Nerve cell

lecture 8a

What does the word “innervates” mean?

Refers to a nerve supplying a muscle or organ. For

example, “The phrenic nerve innervates the diaphragm

muscle”.

3 parts of the Nervous System

1. Central Nervous System (CNS): brain and spinal

cord.

2. Peripheral Nervous System (PNS): nerves of the

body

3. Autonomic Nervous System (ANS): has parts of

the CNS and PNS.

What are the two parts of the CNS?

Brain and Spinal cord

What does the Autonomic Nervous System

control and what are its 2 divisions?

Controls autonomic function (blood pressure,

digestion, etc).

a. Sympathetic division

b. Parasympathetic division

What kinds of neurons enter the CNS?

Sensory (afferent) signals picked up by sensor

receptors. They are carried by nerve fibers of PNS to the

CNS

What kind of neurons leave the CNS?

Motor (efferent) signals are carried away from the CNS.

They innervate muscles and glands

What sheath covers the axon (not referring

to myelin)?

Endoneurium

What sheath covers a fascicle (bundle of

neurons)

Perineurium

What sheath covers a bunch of fascicles?

Epineurium

What is the neurolemma?

Outermost covering of a neuron (plasma membrane)

What is movement of nutrients, wastes, and

organelles between the cell body and axon

terminals

Axoplasmic transport

What three things do all neurons do?

1. Receive a signal. Can be any type of stimulus

(change in environment, signal from another neuron,

etc).

2. Transmit a signal to another location. E.g. finger

touching something → signal to spinal cord or brain.

3. Stimulate another cell

a. Another neuron → transmit signal

b. Muscle → contraction

c. Gland → secretion

What three characteristics do all neurons

share?

1. Longevity – can live and function for a lifetime

2. Do not divide – fetal neurons lose their ability to

undergo mitosis (the y lose their centrioles);

neural stem cells are an exception

3. High metabolic rate – require abundant oxygen

and glucose

Picture of Sensory vs Motor Neurons

photo of neuron anatomy

What receives the signal and carries the

nerve conduction toward the cell body?

DENDRITES

Where are the nucleus, ribosomes, and

most organelles located?

The CELL BODY

What has the function of transmitting

signals from the cell body to the area with

neurotransmitters?

AXON

What part of a neuron stimulates another

cell?

SYNAPTIC KNOBS

Describe the correct path an impulse takes

across a synapse

Axon of presynaptic neuron → SYNAPTIC CLEFT →

dendrite of post synaptic neuron

What are synaptic knobs filled with?

What are 4 types of glia cells?

Oligodendrocyte

Schwann Cell

Astrocyte

Microglia

What is the function of glia cells?

They support the neurons

Do glia cells carry nerve impulses?

No. The impulses jump over the oligodendrocytes and

Schwann cells, and astrocytes and microglia are not

involved in nerve impuses at all.

Do glia cells process information in the

nervous system?

No, the interneurons do that

What are the supporting cells of the nervous

system?

GLIA

Where do most tumors originate from?

Most tumors of the brain originate from glial cells

What is Wallerian Degeneration?

process that results when a nerve fiber is cut or crushed,

in which the part of the axon separated from the

neuron's cell body degenerates distal to the injury.

What are the types of synapses?

axosomatic

neuroeffector synapses

axodendritic

axoaxonic

photo of 2 types of the b4 types of glial cells

Which cells provide the myelin sheath for

neurons in the CNS?

OLIGODENDROCYTES

Which cells provide the myelin sheath for

neurons in the PNS?

SCHWANN CELLS

What is the function of MYELIN

SHEATHS

to speed up the rate of nerve impulse conduction.

What are the BARE regions of axonal

membranes found only in myelinated axons

called?

NODES OF RANVIER

What conducts impulses faster – myelinated

or unmyelinated axon?

Myelinated

Where are unmyelinated axons found?

Neuron cell bodies, dendrites, and unmyelinated axons in

the PNS and CNS.

Are unmyelinated axons thinner or thicker

than myelinated?

Unmyelinated axons are thinner

What is myelin made of?

Mostly lipid

What is an autoimmune disease where the

oligodendrocytes (the myelin sheaths) are

destroyed, interfering with the neuron

functions in the CNS and brain?

MULTIPLE SCLEROSIS

What is the most common neurological

disease of young adults?

MULTIPLE SCLEROSIS

What are the two differences between

SCHWANN CELLS and

OLIGODENDRICYTES?

Schwann cells are in PNS and each cell only forms one

myelin sheath.

Oligodendricytes are in CNS and each cell can form more

than one myelin sheaths.

What are the 3 functions of an

ASTROCYTE?

a. Physically supports the neurons

b. Transmits materials from capillaries to neurons

c. Forms blood-brain barrier (BBB), which keeps out

harmful substances and many medicines

What is the only function of the blood-brain

barrier BBB?

The only function of the blood-brain barrier is to help

protect the central nervous system

Define MICROGLIA and their function

They are macrophages

They pick up bacteria and debris

What are ependymal cells?

Cells that line the ventricles of the brain and produce

cerebral spinal fluid (CSF)

What is the portion of the CNS that is

unmyelinated (cell bodies of neurons, glia, and

dendrites)?

GREY MATTER

What is the portion of the CNS with myelin

WHITE MATTER

What is a collection of axons in the PNS?

NERVE; No cell bodies, dendrites, or synapses; just

axons.

What is a collection of axons in the CNS

TRACT

Where is most information processed?

SYNAPSES in the CNS

What is a collection of cell bodies in the

PNS?

Ganglion

What is a network of nerves called?

NERVE PLEXUS

What are the neurons that leave the CNS to

effect a muscle or gland?

MOTOR NEURONS

What neurons go from body to CNS,

carrying sensory information?

SENSORY NEURON

What is a small neuron found only in the

CNS?

INTERNEURON

What is the function of interneuron?

it connects two other neurons in the spinal cord

What makes the CNS complex?

The large number of interneurons in the CNS

Where are the cell bodies of motor neurons

and interneurons located?

In gray matter

Gray matter in the CNS contains what

structures?

Neuroglia, neuron cell bodies, dendrites. Everything

except myelinated neurons

For a substance to diffuse across a

semipermiable membrane, what two

conditions must be met?

a) The membrane must be permeable to the substance

b) The substance must have a concentration gradient

At resting membrane potential, is the inside

of the cell membrane positive or negative?

What about the outside of the cell

membrane?

Inside is negative, outside is positive

Inside is negative, outside is positive

Proteins inside the cell make it negative

What changes the overall charge on the

inside and outside of the cell membrane?

The charges change when sodium channels open

during neuron stimulation

When a cell is at resting membrane potential

and is then stimulated by a neuron, what is the

first thing that happens to start the change in

the overall charge on the inside of the cell?

Sodium channels open and sodium enters the cell.

Does potassium leave the cell because of

neuron stimulation?

No, it can leave anytime because its channel is leaky

Why does sidedness exist (inside of cell

negative, outside positive)?

a) The cell membrane has different permeabilities to

each ion

b) Pumps exist which force particular ions into or out of

the cell

c) Channels made out of protein selectively allow

particular ions into or out of the cell.

Why does potassium constantly want to leave a

cell?

It wants to leave to diffuse down its concentration gradient

Why does potassium want to get back into a

cell?

It wants to get back into a cell because it is attracted to the

negative charges on the protein inside the cell

What is the resting membrane potential of a

cell? Why does potassium constantly want to

leave a cell?

The resting membrane potential is how negative or positive

the charge of the cell membrane is when it is not being

stimulated by a neuron. The resting membrane potential is

Minus 70-minus 90 mV

When does Depolarization occur?

Enough sodium ions flow into the cell to make the membrane

potential become positive

When does Repolarization occur?

Enough sodium ions flow out of the cell to make the

membrane potential become negative

What is an action potential?

Action Potential = depolarization + repolarization

What is the correct sequence of events at a

synapse?

The nerve impulse arrives at the synaptic knob of the

presynaptic cell, then the neurotransmitter is released. The

NT binds to receptors on the postsynaptic cell, generating an

action potential in the postsynaptic cell axon. Then the NT is

removed from the receptors of the postsynaptic cell, either by

an enzyme, or they are taken back up into the presynaptic

terminal knob and recycled.

What are the three structural classifications of

neurons?

1. Unipolar

2. Bipolar

3. Multipolar

What are the structural classification of

neurons based on ?

the number of processes that project from the cell body.

What happens if a neuron’s supply of

neurotransmitters is exhausted?

It might be temporarily unable to transmit an impulse to

another cell