Lecture 1: Nervous system 1 cells of NS Flashcards
What is the information the nervous system receives from the outside world
stimulus or sensory information
How is input carried from the outside world into the nervous sytem
by afferent or sensory paths
what is the main integration center of nervous system
the brain
How is nervous response / output carried through system
efferent or motor paths (output of the system)
What is the organization in order of the nervous system function
- NS receives info from outside world
- Info carried by afferent / sensory paths
- info carried to integration center
- nervous response / output carried by efferent / motor paths
- results in motor action
What are 2 main components of NS
- Central nervous system (CNS)
2. Peripheral Nervous System (PNS)
what is the CNS comprised of
brain and spinal cord
what is PNS comprised of
cranial nerves (12) and spinal nerves
What are 2 subdivisions of the PNS
- Somatic nervous system
2. Autonomic nervous system
what is the somatic nervous system
voluntary
-muscle movement
what is the autonomic nervous system
involuntary
- sympathetic (adrenergic)
- parasympathetic (cholinergic)
What are 2 major categories of cells of nervous system
- Neurons
2. Glial cells
What are the 2 other names for Glial cells
- Gliocytes
- Neuroglia
how many distinct types of Glial cells are found throughout the NS
6
What are the 4 types of Glial cells that are part of the CNS
- Astrocytes
- Microglia
- Ependymal cells
- Oligodendrocytes
What are the 2 types of Glial cells that are part of the PNS
- Satellite cells
2. Schwann cells
What is 3 main functions of Glial cells
- surround
- protect
- assist neurons with their functions
What is the structure of Astrocytes (CNS)
- star shaped cell (name “astro”)
- most abundant cell in the brain
What is the function of Astrocytes (CNS)
- creates bridge btw capillaries and neurons
- maintains extracellular fluid surrounding CNS neurons with bulbous feet
- Part of the blood brain barrier
What does the blood brain barrier do
protects neurons from potential toxins in blood
What is structure of Microglia (CNS)
-small cell with many spiny extensions
the extensions are in direct contact with neurons
What is function of Microglia (CNS)
- detects damaged and infected neurons
- migrates to the damaged and infected cells and becomes a macrophagocyte
What is the structure of Ependymal cells (CNS)
- squamous or columnar shape cells
- generally ciliated
What is the function of Ependymal cells (CNS)
- lines central cavities of brain & spinal cord where CSF circulates
- has tight junctions and ion pumps to assess CSF composition
What do cilia do throughout ventricles and spinal column
They are orchestrated waves beating to help circulate CSF
What is the structure of Oligodendrocytes (CNS)
- forms the Myelin Sheath of the neurons of the CNS by wrapping around many axons at a time
- Myelin (CT) is formed by oligodendrocytes wrapping their foot-like extensions around axons
What is the function of Oligodendrocytes (CNS)
-increases speed of action potentials (electrical signaling)
What is the structure of Satellite cells (PNS)
-flat shaped cell that surrounds the cell body of the neurons
What is the function of Satellite cells (PNS)
- assist with PNS neuron metabolism
- regulates the extracellular liquid
What is structure of Schwann cells (PNS)
- round and flattened
- forms the Myelin sheath of the PNS neurons by individually wrapping around an axon
What is the function of Schwann cells (PNS)
-plays a role in the regeneration of peripheral neurofibers
What type of cells are mature neurons
amitotic cells
-they do not divide (regenerate)
What happens when mature neurons are damaged
- minor damage leads to shrinking of neurons
- severe damage = neuron dies
When can regeneration occur in the PNS
- If an axon is crushed or sectioned regeneration is possible
- when cell body is harmed cell is lost
When can regeneration occur in the CNS
NEVER
-damage is irreversible in the brain and spinal cord
How many layers are in peripheral nerves layered bundle
3
What are the layers of peripheral nerves
- Epineurium
- Perineurium
- Endoneurium
What is the Epineurium
The outer-most layer surrounding a bundle of nerve fibers
What is the Perineurium
the middle layer surrounding a bundle of nerve fibers
What is the Endoneurium
- surrounding a single nerve fiber
- lying on top of the myelin sheath
Central nerves form tracts that connect
different areas of the CNS
-they are not bundled
What is the name of the key locations where PNS gather
PLEXUS
What are the 2 major categories of Plexus
- Spinal plexuses
2. Autonomic Plexuses
What is step 1 of peripheral nerve regeneration
- rapid swelling from because of cell leakage
- in a few hrs, axon/ myelin sheath disintegrates distal to site of injury
What is step 2 of peripheral nerve regeneration
- Schwann cells & macrophages phagocytize the myelin sheath & the axon (degraded in 1 week)
- The neurilemma (cytoplasm + nucleus) remain intact within the endoneurium
What is step 3 of peripheral nerve regeneration
Schwann cells:
- divide and grow due to substances secreted by macrophages
- migrate to the site & release growth and other factors that encourage axonal growth
- form cellular cords (regeneration tube) that guide the new regenerating axon
What is step 4 of peripheral nerve regeneration
- the axon regenerates and a new myelin sheath forms
- Schwann cells protect, support & remyelinate the axon
What are the 4 functional structures of neurons
- Reception / input
- Dendrites - Integration
- Soma/ cell body - Conduction / output
- Axons - Secretion
- Axonal terminals
What are the Dendrites (receiver)
- Extension
- Sometimes very numerous
- receive many inputs potentials through synapse with other neurons & transmit them to the cell body
What is structure and function of cell body (integrator)
- responsible for the neuron’s metabolism
- contains all the organelles except centrioles
- amitotic (do not replace if destroyed)
- live >100 yrs with O2 and glucose
What are the endoplasmic reticulum and ribosomes considered
- Chromatophilic substance or Nissl bodies
- Certain types of stains ( Nissl)
What is structure of Axon
- few or many long extensions
- myelinated or unmyelinated
- long axon are called nerve fiber
- has axon hillock
- has complex cellular skeleton
What is the Axon Hillock
- Portion of axon beside cell body
- Trigger zone of the action potential
Why does axon have no RoughER or Golgi apparatus
cellular skeleton permits transport of organelles & molecules produced in the cell body from end to another of the neuron
Cellular skeleton of the axon is involved with
transporters that use ATP to move substances along itself
What is retrograde axonal transport
- where certain organelles & components are transported back to the cell to get broken down
- follows the peripheral nerves up the brainstem & into the brain
What are axon collaterals
- axons that branch out at right angles
- collaterals usually ramified in millions of telodendria that have bulbous distal ends (axonal terminals or synaptic knobs)
- endings have vesicles filled with neurotransmitters to be released in the chemical synapse
Where are myelin sheath
- on myelinated axons
- lipoproteins
How are myelin sheath formed
by wrapping around the axon:
- Oligodendrocytes (CNS)
- Schwann cells (PNS)
What is the speed of transmission of a nerve impulse
- 100m/s (myelinated) vs 1 m/s (unmyelinated)
- touch vs pain
Why is Myelin sheath an exceptional insulator
50 - 100 layers of membranes rich in myelin form the sheath of myelin
What is the 1st external layer of myelin sheath called
- Neurilemma and it is also sheath of Schwann cells
What are the growth and other factors involved in peripheral nerve regeneration
NGF- nerve growth factor
BDNF - Brain derived neurotrophic factor
IGF - Insulin-like growth factor
What are Nodes of Ranvier
Specialized gaps in myelinated neurons where axon is bare (~1um)
- region rich in voltage gated sodium channels
- help propel action potential down axon barrel
how does an action potential spread along a myelinated axon
by Saltatory Conduction
- depolarization jumps from 1 node to the next
- propagation is concentrated and faster compared to unmyelinated axons
What happens to voltage of action potential in bare plasma membrane
it decays as it leaks into the membrane (same as on Dendrites)
What happens to voltage of an action potential in unmyelinated axon
There are voltage gated sodium potassium channels that have to recreate the action potential at each point along the axon. voltage does not decay but conduction is slow
What is White Matter
Myelinated axons of the CNS
What is Gray Matter
Groups of cell bodies of the CNS
-aka Nuclei
What are the 2 main group classifications of neurons
- Structural
2. Functional
What are the 3 structural classifications of Neurons
- Multipolar neurons
- Bipolar Neurons
- Unipolar neurons
Describe multipolar neurons
- 3 or more extensions
- lots of dendrites, 1 axon
- most common in the CNS
Describe Bipolar neurons
- 2 extensions: 1 dendrite, 1 axon
- rare
- sensory neurons (smell, vision)
Describe Unipolar neurons
1 extension -peripheral cell body -only distal extremities are dendrites Central process Cell body found in the sensory ganglia & PNS
What are the 3 functional classifications of neurons
- Afferents neurons (sensory/input)
- Efferent Neurons (motor/output)
- Association neurons (interneurons)
What is function of Afferents neurons
Sensory / input
- transmit the nerve impulse towards CNS (brain or spinal cord)
- transmits impulses towards a brain nucleus
What is function of Efferent neurons
Motor / Output
- moves the nerve impulse away from the CNS (brain or spinal cord)
- transmits impulses away from a given brain nucleus
What is function of Association neurons
Interneurons
- in PNS link btw sensory (afferent) & motor (efferent) neurons
- in CNS they link btw neurons (mostly inhibitory)
What is structure of Association neurons
- Multipolar (most neurons are this type)
- in the brain these neurons are mostly inhibitory (reduced the amount of signal being received)
What is the reflex arc
an involuntary, unplanned sequence or action that is nearly instantaneous in response to stimulus
ex. touch something burning hot and your hand automatically pulls away from the pain
What forms the basis of the reflex arc
the 3 functional classes of neurons
- receptors (ex. on skin) send info down the afferent neurons
- association neurons in spinal cord send an automatic reaction bypassing the action of sending it to brain to process
- efferent neurons send action to effectors (ex. muscles)
