Download Nervous System Overview

Nervous System Overview
Subdivisions of Nervous System
Subdivisions of Nervous System
Two major subdivisions
• Central nervous system (CNS)
– brain and spinal cord
– Is protected by the cranium and vertebral column
– Nucleus = a group of cell bodies in the CNS
• Peripheral nervous system (PNS)
– Consist of the rest of the nervous system.
– 31 Spinal nerves and 12 cranial nerves are bundled
extend of both the brain and spinal cord.
– ganglion = groups of cell bodies in a nerve that are
located outside the (CNS)
Gray and White Matter
•
•
Gray matter = neuron cell bodies,
dendrites, and synapses
– forms cortex over cerebrum
and cerebellum
– forms nuclei deep within brain
White matter = bundles of axons
– forms tracts that connect parts
of brain
Meninges
• Dura mater: outermost,
tough membrane
– outer periosteal layer
against bone
• Arachnoid layer:
– subarachnoid space
were cerebral spinal fluid
flows
• pia mater:
– is thin layer in direct
contact with brain tissue
Meningitis
• Inflammation of the meninges
• Disease of infancy and childhood
– between 3 months and 2 years of age
• Bacterial and virus invasion of the CNS by
way of the nose and throat
• Signs include high fever, stiff neck,
drowsiness and intense headache and
may progress to coma
• Diagnose by examining the CSF
– lumbar puncture (spinal tap)
Cerebrospinal Fluid
• Choroid plexus creates CSF by filtration of blood which
then fills ventricles and subarachnoid space
• Functions
– Creates a buoyant environment for the brain and spinal.
• Blood-brain barrier is endothelium that is permeable to lipidsoluble materials
• alcohol, O2, CO2, nicotine and anesthetics
• 3rd and 4th ventricles are breaks in the barrier where
blood has direct access
– monitors glucose, pH, osmolarity
Flow of Cerebrospinal Fluid
Cerebral Cortex
Newest part of brain consisting of 4 lobes
– frontal, parietal, temporal and occipital
– The cortex is involved in sensory perception of all 5 senses,
motor control of skeletal muscles, memory, emotion and the
ability to learn learning
Functions of Cerebrum - Lobes
• Frontal
– voluntary motor functions
– planning, mood, smell and social judgement
• Parietal
– receives and integrates sensory information
• Occipital
– visual center of brain
• Temporal
– areas for hearing, smell, learning, memory,
emotional behavior
Functional Regions of Cerebral Cortex
Hypothalamus
• Functions in regulating many
primal regulatory functions.
– hormone secretion
– Regulation of Pituitary gland
– autonomic NS control
– thermoregulation
– food and water intake (hunger
and satiety)
Cerebellum
• Cerebellum
– Important for coordinating
various sensory and motor
inputs.
– Involved in coordinating
– Thoughts and planning
events
– maintains posture
influences volitional
movement
– Aids in speech and
distinguishing pitch and
similar sounding words
Brain Stem
Medulla Oblongata
Cardiac center
– Acceleratory center: increases
blood pressure, heart rate and
force of heart contraction by
stimulating the sympathetic
nervous system
– Inhibitory center: decreases
heart rate and force by
stimulating parasympathetic
nervous system
• Respiratory centers
– Works with Pons in controlling
rate and depth of breathing
• Pons
– concerned with posture, sleep,
hearing, balance, taste, eye
movements, facial expression,
facial sensation, respiration
Cranial Nerves
• 12 pairs of cranial nerves originate from the base of the brain
• They control a variety of functions relating to the head, neck, and
internal organs
• They can be sensory ,motor or both
Overview of Spinal Cord
• Information highway between brain and body
• Cylinder of nerve tissue within the
vertebral canal (thick as a finger)
• The spinal cord has 31 pairs of spinal
nerves.
– sensory component which enters the back of the cord
– motor component that exits the front of the spinal cord
to their specific muscles or glands.
• Spinal cord is a part of the central nervous
system
• Spinal nerves are part of the peripheral nervous
system
Gross Anatomy of Lower Spinal Cord
Meninges of Vertebra and Spinal
Cord
Cross-Sectional Anatomy of the Spinal
Cord
• Central area of gray matter shaped like a butterfly and
surrounded by white matter in 3 columns
• Gray matter = neuron cell bodies with little myelin
• White matter = myelinated axons
Gray Matter in the Spinal Cord
• Pair of dorsal or posterior horns
– Sensory input returns to the spinal cord via the dorsal root of spinal nerve
– Here it may synapse with an interneuron, motor neuron or ascend up the
spinal cord
• Pair of ventral or anterior horns
•
– Motor fibers descending from the brain leave the spinal cord via ventral root
of spinal nerve.
Central cavity :location of cerebrospinal fluid (CSF)
Sensory Receptors
• Specialized structures that detect change in the environment.
Stimulation of sensory receptors results stimulates afferent impulse
to the CNS The brain or spinal cord will interpret the afferent impulse
and respond accordingly.
Sensory Receptors
• Mechanoreceptors : respond to physical deformation
such as vibration, pressure, stretch and tension
• Thermoreceptors : respond to heat and cold
• Photoreceptors: Located in the eyes respond to light
• Chemoreceptors : respond to chemical change in the
body such a taste smell and body fluid composition
• Nociceptors : respond to pain
• Proprioceptors: gives your body a sense of position
and movements
– Located in joint capsules, muscles and tendons.
Sensory Perception
• Specific receptors for touch, pressure, stretch,
temperature, and pain transmit afferent impulses to
cortex
• Somatosensory area in postcentral gyrus
Sensory Homunculus
• Area of cortex dedicated to sensations of body parts is
proportional to the sensitivity of that body part (# of
receptors)
Somesthetic
Projection
(Ascending)
Pathways
• Pain or temperature ascends via the anterolateral pathway
• Proprioception( awareness of where one’s body is ), touch and
pressure ascends via the dorsal column pathway.
• Sensation is projected to the other side of the brain.
Motor Control
• Intention to contract a
muscle begins in motor
association (premotor) area
of frontal lobes
• Precentral gyrus (primary
motor area) relays signals
to spinal cord to stimulate
muscles on the opposite
side of the body.
• Motor homunculus proportional to number
of muscle motor units in a
region
Corticospinal Tract
• Skeletal muscle control has a
2 neuron pathway
– A neuron from the cerebral
cortex ( precentral
gyrus)descends downward.
– The axons cross in the
medulla before the
terminate at the alpha
motor neuron
(upper motor neuron)
– The upper motor neuron
synapses with the alpha
motor neuron in the ventral
horn of the spinal cord.
– The axons of the alpha
motor neurons project to
specific muscles.
(lower motor neuron)
Spina Bifida
• Congenital defect in 1 baby out of 1000
• Failure of vertebral arch to close covering spinal cord
• Folic acid (B vitamin) as part of a healthy diet for all
women of childbearing age reduces risk
Functional Divisions of PNS
• Sensory (afferent) divisions (receptors to CNS)
– visceral sensory( messages from organs) allow our
CNS to interpret internal environments.
– somatic sensory division ( messages from skin, joints,
muscles) allow our CNS to interpret both our external
environments.
• Motor (efferent) division (CNS to effectors) response to the
environment through excitation of:
– visceral motor division (ANS) Involuntary
effectors: cardiac, smooth muscle, glands
• sympathetic division (fight or flight)
• parasympathetic division (rest and digestion)
– somatic motor division (voluntary)
effectors: skeletal muscle
Anatomy of a Nerve
• A nerve is a bundle of nerve fibers (axons)
• Epineurium covers nerves, perineurium surrounds a
fascicle and endoneurium separates individual nerve
fibers
Anatomy of Ganglia in the PNS
• Cluster of neuron cell bodies in nerve in PNS is the
dorsal root ganglion
Autonomic Nervous System
• Motor nervous system controls glands, cardiac
and smooth muscle
– also called visceral motor system
• Regulates unconscious processes that
maintain homeostasis
– BP, body temperature, respiratory airflow
• ANS actions are automatic
– biofeedback techniques such as controlling
breathing rate can dramatically alter the bodies
internal state.
• train people to control hypertension, stress , anxiety, and
migraine headaches
Divisions of ANS
•
Two divisions innervate same target organs
–
may have cooperative or contrasting effects
1. Sympathetic division
–
prepares body for physical activity or any kind of stress!
•
increases heart rate, BP, airflow to organs vital for dealing with
the stress( skeletal muscles, heart and brain), blood glucose,
fatty acids levels all increase
–
If you are chased by a tiger he won’t be very sympathetic
2. Parasympathetic division
–
calms many body functions and assists in rest and
restoration functions such as digestion and waste
elimination.
•
Decreased heart rate, BP and blood will be shunted away from
skeletal muscles and towards vital organs i.e. intestinal tract
,kidneys and reproductive organs
What part of the ANS is this person
activating.
Efferent Sympathetic vs. Parasympathetic
Dual Innervations of the Iris
•
•
•
ANS has membrane receptors to both
ACh and NE
Depending on which neurotransmitter
is released
– PNS causes the release of ACH
from its postganglionic neuron
ACH then binds to its receptor on
the will cause the effector to
respond in one way ( pupils
constrict)
– The SNS causes the release of
NE from the postganglionic
neuron. That will bind to its
receptor causing the effector to
respond in the opposite manor
( pupils dilate)
Some organs have receptors for both.
The heart :
– NE increases both force and rate
of heart contraction
– ACh decreases both force and
rate heart contraction.
Blood Flow in Response to Needs
The Stretch (Myotatic) Reflex
• When a muscle is stretched, it contracts and
maintains increased tonus (stretch reflex)
– helps maintain equilibrium and posture
• head starts to tip forward as you fall asleep
• muscles contract to raise the head
– stabilize joints by balancing tension in extensors and
flexors smoothing muscle actions
• Very sudden muscle stretch causes tendon reflex
– knee-jerk (patellar) reflex is monosynaptic reflex
– testing somatic reflexes helps diagnose many diseases
• Reciprocal inhibition prevents muscles from
working against each other
– When the biceps contracts which muscle is inhibited?
The Patellar Tendon Reflex Arc
13-43
Golgi Tendon Reflex
• Proprioceptors in a
tendon near its
junction with a muscle
-- 1mm long,
encapsulated nerve
bundle
• Excessive tension on
tendon inhibits motor
neuron
– muscle contraction
decreased
The Eye
• Humans have binocular
vision (use both eyes)
• Sclera is the white of the
eye provides protection
and site for muscular
attachment.
• The iris contracts and
dilates controlling the
amount of light that
enters the eye
• Ciliary muscle change the
shape of the lens enabling
the eyes to focus at
different distances.
• Extra ocular eye muscles and nerves
Retina
• Light gets focused here. Photoreceptors are a specialized receptors
that convert light waves into electrical impulses.
– Rods allow for tracking of objects, night and peripheral vision .
Most abundant receptor of the retina.
– Cones : color vision and acuity. In highest concentration of in
the fovea. ( turn heads towards objects)
– Optic disc is where the blood vessels enter and optic nerve exits
the retina to project to the cortex. (blind spot)
The Retina
Visual Cortex
•
•
•
•
•
Images from the retina are projected
to the cortex.
The optic nerves join at the optic
chiasm. Half of the neurons will cross
here before they project to the cortex
via the optic tracts.
Left optic tract :
• L lateral retina medial vision for
the Left eye
• R medial retina for lateral vision
of the right eye
Optic tracts synapse in the thalamus
and then project to the visual cortex
of the occipital lobe.
What effect will cutting the optic
chiasm in the sagittal plane have on
vision?
.
What Do You See?
• Ambiguous images will
appear the same on the
retina however can often be
interpreted differently in the
visual cortex.
• The association areas are
influenced by previous
exposure, mood and
environment.
The Ear
Outer, Middle and Inner Ear
•
Outer Ear
•
Middle Ear
•
Inner Ear
– auricle
• focuses sound into the auditory canal towards the tympanic
membrane (ear drum)
– auditory (Eustachian) tube connects to nasopharynx
• equalizes air pressure on tympanic membrane
– ear ossicles
• malleus
• incus
• Stapes
– cochlea
• organ of sound reception
– vestibular apparatus
• semicircular ducts, utricle and saccule
– organs of equilibrium and balance
Stimulation of Cochlear Hair Cells
• Vibration of ossicles causes vibration of basilar
membrane under hair cells.
– as often as 20,000 times/second
Spiral Organ
• Stereocilia of hair cells
attach to gelatinous
tectorial membrane
• Inner hair cells
– hearing
• Outer hair cells
– adjust cochlear
responses to different
frequencies
– increase precision
Sensory Coding of Sound
• Sensory neurons associated with the hair cells exit the
cochlea via the cochlear nerve and ultimately project
to the primary auditory cortex
• Vibrations of the basilar membrane excite more inner
hair cells over a larger area
• louder sound
– triggers higher frequency of action potentials
• Pitch depends on which part of basilar membrane
vibrates
– at proximal end, membrane narrow and stiff
• brain interprets signals as high-pitched
– at distal end, membrane wider and more flexible
• brain interprets signals as low-pitched
Equilibrium
• Control of coordination and balance
• Receptors in vestibular apparatus
• Static equilibrium – perceived by macula
– perception of head orientation
• Dynamic equilibrium
– perception of motion or acceleration
• linear acceleration perceived by macula ( moving in a
car)
• angular acceleration perceived by crista ( turning head)
Macula
•
•
•
•
•
Made up of the saccule
and utricle
Require gravity to work.
Static equilibrium - when
head is tilted, weight of
membrane bends the
stereocilia
Moving in a car the linear
acceleration is detected as
otoliths lag behind.
This bends the stereocilia
and one kinocilium resulting
in a specific direction would
result in stimulation of the
vestibulocochlear nerve
Saccule and Utricle
•
•
•
Referred to as the
gravitational receptors.
– hair cells with stereocilia
and one kinocilium
buried in a gelatinous
otolithic membrane
– Otoliths embedded in the
membrane (CaC03 add to
the density which
increases inertia and
enhance the sense of
gravity and motion
Utricular hairs respond to
horizontal movement(
driving)
Saccular hairs respond to
vertical movement ( elevator)
Semicircular Channels
•
•
•
Crista ampullaris :consists
of hair cells buried in a
mound of gelatinous
membrane (one in each
duct)
Orientation causes ducts
to be stimulated by
rotation in different planes
The combination of 6
channels can provide
sensory feedback in all
planes of motions.
– Each channel signals
2 direction. (Forward
and backwards)
– This gives us
information regarding
acceleration and
deceleration.
Crista Ampullaris - Head Rotation
•
•
As head turns,
endolymph lags behind,
pushes cupula,
stimulates hair cells
This results in
stimulation of the
vestibular division on the
vestibulocochlear nerve
Psychological Disorders
• Anxiety: involves the
hippocampus (memory) and
amygdala (fear) of the
limbic system.
– Characterized as an intense
fear, apprehension, or
worrying.
– Neural connections to the
hypothalamus result in a
sympathetic response.
• Increases in
– Heart rate (palpations)
– Blood pressure (Headache)
– Excessive sweating
(diaphoreses)
The Red Flags For Systemic
Pathology
The ANS is talking to you!
1. Diaphoresis / Night sweats
2. Nausea
3. Diarrhea
4. Pallor
5. Dizziness / Syncope
6. Fever
How can the above symptoms be related to the ANS?
Common Medication Side Effects
and the ANS
•  GI motility & distress :( Almost all medications
taken orally)
• Bradycardia/Tachycardia ( Beta Blockers vs
Pseudoephedrine)
• Pupils dilated /constricted (Amphetamine vs
Alcohol)
• Difficulty breathing /Bronchoconstriction (Non
specific Beta Blockers)
• Dizziness Syncope/ Orthostatic hypotension
/(Blood pressure meds)
• (Nicotine) ?
• Pain stimuli arising from the viscera are perceived as
somatic in origin
• This may be due to the fact that visceral pain afferents
travel along the same pathways as somatic pain fibers
CNS Modulation of Pain
• CNS activity can suppress painful sensory
information by inhibiting the spinothalamic
pathway through the secretion of opiods.
– enkephalins, endorphins and dynorphins