MNSR 12 Flashcards
The function of a nervous system is:
To coordinate the activity of the muscles
To monitor the organs
To construct and stop input from the senses (sight, hearing, touch, smell, taste)
To initiate actions
Cells that receive sensations are called…
receptors, e.g. nerves of the olfactory bulb
Cells that make the appropriate response are called…
effectors, e.g. Knee-jerk reflex (Patellar tendon reflex)
What are the two sub divisions of the nervous system and what’s in there?
Central Nervous System (CNS)
Brain
Spinal cord
Peripheral Nervous System (PNS)
All other nerves and neurons that do not lie within the CNS
Tissues of the body develop from three primary germ layers:
Ectoderm, Endoderm, and Mesoderm
What is the Central Nervous System (CNS)?
Develops from a specialized region of ectoderm called the neural plate.
Development of the neural system called “neurulation”.
Some mesodermal cells form a hollow tube in the midline which by day 22-24 forms a…
solid cylinder of cells (notochord)
The notochord drives…
neurulation
What is neurulation?
Induction of overlying ectoderm to form the neural tube (which will become brain and spinal cord).
Malformations of the neural tube are known as…
Neural Tube Disorders (NTDs)
Most common tube defects include…
Anencephaly (head)
Encephalocele (Head)
Spina bifida (spine)
What are Folic Acid Supplements?
Supplementation prevents neural tube defects.
Also known as Natural B vitamin (vitamin B9).
First isolated from spinach leaves.
Needed to synthesize DNA bases.
~70% reduction in NTDs with 400mg/daily (100% RDA) periconceptional use.
The PNS is divided into…
The Autonomic Nervous System (ANS) and the Somatic Nervous System (SNS)
The ANS is divided into…
Sympathetic, Parasympathetic, and Enteric
The SNS…
Includes all neurons connected with the muscles, sense organs and skin.
Deals with sensory information (Afferent nerves) from sense receptors to spinal chord.
Controls the movement of the body (Efferent nerves) from spinal chord to muscles
The structural and functional unit of the nervous system is the…
neuron.
The neuron consists of…
Dendrites
Soma (cell body)
Axon
Synaptic terminal
Within the soma is a…
large and usually centrally placed nucleus.
What is the cytoplasm of the neuron called?
Perikaryon
Within the cytoplasm (perikaryon) we find:
Nissl bodies:
- Formed of large aggregations of rough ER
- Site of protein synthesis
Microfilaments called neurofilaments
Microtubules called neurotubules
- Found in the axons and dendrites
In general dendrites are short so around <…
<1 mm
Axons may be up to _______ in length.
1 meter
Longest nerve is the…
Sciatic nerve (ischiatic nerve).
Damage to the Sciatic nerve called…
sciatica
Essentially there are three types of neurons:
Pseudo-unipolar – sensory.
Bipolar – specialised. sensory neurons found in the retina, inner ear and olfactory mucosa.
Multipolar - the most common.
Describe the pseudounipolar (unipolar) neuron:
Sensory neuron in the PNS
- Connects sensory organ to the spinal cord
A single process extending from the soma
One long dendrite (exception!)
One short axon
- Connects to the spinal cord
The dendrite of a pseudo-unipolar neuron is structurally and functionally an axon.
Myelinated
Describe the bipolar neuron:
Transmission of specialized senses (e.g. eye)
One dendrite
One axon
Part of the sensory pathway
Smell, sight, taste, hearing and vestibular functions
Describe the multipolar neuron:
Many dendrites
One single axon (usually long and may branch)
Large amounts of information received
Largely based in the CNS
Motor neurons (efferent)
Interneurons
Most of the nerve cell bodies (soma {singular}, somata {Plural}) are situated within…
the walls of the central nervous system (e.g. grey matter of spinal cord).
Where they are not, they form…
ganglia (singular = ganglion), a mass of nerve cell bodies and dendritic structures.
The ______ is in essence a fusion of many ganglia.
brain
The ganglia often interconnect with other ganglia to form a complex system of ganglia known as a…
plexus.
What do ganglions do?
Provide relay points and intermediary connections between different neurological structures in the body, such as the peripheral and central nervous systems.
What is the Brachial Plexus?
Nerve supply to shoulders and upper limbs.
Many brachial plexus injuries happen during birth.
The baby’s shoulders may become impacted (compressed) during the birth process causing the brachial plexus nerves to stretch or tear. What happens due to this?
Limp or paralyzed arm, lack of muscle control in the arm, hand, or wrist, and lack of feeling or sensation in the arm or hand.
In the CNS the cellular and fibrous elements of the neurons divide into:
Grey matter
Contains the somata, dendrites and a few axons
White matter
Formed exclusively of axons
Nerve cells and their extensions are surrounded by non-nervous cells called:
glial cells
In the CNS they are called…
neuroglia
In the PNS the glial cell is called the _______ which…
Schwann cell,
May wrap around the axon
Forms a myelin sheath
The____is a layer of myelin and connective tissue that surrounds and insulates fibres in the _____.
nerve sheath, peripheralnerves.
This sheath is usually as thick as the axon but may be up to…
2.5µm thick in large fibres.
Largely composed of a lipid (________), which forms much of the concentric wrappings of the Schwann cell membrane.
sphingomyelin
The rotation of the Schwann cell itself forms the _________
concentric sheath.
In the CNS, a neuroglial cell called the _________ forms the myelin sheath, usually around several axons.
oligodendrocyte
In Myelinated Nerve Fibres, one axon is wrapped within ___ produced by _____.
layers of myelin, a single Schwann cell.
The process of myelination starts during…
foetal life in the fourth month, and continues for a considerable time after birth.
As the process continues the cytoplasm is…
excluded so at maturity the sheath consists of many regular layers of plasma membrane.
Between the adjacent Schwann cells in myelinated fibres are gaps called the…
nodes of Ranvier.
Here the axon is not covered by the myelin sheath, the ______ (=plasma membrane of axon) shows.
axolemma
Almost all axons greater than ___ in diameter are myelinated.
2 µm
In non-myelinated nerve fibres, the axons are not wrapped in myelin but ______ cytoplasm, which fuses forming the _____.
embedded in a groove in the Schwann cell, mesaxon (=a pair of parallel plasma membranes of a Schwann cell, marking the point of Schwann cell encircling the axon).
What do peripheral nerves do?
Connect the brain and spinal cord (=CNS) to the entire human body.
These are anatomical structures consisting of many…
nerve fibres.
The cell bodies or somata of these fibres are located either in the…
CNS or in cranio-spinal ganglia.
A single bundle of nerve fibres is called a…
fascicle.
Each fascicle consists of nerve fibres in a matrix of loose collagen fibres and blood capillaries the…
endoneurium
Each fascicle is bound by a dense layer of collagen called the…
perineurium
Fascicles in large nerve trunks are bound within an outer layer of connective tissue called the…
epineurium
Multiple Sclerosis is a…
CNS disease characterized by loss of the myelin sheath.
Primarily attacks individuals between the…
second and fifth decades of life with a rate of 80 per 100,000 of the population.
The oligodendrocytes in the CNS which ______ are the target of recurrent autoimmune cell-mediated attack. (in MS)
produce myelin
Loss of myelin is selective and patchy:
Characteristic lesions or plaques of demyelination
The ‘denuded’ axons also undergo large-scale degeneration
Neurogenesis refers to the…
growth and development of neurons from neural stem cells and progenitor cells (=a biological cell that, like a stem cell, has a tendency to differentiate into a specific type of cell, but is already more specific than a stem cell and is pushed to differentiate into its “target” cell.)
Neurogensis is most active while a…
baby is developing in the womb and is responsible for the production of the brain’s neurons.
Adult neurogenesis is known to occur inthreeregions in the mammalian brain:
In thehippocampus, which is a region that is involved in regulating learning and memory
thesub-ventricular zone(SVZ), which is situated throughout the lateral walls of the brain’s lateral ventricles
the Amygdala
Ion channels are transmembrane proteins specifically involved with the transport of…
inorganic ions like Na+, K+, Ca2+, or Cl-.
Ion channels are “gated” meaning they…
open in response to a specific stimulus, such as a change in membrane potential (voltage-gated ion channels) or the binding of a neurotransmitter (ligand-gated ion channels).
Ion channels allow ions to move passively ______ their concentration gradient.
down
Two types of ion channels:
Ligand-gated and Voltage gated ion channels.
Voltage-gated ion channels (VGCs) are:
A class of transmembrane proteins that forms an ion channel.
Primarily responsible for generation and propagation of action potentials in excitable tissue.
How do VGC’s work?
Usually closed at resting membrane potential
A change in the membrane potential near the channel causes a conformational changes that result in the opening of the channel (voltage-dependent activation), followed by conformational change (inactivation) that closes the channel.
Ligand-gated ion channels (LGICs) constitute the hardwiring of…
chemical synapses; mediate fast synaptic transmission, on a millisecond time scale, in nervous system and at the somatic neuromuscular junction.
LGIC’s are integral membrane proteins that contain a pore which allows…
the regulated flow of selectedionsacross the plasma membrane.Ionflux is passive and driven by the electrochemical gradient for theions.
How do LGIC’s work?
The ion channel undergoes a conformational change following the binding of an extracellular ligand to its site on the channel.
This conformational change allows for opening of the ion pore.
This gating will cease when the ligand disassociates from the binding site.
The LGIC group includes the nicotinic acetylcholine receptor (nAChR).
Together, the combined activity of ligand-gated and voltage-gated ion channels gives rise to…
many complex physiological processes from cardiac and skeletal muscle contraction to the more enigmatic behaviours of the CNS such as cognition and memory.
Ion pumps, also called transporters, are transmembrane proteins that..
actively move ions and/or solutes against a concentration or electrochemical gradient across biological membranes.
Pumps generate a membrane potential by creating an electrochemical gradient across the membrane.
Primary active transportersare usually…
transmembrane ATPases, that hydrolyse ATP to produce energy in order to transport ions up a concentration gradient.
Secondary active transporters, also known as co-transporters, pump…
ions against the concentration gradient by using the electrochemical gradient created across the membrane by pumping ions in or out of the cell.
Two types of secondary active transporters, which are classified based on the direction that they move ions:
Antiporterspump two different ions or solutes in opposite directions across the membrane. One moves with the concentration gradient (high to low) which powers the movement of the other against the gradient (low to high). Examples: CLCN3, NHE3.
Symporters pump two different ions or solutes in the same direction, moving one with the concentration gradient (high to low), and the other against the concentration gradient (low to high). Examples: KCC2, NCC, NIS, NKCC2.
