The Nervous System. Nervous system Structure The Neuron.
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Transcript of The Nervous System. Nervous system Structure The Neuron.
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The Nervous System
CLS 224Deemah Dabbagh
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Nervous system•Composed of:• Brain (CNS)• Spinal cord (CNS)• Nerves to body parts (PNS)
• Function:•Maintain homeostatis by
detecting stimuli in the environment
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Structure
•The nervous system is composed of two general types of cells:
1. Neurons (nerve cells): building blocks of the NS
2. Neuroglia cells (supporting cells)
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The Neuron
•Also known as the nerve cell•Basic unit of the nervous system•Composed of:• A cell body• Dendrites• An axon
•Responsible for receiving and transmitting nerve impulses and forming long fibers by linking together
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Important physiological properties of a Neuron
• Excitability: respond to a stimuli (e.g. change in environment)
• Conductivity: Ability to transmit a signal (pass it on to other cells)
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Neuron Cell body• Also called soma or
perikaryon
• Contains:• Nucleus , nucleolus• cytoplasm• organelles responsible for
cell maintenance
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Neuron Cell Body
• Nissl Bodies• A unique structure
to neurons
• Large granular bodies , clusters of rough ER
• Gives the cell body its gray color (gray matter)
• Synthesize and release proteins
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Dendrites• Extensions of the cell
body
• Multi-branched portions which receive impulses and bring them towards cell body
• Increase the surface area for connection with other neurons
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Axon• “The tail of the neuron”
• A long cell process arises from a slight elevation of the cell body (Axonal Hillock)
• Propagates the signal down the neuron and then to other cells
• May have branches called collaterals
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Axonal Transport• Occurs through microtubules
• Materials can move up the axon towards the cell body (retrograde transport)
• Materials can move down the axon away from the cell body (anterograde transport)
• Transport can:• Fast (mitochondria, pathogens, synaptic vesicles)• Slow (enzymes and other substances)
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Classification of Neurons
1. Based on their anatomy
2. Based on what they do
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Anatomical Classification
•Unipolar
•Bipolar
•Multipolar
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Unipolar Neuron • A single process• called “pseudounipolar” in
humans
• One process protruding from cell body
• At a short distance from the cell body the process divides into two branches (central and peripheral)
• It is a sensory (touch, pain) neuron in the peripheral nervous system
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Bipolar Neuron• Two processes protruding from cell body; axon and dendrite
•Dendrites receive information and axon gives information
• Sensory neuron e.g. retinal neuron, olfactory neuron
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Multipolar Neuron• Neuron with a cell body and
3 or more processes
• One process is the axon, the others are dendrites
• Most abundant in the brain and spinal cord
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Functional Classification of Neurons
•Sensory
•Motor
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Sensory Neurons
• Afferent: carry impulses from peripheral body toward the CNS
•Most sensory neurons are unipolar. Some are bipolar.
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Motor Neurons
• Efferent: carry information from the CNS to the periphery
•Multipolar
• Send CNS signals down to body parts, like glands and muscles
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Neurotransmission
•Neurotransmission depends on action potential:
• Short lasting electrical event on the plasma
membrane of neurons.
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Action Potential (AP)• All cells, including neurons, have a maintained polarity on both sides of
their membrane
• the polarity is maintained by stable concentrations of Na+ outside the cell and K+ inside the cell
• Stimulus causes the polarity to change
• This creates an electrical potential
• Electrical potential propagates along the axon until it reaches the axonal terminal branches
• Signal is the transmitted to the next neuron
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Transmission of signal from presynaptic neuron to post-synaptic neuron
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Some important notes:• Clusters of cell bodies are named differently when
they are in the CNS and PNS
• In the CNS,• Clusters of cell bodies are called nuclei
• In the PNS, • Collections of cell bodies are called ganglia
• White matter: myelinated regions of CNS containing mostly nerve fibers
• Gray matter: unmyelinated regions of CNS containing mostly cell bodies
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Neuroglial Cell
• Also known as• glia cell• Glia
• General Functions:• Support• Nutrition• Help maintain homeostasis• Form myelin• Help in signal transmission within
the nervous system
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Types of Neuroglial Cells
•Astrocytes
•Oligodendrocytes
•Microglial cells
•Ependyma
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Astrocytes
• Structural support
• Most abundant of all the glial cells
• Found between blood vessels and neuron cell bodies
• Play an important role in the blood brain barrier
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Oligodendrocytes• Found in the CNS
• Produce myelin• Myelin sheath is a fatty
insulator protecting nerve fibers (axons)
• They can myelinate multiple neurons
In the PNS myelination of neurons is done by Schwann cells. (one cell per schwann)
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Microglia cells
•Fewer in number than all other glia cells
•Have a phagocytic function (engulf pathogens, damaged neurons ect…)
•They increase in number during infections
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Epyndema Cells•cuboidal epithelial cells
•Line the cavities of the brain and spinal cord
•Ciliated, helps in circulating CSF that fills those cavities
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Divisions of the Nervous system
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Divisions of the Nervous System
•Central nervous system (CNS)• Brain (coordinates all bodily activities)• Spinal cord (connects brain to body)
•Peripheral nervous system (PNS)•Made up of nerves outside of the CNS:• Somatic• Autonomic
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Central Nervous System
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Central Nervous System CNS
•The Brain:•Cerebrum•Diencephalon •Cerebellum•Brain stem
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The Central Nervous System
•Cerebrum:
• The largest part of the brain• Two lateral hemispheres (left and
right)• Left side is logical, right side is
creative• Connecting the 2 hemispheres is a
layer of neurons called the corpus collosum.• Cerebrum is divided into 4 lobes
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The Central Nervous System•Cerebrum:
• Functions:
• Provides higher brain functions (deep thinking,
intelligence,learning)
• memory
• Sensory information (touch, smell, taste, visual, hear)
• Coordinates skeletal muscles
• Language, comprehension, speech
• Personality development (sense of humor, competitiveness
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The Central Nervous System
•Cerebrum:• Frontal lobe
• Primary motor area: conscious movement of all skeletal muscles• Higher intellectual reasoning
• Parietal lobe:• Somatic sensory cortex area: Touch, pain, temperature..etc)
• Temporal lobe:• Auditory area, olfactory area
• Occipital lobe:• Visual area
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The Central Nervous System
•Diencephalon:
• Composed of:1. Thalamus2. Hypothalamus3. Epithalamus
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Diencephalon cont:• Thalamus:
• Relay station for sensory impulses• Cerebrum Sensory signals thalamus brain stem spinal cord PNS
• Hypothalamus:• Regulates body temp, water balance, metabolism (TSH)• Stress management: by adrenocorticotropic hormone (ACTH) adrenal
glands• Controls pituitary gland:
• GH, prolactin, oxytocin…etc.• Important part of the “limbic system” or emotional visceral brain (thirst,
appetite, pleasure, pain..etc)• Influences controls of the medulla oblongata
• Epithalamus:• Contains pineal gland melatonin (sleep hormone)• Choroid plexux forms CSF
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The Central Nervous System
•Brain Stem:• Midbrain
• Bulges in front called cerebral peduncles: coordinate fine motor movements (e.g. grasping an object between a thumb and a finger)
• Dorsally: protrusions called corpora-quadrigemina: involved in vision and hearing
• Pons• Involved in the control of breathing
• Medulla oblongata• Cardioregulatory centers (heartbeat, blood
pressure, vasoconstriction…)• Breathing, swallowing, vomiting
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The Central Nervous System
•Cerebellum:
• Located under the cerebrum
• Functions:• Controls balance and
movement coordination • By receiving information from
the body and sending information to the body
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The Central Nervous System
•Spinal Cord:
• Receives signals from
the brain
• Passes signals to the
PNS (which take them
to the rest of the body)
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Peripheral Nervous System is Subdivided into:
•Somatic nervous system
•Autonomic nervous system
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Somatic Nervous System
•Connects CNS to skeletal muscles and skin
•Conscious control
•voluntary
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Autonomic Nervous System
• Connects CNS to viscera and glands
• Unconscious, involuntary control (breathing, heartbeat, digestive system..etc)
• Further subdivided to:• Sympathetic• parasympathetic
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Sympathetic VS Parasympathetic• Sympathetic:
• Also called thoracolumbar division
• Fight or flight (scared, excited, thriving for survival..etc)
• Dialation of pupils
• Inhibit salivation
• Relax bronchi (to get more air in)
• Accelerate heartbeat
• Inhibit peristalsis and secretion (can survive longer without food)
• Stimulate glucose production and release
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Sympathetic VS Parasympathetic• Parasympathetic:
• The “craniosacral division”
• Relaxed mode
• Constrict pupils
• Stimulate flow of saliva
• Constrict bronchi
• Slow heartbeat
• Stimulate peristalsis and secrestion
• Stimulate bile release
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Autonomic Nervous system
• Two primary neurotransmitters:
• Acetylcholine• Major neurotransmitter• Used by parasympathetic and sympathetic nervous
system
• Norepinephrine• Used by sympathetic nervous system
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Protection of CNS
•Meninges
•Blood Brain barrier
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Meninges
•Three C.T. membranes covering structures of the brain:
1.Dura matter (outer most)
2.Arachnoid matter (middle)
3.Pia matter (inner most)
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Blood Brain Barrier
• Protects brain from blood borne substances
• Composed of the least permeable capillaries in the body (brain capillaries).
• Only water, glucose and essential a.a can pass through its capillaries walls.
• Metabolic wastes; urea, toxins..etc are prevented