Lecture 2 - Cells of the Nervous System Flashcards
Central Nervous System (CNS)
- comprised of the brain and spinal cord.
- encased within the skull and spinal column.
Peripheral Nervous System (PNS)
comprised of nerve tissue located outside of the brain and spinal cord.
Can nerves regrow, if damaged in the CNS or PNS?
nerves can regrow if damaged in the PNS only
What is part of the basic structure of a neuron?
- soma
- dendrite
- axon hillock
- axon
- terminal button
- synapse
Soma
The cell body of a neuron, which contains the nucleus
Dendrite
A branched treelike structure attached to the soma of a neuron; receives information from the terminal button of other neurons
Axon hillock
Site of summation for incoming information
Axon
The long, thin cylindrical structure that conveys information from the soma of a neuron to its terminal button
Terminal button
The bud at the end of a branch of an axon; forms synapses with another neuron; sends information to that neuron
Synapse
A junction between the terminal button of an axon and the membrane of another neuron
What are the 4 basic components of a neuron?
input, integration, conduction, output
Describe the information flow of neurons
- Information from other neurons is collected at dendrites
- processed in the cell body,
- passed on to the axon,
- then to the end feet, where it is passed on to a target neuron
Describe Terminal buttons
end point of axons – transform electrical signal from the axon into a chemical signal sent across the synaptic cleft.
Neurotransmitter
A chemical that is released by a terminal button; has an excitatory or inhibitory effect on another neuron.
What are the 3 classifications of neurons in terms of SHAPE?
- Bipolar neurons
- Multipolar neurons
- Unipolar neurons
Bipolar neurons SHAPE
A neuron with one axon and one dendrite attached to its soma.
SENSORY
Multipolar neurons SHAPE
A neuron with one axon and many dendrites. Most common in CNS.
Unipolar neurons SHAPE
A neuron with one axon attached to its soma; the axon divides, with one branch receiving sensory information and the other sending the information into the central nervous system.
SOMATOSENSORY (TOUCH, PAIN)
What are the 2 classifications of neurons in terms of SIZE?
- large (e.g., pyramidal)
- small (e.g., granular)
Sensory neuron FUNCTION
transmits sensory information to the central nervous system.
ex: somatosensory (pressing on skin - sends signal to brain)
Motor neuron FUNCTION
controls the contraction of a muscle or the secretion of a gland.
ex: MOVE arm if you don’t like being touched
Interneuron FUNCTION
located entirely within the central nervous system.
ex: connect everything (in order for muscle to contract for ex, part of the circuit)
- in b/t helpers
The Mighty Neuron!
- 1 neuron receives info from the end feet of another neurons
- if that info summates at the axon hillock and theirs enough to drive an AP (electrical signal down the axon)
- we then can get connections with other neurons, forming synaptic connections where n.t. is released & we influence the neighbouring neurons all forming part of a network
Internal mileu
chemical makeup inside cell body
contains:
- membrane
- cytoplasm
- nucleus
- mitochondria
- adenosine triphosphate (ATP)
- Endoplasmic reticulum (rough & smooth)
- Golgi apparatus
- Lysosome
Membrane
A structure consisting primarily of lipid (fat-like) molecules that makes up the outer boundary of a cell.
- (like skin)
Cytoplasm
The viscous, semi-liquid substance inside the cell. GOOP!
Nucleus
Contains all of the genetic material that the neuron needs to function (chromosomes).
Mitochondria
Double membrane. Contain their own DNA and replicate independently of cells. Converts nutrients into ATP.
Adenosine triphosphate (ATP)
The cell’s primary energy source.
Describe Mitochondria
Mitochondria represent formerly free-living bacteria that were taken inside another cell around 1.5 billion years ago.
- double membrane and their own DNA
- you inherit your mitochondrial DNA from your mother.
Describe 23andMe and its relation to mitochondria
Mito is short for “mitochondria,” which are small structures inside of cells that have their own DNA. Since children (both boys & girls) only inherit their mitochondrial DNA from their mother, it can be used to trace a person’s maternal line
Endoplasmic reticulum
storage reservoir and channel for transporting chemicals through the cytoplasm appears in two forms…
- rough & smooth
Rough Endoplasmic reticulum
Produces proteins that are either transported out of the cell (attached) or distributed around cytoplasm (free-floating).
Smooth Endoplasmic Reticulum
lipids produced here.
Golgi apparatus
Generates and secretes neurochemicals (EXOCYTOSIS). Wrapping and packing.
- ready for transport
Lysosome
An organelle surrounded by membrane; contains enzymes that break down waste products.
- part of custodian system for the cell
- can also recycle some waste products
Cytoskeleton
Matrix of protein strands that give the neuron its shape.
Microtubule
A long strand of bundles of protein filaments arranged around a hollow core; part of the cytoskeleton and involved in transporting substances from place to place within the cell.
- inside axon
- kinesin is attached, which walks down the microtubules, down axon & transport the sacs filled with chemicals
Axoplasmic transport
An active process by which substances are propelled along microtubules that run the length of the axon.
- can go in 2 directions: anterograde & retrograde
Anterograde
In a direction along an axon from the cell body to the terminal buttons. FAST (500 mm/day)
Retrograde
In a direction along an axon from the terminal buttons toward the cell body. SLOWER (half as fast)
Why are there 2 axoplasmic transport directions?
do diff. things:
anterograde: to generate neural chemicals in the cell body, that needs to get to the end foot for storage & release into the synapse
retrograde: retaking up some of the n.t. (some will be processed right away, others will be brought back to the cell body & recycled)
Kinesin
Kinesin molecules “walk” like an inchworm down a microtubule, carrying their cargo from the soma (bag of neural chemicals) to the terminal buttons.
Neurons & Glia are…
building blocks of the nervous system.
Neurons (grey matter)
electro-chemical transfer of information from one region to another.
Glia (white matter)
Greek for glue; outnumber neurons 10:1, supporting cast.
Glia
- modify chemical milieu.
- guide neurons to final site during development.
- remove dead neurons after damage.
- PHAGOCYTOSIS – eat them up and get them out.
- serve some nutritive needs.
- maintain the blood – brain barrier.
CARETAKERS OF NEURONS
Astrocytes (form of Glia)
surround neurons and contact blood vessels via end-feet.
- allow transmission of ions across vascular wall and forms blood-brain barrier.
- provides physical support.
- provide nourishment.
- maintain chemical milieu surrounding neurons.
Describe what astrocytes supply neurons with
- astrocytes supply neurons with glucose obtained from capillaries.
- glucose is processed within the astrocyte to produce lactate which is then released into the extracellular fluid surrounding the neuron. the lactate is taken up by the neuron for use by mitochondria.
- Camillo Golgi
Oligodendrocytes (form of Glia)
produce myelin, the fatty sheath that covers the axon – can myelinate MULTIPLE axons in CENTRAL NERVOUS SYSTEM.
- Can produce up to 50 segments of myelin.
- Not all axons are myelinated.
Schwann cells
– involved in production of myelin in PERIPHERAL NERVOUS SYSTEM – only myelinates a SINGLE nerve.
- also digest dead axons and provide process for regrowth.
Nodes of Ranvier (Oligodendrocytes and Schwann cells)
- myelin sheath (tubular) is not continuous along the axon (sections of ≈ 1-2µm)
- gaps in the myelin sheath are known as NODES OF RANVIER – unmyelinated areas of axon
Fibre tracts and myelin
- Myelination speeds up the conduction of the neural signal – when a group of cells send their signal to one specific place this is known as a FIBRE TRACT (e.g. the corpus callosum).
- The fat in myelin makes “white-matter” white.
Blood-Brain Barrier
- Regulates the chemicals that can enter the CNS from the blood. Prevents many low-life forms, such as toxins, that make it into the blood stream from infecting the brain.
- Helps the CNS maintain the proper composition of fluids inside and outside the neurons.
Jim Hanson got brain infection & died
Dopamine doesn’t cross the BBB, but L-dopa can cross (help Parkinson’s)
- selectively permeable – some things can get through.
- the chemical milieu inside and outside the neuron is delicate – the blood brain barrier protects the balance of chemicals.
- not uniform throughout – AREA POSTREMA
Area postrema
maintains a weak blood-brain barrier which allows for the detection of toxins in the blood stream and triggers vomiting response. (to get position out)
The BBB can be broken down by:
- hypertension (high blood pressure): high blood pressure opens the BBB
- development: the BBB is not fully formed at birth.
- hyperosmolarity: a high concentration of a substance in the blood
- microwaves & radiation
- infection: exposure to infectious agents
- trauma, ischemia, inflammation, pressure: injury to the brain
Microglia (form of Glia)
damaged neural tissue is invaded by microglia which then remove dead cells
- protect the brain from invading micro-organisms
________ neurons gather information from the environment related to light, odors, and contact with objects.
A) Sensory B) Motor C) Inter- D) Relay inter- E) Local inter-
A) Sensory
The ________ is defined as comprised of the brain and spinal cord.
A) peripheral nervous system B) central nervous system C) enteric nervous system D) human nervous system E) local circuit system
B) central nervous system
The ________neuron is the most common nerve cell type in the central nervous system.
A) apolar B) multiglial C) unipolar D) bipolar E) multipolar
E) multipolar
Nerve damage that impaired the ability to sense temperature and touch might be expected to involve which type of nerve cell?
A) bipolar neurons B) multipolar neurons C) unipolar neurons D) apolar neurons E) B and D are correct.
C) unipolar neurons
Which of the following is NOT a function of the glial cells?
A) provision of nutrition to the brain
B) removal of physical debris from the brain
C) physical support of neurons
D) insulation of nerve cells from each other
E) the conduction of action potentials
E) the conduction of action potentials
Which of the following cells are important for the supply of energy for neurons?
A) Schwann cells B) phagocytes C) dendrocytes D) astrocytes E) nanotubules
D) astrocytes
Input zone of the neuron
dendrites, cell body, nucleus
Integration zone of the neuron
axon hillock
Conduction zone of the neuron
axon
Output zone of the neuron
axon terminals
