Cells and Tissues of the Nervous System Flashcards
Describe the divisions of the nervous system
CNS (brain & spinal cord) -> PNS (cranial & spinal nerves) -> Sensory (afferent) Motor (efferent) -> Somatic Motor Autonomic -> Sympathetic Parasympathetic
Describe neurons
Structural and fictional units of the NS. They are excitable, their impulses are carried as action potentials
Describe glial cells
Non-excitable supporting cells, they are much smaller than neurons
What is the basic anatomy of a typical neuron?
Contains multiple dendrites and one axon
What are the cell organelle of a neuron?
Mitochondria, rER, diffuse Golgi apparatus
Is the metabolic rate of neurons high or low?
High
What is the cytoplasm in the cell body called?
Perikaryon
What is the cytoplasm in the axon called?
Axoplasm
Are neurons amitotic?
Yes
What is the determining factor in the regrowth of axons?
If only the axons are damaged, there is potential for them to grow back, but if the corresponding cell body is damaged, the axons cannot regrow
What is the function of the myelin sheath?
To increase conduction speed across axons
How are the myelin sheaths formed?
PNS - Schwann cells
CNS - Oligodendrocytes
Describe the process of axon myelination
Schwann cells wrap around the axons
A mesaxon is formed
The cytoplasm of the Schwann cell gets extruded leaving only the cell membrane
Outline the features of Multiple Sclerosis
Loss of myelin sheath in patches, results in abnormal axon conduction
Cause is unknown (idiopathic)
MRI shows whitish plaques of demyelination
Prognosis variable
Scotland has the highest incidence in the world
What are the three kinds of neuron?
Multipolar, bipolar, pseudounipolar
Where are bipolar neurons found?
Olfactory mucosa, retinal nerve fibres
What type of neurons are sensory?
Pseudounipolar
What type of neurons are interneurons and motor neurons?
Multipolar
In what direction does the impulse travel in in the multipolar nerurons?
From the dendrites via the cell body and along the axon
In wat direction do the impulses travel in unipolar neurons?
From the dendrites along the axon to the cell body and then along the rest of the axon
What are the glial cells of the PNS?
Schwann cells
Satellite cells
What is the function of satellite cells?
Surrounding the neuronal cell bodies in the PNS
What are the glial cells of the CNS?
Ependymal cells
Microglia
Oligodendrocytes
Astrocytes
What is the function of astrocytes in the CNS?
Have end feet which surround synapses and capillaries. They help in potassium buffering
What is the function of the oligodendrocytes in the CNS?
Myelination
What is the function of the ependymal cells in the CNS?
Lining vesicles
What are the functions of the microglia in the CNS?
Phagocytosis, scar tissue formation
What are myelin sheaths made of?
Cell membrane
What are cell membranes made of?
Lipids (fats)
What colour are fats?
Yellow/White
How do myelinated axons together look in terms of colour?
White
What colour do bundles or neurones/non-myelinated axons look?
Grey
What do diffuse bundles of cell bodies and non-myelinated axons in the CNS form?
Grey matter
What do localised collections of cell bodies and non-myelinated axons in the CNS form?
Nucleii
What do diffuse collections of myelinated axons in the CNS form?
White matter
What do localised collections of myelinated axons in the CNS form?
Tracts
What do myelinated axons in the PNS form?
Nerves
What do cell bodies in the PNS form?
Ganglia
Describe the formation of the nervous system
Surface ectoderm of the embryo develops into a thickening called a neural groove and eventually tube
This goes on to form the nervous system
Describe the formation of the vesicles
When the neural tube is formed, it divides into three primary vesicles in week 4. It then divides further into two tertiary vesicles in week 5
These vesicles develop into the adult brain
What are the derivatives of the telencephalon (first two lateral vesicles)?
Cerebral cortex, basal ganglia
What are the derivatives of the Diencephalon? (third vesicle)
Thalamus, hypothalamus
What are the derivatives of the mesencephalon?
Midbrain
What are the derivatives of the metencephalon?
Pons, cerebellum
What are the derivatives of the myelencephalon? (fourth vesicle)
Medulla
What do the ventricles contain?
CSF
Describe the lateral ventricles
C-shaped cavities which lie in the cerebral hemispheres
What is the inter ventricular foramen?
Connects the lateral ventricles with the third ventricle, the cavity within the diencephalon
Where does the cerebral aqueduct lie?
In the midbrain
What shape is the 4th ventricle and where does it lie?
Diamond shaped, hindbrain
What is the inner layer covering of the CNS?
The pia mater, it is thin and vascular
What is the middle layer covering the CNS?
The arachnoid matter, it is spider-web like
What is the outer layer covering the CNS? What feature does it have?
The dura mater, it is thick and tough
Dural folds
What is the subdural space?
A potential space traversed by blood vessels penetrating into the CNS
What does the subarachnoid space contain?
CSF
What is CSF?
Fluid found in the ventricles and central canal, responsible in part for maintenance of intracranial pressure
Also present between the pia and arachnoid coverings of the meninges
Where is CSF produced?
The choroid plexus
How is SCF absorbed?
By the arachnoid villa
What are the three layers of the meninges?
Dura mater
Arachnoid mater
Pia mater
What are the key folds of the dura?
Falx cerebri, tentorium cerebelli, falx cerebelli, diaphragma sellae
What is the blood brain barrier?
A protective mechanism that helps maintain a stable environment for the brain and prevents harmful amino acids and ions entering the bloodstream and blood cells from entering the brain
What is the BBB made up of?
Endothelium - tight junctions
Thick basal lamina
Foot processes of astrocytes
Where in the brain is the BBB absent?
Parts of the hypothalamus, posterior pituitary
What is the clinical significance of the BBB in terms of drugs?
Plays a major role in delivery to CNS. Drugs must be lipid soluble or use suitable vectors
