THE CENTRAL NERVOUS SYSTEM
Brain
Characteristics:
Pinkish-gray, wrinkled
Texture of cold oatmeal
3 – 3.5 pounds in a typical adult
Intelligence
NOTE:
Size is not related to intelligence
Connections between neurons determines intelligence
100 billion neurons in the brain and each can be connected to as many
as 1000 others.
REGIONS OF THE BRAIN (4)
Ventricles
Cerebral hemispheres (cerebrum)
Diencephalon:
Thalamus
Hypothalamus
Epithalamus
Brain stem:
Midbrain
Pons
Medulla oblongata
Cerebellum
VENTRICLES
Introduction
NOTE: the brain is not solid
Ventricles are hollow chambers within the brain connected to each
other and the spinal cord canal.
Cerebrospinal fluid (CSF) fills these chambers.
Anatomy of the ventricles
Lateral ventricles, each hemisphere has:
One lateral ventricle
Interventricular foramen which is a small opening in each lateral
ventricle that leads to the third ventricle.
Third ventricle is a slit in the diencephalon
NOTE: the third ventricle is connected to the:
Lateral ventricle via the interventricular foramen
Fourth ventricle via the cerebral aqueduct
Fourth ventricle
Between the brain stem and the cerebellum
Openings in its walls lead to:
Central canal of the spinal cord
Subarachnoid space which is a fluid filled space sorrounding the
brain.
CEREBROSPINAL FLUID
Characteristics:
Liquid cushion in and around the brain and spinal cord
Function is to absorb shocks, float the brain and help nourish the
brain
Composition is 99% water
Source: choroid plexus which is a clust of capillaries in each
ventricle that continuously makes CSF.
Circulation of CSF
Ependymal cells are ciliated to create a current to circulate the
fluid.
Route of CSF is from the ventricles, in and around the spinal cord
and around the brain.
Obstructions would cause the fluid to build up
Hydrocephalus – water on the brain (p. 467)
CEREBRAL HEMISPHERES
Cerebrum – divided into 2 halves
External anatomy:
Gyri (singular is gyrus) are the outward folds
Grooves:
Sulci are shallow grooves
Examples:
Central sulcus which divides the frontal lobe from the porietal lobe.
Lateral sulcus which outlines the temporal lobe
Parieto-occipital sulcus (not visible externally)outlines the
occipital bone or suture.
Fissures are deep grooves
Example – longitudinal fissure seperates the two hemispheres.
Lobes – named after bones they're beneath:
Frontal
Parietal
Occipital
Temporal
Internal anatomy or regions
Composed of 3 general regions:
Cerebral cortex – thin outer layer of gray matter
White matter is on the inside and connects the two hemispheres.
Basal nuclei – island clusters of gray matter scattered throughout
the white matter.
Cerebral cortex
Produces our most distinctive human skills
Examples:
Speech
Emotions
Intelligence
Brodmann (1906) mapped functional areas of the cerebral cortex
3 types of functional areas
Motor – control of voluntary movement
Sensory – receives messges
Association – interpretation, analysis of information
Motor areas
Primary motor area – sends commands to the skeletal muscles
NOTE: The right hemisphere controls the left side of the body
Precentral gyrus (4){Brodman's numbering} contains the primary motor
area
Motor homunculus – little man drawn on gyrus – to represent the body
region controlled by that area of the brain
Broca's area – planning speech and speaking
Overlaps Brodmanns area 44 & 45, present in only one hemisphere,
usually left
Sensory areas
3 neurons minimum:
Receptors to spinal cord
Spinal cord to thalamus
Thalamus to the cortex
Primary somatosensory cortex
Receives signals from body receptors for touch, pain, temperature and
pressure – spatial discrimination.
Postcentral gyrus (1 – 3) behind the central sulcus and contains the
primary somatosensory cortex
Somatosensory homunculus – amount of cortex dedicated to an area is
related to how sensitive the area is.
Somatosensory association area (5 – 7) – interprets the incoming
sensory information.
NOTE: It works on prior knowledge.
Primary visual cortex – receives information (impulses) from eyes
Visual association area, interprets what we see
Occipital lobe
Primary auditory area – hearing
Temporal lobe
Olfactory cortex – smell
Medial part of temporal lobe
Gustatory cortex – taste
Parietal lobe
Wernick's area
Speech area
Sounding unfamiliar words
Probably not the complex language comprehension center
Association area – makes sense of the incoming information
NOTE:
Sites of higher mental activities "thinking" and understanding
abstract ideas
Use the various inputs to make judgements, evaluate consequences,
planning
Necessary for reasoning & concerns
Especially important – prefrontal cortex – sets humans apart because
it gives us intelligence.
Lateralization – each hemisphere has its own unique properties
The 2 cerebral hemispheres differ in structure and function
Their primary motor and sensory areas dominate different sides of the
body
Left and right association areas function differently
Left hemisphere is in charge of language, math, logic, science,
analyzing, reasoning and memorizing.
Right hemisphere has greater control over music, art, poetry and
creative design.
Cerebral white matter—for communication between the cerebral
hemispheres and other CNS centers
Corpus callosum—thick band of nerve fibers that connects the
hemispheres and allows them to function as a whole.
Basal nuclei
Islands of gray metter in the white matter
Important in motor coordination; like starting and stopping.
Parkinson's disease—could result from problems with the basal nuclei.
DIENCEPHALON: THALAMUS, HYPOTHALAMUS, EPITHALMUS
Thalamus
Forms the side walls of the third ventricle
Two masses of gray matter joined by a bridge of gray matter called
the gray commissure
Function—relays all sensory information (except smell) to the
cerebral cortex.
NOTE: 3 neurons:
Receptor --- spinal cord --- thalamus --- primary somatosensory
cortex
Hypothalamus
Forms the floor of the third ventricle
Small but important
Function helps regulate homeostasis
Controls hormone secretion by the pituitary gland
Regulates organ systems to maintain homeostasis
Influences eating, drinking, sleeping and body temperature
Helps us experience emotions, pleasure, fear, anger
NOTE: connects the nervouse and the endocrine systems
Epithalamus
Forms the roof of the third ventricle
Contains pineal gland and associated with
Melatonin
Chemical that regulates our biological clock
BRAIN STEM: MIDBRAIN, PONS, MEDULLA OBLONGATA
NOTE: houses all the sensory and motor neurons between spinal cord
and upper brain regions.
Midbrain—top of the brain stem
Cerebral peduncles (paired & ventral)—contain motor nerves going down
to the spinal cord.
Corpora quadrigemina (4 & dorsal)
Visual reflex centers –moving eyes and head when you visually follow
a moving object or if you reflexively turn to look at something.
Auditory reflex centers—moving head towards sound
Pons—the enlarged region of the brainstem
NOTE:
Mainly fibers that connect the various parts of the brain to the
spinal cord
Respiratory centers: help control breathing
Medulla oblongata
Lowest part of brainstem, blends into the spinal cord
Pyramids—2 ridges that contain motor nerve tracts that cross to
opposite sides of the brain.
Decussation of pyramids:
Point where most of these fibers cross
Each hemisphere controls the opposite side of the body
Three vital reflex centers:
Cardiac center—controls the heart
Vasomotor center—regulates blood pressure by controlling the diameter
of the blood vessels
Respiratory center—affects breathing
Non-vital reflexes—vomiting, hiccuping, coughing and sneezing.
NOTE: a blow to the medulla can be fatal
CEREBELLUM
Anatomy of the cerebellum
Two hemispheres—have fine parallel gyri
Vermis—worm like connection between the two hemispheres
Cerebellar cortex—the outer layer of the cerebellum
Arbor vitae—when cut, inside surface looks like a branching tree
Functions—planning center for subconscious events
Makes movements that are complex & smooth. EX: driving a car, riding
a bicycle, typing and skating.
Helps maintain posture
Maintains balance and equilibrium (information from inner ear)
Receives information about muscle tension
FUNCTIONAL BRAIN SYSTEMS
Work together but are not localized in a specific region
Limbic system
Location—structures in cerebrum and diencephalon that encircle the
upper brain stem
Function—responsible for emotion and memory
NOTE:
Origin in primitive smell are of the brain
Smells cause emotions and memories
Reticular system
Location—extends throughout the brain stem, connections to all areas
of the brain.
Function—regulates the reticular activating system (RAS)
Sends impulses to cerebral cortex which keeps it alert and conscious
Inhibited by sleep centers, alcohol and tranquilizers
Damge can produce unconsciousness or coma
PROTECTION OF THE BRAIN
Protective structures or fluids
Bones of the skull
Meninges which are membranes wrapped around the brain
Cerebrospinal fluid
Blood-brain barrier
Meninges—3 layers of membranes
Dura mater—"tough mother"
Outer layer (membrane)—double layered
Lines cranial cavity and is attached to the skull
Inward folds—to anchor the brain
Subdural space—containing serous fluid
Arachnoid mater—arachnoid is "spider web"
Thin net like covering
Subarachnoid space—filled with CSF
Pia mater—"gentle mother"
Delicate
Adheres to the surface of the brain
Meningitis
Inflammation of meninges
Caused by viruses or bacteria
May spread to the brain
Swelling around brain—a stiff neck, fever and headache
Encephalitis—inflammation of the brain
Blood-brain barrier
Brain capillaries (tiny blood vessels) differ from others in the body
How? Less permiable
Capillaries allow nutrients (glucose) in but keep others out
Excludes non-essential chemicals: drugs
Fat-soluble material can diffuse through. EX: anesthetics, nicatine
and alcohol.
TRAUMATIC INJURIES TO THE BRAIN
Can cause damage
Concussion—slight injury with mild symptoms but no permanent damage.
Contusion—marked tissue destruction with variety of symptoms
including a coma
DEGENERATIVE DISEASES
Cerebrovascular accident (CVA) "stroke"—occurs when a local region of
the brain has neuron death from ischemia
Ischemia—a lack of blood
Alzheimer's disease—it could result from a gene that causes neurons
to die
SPINAL CORD
Characteristics:
Located within the vertebrae
Continuous with the medulla oblongata
Extends from foramen magnum to bottom of 1st lumbar vertebra (17
inches long; thumb width wide)
Functions:
Transmits messages to and from the brain
Forms reflexes
Protection—bone, CSF & meninges
Meninges:
Dura mater forms sheath around the spinal cord
Epidural space between the dura mater and the bone
NOTE:
The epidural space is filled with fat and blood vessels
"saddle block" is given to block pain messages in this space
Arachnoid
Subarachnoid space
Filled with CSF
Below L3, is site for spinal taps (lumbar punctures)
Pia mater—the inner layer
Anatomy of the spinal cord and associated structures
4 general regions—cervical, thoracic, lumbar and sacral
Specific regions posterior to the lumbar region:
Conus medullaris—the cone shaped bottom of the spinal cord
Cauda equina—the horse tail, nerve fibers below the spinal cord
Filum terminale—the fibrous anchors for the spinal cord
Spinal nerves – their exit from the spinal cord
31 pair of spinal nerves exit via intervertebral foramina – go to the
body parts.
cervical enlargement goes to the arms
lumbar enlargement goes to the legs
cauda equina
spinal nerves below L1 angle down before exiting the foramina.
Collection of nerves at the bottom
cross-section anatomy – the spinal cord is a flat oval
two grooves divide the spinal cord into a right and a left half
anterior median fissure which is deep
posterior median sulcus which is shallow
gray matter and spinal roots
gray matter: H-shaped – butterfly shape
gray commissure – is the median cross bar
posterior (dorsal) horns are cell bodies of sensory neurons coming in
anterior (ventral) horns are cell bodies of motor neurons going out
to muscles
later horns are cell bodies of motor-neurons going out to organs
ventral root is where axons of all motor neurons leave
dorsal root is where sensory neurons enter
dorsal root ganglion – enlargement containing cell bodies of sensory
nerves
NOTE: dorsal and ventral roots are short and fuse to form the spinal
nerve at the ganglion.
white matter is mostly myelinated nerve fibers
funiculi – columns of white matter on each side of the spinal cord
examples – posterior, anterior, lateral
NOTE: each column contains several fiber tracts which are axons with
similar destinations.
ascending tracts conduct sensory messages up
descending tracts deliver motor impulses down.
THE PERIPHERAL NERVOUS SYSTEM
PNS overview – links the central nervous system to the various parts
of the body.
NOTE: consists of nerves running to and from the CNS
Nerve – cord like bundle of axons
Connective tissue associated with nerves: (see diagram below)
endoneurium – connective tissue around each axon
fascicles – a bundle of axons
perineurium – connective tissue around each fascicle
epineurium – connective tissue around all the fascicles
Functional divisions of nerves:
sensory – carry messages to the CNS
motor – carry messages away
*Most nerves are mixed, have both sensory and motor
CRANIAL NERVES
Function and Location:
connect the brain with receptors, muscles and glands
mainly in the head, face and neck
12 pairs – viewed from ventral (under) side of the brain
names of the cranial nerves
NOTE: Roman numerals indicate their order anterior to posterior
I – olfactory
II – optic
III – oculomotor
IV – trochlear
V – trigeminal
VI – abducens
VII – facial
VIII – vestibulocochlear (auditory)
IX – glossopharyngeal
X – vagus
XI – accessory (spinal accessory)
XII – hypoglossal
Mnemonics: "Oh Oh Oh, To Touch And Feel A Girl's Vagina Ahh Heaven"
functions of the cranial nerves:
I – olfactory (sensory) transmits sensory (smell) impulses from the
nasal cavity through the cribriform plate of the ethmoid bone.
II – optic (sensory)
transmits sensory impulses for vision
lead from retina through optic foramen into cranial cavity
some fibers cross over to the other side at the X shaped optic
chiasma
NOTE: damage to the optic nerve would result in blindness
III – oculomotor (motor)
control most of the muscles that help move "focus" the eye.
Internal muscles that move the eyeball in its orbit
Ptosis – upper eyelid droops because the nerve is damaged
IV – trochlear (motor) pulley
only ones to emerge from dorsal side
control eye muscles
V – trigeminal (both) the largest nerve with three branches
- motor portions to muscles involved in chewing
- sensory the major sensory nerve of the face
- 3 divisions
(1) opthalmic – transmit sensory impulses from the scalp,
The eye and nose.
Testing – corneal reflex – is that anything
touching
Cornea will cause blinking and tearing.
maxillary – transmit sensory impulses from the middle of the face.
Mandibular – transmit sensory impulses from the bottom of the face
NOTE: inflammation – trigeminal neuralgia – tic douloureux –
excruciating pain of unknown cause
VI – abducens (both) supply nerves to muscles which cause
lateral eye
Movements
VII – facial (both)
sensory from the taste buds on the front of the tongue
motor main motor nerve of the face – control facial expressions and
glands
5 branches:
(1) temporal
(2) zygomatic
(3) buccal
(4) mandibular
(5) cervical
NOTE: inflammation – Bell's palsy paralysis of facial
muscles on 1 side
Results in drooping eye lids, sagging mouth and dripping
tears
VIII – vestibulocochlear (sensory) – sensory nerves from
the inner ear
vestibular branch for balance
cochlear branch sound
IX – glossopharyngeal (both)
motor – controls swallowing
sensory – transmits taste & sensation from the back of the mouth
X – vagus (both)
NOTE: only cranial nerve that goes down to chest and abdomen,
Called the wanderer.
motor fibers
go to the throat and larynx (swallowing & speech) – if it is damaged
you would have problems swallowing or speaking
regulate – breathing, heart rate and digestion
sensory portion – transmits sensory impulses from the same organs
NOTE: damage – you would die; heart could not beat and you could not
breath.
XI – accessory (motor)
motor fibers to throat & to muscles involved in turning the
head and shrugging the shoulders
XII – hypoglossal (both)
motor fibers to the tongue
SPINAL NERVES
Distribution of spinal nerves
31 pairs – all mixed – both motor and sensory
Categories:
cervical nerves – 8 pairs – exit above each vertebrae
thoracic nerves – 12 pairs – exit below
lumbar nerves – 5 pairs
sacral nerves – 5 pairs
coccygeal nerves – 1 pair
Nerve roots – emerge from the spinal cord
ventral root – contains motor fibers
dorsal root – contains sensory fibers
NOTE:
these 2 roots fuse to form a spinal nerve
the spinal nerve exits the vertebral column through the foramina
once outside the intervertebral foramen each spinal nerve branches to
form rami
rami:
dorsal ramus – is small and serves the back
ventral ramus – serves rest of the body
meningeal ramus – reenters vertebral canal to innervate the meninges
Innervation of the Anterolateral Thorax and Abdominal Wall
Intercostal nerve is a branch of the thoracic nerve
NOTE: the ventral rami of all other spinal nerves except thoracic
intertwine and criss-cross to form a plexus
Plexuses Serving the Neck and Limbs
cervical plexus – neck
located deep in neck under sternocleidomastoid
phrenic nerve – motor fibers to the diaphragm
NOTE:
irritation causes hiccups – no cure
both phrenic nerves destroyed – you cannot breath on your own.
brachial plexus – arms
location – in shoulder between the neck and arm pit
supplies – most of the nerves of the arm
major nerves:
axillary – is in the arm pits
musculocutaneous – muscles that flex the forearm
median – muscles that pronate the forearm and flex the wrist and
fingers
ulnar – behind medial epicondyle of the humerus
radial
triceps brachii
compression would result in the inability to extend the hand at the
wrist
lumbar plexus – is in the small of the back
serves most nerves of the thigh
femoral nerve serves the quadriceps
NOTE: if slipped disc compresses lumbar plexus you could have trouble
walking
sacral plexus above the sacrum
nerves that serve the buttocks and legs
sciatic nerve – the thickest, longest nerve in the body
its branches supply all the muscles of the leg
injury
impairs the lower limbs
severed you could be paralyzed
sciatica – stinging pain in you leg
Innervation of the Skin, Dermatomes and Referred Pain
general statements
cranial nerves send branches to the skin of the face and scalp.
all spinal nerves except C1 send branches to the skin of the rest of
the body
dermatomes area of skin served by a spinal nerve
referred pain
nerves serving certain internal organs and dermatomes to the same
region of the spinal cord
NOTE: it is not understood why, but the brain may
interpret pain
as coming from a dermatome or skin area
example – heart pain – is felt as pain in the left arm
REFLEX ACTIVITY
Spinal cord has 2 main functions:
carry information to and from the brain
form reflexes
reflexes – rapid, predictable, involuntary responses to stimuli
types of reflexes:
autonomic reflexes – not conscious of these – they control visceral
activities (digestion, urine, eggs, hormones, sperm, etc.)
somatic reflexes
involves stimulation of somatic sensory receptors
aware of these
example to touch a hot stove
reflex arcs – the neural pathways that reflexes travel
components:
receptors – is the site of the stimulus
sensory neuron transmits the impulse to the spinal cord
integration center within the spinal cord relays the information to
the motor neuron
motor neuron transmits the impulse from the integration to the
effector
effector – the muscle, gland or organ that responds
types of reflexes:
monosynaptic – only one synapse
simplest type
sensory neuron synapses directly with motor neuron in spinal cord
patellar reflex or knee jerk is an example
NOTE: most reflexes are more complicated and include one or more
inter-neurons in the spinal cord.
THE AUTONOMIC NERVOUS SYSTEM
Characteristics:
- Division of PNS
- Involuntary – regulates activities, not under our conscious
control
- Composed of motor neurons serving smooth and cardia muscle
- Important in maintaining homeostasis by regulating activity
of organs
Examples: heart rate, breathing, digestion, blood
pressure
- Functions of reflexes and may be effected by stress
- Composed of 2 sets of neurons with opposite effects
Parasympathetic division – most active under calm
conditions
Examples: lower heart rate and breathing
Sympathetic division "fight or flight" – active during
emergencies
Examples: speeds up heart rate and breathing
NOTE: these are opposite extremes; most organs receive both
parasympathetic and sympathetic signals which adjust the activities
to a suitable level
- Comparison of efferent pathways of the somatic and autonomic
nervous
System
Preganglionic – cell body lies in the brain or spinal
cord and its axon
Synapses with another neuron.
Parasympathetic = lonfiltered= short
Postganglionic – cell body lies in a ganglion outside the
CNS and
Its axon synapses with the effector
Parasympathetic = short sympathetic = long
Diagram & summary/comparison of somatic and autonomic nervous
Systems (see page 534)
PARASYMPATHETIC DIVISION (CRANIOSACRAL)
Neurotransmitter of the parasympathetic division is ACh
Note: both pre and postganglionic neurons release ACh
Cranial outflow = cranial nerves with parasympathetic function:
- Cranial nerve III innervates the eye muscles
- Cranial nerve VII innervates major glands of the face
Examples: the salivary glands
- Cranial nerves IX innervates the parotid salivary glands
- Cranial nerve X sends branches to several plexuses and
innervates many
Organs
Examples:
Cardiac plexuses – will go to the heart
Pulmonary plexuses – will go to the lungs
Esophageal plexuses – will go to the esophagus
Sacral outflow – sacral spinal nerves with parasympathetic function:
Where? S2 – S4 – innervate several visceral organs: to control
digestion
Examples: send preganglionic fibers to innervate several
visceral
Organs of the intestines, the bladder and the genitals.
SYMPATHETIC DIVISION (THORACOLUMBAR)
Neurotransmitters:
- Preganglionic fibers release ACh
- Postganglionic fibers release E and NE
- Norepinephrine (NE) = noradrenalin – the
neurotransmitter released
By the adrenal gland
- Epinephrine is released from the adrenal gland
NOTE: percentage of E:NE = 80:20
Sympathetic Complexity
NOTE: the sympathetic division of the autonomic nervous system
is much
More complex than the parasympathetic
Examples of structures under sympathetic control:
blood vessels,
Sweat glands, arrector pili muscles, heart, the lungs and digestive
organs
Origin, function & ganglia associated with sympathetic fibers
- Preganglionic neurons are found in spinal cord segments T1
through L2
- Sympathetic fibers from these neurons emerge from the
thoracic and
Lumbar regions of the spinal cord to form ganglia
- Chain ganglia – line each side of the vertebral column
- Collateral ganglia – are located in front of the
vertebral column
Chain ganglia fibers supply:
Examples: the salivary glands and the thoracic
glands
- Collateral ganglia and the organs their fibers supply:
Superior mesentric
The upper abdominal
organs:
Liver, gallbladder,
stomach, spleen
Celiac
Inferior mesenteric
The lower digestive
and reproductive
Organs: small
intestine, kidneys,
bladder, ovaries
Hypogastric
RECEPTORS OF THE AUTONOMIC NERVOUS SYSTEM
Cholinergic Receptors (parasympathetic) – receptors are responsive to
ACh
Types:
- Nicotinic – when nicotine binds to these, it produces
same effect
As ACh
ACh stimulates nicotine receptors
Types of nicotinic receptors (examples):
N1 – are found at all post ganglionic sites
N2 – are found at the neuromuscular junctions
- Muscarinic – these bind a poison (muscarine) from
mushrooms
Respond to ACh and produce similar effects
NOTE:
Usually excitatory but can be
inhibitory
Examples: digestive and sweat glands – E
Heart rate and blood pressure – I
Adrenergic "adrenal gland" (sympathetic) Receptors
Two types:
Alpha – is mainly stimulatory
Types:
Alpha 1
Alpha 2
Beta – is usually inhibitory
Types:
B1
B2
NOTE: knowing the location of cholinergic and adrenergic receptors
and their subtypes is useful.
Example: important clinical breakthrough was the discovery of
adrenergic blockers that attach beta blockers; are used to reduce
heart rate and prevent irregular heart beat.
SOURCE:Good Nurse's Club
