Download The Peripheral Nervous System

The Peripheral
Nervous System
The Peripheral Nervous System
What we already know… the PNS is/has
– Nervous structures outside the brain and spinal cord
– Nerves allow the CNS to receive information and take action
– Functional components of the PNS
• Afferent (Sensory)
– Has somatic and visceral components
» Each with a general and special functional subdivision
• Efferent (Motor)
– Has somatic and visceral components
» Somatic efferent – voluntary skeletal muscles
» Visceral efferent – Autonomic Nervous System (ANS)
divided into the Sympathetic & Parasympathetic Divisions
The Peripheral Nervous System
• Basic structural components of the PNS
– Sensory receptors
• Respond by transducing the stimulus into an action potential
– Motor endings
• The interface between the efferent neurons and the effector (neuromuscular junctions, neuroglandular junctions)
– Nerves & Ganglia
The Peripheral Nervous System
Peripheral Sensory Receptors
• Structures that pick up sensory stimuli
– Initiate signals in sensory axons
• Classification of peripheral sensory receptors may be
– By location
– By stimulus detected
– By structure
Classification by Location
• Exteroceptors
– located at or near body surfaces
• sensitive to stimuli arising from outside the body
• Include receptors for touch, pressure, pain, and temperature as well as receptors of special senses
• Interoceptors
– located in the viscera (visceroceptors) • receive stimuli from internal viscera
• monitor a variety of stimuli
– Pain (visceral), hunger & satiety, nausea
• Proprioceptors
– located in musculoskeletal organs
• monitor degree of stretch
Classification by Structure
• Peripheral Sensory Receptors are divided into two groups
– Free nerve endings
– Encapsulated nerve endings
• Both types are general sensory receptors with. . .
– Wide distribution – Nerve endings that monitor:
• Touch, pressure, vibration, stretch, pain, temperature and proprioception Three Types of Proprioceptors
• Muscle spindles
– Imbedded in the perimysium between muscle fascicles
– measure the changing length of a muscle
• Golgi tendon organs
– located near the muscle‐tendon junction
– Monitor tension within tendons • Joint kinesthetic receptors – Sensory nerve endings within the joint capsules
Neural Junctions in the PNS
• Neuromuscular
• Neuroglandular
• Neuralneural
The PNS Nerves & Ganglia
• Cranial Nerves
• Spinal Nerves
• Autonomic Nervous System
Cranial Nerves
• Attach to the brain and pass through foramina of the skull
• Numbered from I–XII
• Cranial nerves I and II attach to the forebrain
– All others attach to the brain stem
• Primarily serve head and neck structures
– The vagus nerve (X) extends into the abdomen The 12 Pairs of Cranial Nerves
Figure 14.8
Cranial Nerve Mnemonic Devices
• Name
– Oh, Oh, Oh To Touch And Feel Very Green Vegetables, Always Heavenly
• Function
– Some Say Marry Money But My Brother Says Bad Boys Marry Money
I. Olfactory
• Sensory‐ Smell
– Passes through cribiform plate of ethmoid bone
– Origin in olfactory bulbs
*
II. Optic
• Sensory‐ sight
• Signals terminate in occipital lobe via lateral geniculate nucleus in thalamus
• Optic chiasma‐
optic nerves cross (Named for the Greek letter Chi X)
*
III. Oculomotor
• Somatic motor‐eye movement: controls 4 of 6 eye muscles (superior, inferior & medial rectus muscles and inferior oblique) and upper eyelid
*
IV. Trochlear
• trochlea= pully
• Somatic motor‐ controls superior oblique of eye (this muscle has a pulley)
*
V. Trigeminal
• Mixed(sensory & motor)
• Three branches
– Opthalmic branch‐ sensory(orbit, nose, sinuses, forehead, eyelids & eyebrows)
– Maxillary branch‐ sensory(lower eyelid, upper lip, nose, cheek, gums & teeth)
– Mandibular branch‐ mixed(motor & sensory)
• Motor‐ muscles of mastication
• Sensory‐ proprioception, temples, salivary glands, teeth & gums, anterior tongue
V. Trigeminal
*
VI. Abducens
• Somatic motor‐ eye movement: lateral rectus
*
VII. Facial
• Mixed(sensory & motor)
– Sensory‐
proprioception of face, and taste
– Somatic Motor‐
superficial muscles of face & scalp, – Autonomic motor‐
lacrimal gland, nasal cavity & pharynx, salivary glands
*
Bells palsy- paralysis of facial nerve
(the most common acute mononeuropathy)
VIII. Vestibulocochlear
Sensory‐ balance, equilibrium, (vestibule/semicircular canals) hearing(cochlea)
*
IX. Glossopharyngeal
• Mixed (sensory & motor)
– Sensory‐ posterior tongue pharynx & palate, carotid arteries(blood pressure & pH
– Somatic motor‐
swallowing
*
X. Vagus
*
• Mixed (sensory & motor)
– Visceral sensory‐
pharynx, auricle, external auditory meatus, diaphragm and visceral organs
– Visceral motor‐
autonomic: heart, respiratory tract, stomach and intestines
XI. Accessory
• Somatic Motor‐
swallowing and vocal cords
• Note that some motors fibers originate from spinal cord in the neck(spinal root & merge with the cranial root
*
XII. Hypoglossal
• Somatic Motor‐
tongue
Gloss= tongue
Hypo= below
*
Spinal Nerves
• 31 pairs – contain thousands of nerve fibers
• Connect to the spinal cord
• Named for point of issue from the spinal cord
– 8 pairs of cervical nerves (C1‐C8)
– 12 pairs of thoracic nerves (T1‐T12)
– 5 pairs of lumbar nerves (L1‐L5)
– 5 pairs of sacral nerves (S1‐S5)
– 1 pair of coccygeal nerves (Co1)
Spinal Nerves Posterior View
Figure 14.9
Spinal Nerves
• Branch into dorsal ramus and ventral ramus
• Rami communicantes connect to the base of the ventral ramus
– Lead to the sympathetic chain ganglia
• Dorsal and ventral rami contain sensory and motor fibers
Spinal Nerves
Figure 14.10a
Innervation of the Back
Figure 14.10b
Nerve Plexuses
• Nerve plexus – a network of nerves
• Ventral rami (except T2‐T12)
– Branch and join with one another – Form nerve plexuses
• In cervical, brachial, lumbar, and sacral regions
– Primarily serve the limbs
– Fibers from ventral rami crisscross The Cervical Plexus
• Buried deep in the neck
– Under the sternocleidomastoid muscle
• Formed by ventral rami of first four cervical nerves
• Most are cutaneous nerves
• Some innervate muscles of the anterior neck
• Phrenic nerve – the most important nerve of the cervical plexus
Cervical Plexus Nerves
The Brachial Plexus and Innervation of the Upper Limb
• Brachial plexus lies in the neck and axilla
• Formed by ventral rami of C5‐C8
• Cords give rise to main nerves of the upper limb Figure 14.12d
Brachial plexus & nerves
The Lumbar Plexus and Innervation of the Lower Limb
• Lumbar plexus – Arises from L1‐L4
– Smaller branches innervate the posterior abdominal wall and psoas muscle
– Main branches innervate the anterior thigh
• Femoral nerve – innervates anterior thigh muscles
• Obturator nerve – innervates adductor muscles
The Sacral Plexus
• Arises from spinal nerves L4‐S4
• Caudal to the lumbar plexus
• Often considered with the lumbar plexus
– Lumbosacral plexus
Innervation of the Skin: Dermatomes
• Dermatome –
– an area of skin that is innervated by cutaneous branches of a single spinal nerve
• Upper limb
– skin is supplied by nerves of the brachial plexus
• Lower limb – Lumbar nerves – anterior surface
– Sacral nerves – posterior surface
Map of Dermatomes
Figure 14.17a,b
The Autonomic Nervous System and Visceral Sensory Neurons
The Autonomic Nervous System and Visceral Sensory Neurons
• The ANS – a system of motor neurons
– The general visceral motor division of the PNS
– Innervates smooth muscle, cardiac muscle, and glands
– Regulates visceral functions
• Heart rate, blood pressure, digestion, urination . . .
The Autonomic Nervous System and Visceral Sensory Neurons
Comparison of Autonomic and Somatic Motor Systems
• Somatic motor system
– One motor neuron extends from the CNS to skeletal muscle
– Axons are well myelinated, conduct impulses rapidly
• Visceral Motor (Autonomic nervous) system
– Chain of two motor neurons
• Preganglionic neuron
• Ganglionic neuron
– Conduction is slower due to thinly or unmyelinated axons
Comparison of Autonomic and Somatic Motor System Pathways
Divisions of the Autonomic Nervous System
• Sympathetic and parasympathetic divisions
– Chains of two motor neurons
• Exhibits dual innervation
– Nerves of both divisions innervate mostly the same structures
• Cause opposite effects
• Sympathetic – “fight, flight, or fright”
– Activated during exercise, excitement, and emergencies
– Concerned with liberating energy resources
• Parasympathetic – “rest and digest”
– Concerned with conserving and storage of energy
Differences in ANS Divisions
• From different regions of the CNS
– Sympathetic – also called the thoracolumbar division
– Parasympathetic –
also called the craniosacral division
Differences in ANS Divisions
• Length of postganglionic fibers
– Sympathetic – long postganglionic fibers
– Parasympathetic – short postganglionic fibers
• Branching of axons
– Sympathetic axons – highly branched • Influences many organs
– Parasympathetic axons – few branches • Localized effect
• Neurotransmitter released by postganglionic axons
– Sympathetic – most release norepinephrine (adrenergic)
– Parasympathetic – release acetylcholine
Sympathetic Pathway
Parasympathetic Pathway
The Parasympathetic Division
• Cranial outflow – Comes from the brain
– Innervates organs of the head, neck, thorax, and abdomen
• Sacral outflow – Supplies remaining abdominal and pelvic organs
The Sympathetic Division
• Basic organization
– Issues from T1‐L2
– Preganglionic fibers form the lateral gray horn
– Supplies visceral organs and structures of superficial body regions
– Contains more ganglia than the parasympathetic division
• Sympathetic trunk ganglia
• Prevertebral ganglia
The Role of the Adrenal Medulla in the Sympathetic Division
• Major organ of the sympathetic nervous system
• Constitutes largest sympathetic ganglia • Secretes great quantities of norepinephrine and adrenaline • Stimulated to secrete by preganglionic sympathetic fibers
Visceral Sensory Neurons
• General visceral sensory neurons monitor:
– Stretch, temperature, chemical changes, and irritation
• Cell bodies are located in the dorsal root ganglia
• Visceral pain – perceived to be somatic in origin
– Referred pain
A Map of Referred Pain
Visceral Reflexes
• Visceral sensory and autonomic neurons
– Participate in visceral reflex arcs
• Defecation reflex
• Micturition reflex
• Some are simple spinal reflexes
• Others do not involve the CNS – Strictly peripheral reflexes
Visceral Reflex Arc
Special Senses
• Senses that have specific concentration of receptors
– Vision
– Hearing/Equilibrium
– Smell
– Taste
Visual Pathway
• Optic nerve
• Optic chiasma
• Optic radiations
– Lateral geniculate body radiates to visual cortex
– Pulvinar (lateral thalamic mass) radiates to visual association areas
– Other radiations to various nuclei involved in visual reflexes Vision
• The Eye
Vision
• Retinal Layers
– Outer
• Photoreceptors
– Inner
• bipolar, horizontal and amacrine cells
– Ganglion layer
• Ganglion cells
– Optic fiber layer
• Forms the optic nerve
The Ear – Hearing & Equilibrium
1.
Sound
waves enter
2.
Sound
waves
modified
3.
4.
Sound
waves
parsed &
transduced
Action
potentials
sent
4
2
1
3
The Ear – Cochlea Detail
1. scala vestibuli
2. scala media
(chochlear duct)
3. scala tympani
4. hair cells
5. tectorial
membrane
6. cochlear nerve
fibers
7. basilar membrane
8. spiral lamina
(osseous)
8
1
2
5
7
4
6
3
Basilar Membrane Resonance Frequencies
The Ear – Vestibule & Semicircular Canals
Relationship between bony and membranous labyrinth in the inner ear
Olfaction
Taste
Taste