Nerve Tissue Physiology

• Central Nervous System (CNS)
• Peripheral Nervous System (PNS)

The Brain and Spinal Cord

• 1. The Somatic Nervous System (motor neurons)
• 2. The Autonomic Nervous System (ANS)

All other nerve tissues

• Sympathetic nervous system
• Parasympathetic nervous system

Neuron and Glial Cells

Transmits nerve impulses from one part of the body to another

They are the support cell for the nervous system. Some glial cells are found in the CNS, others in the PNS.

There are 4 glial cells in the CNS,and they are the Astrocytes, Ependymal cells, Oligodendrocytes, and Microglia.

Constitute 90% of CNS tissue in some areas of the brain. Star-like shape. Physically support neurons and form the Blood-Brain-Barrier (BBB)

Like cubodial epithelium (but no basement membrane). Line the internal cavities of the brain. Create the cerebrospinal fluid by filtering fluid out of the choroid plexus (a tuft of blood vessels next to the brain).

They form the myelin sheath in the CNS by wrapping each arm around a neuron. Look like an octopus, with up to 15 arms (one cell can wrap up to 15 neurons).

It acts as immune cells for nervous tissue. Phagocytize (=eat) dead matter or debris in the CNS, respond to infections

Schwann cells and Satellite cells

Form the myelin sheath in the PNS by wrapping themselves around neurons. Unlike oligodendrocytes, one Schwann cell wraps around one neuron.

They surround neuron cell bodies. Function unknown.

• Epineurium-surrounds the nerve as a whole
• Perineurium-surrounds each fascicle (bundle of neurons)
• Endoneurium-surrounds each neuron on the outside of the myelin sheath
• Neurons are arrange in connective tissue sheaths similar to muscles. The terms "neuron" and "nerve" are NOT synonymous.

• 1. Sensory receptor
• 2. Sensory (afferent) neuron
• 3. Interneuron
• 4. Motor (efferent) neuron
• 5. Muscle or gland

Such as a receptor on the skin. Receives input from the environment, such as pain from putting your hand on a hot stove.

It transmits the pain signal from the receptor to the CNS.

Inside the spinal cord. A neuron that connects the sensory neuron with the motor neuron. Makes up 90% of the body's neurons. Process information and make decisions about how to respond to stimuli.

Carries information from the CNS to muscles (skeletal muscles) and glands (smooth muscles).

Contracts in an adaptive response to the original stimulus.

Cell body (soma), dendrite, axon hillock, axon, synaptic knob, axolemma, neurilemma, myelin sheath, node of ranvier, synaptic gap

It contains the nucleus, endoplasmic reticulum, mitochondria, ribosomes, etc.

It receives the nerve impulse coming from the pre-synaptic neuron, or repsonds to the mechanical, electrical, or thermal (heat/cold) stimulation.

It the the enlarged portion of the axon, where the cell body connects with the axon.

It transmits action potential to the synaptic bulb.

(=synaptic bulb, terminal button) it is a small enlargement at the end of the axon; contains neurotransmitters

The cell membrane around the axon.

The outermost layer of the Schwann cell around the neuron.

Fatty substance surrounding many neurons, speeds up impulse transmission.

The small gap between myelin sheaths, about 1mm apart, where the axon is exposed to the extracellular fluid.

The tine space between the pre-synaptic neuron and the target tissue (dendrite of post-synaptic neuron, muscle sarcolemma, gland, etc) Not technically part of the neuron.

It contains rough endoplasmic reticulum (=ER + attached ribosomes), which is also known as Nissl substance ( or Nissl bodies) in the neuron

• Outside the axon: sodium (+), chloride (-)
• Inside the axon: proteins (-), potassium (+)

-70mV

TRUE

TRUE

The membrane is hardly permeable to both Na+ and K+, but is slightly more permeable for K+ than for Na+

• Potassium Leak Channels: Allow a small amount of potassium to leak out of the cell
• Sodium Leak Channels: Allow a very small amount of sodium to leak into the cell

Uses active transport to simultaneously pump 3Na+ OUT and 2K+ IN. Consumes 1 ATP for every exchange cycle.

A change in the membrane potential toward zero

A change in the membrane potential back toward the negative

A change in the membrane potential beyond the resting potential (below -70mV)

Involves the movement (=propagation) of the nerve impulse down the axon, by using changes in the membrane potential. An action potential only occurs if the threshold (-55mV) is met.

• 1. A neuron at rest maintains a resting potential of -70mV
• 2. An incoming impulse cause the potential to become slightly depolarized
• 3. If the threshold is reached, the action potential will occur. If the threshold is NOT reached, the potential will just fall back to the resting potential. This is called the "All-or-None Principle"
• 4. If the threshold is reached, the sodium voltage-gated channels will open, and sodium will rush INTO the axon. This causes the membrane potential to rise quickly from -55mV up to about +35mV (=depolarization)
• 5. At this peak, the sodium voltage gated channels will close, and potassium voltage-gated channels will open, allowing potassium to rush OUT of the azon. This causes the membrane potential to drop back down to -70mV and beyond (=repolarization)
• 6. Because potassium gates stay open longer than sodium gates, the potential typically drops below 70mB, moving down to about -72mV. The name of this phase where the potential goes very low is-hyperpolarization. During hyperpolarization the action potential cannot be re-activated because the starting point would be too low for the initial stimulus to reach the threshold - this is called the refractory period. At the end of this phase, both sodium and potassium voltage-gated channels are closed.
• 7. The Na+K+ pump now quickly pumps out the sodium back out and the potassium back in, using a 3 Na+/2K+ ratio. This causes the membrane potential to move back up to the resting potential of -70mV. The neuron is now ready to "fire" again.

Is an example of a positive feedback system (where the "outcome accelerates the process") because depolarization of one area of the axon triggers depolarization of the next area.

The action potential causes full depolarization of area #1. That area becomes overall positive, which attracts the negative proteins from area #2. As area #2 now becomes slightly more positive (=less negative), it reaches threshold, causing the opening of sodium voltage-gated channels, and sodium rushes into the axon. As the inside of the axon in area #2 becomes fully positive, that attracts proteins from area #3. And so on. This movement of the action potential is called propagation or conduction.

The movement of an action potential down an umyeylinated axon using the mechanism described above in propagation. Relatively slow, around 2m/sec

The movement of an action potential down a myelinated axon. The neural impulse "jumps" from one node of Ranvier to the next (they are spaced about 1mm apart), and gets recharged at the Node of Ranvier. Much faster: up to 120m/sec

The area where one neuron's synaptic bulb meets up with the target tissue (muscle cell, second neuron, etc.)

The microscopic gap between the pre-synaptic neuron and the target tissue (if neuron, called post-synaptic neuron).

True

True

True

The target tissue is excited (=stimulated) or the target tissue is inhibited

Acetylcholine, Norepinephrine, Dopamine, Serotonin, Glycine, GABA, and Glutamate.

Used for activating skeletal muscle cells, and used for activating neurons in the autonomic nervous system. For skeletal muscle cells, the acetylcholine is released from the pre-synaptic neuron. Acetylcholine binds to receptors on the sarcolemma at the neuromuscular junction. This triggers activation of an action potential that spreads across the sarcolemma, dives down the T-tubule, triggers release of calcium from the SR, etc. End result: MUSCLE CONTRACTION

Has a primary role in the sympathetic division of the autonomic nervous system. Also has a role in dreaming, waking, and elevating mood.

Found in the "pleasure center" of the brain. Involved in elevation of mood and control of skeletal muscles.

Has a role in relaxing the body during sleep, and elevating mood

Inhibitory neurotransmitter, and also an amino acid

An inhibitory neurotransmitter, and also an amino acid

Excitatory neurotransmitter, and also an amino acid. Involved in learning and memory. MSG (monosodium glutamate, a food additive) causes overstimulation of these receptors.

True

• Diverging Circuit
• Converging Circuit
• Reverberating Circuit

One nerve fiber synapses with several postsynaptic cells. Allows one motor neuron to ultimately stimulate thousands of muscle fibers

several nerve fibers converge into one neuron. Allows multiple neurons to be channeled to a particular area of the brain

Neurons stimulate each other in a linear sequence, but some neurons send an axon collateral back to the first neuron. Allows repetitious signals to be sent to your diaphragm, to make you inhale.