Cells and Tissue of the Nervous System Flashcards
What are the two different cell types in the nervous system?
Neurons and glial cells
What are the features of neurone?
- Structural and functional unit
- Excitable cells
- Impulses carried as action potentials
What are the features of glial cells?
- Non-excitable supporting cells
* Much smaller than neurones
Describe the structure and function of a typical neurone
• Multiple dendrite, one axon • Impulse transmission is by action potential which can travel in only one direction from the cell body to the synaptic terminal
Describe the different parts to the neurone
- Nucleus - loose chromatin, prominent nucleolus
- Cell organelles - mitochondria, rER, diffuse Golgi apparatus
- High metabolic rate
- Cytoplasms in the cell body is perikaryon, and in the axon is axoplasm
- Long living and amitotic
What covers the axons?
Myeline sheath
What is the benefit of the myelin sheath?
Increases conduction speed by ‘saltatory conduction’
What is saltatory conduction?
The propagation of action potentials along myelinated axons from one node of Ranvier to the next node
What is the myeline sheath formed by?
- Schwann cells in PNS
* Oligodendrocytes in CNS
What is the clinical importance of the myeline sheath?
Multiple sclerosis:
Patchy loss/scarring of myelin sheath (demyelination) -> nerve conduction across affected axons abnormal
What is the cause and sign on MRI of multiple sclerosis?
- Cause unknown
- MRI shows whitish plaques of demyelination
- Prognosis variable
What does the spinal cord consist of?
Grey and white matter
What is the difference between grey and white matter?
- White matter contains myelinated axons on neurones (myeline sheath give white appearance)
- Grey matter contain neural cell bodies
Define the different horns in the the grey matter of the spinal cord
- Dorsal horn - sensory fibres from the dorsal roots synapse with interneurons here. Their cell bodies are organised into visceral and somatic
- Ventral horns - cell bodies of motor neurone
What is the nuclei of the cerebral hemisphere?
Localised collection of neuronal cell bodies in the grey matter
What is the dorsal root ganglion?
Collection of neurone cell bodies outside in the cerebral hemisphere
Describe the white matter
It is divided into columns composed of tracts of axons that transfer information up and down the spinal cord.
How is grey matter arranged?
It is diffuse
What are the three different types of neurones?
- Multipolar
- Bipolar
- Pseudounipolar
Describe the structure of pseudounipolar neurones
Long dendrite and has a separate neck to cell body
They are sensory neurones
Describe the structure of bipolar neurones
Two relatively equal fibres extending off the central body
What type of fibres do multipolar neurones carry?
Motor
Describe the pathway of a sensory neurone
Pathway of pseudounipolar neurone (as it’s sensory):
- Cutaneous receptors in the skin
- Collection of neuronal cell bodies
- Tract in the white matter (fibre pathway)
- Synapses into a discrete collection of neuronal cell bodies in grey matter
- To cerebral hemisphere
What is the main types of Glial cell?
Astrocytes in the CNS which have multiple end feet which surround synapses and capillaries to help in K+ buffering - forms blood brain barrier
What is the blood brain barrier?
Protective mechanism hat helps maintain a a stable environment fro the brain and prevents harmful amino acid and ions resent in the bloodstream and blood cells from entering
What are the layers on the blood brain barrier?
- Endothelium - tight junction (fenestrated outside brain)
- Thick basa lamina
- Foot processes of astrocytes
What is allowed through the blood brain barrier?
Lipid soluble molecules, O2, H2O - major role in drug delivery to CNS but they have to be lipid soluble or use suitable vectors
Water soluble molecules (glucose, AA) are pump mediated
What artery forms grooves in the dura matter?
Middle meningeal artery (branch of ECA)
What doe the falx cerebra separate?
Two cerebral hemispheres
NAme four important parts of the topography of the brain
- Cerebrum
- Diencephalon
- Brainstem
- Cerebellum
What is the cerebellum responsible for?
Balance and coordination
What is the cerebrum responsible for?
Consciousness
What is the brainstem responsible for?
- It contains vital centres i.e. cardiorespiratory
* Pathway for fibre tracts
What is the diencephalon responsible for?
Contains hypothalamus, and pituitary stalk (connection to pituitary gland
What are the three parts to eat brain stem?
- Midbrain
- Pons
- Medulla
Define ventricles
Spaces inside the brain
What are the different parts of the ventricle in the brain?
- Lateral ventricles (in cerebral hemisphere)
- Interventricular foramen - connects to 3rd ventricle in the diencephalon
- Cerebral aqueduct (midbrain)
- 4th ventricle (diamond-shaped) in hindbrain
Where is the third ventricle located?
In the diencephalon
Where is the fourth ventricle located?
Between the pons and medulla (in front) and cerebellum (at back)
What lies inside the ventricles?
CSF
Describe the dura mater
Tough, fibrous and has dural folds
Describe the Pia mater
Vascularised and dips into he folds of the brain
What is the significance of the subdural space?
Potential space which is traversed by blood vessels penetrating into the CNS
Between what meningeal layers is the CSF found?
Arachnoid and pia - subarachnoid space
Where is the cerebrospinal fluid found?
Fluid inside the cavity of brain (ventricles) and central canal of spinal cord
Also present surrounding the brain and spinal cord in between the layers of meninges which are coverings of the brain (between the pia and arachnoid)
Where is CSF formed?
Choroid plexus in each ventricle
Where is CSF absorbed?
It leaves at the back of the 4th ventricle through 3 small holes and goes into the subarachnoid space
At the top of the brain, arachnoid villi drain into the saggital sinus (venous channel in brain) for CSF to be reabsorbed by the venous system
