Physio- Unit 7

What kind of cell signaling occurs in the nervous system?

Synaptic signaling

What are the divisions of the Nervous system?

CNS and PNS

What is the CNS made up of

brain and spinal cord

What is the PNS made up of

Cranial nerves and spinal nerves

What are the divisions of the cranial nerves?

Afferent (sensory) and Efferent (motor)

What are the divisions of the spinal nerves

Afferent (sensory) and Efferent (motor)

What is afferent?

Sensory info that goes toward CNS

What is efferent?

Motor info that goes away from the CNS to effector organs 

Parts of the Afferent Division

Somatic senses and special senses

Where is the afferent division and where does it’s components go?

The afferent division is inside the PNS and it is the somatic and special senses that send the sensory input to the CNS

What are somatic senses?

General sensation: touch, pain, etc.

Parts of the Efferent Division

Somatic nervous system and autonomic nervous system

What are the parts of the autonomic nervous system?

Sympathetic nervous system, parasympathetic nervous system, and enteric nervous system

Where does the somatic NS occur

Skeletal muscles

what is the sympathetic nervous system and where does it occur?

“fight or flight” and occurs in smooth muscle, cardiac muscle and glands

what is the parasympathetic nervous system and where does it occur?

“rest and digest” occurs in smooth muscle, cardiac muscle and glands

Where is the efferent division and where does it’s components go/ come from?

The efferent division is located in the PNS and it receives motor output from the CNS  which enters the PNS and goes to somatic NS or autonomic NS

What are the functions of the nervous system?

Sensory, integration, and motor

What is Sensory function?

receptors that detect external or internal stimuli, and relay sensory info to the brain and spinal cord for integration 

What is Integration function?

CNS analyzes sensory information,, and makes decisions for appropriate responses

What is Motor function?

Motor info is conveyed from the CNS through cranial & spinal nerves of the PNS to appropriate effectors (muscles and glands) 

What is the nueron?

Functional unit of the nervous system

What are the major parts of the neuron

cell body, dendrites, and axon

What does the cell body do?

The input portion that contains organelles

What are dendrites?

Input portion, that receives input from environment or other neurons

What are the different parts of the axon ?

Axon hillock- trigger zone

Axon collaterals- branch off axon

Axon terminal- end of axon 

• Synaptic end bulb- synapse with cells

• Synaptic vesicles- contain neurotransmiter

Ganglia

cluster of cell bodies in the PNS

Nucleus

Cluster of cell bodies in the CNS

Nerve

bundle of axons in the PNS

Tract

Bundle of axons in the CNS

What are the 2 types of axonal transport

Anterograde and retrograde

What is anterograde transport? What type of motor protein does it use?

Transports organelles and synaptic vesicles from the cell body to the axon terminal. Uses Kinesin motor neurons

What is retrograde transport? What type of motor protein does it use?

Transports membrane vesicles and other materials “back” from the axon terminal to the cell body to be degraded. Uses Dynein motor proteins

What are interneurons

Occur between the sensory and motor neurons and are in the CNS.

Info from sensory neuron (in PNS) is synapsing with interneuron in CNS which synapses with motor neuron in the CNS which extends to PNS and the effector muscle or gland. 

What is neuroglia?

Support the neurons and other tissues in the NS

What are the neuroglia in CNS?

Astrocytes

Oligodendrocytes

Microglia

Ependymal cells 

What are astrocytes?

Most numerous. help maintain blood-brain barrier, maintain extracellular chemical environment (ionic content), guide neurons during development, and play role in synapse formation. 

What does the blood brain barrier do?

limits what can go into/out of the brain (toxins, etc) and protects the neurons

What are oligodendrocytes?

Form and maintain the myelin sheath in the CNS

What are Microglia?

They are phagocytes, which remove debris, damaged cells, and pathogens

What are ependymal cells

Produce and assist in circulation of cerebral spinal fluid and line the cavities 

What are the Neuroglia of the PNS?

Schwann cell and Satellite cells

What are Schwann cells

They form and maintain the myelin sheath in the PNS and participate in PNS axon regeneration

What are Satellite cells 

They surround cell bodies of PNS neurons, provide structural support, and regulate exchange of materials between cell bodies and interstitial fluid

What type of insulation does the myelin sheath function as and what does it do? 

Electrical insulation to increase the speed of conduction of action potentials 

Where is the myelin sheath found in both the CNS and PNS

PNS= Schwann cell

CNS= Oligodendrocyte

What are the Nodes of Ranvier?

Gaps in myelination which speed up the action potential down the axon.

Myelin sheath makes up what type of matter

white matter

Which of the following is a correct difference between CNS and PNS myelin? 

A CNS oligodendrocyte myelinates parts of several different axons while each PNS Schwann cell myelinates a single axon segment 

What is Grey matter

Cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia

White matter

Myelinated neurons

Plasticity

Ability to change throughout life

Repair

Regeneration after damage

When does regeneration of neurons occur in the PNS?

Occurs when the cell body is still intact and the Schwann cell remains active. The Schwann cells form regeneration tube which guides and stimulates regrowth of the axon. 

When does regeneration of neurons occur in the CNS?

Little to no regeneration can occur and the CNS damage is permanent. 

What are the possible reasons why CNS regeneration doesn’t occur?

-Inhibitory proteins released by neuroglia

-Absence of growth stimulating cues

-Scar tissue formation

What type of signals are in the brain?

Electrical signals

Why do electrical signals happen and what are the two types?

Occur because of small deviations in the membrane potential. The two types are graded potentials and action potentials

In the CNS, where are synapses between neurons located? 

Mostly grey matter 

What does it mean when we say an ion channel is gated?

It requires a stimulus to open or close it

Ion Channels: Leak

Leak channels have gates that randomly alternate between open and closed positions

Ion Channels: Ligand-gated

A ligand gated channel opens or closes in response to specific ligand (chemical) stimulus

Ion Channels: Mechanically-gated

MechanicallyOpen or close in response to mechanical stimulation. That stimulation could be in the form of touch, pressure, tissue stretching, and vibration

Ion Channels: Voltage-gated

A voltage-gated channel opens in response to change in membrane potential (voltage)

Where are leak channels located? 

Found in nearly all cells, including dendrites, cell bodies, and axons of all types of neurons

Where are ligand-gated channels located?

Dendrites of some sensory such as pain receptors and dendrites and cell bodies od interneurons and motor neurons

Where are mechanically-gated channels located?

Dendrites of some sensory neurons such as touch receptors, pressure receptors, and some pain receptors

Where are voltage-gated channels located?

Axons of all types of neurons

What are the excitable cells?

neurons and muscle cells

Unstimulated cells display what? What is the range in neurons?

Resting membrane potential which ranges from -40mV to -80mV in neurons. Typically around -70mV

Resting membrane potential

Is when there is a voltage that exists across the plasma membrane. This is due to the presence of the plasma membrane creates and unequal distribution of positive and negative changes.

What are the determinants of resting membrane potential? 

• Unequal distribution of ions in the ECF and cytosol. 

• Differences in membrane permeability

• Action of the Na+/K+ ATPase’s also contributed to the generation of the resting membrane potential

What cannot leave the cytosol of neurons?

negatively charged (anions) molecules like proteins and phosphate groups 

With respect to differences in membrane permeability in establishing the resting membrane potential, what is the plasma membrane more permeable to? 

More permeable to K+ than Na+

Membrane potential: K+ only cell

• K+ leak channels allow K+ to move out of the cell according to concentration gradient

• As K+ leaves cell, this increases electronegativity inside the cell 

• increased electronegativity inside the cell favors movement of K+ back into the cell

• K+ equilibrium potential

What is the K+ equilibrium potential

-Membrane potential at which there is no net movement of K+ back into the cell. Magnitude of K+ concentration gradient and magnitude of K+ electrical gradient are equal. Occurs at -90mV.,

Membrane potential: Na+ only cell

• Na+ leak channels allow Na+ to move into the cell according to concentration gradient

• As Na+ enters cell, this increases electropositivity inside the cell 

• Increased electropositivity inside the cell favors the movement of Na+ back out of cell 

• Na+ equilibrium potential 

What is the Na+ equilibrium potential 

Membrane potential at which there is no net movement os Na+ into or out of the cell

Magnitude of Na+ concentration gradient and magnitude of Na+ electrical gradient are equal. Occurs at +60mV.,

What is the equilibrium potential

The point at which ther is no net flow of ions and the chemical and gradient gradient are equal and opposite

Membrane potential: typical cell

• Neurons are permeable to both K+ and Na+

• More permeable to K+ than Na+

• Na+/K+ - ATPase pumps pump more Na+ out than K+ in

• Maintains resting membrane potential at -70mV

What are graded potentials?

A small deviation resting membrane potential

What does depolarizing mean

makes the membrane potential less polarizes (more positive)

What does hyperpolarizing mean?

Makes the membrane potential more polarized (more negative)

Ligand and mechanically gated ion channels are located where

dendrites and cell bodies

Where do graded potential occur?

at dendrites and cell bodes of neurons

Which of the following is NOT involved in the formation of graded potentials triggered by extracellular cues?

Voltage gated channel

Graded potential vary in amplitude depending on what 

strength of stimulus 

A stronger stimulus does what to the amplitude

increases the amplitude

Can action of graded potentials die out before they reach trigger zone

graded potentials can

What are the different names of the graded potentials 

• postsynaptic potential 

• Receptor potential 

• End-plate potential 

What a postsynaptic potential

another neuron

What is a receptor potential 

at sensory receptor 

What is an end-plate potential

at skeletal muscle

What is the summation of graded potentials

when two or more graded potentials are added together

What is needed for an action potential to genreratied?

• Threshold must be reached (-55) 

• A stimulus must b e strong enough to depolarize the membrane to threshold

• Action potential is all-or none

What is a subthreshold stimulus

a stimulus not strong enough to generate an AP 

What is a suprathreshold stimulus

stronger stimulus than necessary to generate an AP 

What is threshold

-55mV

Where does the action potential occur and what type of channel is used 

Occurs in the axon terminal and uses voltage-gated channels

What are the 3 phases of an action potential?

Depolarizing phase: gets more +

repolarizing phase: gets more -

After-hyperpolarizing phase: pushes past resting membrane potential (more -)