Human Anatomy and Physiology Chapter 11

Nervous System; 3 Overlapping functions
Sensory Input, Integration, Motor Output

Somatic Sensory Fibers
Conveys impulses from the skin, skeletal muscles and joints

Visceral Sensory Fibers
Transmit impulses from the visceral organs (within ventral body cavity)

Motor/Efferent Division; 2 Main parts
Somatic Nervous System-Conduct impulses from the CNS to skeletal muscles. Voluntary.
Autonomic Nervous System (ANS)-Consists of visceral nerve fibers that regulate activity of smooth muscle, cardiac muscle, and glands. (A.K.A.- Involuntary Nervous System)

Autonomic Nervous System; 2 functional Divisions
Sympathetic Division, Parasympathetic Division

Neuroglia in CNS
Astrocytes, Microglial Cells, Ependymal Cells, Oligodendrocytes

Neuroglia un PNS
Satellite Cells, Schwann Cells

Astrocytes (in CNS)
Most Abundant, versatile, highly branched cells. Cling to Neurons, Synaptic endings and Capillaries.
Functions; Support and brace neuron, guide migration of young neurons, control chemical environment. Plays role in exchange between capillaries and neurons (Most important)

Microglial Cells (in CNS)
Small ovoid cells with thorny processes that touch and monitor neurons. Migrate toward injured neurons. Can transform and phagocytize microorganisms and neural debris (old and infected cells)

Ependymal Cells (in CNS)
Range from squamous to columnar. May be ciliated (beat to circulate cerebral spinal fluid). Line central cavities of brain and spinal column. Permiable barrier between CSF in cavities and tissues. Bathes cells

Oligodendrocytes (in CNS)
Branched Cells. Procces wrap CNS nerve fibers, forming insulating myelin sheaths.

Sattelite Cells & Schwann Cells (in PNS)
Satellite Cells-Surround neuron cell bodies in PNS (Similar to astrocyte in CNS)
Schwann Cells (Neurolemocytes)-Surround all perepheral nerve fibers and form myelin sheaths in thick nerve fibers. (Similar to oligodendrocytes in CNS)

Neurons
Structural units of the nervous system. Typically large highly specialized cells that conduct messages in the form of nerve impulses. 3 Characteristics: Extreme longevity, Amitotic (can’s divide), High metabolic rate.

Neuron Cell Body
A.K.A. Soma, perikaryon.
Rough ER-Chromatophilic substance
Neurofibrils-bundles of intermediate filaments (neurofilaments). Maintains shape and integrity.
Nuclei-Clusters of cell bodies in CNS
Ganglia-Lie along nerves in PNS

Neuron Processes
Armlike processes extend from cell body of all neurons. Bundles of processes called tracks.
2 Types; Dendrites-main receptive or input regions. Many!
Axons-only one! Conducting region.

Axon Characteristics
Conducting region of neuron. Generates impulses away from cell body, along plasma membrane (axolemma). Axon terminals-secretory region

Axon Structure
Axon Hillock-Cone shaped area of cell body leading to axon.
Nerve Fiber-Any long axon
Axon Collaterals-Extend from axon at (more or less) right angles.
Terminal Branches-many branches at end of axon.
Axon Terminals/Boutons-Knoblike distal endings of the terminal branches.

Sensory/Afferent neurons
Transmit impulses from sensory receptors in the skin and integral organs toward or into the CNS. Virtually all sensory neurons are unipolar, and their cell bodies are located in sensory ganglia outside the CNS.

Motor/Efferent neurons
Carry impulses away from the CNS to the effector organs (Muscles and glands). Motor neurons are multipolar. Except for some neurons of the autonomic nervous system, their cell bodies are located in the CNS.

Interneurons
Association neurons. Lie between motor and sensory neurons and shuttle signals through CNS pathways where integration occurs. Most confined within CNS and make up over 99% of neurons in the body, including most of the CNS.

Chemically Gated Channels
Open when a neurotransmitter binds

Voltage Gates Channels
Open and close in response to changes in membrane potential

Mechanically Gates Channels
Open in response to physically deformation of the receptor (as in sensory receptors for touch and pressure)

Resting Membrane Potential
Inside of the cell membrane is a negative charge at -70 mV. Cell cytosol contains higher concentration of K+ and extracellular fluid contains higher concentration of Na+.

Sodium Potassium Pump
Stabilizes resting membrane potential by maintaining the concentration gradients for sodium and potassium. (3 Na+ out 2 K+ in)

Graded Potentials
Short lived-either depolarizations or hyperpolarizations. Stronger stimulus=More voltage changes and further current flow.

Types of graded potentials
Receptor/graded potential-when stimulus is excited by energy form (heat, light, other)
Postsynaptic potential-stimulus is neurotransmitter released by another neuron.

Action Potentials
Only cells with excitable membranes can generate action potentials (neuron and muscle cells)
Brief reversal of membrane potential

Events in Action Potential
#1 Resting State- All gated Na+ and K+ channels are closed.
#2 Depolarization- Na+ channels open
#3 Repolarization- Na+ channel are inactivated and K+ channels open.
#4 Hyperpolarization- Some K+ channels remain open, and Na+ channels reset

Voltage Gates Na+ Channels
Closed at resting state, opened by depolarization and Na+ enters cell, Inactivated soon after they open by inactivation gate.

Voltage Gated K+ Channels
Closed at resting state, opened by depolarization, after a delay, allowing K+ to exit cell.

Synapse
Junction the mediated information transfer from one neuron to the next. Or from one neuron to an effector cell. Where the action is!

Axodendritic Synapses
Synapse between the axon endings of one neuron and the dendrites of other neurons.

Axosomatic Synapses
Synapse between axon endings of one neuron and cell bodies (soma) of other neurons. Key word: Soma

Presynaptic Neuron
Neuron conducting impulses toward the synapse. Sends the information.

Postsynaptic Neuron
Neuron transmitting impulse away from synapse. Receives the information.

Electrical Synapse
Less common,consists of gap junctions (like those found in certain other body cells). Contain protein channels that intimately connect cytoplasm of adjacent neurons allowing flow of ions and small molecules to flow from one to the next.

Chemical Synapse
Allow the release and reception of chemical neurotransmitters.

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glial cells Supporting cells in the nervous system. Works to allow neurons to operate glia Non-excitable support cells in the nervous system. Size: generally smaller than nerve cells. ~1.5×10^11 cells. ratio to to neurons is between 1:1 and 5:1. Half …

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