Nervous system Flashcards
Functions of the Nervous System?
*Sensory input
- Sensory receptors monitor internal
and external stimuli
*Interpretation and integration of
sensory input
- Processes information from multiple
receptors and dictates a response
*Motor output
- Effector organs (muscles or glands) are
activated →response
What is the Flow of Impulses Through Nervous System? Example
*SENSORY INPUT→fly lands on arm and bends one or more hairs activating neurons wrapped around hair root
*INTEGRATION→activation of neurons processed by brain and/or spinal cord
*MOTOR RESPONSE→muscles of your other arm are activated so you can reach over and brush off fly
* Results in rapid communication throughout the
body and maintenance of homeostasis
What are the divisions of the Nervous System?
*Central Nervous System (CNS)
*Peripheral Nervous System (PNS)
What is the Central Nervous System (CNS)?
Central Nervous System (CNS)
* Integration and interpretation of sensory
input
* Dictates motor response
* Brain and spinal cord
What is the Peripheral Nervous System (PNS)?
Peripheral Nervous System (PNS)
* Neurons transport sensory input toward
CNS & motor output away from CNS
* Afferent (sensory) division
* Efferent (motor) division
* Includes cranial and spinal nerves
What are the Further Divisions of Sensory and Motor Components?
These divisions are associated with the body regions they serve
* Visceral functions: organs within body cavities
* Somatic functions: all other structures, esp. muscles and skin
What are the nervous tissue cell types?
Cell types:
* Neurons
* Neuroglia
*Cell body (soma)
*Dendrites
* Axon
What are neurons?
- Neurons
- Able to respond to a stimulus and carry and electrical impulse
- Excitable cells
What are Neuroglia?
Neuroglia
* Help neurons function more efficiently
* Non-excitable cells
- Current research is disputing the generalized classification of glial cells as helpers for neurons
– Ex. Glial cells and pain modulation (see
What are Cell body (soma)?
Cell body (soma)
* Single nucleus and organelles
What are Dendrites?
Dendrites
* Receptive (input) regions
* Carry information toward cell body
* Number can vary dramatically
What are axons?
Axon
* Carries information away from cell
body
* One per neuron
* Can be very short or very long (4 feet)
* End at axon terminal →synapse
* Often surrounded by myelin sheaths
What are the classifications of neuron structure?
*Multipolar
*Bipolar
*Unipolar
What are Multipolar neurons?
Multipolar: many dendrites, single axon
* Most neurons in CNS
* Motor neurons and interneurons
What are bipoalr neurons?
Bipolar: single dendrite, one axon
attached to cell body
* Only found in a few locations
* Special sensory neurons
- Retina, olfactory mucosa
What are unipolar neurons?
*Unipolar: single axon connected via
short process to cell body
- Typical sensory neuron
Types Neurons Classified by Function (PNS)
*Sensory neuron = afferent neuron
*Motor neuron = efferent neuron
*Interneuron
What are the components of Sensory neuron?
Sensory neuron = afferent neuron
* Brings impulses to CNS
* Cell bodies are clustered in ganglia (outside of CNS) = Dorsal root ganglion
* Unipolar
What are the components of motor neurons?
Motor neuron = efferent neuron
* Takes impulse away from CNS
* Cell bodies are within CNS
* Multipolar
What are the components of interneuron?
Interneuron
* Neurons within CNS
* Accounts for 99% of all neurons of body (all within CNS)
* Multipolar
Neuroglia in CNS?
In CNS:
* Astrocytes
* Microglia
* Ependymal cells
* Oligodendrocytes
Neuroglia in PNS?
In PNS
* Satellite cells
* Schwann cells
What are the components of astrocytes?
- Most abundant glial cell
- Surround capillaries and neurons
- Numerous functions
- Forms the blood brain barrier (more later)
- Regulate neurotransmitter levels
- Increase blood flow to active brain regions
- Produce BDNF (brain-derived trophic factor)
which promotes neural growth - New research (FYI): Role in sleep cycles
What are the components of Microglia?
*Smallest and least abundant glial cell in CNS
*Macrophages
- Consume microorganisms and dead neurons
- Originate in red bone marrow and migrate to CNS during fetal development
What are the components of Ependymal Cells?
*Form simple epithelium that lines hollow portions of brain and spinal cord
- Ventricles of brain
- Central canal of spinal cord
*Have cilia that help circulate cerebrospinal fluid in CNS
What are the components of Oligodendrocytes?
*Myelin sheaths are formed by oligodendrocytes in the CNS
*Oligodendrocytes have many processes that wrap around many different axons
*Result of myelination is increased speed of conduction of action potential
What are the components of satellite cells?
*In PNS
*Surround cell bodies
*Prevent “crossover” when many cell bodies are crowded together
- Ganglia are full of cell bodies
What are the components of Schwann Cells?
*Surround axon, form myelin sheaths in PNS
- Increase speed of action potential
What is Myelin Sheaths in PNS?
*Myelin sheaths increase speed of action potential down axon
- Myelin sheaths are made of Schwann cell’s compacted plasma membranes (made o
phospholipids) →white in color
*Also insulate axons from each other (prevents action potential “cross talk”)
What are the Myelinated Axons in the PNS?
*Schwann cell wraps around an axon
*One axon will have numerous
Schwann cells
- Schwann cells do not touch each other
- Gaps are left = nodes of Ranvier
Purpose of Myelinated Axons?
*Action potentials jump over the myelin, jumping from node of Ranvier to node of Ranvier = Saltatory Conduction
What are the NonMyelinated Axons in the PNS?
*Only thick, fast conducting axons are myelinated
- Thin, slower are not
*Unmyelinated axons have a Schwann cell partly enclose 15 or more unmyelinated axons
- Axons are separated
*Slower conduction
What is Multiple Sclerosis?
*Autoimmune disease where myelin is
attacked in CNS
- Oligodendrocytes are destroyed
- Plaques develop when myelin is destroyed
- Inflammation develops and can damage
axons
*Overall: action potentials are disrupted
causing motor and sensory issues
What are gliomas?
*In general, neurons have limited ability to regenerate or undergo mitosis
- As a result, most brain tumors are derived from glial cells = glioma
Nerve versus Nerve Tract
Nerve
*In PNS, axons of sensory and
motor neurons
*Example
- Nerves off of spinal cord
Nerve Tract
*In CNS, axons of interneurons
*Example
- Corpus callosum of brain
Are nerves mixed?
*Most nerves contain both sensory and motor neurons
- “Mixed” nerves are typical (ex. Spinal nerves)
Are all nerves mixed?
*There are exceptions
- Ex. Some cranial nerves are sensory (optic nerve) or motor (hypoglossal nerve) only
What is the structure of a nerve?
A nerve is an organ
* Cells (axons of neurons, Schwann cells)
* Connective tissue
- Epineurium (dense irregular CT)
- Perineurium (fibrous CT)
- Endoneurium (over myelin, thin reticular)
* Blood vessels
What are Synapses?
*Synapse = site where neurons communicate
with each other or with other cell types
Movement of nerve impulse?
Nerve impulse: from presynaptic axon terminal to postsynaptic dendrite
What are the components of synapse?
*Presynaptic axons end at axon terminals
*Within axon terminals are synaptic vesicles containing
neurotransmitters
* Neurotransmitters are chemical messengers
* Ex. Acetylcholine, Norepinephrine
*Neurotransmitters are released into a synaptic cleft (space between
synapsing neurons)
*Receptors on postsynaptic cell (dendrite or cell body) bind the
neurotransmitters
* This initiates an impulse or response
What are the Types of Synapses?
There are different types of neuron to
neuron synapses
* Axodendritic
- Presynaptic axon to postsynaptic dendrite
- Most common
* Axosomatic
- Presynaptic axon to postsynaptic cell body
Electrical and chemical synapse?
*Some synapses are gap junctions between neurons (referred to as electrical synapse)
*Not as common as chemical synapse (more common in invertebrates)
What happens when concentrations of some neurotransmitters are high?
Higher than normal concentrations of some neurotransmitters can be toxic and these toxic levels have been shown to play a role in the degeneration of neurons associated with conditions such as:
* Multiple sclerosis
* Alzheimer’s disease
* Amyotrophic lateral sclerosis (ALS)
* Parkinson’s disease
What is Tic Douloureux?
*Means: “painful twitching”
*Also called Trigeminal Neuralgia
*Extremely painful chronic condition
- A blood vessel compresses the trigeminal nerve causing loss of myelination of sensory nerve fibers
- The lack of insulation allows touch and pain nerve fibers to cross-talk
- Touch is perceived pain by brain
What is Neuronal Regeneration in PNS?
In the PNS
* If only axon is destroyed (not cell body), Schwann cells help axon sprout through a regeneration tube
* There can be partial recovery
What is Neuronal Regeneration in CNS?
In the CNS
- Historically, there has been the “no-new-neuron doctrine”
– Once neurons die, they are not replaced by new neurons
- HOWEVER…recently, neural stem cells have been discovered in the brain
– In the hippocampus (memory center) and olfactory bulb (smell)
* The implication have profound potential for brain and spinal cord injuries
*And, that you actually can teach an old dog new tricks!
