Download - Chapter 14 The Somatic Nervous System
Chapter 14
The Somatic Nervous
System
Neural Information
An Overview of Neural Integration.
Ch 14 Ch 15
Somatic Nervous System (SNS)
Nervous system- responsible for our conscious
perception of the environment and our
voluntary responses to our perceptions with
skeletal muscles.
Receive- Incoming( Afferent)sensory
information- process this information- and send
out information through motor neurons and
pathways that control skeletal muscles.
Nervous Information Review
Afferent Division of the Nervous System
Receptors (General and Special senses)
Sensory neurons
Sensory pathways
Efferent Division (from CNS) of the Nervous
System
Nuclei
Motor tracts
Motor neurons
Sensory Information
Sensory Receptors
Specialized cells that monitor specific
conditions in the body or external environment
When stimulated, a receptor passes
information to the CNS in the form of action
potentials along the axon of a sensory neuron
Sensory Information
Sensory (Afferent) Pathways
Deliver somatic and visceral sensory
information to their final destinations
inside the CNS using
Nerves
Nuclei (CNS)
Tracts (CNS)
Sensory Motor Information
Somatic Motor Portion of the Efferent Division
Controls peripheral effectors
Somatic Motor Commands
Travel from motor centers in the brain along
somatic motor pathways of
Motor nuclei (CNS)
Tracts (CNS)
Nerves
14-1 Sensory Receptors
and PerceptionGeneral and Special Senses
1. General Senses
Describe our sensitivity to
Temperature
Pain
Touch
Pressure
Vibration
Proprioception
Sensory Receptors
Sensation
The arriving information from these senses
Perception
Conscious awareness of a sensation through
processing in primary sensory areas of
cerebral cortex.
Sensory Receptors
2. Special Senses
Olfaction (smell)
Vision (sight)
Gustation (taste)
Equilibrium (balance)
Hearing
Sensory Receptors
Special senses are provided by special
sensory receptors
Special sensory receptors
Are located in sense organs such as the eye
or ear
Are protected by surrounding tissues
Sensory Receptors
The Detection of Stimuli
Receptor sensitivity
Each receptor has a characteristic sensitivity
Receptive field
Area is monitored by a single receptor cell
The larger the receptive field, the more difficult it is
to localize a stimulus
Sensory Receptors
Receptors and Receptive Fields
Sensory Receptors
The Interpretation of Sensory Information
Arriving stimulus
Takes many forms:
– physical force (such as pressure)
– dissolved chemical
– sound
– light
Interpretation Sensory Information
Sensations
Taste, hearing, equilibrium, and vision provided by
specialized receptor cells
Communicate with sensory neurons across
chemical synapses
Adaptation
Reduction in sensitivity of a constant stimulus (smells)
Your nervous system quickly adapts to stimuli that are
painless and constant
Classifying Sensory Receptors
General sensory receptors are divided into types
by the nature of the stimulus that excites them
Nociceptors (pain)
Thermoreceptors (temperature)
Mechanoreceptors (physical distortion)
Chemoreceptors (chemical concentration)
Osmoreceptors (concentration of body fluids)
Classifying Sensory Receptors
Nociceptors
Are free nerve endings with large receptive
fields
Not protected by accessory structures
Can be stimulated by many different stimuli
Sensations reach the CNS quickly and often
trigger somatic reflexes
Relayed to the primary sensory cortex and receive
conscious attention
Classifying Sensory Receptors
Thermoreceptors - Are free nerve endings
located in
The dermis, skeletal muscles, liver, hypothalamus
Conducted along the same pathways that carry
pain sensations
Sent to:
– the reticular formation
– the thalamus
– the primary sensory cortex (to a lesser extent)
Classifying Sensory Receptors
Mechanoreceptors -Sensitive to stimuli that distort
their plasma membranes
Contain mechanically gated ion channels whose
gates open or close in response to
Stretching
Compression
Twisting
Other distortions of the membrane
Classifying Sensory Receptors
Three Classes of Mechanoreceptors
1. Tactile receptors
provide the sensations of touch, pressure,
and vibration:
– touch sensations provide information about
shape or texture
– pressure sensations indicate degree of
mechanical distortion
– vibration sensations indicate pulsing or
oscillating pressure
Classifying Sensory Receptors
Tactile Receptors in the Skin.
Pacinian
corpuscle
Classifying Sensory Receptors
2. Baroreceptors
Detect pressure changes in the walls of
blood vessels and in portions of the
digestive, reproductive, and urinary tracts
3. Proprioceptors
Monitor the positions of joints and muscles
The most structurally and functionally
complex of general sensory receptors
Classifying Sensory Receptors
Mechanoreceptors: Tactile Receptors
Fine touch and pressure receptors
Are extremely sensitive
Have a relatively narrow receptive field
Provide detailed information about a source of
stimulation, including:
– its exact location, shape, size, texture, movement
Tactile Receptors
Tactile Receptors in the Skin.
Tactile Receptors
Tactile Receptors in the Skin.
Tactile Receptors
Tactile Receptors in the Skin.
Meissner
corpuscle
Baroreceptors
Monitor change in pressure
Consist of free nerve endings that branch
within elastic tissues in wall of distensible
organ (such as a blood vessel)
Respond immediately to a change in
pressure, but adapt rapidly
Chemoreceptors
Respond only to water-soluble and lipid-soluble
substances dissolved in surrounding fluid
Receptors exhibit peripheral adaptation over
period of seconds
Located in the
Carotid bodies, Aortic bodies:
– between the major branches of the aortic arch
Receptors monitor pH, carbon dioxide, and oxygen
levels in arterial blood
Special Senses
Five Special Senses
Olfaction
Gustation
Vision
Equilibrium
Hearing
Figure 17–1a
Smell (Olfaction)
Olfactory Organs
Provide sense of smell
Located in nasal cavity on either side of
nasal septum
Made up of two layers
Olfactory epithelium
Lamina propria
Smell (Olfaction)
The Olfactory Organs.
Smell (Olfaction)
Olfactory Glands -Secretions coat surfaces of olfactory
organs
Olfactory Receptors- Highly modified neurons
Olfactory reception -Involves detecting dissolved
chemicals as they interact with odorant-binding proteins
Axons leaving olfactory epithelium
Penetrate cribriform plate of ethmoid
Reach olfactory bulbs of cerebrum where first synapse
occurs -Axons leaving olfactory bulb: travel along olfactory tract
to reach olfactory cortex, hypothalamus, and portions of limbic
system
Taste (Gustation)
Gustation provides information about the
foods and liquids consumed
Taste receptors (or gustatory receptors)
are distributed on tongue and portions of
pharynx and larynx
Clustered into taste buds
Taste (Gustation)
Gustatory
Receptors.
Taste (Gustation)
Taste buds contain
Basal (stem) cells
Gustatory cells
Extend taste hairs through taste pore
Survive only 10 days before replacement
Monitored by cranial nerves (VII-facial) that synapse
within the medulla oblongata, then on to thalamus
and primary sensory cortex
The Eye
Accessory Structures of the Eye
Provide protection, lubrication, and support
Includes
The palpebrae (eyelids)
The superficial epithelium of eye
The lacrimal apparatus
Eyelids (Palpebrae) -Continuation of skin
Blinking keeps surface of eye lubricated, free of dust
and debris
Accessory Structures of the EyeLacrimal caruncle -soft tissue with glands producing thick
secretions
Contributes to gritty deposits that appear after good night’s
sleep
Conjunctiva
Epithelium covering inner surfaces of eyelids (palpebral
conjunctiva) and outer surface of eye (ocular
conjunctiva)
Lacrimal Apparatus
Produces, distributes, and removes tears
Lacrimal gland (tear gland)
Accessory Structures of the Eye
Gross and Superficial Anatomies of the Accessory Structures.
Accessory Structures of the Eye
The Organization of the Lacrimal Apparatus.
The Eye
Three Layers of the Eye (know anatomy & functions)
Outer fibrous tunic- sclera, cornea, limbus
Middle vascular tunic- iris, ciliary body, choroid
Inner neural tunic- retina (rods & cones), optic disk,
associated cells
Eyeball
Is hollow
Is divided into two cavities (segments in lab):
Large posterior cavity
Smaller anterior cavity
The Eye
The Sectional Anatomy of the Eye.
The Eye
The Sectional Anatomy of the Eye.
The Eye
The Sectional Anatomy of the Eye.
The Eye
The Pupillary Muscles.
The Eye
The Optic Disc
of the Retina.
The Eye
The Cellular Organization of the Retina.
The Eye
Photograph of the Retina as Seen through the Pupil.
The Chambers of the Eye
Ciliary body and lens divide eye into
Large posterior cavity (vitreous body-supports
retina)
Smaller anterior cavity (aqueous humor- shape):
The Eye
The Circulation of Aqueous Humor.
The Eye- Lens
Lens fibers
Cells in interior of lens-No nuclei or organelles
Filled with crystallins, which provide clarity and focusing
power to lens
Cataract
Condition in which lens has lost its transparency
Light refraction
Bending of light by cornea and lens
Focal point Focal distance
The Eye
Factors Affecting Focal Distance.
C
The Eye
Light Refraction of Lens
Accommodation
Shape of lens changes to focus image on retina
Astigmatism
Condition where light passing through cornea and lens is not
refracted properly
Visual image is distorted
Visual acuity – highest at fovea
Clarity of vision
“Normal” rating is 20/20
The Eye
Accommodation.
The Eye
Visual
abnormalities
Nearsightedness
Farsightedness
Visual Physiology
Rods - Respond to almost any photon, regardless of energy
content Cones - Have characteristic ranges of sensitivity
Visual Physiology
Visual pigments
Is where light absorption occurs
Derivatives of rhodopsin (opsin plus retinal)
Retinal: synthesized from vitamin A
Photoreception- Photon strikes retinal portion of rhodopsin molecule
embedded in membrane of disc
Opsin is activated
Bound retinal molecule with two possible
configurations.(isomers)
Visual Physiology
Photoreception pigment molecule structural change leads to changes in membrane potential of rods /cones.
Visual Physiology
Cone Types and Sensitivity to Color.
Figure 17–16
Color Vison
Integration of information from red,
green, and blue cones
Color blindness
Inability to detect certain colors
Visual Physiology
The Visual Pathways
Begin at photoreceptors
End at visual cortex of cerebral hemispheres
Message crosses two synapses before it
heads toward brain
Photoreceptor to bipolar cell
Bipolar cell to ganglion cell
Processing Visual Information
Axons from ganglion cells converge on optic disc
Proceed toward diencephalon as optic nerve (II)
Two optic nerves (one for each eye) reach
diencephalon at optic chiasm
From combined field of vision arrive at visual
cortex of opposite occipital lobe
Left half arrive at right occipital lobe
Right half arrive at left occipital lobe
The Visual
Pathways.
The Ear
External Ear –auricle, acoustic meatus, and tympanic
membrane (Separates external ear from middle ear), ceruminous
glands
Middle Ear
Communicates with nasopharynx via auditory tube
(Permits equalization of pressures on either side of
tympanic membrane)
Encloses and protects three auditory ossicles
Malleus (hammer), Incus (anvil), Stapes (stirrup)
The Ear
The Tympanic Membrane and Auditory Ossicles of the Middle Ear.
Tympanic Membrane
Converts arriving sound waves into mechanical
movements
Auditory ossicles conduct vibrations to inner ear
Tensor tympani muscle
Stiffens tympanic membrane
Stapedius muscle
Reduces movement of stapes at oval window
The Inner Ear
Contains fluid called endolymph
Bony labyrinth surrounds and protects membranous
labyrinth- subdivided into vestibule, semicircular
canals, and cochlea.
The Inner Ear
Vestibule (Encloses saccule and utricle)
Receptors provide sensations of gravity
and linear acceleration
Semicircular canals
Receptors stimulated by rotation of
head- rotational/angular movements
Cochlea -Contains cochlear duct (elongated
portion of membranous labyrinth)
Receptors provide sense of hearing -
Round window and oval window
Equilibrium
Sensations provided by receptors of vestibular complex
Hair cells
Basic receptors of inner ear
Provide information about direction and strength of
mechanical stimuli
The Semicircular Ducts
Are continuous with utricle- each duct contains- Ampulla
with gelatinous cupula, associated sensory receptors- hair cells with
cilia
The Ear
The Semicircular Ducts.
The Utricle and Saccule
Provide equilibrium sensations- linear acceleration
and gravity
Are connected with the endolymphatic duct, which
ends in endolymphatic sac
Maculae- oval structures where hair cells cluster
Statoconia -densely packed crystals
on surface of gelatinous mass
Otolith (ear stone)
= gel and statoconia
The Ear
Macular Function.
Neural Pathways for Equilibrium
SensationsVestibular receptors- Activate sensory neurons of
vestibular ganglia
Axons form vestibular branch of vestibulocochlear nerve
(VIII) – Synapse within vestibular nuclei
Integrate sensory information about balance and
equilibrium from both sides of head
Relay information from vestibular complex to cerebellum
Relay information from vestibular complex to cerebral
cortex
Provide conscious sense of head position and
movement
The Ear
Pathways for Equilibrium Sensations.
Hearing
Cochlear duct receptors
Provide sense of hearing
HearingAuditory ossicles -Convert pressure fluctuation in air into
much greater pressure fluctuations in perilymph of cochlea
Frequency of sound:
– determined by which part of cochlear duct is stimulated
Intensity (volume):
– determined by number of hair cells stimulated
Cochlea – three fluid-filled chambers-
Upper chamber – oval window membrane vestibule –
vestibular duct
Middle chamber- contains organ of Corti with sensory hair
cells – in cochlear duct
Lower chamber- tympani – tympanic duct -round window
membrane to middle ear chamber.
Stapes hits oval window and creates fluid (perilymph) pressure in vestibule
through tympani chambers- distorting basilar membrane of middle chamber
(cochlear doctor scala media).
The Cochlea- Unwound
Cochlear Duct Receptors
Basilar membrane:
– separates cochlear duct from tympanic duct
– hair cells with stereocilia in contact with overlying
tectorial membrane
The Ear
The Organ of Corti.
The Ear
Hearing.
The Ear
Pressure Waves
Wavelength- Distance between two adjacent wave troughs
Frequency -Number of waves that pass fixed reference point at
given time -Use term cycles instead of waves:
– Hertz (Hz): cycles/second (cps)
Pitch -Our sensory response to frequency
Amplitude -Intensity of sound wave
Sound energy is reported in decibels
Auditory Pathways
Cochlear branch
Formed by afferent fibers of ganglion neurons:
– enters medulla oblongata
– synapses at dorsal and ventral cochlear nuclei
– information crosses to opposite side of brain:
» ascends to inferior colliculus of mesencephalon
Ascending auditory sensations
Synapse in thalamus
Projection fibers deliver information to auditory cortex of
temporal lobe
Figure 17–31
Pathways for Auditory Sensations
The Ear
With age, damage accumulates
Tympanic membrane gets less flexible
Articulations between ossicles stiffen
Round window may begin to ossify
14.2 Somatic Sensory (Ascending)
Pathways-Carry sensory information from the skin and
musculature of the body wall, head, neck, and limbs
Three major somatic sensory (Ascending) pathways
–lateral and posterior spinal tracts
The spinothalamic, spinocerebellar, and posterior column
pathway-
Involve three neurons – Neurotransmitter = (Ach)
First order-from receptors to medulla;
Second- from medulla to thalamus;
Third -from thalamus to sensory homunuculus.
Sensory Pathways
Sensory Pathways and Ascending Tracts in the Spinal Cord.
The Posterior
Column Pathway.
Posterior Column Pathway
Sensory homunculus
Functional map of the primary sensory cortex
Distortions occur because area of sensory cortex
devoted to particular body region is not
proportional to region’s size, but to number of
sensory receptors it contains
Spinothalamic Tract
Feeling Pain (Lateral Spinothalamic Tract)
An individual can feel pain in an uninjured part of the
body when pain actually originates at another location
Strong visceral pain
Sensations arriving at segment of spinal cord can stimulate
interneurons that are part of spinothalamic pathway
Activity in interneurons leads to stimulation of primary
sensory cortex, so an individual feels pain in specific part of
body surface:
– also called referred pain
Sensory Pathwa
The Spinothalamic Tracts of the Spinothalamic Pathway.
14.3 Somatic Motor (Descending)
Pathways
SNS controls contractions of skeletal
muscles
Always involve at least two motor neurons
1. Upper motor neuron
Cell body lies in a CNS processing center
Synapses on the lower motor neuron
Innervates a single motor unit in a skeletal muscle:
– activity in upper motor neuron may facilitate or inhibit
lower motor neuron
Somatic Motor Pathways
Always involve at least 2 motor neurons
2. Lower motor neuron
Cell body lies in a nucleus of the brain stem or
spinal cord
Triggers a contraction in innervated muscle:
– only axon of lower motor neuron extends outside CNS
– destruction of or damage to lower motor neuron
eliminates voluntary and reflex control over innervated
motor unit
Somatic Motor (Descending)Pathways
1. The Corticospinal tract
Sometimes called the pyramidal system
Provides voluntary control over skeletal muscles
System begins at pyramidal cells of primary motor cortex
Axons of these upper motor neurons descend into brain stem
and spinal cord to synapse on lower motor neurons that
control skeletal muscles
Contains three pairs of descending tracts
Corticobulbar, Lateral corticospinal and Anterior corticospinal
tracts
The Corticospinal tract
Motor homunculus
Primary motor cortex corresponds point by point with specific
regions of the body
Cortical areas have been mapped out in diagrammatic form
Homunculus provides indication of degree of fine motor
control available:
– hands, face, and tongue, which are capable of varied and
complex movements, appear very large, while trunk is relatively
small
– these proportions are similar to the sensory homunculus
The Corticospinal
Pathway.
Upper
motor neuron
Lower
motor neuron