Transcript NERVOUS SYSTEM

NERVOUS SYSTEM
Homeostasis controlled by
• Nervous system
• Endocrine system
Divisions of the nervous system
• Central nervous
system (CNS)
• Spinal cord
• brain
• Peripheral Nervous
system (PNS)
• Nerves that carry
impulses to and from
CNS
Functions
• Monitoring changes inside and outside of
body – (stimuli) and gathers sensory input
• Integration – processes and interprets the
sensory input and makes decision about
what is to be done
• Effects a response by activating a muscle or
gland – response is called motor output
Neuron
Nerve cell
Parts of a neuron
• Dendrite – carries impulses to the cell body
• Axon – carries impulses from the cell body
• Myelin sheath – protective layer formed by
Schwann cells
• Nodes of Ranvier – gaps between the
sheaths ( not present in all neurons)
• Axonal terminals – branches located at the
terminal end of the neuron
• Neurilemma – sheath of Schwann
• Collateral branch – branch arising from the
axon ( not present in all axons)
• Oligodendrocytes – take the place of the
Schwann cells in the CNS
SUPPORTING CELLS neuroglia
• Astrocytes – numerous projections with swollen
ends that cling to neurons. Anchoring the neurons
to their blood supply
• Microglia – phagocytes that dispose of debris such
as dead brain cells, bacteria, ect.
• Ependymal cells = line cavities of the brain and
spinal cord. Have cilia that beat to circulate the
cerebrospinal fluid
• Oligodendrocytes
• Satellite cells – protective and cushion nerve cells
TYPES OF NEURONS
1. Afferent
• Also called sensory
• Carry nerve impulses toward CNS
2. Efferent
• Also called motor neuron
• Carries impulses away from CNS
3. Interneuron
• Also called association neuron
• Connect motor and sensory neuron in neural
pathways
CONDUCTION OF A NERVE
IMPULSE
RESTING POTENTIAL
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Membrane is polarized
Not conducting an impulse
-65mV to –70 mV
Na+ greater concentration on outside
K+ greater concentration on inside
Overall charge is + on outside and – on inside
Na/K pumps maintains this difference
DEPOLARIZATION
• Activates the neuron to transmit and action
potential (AP) also called a nerve impulse
• All or nothing response – AP is either
propagated or not
• Threshold must be reached –55mv
• Na+ gates open and Na+ flows inside
neuron
• Voltage changes from –65 to +40
REPOLARIZATION
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Na+ gate closes
K+ gate open and K+ flows to outside
Voltage change from +40 to –65
Na/K pumps return Na+ and K+ back to
normal
• Thus neuron returns to resting potential
REFRACTORY PERIOD
• AP has passed
• Na gate can’t open
• Keeps AP from traveling in the wrong
direction
CROSSING THE SYNAPSE
• Synapse – gap between the presynaptic and
postsynaptic membrane
• AP arrives at the presynaptic membrane
• Presynaptic membrane becomes permeable
to Ca++
• Vesicles move to the presynaptic mb.
• They release neurotransmitter
Myelinated neurons
• Conduction occurs faster because the nerve
impulses jump from node to node along the
length of the fiber
• Saltatory conduction – faster conduction in
myelinated neurons
External impairment of
conduction
• Alcohol, sedatives, and anesthetics block
nerve impulses by reducing membrane
permeability to sodium ions
• Is no Na ions can enter the neuron then no
AP will occur
• Cold and pressure hinder impulse
conduction because the interrupt blood
circulation
• Neurotransmitter diffuses across the
synaptic cleft
• At the postsynaptic mb. The
neurotransmitter merges with receptor sites
• AP starts at the postsynaptic mb
• Neurotransmitters may be broken down by
enzymes, washed away, or recycles
• Axons may synapse with many other
neurons
25 different neurotransmitters
acetyocholine
norepinephrine
NERVE
A bundle of axons
also called nerve fibers
REFLES ARC
• Rapid predictable and involuntary responses
to stimuli
PERIPHERAL NERVOUS
SYSTEM
• Made up of nerves that lie outside the CNS
• cell bodies (called ganglia) found outside
the CNS
• 2 structural types
– cranial nerves
– spinal nerves
Cranial nerves
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Carry impulses to and from the brain
12 pairs
some are sensory
some are motor
some are mixed
Spinal nerves
• Carry impulses to and from spinal cord
• all are mixed
• 31 pairs
Functional classification of PNS
Sensory
• Carries information to CNS from sense
organs and sensory receptors
• example: eye, Merkel discs
Motor
• Somatic - allows one to consciously control
skeletal muscles
• autonomic nervous system - regulates
activity of smooth and cardiac muscles and
glands
2 branches of the autonomic
nervous system
• Sympathetic nervous system
• parasympathetic nervous system
SYMPATHETIC
• Controls body’s response to emergency situation
and stress
• increase blood glucose levels in blood
• in heart rate
• increases oxygen uptake
• decrease activity of digestive system and urine
output
• dilates pupils
• goosebumps/ perspiration
PARASYMPATHETIC
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Opposite
normal no stress situations
steadies heart rate
constricts pupils
no effect on sweat glands
CNS
PROTECTION
• Meninges - connective tissue membranes
around the brain
• cerebrospinal fluid - cushions,
– formed by choroids plexuses,
– fluid continually moves through ventricles and
between the brain and spinal cord,
– 1/2 cup of fluid
SPINAL CORD
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17 inches long
2 way connection with brain
ends at lumbar vertebrae #2
rest of column filled with spinal fluid
has gray and white matter
• Caudal equina – collection of spinal nerves
that extend from the end of the spinal cord
• Paralysis – result of injury to cord
• Severity due to location on spinal cord
GRAY MATTER
• Contains cell bodies and nonmyelinated
fibers
• contains portions of sensory and motor
neurons
WHITE MATTER
• Myelinated axons of interneurons that run
to the brain and from one side of the SC to
the other side ( called tracts)
PARTS OF THE BRAIN
http://www.psych.ualberta.ca/~ITL/br
ain/
Ventricles
• Interconnecting cavities filled with CSF
• 4: 4th, 3rd, and 2 lateral ventricles
Medulla Oblongata
• Regulates heart beat, blood pressure, and
breathing,
• Has reflex centers for swallowing,
coughing, sneezing, hiccupping and
vomiting
• Has nerve tracts between the spinal cord
and brain
Pons
• Works with medulla to regulate breathing
rate
• Mostly a fiber tract
MIDBRAIN
• Relay station for tracts passing between the
cerebrum and the spinal cord or cerebellum
• Has reflex centers for visual, auditory, and
tactile responses
• Contains the cerebral peduncles and corpora
quadrigemina
CEREBELLUM
• Maintains normal muscle tone, posture,
balance
• Ensures that all of the skeletal muscles work
together to produce smooth and coordinated
movements
• Essential for skills such as playing the piano
or hitting a baseball.
hypothalamus
• Forms floor of the 3rd ventricle
• Maintains homeostasis by regulating hunger,
sleep, thirst, body temperature and water balance.
• Sex, pain , and pleasure centers are located here
• Part of the limbic system
• Called emotion visceral brain
• Regulates the pituitary gland therefore it is the link
between the nervous system and the endocrine
system
THALAMUS
• Serves as a relay station for sensory
impulses traveling upward to other parts of
the brain to the cerebrum
• Involved in arousal and higher mental
functions such as memory and emotion
• Gives one a crude awareness of whether the
sensation will be pleasant or not
Pineal gland
• Secretes the hormone melatonin
• At night the pineal gland produces
melatonin - causes one to fall asleep
LIMBIC SYSTEM
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System of tracts and nuclei
Surround the brain stem
Called emotional brain
Blends higher mental functions and
primitive emotions into a whole
• Area that makes eating and sexual behavior
seem pleasant
Parts of limbic system
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Hippocampus
Amygdala
Thalamus
Hypothalamus
Frontal lobe
hippocampus
• Area through which incoming sensory
signals generate particular limbic response
• example
Amygdala
• Associated with fear conditioning and
associating danger with sensory stimuli
• May be responsible for controlling human
aggression
Frontal lobe
• Keeps limbic system in check
• It uses reason to keep us from acting out
strong feelings
• Alcohol suppresses the frontal lobe and the
limbic system takes over
RETICULAR FORMATION
• Nuclei and fibers that extend the length of
the brain stem
• Reticular activating system
• Controls the sleep/wake cycle
• Severe damaged can cause one to be
comatose
CEREBRUM
CEREBRUM
• Largest portion of the brain
• Divided into left and right cerebral
hemispheres
• Surface has gyri – elevated ridges of tissue
• Sulci – shallow grooves
• Fissures – deeper grooves
• Divided into lobes
• Lobes named after cranial bones
• Gray matter
• Center for association, integration, and
learning
CORPUS CALLOSUM
• Bridge of nerve tracts that connect the right
and left hemispheres
• Tracts cross – left controlled by right side of
brain
• White matter – tracts that carry information
from 1 part of cerebrum to another part
• Basal nuclei – relay stations that help to
regulate motor activities – islands of gray
matter found deep within the white matter
LOBES
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Occipital – vision
Temporal – hearing
Frontal - olfactory and higher learning
Parietal
Functional areas of the cerebral
cortex
• Somatic sensory area
– Impulses from the body’s sensory receptors,
except for the special senses, are localized and
interpreted in this area of the brain
• Primary motor area
– Allows us to consciously move our skeletal
muscles
GENERAL INFORMATION
Falling in love
• Pleasure center in the hypothalamus
• Brain neurotransmitters – norepinephrine
and dopamine
• They give brain a pleasure flush (cousins of
amphetamines)
• Falling in love – pleasure center is bathed
with dopamine and norepinephrine
BLOOD BRAIN BARRIER
• Composed of least permeable capillaries in
the body
• Prevents urea and most drugs from entering
the brain tissue
• Useless against fats, respiratory gases
• Keeps internal environment of brain very
controlled
DISEASES/DISORDERS
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Multiple sclerosis
Huntington’s chorea
Parkinson’s disease
Meningitis
Hydrocephalus
Concussion
Contusion
Cerebral edema
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CVA
TIA
Alzheimer’s disease
Quadriplegic
Paraplegic
Type A personality
Cerebral palsy
Spina
bifida