Fundamentals of the Nervous System and Nervous Tissue Marieb Chapter 11 PART 1

Ganglia

lie along nerves in PNS

Neurons can be classified structurally by the number of processes extending from their cell bodies. What is the most common neuron type in humans?

multipolar

Long axons are also called

nerve fibers

Nodes of Ranvier

- Myelin sheath gaps b/w adjacent schwann cells - Sites where axon collaterals can emerge

Interneurons

-Association neurons -Lie b/w motor and sensory neurons -Shuttle signals through CNS pathways -Most are entirely within the CNS -found in 99% of the body's neurons

Motor Neurons

-Carry impulses from the CNS to effectors -multipolar -found in most cell bodies in the CNS

Meylin Sheath

-Composed of whitish, protein-lipid substance. Segmented covering around most long or large-diameter axons. -Protects and electrically insulates axon/neuron fibers. Increases speed of nerve impulse transmission.

Other functions of axons:

-Conducting region of neuron -Generates nerve impulses -Transmits nerve impulses along the axolemma to the axon terminal -Carries on many conversations with different neurons at the same time

Differences in Ionic Composition of resting membrane potential:

-ECF has a higher concentration of Na+ than ICF (balanced by Cl-) -ICF has higher concentration of K+ than ECF (balanced by negative proteins) -K+ plays most important role in membrane potential

When gated channels are open:

-Ions diffuse quickly across membrane along electrochemical gradients, from higher to lower concentrations -Ion flow creates an electrical current and voltage changes across membrane

Membrane Potentials

-Neurons are highly irritable -Respond to adequate stimulus by generating an action potential -Impulse is always the same regardless of stimulus

Basic Principles of Electricity

-Opposite charges attract each other -Energy is required to separate opposite charges across a membrane -Energy is liberated when the charges move toward one another -If opposite charges are separated, the system has potential energy

Neuron Cell Body

-Spherical nucleus with large nucleolus -has free ribosomes & large rough ER called nissl bodies -has mitochondria, microtubles. neurofibrils

Sensory Neurons

-Transmit impulses from sensory receptors toward CNS. -Almost all are unipolar -cell bodies are in ganglia in the PNS

when the sodium-potassium pump stabilizes resting membrane potential...

...concentration gradients for Na+ and K+ (more Na+ pumped out of cell and less K+ is pumped in)

Unipolar Neurons

1 short process, divides T-like - both branches are now considered axons. Distal process is associated with sensory receptor. Proximal process enters CNS.

Membrane potential changes when:

1. Concentrations of ions across membrane change 2. Membrane permeability to ions changes. (Only changes when ions start moving across the cell, which only happens if the channel allows them to)

Axon Hillock

Cone-shaped area of cell body

Central Nervous System (CNS)

Contains brain and spinal cord of dorsal body cavity; is the integration and control center. Interprets sensory input and dictates motor output.

the two types of neuron processes

Dendrites and axon

Resting membrane potential is generated by

Differences in ionic makeup of ICF and ECF & the differential permeability of the plasma membrane.

Dendrites

Found in motor neurons; 100s of sort branched processes (same organelles as in the body) -Receives signals from other neurons -Convey incoming messages toward cell body as graded potentials -always unmyelinated

Sensory Input

Information gathered by sensory receptors about internal and external environments

What are the two principal cell types of nervous tissue?

Neuroglia & neurons; highly cellular with little extracellular space

Voltage Gated Channels

Open and close in response to changes in membrane potential

Mechanically Gated Channels

Open and close in response to physical deformation of receptors, as in sensor receptors

Chemically Gated Channels (ligand channels)

Open with binding of a specific neurotransmitter

Schwann Cells

PNS; Surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers (similar to oligodendrocytes). They are vital to the regeneration of damaged peripheral nerve fibers.

Satellite Cells

PNS; Surround neuron cells bodies in PNS & function similar to the astrocytes of CNS

Resting membrane potential

Potential difference across membrane of resting cell. ~-70mV in neurons & the membrane is polarized.

Integration

Processing and interpretation of sensory input

non-gated channels(leakage channels)

Refers to channels that are always open

White Matter

Regions of brain and spinal cord with dense collections of myelinated fibers - usually fiber tracts

Which part of the action potential occurs when the Na+ channels are inactivating and K+ channels open?

Repolarization

What are the 3 functional classifications of neurons?

Sensory (afferent), motor (efferent), interneurons

name 3 functions of the nervous system?

Sensory Input Integration Motor output

Somatic Nervous System

Somatic motor nerve fibers conduct impulses from the CNS to skeletal muscle; part of the voluntary nervous system (conscious control of skeletal muscles)

What are the 2 divisions of the Motor Division?

Somatic nervous system and autonomic nervous system

Neurons

Structural units of the nervous system; large, highly specialized cells that conduct impulses. They have extreme longevity (100 years or more). Amitotic, high metabolic rate, and have a cell body with one or more processes. -Excitable cells; transmit electrical signals

What are the 2 functional subdivisions of the autonomic nervous system?

Sympathetic & parasympathetic - work in opposition to each other

Peripheral Nervous System

The portion of the nervous system outside the CNS. Consists mainly of brain nerves and spinal cord. nerves

Nuclei

clusters of neuron cell bodies in CNS

unmyelinated fibers

conduct impulses slowly

Bipolar Neurons

have 2 processes, 1 axon, 1 dendrite. These are rare, found in the retina and olfactory mucosa.

Multipolar Neurons

have 3 or more processes, 1 axon, other processes are dendrites. These are the most common and are the major neuron in the CNS. -99% of all neurons in body

Which type of ion channel opens when a chemical binds to it?

leakage channels

The movement of which ion through leakage channels establishes the negative membrane potential?

potassium

The interior of a nerve cell has a slight excess of negative charge because (__________.)

potassium diffuses out of the cell

Voltage

potential energy generated by separated charge *the charge difference across membranes: great charge difference b/w points = higher voltage

axon

region of the neuron and generates nerve impulses and transmits them. does not contain Nissl bodies and golgi apparatus.

Action Potential

the local voltage change across the cell wall as a nerve impulse is transmitted

Role of Membrane Ion Channels

-Large proteins serve as selective channels

Permeability of Plasma Membrane

1. Impermeable to large anionic proteins 2. Slightly permeable to Na+ 3. Much more permeable to K+ than Na+ 4. Very permeable to Cl-

3 types of Gated Channels

Chemically gated Voltage-gated Mechanically gated

Gray Matter

Mostly neuron cell bodies and nonmyelinated fibers.

What are the 3 types of structural classifications of neurons?

Multipolar, bipolar, unipolar

Axolemma

Neuron cell membrane

Neuroglia (glia cells)

Small cells that surround and wrap delicate neurons

Axon Collaterals

an axon that has divided into several branches allowing a single nerve cell to influence a wide array of other cells

Motor (efferent) Division

Transmits impulses from the CNS to effector organs (muscles and glands)

Autonomic Nervous System

Visceral motor nerve fibers that regulate smooth muscle, cardiac muscle, and glands. Part of the involuntary nervous system

Motor Output

Activation of effector organs (muscles and glands) produces a response

Oligodendrocytes

CNS; Branched cells; processes wrap CNS nerve fibers, forming insulating myelin sheaths thicker nerve fibers

Astrocytes

CNS; most abundant & versatile glial cells; cling to neurons, synaptic endings, and capillaries. support and brace neurons, guide migration of young neurons, control chemical environment around neurons, respond to nerve impuses and neurotransmitters, play role in exchanges between capillaries and neurons.

Ependymal Cells

CNS; range from squamous to columnar and may be ciliated. Line the central cavities of the brain and spinal column and form permeable barrier b/w cerebrospinal fluid in cavities and tissue fluid bathing CNS cells

Microglial Cells

CNS; small, ovoid cells with thorny processes that touch and monitor neurons. They migrate toward injured neurons & can transform to phagocytize microorganisms and neuronal debris

What happens when more K+ diffuses out than Na+ diffuses in?

The cell becomes more negative inside, and it establishes resting membrane potential.

What best describes the concept of integration?

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

Nonmyelinated Fibers

Thin fibers not wrapped in myelin; surrounded by schwann cells but no coilin