Essentials of Anatomy & Physiology, Chapter 8, Nervous System

Satellite cell

A neuroglial cell in the PNS. They surround and support neuron cell bodies They have a similar function to the astrocytes in the CNS.

What projects from the cell body?

A number of dendrites, a single large axon. The axon may have branches called collaterals. Axon terminal's are at the end of the branches. And an axon hillock, which is the thickened region

Action potential

A propagated change in the membrane potential of the entire plasma membrane Only skeletal muscle fibers and the axons of neurons have excitable membranes that conduct action potentials. No action potentials are possible on the skin or other cells.

Neural cortex

A thick layer of gray matter covering the brain surface

How do you tracts differ from a nerve?

A tract is a bundle of nerve fibers in the CNS. A nerve is a bundle of nerve fibers in the PNS.

Major events that occur at a cholinergic synapses:

Action potential arrives at the axon terminal this Depolarizes the presynaptic membrane Calcium enters and triggers exocytosis of ACh ACh is released and diffuses across synaptic cleft ACh binds to receptors and triggers depolarization of the postsynaptic membrane Opens sodium ion channels, triggering an influx of sodium ACh is removed by AChE -acetylcholinesterase

Saltatory propagation

Action potential leaps from node to node, skipping the myelinated membrane surface

Peripheral nervous system

All the neural tissue's outside of the central nervous system. The connection between the central nervous system and the rest of the body.

Sensory neurons

Also called afferent neurons. The human body has approximately 10 million sensory neurons. They received information from sensory receptors monitoring the external and internal environments and relay the information to other neurons in CNS.

Neuroglia

Also called glial cells. They support neurons by regulating the environment around neurons, provide a supporting framework for neural tissue, and act as phagocytes. Although neuroglia are much smaller cells, they far outnumber neurons. Most glial cells retain the ability to divide.

Norepinephrine (NE), a neurotransmitter

Also called noradrenaline In the brain and part of the autonomic nervous system, are released from adrenergic synapses Usually has a depolarizing effect on postsynaptic neurons With the potential of reaching threshold which isa stimulatory effect

Polarized plasma membrane

And undisturbed cell has a plasma membrane that is polarized because it separates an excess of positive charges on the outside from an excess of negative charges on the inside.

Sensory pathways

Are ascending pathways and distribute information from sensory receptors to processing centers in the brain

Motor pathways

Ascending pathways - which began in the CNS centers concerned with motor activity and end at the skeletal muscles that control.

Four types of Neuroglia in the Central Nervous system:

Astrocytes - largest, most numerous and Oligodendrocytes - myelinates central Nervous system axons and Microglia - phagocytic cells and Ependymal - makes cerebralspinal fluid in the brain

Which glial cells are most abundant in the body?

Astrocytes are the most numerous glial cell.

A synapse between two neurons occurs:

Between the axon terminals of the presynaptic neuron, across the synaptic cleft, to the dendrite or cell body of the postsynaptic neuron

What effect would blocking calcium channels at the cholinergic synapse have on synapse function?

Blocking calcium channels at the presynaptic terminal of a cholinergic synapse would prevent the influx of calcium that triggers the release of acetylecholine, so no communication would occur across the synapse, and the postsynaptic neuron would not be stimulated.

Tracts

Bundles of axons that share a common origins, destinations, and functions found in the white matter of the CNS.

Unipolar neurons

Cell body is off to the side and Most sensory neurons in the peripheral nervous system are unipolar.

Neuroglial cells

Cells that make up about half of the volume of the nervous system. They are found in both the CNS and PNS, but the CNS has a greater variety of glial cells.

Collections of neuron cell bodies with the common function are called ______, which have discrete boundaries called _____.

Centers Nuclei

Passive forces are chemical and electrical

Chemical concentration gradients move potassium ions out of the cell and sodium ions into the cell through separate leak channels It's easier for potassium ions to diffuse through a potassium channel than sodium ions to diffuse through sodium channels, potassium ions diffuse out of the cell faster than sodium ions enter the cell.

neurotransmitters

Chemical messenger Stored in vesicles of the axon terminals Released into the synaptic cleft and binds to receptors on the postsynaptic membrane. Causes the information transfer of the impulse to another neuron or effector cell

How is a stimulus transmitted across a synapse?

Chemically via the release of a neurotransmitter and binding of the neurotransmitter to the postsynaptic membrane.

Types of stimuli that can change a membrane potential include exposure to:

Chemicals Mechanical pressure Temperature changes Changes in the extracellular ion concentration Result is opening of a gated ion channels Increasing the movement of ions across the membrane.

Nissl bodies

Clusters of rough endoplasmic reticulum and free ribosomes account for the gray matter seen in the brain and spinal cord dissections.

What type of neural circuit permits both conscious and subconscious control of the same motor neuron?

Convergence permits both conscious and subconscious control of the same motor neurons

What would be the effect of damage to the afferent division of the peripheral nervous system?

Damage to the afferent division of the PNS, who's nerves carry sensory information to the brain and spinal cord, would interfere with a persons ability to experience a variety of sensory stimuli.

Short-term memory or primary memories-

Doesn't last long, but can be recalled immediately

Identify the neuroglia of the central nervous system

Ependymal cells Astrocytes Oligodendrocytes Microglia

Somatic sensory receptors

External receptors that detect information from the outside world. They provide information in the form of touch, temperature, pressure, taste, smell, site, equilibrium, and hearing. They work by detecting are physical position in the world in the form of proprioceptors.

Factors determining membrane potential

Extracellular fluid is high in sodium ions and cloride ions Intracellular fluid is high in potassium ions and negatively charged proteins Proteins in the cytoplasm are too large to cross the membrane, and ions can only cross with the aid of channels or carrier protein

Oligodendrites (Neuroglial cell on the CNS)

Found in the CNS. Forms a membranous wrapping around axons called myelin. Not all axons are myelinated.

Dopamine, GABA, and serotonin, neurotransmitters

Function in the central nervous system Usually inhibitory due to hyperpolarization of the postsynaptic neurons An inhibatory response - slows down or stops an action potential by making it farther from threshold

Why is a brain tumor more likely to be formed with glial cells then from neurons?

Glial cells can divide. Most neurons cannot. A criteria of cancer cells is their uncontrolled division.

Neuronal pools

Groups of interconnected neurons with specific functions Divergence - info from one pool into several Convergence - info from several synapses onto one

Bipolar neurons

Has two processes - one dendrite and one axon with the cell body in between. These are uncommon, but occur in special sense organs to relay information about sight, smell, or hearing.

In the PNS, neuron cell bodies are located in ________ and surrounded by neuroglial cells called _______ cells.

In the PNS, neuron cell bodies or gray matter are located in ganglia and are surrounded by satellite cells.

The Prefrontal Cortex

In the frontal lobe Coordinates information from the association areas of the entire cortex

Structural component of a typical neuron

Include cell body, which contains the nucleus and nucleolus, an axon, dendrites, Nissl bodies, an axon Hillock, collaterals, and axon terminal's

Visceral receptors

Internal receptors that monitor the internal organs and activities of the digestive, respiratory, cardiovascular, urinary, and reproductive systems. These receptors provide sensation of distention, deep pressure, and pain.

Cell bodies of neurons

Large round nucleus with a prominent nucleolus Numerous mitochondria, free and fixed ribosomes, and rough endoplasmic reticulum.

Skill memory -

Learned motor behaviors that can become incorporated into unconscious memory - skiing or playing the violin

Ependymal cells (neuroglia cell of the CNS)

Line the central canal of the spinal cord and the chambers or ventricles of the brain. This lining is called ependyma Involved in producing and circulating cerebrospinal fluid around the CNS.

Pathways

Link the centers of the brain with the rest of the body. Examples: sensory pathways and motor pathways

Propagation of an action potential

Local changes in the membrane in one site, result in the activation of voltage-gated channels in the next adjacent site on the membrane Action potential moves only forward, not backward because the previous segment of the axon is still in the refractory period

Interneurons - also called association neurons. They are by far the most numerous type at about 20 billion

Located in the CNS, interconnecting other neurons. They take input and figure out the output linking the systems. The more complex the response to a stimulus, the greater the number of interneurons involved. They play a role and higher functions such as memory, planning, and learning.

Action potential

Membrane depolarizes to threshold First Sodium ion channels open then Depolarization happens then sodium channels close next potassium channels open then returns to resting

Motor neurons

Modify activity of the peripheral tissues

There are three types of neurons structures based on the relationship of the dendrites to the cell body and axon they are:

Multipolar neurons Unipolar neurons Bipolar neurons

Organization of peripheral nervous system or PNS

Neuron cell bodies are organized in clusters called ganglia - gray matter. Axons are bundled together in nerves - white matter. Includes spinal nerves and cranial nerves. Can have both sensory and motor axons.

Neural tissue consists of two kinds of cells

Neurons and neuroglia

Other important neurotransmitters

Norepinephrine or NE Dopamine, GABA, and serotonin At least 50 less-understood neurotransmitters Nitric oxide and Carbon Monoxide Are gases that act as neurotransmitters.

Saltatory propagation

Occurs in myelinated axons and is faster at 40-300 mph it leaps Myelination makes a huge difference in speed

Which glial cell produces the insulating material called Myelin?

Oligodendrocytes produce myelin.

Center

Part of the central nervous system. A collection of neuron cell bodies with common functions.

Functions of Meninges

Provide stability and shock absorption to the central nervous system Blood vessels branch within theses layers to deliver nutrients and oxygen

Two types of neuroglia in the Peripheral nervous system:

Satellite cells - support neuron cell bodies and Schwann cells - myelinate axons in the Peripheral nervous system.

Neurons are sorted into three functional groups

Sensory neurons motor neurons interneurons

Which type of glial cell would increase in number in the brain tissue of a person with a CNS infection?

Small phagocytic glial cells are called microglia and are typically found in increased number in infected or damaged areas of the CNS.

Two types of sensory receptors in which sensory neurons receive information

Somatic sensory receptors Visceral or internal receptors.

Changes in Membrane Potential

Stimuli that alters membrane permeability to sodium or potassium Stimuli that alters activity of the exchange pump will disturb the resting potential of a cell For example: the permeability changes in the sarcolemma of a skeletal muscle fiber trigger a contraction.

The nervous system has two functional divisions

The afferent division and the efferent division

What are two functions of the peripheral nervous system?

The afferent division bring sensory information to the CNS from receptors in the peripheral tissue and organs. The efferent division, carries motor commands from the CNS to the effectors such as muscles and glands.

Neurons

The basic unit of the nervous system. Specialized cells that communicate with one another and other cells.

Neuronal Pools

The complex grouping of neural pathways or circuits

A membrane potential exits across the plasma membrane of all living cells because:

The cytosol differs from extracellular fluid in chemical and ionic composition The plasma membrane is selectively permeable

What would cause the plasma membrane to shift away from its resting state?

The membrane potential changes from moment to moment, as the permeability changes in response to chemical or physical stimuli.

Neurologically, cholinergic is the abbreviated term referring to acetylcholine.

The parasympathetic nervous system, which uses acetylcholine almost exclusively to send its messages, is said to be almost entirely cholinergic.

Fact memory -

The recall of bits of specific information - What is your SSN?

Reticular formation of the midbrain contains

The reticular activating system (RAS), the output of this system directly affects the activity of the cerebral cortex it also Contains the substantia nigra which secretes the neurotransmitter dopamin

Microglia

The smallest and least numerous Neuroglial cells They are phagocytic cells derived from white blood cells that migrated into the CNS as the nervous system formed. They perform protective functions such as an golfing cellular waste and pathogens.

The efferent division is further divided into two systems.

The somatic nervous system. And The automatic nervous system.

Higher centers

The term higher centers refers to the most complex integration centers, nuclei, and cortex area of the brain. Thinking, learning, and memory

Multipolar neurons

These are the most common neurons in the central nervous system. They have two or more dendrites and one axon. All motor neurons that control The skeletal muscles are multipolar.

What happens the same amount of excitatory and inhibitory neurotransmitters are released?

They cancel each other out resulting in no action

Schwann cells

They cover every axon in the PNS. The outer surface of a Schwann cell covering is called neurilemma. Can only myelinated one segment of a single axon Can enclose portions of several different unmyelinated axons.

Astrocytes Largest and most numerous neuroglial in the CNS.

They create a support framework for CNS neurons, perform repairs to damage neural tissues, secrete chemicals vital to the maintenance of the blood brain barrier. The secretions cause the capillaries of the CNS to become impermeable to many compounds that could interfere with neuron function.

Axon hillock

Thickened region of a cell body where action potentials begin.

How does the resting potential remain stable over time? The Sodium-potassium exchange pump.

This ion pump exchanges three intracellular positive sodium ions for two extracellular negative potassium ions. It moves Sodium out as fast as it leaks in. The cell experiences a net loss of positive ions resulting in a resting membrane charge of -70 millivolts.

Motor neurons, also called efferent neurons

Total about half a million They carry instructions from the CNS to other tissues, organs, organ systems. The peripheral targets are called effectors because they respond by doing something. Example: a skeletal muscle is an effector that contracts upon neural stimulation.

Columns

Tracts in the spinal cord that form larger anatomically distiinct groups.

Is a unipolar neuron more likely to be a sensory neuron or a motor neuron?

Unipolar neurons are more likely sensory neurons of the PNS

Membrane potential

When positive and negative charges are held apart, a potential difference exists between them. Because the charges are separated by a plasma membrane this potential difference is called Membrane potential.

Neuroeffector junction

Where the synapse releases neurotransmitters which then communicate with other cell types Events are: Presynaptic neuron to synaptic cleft to postsynaptic neuron If it is a cholinergic synapse - ACh is the neurotransmitter If it is an adrenergic synapse - norepinephrine is the neurotransmitter

In an axon, an action potential begins

near the axon hillock, travels along the axon toward the terminals, where it's arrival activates the synapses

An action potential in a neuron is a

nerve impulse

synapses between a neuron and another cell type is a

neuroeffector junction neuromuscular junction when the neuron communicates with a muscle cell neuroglandular junction controls the activity of a secretory cell.

What is the maximum rate of action potential generation?

500-1000 per second

Nuclei

A center with a discrete boundary.

Symptoms of a concussion

A concussion may lead to thinking, sleeping, and balance problems, and symptoms Warning signs include persistent headache, extreme drowsiness, slurred speech, and repeated vomiting or nausea.

How does a ganglion different from a nucleus?

A ganglion is a cluster of nerve cell bodies in the PNS; a nucleus is a cluster of nerve cell bodies in the CNS.

Ganglia

A group of nerve cell bodies located in the peripheral nervous system

A cholinergic synapse

is a gap where a neuron that produces acetylcholine sends messages to other neurons, or to skeletal muscle cells The neurotransmitter acetylcholine (ACh) is released at cholinergic synapses Cholinergic synapses are throughout the whole body - neuromuscular junction

Interneurons -

located between sensory and motor neurons they Analyze input and coordinate output.

If a combination of graded potentials causes the membrane to reach a critical point of depolarization, it is called

the threshold - every stimulus that brings the membrane to threshold will generate an identical action potential. Pulling the trigger on a gun is an example of this.

Cholinergic synapses are

widespread inside and outside the central nervous system - throughout the whole body - neuromuscular junction