THE NERVOUS SYSTEM: NEURAL TISSUE - PowerPoint PPT Presentation

C H A P T E R T H I R T E E N

THE NERVOUS SYSTEM: NEURAL TISSUE

• Nervous system
• Swift, brief responses to stimuli
• Endocrine system
• Adjusts metabolic operations
• Directs long-term changes

• Central Nervous System
• Brain and spinal cord
• Peripheral Nervous System
• All neural tissue outside CNS

• 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

• Neurons

• Neuroglia

• 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

http://www.horton.ednet.ns.ca/staff/selig/Activities/nervous/na1.htm

• -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

Neurons

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

http://bcs.whfreeman.com/thelifewire/content/chp44/4401s.swf

• 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

• 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)

http://www.blackwellpublishing.com/matthews/channel.html

• 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

• 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

Neuropeptides

• 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)

• 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

• 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)

• 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

-

Major Regions of the Brain

http://www.wisc-online.com/objects/framz.asp?objID=OTA502

I - Olfactory

II - Optic

III - Oculomotor

IV-Trochlear

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”

http://www.wisc-online.com/objects/index.asp?objID=AP11504

• Carries sensory information
• Sense of smell from nasal mucosa to brain
• Branches enter skull through cribiform plate
• Synapses within olfactory bulbs

• 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

• 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

• Mixed nerve
• Controls muscles of scalp and face
• Pressure sensations from face
• Taste sensations from tongue

• 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

• 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)

• Vestibular nerve
• Monitors sense of balance, position and movement
• Cochlear nerve
• Monitors hearing

• 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

• 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

• Internal branch
• Innervates swallowing muscles
• External branch
• Controls muscles associated with pectoral girdle

• The hypoglossal nerve (XII)
• Voluntary motor control over tongue movements

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

foramen

- 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)

External Anatomy of Spinal Cord

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

• 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

• 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
• C1-C4 ventral rami
• Some fibers from C5
• Innervates muscles of the neck and diaphram
• Phrenic nerve