Lab 4.1-4.2

what is the nervous system responsible for

detecting internal and external stimuli, interpreting that information, and coordinating appropriate responses, whether automatic or voluntary.

neurohistology

focuses on the microscopic anatomy of nervous tissue. It helps us understand the different types of cells and how they are organized to form functional networks.

neurophysiology

deals with how neurons function, especially how they transmit signals.

nerve cell or neuron 

basic functional unit of the nervous system

where is a nerve cell or neuron located

throughout the nervous system.

neuron

The communicative role of the nervous system is carried out by neurons.

what are the three basic parts of a neuron

1. neurosoma

2. axon

3. dendrite 

neurosoma

The nerve (neuro-) cell body (-soma) and control center

nucleus of neurosoma

the genetic control center

nucleolus of neurosoma

where ribosomes are produced

ribosomes

small granules of protein and RNA.

cytoplasm

Fluid between the nucleus and surface membrane.

what does the cytoplasm contain

1. mitochondria

2. golgi apparatus 

3. lysosomes 

4. external endoplasmic reticulum 

5. cytoskeleton 

6. nissl bodiies

mitochondria

Bean shaped organelle, specialized for synthesizing Adenosine Triphosphate (ATP).

1. ATP: Functions as a universal energy-transfer molecule

golgi apparatus

Resembles a stack of pita bread and it functions to synthesize carbohydrates and protein.

lysosomes

It is a round or oval package of enzymes that hydrolyzes protein and carbohydrates.

(Do not confuse with the enzyme called lysozyme. )

endoplasmic reticulum

"little network within the cytoplasm." It synthesizes steroids and other lipids.

rough endoplasmic reticulum

Network composed of parallel and flattened sacs covered with ribosomes.

smooth endoplasmic reticulum

Tubular network that lacks ribosomes.

cytoskeleton

a collection of protein filaments and cylinders that determine the shape of a cell, lend it structural support, and organize its contents.

nissil bodies

Dark staining regions, made up of rough endoplasmic reticulum and free ribosomes; unique to neurons, which in turn helps with identifying them easily.

axon

A slender, cylindrical, unbranched, and long projection that rapidly conducts the signal away from the neurosoma

which nerve does not have an axon 

the retina (sensory layer in the eyeball).

axoplasm

The cytoplasm of the axon.

axolemma

The membrane of the axon.

axon hillock

A mound where the axon originates, it is wide coming from the neurosoma and narrows down as it approaches the initial segment of the axon.

initial segment of axon

The initial narrow part of the axon coming out of the axon hillock.

neurofibrils

They are part of the cytoskeleton which are made up of bundles of actin filaments.

telodendria

Extensive complex fine branches that gives rise to the axon terminals.

axon terminals

A bulbous end, which forms the synapse to the next nerve.

dendrite

• A few thick processes that branch out of the neurosoma.

• Primary site for receiving signals from other neurons, named for resembling tree branches

• some neurons have only one dendrite and some have thousands, thus the more dendrites it has, the more information it can receive and incorporate into its decision making.

dendritic branches

smaller branches arising from big and thicker dendrites

epineurium of a nerve branch 

• outer layer 

• a tough layer of dense irregular connective tissue that surrounds and protects the entire nerve.

perineurium

• middle layer 

• Each fascicle is surrounded by the this layer, which is composed of up to 20 layers of overlapping, squamous, epithelial-like cells.

• This layer helps form a barrier that maintains the internal environment of the nerve fascicle and provides protection.

what does the perineurium help with

form a barrier that maintains the internal environment of the nerve fascicle and provides protection.

fascicle of a nerve

bundles of axons

endoneurium

• inner layer

• individual nerve fibers (axons) are wrapped in a a thin, delicate layer of loose connective tissue

what does the endoneurium provide

structural support and electrical insulation to each axon.

myelin sheath structure

a spiral layer of lipid-rich insulation that surrounds certain axons

myelination

formed by specialized glial cells

what does myelin give

gives white matter in the brain its pale appearance due to its high fat content

when the myelin sheath is present it does? 

• Insulates the axon from the surrounding extracellular environment

• Greatly increases the speed and efficiency of nerve signal conduction

axon terminal

a synapse, where a neurotransmitter, such as: acetylcholine, epinephrine, or serotonin is released, and the next cell in the circuit responds to the neurotransmitter, just like in a neuromuscular junction

structural classification of a neuron

the number of processes extending from the neurosoma.

multipolar neurons

They have multiple dendrites and one axon.

what is the most common type of neuron

multipolar

• includes neurons of brain and spinal cord 

bipolar neurons

they have one long dendrite and one axon

where are bipolar neurons found

• retina

• olfactory cells of nasal cavity 

• sensory neurons of inner ear 

pseudounipolar neurons

Appears to have two branches and is shaped like a T, but in reality, it has a single axon with dendrites at one end and a synapse at the other;

what do the pseudounipolar neurons do 

one long fiber that bypasses the neurosoma and carries nerve signals directly to the spinal cord.

anaxonic neurons

They have multiple dendrites but no axon

function of anaxonic neurons

they communicate through their dendrites and do not produce action potentials.

location of anaxonic neurons

found in the brain, retina (for perception of contrast), and adrenal medulla.

sensory ( afferent) neurons

• detects stimuli such as light, heat, pressure, and chemicals, and transmit information about them to the CNS.

• They begin in almost every organ of the body and end in the CNS.

• Afferent refers to signal conduction toward the CNS.

interneurons

• association neurons

• lie entirely within the CNS

• 90& of neurons are this 

function of interneurons

receive signals from many other neurons and carry out the integrative function of the nervous system- that is, they process, store, and retrieve information and "make decisions" that determine how the body responds to stimuli.

motor (efferent) neurons

• send signals predominantly to muscle and gland cells, the effectors that carry out the body's responses to stimuli. T

• most of them lead to muscle cells, and efferent neurons signify the signal conduction away from the CNS.

neuroglia

• glial cells

• majority of nervous system

• five glial cell types 

• protect and support the structure and function of neurons: 

astrocytes

Star-shaped cells with long projections that wrap around the blood vessels of the brain, and are an important component of the blood-brain barrier (BBB)

• most abundant cell in CNS 

why are astrocytes blood brain barrier cells

they control what substances from the blood enter nerve tissue.

since astrocytes are most abundant they are involved in what?

nourishing neurons

ependymal cells

Resembles a cuboidal epithelium, it covers the choroid plexus which lines the ventricles and canals in the brain and spinal cord

what do ependymal cells produce

produces cerebrospinal fluid (CSF) and it has patches of cilia on its apical surface that assists with the circulation of CSF through the ventricles and fluid spaces. 

microglia

small macrophages, which are immune system cells that reside and wander in the nervous system and act as phagocytes (cell eaters).

function of microglia

remove damaged neurons and infections to maintain the health of the CNS. 

oligodendrocytes

resembles an octopus, due to its bulbous body and about 15 arm-like processes. It produces myelin sheath in the CNS only

what are nodes of ranvier

are gaps between the myelin sheaths

shwann cells

Produce myelin sheath in the PNS only and it can also assist in the regeneration of damaged fibers

excitability

• irritability

• The ability to respond to a stimulus that may be mechanical, chemical, or electrical

conductivity

The capacity to carry the excitation signal along the entire length of the axon

secretion

When the electrical signal reaches the end of the axon, the neuron secretes a chemical neurotransmitter that crosses the synaptic gap and stimulates the next cell

before any signal be sent what must happen

neuron must maintain an internal electrical environment different from the outside

nerve cell membrane

separates intracellular fluid from extracellular fluid

intercellular fluid

inside the cell

• contains high levels of potassium (K⁺) and low levels of sodium (Na⁺)

extracellular fluid

outside of cell

• contains high levels of sodium (Na⁺) and low levels of potassium (K⁺)

electrical difference 

caused by the uneven distribution of ions across the membrane

voltage

• resting membrane potential

• -70 mV

sodium potassium pump

maintains this resting state by actively moving Na⁺ out and K⁺ into the cell

triggering a response: depolarization to action potential

once a neuron is stimulated

when sodium channels open, what happens

Na⁺ to enter the cell from the extracellular space

depolarization

influx of positive ions causes the inside of the membrane to become less negative

when depolarization reaches a critical level, it is called

• threshold 

what happens during a threshold

the neuron fires an action potential or nerve impulse

wave of depolarization

The action potential travels along the axon

repolarization

After the action potential has passed

what happen during repolarization

This outflow of positive ions returns the membrane potential to a more negative value

restoring the resting state 

• The neuron resets itself to be ready for the next signal

• Potassium channels open, allowing K⁺ to exit the cell

Communication Across the Synapse

When the action potential reaches the axon terminal of the presynaptic neuron

what happens during communication across a synapse

1. oltage gated calcium channels open

2. Calcium ions enter, triggering exocytosis of synaptic vesicles that contain acetylcholine (ACh)

3. ACh is released into the synaptic cleft and binds to neurotransmitter receptors on the postsynaptic cell

what triggers exocytosis of synaptic vesicles

calcium ions

what is similar to communication across the synapse

neuromuscular junction (NMJ).

combination of resting membrane potential, action potential transmission, and synaptic signaling enables the nervous system to?

• Detect and respond to stimuli

• Process and relay information

• Coordinate muscle movement and other body functions

conditions this reflects?

seizures, nerve damage, paralysis, neurodegenerative diseases, cardiac arrhythmias, and even basic reflex dysfunction

two main parts of the nervous system

1. central nervous system (CNS) 

2. peripheral nervous system (PNS)

function of central nervous system

serve as the control centers for processing and integrating information.

what is included in the central nervous system

brain and spinal cord

what is included in the peripheral nervous system

nerves and ganglia

nerves

bundle of nerve fibers wrapped in connective tissue that carries signals to and from the CNS

how do nerves exit the brain and spinal cord

through openings in the skull and vertebral column

ganglion

knotlike swelling along a nerve that contains the cell bodies of neurons.