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C H A P T E R T H I R T E E N. THE NERVOUS SYSTEM: NEURAL TISSUE. Two organ systems coordinate and direct activities of body. Nervous system Swift, brief responses to stimuli Endocrine system Adjusts metabolic operations Directs long-term changes.

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the nervous system neural tissue



two organ systems coordinate and direct activities of body
Two organ systems coordinate and direct activities of body
  • Nervous system
    • Swift, brief responses to stimuli
  • Endocrine system
    • Adjusts metabolic operations
    • Directs long-term changes
nervous system includes all neural tissue in body
Nervous system includes all neural tissue in body
  • Central Nervous System
    • Brain and spinal cord
  • Peripheral Nervous System
    • All neural tissue outside CNS
functional divisions of nervous system
Functional divisions of nervous system
  • Afferent
    • Sensory information from receptors to CNS
  • Efferent
    • Motor commands to muscles and glands
    • Somatic division
      • Voluntary control over skeletal muscle
    • Autonomic division
      • Involuntary regulation of smooth and cardiac muscle, glands
cells in nervous tissue
Cells in Nervous Tissue
  • Neurons
  • Neuroglia
neuroglia glia
Neuroglia (Glia)
  • about half the volume of cells in the CNS
  • smaller than neurons
  • 5 to 50 times more numerous
  • do NOT generate electrical impulses
  • divide by mitosis
  • Four types in the CNS
    • Astrocytes
    • Oligodendrocytes
    • Microglia
    • Ependymal cells
  • Largest of glial cells
  • Most numerous
  • Star shaped with many processes

projecting from the cell body

  • Help form and maintain blood-brain barrier
  • Provide structural support for neurons
  • Maintain the appropriate chemical

environment for generation of nerve impulses/action potentials

  • Regulate nutrient concentrations for neuron survival
  • Regulate ion concentrations - generation of action potentials by neurons
  • Take up excess neurotransmitters
  • Assist in neuronal migration during brain development
  • Perform repairs to stabilize tissue
  • Most common glial cell type
  • Each forms myelin sheath around the axons of neurons in CNS
  • Analogous to Schwann cells of PNS
  • Form a supportive network around CNS neurons
  • fewer processes than astrocytes
  • round or oval cell body
  • few processes
  • derived from mesodermal cells
  • that also give rise to monocytes
  • and macrophages
  • Small cells found near blood vessels
  • Phagocytic role - clear away dead cells
  • protect CNS from disease through phagocytosis of microbes
  • migrate to areas of injury where they clear away debris of

injured cells - may also kill healthy cells

representative neuron
Representative Neuron

  • -neurofilaments or neurofibrils give cell shape and support - bundles of
  • intermediate filaments
  • -microtubules move material inside cell
  • -lipofuscin pigment clumps (harmless aging) - yellowish brown
  • 1. cell body or soma
    • -single nucleus with prominent nucleolus
    • -Nissl bodies
      • -rough ER & free ribosomes for protein synthesis
      • -proteins then replace neuronal cellular components for growth
      • and repair of damaged axons in the PNS


2. Cell processes = dendrites (little trees)

- the receiving or input portion of the neuron

-short, tapering and highly branched

-surfaces specialized for contact with other neurons

-cytoplasm contains Nissl bodies & mitochondria


3. Cell processes = axons

  • Conduct impulses away from cell body-propagates nerve impulses to another neuron
  • Long, thin cylindrical process of cell
  • contains mitochondria, microtubules & neurofibrils - NO ER/NO protein synth.
  • joins the soma at a cone-shaped elevation = axon hillock
  • first part of the axon = initial segment
  • most impulses arise at the junction of the axon hillock and initial segment = trigger zone
  • cytoplasm = axoplasm
  • plasma membrane = axolemma
  • Side branches = collaterals arise from the axon
  • axon and collaterals end in fine processes called axon terminals
  • Swollen tips called synaptic end bulbs contain vesicles filled with neurotransmitters

  • Ability of cell membrane to conduct electricity
    • Skeletal muscle fibers
    • Most neurons
  • Changes in membrane potential induces an action potential (AP)
    • the PM of neurons exhibits a membrane potential = electrical voltage difference across the membrane
    • in excitable cells like neurons this potential = resting potential
    • due to differences in sodium and potassium ion concentration in and out of the cell
      • potassium is higher inside cell, sodium is higher outside
      • inside of the cell has a higher concentration of negative phosphate ions and proteins = potential of -40 to -90 mV
  • the cell is said to be polarized
  • membrane has sodium/potassium pumps
  • to maintain specific concentrations of these ions in
  • & out of the neurons and therefore maintain the
  • resting membrane potential
  • -move three Na+ out and 2 K+ in
  • -inside of the neuron is slightly
  • negative
action potential
Action Potential
  • Resting membrane potential is -70mV
  • threshold usually -55 MV
  • Depolarization is the change from -70mV to +30 mV
  • Repolarization is the reversal from +30 mV back to -70 mV)

  • action potential = nerve impulse
  • takes place in two stages: depolarizing phase (more positive) and repolarizing phase (more negative - back toward resting potential)
  • followed by a hyperpolarizing phase or refractory period in which no new AP

can be generated


depolarization (increase in MP) results from opening of Na+ channels. Once threshold is

reached, more Na+ channels open and a rapid

increase in MP results

outflow of K+ restores the MP. Na+ channels begin to open and K+ channels close. K+ outflow results in hyperpolarization (below resting)

results in a refractory period.

more slowly, depolarization also

opens K+ channels which permit

the outflow of K+ . The Na+ close

the MP becomes more negative

returning to resting

local anesthetics
Local Anesthetics
  • Prevent opening of voltage-gated Na+ channels
  • Nerve impulses cannot pass the anesthetized region
  • Novocaine and lidocaine – blocks nerve impulses along nerves that detect pain
  • Synapse
    • Site of intercellular communication between 2 neurons or between a neuron and an effector (e.g. muscle)
  • Originates in the soma
  • Travels along axons
  • Permit communication between neurons and other cells
    • Initiating neuron = presynaptic neuron
    • Receiving neuron = postsynaptic neuron
  • two types: chemical & electrical
  • NT will cause either and excitatory or inhibitory response
  • If the NT depolarizes the postsynaptic neuron= excitatory
  • More than 100 identified
  • Some bind receptors and cause channels to open
  • Others bind receptors and result in a second messenger system
  • Results in either excitation or inhibition of the target
  • botulism causes paralysis through blockage of AcH release from motor
  • neurons
  • 1. small molecules: e.g. Acetylcholine (ACh)
    • -All neuromuscular junctions use ACh
    • -ACh also released at chemical synapses in the PNS and by some CNS neurons
    • -Can be excitatory at some synapses and inhibitory at others

2. Amino acids: glutamate & aspartate & GABA

  • Stimulate most excitatory neurons in the CNS (about ½ the neurons in the brain)
  • Binding of glutamate to receptors opens calcium channels = excitatory response
  • GABA (gamma amino-butyric acid) is an inhibitory neurotransmitter for 1/3 of all brain synapses

Valium is a GABA agonist - enhancing its inhibitory effect


3. Biogenic amines: modified amino acids

  • catecholamines:norepinephrine (NE), epinephrine, dopamine (tyrosine)
  • serotonin - concentrated in neurons found in the brain region = raphe nucleus
    • derived from trytophan
    • sensory perception, temperature regulation, mood control, appetite, sleep induction
    • feeling of well being
  • NE - role in arousal, awakening, deep sleep, regulating mood
  • epinephrine (adrenaline) - flight or fight response
  • dopamine - emotional responses and pleasure, decreases skeletal muscle tone
  • Parkinsons - muscle stiffness due to degeneration of dopanergic nerves
      • patients given L-Dopa (dopamine precursor)
  • amphetamines promote dopamine and NE release
  • isoproterenol binds to epinephrine receptors
    • - used in asthma to mimic the effects of epinephrine
  • schizophrenia - excess of dopamine
    • Zyprexa blocks dopamine and serotonin receptors
      • -antagonizes the effects of serotonin and dopamine
  • cocaine: blocks transporters for dopamine reuptake
  • Prozac, Paxil: blocks transporters for serotonin reuptake

Other types:

Nitric oxide - formed on demand in the neuron then release (brief lifespan)

-role in memory and learning

-produces vasodilation - Viagara enhances the effect of NO



  • widespread in both CNS and PNS
  • excitatory and inhibitory
  • act as hormones elsewhere in the body
  • -Substance P -- enhances our perception of pain
  • -opoid peptides: endorphins - release during stress, exercise
  • enkephalins - analgesics
  • (200x stronger than morphine)
  • -pain-relieving effect by blocking the release of
  • substance P
  • dynorphins - regulates pain and emotions
  • **acupuncture may produce loss of pain sensation because of release of opioid-like substances such as endorphins or dynorphins

Divisions of the nervous system

  • Sensory pathway
    • Ascending
    • Information from sensory receptors to CNS
  • Motor pathway
    • Descending
    • Information from CNS to skeletal muscle or glands
    • Direct pathways – cause precise, voluntary movements
    • Indirect pathways – result in involuntary movement (from brain stem)
functional classification of neurons
Functional Classification of Neurons
  • Sensory (afferent) neurons
    • transport sensory information from skin, muscles, joints, sense organs & viscera to CNS
  • Motor (efferent) neurons
    • send motor nerve impulses to muscles & glands
  • Interneurons (association) neurons
    • connect sensory to motor neurons
    • 90% of neurons in the body
sensory neurons
Sensory Neurons
  • Afferent division of PNS
  • Deliver sensory information from sensory receptors to CNS
    • free nerve endings: bare dendrites associated with pain, itching, tickling, heat and some touch sensations
    • Exteroceptors: located near or at body surface, provide information about external environment
    • Proprioceptors: located in inner ear, joints, tendons and muscles, provide information about body position, muscle length and tension,

position of joints

    • Interoceptors: located in blood vessels, visceral organs and NS

-provide information about internal environment

-most impulses are not perceived – those that are,

are interpreted as pain or pressure


Sensory Neurons

  • Sensory receptors cont…
    • mechanoreceptors: detect pressure, provide sensations of touch, pressure,

vibration, proprioception, blood vessel stretch, hearing and equilibrium

    • thermoreceptors: detect changes in temperature
    • nociceptors: respond to stimuli resulting from damage (pain)
    • photoreceptors: light
    • osmoreceptors: detect changes in OP in body fluids
    • chemoreceptors: detect chemicals in mouth (taste), nose (smell)

and body fluids

-analgesia: relief from pain

-drugs: aspirin, ibuprofen – block formation of prostaglandins that

stimulate the nociceptors

-novocaine – block nerve impulses along pain nerves

-morphine, opium & derivatives (codeine) – pain is felt but not perceived in

brain (blocks morphine and opiate receptors in pain centers)

motor neurons
Motor Neurons
  • Efferent pathways
  • Stimulate peripheral structures
    • Somatic motor neurons
      • Innervate skeletal muscle
    • Visceral motor neurons
      • Innervate all other peripheral effectors
      • Preganglionic and postganglionic neurons

Somatic nervous system (SNS):

1. sensory - neurons that convey sensory information from somatic

receptors in the head, body wall, senses - to the CNS

2. control of motor output - neurons that conduct voluntary impulses to skeletal muscles

-contributions from the basal ganglia, cerebellum, brain stem and SC

3. one neuron pathway – somatic motor neurons synapse directly with the effector

4. neurotransmitter – usually acetylcholine

5. effectors – skeletal muscles

6. responses - contraction


Autonomic nervous system (ANS):

  • sensory - neurons that convey info from autonomic sensory receptors in the visceral organs - to the CNS
  • 2. control of motor output - neurons that conduct impulses from the CNS to
  • smooth and cardiac muscle & glands
  • 3. two neuron pathway – preganglionic neurons extend from CNS and synapse with postganglionic neurons in an autonomic ganglion, postganglionic neurons then synapse with the effector
  • 4. neurotransmitter – preganglionic – ACh
  • -postganglionic – ACh or norepinephrine
  • 5. effectors – smooth & cardiac muscle, glands,
  • 6. responses – contraction or relaxation of SM
  • -increased or decrease heart contraction
  • -increased or decreased gland secretions

- motor output branch has two divisions:

1. sympathetic

2. parasympathetic

-most organs are innervated by

both divisions which have

opposing functions

e.g. sympathetic – increases heart rate

parasympathetic – decreases rate


figure 15 1 major divisions of the brain

Major Regions of the Brain

Figure 15.1 Major Divisions of the Brain


I - Olfactory

II - Optic

III - Oculomotor


V - Trigeminal

VI - Abducens

VII - Facial

VIII - Acoustic

IX - Glossopharyngeal

X - Vagus

XI - Accessory

XII - Hypoglossal

  • -cranial nerves – 12 pairs
  • -considered part of the peripheral nervous system (PNS)
  • -olfactory & optic contain only sensory axons = sensory nerves
  • -some are motor nerves – e.g. oculomotor, trochlear etc….
  • remaining are mixed nerves – both motor and sensory axons
  • “some say my mother bought my brother some bitter beer, my, my”

the olfactory nerve i
The Olfactory Nerve (I)
  • Carries sensory information
    • Sense of smell from nasal mucosa to brain
  • Branches enter skull through cribiform plate
    • Synapses within olfactory bulbs
The optic nerve (II) (sensory)
    • Carries visual information
    • enters skull through optic canal

of the sphenoid

-right and left join at the

optic chiasma (site of cross-over)

-continue to brain as optic tracts


The oculomotor nerve (III) [Motor]

    • Primary source of innervation for extra-ocular muscles
    • also carries postganglionic fibers that innervate the ciliary muscles (lens shape)
    • exits through superior orbital fissure
  • The trochlear nerve (IV) [Motor]
    • Smallest cranial nerve
    • Innervates superior oblique eye muscle
    • also provides proprioception info
    • exits through S.O.F
  • The abducens nerve (VI) [Motor]
    • Innervates lateral rectus muscle of eye
    • exits through S.O.F
the trigeminal nerve v mixed
The Trigeminal Nerve (V) [Mixed]
  • Largest cranial nerve
  • Mixed nerve
    • sensory – touch, pain & thermal
    • Ophthalmic branch
    • sensory – upper eyelid, eyeball

lacrimal glands, side of nose, forehead

and scalp

  • Maxillary branch
    • sensory – nose, palate, part

of pharynx, upper teeth, upper

lip and lower eyelid

  • Mandibular branch
    • sensory – tongue, cheek,

lower teeth, skin over mandible

and side of head anterior to ear

-motor – muscles of chewing

-inferior alveolar nerve (branch of mandibular)

-often anesthetized in dental procedures – lower jaw

-numbs to mental nerve (branch of the IAN)

-superior alveolar nerve (branch of the maxillary)

-numbs the upper jaw

the facial nerve vii mixed
The Facial Nerve (VII) [Mixed]
  • Mixed nerve
  • Controls muscles of scalp and face
  • Pressure sensations from face
  • Taste sensations from tongue
facial nerve vii
Facial Nerve VII
  • efferent branches supply muscles of facial expression
    • also carries preganglionic parasympathetic fibers to the lacrimal, sub-mandibular and sub-maxillary glands
  • afferent branches serves a tiny patch of skin behind the ear
    • also provides taste information and sensation to the body of the tongue
facial nerve vii40
Facial Nerve VII
  • Greater Petrosal
    • branches off before exiting skull
    • motor fibers + Pre/para fibers to pterygopalatine ganglion
    • postganglionic fibers leave the ganglion to join with branches of the maxillary division or V -> lacrimal gl, nasal cavity and minor salivary glands of the palate
    • also taste sensation
  • Chorda Tympani
    • parasympathetic, motor for SMn and SL salivary glands
    • sensory for taste at the body of the tongue
    • crosses the tympanic membrane before exiting the skull
    • travels with the lingual n. to the floor of the mouth
  • Posterior Auricular, Diagastic and Stylohyoid
    • branches after VII exits the stylomastoid f.
    • all are motor – epicranial m., diagastic and stylohyoid muscles
  • facial expression
    • temporal (anterior to ear), zygomatic (inferior orbicularis oculi + ZMj, ZMn), buccal (upper lip, nose, buccinator, risorius and orbicularis oris), mandibular ( lower lip and mentalis) and cervical (plastysma)
the vestibulocochlear nerve viii sensory
The Vestibulocochlear Nerve (VIII) [Sensory]
  • Vestibular nerve
    • Monitors sense of balance, position and movement
  • Cochlear nerve
    • Monitors hearing
the glossopharyngeal nerve ix mixed
The Glossopharyngeal Nerve (IX) [Mixed]
  • Innervates the tongue, pharyngeal muscles, stylopharyngeus m.
    • Controls swallowing
    • the efferent portion also sends pre/para fibers to the parotid gland (salivation)
  • also receives sensory info from taste receptors and general sensation from the tongue
the vagus nerve x mixed
The Vagus Nerve (X) [Mixed]
  • Vital to autonomic control of visceral function
  • large efferent portion to the soft palate, pharynx and larynx
  • many other parasympathetic fibers to the organs of the gut, respiratory and CV systems
  • small afferent portion receives sensory information from around the ear and for taste info from the epiglottis
  • passes through the jugular foramen
The accessory nerve (XI)
    • Internal branch
      • Innervates swallowing muscles
    • External branch
      • Controls muscles associated with pectoral girdle
  • The hypoglossal nerve (XII)
    • Voluntary motor control over tongue movements
trigeminal nerve and branches
Trigeminal Nerve and Branches
  • bulge in the dorsal root of V = trigeminal ganglion
    • also called the semilunar ganglion
      • ganglion = collection of neuronal cell bodies
  • comprised of a motor root and a sensory root
    • supplies the muscles of mastication
    • exits via the forament ovale in the sphenoid
    • travels with mandibular division of V (V3)
  • sensory root divides into three portions
    • 1. Opthalmic
    • 2. Maxillary
    • 3. Mandibular
opthalmic division
Opthalmic Division
  • smallest division = V1
  • sensory information from: conjuctiva, cornea, eyeball, orbit, forehead, ethmoid and frontal sinuses
  • also part of dura mater
  • carries its sensory info by way of the superior orbital fissure along with III, IV & VI
  • formed from the union of:

the frontal, lacrimal and

nasociliary branches

Frontal branch: supraorbital + supratrochlear
    • SO: forehead, anterior scalp
    • ST: bridge of nose, upper eyelid, medial forehead
    • runs along roof of orbit
  • Lacrimal branch
    • lateral eyelid, conjuctive & lacrimal gland
    • also provides post/para fibers to the lacrimal gland – tear production
  • Nasociliary branch: infratrochlear + ciliary nerves + anterior ethmoid n.
    • runs superior to II within the orbit
    • IT: medial eyelid skin, side of nose
    • Ciliary: eyeball
    • AE: nasal cavity &

paranasal sinuses

maxillary division
Maxillary Division
  • V2
  • sensory information from: maxilla & skin, maxillary sinuses, nasal cavity, palate & nasopharynx + part of dura mater (meningeal branches)
  • forms in the pterygopalatine fossa
  • enters skull through the foramen rotundum
  • prior to branching = pterygopalatine ganglion
    • parasympathetic relay station for branches that

arise from the facial nerve

  • branches:
    • zygomatic
    • infraorbital
    • anterior superior alveolar
    • middle superior alveolar
    • posterior superior alveolar
    • greater & lesser palatine
    • nasopalatine
    • zygomaticotemporal + zygomaticofacial
    • enters pterygopalatine fossa through the infraorbital fissure and joins to contribute to the maxillary nerve
    • zygo.facial – skin of cheek
      • through the frontal process of the zygomatic bone and enters the orbit thru the lateral wall
    • zygo.temporal – skin of the temporal bone
      • through the temporal process of the zygomatic bone and travels along the lateral wall of the orbit
  • Infraorbital: IO
    • formed from cutaneous branches

from the upper lip, medial portion of cheek

lower eyelid and side of nose

    • runs into the infraorbital foramen of

the maxilla

    • travels along the infraorbital canal

with the infraorbital blood vessels

    • joins with the anterior superior

alveolar nerve

Anterior Superior Alveolar (ASA)
    • sensation + pain from the maxillary central incisors, lateral incisors, canines and their tissues + facial gingiva
    • originates as dental branches supplying the pulp + interdental branches of the associated periodonteum = dental plexus of the maxilla
    • joins with the IO within the IO canal
  • Middle Superior Alveolar (MSA)
    • sensation + pain from the maxillary premolars and first molar +

periodonteum and their buccal gingiva

    • originates from dental, interdental and interradicular branches (dental plexus) – pulp and periodonteum
    • forms this plexus with the ASA and PSA
    • joins the IO
    • MSA is not present in all patients
      • can be replaced by the ASA or PSA
Posterior Superior Alveolar (PSA)
    • sensation from 2nd and 3rd molar, root of 1st , their periodonteum + buccal gingiva, maxillary sinuses
    • joins the IO in the pterygopalatine fossa
    • branches:

a. dental branches + interdental + interradicular

(dental plexus)

b. internal branches – exit from the posterior superior alveolar foramina (with the posterior superior alveolar arteries)

c. external – receive information from buccal gingiva and associated molars

    • originates in the mucosa of the anterior hard palate posterior to the maxillary teeth
    • enters the skull through the incisive foramen
    • travels along the nasal septum
    • receives info from the anterior hard palate, lingula gingiva of anterior maxillary teeth

and nasal septum

  • Greater palatine (GP)
    • lies between the periosteum and bone of the anterior hard palate
    • sensory for the posterior hard palate + posterior lingual gingiva
    • enters through the greater palatine foramen near the 2nd or 3rd molar
    • travels through the pterygopalatine canal with the GP blood vessels
  • Lesser Palatine (LP)
    • sensory for the palatine tonsils and soft palate
    • enters through the LP foramen (near the junction of the palatine and the pterygoid processes of the sphenoid)
    • joins with the GP in the canal
    • joined by the nasal branches which

receive info from the nasal cavity

mandibular division
Mandibular Division
  • V3
  • forms from the union of smaller anterior and larger posterior trunks in the infratemporal fossa
  • passes through the foramen ovale
  • joins with the Opthal. and Maxillary at the trigeminal ganglion
  • before dividing into the trunks – sends off small meningeal branches to the dura mater + small muscular branches to the medial pterygoid m.
  • anterior trunk = buccal + muscular branches
  • posterior trunk = auriculotemporal, lingual and inferior alveolar branches
Buccal nerve – sensory
    • sensory
    • skin of cheek, buccal mucosa and buccal gingiva of posteior mandibular teeth
    • found on the surface of the buccinator and travels deep to the masseter
  • Muscular branches
    • motor
    • from the motor/ventral root of V
    • deep temporal branch – motor to temporalis
    • masseteric branch – motor to masseter
    • lateral pterygoid branch
    • travels with the superficial temporal artery and vein
    • sensory for external ear and scalp
    • also carries parasympathetic fibers from IX and communicates with II
    • sensory from the body of tongue, floor of mouth, and lingual gingiva
    • passes from the medial to the lateral side of the duct of submandibular gland
    • base of tongue – runs between the medial pterygoid and mandible (slightly medial to the inferior alveolar nerve)
    • near the root of the last mandibular molar is can be visualized clinically (can be damaged upon extraction of 3rd molar)
    • communicates with the submandibular ganglion located superior to the SMn gland (part of Parasympathetic NS)
  • Inferior Alveolar (IAN)
    • sensory from mandibular teeth
    • merger of the mental and the incisive
    • travels through the mandibular canal and is joined by the mandibular dental plexus
    • exits through the mandibular foramen
    • joined by a mylohyoid branch
    • can be found paired on one or both sides
      • with two mandibular canals and foramen

Mental branch of the IAN

- union of several external branches

- sensory from the chin, lower lip and labial mucosa

- enters the skull at the mental foramen

- then merges with the lingual branch of the IAN

Lingual branch of the IAN

- made up of dental branches from anterior mandibular teeth, interdental

branches form the surrounding periodonteum = dental plexus

-sensory information for the anterior mandibular teeth

Mylohyoid branch of the IAN

- joins with the mental and lingual after it emerges from the mandibular


- pierces the sphenomandibular ligament

- runs in the mylohyoid groove then onto the mylohyoid muscle

- motor commands to this muscle + anterior belly of the diagastric

(posterior belly is innervated by the facial nerve)


Inferior End of Spinal Cord

  • Conus medullaris
    • cone-shaped end of spinal cord
  • Filum terminale
    • thread-like extension of pia mater
    • stabilizes spinal cord in canal
  • Caudae equinae (horse’s tail)
    • dorsal & ventral roots of lowest spinal nerves
  • Spinal segment
    • area of cord from which each pair of spinal nerves arises
spinal nerve
Spinal Nerve
  • after passing through intervertebral foramina the spinal nerve branches = ramus/rami
  • Dorsal ramus
    • Sensory/motor innervation to skin and muscles of back
  • Ventral ramus
    • -Ventrolateral body surface, body wall structures, muscles of the upper and lower limbs
    • -Pairs of spinal nerves monitor dermatomes
nerve plexuses
Nerve Plexuses
  • Joining of ventral rami of spinal nerves to form nerve networks or plexuses
  • Found in neck, arm, low back & sacral regions
  • No plexus in thoracic region
    • intercostal nn. innervate intercostal spaces
    • T7 to T12 supply abdominal wall as well
  • Four major plexuses
    • Cervical plexus
    • Brachial plexus
    • Lumbar plexus
    • Sacral plexus
cervical plexus
Cervical Plexus
  • Cervical plexus
  • C1-C4 ventral rami
  • Some fibers from C5
  • Innervates muscles of the neck and diaphram
    • Phrenic nerve