye

3 oculomotor

• motor

• most of eye muscle

4 Trochlear

• motor

• dorsal oblique muscle of the eye

5 Trigeminal

• mixed

• three branches

• sensory to eye and face

•  motor to muscles of mastication

6 Abducens

• motor

• retractor and lateral muscles of the eye

• moves eyes laterally

7 Facial

• mixed

• sensory

  • ear, cranial ⅔ tongue

• motor

  • muscles of facial expression

  • squinting, smiling, chewing

8 Vestibulocochlear

• sensory

• cochlea - hearing 

• semicircular canals - equilibrium

9 Glossopharyngeal

• mixed

• sensory

  • pharynx

  • tase to caudal aspect of tongue

• motor

  • muscles of pharynx

10 Vagus

• mixed

• sensory

  • pharynx and larynx

• motor

  • larynx

• parasympathetic

  • visceral structures in the thorax and abdomen

11 Accessory

• motor

• muscles of shoulder and neck

12 Hypoglossal

• motor 

• muscles of tongue 

innervation of appendages

• innervated by the ventral branches of several spinal nerves

• join together in braid-like arrangements known as plexuses

• brachial plexus

  • supplies nerves to the forelimbs

• lumbosacral plexus

  • supplied by nerves to the hindlimbs

autonomic nerves basics

• visceral nerves

• involuntary functions 

  • smooth, cardiac, glands

• essential for maintaining normal organ function, adapting to environmental change, and replying to stresses

• sympathetic nervous system

• parasympathetic nervous system

• enteric nervous system

• thoracolumbar

• craniosacral

• two neurons

sympathetic nervous system

• associated with the body’s response to stress

• fight, fright, flight

• preganglionic neuron short, postganglionic long

  • bilateral ganglia along length of spinal cord

parasympathetic nervous system

• associated with homeostatic functions in the absence of stress

• eat or sleep

• preganglionic long, postganglionic short

  • ganglia near effector organs

enteric nervous system

• associated with regulation of the gastrointestinal system

thoracolumbar

• sympathetic

• cells or origin located on lateral masses of ventral horns and thoracic and lumbar spinal cord

craniosacral

• parasympathetic

• cells or origin are located in the brainstem and sacral segments of spinal cord

two neurons

• preganglionic

  • transmit impulse from cells of origin in the spinal cord to brain to second neuron

• post-ganglionic 

  • transmit impulse to effector organ

autonomic reflexes

• autonomic function is based on reflex activity

• functions as blood pressure, heart rate, and activity of the digestive and urogenital systems

• some afferent information reaches conscious level

  • feeling of full bladder

  • most restricted to level of spinal cord

neurotransmitters

• nerve impulse causes and effect at a synapse or at the structure being innervated

• axon branches terminate with a structure known as a presynaptic terminal bulb

• terminations have vesicles containing chemical substances that are liberated when the impulse arrives

• chemical substance then diffuses to the membrane of the postsynaptic neuron or structure

peripheral neurotransmitters

• neurotransmitters of the somatic PNS are excitatory

• increase the permeability of the affected membrane for sodium ion

• ACh for the somatic spinal and cranial nerves

• Cholinergic system

• Adrenergic system

Cholinergic system

• parasympathetic

• ACh the preganglionic and postganglionic terminal neurotransmitter for the parasympathetic division

Adrenergic system

• sympathetic

• ACh is the neurotransmitter for the preganglionic neuron

• norepinephrine at the post ganglionic neuron

inhibitory neurotransmitters

• neurotransmitters decrease post synaptic membrane permeability to sodium

  • don't send the signal

  • gamma-aminobutyric acid and glycine

excitatory neurotransmitters

• neurotransmitters increase postsynaptic membrane permeability for sodium

  • send signal

  • ACh, norepinephrine, glutamate

ANS

• sympathetic

• parasympathetic

sympathetic - basics

• adrenal medulla makes and releases adrenaline

  • sympathetic response when sympathetic nerves are stimulated

sympathetic - receptor classes

• 2 receptors receive signals

  • alpha adrenergic

  • beta adrenergic

  • different receptors bind epinephrine and norepinephrine preferentially

    • slightly different response in similar body tissues in different body parts

    • sympathetic stimulation causes general vasoconstriction but causes vasodilation in heart and skeletal muscle 

sympathetic - effects on body

• fight or flight

• increases heart rate

• force of contraction of heart

• increase blood pressure

• general vasocontraction but vasodilation to cardiac and skeletal muscles

  • blood vessels limit blood supply to important areas

• decreased gastrointestinal activity

• pupil dilation

  • mydriasis

• bronchodilation

  • more oxygen enters the lungs

parasympathetic - basics

• resting

• 2 sets of neurons begin in craniosacral region with long preganglionic fibers that release ACh at NT synapse

• ganglia near or in wall of organs

• short postganglionic fibers with ACh at NT synapse with organ cells

• always ACh released at preganglionic fibers

parasympathetic - receptor classes

• nicotinic

  • reacts with nicotine

• muscarinic

  • reacts with muscarine

parasympathetic - effects on body

• decreases HR and BP

• increased gastrointestinal activity

• general vasodilation

• pupil restriction

• bronchoconstriction

  • not as much oxygen needed