Anatomy Chapter 11 Fundamentals Of The Nervous System And Nervous Tissue

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Nervous System

Back 1

- Master controlling and communicating system of the body

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1. Sensory Input

2. Integration

3. Motor Output

Back 2

3 Overlapping functions of the Nervous System

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Sensory Input

Back 3

- Nervous system uses it millions of sensory receptors to monitor changes occurring both inside and outside the body

- The gathered information is called?

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Integration

Back 4

- The nervous system processes and interprets sensory input and decides what should be done at each moment - a process called what?

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Motor Output

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- The nervous system activates effector organs such as the muscles and glands to cause a response, called the?

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Central Nervous System

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- Consists of the brain and spinal cord

- Integrating and control center of the nervous system

- Interprets sensory input and dictates motor output based on reflexes, current conditions and past experience

- Tracts (bundle of axons)

- Nuclei (collection of nerve cell bodies)

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Peripheral Nervous System

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- Consists mainly of nerves (bundles of axons) that extend from the brain and spinal cord, and ganglia (collections of neuron cell bodies)

- Cranial and spinal nerves carry impulses to and from the brain and spinal cord

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Sensory (Afferent = "carrying toward")

Motor (Efferent = "carrying away")

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PNS 2 Functional Subdivisions

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Sensory Afferent Division

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- Consist of nerve fibers (Axons) that convey impulses to the central nervous system from sensory receptors located throughout the body

- Somatic: Convey impulses from the skin, skeletal muscles and joints

- Visceral: Transmit impulses from the visceral organs (organs within the ventral body cavity)

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Motor Efferent Division

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- Transmits impulses from the CNS to effector organs, which are the muscles and glands, and activates them to contract or secrete

- Two main parts called the somatic and autonomic/visceral nervous system

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Somatic nervous System

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- Composed of somatic motor nerve fibers that conduct impulses from the CNS to skeletal muscles

- Cell bodies are located in the CNS

- Voluntary

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Automatic nervous System

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- Consists of visceral motor nerve fibers that regulate the activity of smooth muscles, cardiac muscles and glands

- Involuntary

- Two function subdivisions called the sympathetic and parasympathetic division

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Interneurons

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- AKA associated neurons, lie between motor and sensory neurons in neural pathways and shuttle signals through CNS pathways where integration occurs

- Multipolar

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Neuroglia

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- Supporting cells that surround and wrap the more delicate neurons

- Darker stained nuclei, small, out number neurons by 10 to 1

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Neurons

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- Nerve cells that are exciteable (responsive to stimuli) and transmit electrical signals

- Can have more than one nucleolus to form more ribosomes

- Processes called dendrites

- Rough ER like organelle called Nissl bodies

- Synaptic terminals or bulbs at the end of the axon is where neurotransmitters are stored.

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Nuclei

Tracts

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Central Nervous System

What is the collection of cell bodies called?

The bundle of axons?

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Ganglia

Nerves

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Peripheral Nervous System
What is the collection of cell bodies called?
The bundle of axons?

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Brain of the Central Nervous System

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Gray Matter: Outer layer (Cortex) Consist of Nuclei

White Matter: Deeper, whiter layer, consists of tracts.

Describes what part of the CNS?

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Spinal Cord of the Central Nervous System

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White Matter: Outer lighter layer. Tracts.

Gray Matter: Inner darker layer. Nuclei.

Describes what part of the CNS?

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Cell Body

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Can also be called soma, perikaryon

- Contains a very conspicuous nucleolus

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Myelin

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- Phospholipid covering

- Speeds up impulses/action potential

- Insulates axons

- Made by oligodendrocytes in the CNS and Schwann Cells in the PNS.

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Motor

Sensory

Integrative

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3 Functions of Neurons

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Multipolar

Bipolar

Unipolar

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3 Types (Shapes) of Neurons

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Multipolar Neurons

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- Most common type of neuron shape

- Major type in CNS, interneurons

- Motor neurons of PNS

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Bipolar Neurons

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- neuron shape Found in neurons of the Retina, olfactory cells, inner ear

- Almost always sensory afferent ganglia of PNS

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Unipolar

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- Shape of neuron

- Always sensory information, found in the spinal cord

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Astrocytes

Microglial Cells

Ependymal Cells

Oligodendrocytes

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4 Types of Neuroglia in the Central Nervous System

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Astrocyte

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- Most abundant and versatile star-shaped glial cells and perivascular feet

- The feet surround blood capillaries in the brain and form a tight seal called the blood-brain barrier

- Numerous radiating processes

- Support and brace the neurons and anchor them to their nutrient supply lines

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Microglia

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- Small macrophages derived from white blood cells called monocytes

- Phagocytize dead nervous tissue

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Ependymal Cells

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- Line the internal cavities of brain (ventricles) and spinal cord's central canal

- Secrete cerebro-spinal fluid: fluid that bathes the CNS

- Cuboidal columnar cells with cilia to help circulate the cerebro-spinal fluid

- Carries electrolytes and nutrient

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Oligodendrocytes

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- Produces the myelin sheath in axons in the CNS

- One cell wraps segments of several axons and make several myelin sheaths at a time

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Astrocytes receive oxygen and nutrients from blood but prevents hemorrhage with the blood brain barrier. Hemoglobin is toxic to the brain.

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Why is the astrocyte so important?

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Schwann Cell

Satellite Cell

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2 Types of Neuroglia in PNS

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Schwann Cell

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- Produces the myelin sheath for the PNS by winding around the axon several times

- The outermost thickest coil of the sheath contains most of the cytoplasm and is called a Neurilemma

- Assist in regeneration of nerve fibers (axons)

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Satellite Cell

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- Surround and supports the main neuron in the PNS

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Nodes of Ranvier

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- Production of myelin in CNS and PNS is laid down in segments

- Areas of axon between the segments not covered by the myelin sheath

- Allow very quick conduction action potential

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Internodes

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- Segments covered by myelin sheath on the axon of the neuron

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Neurilemma

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- Nucleated cytoplasmic layer of the Schwann cell

- Outermost thickest coil of the sheath contains most of the cytoplasm

- Assist in regeneration of nerve fibers (axons)

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Multiple Sclerosis

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- Myelin sheaths & oligodendrocytes in CNS degenerate

- Autoimmune disorder

- Blindness, speech deficits, tremors and numbness

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Leakage/Nongated channels

Gated channels

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Two types of Membrane Channels

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Voltate Gated Channels

Chemically Gated Channels

Mechanically Gated Channels

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3 Types of Gated Channels

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Voltage Gated Channels

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- Open and close in response to changes in the membrane potential

(ALL OR NONE)

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Chemically Gated Channels

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- Known as 'ligand-gated channels,' open when the appropriate neurotransmitter binds

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Mechanically Gated Channels

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- Open in response to physical deformation of the sensory receptor

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Resting Membrane Potential

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- Potential difference across the membrane in a resting neuron (Vr), between the extracellular fluid (sodium) and within the neuron (potassium and negative proteins)

- Means the membrane is polarized

- Approximately -70mv

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- Differences in the ionic composition of the intracellular and extracellular fluids

- Differences in the permeability of the plasma membrane to those ions

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- Two factors generating the resting membrane potential

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Action Potential

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Neurons use changes in their membrane potential as signals to receive, integrate and send information. Changes in membrane potential can produce an _____________________ ______________________________________, long distance signal of axons.

- Brief reversal of membrane reversal with a total amplitude of about 100 mV

- Called nerve impulse in a neuron, generated only in axons

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Depolarization

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- Decrease in membrane potential, inside of membrane becomes less negative than resting potential

- Na+ into cell through gated sodium gates

- Occurs when a stimulus binds to receptors on neuron

- Receptors are Ligand or Mechanically gated sodium gates

- Approximately -55 to -60mv threshold, then goes to +30mv when more Na+ chemical gates open, allowing Na+ in

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Repolarization

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- K+ out of the cell

- K+ gates open slower than Na+ gates, open when depolarization of the membrane has peaked

- Outflow of K+ brings inside of membrane back to negative numbers

- K+ gates stay open longer than Na+ gates, so more K+ out than Na+ in, so membrane potential initially drops to more negative than Resting Potential (Undershoot)

- Approximately -80mv

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Threshold

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- Approximately -55mv

- When depolarization reaches a critical level, becomes self-generating, urged on by positive feedback

- Na+ enters, and more channels open until all Na+ channels open

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Resting State:

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- All gated Na+ and K+ channels are closed

- Only leakage channels open, maintaining resting membrane potential

What stage of generating action potential? (1-4)

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Depolarization:

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- Na+ channels open

- Na+ rushed into cell, reaching threshold (-55mv), becomes self-generating and opens more Na+ channels

- Overshoots to about +30mv

- This spike of action gives the action potential

What stage of generating action potential? (1-4)

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Repolarization

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- Na+ channels are inactivating, and K+ channels open

- Abrupt decline in Na+ permeability and increased permeability to K+

What stage of generating action potential? (1-4)

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Hyperpolarization

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- Some K+ channels remain open, and Na+ channels reset

- Excessive K+ before closing cause overshoot of repolarization

- Approximately -80mv

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Saltatory Conduction

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- Type of conduction where the electrical signal appears to jump from gap to gap along the axon

- 30 times faster than continuous conduction

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Continuous Conduction

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- Action potential propagation involving nonmyelinated axons, these channels are immediately adjacent to each other

- Relative slow conduction

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Chemical Synapses

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Most common type of synapse

- Specialized to allow the release and reception of chemical messengers known as neurotransmitters

- Presynaptic: Made up of a knoblike axon terminal, containing synaptic vesicles, and each of these containing neurotransmitters

- Postsynaptic: Receptor region usually located on a dendrite or cell body

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Information Transfer across Chemical Synapses

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- Action potential arrives at presynaptic axon terminal

- Voltage-gated Ca2+ channels open and allows entrace into axon terminal because of depolarization

- Ca2+ entry allows release of neurotransmitters by exocytosis

- Neurotransmitter diffuses across synaptic cleft and binds to specific receptors on postsynaptic membrane

- Binding of neurotransmitter opens channels, creating graded potentials

- Empty vesicles recycle back to presynaptic knob to be reused

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Axon Hillock

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- Decision making

- Interprets all of the information coming from the presynaptic neurons

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Excitatory postsynaptic potentials

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- Instead of action potentials, local graded depolarization events occur at the ___________ postsynaptic membrane

- Help trigger action potential distally at the axon hillock of the postsynaptic neuron

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Inhibitory Postsynaptic potentials

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- Open K+ and Cl- channels to hyperpolarize postsynaptic membrane

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Temporal Summation of the Postsynaptic Neuron

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- Occurs when one or more presynaptic neurons transmit impulses in rapid-fire order and bursts of neurotransmitters are released in quick succession

- First impulse produces small EPSP, and before it dissipates, successive impulses trigger more EPSPs

- Cause postsynaptic membrane depolarization to reach threshold

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Spatial Summation of the Postsynaptic Neuron

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- Occurs when the postsynaptic neuron is stimulated simultaneously by a large number of terminals

- Dramatically enhances depolarization to reach threshold

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Acetylcholine

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- Released at vertebrae neuromuscular junctions in both CNS and PNS

- Excitatory neurotransmitter

- Decrease in Alzheimer's disease

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GABA

Glutamate

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2 Types of Amino Acid derivatives Neurotransmitters

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GABA

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- Principal Inhibitory in CNS, brain

- Secreted in invertebrate neuromuscular junction

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Glutamate

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- Excitatory in CNS, brain

- Secreted in invertebrate neuromuscular junction

- "Stroke Neurotransmitter": excessive release produce excitotoxicity, stimulation to death

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Dopamine

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- Fine motor muscle control, often inhibitory but can be excitatory too

- In both PNS and CNS, "feel good" neurotransmitter

- Deficient in Parkinson's disease

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Serotonin

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- Inhibitory in CNS, plays a role in sleep, regulating mood

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Gases Nitric Oxide

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- Blood vessel dilation to relax smooth muscle

- Can be excitatory or inhibitory in CNS and PNS

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Neuropeptides

- Endorphins

- Enkephalins

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- Inhibitory in CNS

- Inhibit pain, "pain killers"

(2 Types)

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Graded Potential

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- Located in cell body and dendrites

- Travels short distance to axon hillock

- Various amplitudes; decays with distance

- Chemical or sensory stimulus

- Repolarization is voltage independent, when stimulus no longer present

- Temporal and Spatial Summation

- Excitatory EPSP or Inhibitory IPSP functions

- Depolarization toward 0mv or hyperpolarizes toward -90 mv

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Action Potential

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- Located from axon hillock to axon

- Travels long distance across axon

- Same amplitude; no decaying with distance

- Stimulus by voltage (Reaching threshold)

- Repolarization is voltage regulated

- All-or-none

- Function is to constitute nerve impulse

- Peak membrane potential +30 to +50 mv