INTEGRATIVE PHYSIOLOGY EXAM 2 :NERVOUS & MUSCLE TISSUE

Electrical Excitability

The ability to produce action potentials in response to stimuli

Central Nervous System

Consisting of the brain/spinal cord where brain is located in the skull while the spinal cord is connected on the brain with the vertebral column bones covering it

Peripheral

Consisting of all nervous tissues outside the CNS including nerve and sensory receptors. Which are divided into 2 divisions (afferent/efferent divison)

Nerve

Bundle of axons that lie outside the brain/spinal cord

Sensory Receptor

A structure that monitors changes in internal/external environment (touch receptor in the skin, olfactory receptors in nose, & strech receptors in the stomach walls)

Efferent Nervous System

Conveys the output from the CNS to effectors (muscles and glands)

Afferent Nervous System

Conveys output from the CNS to effectors (muscles and glands). This division is further subdivided into a somatic nervous system and an autonomic nervous system

Somatic Nervous System

conveys output from the CNS to skeletal muscles only. (its motor responses can be consciously controlled, the action of this part of the PNS is voluntary.)

Autonomic Nervous System

conveys output from the CNS to smooth muscle, cardiac muscle, and glands. Because its motor responses are not normally under conscious control, the action of the ANS is involuntary (divided into two parts)

Parasympathetic

Concerned with activities that conserve & restore body energy (rest & digest)

Symapthetic

Primarily concerned with processes that involve the expenditure of energy (“fight or flight"

Enteric Nervous System

The third branch that had an extensive networks of neurons confined to the wall of the GI tract

Sensory, integrative, and motor

What are the unique functions of the nervous system?

Sensory Function

Sensory receptors detect external or internal stimuli, such as a raindrop landing on your arm or an increase in blood acidity. This sensory information is then conveyed through cranial and spinal nerves of the PNS into the brain and spinal cord of the CNS.

Integrative function.

The CNS processes sensory information by analyzing it and making decisions for appropriate responses—an activity known as integration.

Motor function.

Once sensory information is integrated, the CNS may elicit an appropriate motor response. For this to occur, motor information is conveyed from the CNS through cranial and spinal nerves of the PNS to effectors (muscles and glands). Stimulation of the effectors causes muscles to contract and glands to secrete.

Neurons

The basic functional units of the nervous system. → thinking, remembering, controlling muscle activity, and regulating glandular secretions.

dendrites

short, highly branched processes that extend from the cell body. Because they receive signals from other neurons or from stimuli in the environment, function as the main input portions of the neuron.

dendritic spines

These structures increase the surface area for interactions with other neurons and they contain receptor sites that bind chemical messengers from these neurons. Most neurons have numerous dendrites, an aspect that further increases the receptive surface area of the cell.

cell body (soma)

contains most of the organelles, including the nucleus. Because of its ability to direct protein synthesis and other cellular activities, it functions as the control center of the neuron

axon

a single long, thin process that extends from the cell body. It functions as the output portion of the neuron by generating action potentials and then conducting them toward another neuron, a muscle fiber, or a gland cell.

axon hillock

The axon usually connects to the cell body at a cone-shaped region called this → action potentials arise at this from which they travel along the axon to their destination ( trigger zone)

axon collaterals

side branches along the length of an axon may extend off

axon terminals

The axon and its collaterals end by dividing into smaller processes

synaptic end bulbs

the tips of the axon terminals swell into this & can form synapses with other cells

axonal transport

For an axon to function, materials must move between the cell body and axon terminals, a process known as this

kinesins & dyneins

Used as motors to transport materials along surfaces of microtubules of the neuron’s cytoskeleton

anterograde

Axonal transport that occurs in this forward direction involves kinesins

retrograde

Axonal transport that occurs in a backward direction involves dyneins.

trophic chemicals

Substances that enter the neuron at axon terminals are moved by retrograde transport (can be this or harmful agents) like nerve growth factor

Sensory or afferent neurons

convey action potentials into the CNS.

Motor or efferent neurons

convey action potentials away from the CNS to effectors in the periphery.

Somatic motor neurons

part of the somatic nervous system; they convey action potentials to skeletal muscles.

Autonomic motor neurons

convey action potentials to cardiac muscle, smooth muscle, or glands

Interneurons or association neurons

located entirely within the CNS between sensory and motor neurons. → responsible for integration where they process incoming sensory information from sensory neurons and then may elicit a motor response by activating the appropriate motor neurons.

Neuroglia

make up about half the volume of the CNS. Their name derives from the idea of early histologists that they were simply the “glue” that held nervous tissue together, providing physical support to neurons

gliomas

Brain tumors derived from glia tend to be highly malignant and to grow rapidly

Astrocytes, Oligodendrocytes, Microglia, Ependymal cells

Name the Neuroglia of the CNS

Astrocytes

are the most numerous of the neuroglia. They have processes that wrap around capillaries (the smallest blood vessels) in the CNS. The walls of brain capillaries consist of endothelial cells (see Figure 8.5b) that are joined together by tight junctions. In effect, the tight junctions between the endothelial cells create a blood–brain barrier, which isolates neurons of the CNS from harmful agents and other substances in the blood

Oligodendrocytes

are responsible for forming and maintaining the myelin sheath around axons of neurons in the CNS. The myelin sheath is a multilayered lipid and protein covering that will be described in more detail shortly.

Microglia

function as phagocytes. They remove cellular debris formed during normal development of the nervous system and phagocytize microbes and damaged nervous tissue.

Ependymal cells

line the ventricles of the brain and central canal of the spinal cord. → produce and assist in the circulation of cerebrospinal fluid.

myelin sheath

a multilayered covering composed of lipids and proteins. Like insulation covering an electrical wire, this insulates the axon of a neuron and increases the speed of conduction of action potentials.

nodes of Ranvier

Gaps in the myelin sheath that appear at intervals along the axon

myelinated

Axons in the CNS or PNS that have a myelin sheath are said to be ______________.

unmyelinated

Axons in the CNS or PNS that do not have a myelin sheath are said to be ______________.

White matter

Within the brain and spinal cord are regions

gray matter

contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia. (appears to be this color due to lack of myelin)

neural plasticity

the capability of the nervous system to change based on experience.

regeneration

Mammalian neurons have very limited powers of ____________.

regeneration tube

schwaan cells can aid the repair process by guiding and stimulating regrowth of the axon.

Multiple sclerosis (MS)

a disease that causes a progressive destruction of myelin sheaths of neurons in the CNS.

Neurogenesis

the birth of new neurons from undifferentiated stem cells—occurs regularly in some animals.

1) Stimulus obtained

2) triggers axon to form an action potential

3) neurotransmitter stimulates interneuron to form graded potential

4) axon forms a nerve action potential in response

5) Process repeats until reaches higher parts of brain

6) stimulus in brain causes graded potential to form in dendrites and cell body of upper motor neuron

7) Generates graded potential in a lower motor neuron that supplies skeletal muscle fibers

8) Stimulates muscle fibers to contract

What are the typical steps to pass on an electrical signal (nerve) to another cell?

leak channels

randomly alternate between open and closed positions (more K⁺ leak channels due to the membrane’s permeability) → Found in nearly all cells, including dendrites, cells bodies, and axons of all types of neurons.

ligand-gated channel

opens or closes in response to a specific ligand (chemical) stimulus. A wide variety of ligands—including neurotransmitters, hormones, and chemicals in food or an odor—can open or close this (Na⁺ and Ca²⁺ to diffuse inward and K⁺ to diffuse outward thanks to the neurotransmitter acetylcholine) Found in some Dendrites of some sensory neurons such as pain receptors and dendrites and cell bodies of interneurons and motor neurons.

mechanically-gated channel

opens or closes in response to mechanical stimulation in the form of touch, pressure, tissue stretching, or vibration (such as sound waves) (Figure 7.12c). The force distorts the channel from its resting position, opening the gate. (found in touch receptors or pressure receptors in the skin)

voltage-gated channel

opens in response to a change in membrane potential (voltage). found in axons of all of neurons

resting membrane potential

When a cell is at rest (unstimulated), the voltage that exists across the plasma membrane is specifically termed this

membrane potential (V_m)

The voltage that exists across the plasma membrane of a cell

polarized

A cell that exhibits a membrane potential

−40 to −90 mV

the resting membrane potential

• Unequal distribution of ions in the ECF and cytosol.

• Differences in membrane permeability to various ions.

• Action of the Na+/K+ATPases. The Na+/K+ATPases

What are factors that affect the resting membrane potential?

K+ equilibrium potential (EK)

−90 mV (As the membrane potential becomes even more negative, the magnitude of the K+ electrical gradient increases. and eventually will be equal in magnitude)

equilibrium potential

the concentration gradient and electrical gradient for a particular ion are equal in magnitude but opposite in direction and there is no net movement of that ion across the plasma membrane.

Na⁺ equilibrium potential (ENa)

equal to +60 mV → As the membrane potential becomes even more positive, the magnitude of the Na+ electrical gradient increases. Eventually, the Na+ electrical gradient becomes equal in magnitude to the opposing Na+ concentration gradient and there is no net movement of Na+ ions into or out of the neuron

K⁺

What is typically greater in terms of what comes out of leak channels?

Graded Potentials

Local changes in the membrane potential (can vary in amplitude or be less polarized)

Depolarizing Phase

Rising phase when the negative membrane potential becomes less negative and eventually reaches zero and becomes positive (overshoot & (+) feedback cycle: 0 to 30 mV)

Repolarizing Phase

Falling phase where membrane potential is restored to the resting state of -70 mV → K channels open and making it rush to the cell (from 30mV to -70mV)

After-hyperpolarizing phase

Undershoot during which membrane’s potential temporarily becomes more negative than resting level (K channels remain open after repolarization) → below -70mV

Subthreshold stimulus

Weak depolarization that cannot bring membrane potential to threshold

Threshold stimulus

Strong enough to depolarize membrane to threshold (-55mV)

supathreshold stimulus

Strong enough to depolarize membrane above the threshold

Activation Gate

Activated state of Na⁺ channel will open this

Inactivation gate

Resting state of Na⁺ channel will open this and close activation gate

Refractory Phase

Phase when excitable cell cannot generate another action potential in response to a normal threshold stimulus.

Conduction

The mode of travel of action potentials when it travels along the membrane (cannot travel back to cell body but can regenerate!)

Saltatory Conduction

Myelinated sheaths exhibit a special type of action due to uneven distribution of voltage-gated channels (leaps from one action potential to another)

Unmyelinated axons

The action potential spreads along each adjacent segment of the plasma membrane

Myelinated Axons

Travel more rapidly due to the insulated myelin and being able to jump around each nodal area.

Axon Diameter

Larger ____________ means faster action potential (circuits from physics)

A-fibers

Conduction of action potentials at velocities ranging from 12-130 m/sec

C-fibers

Conduction of small diameter, unmyelinated axons that can conduct action potentials at velocities from a 0.5-2 m/sec

Normokalemia

Suprathreshold stimulus will fire action potential

Hyperkalemia

Increased blood Potassium ion concentrations brings membrane closer to threshold

Hypokalemia

Decreased blood Potassium concetrations that hyperpolarizes the membrane which makes neurons less likely to fire an action potential

Ca²⁺

When this ion binds, this will alter the voltage needed for Sodium channels to open

synapse

the site of communication between two neurons or between a neuron and an effector cell.

presynaptic neuron

the neuron sending the signal at the synapse is

postsynaptic neuron

the neuron receiving the signal at the synapse is

axodendritic

from axon to dendrite

axosomatic

from axon to cell body

axoaxonic

from axon to axon

electrical synapse

action potentials conduct directly between adjacent cells through gap junctions

Faster communication & Synchronization

Two advantages of electrical synapses?

Excitatory postsynaptic potential (EPSP)

A depolarizing postsynaptic potential

inhibitory postsynaptic potential (IPSP)

A hyperpolarizing postsynaptic potential

ionotropic receptor

a type of neurotransmitter receptor that contains both a neurotransmitter binding site and an ion channel as part of its structure. (ligand gated channels) → EPSP result from these receptors

metabotropic receptor

a type of neurotransmitter receptor that contains a neurotransmitter binding site and a site that is coupled to a G protein. The G protein, in turn, either directly opens (or closes) an ion channel or it activates a second messenger pathway that opens (or closes) an ion channel or causes another response in the cell, such as increasing the synthesis of new proteins, modifying the activity of existing proteins, or increasing the intracellular Ca2+ levels. (can also cause K levels to increase)