Nervous System
Feb 23, 2016
Nervous System
Nervous System Cell types of
Neural tissue Neurons Neuroglial cells
Divisions of the Nervous System
Central Nervous System Brain Spinal cord
Peripheral Nervous System Peripheral nerves
Cranial nerves Spinal nerves
Divisions of Peripheral Nervous System Sensory Division
Picks up sensory information and delivers it to the CNS
Motor Division Carries information to muscles and glands Divisions of the Motor Division
Somatic – carries information to skeletal muscle Autonomic – carries information to smooth
muscle, cardiac muscle, and glands.
Divisions Nervous System
Functions of Nervous system Sensory Function
Sensory receptors gather information
Information is carried to the CNS
Integrative Function Sensory information
used to create Sensations Memory Thoughts Decisions
Motor Function Decisions are acted
upon Impulses are carried
to effectors
Neuron Structure
Myelination of Axons White Matter
Contains myelinated axons
Gray Matter Contains
unmyelinated structures
Cell bodies, dendrites
Classification of Neurons Bipolar
Two processes Eyes, ears,
nose Unipolar
One process Ganglia
Multipolar Many
processes Most neurons
of CNS
Classification of Neurons Sensory Neurons
Afferent Carry impulse to CNS Most are unipolar Some are bipolar
Interneurons Link neurons Multipolar In CNS
Motor Neurons Multipolar Carry impulses
away from CNS Carry impulses to
effectors
Types of Neuroglial Cells Schwann Cells
Peripheral nervous system
Myelinating cell Oligodendrocytes
CNS Myelinating cell
Microglia CNS Phagocytic cell
Astrocytes CNS Scar tissue Mop up excess ions, etc Induce synapse formation Connect neurons to blood
vessels Ependyma
CNS Ciliated Line central canal of spinal
cord Line ventricles of brain
Types of Neuroglial Cells
Regeneration of A Nerve Axon
Resting Membrane Potential Inside is negative relative to the outside Polarized membrane Due to distribution of ions Na+/K+ pump
Potential Changes At rest membrane
is polarized Threshold stimulus
reached Sodium channels
open and membrane depolarizes
Potassium leaves cytoplasm and membrane repolarizes
Local Potential Changes Occur on membranes of dendrites and cell bodies Caused by various stimuli
Chemicals Temperature changes Mechanical forces
If membrane potential becomes more negative, it has hyperpolarized
If membrane potential becomes more positive, it has depolarized
Graded (see paragraph under potential changes) Summation can lead to threshold stimulus that starts
an action potential
Action Potentials Nerve impulse Occur on axons All-or-none Refractory period
Absolute – time when threshold stimulus does not start another action potential
Relative – time when stronger threshold stimulus can start another action potential
Action Potentials
Impulse ConductionEVENTS LEADING TO THE CONDUCTION OF A NERVE IMPULSE
1. Neuron membrane maintains resting potential.2. Threshold stimulus is received.3. Sodium channels in the trigger zone of the neuron open.4. Sodium ions diffuse inward, depolarizing the membrane.5. Potassium channels in the membrane open.6. Potassium ions diffuse outward, repolarizing the
membrane. 7. The resulting action potential causes a local bioelectric
current that stimulates adjacent portions of the membrane.8. A wave of action potentials travels the length of the axon as
a nerve impulse.
Saltatory Conduction
The Synapse Nerve impulses pass from neuron to neuron at
synapses
Synaptic Transmission Neurotransmitters
are released when impulse reaches synaptic knob.
Synaptic Potentials EPSP
Excitatory postsynaptic potential Graded Depolarizes membrane of postsynaptic neuron Action potential of postsynaptic neuron becomes more
likely IPSP
Inhibitory postsynaptic potential Graded Hyperpolarizes membrane of postsynaptic neuron Action potential of postsynaptic neuron becomes less
likely
Summation of EPSPs and IPSPs EPSPs and IPSPs are added together in a process called summation
More EPSPs lead to greater probability of action potential
Neurotransmitters
Impulse Processing Neuronal Pools
Groups of interneurons that make synaptic connections with each other
Interneurons work together to peform a common function
Each pool receives input from other neurons Each pool generates output to other neurons
Convergence Neuron receives input from
several neurons Incoming impulses represent
information from different types of sensory receptors
Allows nervous system to collect, process, and respond to information
Makes it possible for a neuron to sum impulses from different sources
Divergence One neuron sends
impulses to several neurons
Can amplify an impulse
Impulse from a single neuron is CNS may be amplified to activate enough motor units needed for muscle contraction
Clinical Application Multiple Sclerosis Symptoms
Blurred vision Numb legs or arms Can lead to paralysis
Treatments No cure Bone marrow transplant Interferon (anti-viral drug) hormones
Causes Myelin destroyed in various parts of CNS Hard scars (scleroses) form Nerve impulses blocked Muscles do not receive innervation May be related to a virus
Meninges of the Spinal Cord Meninges
Membranes surrounding CNS Protect CNS Three layers
Dura mater – outer, tough Arachnoid mater – weblike Pia mater – inner, delicate
Meninges of the Spinal Cord
Spinal Cord Structure Extends foramen
magnum to 2nd lumbar vertebra.
Cross Section of Spinal Cord
Spinal Cord Functions Center for spinal reflexes Conduit for nerve impulses to and from the
brain
Reflex Arcs Reflexes – automatic, subconscious responses
to stimuli
Knee-jerk Reflex Helps maintain posture
Withdrawal Reflex Protective
Crossed-Extensor Reflex Flexor muscles contract Flexor muscles on opposite side inhibited Extensor muscles on opposite side contract
for balance
Tracts of the Spinal Cord Ascending tracts conduct sensory impulses
to the brain Descending tracts conduct motor impulses
from the brain to motor neurons reaching muscles and glands.
Ascending Tracts
Fasciculus cuneatus Lateral spinothalamic
Brain Functions
interprets sensations determines perception stores memory reasoning makes decisions coordinates muscular
movements regulates visceral activities determines personality
Major Parts cerebrum
two cerebellar hemispheres
diencephalon brain stem cerebellum
Structure of Cerebrum corpus callosum
connects hemispheres convolutions
bumps or gyri sulci
grooves longitudinal fissure
separates hemispheres transverse fissure
separates cerebrum from cerebellum
Lobes of Cerebrum
Frontal Parietal Temporal Occipital Insula
Functions of Cerebrum
interpretation initiating voluntary movements storing memory retrieving memory reasoning center for intelligence and personality
Functional Regions of Cerebral Cortex Cerebral Cortex – thin layer of gray matter
that constitutes the outermost portion of cerebrum; contains 75% of all neurons in nervous system
Motor Areas Primary Motor Areas
frontal lobes control voluntary muscles
Broca’s Area anterior to primary motor cortex usually in one hemisphere controls muscles needed for speech
Frontal Eye Field above Broca’s area controls voluntary movements of eyes and eyelids
Motor Areas
Sensory Areas Cutaneous Sensory Area
parietal lobe interprets sensations on skin
Visual Area occipital lobe interprets vision
Auditory Area temporal lobe interprets hearing
Sensory Areas
Association Areas regions of cortex that are not primary motor or
primary sensory areas widespread throughout the cerebral cortex analyze and interpret sensory experiences provide memory, reasoning, verbalization,
judgment, emotions
Association Areas Frontal Lobe Association
Areas concentrating planning problem solving judging
Parietal Lobe Association Areas understanding speech using words to express
thought
Temporal Lobe Association Areas remember visual scenes remember music remember complex
patterns Occipital Lobe
Association Areas combine visual images
with other sensory experiences
Hemisphere Dominance Dominant hemisphere
controls speech writing reading verbal skills analytical skills computational skills
In over 90% of population, left hemisphere is dominant
Nondominant hemisphere controls nonverbal tasks motor tasks understanding and
interpreting musical and visual patterns
provides emotional and intuitive thought processes
Memory Short Term
working memory closed circuit circuit is stimulated
over and over when impulse flow
stops, memory disappears
Long Term changes structure and
function of neurons enhanced synaptic
transmission
Basal Nuclei masses of gray
matter deep w/in cerebral
hemispheres caudate nucleus,
putamen, globus pallidus
produce dopamine control certain
muscular activities
Diencephalon between cerebral hemispheres and brainstem surrounds third ventricle thalamus hypothalamus optic tracts optic chiasm infundibulum posterior pituitary mammillary bodies pineal gland
Diencephalon Thalamus
gateway for sensory impulses heading to cerebral cortex
receives all sensory impulses (except smell) channels impulses to appropriate part of cerebral
cortex for interpretation Hypothalamus
maintains homeostasis by regulating visceral activities
links nervous and endocrine systems
Limbic System Consists of
portions of frontal lobe portions of temporal lobe hypothalamus thalamus basal nuclei other deep nuclei
Functions controls emotions produces feelings interpret sensory impulses
Brain Stem Three Parts
Midbrain Pons Medulla
Oblongata
Midbrain between diencephalon
and pons contains bundles of
fibers that join lower parts of brainstem and spinal cord with higher part of brain
cerebral aqueduct cerebral peduncles –
bundles of nerve fibers corpora quadrigemina –
centers for visual and auditory reflexes
Pons rounded bulge on underside of brainstem between medulla oblongata and midbrain helps regulate rate and depth of breathing relays nerve impulses to and from medulla
oblongata and cerebellum
Medulla Oblongata enlarged continuation of
spinal cord conducts ascending and
descending impulses between brain and spinal cord
contains cardiac, vasomotor, and respiratory control centers
contains various nonvital reflex control centers (coughing, sneezing, vomiting)
Reticular Formation complex network of nerve
fibers scattered throughout the brain stem
extends into the diencephalon
connects to centers of hypothalamus, basal nuclei, cerebellum, and cerebrum
filters incoming sensory information
arouses cerebral cortex into state of wakefulness
Types of Sleep Slow Wave
person is tired decreasing activity of reticular system restful dreamless reduced blood pressure and respiratory rate ranges from light to heavy alternates with REM sleep
Rapid Eye Movement (REM) some areas of brain active heart and respiratory rates irregular dreaming occurs
Cerebellum inferior to occipital lobes posterior to pons and medulla oblongata two hemispheres vermis connects hemispheres cerebellar cortex – gray matter arbor vitae – white matter cerebellar peduncles – nerve fiber tracts dentate nucleus – largest nucleus in cerebellum integrates sensory information concerning position of
body parts coordinates skeletal muscle activity maintains posture
Cerebellum
Peripheral Nervous System Cranial nerves arising from the brain
Somatic fibers connecting to the skin and skeletal muscles
Autonomic fibers connecting to viscera Spinal nerves arising from the spinal
cord Somatic fibers connecting to the skin and
skeletal muscles Autonomic fibers connecting to viscera
Structure of a Peripheral Nerve
Nerve Fiber Classification Sensory Nerves – conduct impulses into CNS Motor Nerves – conduct impulses to muscles or glands Mixed Nerves – contain both sensory nerve fibers and
motor nerve fibers; most nerves General somatic efferent fibers
carry motor impulses from CNS to skeletal muscles General somatic afferent fibers
carry sensory impulses to CNS from skin and skeletal muscles
General visceral efferent fibers carry motor impulses away from CNS to smooth
muscles and glands General visceral afferent fibers
carry sensory impulses to CNS from blood vessels and internal organs
Nerve Fiber Classification 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
Cranial Nerves
Spinal Nerves
mixed nerves 31 pairs
8 cervical (C1 to C8) 12 thoracic (T1 to T12) 5 lumbar (L1 to L5) 5 sacral (S1 to S5) 1 coccygeal (Co)
Spinal Nerves Dorsal root
axons of sensory neurons in the dorsal root ganglion
Dorsal root ganglion cell bodies of sensory neurons
Ventral root axons of motor neurons whose cell bodies are in
spinal cord Spinal nerve
union of ventral root and dorsal root
Spinal Nerves
Dermatome An area of skin that the sensory nerve fibers
of a particular spinal nerve innervate
Autonomic Nervous System functions without conscious effort controls visceral activities regulates smooth muscle, cardiac muscle,
and glands efferent fibers typically lead to ganglia outside
CNS Two Divisions
sympathetic – prepares body for fight or flight situations
parasympathetic – prepares body for resting and digesting activities
Autonomic Nerve Fibers all are motor (efferent) preganglionic fibers
axons of preganglionic neurons
neuron cell bodies in CNS
postganglionic fibers axons of postganglionic
neurons neuron cell bodies in
ganglia
Sympathetic Division thoracolumbar divison – location of
preganglionic neurons preganglionic fibers leave spinal nerves
through white rami and enter paravertebral ganglia
paraverterbral ganglia and fibers that connect them make up the sympathetic trunk
Sympathetic Division
Sympathetic Division postganglionic fibers extend
from sympathetic ganglia to visceral organs
postganglionic fibers usually pass through gray rami and return to a spinal nerve before proceeding to an effector
preganglionic fibers to adrenal medulla do not synapse with postganglionic neurons
Sympathetic Division
Sympathetic Division
Parasympathetic Division craniosacral division
– location of preganglionic neurons
ganglia are near or within various organs
short postganlionic fibers
preganglionic fibers of the head in III, VII, and IX
preganglionic fibers of thorax and abdomen in X
Parasympathetic Division
Control of Autonomic Activity
Controlled largely by CNS Medulla oblongata regulates cardiac,
vasomotor and respiratory activities Hypothalamus regulates visceral functions Limbic system and cerebral cortex control
emotional responses
Life-Span Changes Brain cells begin to die before birth Over average lifetime, brain shrinks 10% Most cell death occurs in temporal lobes By age 90, frontal lobe has lost half its neurons Number of dendritic branches decreases Decreased levels of neurotransmitters Fading memory Slowed responses and reflexes Changes increase risk of falling Sleep problems common
Clinical ApplicationCerebral Injuries & Abnormalities
Concussion brain jarred against
cranium loss of
consciousness temporary loss of
memory mental cloudiness headache recovery usually
complete
Cerebrovascular Accident stroke sudden interruption in blood
flow brain tissues die
Cerebral Palsy motor impairment at birth caused by blocked cerebral
blood vessels during development
seizues learning disabilities
Somatic and Special Senses
Sensory Receptors specialized cells or multicellular structures
that collect information stimulate neurons to send impulses along
sensory fibers to the brain
Receptor Types Chemoreceptors
respond to changes in chemical concentrations Pain receptors
respond to tissue damage Thermoreceptors
respond to changes in temperature Mechanoreceptors
respond to mechanical forces Photoreceptors
respond to light
Sensory Impulses stimulation of receptor causes local change in its
membrane a graded electrical current is generated that reflects
intensity of stimulation if receptor is part of a neuron, the membrane
potential may generate an action potential if receptor is not part of a neuron, the receptor
potential must be transferred to a neuron to trigger an actin potential
peripheral nerves transmit impulses to CNS Sensation
feeling that occurs when brain interprets sensory impulse
Sensory Adaptation adjustment of sensory receptors from
continuous stimulation stronger stimulus required to activate
receptors smell receptors undergo sensory adaptation
Somatic Senses senses associated with skin, muscles, joints,
and viscera three groups
exteroceptive senses – senses associated with body surface; touch, pressure, temperature, pain
proprioceptive senses – senses associated with changes in muscles and tendons
visceroceptive senses – senses associated with changes in viscera
Touch and Pressure Senses Free nerve endings
common in epithelial tissues
detect touch and pressure
Meissner’s corpuscles abundant in hairless
portions of skin detect light touch
Pacinian corpuscles common in deeper
subcutaneous tissues, tendons, and ligaments
detect heavy pressure
Touch and Pressure Senses
Temperature Senses Warm receptors
sensitive to temperatures above 25oC (77o F) unresponsive to temperature above 45oC (113oF)
Cold receptors sensitive to temperature between 10oC (50oF)
and 20oC (68oF) Pain receptors
respond to temperatures below 10oC respond to temperatures above 45oC
Sense of Pain free nerve endings widely distributed nervous tissue of brain lacks pain receptors stimulated by tissue damage, chemical,
mechanical forces, or extremes in temperature
do not adapt Visceral Pain
may exhibit referred pain not well localized
Referred Pain may occur due to sensory impulses from two
regions following a common nerve pathway to brain
Pain Nerve Fibers Acute pain fibers
thin, myelinated conduct impulses
rapidly associated with
sharp pain well localized
Chronic pain fibers thin, unmyelinated conduct impulses
more slowly associated with dull,
aching pain difficult to pinpoint
Regulation of Pain Impulses Thalamus
allows person to be aware of pain
Cerebral Cortex judges intensity of pain locates source or pain produces motor
response to pain produces emotions to
pain
Pain Inhibiting Substances enkephalins serotonin endorphins
Stretch Receptors
proprioceptors send information to CNS concerning
lengths and tensions of muscles 2 main kinds of stretch receptors
muscle spindles – in skeletal muscles Golgi tendon organs – in tendons
Stretch Receptors
Special Senses
sensory receptors are within large, complex sensory organs in the head
smell in olfactory organs taste in taste buds hearing and equilibrium in ears sight in eyes
Smell
Olfactory Receptors chemoreceptors respond to chemicals dissolved in liquids
Olfactory Organs contain olfactory receptors and supporting
epithelial cells cover parts of nasal cavity, superior nasal
conchae, and a portion of the nasal septum
Olfactory Receptors
Olfactory Nerve Pathways
Once olfactory receptors are stimulated, nerve impulses travel through olfactory nerves to olfactory bulbs to olfactory tracts to limbic system (for emotions) and olfactory cortex
(for interpretation)
Taste
Taste Buds organs of taste located on papillae of tongue, roof of mouth,
linings of cheeks and walls of pharynx Taste Receptors
chemoreceptors taste cells – modified epithelial cells that function
as receptors taste hairs –microvilli that protrude from taste
cells; sensitive parts of taste cells
Taste Receptors
Taste Sensations
Four Primary Taste Sensations sweet – stimulated by carbohydrates sour – stimulated by acids salty – stimulated by salts bitter – stimulated by many organic compound
Spicy foods activate pain receptors
Taste Nerve Pathways
Sensory impulses from taste receptors travel along cranial nerves to medulla oblongata to thalamus to gustatory cortex (for interpretation)
Hearing
Ear – organ of hearing 3 Sections
External Middle Inner
External Ear auricle
collects sounds waves external auditory meatus
lined with ceruminous glands carries sound to tympanic
membrane terminates with tympanic
membrane tympanic membrane
vibrates in response to sound waves
Middle Ear tympanic cavity air-filled space in
temporal bone auditory ossicles
vibrate in response to tympanic membrane
malleus, incus, and stapes oval window
opening in wall of tympanic cavity
stapes vibrates against it to move fluids in inner ear
Auditory Tube eustachian
tube connects
middle ear to throat
helps maintain equal pressure on both sides of tympanic membrane
usually closed by valve-like flaps in throat
Inner Ear complex system of
labyrinths osseous labyrinth
bony canal in temporal bone
filled with perilymph membranous
labyrinth tube within osseous
labyrinth filled with
endolymph
Inner Ear 3 Parts of Labyrinths
cochlea functions in hearing
semicircular canals functions in equilibrium
vestibule functions in equilibrium
Cochlea Scala vestibuli
upper compartment leads from oval
window to apex of spiral
part of bony labyrinth Scala tympani
lower compartment extends from apex of
the cochlea to round window
part of bony labyrinth
Cochlea Cochlear duct
portion of membranous labyrinth in cochlea
Vestibular membrane separates cochlear
duct from scala vestibuli
Basilar membrane separates cochlear
duct from scala tympani
Organ of Corti group of hearing
receptor cells (hair cells) on upper surface of
basilar membrane different frequencies of
vibration move different parts of basilar membrane
particular sound frequencies cause hairs of receptor cells to bend
nerve impulse generated
Organ of Corti
Auditory Nerve Pathways
Summary of the Generation of Sensory Impulses from the Ear
Equilibrium
Static Equilibrium vestibule sense position of head when body is not moving
Dynamic Equilibrium semicircular canals sense rotation and movement of head and body
Vestibule Utricle
communicates with saccule and membranous portion of semicircular canals
Saccule communicates
with cochlear duct Mucula
hair cells of utricle and saccule
Macula responds to changes in head position bending of hairs results in generation of
nerve impulse
Semicircular Canals three canals at right
angles ampulla
swelling of membranous labyrinth that communicates with the vestibule
crista ampullaris sensory organ of
ampulla hair cells and supporting
cells rapid turns of head or
body stimulate hair cells
Crista Ampullaris
Sight
Visual Accessory Organs eyelids lacrimal apparatus extrinsic eye muscles
Eyelid palpebra composed of four layers
skin muscle connective tissue conjunctiva
orbicularis oculi - closes levator palperbrae
superioris – opens tarsal glands – secrete oil
onto eyelashes conjunctiva – mucous
membrane; lines eyelid and covers portion of eyeball
Lacrimal Apparatus lacrimal gland
lateral to eye secretes tears
canaliculi collect tears
lacrimal sac collects from canaliculi
nasolacrimal duct collects from lacrimal sac empties tears into nasal
cavity
Extrinsic Eye Muscles Superior rectus
rotates eye up and medially
Inferior rectus rotates eye down
and medially Medial rectus
rotates eye medially
Extrinsic Eye Muscles Lateral rectus
rotates eye laterally
Superior oblique rotates eye down
and laterally Inferior oblique
rotates eye up and laterally
Structure of the Eye hollow spherical wall has 3 layers
outer fibrous tunic middle vascular
tunic inner nervous tunic
Outer Tunic Cornea
anterior portion transparent light transmission light refraction
Sclera posterior portion opaque protection
Middle Tunic Iris
anterior portion pigmented controls light intensity
Ciliary body anterior portion pigmented holds lens moves lens for focusing
Choroid coat provides blood supply pigments absorb extra light
Anterior Portion of Eye filled with aqueous humor
Lens transparent biconvex lies behind iris largely composed of lens fibers elastic held in place by suspensory ligaments of ciliary
body
Ciliary Body forms internal ring around front of eye ciliary processes – radiating folds ciliary muscles – contract and relax to move
lens
Accommodation changing of lens shape to view objects
Iris composed of
connective tissue and smooth muscle
pupil is hole in iris dim light stimulates
radial muscles and pupil dilates
bright light stimulates circular muscles and pupil constricts
Aqueous Humor fluid in anterior cavity of eye secreted by epithelium on inner surface of
the ciliary body provides nutrients maintains shape of anterior portion of eye leaves cavity through canal of Schlemm
Inner Tunic retina contains visual receptors continuous with optic nerve ends just behind margin of the ciliary body composed of several layers macula lutea – yellowish spot in retina fovea centralis – center of macula lutea; produces
sharpest vision optic disc – blind spot; contains no visual receptors vitreous humor – thick gel that holds retina flat
against choroid coat
Layers of Retina receptor cells, bipolar cells, and ganglion
cells - provide pathway for impulses triggered by photoreceptors to reach the optic nerve
horizontal cells and amacrine cells – modify impulses
Light Refraction Refraction
bending of light occurs when light waves pass at an oblique angle
into mediums of different densities
Types of Lenses Convex lenses cause light waves to
converge Concave lenses cause light waves to diverge
Focusing On Retina as light enters eye, it is refracted by
convex surface of cornea convex surface of lens
image focused on retina is upside down and reversed from left to right
Visual Receptors
Rods long, thin projections contain light sensitive pigment called rhodopsin hundred times more sensitive to light than cones provide vision in dim light produce colorless vision produce outlines of objects
Cones short, blunt projections contain light sensitive pigments called erythrolabe,
chlorolabe, and cyanolabe provide vision in bright light produce sharp images produce color vision
Rods
Visual Pigments Rhodopsin
light-sensitive pigment in rods
decomposes in presence of light
triggers a complex series of reactions that initiate nerve impulses
impulses travel along optic nerve
Pigments on Cones each set contains different
light-sensitive pigment each set is sensitive to
different wavelengths color perceived depends
on which sets of cones are stimulated
erythrolabe – responds to red
chlorolabe – responds to green
cyanolabe – responds to blue
Stereoscopic Vision provides perception of distance and depth results from formation of two slightly different
retinal images
Visual Pathway
Life-Span Changes Age related hearing loss due to
damage of hair cells in organ of Corti degeneration of nerve pathways to the brain tinnitus
Age-related visual problems include dry eyes floaters (crystals in vitreous humor) loss of elasticity of lens glaucoma cataracts macular degeneration
Clinical Application- Refraction Disorders concave lens corrects
nearsightedness convex lens corrects
farsightedness