A&P 1 CHAP.12 - NEURAL TISSUE

This is the ________________ because graded potentials must reach this area of the neuron before they can be converted into action potentials

"trigger zone"

Divisions of the Nervous System

-Central Nervous System or CNS -Peripheral Nervous System or PNS

Central Nervous System or CNS

-Composed of the brain and spinal cord -It interprets sensory input and dictates motor responses based on past experiences, reflexes, and current conditions.

Peripheral Nervous System or PNS

-Composed of the cranial and spinal nerves. -These are the communication lines between the CNS and the rest of the body.

Sensory Division (afferent)

-Conducts impulses from sensory receptors to the CNS. -Sensory receptors are within somatic (skin, muscle, joints) and visceral (organs) systems. -The sensory division is considered the input region.

Motor Division (efferent)

-Consists of the motor neurons, which conduct impulses from the central nervous system to the effectors (muscles and glands). -The motor division is considered the output region.

Neurons exhibit several unique characteristics.

-Excitable, Longevity -High metabolic rate -Can be large -Amitotic

Oligodendrocytes

-Few branches (at least compared to Astrocytes and Microglia). -These cells line up along thicker neuron fibers in the CNS and wrap their extensions around nerve fibers forming the myelin sheath to insulate the neurons from each other.

Schwann cells

-Forms the myelin sheath around large nerve fibers in the PNS. -Can also act as phagocytic cells that engulf damaged or dying nerve cells and are important in directing the process of regeneration.

Ependymal cells

-Line the central cavities of brain and spinal cord, creating a barrier between the CNS cavities and the tissues surrounding the cavities. -Assist in producing, monitoring, and circulating cerebrospinal fluid, CSF. -They use their cilia to circulate the CSF within the cavities of the CNS.

Astrocytes

-Make up half of all neural volume and are star-shaped. -They possess numerous projections with bulbous ends that cling to neurons and capillaries therefore they serve as connections between neurons and blood/nutrient supply. This is called the blood-brain barrier. -Control the chemical environment around neurons by regulating ions, nutrients, dissolved gas concentrations, and hormones. They also absorb and recycle neurotransmitters that cannot be broken down and they form scar tissue after injury

Voltage-gated ion channels

-Open in response to changes in the membrane potential. -These are important in the generation and propagation of an action potential and are located only on the axon.

Chemically-gated ion channel

-Open when the appropriate neurotransmitter (chemical) binds to the receptor site on the protein. -These are important for depolarization and production of the graded potential and are located only on the dendrites and cell body.

Microglia

-Ovoid cells with highly branched processes -These act as macrophages that engulf microbes and dead neural cells as well as remove cellular debris, waste products, and pathogens.

Two divisions of the peripheral nervous system

-Sensory Division (afferent) -Motor Division (efferent)

Electrical synapses

-The cell membranes of the two neurons are actually connected by gap junctions that allow ions from the Presynaptic neuron to flow into the postsynaptic neuron so that the propagation of the action potential is continued in the next neuron. -This type of synapse can be found in both the CNS and PNS but are relatively rare.

Satellite cells

-These surround the nerve cell body. -May aid in controlling chemical environment about the neuron much like the astrocytes of the CNS.

Each neuron possesses only ______ axon, it may branch to form _____________ _____________.

1 collateral axons

The responses of postsynaptic neurons to the activation of a presynaptic neuron can be altered by :

1) the presence of chemicals that cause facilitation or inhibition at the synapse 2) activity under way at other synapses affecting the postsynaptic cell 3) modification of the rate of neurotransmitter release through stimulation or inhibition by regulatory neurons.

Name the 4 steps of the transmission of a nerve impulse.

1. Resting membrane potential (polarized cell membrane). 2. Depolarization and production of a graded potential. 3. Conversion of the graded potential to an action potential and then the propagation of an Action potential down the length of the axon to the synaptic terminals. 4. Repolarization or re-establishing the resting membrane conditions

Functions of Nervous Tissue

1. Use sensory receptor to monitor changes both inside and outside the body (INPUT) 2. Process and interpret sensory input (INTEGRATION) 3. Effects a response appropriate to the stimulus (MOTOR OUTPUT) 4. Maintain homeostasis by acting as a regulatory or control center.

- Na+ is stuck inside (supposed to be outside) and K+ is stuck outside (supposed to be inside) the sodium-potassium pump turns on and pumps ________________ to the outside for every _______________pumped to the inside. This reestablishes the resting location of the ions while also reestablishing the -70mV.

3 Na+ ions 2 K+ ions

There are ________________ neuroglial cells per neuron.

700-900

Chemical synapses

A synaptic cleft is formed between the two neurons and the Presynaptic neuron releases neurotransmitters that stimulate an action potential in the postsynaptic neuron.

What are the selected neurotransmitters?

Acetylcholine (ACh) Norepinephrine (NE) Epinephrine (E) Serotonin Glutamate Gamma-aminobutyric acid (GABA)

Neurons are classified by their structure (number of cell processes)

Anaxonic Neurons Bipolar Neurons Unipolar Neurons Multipolar neurons

Telodendria

As the axon approaches the next cell, many fine extensions branch from its end forming__________________.

The plasma membrane surrounding the axon is called the ________________ while the cytoplasm is called the __________________.

Axolemma Axoplasm

synaptic terminal

Axon terminal are also known as a ____________________________.

____________ are capable of generating action potentials and transmit nerve impulses away from the cell body during ____________ transport. Whenever the signal travels from the axon terminals back toward the cell body, it is called retrograde flow.

Axons Axoplasmic

myelin sheath

Axons are often covered with a whitish, fatty (protein-lipoid), and segmented ___________________

_________________ neurons-special sense organs; retina

Bipolar

Nuclei

Clusters of cell bodies in the CNS

Ganglia

Clusters of cell bodies within the PNS

Unmyelinated fibers

Conducts impulse quite slowly and forms the gray matter of the nervous tissue.

Myelinated fibers Conducts impulses rapidly and form the white matter of the nervous tissue.

Conducts impulses rapidly and form the white matter of the nervous tissue.

Parasympathetic nervous system

Conserves energy and promotes non-emergency functions such as during "rest and digest".

Gamma-aminobutyric acid (GABA)

Direct or indirect (G proteins), depending on type of receptor

Excitable

Excitable Neurons possess a polarized membrane which allows them to conducts messages in the form of a nerve impulse from one part of the body to another.

Neuroglial cells (which are often simply called glial cells).

Feed, protect, and insulate neurons.

Association (interneurons) neurons

Found in CNS (brain and spinal cord) only

Multipolar neurons

Has one axon and two or more dendrites. These are the most common neurons of the CNS and all motor neurons that control skeletal muscles ___________________.

Bipolar Neurons

Has two cell processes - one dendrite and one axon. While rare they occur in the retina of the eye and within the nasal mucosa.

Norepinephrine (NE)

Indirect, through G proteins and second messengers

Epinephrine (E)

Indirect: G proteins and second messengers

Glutamate

Indirect: G proteins and second messengers Direct: opens calcium/sodium channels

action potentials

Information is relayed in the form of ____________________.

Autonomic nervous system

Involuntary because it conducts impulses from the CNS to cardiac muscles, smooth muscle, and glands.

____________ is in highest concentration of the inside of the cell

K+

Anaxonic Neurons

Lack the features that typically distinguish dendrites from axons; all the cell processes look alike. These are found in the brain and in special sense organs. Their functions are poorly understood.

Sympathetic nervous system

Mobilizes the body during emergency situations "fight or flight".

Amitotic

Most CNS neurons lose their ability to divide after they assume the role as communication lines. They do not possess centrioles. PNS nerves may regenerate.

Association (interneurons) neurons

Mostly multipolar and 99% of all neurons

saltatory conduction

Myelin on the myelinated nerves causes the local depolarization to jump to the next Node of Ranvier and then from node to node. This type of propagation is called __________________________which is very rapid.

Schwann cells

Myelin sheaths are formed by ___________________ in the PNS.

____________ is in highest concentration outside the cell.

Na+

Dendritic Spines.

Neuron process, which possess large surface area because of its numerous branches known as what?

Longevity

Neurons can function for 100+ years. The neurons your born with are essentially the same neurons you die with.

High metabolic rate

Neurons cannot survive more than a few minutes without oxygen, glucose, or ATP therefore they possess a large number of mitochondria and tremendous vascularity.

Nissl bodies

Neurons possess large numbers of rough ER clustered within the cell body to form.

Nodes of Ranvier

Nodes of Ranvier Gaps between each Schwann cell are called ________________________, which also aids in impulse transmission.

continuous conduction pattern

On unmyelinated nerves, local depolarizations must spread to sites immediately adjacent to each other creating a __________________________. This type of propagation is relatively slow.

All or None Principle.

Once generated, an action potential cannot be stopped!! This is referred to as the___________________________________.

Mechanical-gated ion channels

Open in response to physical deformation of the membrane surface caused by exposure to touch, pressure, or vibration.

The cytoplasm surrounding the nucleus is called the __________________ and it contains numerous __________________ that make up the cytoskeleton of the neuron.

Perikaryon Neurofilaments

Acetylcholine ACh

Primarily direct, through binding to chemical gated channels.

Serotonin

Primarily indirect: G proteins and second messengers

Myelin

Protects and electrically insulates fibers from one another.

Passive, or leakage, channels

Protein channels that are always open allowing certain ions to pass through. -These channels are responsible for maintaining the resting membrane potential and are located all over the surface of a neuron.

Active, or gated, channels

Proteins channels that open and close in response to various signals.

polarized

RESTING MEMBRANE POTENTIAL -the cell membrane is _______________.

Dendrites _______________ chemical signals as well as conduct electrical signals towards the cell body.

Receive

Whenever the signal travels from the axon terminals back toward the cell body, it is called __________________________.

Retrograde Flow.

The myelin sheath forms by the ___________________ wrapping around and around the axon. The inner compressed layers are the myelin while the outermost metabolically active layer is called the ___________________. Gaps between the Schwann cells are called the ___________________.

Schwann cells Neurilemma Nodes of Ranvier

Neurons are also classified by their functions

Sensory (afferent) neurons Motor (efferent) neurons Association (interneurons) neurons

1. Synapses with another neuron. 2. Synapses with a skeletal muscle cell forming a neuromuscular junction. 3. Synapses with a gland or glandular cells.

Several types of synapses

Neurons

Some of the largest cells in the body

Axon Hillock

The axon forms at a tapered area called

Presynaptic Neuron

The cell conducting the impulse towards the synapse is called the _______________________.

Postsynaptic Neuron

The cell transmitting the impulse away from the synapse is the ________________________________.

Unipolar Neurons

The dendrites and axon are continuous and basically fuse with the cell body located off to the side. Most sensory neurons of the PNS are _________________.

stimuli

The effect on the axon's initial segment reflects a summation of the _______________ arriving at any moment. The frequency of action potentials generated is an indication of the degree of sustained depolarization at the axon hillock.

Cell body (also called soma)

The enlarged metabolic region of the cell where the nucleus is located.

Neurilemma

The exposed portion of the Schwann cell is called

axon hillock

The frequency of action potentials generated is an indication of the degree of sustained depolarization at the _________________________________.

Neurons

The functional cells of nervous tissue responsible for receiving, interpreting, and sending stimuli.

concentration gradient

The presence of a neurotransmitter within the synaptic cleft opens the Na+ chemically-gated channels and sodium begins to rush into the neuron down its _____________________________________.

neurotransmitter Na+ potassium ions

The removal of the __________________ from the synaptic cleft causes the ___________ channels to close so that no additional sodium enters the cell. HOWEVER, ________________________ are allowed to flow out of the cell.

graded potential.

The switch in charge begins to spread across the dendrites and cell body and is now called a ________________.

Motor (efferent) neurons

Transmit impulses away from CNS to the organs and glands

Sensory (afferent) neurons

Transmit impulses from sensory receptors towards the CNS.

Association (interneurons) neurons

Transmit impulses within CNS (usually between sensory and motor)

___________________ neurons-skin or internal organs to the CNS for interpretation

Unipolar

propagation of the action potential

Voltage channels to start opening all the way down the axon and the action potential now moves down the length of the axon. This is called the __________________________________ and generates a change in charge from -60 mV to +30 mV.

Somatic nervous system

Voluntary system that conducts impulses from the CNS to skeletal muscles

Ion channels

What plays a crucial role in establishing ion concentrations on either side of the neuron cell membrane?

refractory period

While the cell is repolarizing, the cell is insensitive to another stimulus and is called the ______________________.

Oligodendrocytes Within the CNS, the myelin sheath is formed by

Within the CNS, the myelin sheath is formed by

Neurotransmitters

_______________________ released at a synapse may have an excitatory or inhibitory effect.

Neurons

___________________may be facilitated or inhibited by extracellular chemicals other than neurotransmitters

If the graded potential reaches the _________________, voltage-gated channels within the _________________ open which cause the Na+ ions to flow into the axon switching the charge across the ______________________.

axon hillock axon hillock axolemma

In the body, electrical currents correspond to the flow of ions across ___________________________________.

cellular membranes

All voltage-gated Na+ and K+ ion channels are ____________ so that the neuron cell membrane is relatively impermeable to the two ions. Passive gates for both ions remain _____________ but movement is minimal.

closed open

The Presynaptic and Postsynaptic Neurons communicate via either an _______________ synapse or a ________________ synapse.

electrical chemical

Electrical signals are not nerve impulses; they are called ______________ _________________.

graded potentials

Because the K+ channels stay open longer than the Na+ channels did, the membrane may become ____________________________ (-90mV).

hyperpolarized

In that local patch of the membrane, the ___________________ side of the membrane begins to change from a negative charge to a more positive charge while the ________________ changes from positive to negative. Any change from -70 mV is called __________________.

interior exterior depolarization

The resting membrane potential exists only across the ________________; that is to say, the bulk solutions inside and outside the cell are electrically neutral. The resting membrane potential is approximately _____________.

membrane -70mV

Almost all motor neurons are _______________

multipolar

The inside of the neuron's membrane is _________________ charged while the outside of the neuron's membrane is __________________charged.

negatively positively

Multipolar neurons have the cell body located within the CNS and the axons form the ____________________ with effector cells

neuromuscular junctions

The rapid outflow reduces the total number of ________________ charges within the cell causing the charge to switch back across the membrane (from +30mV to -70 mV).

positive

The degree of _____________________or the strength of the _________________ is proportional to the frequency of the action potentials.

sensory stimulation motor response

synapse

synapse Many electrical impulses must travel from neuron to neuron or from neuron to muscles or glands. When the message has to be sent from one cell to another, the cells are connected by a __________________.

The synaptic terminals possess many _______________that contain __________________, which are used to cross the synapse or synaptic cleft found between the ________________ cell and the ________________ cell.

synaptic vesicles neurotransmitters presynaptic postsynaptic

Cellular processes are either called __________ (in CNS) or __________ (in PNS).

tracts nerves