The Nervous System It is comprised of 3 basic components Brain Spinal cord Nerves.
Transcript of The Nervous System It is comprised of 3 basic components Brain Spinal cord Nerves.
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The Nervous System
It is comprised of 3 basic components
Brain Spinal cord Nerves
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General Functions of the Nervous System
Sensation Monitors changes/events occurring in and outside the
body. Such changes are known as stimuli and the cells that monitor them are sensory receptors.
Integration The parallel processing and interpretation of sensory
information to determine the appropriate response (Conscious or subconscious)
Reaction Motor output or the activation of effectors such as muscles
or glands (typically via the release of neurotransmitters).
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Organization of the Nervous System
2 big initial divisions:1. Central Nervous
System The brain + the spinal
cord The center of integration
and control
2. Peripheral Nervous System
The nervous system outside of the brain and spinal cord
Consists of: 31 Spinal nerves
Carry info to and from the spinal cord
12 Cranial nerves Carry info to and
from the brain
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What is the basic functional unit of the nervous system?
Neuron! What does the neuron do? Carries messages throughout
the body How does it carry the messages? By conducting electrical signals What are these signals called? Nerve impulses!
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Neuron Anatomy Three parts to a
NEURON:
1. Cell body: Large, central portion of the neuron where all organelles are located.
What is its job? Interpret incoming
signals
Cell Body
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Neuron Anatomy
2. Dendrites:Short, highly branched fibers What is its job? Carries impulses
toward the cell body Referred to as the
afferent process
Dendrites
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Neuron Anatomy
3. Axon:Long, slightly branched fiber What is its job? Carry impulses away from the cell body Referred to as the efferent process
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Neuron Anatomy
Three parts of the Axon:A. Axon hillock: site of initiation of an
action potential (point where axon and cell body meet)
B. B. Axon fiber: the main portion of the axon
C. C. Axon terminal:branched end of the axon (point of communication with other cells)
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The Axon
Axon Terminals
Axon Hillock
fiber
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Neuron AnatomyAdditional Parts of a Neuron
Dendrite
Cell body
Axon terminal
Myelin sheath
Nodes ofRanvier
AxonNucleus
Structure of a Typical Neuron
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Neuron anatomyWhat do you remember?
3
1
2
4
5
6
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dendrites
nucleus
Cell body
axon
Nodes ofRanvier
Myelinsheath
Axonterminals
Direction of impulse
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3 Types of Neurons
A. Sensory Neurons: Receive incoming stimuli
Five types of sensory neurons:o Thermo-receptorso Mechano-receptorso Chemo-receptorso Photo-receptorso Pain-receptors
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Thermo-receptors
Location: Skin Hypothalamus Body Core
Function: Sensation of hot and
cold Detects change in
body core temp.
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Mechano-receptors Location:
Skin Skeletal muscle Inner ear
Function: Touch Pressure Muscle movement Motion Sound
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Chemo-receptors
Location: Nose Tongue (taste buds) Blood vessels
Function: Smell Taste Detects levels of CO2
in blood
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Photo-receptors
Location: Eyes
Function: Allow vision thru detection of light
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Pain-receptors
Location: Everywhere, except
the brain Function:
Sensation of pain Detects chemicals
released by damaged cells
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Three Types of Neurons
B. Motor Neurons:Carry impulses to muscles and glandsCause a response to some stimuli
C. Interneurons:Connect sensory and motor neuronsAllow for quick response (reflex action)
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Three types of neurons
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Structural diversity in neurons Multipolar- many dendrites, one axon
Most neurons in CNS Bipolar- one dendrite, one axon
Sensory organs Unipolar- sensory
Axon termini extend into CNS
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Neurons
What is grey matter? Collective cell bodies and
dendrites of all neurons
What is white matter? Myelinated nerve fibers Axons of all neurons Can be approximately
one meter in length
White matter
Gray matter
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What is a Nerve? Bundle of axons
held together by connective tissue.
What color isa nerve?
White! Why? Because axons
are white matter and they composenerves
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How are nerves held together? Connective tissue What is this connective tissue called? Neuroglial cells (nerve glue) Approximately half of the
volume of the brain is composed of neuroglial cells
Most brain tumors develop in mesoglial cells – NOT neurons
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What do neuroglial cells do? Support the axons Insulate the electrical impulses Like electrical tape insulates
electric wires this prevents “leaking”of electric signals
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Four types of neuroglia in CNS Oligodendrocytes
Myelinating cells Astrocytes
Connects neurons and blood vessels together
Microglia Phagocytes (from bone marrow)
Ependymal cells Line ventricles of brain; produce
cerebrospinal fluid (CSF)
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Neuroglia of the PNS
Schwann cells Myelinating cells Help direct axon
regeneration Satellite cells
Support, protection, regulation of molecular exchange
“Filter out” other stimuli
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The Nerve Impulse
Resting potential – the charge that exists across a neuron’s membrane while at rest. -70 mV. This is the starting point for an action
potential.
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The Nerve Impulse
A nerve signal or action potential is an electrochemical message of neurons. An all-or-none phenomenon – either the
fiber is conducting an action potential or it is not.
Across its plasma membrane, every cell has a voltage called a membrane potential.
The inside of a cell is negative relative to the outside.
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The Nerve Impulse
Neuron at rest – active transport channels in the neuron’s plasma membrane pump: Sodium ions (Na+) out of the cell. Potassium ions (K+) into the cell.
More sodium is moved out; less potassium is moved in. Result is a negative charge inside the cell. Cell membrane is now polarized.
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Sodium-Potassium Exchange Pump
Na+ flows into the cell during an action potential, it must be pumped out using sodium pumps so that the action potential will continue.
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The Nerve Impulse A nerve impulse starts when pressure or
other sensory inputs disturb a neuron’s plasma membrane, causing sodium channels on a dendrite to open. Sodium ions flood into the neuron and the
membrane is depolarized – more positive inside than outside.
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The Nerve Impulse This moving local reversal of voltage is called an
action potential. A very rapid and brief depolarization of the cell
membrane. Membrane potential changes from -70 mV to +35 mV.
After the action potential has passed, the voltage gated channels snap closed and the resting potential is restored. The membrane potential quickly returns to -70 mV
during the repolarization phase. An action potential is a brief all-or-none
depolarization of a neuron’s plasma membrane. Carries information along axons. An action potential is self-propagating – once started it
continues to the end.
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Synapses: Junctions Between Nerves
Eventually, the impulse reaches the end of the axon.
Neurons do not make direct contact with each other.
The junction between the axon of one neuron and the dendrite of the next is called a synapse .
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Synaptic Pathways
Presynaptic neurons bring action potentials toward the synapse.
Postsynaptic neurons carry action potentials away from the synapse.
A synaptic cleft is the small gap between the two neurons.
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Neurotransmitters
Chemical messengers called neurotransmitters carry the message of the nerve impulse across the synapse.
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Neurotransmitters
Neurotransmitters are released into the synapse and bind with receptors on the postsynaptic cell membrane, which cause ion channels to open in the new cell.
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Acetylcholine – Example Neurotransmitter
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Reflex Arc A simple reflex produces a very fast motor
response to a stimulus because the sensory neuron bringing information about the stimulus passes the information directly to the motor neuron.
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Reflex Arc Usually, there are interneurons between
sensory and motor neurons. An interneuron may connect two neurons on the
same side of the spinal cord, or on opposite sides.
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The Central Nervous System
Meninges – are membranes that protect the brain and spinal cord Dura mater (outermost layer) Arachnoid membrane ( middle layer) Pia mater (innermost layer)
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The Central Nervous System Cerebrospinal Fluid (CSF) Located between the arachnoid mater and
pia mater is an area called the subarachnoid space
Continuously secreted from specialized cells (ependymal cells) in the choroid plexus in ventricles
Functions: Physical and chemical protection of the CNS
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45Spinal Cord
Slender structure that is continuous with the brain
Descends into the vertebral canal and ends around the level of the first or second lumbar vertebra.
Function of the spinal cord is to carry sensory information to and from the brain
31 spinal segments: 8 cervical segments 12 thoracic segments 5 lumbar segments 5 sacral segments 1 coccygeal segment
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Spinal Cord - Ascending and Descending Tracts
Ascending tracts - carry sensory information up to the brain
Descending tracts - carry motor information down from the brain to muscles and glands
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The Brain
Four Parts:Four Parts: Cerebrum Diencephalons Brain stem Cerebellum
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The Brain - Cerebrum
Largest part of the brain
Two halves cerebral hemispheres
Thick bundle of nerve fibers called the corpus callosum connect the two hemispheres
Lobes Frontal Parietal Temporal Occipital
Cortex Ventricles
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The Brain - Diencephalons
Thalamus - relay station for sensory information that heads to the cerebral cortex for interpretation
Hypothalamus - maintains balance by regulating many vital activities such as heart rate, blood pressure, and breathing rate.
Located between the cerebral hemispheres and is superior to the brain stem Located between the cerebral hemispheres and is superior to the brain stem
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The Brain - Brain stem
Midbrain Midbrain - controls both visual and auditory reflexes
PonsPons - regulates breathing
Midbrain Midbrain - controls both visual and auditory reflexes
PonsPons - regulates breathing
Medulla oblongataMedulla oblongata - controls many vital activities such as heart rate, blood pressure, and breathing
Connects the cerebrum to the spinal cordConnects the cerebrum to the spinal cord
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The Brain - Cerebellum
Inferior to the occipital lobes of the cerebrum
Posterior to the pons and medulla oblongata
Inferior to the occipital lobes of the cerebrum
Posterior to the pons and medulla oblongata
Coordinates complex skeletal muscle contractions that are needed for body movements
Coordinates complex skeletal muscle contractions that are needed for body movements
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Diseases and Disorders of the Nervous System Cerebrovascular Accident:
CVA Commonly called a stroke The result of a ruptured
blood vessel supplying (cerebral hemorrhage) a region of the brain or a vessel is obstructed by a clot.
Brain tissue supplied with oxygen from that blood source dies, swelling occurs in the brain due to leaking of blood from vessels.
Loss of some functions or death may result
This is due often to elevated blood pressure or hypertension.
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Diseases and Disorders of the Nervous System Epilepsy: This disease is
due to random, mis-firing of neurons within the brain affecting sensory and motor regions of the brain. Ranging in effects from sleep-like state of consciousness (narcolepsy), muscle paralysis and spasms (Petit mal and Grand mal seizures). Still not understood why this disease occurs. However in some cases it can result from brain trauma or injury.
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