Transcript Nerves and Special Senses

Nerves and Special Senses
Anatomy & Physiology
Rainier Jr/Sr High School
Mr. Taylor
Structure of a Nerve
• Endoneurium
surrounds each fiber
• Groups of fibers are
bound into fascicles by
perineurium
• Fascicles are bound
together by epineurium
Figure 7.20
Classification of Nerves
• Afferent (sensory) nerves – carry impulses
toward the CNS
• Efferent (motor) nerves – carry impulses away
from the CNS
• Mixed nerves – both sensory and motor fibers
Functions of the Nervous System
• Sensory input – gathering information
– To monitor changes occurring inside and outside
the body
– Changes = stimuli
• Integration
– To process and interpret sensory input and decide
if action is needed
• Motor output
– A response to integrated stimuli
– The response activates muscles or glands
Structural Classification of the Nervous
System
• Central nervous system (CNS)
– Brain
– Spinal cord
• Peripheral nervous system (PNS)
– Nerves outside the brain and spinal cord
• Afferent (sensory) division
• Efferent (motor) division
– 2 subdivisions
» Somatic (voluntary)
» Autonomic (involuntary) (2 subdivisions)
»
Parasympathetic
»
Sympathetic
Functional Classification of the
Peripheral Nervous System
• Sensory (afferent) division
– Nerve fibers that carry information to the central
nervous system
Figure 7.1
Functional Classification of the
Peripheral Nervous System
• Motor (efferent) division
– Nerve fibers that carry impulses away from the
central nervous system
Figure 7.1
Functional Classification of the
Peripheral Nervous System
• Motor (efferent) division
– Two subdivisions
• Somatic nervous system = voluntary
• Autonomic nervous system = involuntary
Figure 7.1
Organization of the Nervous System
Figure 7.2
Peripheral Nervous System
• Nerves and ganglia outside the central
nervous system
• Nerve = bundle of neuron fibers
• Neuron fibers are bundled by connective
tissue
Nervous Tissue: Support Cells
(Neuroglia)
• Astrocytes
– Abundant, star-shaped cells
– Brace(support) neurons
– Form barrier
between capillaries
and neurons
– Control the chemical
environment of
the brain
Figure 7.3a
Nervous Tissue: Support Cells
• Microglia
– Spider-like phagocytes
– Dispose of debris
• Ependymal cells
– Line cavities of the
brain and spinal cord
– Circulate
cerebrospinal
fluid
Figure 7.3b–c
Nervous Tissue: Support Cells
• Oligodendrocytes
– Produce myelin sheath around nerve fibers in the
central nervous system
Figure 7.3d
Nervous Tissue: Support Cells
• Satellite cells
– Protect neuron cell bodies
• Schwann cells
– Form myelin sheath in the peripheral nervous
system
Figure 7.3e
Nervous Tissue: Neurons
• Neurons = nerve cells
– Cells specialized to transmit messages
– Major regions of neurons
• Cell body – nucleus and metabolic center of the cell
• Processes – fibers that extend from the cell body
– Axons carry signals away from the body
– Dendrites carry signals toward the body
Neuron Anatomy
• Extensions outside
the cell body
– Dendrites –
conduct impulses
toward the cell
body
– Axons – conduct
impulses away
from the cell
body
Figure 7.4a
Axons and Nerve Impulses
• Axons end in axonal terminals
• Axonal terminals contain vesicles with
neurotransmitters
• Axonal terminals are separated from the
next neuron by a gap
– Synaptic cleft – gap between adjacent neurons
– Synapse – junction between nerves
Nerve Fiber Coverings
• Schwann cells –
produce myelin
sheaths in jelly-roll
like fashion
• Nodes of Ranvier –
gaps in myelin sheath
along the axon
Figure 7.5
Neuron Cell Body Location
• Most are found in the central nervous system
– Gray matter – cell bodies and unmylenated fibers
– Nuclei – clusters of cell bodies within the white
matter of the central nervous system
• Ganglia – collections of cell bodies outside the
central nervous system
Functional Classification of Neurons
• Sensory (afferent) neurons
– Carry impulses from the sensory receptors
• Cutaneous sense organs
• Proprioceptors – detect stretch or tension
• Motor (efferent) neurons
– Carry impulses from the central nervous system
Functional Classification of Neurons
• Interneurons (association neurons)
– Found in neural pathways in the central nervous
system
– Connect sensory and motor neurons
Neuron Classification
Figure 7.6
Functional Properties of Neurons
• Irritability – ability to respond to stimuli
• Conductivity – ability to transmit an impulse
Starting a Nerve Impulse
• The plasma membrane at rest is
polarized
– Fewer positive ions are inside
the cell than outside the cell
• Depolarization – a stimulus
depolarizes the neuron’s
membrane
• A deploarized membrane allows
sodium (Na+) to flow inside the
membrane
• The exchange of ions initiates an
action potential in the neuron
Figure 7.9a–c
The Action Potential
• If the action potential (nerve impulse) starts, it
is propagated over the entire axon
• Potassium ions rush out of the neuron after
sodium ions rush in, which repolarizes the
membrane
• The sodium-potassium pump restores the
original configuration
– This action requires ATP
Nerve Impulse Propagation
• The impulse
continues to move
toward the cell body
• Impulses travel faster
when fibers have a
myelin sheath
Figure 7.9d–f
Continuation of the Nerve Impulse
between Neurons
• Impulses are able to cross the synapse to
another nerve
– Neurotransmitter is released from a nerve’s axon
terminal
– The dendrite of the next neuron has receptors
that are stimulated by the neurotransmitter
– An action potential is started in the dendrite
The Reflex Arc
• Reflex – rapid, predictable, and involuntary
responses to stimuli
• Reflex arc – direct route from a sensory
neuron, to an interneuron, to an effector
Figure 7.11a
Central Nervous System (CNS)
• CNS develops from the embryonic neural tube
(ectodermal origin)
– The neural tube becomes the brain and spinal
cord
– The opening of the neural tube becomes the
ventricles
• Four chambers within the brain
• Filled with cerebrospinal fluid
Regions of the Brain
•
•
•
•
Cerebral hemispheres
Diencephalon
Brain stem
Cerebellum
Figure 7.12b
Cerebral Hemispheres (Cerebrum)
• Paired (left and
right) superior
parts of the brain
• Include more than
half of the brain
mass
Figure 7.13a
Cerebral Hemispheres (Cerebrum)
• The surface is
made of ridges
(gyri) and
grooves (sulci)
Figure 7.13a
Specialized Areas of the Cerebrum
• Somatic sensory area – receives impulses from
the body’s sensory receptors
• Primary motor area – sends impulses to
skeletal muscles
• Broca’s area – involved in our ability to speak
Specialized Areas of the Cerebrum
• Cerebral areas involved in special senses
– Gustatory area (taste)
– Visual area
– Auditory area
– Olfactory area
Specialized Areas of the Cerebrum
• Interpretation areas of the cerebrum
– Speech/language region
– Language comprehension region
– General interpretation area
Sensory and Motor Areas of the
Cerebral Cortex
Figure 7.14
Specialized Areas of the Cerebrum
Figure 7.13c
Layers of the Cerebrum
• Gray matter
– Outer layer
– Composed mostly
of neuron cell
bodies
Figure 7.13a
Layers of the Cerebrum
• White matter
– Fiber tracts inside
the gray matter
– Example: corpus
callosum connects
hemispheres
Figure 7.13a
Diencephalon
• Sits on top of the brain stem
• Enclosed by the cerebral hemispheres
• Made of three parts
– Thalamus
– Hypothalamus
– Epithalamus
Diencephalon
Figure 7.15
Thalamus
• Surrounds the third ventricle
• The relay station for sensory impulses
• Transfers impulses to the correct part of the
cortex for localization and interpretation
Hypothalamus
• Under the thalamus
• Important autonomic nervous system center
– Helps regulate body temperature
– Controls water balance
– Regulates metabolism
Hypothalamus
• An important part of the limbic system
(emotions)
• The pituitary gland is attached to the
hypothalamus
Epithalamus
• Forms the roof of the third ventricle
• Houses the pineal body (an endocrine gland)
• Includes the choroid plexus – forms
cerebrospinal fluid
Brain Stem
• Attaches to the spinal cord
• Parts of the brain stem
– Midbrain
– Pons
– Medulla oblongata
Brain Stem
Figure 7.15a
Midbrain
• Mostly composed of tracts of nerve fibers
– Reflex centers for vision and hearing
Pons
• The bulging center part of the brain stem
• Mostly composed of fiber tracts
• Includes nuclei involved in the control of
breathing
Medulla Oblongata
•
•
•
•
The lowest part of the brain stem (“reptilian brain”)
Merges into the spinal cord
Includes important fiber tracts
Contains important control centers
– Heart rate control
– Blood pressure regulation
– Breathing
– Swallowing
– Vomiting
Reticular Formation
• Diffuse mass of gray matter along the brain
stem
• Involved in motor control of visceral organs
• Reticular activating system plays a role in
awake/sleep cycles and consciousness
Cerebellum
• Two hemispheres with convoluted surfaces
• Provides automatic (involuntary) coordination
of body movements.
– This allows for the smooth movements of arms,
legs, and body.
– This also allows the fine motor control necessary
for activities such as writing.
Cerebellum
Figure 7.15a
Protection of the Central Nervous
System
• Scalp and skin
• Skull and vertebral
column
• Meninges
Cerebrospinal fluid
Blood brain barrier
Figure 7.16a
Meninges
• Dura mater (literally “tough mother”)
– Double-layered external covering
• Periosteum – attached to surface of the skull
• Meningeal layer – outer covering of the brain
– Folds inward in areas of major fissures.
Meninges
• Arachnoid layer
– Middle layer
– Web-like (hence, arachnoid)
• Pia mater (the “tender mother”)
– Internal layer
– Clings to the surface of the brain
Cerebrospinal Fluid
•
•
•
•
Similar to blood plasma composition
Formed by the choroid plexus
Forms a watery cushion to protect the brain
Circulated in arachnoid space, ventricles, and
central canal of the spinal cord
Cranial Nerves
• 12 pairs of nerves that mostly serve the head
and neck
• Numbered in order, front to back
• Numbers I, II, VIII are purely sensory.
• Numbers III, IV, VI, XI are purely motor.
• Numbers V, VII, IX, X, XII are mixed.
Distribution of Cranial Nerves
Figure 7.21
Cranial Nerves
• I Olfactory nerve – sensory for smell
• II Optic nerve – sensory for vision
• III Oculomotor nerve – motor fibers to eye
muscles
• IV Trochlear – motor fiber to eye muscles
Cranial Nerves
• V Trigeminal nerve – sensory for the face;
motor fibers to chewing muscles
• VI Abducens nerve –
motor fibers to eye muscles
• VII Facial nerve – sensory for taste; motor
fibers to the face
• VIII Vestibulocochlear (old name: Auditory)
nerve – sensory for balance and hearing
Cranial Nerves
• IX Glossopharyngeal nerve – sensory for
taste; motor fibers to the pharynx
• X Vagus nerves – sensory and motor fibers for
pharynx, larynx, and viscera
• XI (Spinal) Accessory nerve – motor fibers to
neck and upper back
• XII Hypoglossal nerve – motor fibers to
tongue, some sensory fibers from tongue.
Blood Brain Barrier
• Includes the least permeable capillaries of the body
– (where are the most permeable capillaries?)
• Excludes (keeps away from the brain) many
potentially harmful substances
• Useless against some substances
– Fats and fat soluble molecules including hormones
– Respiratory gases (oxygen/carbon dioxide)
– Alcohol (all kinds)
– Nicotine (a paralyzing agent)
– Anesthesia
Traumatic Brain Injuries
• Concussion
– Slight brain injury
– No permanent brain damage (latest evidence does
not support this … so let’s say minimal permanent
brain damage)
• Contusion
– Nervous tissue destruction occurs (and nervous
tissue does not regenerate)
• Cerebral edema
– Swelling from the inflammatory response from
any cause (trauma and disease most common)
– May compress and kill brain tissue
Cerebrovascular Accident (CVA)
• Commonly called a stroke
• The result of a ruptured blood vessel supplying a
region of the brain or blockage from a blood clot.
• Brain tissue supplied with oxygen from that blood
source dies
• Loss of some functions or death may result
• Immediate medical attention is necessary to
minimize damage
• (FAST: Face; Arms; Speech; Time)
Alzheimer’s Disease
• Progressive degenerative brain disease
• Mostly seen in the elderly, but may begin in
middle age
• Structural changes in the brain include
abnormal protein deposits and twisted fibers
within neurons
• Victims experience memory loss, irritability,
confusion and ultimately, hallucinations and
death
Spinal Cord
• Extends from the
medulla oblongata to
the region of T12
• Below T12 is the
cauda equina (literal
meaning is “horse
tail”) a collection of
spinal nerves)
• Enlargements occur
in the cervical and
lumbar regions
Figure 7.18
Spinal Cord Anatomy
• Meninges cover the spinal cord
• Nerves leave at the level of each vertebrae
– Dorsal root (afferent neurons)
• Associated with the dorsal root ganglia – collections
of cell bodies outside the central nervous system
– Ventral root (efferent neurons)
Spinal Nerves
• There is a pair of spinal nerves at the level of
each vertebrae for a total of 31 pairs
• Spinal nerves are formed by the combination
of the ventral and dorsal roots of the spinal
cord
• Spinal nerves are named for the region from
which they arise
Spinal Nerves
Figure 7.22a
Anatomy of Spinal Nerves
• Spinal nerves divide soon
after leaving the spinal
cord
– Dorsal rami – serve the
skin and muscles of
the posterior trunk
– Ventral rami – forms a
complex of networks
(plexus) for the
anterior
Figure 7.22b
Autonomic Nervous System
• The involuntary branch of the nervous system
• Consists of only motor nerves
• Divided into two divisions
– Sympathetic division (fight or flight)
– Parasympathetic division (dine and doze)
Differences Between Somatic and
Autonomic Nervous Systems
• Nerves
– Somatic – one motor neuron
– Autonomic – preganglionic and postganglionic
nerves
• Effector organs
– Somatic – skeletal muscle
– Autonomic – smooth muscle, cardiac muscle,
and glands
Differences Between Somatic and
Autonomic Nervous Systems
• Nerurotransmitters
– Somatic – always use acetylcholine
– Autonomic – use acetylcholine, epinephrine, or
norepinephrine
Comparison of Somatic and Autonomic
Nervous Systems
Figure 7.24
Anatomy of the Sympathetic Division
• Originates from T1 through L2
• Ganglia are at the sympathetic trunk (near the
spinal cord)
• Norepinephrine and epinephrine are
neurotransmitters to the effector organs
Anatomy of the Parasympathetic
Division
• Originates from the brain stem and S1 through
S4
• Terminal ganglia are at the effector organs
• Always uses acetylcholine as a
neurotransmitter
Anatomy of the Autonomic Nervous
System
Figure 7.25
Autonomic Functioning
• Sympathetic – “fight-or-flight”
– Response to unusual stimulus
– Takes over to increase activities
– Remember as the “E” division = exercise,
excitement, emergency, and embarrassment
Autonomic Functioning
• Parasympathetic – housekeeping activites
– Conserves energy
– Maintains daily necessary body functions
– Remember as the “D” division - digestion,
defecation, and diuresis
– My nickname for this system is “dine and doze”.
Development Aspects of the Nervous
System
• The nervous system is formed during the first
month of embryonic development
• Any maternal infection can have extremely
harmful effects
• The hypothalamus is one of the last areas of
the brain to develop
Development Aspects of the Nervous
System
• No more neurons are formed after birth, but
growth and maturation continues for several
years
• The brain reaches maximum weight as a
young adult
The Senses
• General senses of touch
– Temperature
– Pressure
– Pain
• Special senses
– Smell
– Taste
– Sight
– Hearing
– Equilibrium
The Eye and Vision
• 70 percent of all sensory receptors are in the
eyes
• Each eye has over a million nerve fibers
• Protection for the eye
– Most of the eye is enclosed in a bony orbit
– A cushion of fat surrounds most of the eye
Accessory Structures of the Eye
• Eyelids
• Eyelashes
Figure 8.1b
Accessory Structures of the Eye
• Meibomian glands –
modified
sebacious
glands
produce an
oily secretion
to lubricate
the eye
Figure 8.1b
Accessory Structures of the Eye
• Ciliary glands –
modified
sweat glands
between the
eyelashes
Figure 8.1b
Accessory Structures of the Eye
• Conjunctiva
– Membrane that lines the eyelids
– Connects to the surface of the eye
– Secretes mucus to lubricate the eye
Accessory Structures of the Eye
• Lacrimal apparatus
– Lacrimal gland –
produces lacrimal
fluid
– Lacrimal canals –
drains lacrimal fluid
from eyes into
lacrimal sac.
Figure 8.1a
Accessory Structures of the Eye
• Lacrimal sac – provides passage of lacrimal
fluid towards nasal cavity
• Nasolacrimal duct – empties lacrimal fluid into
the nasal cavity
Figure 8.1a
Function of the Lacrimal Apparatus
• Properties of lacrimal fluid
– Dilute salt solution (tears)
– Contains antibodies and lysozyme
• Protects, moistens, and lubricates the eye
Extrinsic Eye Muscles
• Muscles attach to the outer surface of the eye
• Produce eye movements
Figure 8.2
Structure of the Eye
• The wall is composed of three tunics
– Fibrous tunic –
outside layer
– Choroid –
middle
layer
– Sensory
tunic –
inside
layer
Figure 8.3a
The Fibrous Tunic
• Sclera
– White connective tissue layer
– Seen anteriorly as the “white of the eye”
• Cornea
– Transparent, central anterior portion
– Allows for light to pass through
– Repairs itself easily and quickly
– The only human tissue that can be transplanted
without fear of rejection
Choroid Layer
• Blood-rich nutritive tunic
• Pigment prevents light from scattering
• Middle part is modified into two structures
– Ciliary body – smooth muscle
– Iris
• Pigmented layer that gives eye color
• Pupil – rounded opening in the iris
Sensory Tunic (Retina)
• Contains receptor cells (photoreceptors)
– Rods
• Most are found towards the edges of the retina
• Allow dim light vision and peripheral vision
• Perception is all in gray tones
– Cones
• Allow for detailed color vision
• Densest in the center of the retina
• Fovea centralis – area of the retina with only cones
– Signals pass from photoreceptors via a two-neuron chain
• Signals leave the retina toward the brain through the optic
nerve
Cone Sensitivity
• There are three
types of cones
• Different cones are
sensitive to
different
wavelengths
• Color blindness is
the result of lack of
one cone type
Figure 8.6
Neurons of the Retina
Figure 8.4
Lens
• Biconvex crystallike structure
• Held in place by
a suspensory
ligament
attached to the
ciliary body
Figure 8.3a
Internal Eye Chamber Fluids
• Aqueous humor
– Watery fluid found in chamber between the lens
and cornea
– Similar to blood plasma
– Helps maintain intraocular pressure
– Provides nutrients for the lens and cornea
– Reabsorbed into venous blood through the canal
of Schlemm
Internal Eye Chamber Fluids
• Vitreous humor
– Gel-like substance behind the lens
– Keeps the eye from collapsing
– Lasts a lifetime and is not replaced
Lens Accommodation
• Light must be
focused to a point on
the retina for optimal
vision
• The eye is set for
distance vision
(over 20 ft away)
• The lens must change
shape to focus for
closer objects
Figure 8.9
Visual Pathway
• Photoreceptors of
the retina
• Optic nerve
• Optic nerve crosses
at the optic chiasma
Figure 8.11
Visual Pathway
• Optic tracts
• Thalamus (axons form
optic radiation)
• Visual cortex of the
occipital lobe
Figure 8.11
Eye Reflexes
• Internal muscles are controlled by the autonomic
nervous system
– Bright light causes pupils to constrict through
action of radial and ciliary muscles
– Viewing close objects causes accommodation
• External muscles control eye movement to follow
objects
• Viewing close objects causes convergence (eyes
moving medially)
The Ear
• Houses two senses
– Hearing
– Equilibrium (balance)
• Receptors are mechanoreceptors
• Different organs house receptors for each
sense
Anatomy of the Ear
• The ear is
divided into
three areas
– Outer (external)
ear
– Middle ear
– Inner ear
Figure 8.12
The External Ear
• Involved in
hearing only
• Structures of the
external ear
– Pinna (auricle)
– External
auditory canal
Figure 8.12
The External Auditory Canal
•
•
•
•
Narrow chamber in the temporal bone
Lined with skin
Ceruminous (wax) glands are present
Ends at the tympanic membrane
The Middle Ear or Tympanic Cavity
• Air-filled cavity within the temporal bone
• Only involved in the sense of hearing
The Middle Ear or Tympanic Cavity
• Two tubes are associated with the middle ear
– The opening from the auditory canal is covered by
the tympanic membrane
– The auditory tube connecting the middle ear with
the throat
• Allows for equalizing pressure during yawning or
swallowing
• This tube is otherwise collapsed
Bones of the Tympanic Cavity
• Three bones span the cavity
– Malleus (hammer)
– Incus (anvil)
– Stapes (stirrup)
Figure 8.12
Bones of the Tympanic Cavity
• Vibrations from
eardrum move the
malleus
• These bones
transfer sound to
the inner ear
Figure 8.12
Inner Ear or Bony Labyrinth
• Includes sense
organs for
hearing and
balance
• Filled with
perilymph
Figure 8.12
Inner Ear or Bony Labrynth
• A maze of bony chambers within the temporal
bone
– Cochlea
– Vestibule
– Semicircular
canals
Figure 8.12
Organs of Hearing
• Organ of Corti
– Located within the cochlea
– Receptors = hair cells on the basilar membrane
– Gel-like tectorial membrane is capable of
bending hair cells
– Cochlear nerve attached to hair cells transmits
nerve impulses to auditory cortex on temporal
lobe
Organs of Hearing
Figure 8.15
Mechanisms of Hearing
• Vibrations from sound waves move tectorial
membrane
• Hair cells are bent by the membrane
• An action potential starts in the cochlear
nerve
• Continued stimulation can lead to adaptation
Organs of Equilibrium
• Receptor cells are in two structures
– Vestibule
– Semicircular canals
Figure 8.14a–b
Organs of Equilibrium
• Equilibrium has two functional parts
– Static equilibrium
– Dynamic equilibrium
Figure 8.14a–b
Static Equilibrium
• Maculae – receptors in the vestibule
– Report on the position of the head
– Send information via the vestibular nerve
• Anatomy of the maculae
– Hair cells are embedded in the otolithic
membrane
– Otoliths (tiny stones) float in a gel around the
hair cells
– Movements cause otoliths to bend the hair cells
Function of Maculae
Figure 8.13a–b
Dynamic Equilibrium
• Crista ampullaris –
receptors in the
semicircular canals
– Tuft of hair cells
– Cupula (gelatinous cap)
covers the hair cells
Figure 8.14c
Dynamic Equilibrium
• Action of angular head
movements
– The cupula stimulates the hair
cells
– An impulse is sent via the
vestibular nerve to the
cerebellum
Figure 8.14c
Chemical Senses – Taste and Smell
• Both senses use chemoreceptors
– Stimulated by chemicals in solution
– Taste has four types of receptors
– Smell can differentiate a large range of chemicals
• Both senses complement each other and
respond to many of the same stimuli
Olfaction – The Sense of Smell
• Olfactory receptors are in the roof of the
nasal cavity
– Neurons with long cilia
– Chemicals must be dissolved in mucus for
detection
• Impulses are transmitted via the olfactory
nerve
• Interpretation of smells is made in the cortex
The Sense of Taste
• Taste buds house
the receptor
organs
• Location of taste
buds
– Most are on the
tongue
– Soft palate
– Cheeks
Figure 8.18a–b
The Tongue and Taste
• The tongue is covered with projections called
papillae
– Filiform papillae – sharp with no taste buds
– Fungifiorm papillae – rounded with taste buds
– Circumvallate papillae – large papillae with taste
buds
• Taste buds are found on the sides of papillae
Structure of Taste Buds
• Gustatory cells are the receptors
– Have gustatory hairs (long microvilli)
– Hairs are stimulated by chemicals dissolved in
saliva
Anatomy of Taste Buds
Figure 8.18
Taste Sensations
• Sweet receptors
– Sugars
– Saccharine
– Some amino acids
• Sour receptors
– Acids
• Bitter receptors
– Alkaloids
• Salty receptors
– Metal ions
Developmental Aspects of the Special
Senses
• Formed early in embryonic development
• Eyes are outgrowths of the brain
• All special senses are functional at birth;
vision takes time to become fully functional