Nervous Tissue Structure And Function Flashcards
What can the nervous system be divided into
Central nervous system and the peripheral nervous system
What does the CNS make up of ?
The brain and spinal cord ( incl the relay neurone)
What does the peripheral nervous system make up of ?
- cranial nerves, spinal nerves , peripheral nerves
- sensory neurones and motor neurones
In a cross section for the human spinal cord , where would you find the white and gray matter ?
The gray matter is roughly in the form of a butterfly ( central bit)
- the white matter surrounds the gray matter.
- ventral horns (VF) are found in the anterior section of the spinal cord
- dorsal horns Are found in the posterior section of the spinal cord.
Where is the main cell body , dendrites and proximal part of the axon found in the nervous system ?
- they are found within the central nervous system
Where is the distal axon and terminal arborisations in the nervous system ?
Peripheral nervous system
In the CNS, the myelin sheath surrounding the axon is produced by what cell?
Oligodendrocyte
In the PNS, the myelin is produced by and is part of what type of cell !
.
Schwann cell
What are the 4 types of neurones ?
1) motor neurone
2) sensory neurone
3) integrative neurone
4) Anaxonic neurone
What is the function of motor neurones?
Send signals to the effector tissues
Where is the location of motor neurones ?
Their cell body is found in the CNS , their axons project into the peripheral nervous system.
Where is the location of sensory neurones ?
Start off in the peripheral nervous system then move towards the central nervous system
Where are integrative neurones found ?
CNS
What is the function of integrative neurones ?
Collate all information
Where is the location of axaxonic neurone ?
Retina ( some parts of the CNS)
What is the function of anaxonic neurones
Act as relays
What are the variations of neurones?
- unipolar
- multipolar
- bipolar
- anaxonic neurone
What is the cause of multiple sclerosis
- an autoimmune condition when’re the body attacks the myelin sheath in the brain and spinal cord.
- this causes the myelin sheath to become inflamed.
- this causes nerve signals to be slowed down , disrupted or sent the wrong way.
- THIS IS RESULTS IN LOSS OF CONDUCTION VELOCITY!
What are symptoms of multiple sclerosis
- fatigue
- slurred speech ( dysarthria)
- vision problems ( Diplopia )
- mobility issues ( muscle spasms )
- constipation
- urinary retention
- erectile dysfunction or inability to ejaculate.
What is anterograde transport
- movement of molecules / organelles from the cell body to the synapse or neurolemma
Outline the process of anterograde transport in an axon :
1) Kinesin ( a transport protein attached to Microtubule structures in the axon) carries secretory vesicles along the axon towards the terminals.
What does an immature vesicles contain moving in the anterograde direction?
- an enzyme in their membranes
What is retrograde movement in neurones?
- movement of organelles/molecules ie veciscles away from the axon terminal towards the cell body
What are the two fates of vesicles ?
1) lost to the neurolemma
2) recycled through Clathrin-coated endocytosis
What type of nerves fibres can peripheral nerves contain ?
Sensory
Integrative
Motor
What are the three connective tissue layers that are found in peripheral nerves ?
1) epineurium
2) perineurium
3) endoneurium
Epineurium
Dense irregular connective tissue
- separates different types of nerves and fills spaces between fascicles
Perineurium
Specialised connective tissue - transport proteins
- surrounds clusters of axons ( fascicles )
Endoneurium
Loose connective tissue
- surrounds single nerve cells
Each fasicle in a peripheral nerve contains ——how many types of neurones ?
ONE type eg one fascicle could have motor neurone whilst another could have sensory neurones
What doestoluidine blue stain ?
fats eg myelin sheath
How does myelination occur in the PNS
- axon sitting in a groove is surrounded by a Schwann cell
- the mesaxon membrane ( pair of parallel plasma membranes of a Schwann cell) initiates myelination by surrounding the embedded axon
- sheet like extension of the mesaxon membrane then wraps around the axon forming multiple membrane layers
- cytoplasm is extruded from the two opposing plasma membranes of the Schwann cell , which then become compacted to form myelin
How does an oligodendrocyte produce meylin in the CNS?
- a1) axon of the nerve is sitting in a groove surrounded by an oligodendrocyte
2) the plasma membranes of the oligodendrocyte initiates myelination by surrounding the axon.
3) a sheet like extension of the plasma membrane then wraps around successively around the axon , forming multiple membrane layers.
4) the cytoplasm is extruded from the two opposing plasma membranes of the oligodendrocyte s , which then becomes compacted to form myelin.
What is the only difference between myelination in an oligodendrocyte and a Schwann cell ?
In an oligodendrocyte, it wraps more than one axon simultaneously whereas in Schwann cells , it myelinates axons one by one.
What is the structure of unmyelinated nerve cells ?
- the individual axons are engulfed by the cytoplasm of a Schwann cell - but there is NO myelin sheath that surrounds the axon.
- this results in slower propagation of action potentials.
Which cells are bigger - oligodendrocyte dendrocytes or schwann cells ?
Schwann cells as oligodendrocyte are incredibly small.
What are a few examples of Neuroglial cells ?
- these comprise of all non-neural cells of the CNS.
oligodendrocyte
- astrocytes
- microglial cells
- ependymal cells
Astrocytes
- star like structure
- largest of the glial cells.
- have perineural feet that contains gap junctions which help with :
- the biochemical support for endothelial cells
- transport nutrients from blood to nerve cells.
- regulate nerve impulses by release glutamate which is an inhibitory neurotransmitter
- contribute to the blood -brain barrier which prevents blood from entering the brain.
- they play a role in repair and scarring process of the brain and spinal cord following traumatic injuries.
Microglial cells
- smallest and rarest of the glial cells
- Elongated , flattened nucleus.
- found throughout the CNS
- they act as the first and main form of active immune defence in the CNS.
- they have unique potassium channels that respond to even small changes in extracellular potassium concentrations which indicates the presence of ruptured cells , such as brain injury.
- they can also phagocytise the dead cells / pathogens then act as antigen-presenting cells at the blood-brain barrier to monocytes in circulation.
Ependymal cell function
Synthesis and secrete cerebrospinal fluid through the ventricles to the spinal cord
- microvilli absorbs cerebrospinal fluid for removal of pathogens
- present pathogens to microglial cells and astrocytes
- have modified right junctions between ependymal cells which control fluid release into the brain, usually they are closed but when cerebrospinal fluid increases , they open.
- They are NOT epithelia because they do not have a basal lamina
Ependymal cell structure and location
- neuronal support cells that forms epithelial lining of the ventricles in the brain and the central canal of the spinal cord.
- they are derived from the neuroectoderm during embryology.
- they look like columnar epithelial cells
- the apical surface have both cilia and microvilli
What are the three main classifications of neurones ?
- unipolar
- bipolar
- multipolar
UniPolar neuron
- these don’t actually exist in humans
- instead , humans have a psuedounipolar neurone
An example of pseudo unipolar neurone
Restricted to sensory neurones only
- located outside the CNS
Structure of pseudo- unipolar neurone
- 2 axonal branches , one extends from the periphery eg the hand and one extends to the spinal cord.
- one process leaving from the cell body.
- there are NO dendrites
- located outside the CNS
Bipolar neurone
- two branches extending from the cell body
- one axon , one dendrite
- found in the retina of the eye and olfactory epithelium.
- located outside the CNS
Multipolar neurone
- accounts for all the rest of the neurones in the body
- one axon extending from the cell body and several dendrites
- located outside the CNS
Anaxonic neurone
- no axons
- cannot send out action potentials throughout the body.
-
Within the cytoplasm of the cell body , what granules are found ?
Nissl substance which are aggregations of rough endoplasmic recticulum which are basophillic ( stain with basic dyes)
In the CNS, grey matter contains almost all the …
Neuronal cell bodies and their associated fibres
In the CNS, white matter consists mainly of …
Nerve fibres
- the white appearance is due to the presence of large amounts of myelin.
Compare the locations of grey and white matter in the spinal cord and brain
- in the spinal cord , the grey matter lies centrally , surrounded by white matter.
- however , In the brain a secondary migration occurs during development , such that the cerebrum and cerebellum the grey matter forms the outer layer called the cortex.
Where are astrocytes located ?
In the CNS.
- they are found between a nerve cell and a brain capillary.
- they transport glucose and lactate directly to the neuron from the capillary.
Relapsing-remitting MS
Most common form of the disease multiple sclerosis
- this is where some patients will have a particular symptom for a while and then it may disappear for several weeks or months.
What occurs during the relapse ( diseased) stage of MS
Demyelination of the myelin around axons in the CNS by autoimmune destruction of the myelin sheath laid down by oligodendrocytes.
- The current idea is that T cells are directed towards an antigen on the surface of myelin that probably mimics a protein present in a virus,
What occurs during the remission stage ( disease absent )
Oligodendrocyte lay down new layers of myelin to protect the axons of the neurones within the CNS.
Is there any cure for MS?
- there is no common cure .
- however , girls who have severe forms of MS are often advised to become pregnant because pregnancy tends to reduce MS symptoms and relapse.
- this is similar to other autoimmune diseases such as Graves’ disease.
