Ch. 11 - Fundamentals Of The Nervous System And Nervous Tissue

Front 1

nervous system

Back 1

the master controlling and communicating system of the body

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1. sensory input

2. integration

3. motor output

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3 overlapping functions of the nervous system

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sensory input

Back 3

the information gathered by the millions of sensory receptors of the nervous system, monitoring changes inside and outside of the body

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integration

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the nervous system processes and interprets sensory input and decides what should be done at each moment

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motor output

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the nervous system activates effector organs (the muscles and glands) to cause a response

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1. central nervous system (CNS)

2. peripheral nervous system (PNS)

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2 principal parts of the nervous system

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central nervous system (CNS)

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the integrating and control center of the nervous system; the brain and spinal cord

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peripheral nervous system (PNS)

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the part of the nervous system outside the CNS; consists mainly of nerves that extend from the brain and spinal cord

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1. sensory division (afferent)

2. motor division (efferent)

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2 functional subdivisions of the PNS

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sensory division (afferent division)

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PNS subdivision consisting of nerve fibers (axons) carrying impulses to the CNS from sensory receptors throughout the body

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somatic sensory fibers

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fibers conveying impulses from the skin, skeletal muscles, and joints to the CNS

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visceral sensory fibers

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fibers transmitting impulses from the visceral organs

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motor division (efferent division)

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PNS subdivision transmitting impulses from the CNS to effector organs (muscles and glands)

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1. somatic nervous system

2. autonomic nervous system (ANS)

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2 main parts of the motor division (efferent division) of the PNS

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somatic nervous system

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the part of the motor division that conducts impulses from the CNS to skeletal muscles; voluntary nervous system

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autonomic nervous system (ANS)

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the part of the motor division that regulates the activities of smooth muscles, cardiac muscles, and glands; involuntary nervous system

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1. sympathetic division

2. parasympathetic division

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2 subdivisions of the autonomic nervous system (involuntary nervous system)

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sympathetic division

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division of the autonomic nervous system that mobilizes body systems during emergencies; fight or flight

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parasympathetic division

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division of the autonomic nervous system that conserves energy; promotes non-emergency functions (resting)

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1. neurons (nerve cells)

2. neuroglia (glial cells)

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2 main cell types of the nervous system

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neuroglia (glial cells)

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supporting cells that surround and wrap the more delicate neurons

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1. astrocytes

2. microglial cells

3. ependymal cells

4. oligodendrocytes

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4 types of neuroglia in the CNS

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astrocytes

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CNS neuroglia that support and brace neurons and anchor them to nutrient supply lines; most abundant and versatile

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microglial cells

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CNS neuroglia that monitor neuron health and phagocytize debris

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ependymal cells

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CNS neuroglia that line the central cavities of the brain and spinal cord, forming a permeable barrier

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oligodendrocytes

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CNS neuroglia that tightly wrap nerve fibers forming the insulating myelin sheath

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1. satellite cells

2. Schwann cells

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2 types of neuroglia in the PNS

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satellite cells

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PNS neuroglia that surround neurons; similar functions to astrocytes of the CNS

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Schwann cells (neurolemmocytes)

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PNS neuroglia that form myelin sheaths around nerve fibers; similar function to oligodendrocytes of the CNS

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neuron

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the structural unit of the nervous system; conducts electrical signals

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1. longevity (100+ years)

2. amitotic

3. high metabolic rate

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3 special characteristics of neurons

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neuron cell body (perikaryon, soma)

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the major biosynthetic center of a neuron; synthesizes proteins

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Nissl bodies (chromatophilic substance)

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the protein- and membrane-making rough ER of a neuron

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neurofibrils

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bundles of intermediate filaments that, along with microtubules, help maintain nerve cell shape and integrity

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nuclei

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clusters of neuron cell bodies in the CNS

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ganglia

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clusters of neuron cell bodies that lie along the nerves of the PNS

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processes

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extensions from the neuron cell body

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tracts

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bundles of neuron processes in the CNS

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nerves

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bundles of neuron processes in the PNS

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1. dendrites

2. axons

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2 types of neuron processes

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dendrites

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short, branching extensions of neuron cell bodies that receive signals from other neurons and relay the signal to the cell body

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axons

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long extensions of neuron cell bodies; generate and transmit nerve impulses

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nerve fiber

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a long axon

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axon hillock

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cone-shaped area of the cell body where an axon arises

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axon collaterals

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branching axons

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terminal branches

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the end branches of an axon; 10,000 or more per neuron

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axon terminals (terminal boutons)

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the knoblike endings of axon branches

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axolemma

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the plasma membrane of neuron cell bodies

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neurotransmitters

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signaling chemicals usually stored in vesicles; excite or inhibit neurons

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anterograde movement

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movement away from the cell body

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retrograde movement

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movement toward the cell body

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myelin sheath

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a white, fatty layer covering nerve fibers; protects and electrically insulates

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myelinated fibers

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axons bearing a myelin sheath; conducts nerve impulses rapidly

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nonmyelinated fibers

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axons without a myelin sheath; conduct nerve impulses more slowly

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myelin sheath gaps (nodes of Ranvier)

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gaps between myelin sheaths, occur at regular intervals

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white matter

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regions of the brain and spinal cord with dense collections of myelinated fibers

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1. multipolar

2. bipolar

3. unipolar

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3 structural classes of neurons

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multipolar neurons

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neurons with three or more processes; one axon and the rest dendrites; ex. brain and motor neurons

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bipolar neurons

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neurons with two processes; one axon and one dendrite; ex. some sensory neurons

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(pseudo)unipolar neurons

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neurons with a single short process that divides in to proximal and distal branches; ex. sensory neurons

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1. sensory neurons (afferent)

2. motor neurons (efferent)

3. interneurons

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3 functional classes of neurons

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sensory neurons (afferent neurons)

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class of neurons that transmit impulses from sensory receptors in the skin or organs toward the CNS; unipolar

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motor neurons (efferent neurons)

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class of neurons that carry impulses away from the CNS to the effector organs (muscles and glands); multipolar

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interneurons (association neurons)

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class of neurons that shuttle signals through CNS pathways, where integration occurs; 99% of all neurons; multipolar

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voltage

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the measure of potential energy generated by separated charge

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current

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the flow of electrical charge from one point to another

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resistance

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the hindrance to charge flow provided by substances through which a current must pass

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leakage channels (nongated)

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plasma membrane channels that are always open

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1. chemically gated (ligand-gated)

2. voltage-gated

3. mechanically gated

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3 main types of gated plasma membrane channels

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chemically gated channels (ligand-gated channels)

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channels that open when the appropriate chemical binds (neurotransmitters)

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voltage-gated channels

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channels that open and close in response to change in the membrane potential

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mechanically gated channels

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channels that open in response to physical deformation of the receptor

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electrochemical gradient

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electrical and concentration gradients combined

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resting membrane potential

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the potential difference in a resting neuron; polarized (approx. -70mV)

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depolarization

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decrease in membrane potential; the inside of the membrane becomes less negative

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hyperpolarization

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increase in membrane potential; the inside of the membrane becomes more negative

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graded potentials

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short-lived, localized changes in membrane potential; used by dendrites, axons, and muscles

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action potential

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a brief reversal of membrane potential; used by nerve axons and muscles

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nerve impulse

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an action potential in a neuron; typically generated only in axons

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resting state (stage 1 of 4)

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Generation of an Action Potential: All gated Na+ and K+ channels are closed.

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depolarization (stage 2 of 4)

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Generation of an Action Potential: Na+ channels open.

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repolarization (stage 3 of 4)

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Generation of an Action Potential: Na+ channels inactivate, and K+ channels open.

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hyperpolarization (stage 4 of 4)

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Generation of an Action Potential: Some K+ channels remain open, and Na+ channels reset.

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sodium-potassium pump

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redistributes ions and restores the membrane potential to its resting state

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threshold

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the critical level that must be reached for depolarization to become self-generating

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all-or-none phenomenon

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an AP either happens completely or not at all

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absolute refractory period

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the period when a neuron cannot respond to another stimulus; from the time Na+ channels open until they begin returning to resting state

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relative refractory period

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the period when a neuron can only generate an AP if the stimulus is great enough; from the time Na+ channels return to their resting state until after hyperpolarization

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saltatory conduction

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an electrical signal jumping from gap to gap along an axon

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multiple sclerosis

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autoimmune disease destruction of myelin sheaths, delaying impulse conduction; characterized by visual disturbances, muscle problems, speech disturbances, etc.

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group A fibers

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nerve fibers with the largest diameter and thick myelin sheaths; ex. somatic sensory and motor fibers

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group B fibers

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nerve fibers with intermediate diameter and lightly myelinated

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group C fibers

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nerve fibers with the smallest diameter and nonmyelinated; slow impulse conduction

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synapse

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a junction that mediates information transfer from one neuron to the next (or to an effector cell)

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axodendritic synapses

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synapses between axon endings of one neuron and the dendrites of other neurons

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axosomatic synapses

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synapses between axon endings of one neuron and cell bodies (soma) of other neurons

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axoaxonic synapses

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synapses between two axons

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presynaptic neuron

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the neuron conducting impulses toward a synapse

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postsynaptic neuron

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the neuron conducting impulses away from the synapse

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1. electrical synapses

2. chemical synapses

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2 varieties of synapses

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electrical synapses

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less common variety of synapses; consist of gap junctions that let ions flow between neurons

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chemical synapses

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variety of synapses that allow the release and reception of neurotransmitters

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synaptic vesicles

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tiny, membrane-bound sacs of the axon terminal that contain thousands of neurotransmitter molecules

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Stage 1 of 6

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Chemical Synapses: AP arrives at axon terminal.

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Stage 2 of 6

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Chemical Synapses: Voltage-gated Ca2+ channels open and Ca2+ enters the axon terminal.

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Stage 3 of 6

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Chemical Synapses: Ca2+ entry causes synaptic vesicles to release neurotransmitter.

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Stage 4 of 6

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Chemical Synapses: Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane.

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Stage 5 of 6

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Chemical Synapses: Binding of neurotransmitters opens ion channels, resulting in graded potentials.

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Stage 6 of 6

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Chemical Synapses: Neurotransmitter effects are terminated by reuptake, degradation, or diffusion.

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excitatory postsynaptic potentials (EPSPs)

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graded potentials that help trigger an AP distally at the axon hillock; both Na+ and K+ channels open, causing depolarization

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inhibitory postsynaptic potentials (IPSPs)

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graded potentials that reduce a postsynaptic neuron's ability to generate an AP; K+ and Cl- channels open, causing hyperpolarization

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temporal summation

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

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spatial summation

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occurs when many presynaptic neurons stimulate the postsynaptic neuron at the same time

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synaptic potentiation

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repeated or continuous use of a synapse enhances its effects; caused by high Ca2+ concentrations

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presynaptic inhibition

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occurs when the release of excitatory neurotransmitter by one neuron is inhibited by the activity of another neuron

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1. acetylcholine (ACh)

2. biogenic amines

3. amino acids

4. peptides

5. purines

6. gases and lipids

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6 classes of neurotransmitters

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acetylcholine

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neurotransmitter used at neuromuscular junctions, and in CNS and autonomic nervous systems

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1. epinephrine

2. norepinephrine

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2 neurotransmitters used in the autonomic nervous system; brain arousal

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serotonin

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neurotransmitter used to stabilize mood

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dopamine

Back 120

reward/pleasure neurotransmitter

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endorphins

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natural painkiller neurotransmitters

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neuromodulator

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a chemical messenger released by a neuron that affects the strength of synaptic transmission; doesn't directly cause EPSPs or IPSPs

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1. channel-linked

2. G protein-linked

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2 main classes of neurotransmitter receptors

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channel-linked receptors

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ligand-gated ion channels that mediate direct neurotransmitter action

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G protein-linked receptors

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neurotransmitter receptors that rely on second messengers; slower, but longer lasting effects

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neuronal pools

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functional groups of neurons that integrate incoming information and then forward it to other destinations

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discharge zone

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area of the neuronal pool that receives the bulk of the synaptic contacts; more likely to fire

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facilitated zone

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area of the neuronal pool farther from the center; less likely to fire

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circuits

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the patterns of synaptic connections in neuronal pools

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1. diverging circuit

2. converging circuit

3. reverberating circuit

4. parallel after-discharge circuit

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4 types of circuits in neuronal pools

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diverging circuit

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circuit with one input, many outputs

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converging circuit

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circuit with many inputs, and one output

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reverberating circuit

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circuit in which the signal travels through a chain of neurons, each feeding back to previous neurons; ex. breathing, short term memory

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parallel after-discharge circuit

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circuit in which the signal stimulates neurons arranged in parallel arrays that eventually converge on a single output cell; ex. precise mental functions

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serial processing

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processing in which the input travels along one pathway to a specific destination

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reflexes

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rapid, automatic responses to stimuli, in which a particular stimulus always causes the same response

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reflex arcs

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the neural pathways among which reflexes occur

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parallel processing

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processing in which the input travels along several different pathways to be integrated in different CNS regions; higher brain functions

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neuroblasts

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potential neurons that usually form in the second month of development

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growth cone

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the growing tip of an axon on a neuroblast