Download lecture 20

Lecture #20
Nervous System
Two organ systems coordinate and
direct activities of a body
• Nervous system
– Swift, brief responses to stimuli
• Endocrine system
– Adjusts metabolic operations
– Directs long-term changes
Anatomical Classification of the Nervous
System
• Central Nervous System
– Brain and spinal cord
• Peripheral Nervous System
– All neural tissue outside CNS
Cells in Nervous Tissue
• Neurons
• Neuroglia
Neuroglia (Glia)
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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
two types in the PNS
– Schwann cells
– Satellite cells
• four types in the CNS
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Astrocytes
Oligodendrocytes
Microglia
Ependymal cells
Astrocytes
• Largest of glial cells
• Star shaped with many processes
projecting from the cell body
• Help form and maintain blood-brain barrier
• Provide structural support for neurons
• Regulate ion concentrations for generation of nerve impulses/action potentials
• Regulate nutrient concentrations for neuron survival
• Take up excess neurotransmitters
• Repair nervous tissue
Oligodendrocytes
• Most common glial cell type
• fewer processes than
astrocytes
• round or oval cell body
• forms myelin sheath around
the axons of neurons in CNS
• form a supportive network
around CNS neurons
• analogous to Schwann cells
of PNS
Microglia
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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
CNS
Ependymal Cells
PNS
Neuron
VENTRICLE
Cilia
Astrocyte
Oligodendrocyte
Schwann cell
Microglial cell
Capillary
Ependymal cell
• epithelial cells that line the cerebral cavities (ventricles) &
central canal
• produce & circulate the cerebrospinal fluid (CSF) found in these
chambers
• form a structure with capillaries called a choroid plexus
• CSF = colourless liquid that protects the brain and SC against
chemical & physical injuries, carries oxygen, glucose and other
necessary chemicals from the blood to neurons and neuroglia
PNS: Satellite Cells
• Flat cells surrounding PNS axons
• Support neurons in the PNS
PNS: Schwann Cells
Neurilemma
• each cell produces part of the myelin sheath
surrounding an axon in the PNS
• outmost layer of the sheath = neurilemma
• contributes to regeneration of PNS axons
• regions of no myelin = Nodes of Ranvier
The Neuron
-comprised of:
1. cell body or soma
2. dendrites
3. an axon
-neurofilaments – cytoskeleton of the neuron
-Nissl bodies – endoplasmic reticulum
-perikaryon – region outside of the nucleus
Neurons
2. Dendrites (little trees)
- the receiving or input
portion of the neuron
-short, tapering and
highly branched
-surfaces specialized for
contact with other
neurons
-bind the chemicals of
neuronal communication
= neurotransmitters
-help trigger the nerve
impulse in neurons =
action potential
3. Axons
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long, thin cylindrical process of the neuron
conduct the action potential away from cell
body toward another neuron
joins the cell body at a cone-shaped elevation
= axon hillock
axon hillock becomes the axon
between the axon hillock and the axon =
trigger zone – site where the action potential
arises
cytoplasm = axoplasm
plasma membrane = axolemma
axon and collaterals end in fine processes
called axon terminals
swollen tips called synaptic end bulbs contain
vesicles filled with neurotransmitters
NTs are released when the action potential
enters the end bulb
Synapses
• synapse points of communication between two neurons
• two types
– 1. chemical – two neurons separated by a synaptic cleft
• requires the release of chemicals called neurotransmitters from the presynaptic neuron and the binding of this neurotransmitter by the postsynaptic neuron
• majority of chemical synapses formed between end bulb and dendrites
• some can form between end bulbs and cell body
Dendrites
Stimulus
2. electrical – direct
connection between
pre- and post-synaptic
neuron
- connected via gap
junctions
faster of the two
synapses
Nucleus
Cell
body
Presynaptic
cell
Signal
direction
Synapse
Neurotransmitter
Axon hillock
Axon
Synaptic terminals
Postsynaptic cell
Synaptic
terminals
Functional Classification of Neurons
• Sensory (afferent) neurons PNS
– transport sensory information
from skin, muscles, joints, sense
organs & viscera to CNS
• Motor (efferent) neurons - PNS
Dendrites
Axon
Cell
body
– send motor nerve impulses to
muscles & glands
• Interneurons (association)
neurons- CNS
– connect sensory to motor neurons
– 90% of neurons in the body
Sensory neuron
Motor neuron
Organization of vertebrate nervous
systems
• brain provides the processing/integrative functions
• the spinal cord conducts information to and from the brain
and body
• spinal cord and brain develop from the dorsal hollow
nerve cord
• front end of the nerve cord expands to become the brain
– embryologic development of the brain results in the formation
of a:
• forebrain – gives rise to the cerebrum & the diencephalon
• midbrain – gives rise to the midbrain
• hindbrain - gives rise to the pons, medulla & cerebellum
• the remaining nerve cord becomes the spinal cord
Divisions of the nervous system
Central Nervous
System
(information processing)
Peripheral Nervous
System
Efferent neurons
Afferent neurons
Sensory
receptors
Autonomic
nervous system
Motor
system
Control of
skeletal muscle
Internal
and external
stimuli
Sympathetic
division
Parasympathetic
division
Enteric
division
Control of smooth muscles,
cardiac muscles, glands
The peripheral nervous system
• the somatic nervous system controls voluntary
motor impulses to skeletal muscle
– also receives sensory input from muscles, joints,
tendons and skin
• the autonomic nervous system has sympathetic,
parasympathetic, and enteric divisions
• the sympathetic division regulates arousal and
the “fight-or-flight” response
• the parasympathetic division has antagonistic
effects on sympathetic target organs and
promotes calming and a return to “rest and
digest” functions
• The enteric division controls activity of the
digestive tract, pancreas, and gallbladder
The ANS
Sympathetic division
Parasympathetic division
Action on target organs:
Action on target organs:
Constricts pupil
of eye
Dilates pupil of eye
Stimulates salivary
gland secretion
Inhibits salivary
gland secretion
Constricts
bronchi in lungs
Cervical
Sympathetic
ganglia
Relaxes bronchi
in lungs
Slows heart
Accelerates heart
Stimulates activity
of stomach and
intestines
Inhibits activity of
stomach and intestines
Thoracic
Stimulates activity
of pancreas
Inhibits activity
of pancreas
Stimulates
gallbladder
Stimulates glucose
release from liver;
inhibits gallbladder
Lumbar
Stimulates
adrenal medulla
Promotes emptying
of bladder
Promotes erection
of genitalia
Inhibits emptying
of bladder
Sacral
Synapse
Promotes ejaculation
and vaginal contractions
Functional divisions of the peripheral
nervous system
• Afferent
– Sensory information from receptors into CNS
• Efferent
– Motor commands from the brain to muscles and
glands
– Somatic division
• Voluntary control over skeletal muscle
– Autonomic division
• Involuntary regulation of smooth and cardiac muscle, glands
• fish:
– CNS consisting of a brain and spinal cord
– sensory receptors widely distributed over the body
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touch and temperature
also are specialized receptors for smell, vision, hearing, equilibrium and balance
e.g. external nares – snouts of fishes – lead to olfactory receptors
receptors for equilibrium, balance and hearing are located in the inner ear
lateral-line system – along each side of the fish and branching over the head
– responsive to pressure, vibration
– how the fish “hears”
• amphibians:
– brain is similar to other vertebrates
– brain develops from three embryologic divisions: forebrain (smell,
autonomic control centers), midbrain (vision) & hindbrain (heart rate
and respiration)
– sensory receptors over the skin
• bare nerve endings for heat, cold and pain
• lateral-line system just like fishes – response to vibrations
• chemoreceptors in the nasal epithelium, linings of the mouth and tongue
and over the skin
– vision becomes an important sense
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hunt via sight
number of adaptations have taken place to create the terrestrial eye
eyes become located on the front of the head – not the sides
this provides binocular vision for improved depth perception
lower eyelid called the nictating membrane is moveable and cleans the
eye surface
orbital glands to wash and lubricate the eye
lens is large and round – set back from the cornea and is surrounded by a
fold of epithelium called the iris
focusing requires refraction of light – provided by the cornea and
changing the position of the lens
to focus on close objects – the lens is moved forward
retina contains photoreceptors called rods and cones
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hearing also becomes well developed in the amphibians
– auditory system transmits both vibrations and sound
– ears of frogs and toads consists of a tympanic membrane, a middle ear and an inner ear
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vocalization
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sound production apparatus – larynx and vocal cords
mainly a reproductive function of the male frog
salamanders do not vocalize
advertisement calls to announce territory
breeding calls
female responds with reciprocation calls to indicate receptiveness
distress calls – loud enough to scare the predator
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reptile:
– brain is similar to other vertebrates
– increased cerebral size vs. amphibians to accommodate the increased
sense of smell
– increased cerebellum
– hearing mainly for the detection of vibration (can have a lateral line system)
– vision is the dominant sense in most reptiles
• optic lobe is larger in reptiles vs. amphibians
• snakes – focus by moving the lens forward
• all other reptiles focus by rounding the lens by the action of ciliary
muscles surrounding the lens
• some reptiles possess a median or parietal eye – for distinguishing light
and dark
– olfactory senses are better developed in reptiles than in amphibians
• development of a partial secondary palate to increase the surface area
for olfactory epithelium
• may also possess blind-ending pouches = Jacobson’s (vomeronasal)
organs
– snakes – use forked tongues to bring in air particles into the
mouth – travel to the Jacobson’s organs for “smelling”
– heat sensitive pits in vipers – “sixth sense”
• pits located between the eyes and nostrils
• minute temp differences are seen as infrared rays
• used in prey location
Major Regions of the Mammalian Brain
Neuronal Organization: CNS
•Two kinds of neural tissue
found in both brain and
spinal cord:
1.
Gray matter =
neuroglial cells +
unmyelinated axons,
and dendrites/cell
bodies of neurons
-when it forms the outer
layer of the cerebrum
= cerebral cortex
-Gray matter also found as
nuclei deep in the brain =
clusters of neuronal cell
bodies in the CNS
-Collections of nuclei can
form a center (higher brain
function)
Neuronal Organization: CNS
• 2. White matter = myelinated axons
• Cell bodies found in gray matter
• White matter tracts = bundles of
axons
– For the conduction of nerve
impulses
– Brain – three types of tracts
(commisural, association,
projection)
– Spinal cord - Two types: sensory and
motor tracts (ascending and
descending)
male vs. female brain:
http://www.youtube.com/watch?v=L29KmQx
EA3E
Cerebrum
• Cerebrum = largest portion
-left and right cerebral hemispheres divided by the longitudinal fissure
-connected by an accumulation of white matter - the corpus callosum
-folded into ridges and grooves: grooves = sulci
-sulci divide the cerebrum into lobes
-ridges = gyri (gyrus)
The Cerebral Cortex
-outermost layer of the cerebrum,
contains billions of gray matter
neurons – less than 5mm thick!!
-white matter tracts extend out and
run to other gray matter areas
(either another gyrus or a nucleus)
-the cortex of each gyri contains
neurons for the specific processing
of sensation, voluntary movement,
speech, all thought processes
-gyri can be classified as: primary or
association areas
-primary areas are for the initial processing of raw sensory information or motor
commands - e.g. primary visual, auditory & gustatory areas
-also contains gyri that are called association areas for integration and analysis of
specific sensory info & help in making of “decisions”
e.g. somatosensory, visual, auditory, language and common integrative areas
The Cerebral Cortex
• awareness of surroundings,
language, cognition,
memory and consciousness
• cognition:
– job of the neocortex
– first 6 layers of the cerebral
cortex
– the more convoluted the
neocortex (i.e more gyri and
sulci) – the higher the
cognitive function????
– may not be true
– birds can be relatively smart
• do not have a convoluted
neocortex
Human brain
Cerebrum (including
cerebral cortex)
Thalamus
Midbrain
Hindbrain
Cerebellum
Avian brain
to scale
Cerebrum
(including pallium)
Avian brain
Cerebellum
Hindbrain
Thalamus
Midbrain
The Cerebral Cortex
• sensory processing:
– numerous gyri whose cerebral
cortex processes sensory
information
– parietal lobe – somatosensory
areas & gustatory areas
• primary somatosensory gyrus –
receives sensory information
from the skin, muscles and joints
– temporal lobe – auditory areas
– occipital lobe – visual areas
– once sensory information is
processed – info gets sent to
the frontal lobe where
movements are planned
– one of the major areas for this
– primary motor area in the
frontal lobe
Frontal lobe
Parietal lobe
Jaw
Tongue
Leg
Hip
Trunk
Neck
Head
Knee
Hip
Genitalia
Toes
Tongue
Pharynx
Primary
motor cortex
Abdominal
organs
Primary
somatosensory
cortex
The Cerebral Cortex
• language and speech:
– French physician Pierre Broca –
involved in mapping cognitive
functions to specific areas of the
cerebral cortex
– became interested in those patients
who could understand language but
could not speak
– identified an area of the left front
lobe in the majority of people =
Broca’s area
– damage to this area results in the
inability to speak (aphasia) – but the
ability to understand language
• responsible for motor commands to
the muscles of the face
• active when speaking
Max
Hearing
words
Seeing
words
– in the left temporal lobe =
Wernicke’s area (Karl Wernicke)
• active when hearing language
– damage to this area – able to speak
BUT unable to understand language
Min
Speaking
words
Generating
words
Lateralization
• Broca’s areas and Wernicke’s area are in the left hemisphere in
most people
– these people are mostly right-handed also
– Broca’s area is active in 96% of right-handed people but only 76% of
left-handed people
• language is principally the job of the left hemisphere
– along with math and logical thought
• right hemisphere will have other distinct functions
– recognition of faces, patterns, spatial relationships and non-verbal
thinking
• differences in the function of the hemispheres is referred to as
lateralization
• when the two hemispheres work together – do so through the
commissures – corpus callosum, anterior & posterior commissures
The Frontal Lobe
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motor commands
personality
decision making
damage to the frontal lobe
can affect all of these
• but intellect and memory are
left intact
• specific destruction of the
frontal lobe to affect
personality = lobotomy
The basal ganglia:
-made up of several gray matter nuclei found deep within the cerebrum
1. receives sensory input from the cerebral cortex & provides output to the
motor areas of the cortex
2. integrates motor commands
3. regulates the initiation & termination of muscle movements
4. also functions to anticipate body movements & controls subconscious
contraction of skeletal muscle
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comprised of the:
1. striatum
– caudate nucleus
– putamen
– nucleus accumbens
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2. globus pallidus
3. claustrum
4. substantia nigra
5. subthalmic nucleus
Diencephalon
• Diencephalon
– includes the hypothalamus,
thalamus, epithalamus and
subthalamus
– thalamus: 80% of the diencephalon
• paired oval shaped lobes of gray
matter organized into nuclei,
interconnected with white matter
tracts
• major relay station for most sensory
impulses from the SC, brain stem into
the cerebrum
• relays motor information from the
cerebellum to the cerebrum (for
coordination)
• crude perception of pain, heat and
pressure (refined in cerebrum)
Diencephalon
Thalamus
Pineal gland
Hypothalamus
Brainstem
Midbrain
Pituitary gland
Pons
Medulla
oblongata
Spinal cord
•hypothalamus
-emotions, autonomic functions,
hormone production
-made of numerous nuclei and
tracts
Diencephalon
1. control of the ANS –
integrates signals from the
ANS (regulated smooth and
cardiac muscle contraction)
major regulator of visceral
activities (heart rate, food
movements, contraction of
bladder)
2. produces hormones &
connects with pituitary to
regulate its activity
3. regulates emotional and behavioral patterns – rage,
aggression, pain and pleasure + sexual arousal
4. regulates eating & drinking – hypothalamus contains
a thirst center which responds to a rise in osmotic
pressure in the ECF (dehydration)
5. controls body temperature – monitors temp of blood
flowing through the hypothalamus
Diencephalon
•epithalamus = pineal gland
– part of the endocrine system
-secretes the hormone melatonin
-increased secretion in dark
-promote sleepiness and helps set the circadian rhythms of
the body (awake/sleep period)
BRAIN STEM
•comprised of three structures: midbrain, pons & medulla
BRAIN STEM
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Medulla oblongata
– continuation of the spinal cord
– inferior part of the brain stem
– relays sensory information and controls
automatic motor functions
– white matter connects the white matter
of the spinal cord with the rest of the
brain
– contains several nuclei also - these nuclei
regulate autonomic functions - reflex
centers for regulating heartbeat and BP
(cardiovascular center), respiration
(respiratory center), plus vomiting,
coughing, sneezing, hiccuping and
swallowing
BRAIN STEM
• Pons
= “bridge”
- connection point from cerebrum to
cerebellum – via white matter tracts
– nuclei help control both voluntary &
involuntary motor responses
• e.g.Pneumotaxic and apneustic
nuclei – help regulate breathing with
medulla
BRAIN STEM
• Midbrain (Mesencephalon)
– relay station between the cerebrum
and the spinal cord and cerebellum
– contains white matter tracts that
connect the midbrain to the cerebrum
= cerebral peduncles
• White matter tracts that conduct
impulses from the cerebrum to the
pons and medulla into the spinal cord
• contains white matter tracts that connect
the midbrain to the cerebellum =
cerebellar peduncles
• one nucleus = substantia nigra –
produces large amounts of dopamine loss of these neurons = Parkinsons
• Cerebellum
– divided into hemispheres with
lobes - like the cerebrum
• anterior and posterior lobes
– has a superficial layer of gray
matter called the cerebellar
cortex - like the brain
– deep to this gray matter are tracts
of white matter (arbor vitae) and
gray matter nuclei
– controls voluntary and
involuntary motor activities
• evaluates and coordinates
motor activities initiated by the
cerebrum and corrects
problems by sending info back
to the cerebrum
• regulate posture & balance
Integrative Functions
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Arousal and Sleep
Memory and Learning
Emotions
Language and speech
Protection: The Cranial Meninges
• Cranium is covered with protective
membranes = meninges
– Cranial meninges are continuous with
spinal meninges
– 3 layers:
– 1. outer, fibrous dura mater – forms
sheets (falx) that separate the cerebrum
and the cerebellum into the hemispheres
and the cerebellum from the cerebrum
– in the cranial region - comprised of an
outer endosteal layer and an inner
meningeal layer
2. middle arachnoid mater
3. inner, thin pia mater
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Cranial Meninges
– -there are spaces between these membranes
– A. subarachnoid space: between the arachnoid and pia mater
» large veins run through the subarachnoid space
» connecting membranes joining the pia and arachnoid mater also found
here (arachnoid trabeculae)
B. subdural space: between the arachnoid and the dura mater
C. epidural space – between the dura mater and the vertebral canal in the spinal
column
• brain contains fluid-filled chambers =
Ventricles
– 2 lateral ventricles, 1 third ventricle, 1 fourth
ventricle
– connects to the central canal which runs into
the spinal canal
– these chambers contain cerebrospinal fluid
– made by specialized structures in the
ventricles – choroid plexus (contain
ependymal cells)
– continually circulates - ventricles and central
canal to subarachnoid space
– all CSF makes its way back to the
subarachnoid space
Protection: CSF
Flow of CSF
draining points for CSF = arachnoid villi
Spinal Cord
• length in adults = 16 to 18 inches
• Cervical and lumbar
enlargements
– cervical = C4 to T1, nerves to and
from upper limbs
– lumbar = T9 to T12, nerves to and
from lower limbs
• Tapers to conus medullaris
• filium terminale arises from the
CM - extension of the pia mater that
anchors the SC to the coccyx
• 31 segments each with
– Dorsal root ganglia
• Sensory neuron cell bodies
– Pair of dorsal roots
– Pair of ventral roots
•Cervical
•and lumbar
enlargements
Histology of the Spinal Cord
• Central gray matter
– organized as gray horns
• Peripheral white matter
– Myelinated and
unmyelinated axons
running up and down the
cord
– Organized as white matter
tracts
Organization of White Matter
• Organization of Gray Matter
• 1. Posterior gray horns
– for incoming sensory information
• 2. Anterior gray horns
– for outgoing somatic motor neurons
• 3. Lateral gray horns
– for outgoing autonomic motor neurons
• Gray commissures
– axons of interneurons crossing the cord
• Organization of White matter
– Anterior, lateral and posterior white
columns
– Contain tracts of myelinated neurons
• Ascending tracts relay sensory
information up the spinal cord to brain
• Descending tracts carry motor
information down the spinal cord