Download Nervous system part 2

Nervous system part 2
Central Nervous System (CNS)
Cephalization
 Evolutionary
development of the anterior
portion of the CNS
 Increases the number of neurons in the head
 Highest level is reached in the human brain
The brain
Embryonic
Neural
development
plate forms from ectoderm
Neural plate invaginates to form a
neural groove and neural folds
Neural groove fuses dorsally to form
the neural tube
Anterior
portion of the neural tube
becomes three primary brain vesicles
Prosencephalon-forebrain
Gives
rise to the telencephalon
(cerebrum) and diencephalon (thalamus,
hypothalamus, epithalamus, and retina)
Mesencephalon-
midbrain
Rhombencephalon-
Gives
hindbrain
rise to the metencephalon (pons
and cerebellum) and myelencephalon
(medulla oblongata)
The brain
 Effect
of space restriction on brain development
Midbrain
flexure and cervical flexure cause forebrain
to move toward the brain stem
Cerebral
Cerebral
hemispheres grow posteriorly and laterally
hemisphere surfaces crease and fold into
convolutions
Regions and organization
Adult
brain regions
Cerebral
hemispheres
Diencephalon
Brain stem (midbrain, pons, and medulla)
Cerebellum
Regions and organization
Spinal
cord
Central
cavity surrounded by a gray
matter core
External white matter composed of
myelinated fiber tracts
Regions and organization
Brain
Similar
pattern with additional areas of gray
matter
Nuclei in cerebellum and cerebrum
Cortex of cerebellum and cerebrum
Ventricles of the brain
 Contain cerebrospinal fluid
Two
C-shaped lateral ventricles in the cerebral hemispheres
Third
ventricle in the diencephalon
Fourth
ventricle in the hindbrain, dorsal to the pons
Cerebral hemispheres
 Surface markings: ridges (gyri), shallow grooves
(sulci), and deep grooves (fissures)
Central
sulcus- separates the precentral gyrus of the
frontal lobe and the postcentral gyrus of the parietal
lobe
Longitudinal
Transverse
fissure- separates the two hemispheres
cerebral fissure- separates the cerebrum and
the cerebellum
Cerebral hemispheres
Lobes
Frontal
Parietal
Temporal
Occipital
Insula
Cerebral hemispheres
 Cerebral
 Thin
 40%
cortex
superficial layer of gray matter
of the mass of the brain
 Site
of conscious mind: awareness, sensory perception,
voluntary motor initiation, communication, memory storage,
understanding
 Each
hemisphere connects to the contralateral side of the body
 Left
controls language, math, and logic
 Right
controls insight, visual-spacial skills, intuition, and artistic skill
 Lateralization
of cortical function in the hemispheres
Cerebral hemispheres
 Functional areas
Motor
areas- control voluntary movement
Primary
motor cortex- conscious control of precise, skilled,
voluntary movements
Premotor
cortex- controls learned, repetitious, or patterned
motor skills
Broca’s
area- motor speech area the directs muscle of the
tongue
Frontal
eye fold- controls voluntary eye movement
Cerebral hemispheres
 Sensory areas- conscious awareness of sensation
Primary
somatosensory cortex- Capable of spatial
discrimination: identification of body region being
stimulated
Somatosensory
association cortex- Determines size,
texture, and relationship of parts of objects being
felt
Visual
areas- Receives visual information from the
retinas
Auditory
areas- Interprets information from inner ear
as pitch, loudness, and location, stores memories of
sounds and permits perception of sounds
Olfactory
cortex- Region of conscious awareness of
odors
Gustatory
cortex- Involved in the perception of taste
Visceral
sensory area- Conscious perception of
visceral sensations, e.g., upset stomach or full
bladder
Vestibular
cortex- Responsible for conscious
awareness of balance (position of the head in space)
Cerebral hemispheres
 Association
areas- integrate diverse information
 Multimodal
association area- receive input from multiple
sensory areas, and sends output to multiple areas

Anterior association area- Involved with intellect, cognition, recall,
and personality, contains working memory needed for judgment,
reasoning, persistence, and conscience, development depends on
feedback from social environment
 Posterior
association area- Plays a role in recognizing patterns and
faces and localizing us in space, involved in understanding written
and spoken language (Wernicke’s area)
 Limbic
association area- Provides emotional impact that helps
establish memories
Diencephalon
 Encloses
 Three
the third ventricle
parts
1.
Thalamus- 80% of the diencephalon, sorts, edits, and relays
information
2.
Hypothalamus- autonomic control center for many visceral
functions: blood pressure, rate and force of heartbeat,
digestive tract motility. Center of emotional response.
Regulates body temperature, food intake, water balance,
and thirst. Regulated sleep and sleep cycle, controls release
of hormones from the pituitary gland
3.
Epithalamus- secretes melatonin that regulates sleep cycle
Brain stem
 Midbrain-
control cranial nerves III (oculomotor) and IV
(trochlear)
 Pons-
Connect higher brain centers and the spinal cord,
Relay impulses between the motor cortex and the
cerebellum
 Medulla
oblongata- Autonomic reflex centers, adjusts
force and rate of heart contraction, adjusts blood vessel
diameter for blood pressure regulation, generate
respiratory rhythm, control rate and depth of breathing,
regulate, vomiting, hiccupping, swallowing, coughing,
sneezing
Cerebellum
 Subconsciously
provides precise timing and appropriate
patterns of skeletal muscle contraction
 Receives
impulses from the cerebral cortex of the intent
to initiate voluntary muscle contraction
 Recognizes
and predicts sequences of events during
complex movements
 Plays
a role in non-motor functions such as word
association and puzzle solving
Functional brain systems
Limbic
system
Emotional
or affective brain
Amygdala—recognizes
angry or fearful facial
expressions, assesses danger, and elicits the fear
response
Cingulate
gyrus—plays a role in expressing
emotions via gestures, and resolves mental conflict
Puts
emotional responses to odors- Example:
skunks smell bad
The
limbic system interacts with the prefrontal lobes,
therefore:
We
can react emotionally to things we consciously
understand to be happening
We
are consciously aware of emotional richness in our lives
Hippocampus
and amygdala—play a role in memory
Functional brain systems
 RAS
(reticular activating system)
 Sends
impulses to the cerebral cortex to keep it conscious and
alert
 Filters
out repetitive and weak stimuli (~99% of all stimuli!)
 Severe
injury results in permanent unconsciousness (coma)
 Motor
function
 Helps
control coarse limb movements
 Reticular
autonomic centers regulate visceral motor functions:
Vasomotor, Cardiac, Respiratory centers
The 12 Pairs of Cranial Nerves
Figure 14.8
I. Olfactory
sense of smell
II. Optic
sight
III. Occulomotor
move eyelids
IV. Trochlear
move eyes
V. Trigeminal
face, jaw, chewing
VI. Abducens
eyes
VII. Facial
facial expressions
VIII. Vestibulocochlear
(Auditory)
sense of equilibrium, hearing
IX. Glossopharyngeal pharynx, tongue
X. Vagus
major organs, viscera
XI. Accessory
shoulders
XII. Hypoglossal
tongue
Need to know all of the cranial nerves ?
On Old October Third
The Airplane Flew
Above Ground Very
Aggressively Home
Higher mental functions
 Brian wave patterns and the EEG
EEG-
record electrical activity that accompanies brain
function and measures electrical potential differences
between cortical areas. Used to diagnose and localize
brain lesions, tumors, infracts, infections, abscesses,
and epileptic lesions
Flat
EEG is clinical evidence of death
Higher mental functions

Brain waves-patterns of neurological activity. Each persons’
brain waves are unique
 Alpha
waves (8–13 Hz)—regular and rhythmic, low-amplitude,
synchronous waves indicating an “idling” brain
 Beta
waves (14–30 Hz)—rhythmic, less regular waves occurring when
mentally alert
 Theta
waves (4–7 Hz)—more irregular; common in children and
uncommon in adults
 Delta
waves (4 Hz or less)—high-amplitude waves seen in deep sleep
and when reticular activating system is damped, or during anesthesia;
may indicate brain damage
Higher mental functions

Brain waves change with age, sensory stimuli, brain disease, and the
chemical state of the body

Epilepsy

A victim of epilepsy may lose consciousness, fall stiffly, and have uncontrollable jerking

Not associated with intellectual impairments

Occurs in 1% of the population

Absence seizures, or petit mal- Mild seizures seen in young children where the
expression goes blank

Tonic-clonic (grand mal) seizures- Victim loses consciousness, bones are often broken
due to intense contractions, may experience loss of bowel and bladder control, and
severe biting of the tongue
Higher mental functions

Consciousness

Conscious perception of sensation

Voluntary initiation and control of movement

Capabilities associated with higher mental processing (memory,
logic, judgment, etc.)

Loss of consciousness (e.g., fainting or syncopy) is a signal that
brain function is impaired

Clinically defined on a continuum that grades behavior in response
to stimuli: Alertness, Drowsiness (lethargy), Stupor, Coma
Higher mental functions

Sleep and sleep-wake cycles

State of partial unconsciousness from which a person can be
aroused by stimulation

Two major types of sleep (defined by EEG patterns)

Nonrapid eye movement (NREM): State of partial unconsciousness
from which a person can be aroused by stimulation

Rapid eye movement (REM)- People deprived of REM sleep become
moody and depressed, REM sleep may be a reverse learning process
where superfluous information is purged from the brain
Higher mental functions

Sleep disorders

Narcolepsy- Lapsing abruptly into sleep from the awake state

Insomnia- Chronic inability to obtain the amount or quality of
sleep needed

Sleep apnea- Temporary cessation of breathing during sleep
Higher mental functions

Language


Language implementation system

Basal nuclei

Broca’s area and Wernicke’s area (in the association cortex on the left
side)

Analyzes incoming word sounds

Produces outgoing word sounds and grammatical structures
Corresponding areas on the right side are involved with nonverbal
language components
Higher mental functions

Memory

Storage and retrieval of information

Two stages of storage

Short-term memory (STM, or working memory)—temporary holding of
information; limited to seven or eight pieces of information

Long-term memory (LTM) has limitless capacity
Higher mental functions

Factors that affect transfer from STM to LTM

Emotional state—best if alert, motivated, surprised, and aroused

Rehearsal—repetition and practice

Association—tying new information with old memories

Automatic memory—subconscious information stored in LTM
Higher mental functions

Declarative memory (factual knowledge)

Explicit information

Related to our conscious thoughts and our language ability

Stored in LTM with context in which it was learned
Higher mental functions

Nondeclarative memory

Less conscious or unconscious

Acquired through experience and repetition

Best remembered by doing; hard to unlearn

Includes procedural (skills) memory, motor memory, and emotional
memory

Procedural memory

Motor memory

Emotional memory
Protection of brain

Bone (skull)

Membranes (Meninges)

Cover and protect the CNS

Protect blood vessels and enclose venous sinuses

Contain cerebrospinal fluid (CSF)

Form partitions in the skull

Three layers

Dura mater, Arachnoid mater, Pia mater
Protection of brain

Watery cushion (Cerebrospinal fluid)

Composition: Watery solution, less protein and different ion
concentrations than plasma, constant volume

Functions

Gives buoyancy to the CNS organs

Protects the CNS from blows and other trauma

Nourishes the brain and carries chemical signals
Protection of brain

Blood-brain barrier

Helps maintain a stable environment for the brain

Separates neurons from some blood borne substances

Absent in some areas, e.g., vomiting center and the hypothalamus, where it is
necessary to monitor the chemical composition of the blood
Homeostatic imbalances in the brain

Traumatic brain injuries

Concussion—temporary alteration in function

Contusion—permanent damage

Subdural or subarachnoid hemorrhage—may force brain stem
through the foramen magnum, resulting in death

Cerebral edema—swelling of the brain associated with traumatic
head injury
Homeostatic imbalances in the brain

Cerebrovascular accidents (CVAs)(strokes)

Blood circulation is blocked and brain tissue dies, e.g., blockage of a cerebral
artery by a blood clot

Typically leads to hemiplegia, or sensory and speed deficits

Transient ischemic attacks (TIAs)—temporary episodes of reversible cerebral
ischemia

Tissue plasminogen activator (TPA) is the only approved treatment for stroke
Homeostatic imbalances in the brain

Degenerative brain disorders

Alzheimer’s disease (AD): a progressive degenerative disease of the brain
that results in dementia

Parkinson’s disease: degeneration of the dopamine-releasing neurons of
the substantia nigra

Huntington’s disease: a fatal hereditary disorder caused by accumulation
of the protein huntingtin that leads to degeneration of the basal nuclei
and cerebral cortex
Spinal cord

Embryonic development


By week 6, there are two clusters of neuroblasts

Alar plate—will become interneurons; axons form white matter of
cord

Basal plate—will become motor neurons; axons will grow to effectors
Neural crest cells form the dorsal root ganglia sensory neurons;
axons grow into the dorsal aspect of the cord
Spinal cord

Gross anatomy and protection



Location

Begins at the foramen magnum

Ends as conus medullaris at L1 vertebra
Functions

Provides two-way communication to and from the brain

Contains spinal reflex centers
Protections

Bone, meninges, and CSF

Cushion of fat and a network of veins in the epidural space between the
vertebrae and spinal dura mater

CSF in subarachnoid space
Spinal cord

Spinal nerves


Cervical and lumbar enlargements


31 pairs
The nerves serving the upper and lower limbs emerge here
Cauda equina

The collection of nerve roots at the inferior end of the vertebral
canal
Spinal cord

Cross –sectional anatomy

Two lengthwise grooves divide cord into right and left halves

Ventral (anterior) median fissure

Dorsal (posterior) median sulcus
Spinal cord

Pathway Generalizations

Pathways decussate (cross over)

Most consist of two or three neurons (a relay)

Most exhibit somatotopy (precise spatial relationships)

Pathways are paired symmetrically (one on each side of the spinal
cord or brain)
Spinal cord

Ascending Pathways

Consist of three neurons

First-order neuron


Second-order neuron


Conducts impulses from cutaneous receptors and proprioceptors, Branches
diffusely as it enters the spinal cord or medulla, Synapses with second-order
neuron
Interneuron, Cell body in dorsal horn of spinal cord or medullary nuclei, Axons
extend to thalamus or cerebellum
Third-order neuron

Interneuron, Cell body in thalamus, Axon extends to somatosensory cortex
Spinal cord

Dorsal Column-Medial Lemniscal Pathways


Anterolateral Pathways


Transmit input to the somatosensory cortex for discriminative
touch and vibrations
Transmit pain, temperature, and coarse touch impulses within the
lateral spinothalamic tract
Spinocerebellar Tracts

Convey information about muscle or tendon stretch to the
cerebellum
Spinal cord

Descending Pathways and Tracts


Deliver efferent impulses from the brain to the spinal cord

Direct pathways—pyramidal tracts

Indirect pathways—all others
Involve two neurons:

Upper motor neurons


Pyramidal cells in primary motor cortex
Lower motor neurons

Ventral horn motor neurons

Innervate skeletal muscles
Spinal cord trauma and disorders

Functional losses

Parasthesias- Sensory loss

Paralysis- Loss of motor function

Flaccid paralysis—severe damage to the ventral root or ventral horn
cells


Impulses do not reach muscles; there is no voluntary or involuntary
control of muscles. Muscles atrophy
Spastic paralysis—damage to upper motor neurons of the primary
motor cortex

Spinal neurons remain intact; muscles are stimulated by reflex activity.
No voluntary control of muscles
Spinal cord trauma and disorders


Transection

Cross sectioning of the spinal cord at any level

Results in total motor and sensory loss in regions inferior to the cut

Paraplegia—transection between T1 and L1

Quadriplegia—transection in the cervical region
Poliomyelitis

Destruction of the ventral horn motor neurons by the poliovirus

Muscles atrophy

Death may occur due to paralysis of respiratory muscles or cardiac arrest

Survivors often develop postpolio syndrome many years later, as neurons are lost
Spinal cord trauma and disorders

Amyotrophic Lateral Sclerosis (ALS)

Also called Lou Gehrig’s disease

Involves progressive destruction of ventral horn motor neurons and fibers
of the pyramidal tract

Symptoms—loss of the ability to speak, swallow, and breathe

Death typically occurs within five years

Linked to glutamate excitotoxicity, attack by the immune system, or both
Developmental aspects of CNS

CNS is established during the first month of development

Gender-specific areas appear in both brain and spinal
cord, depending on presence or absence of fetal
testosterone

Maternal exposure to radiation, drugs (e.g., alcohol and
opiates), or infection can harm the developing CNS

Smoking decreases oxygen in the blood, which can lead to
neuron death and fetal brain damage
Developmental aspects of CNS

The hypothalamus is one of the last areas of the CNS to develop

Visual cortex develops slowly over the first 11 weeks

Neuromuscular coordination progresses in superior-to-inferior and proximalto-distal directions along with myelination

Age brings some cognitive declines, but these are not significant in healthy
individuals until they reach their 80s

Shrinkage of brain accelerates in old age

Excessive use of alcohol causes signs of senility unrelated to the aging process