Anatomy and pattern recognition of the central nervous system normal radiographic appearances and pathology Flashcards
What are the functions of the nervous system
• Sensory input
• Integration
• Motor output
• Homeostasis regulation
• Mental activities
• Reflex actions
• Provides an immediate response when required
• Provide a slower, long term response when required through stimulation of endocrine system and release of hormones
Overview of the NS
• Central nervous system
• Peripheral nervous system
- Sensory
- Motor
• Somatic
• Autonomic nervous system
Sympathetic
parasympathetic
There are 2 principal cells of the nervous system
• Glia cell
• neurons
What is myelin?
• It is a fatty sheath that wraps around the axons of neurons (the bit of the neuron that conducts electrical impulses away from the neuron cells body)
• Composed of lipids and proteins
• Insulates the axons and increases the speed of electrical impulses as they travel along nerve cells.
• Produced by Glia cells
• CNS – oligodendrocytes
• PNS – Schwann cells
Neurons
• Sometimes called a ‘nerve cell’
• Is the fundamental structural unit of the nervous system which transmits information throughout the body.
Types of neurons
• Sensory neurons
• Motor neurons
• Interneurons
Special characteristics
• Longevity
• Amitotic
• High metabolic rate
Grey and white matter
• Grey Matter – collections of nerve cell bodies and their dendrites
• Nuclei
• Ganglia
• White matter – myelinated fibres – tracts conveying nerve impulses from generation site to target
How is a nerve impulse performed?
Membrane potential
• Difference of charges across the plasma membrane
Resting potential
• Resting cells are (-) inside and (+) outside
• Large amounts of Na+ outside the cell and K+
inside
Action potential/impulse
• Rapid reversals in charges across the plasma
membrane
• Caused by the exchange of ions across the
membrane of the neuron
• Threshold level (-55mV) needed to stimulate neurons ALL-OR-NONE principle
How are impulses terminated? – termination of neurotransmitter effects
Degradation of neurotransmitter by enzyme
Reuptake of neurotransmitter
Diffusion of neurotransmitter from synapse
Synapse: Excitatory or Inhibitory
• Excitatory Synapses and Excitatory Postsynaptic Potentials (EPSPs)
• Inhibitory Synapses and Inhibitory Postsynaptic Potentials (IPSPs)
Meninges
• Cover and protect Central Nervous System (CNS)
• Contains Cerebrospinal fluid (CSF)
• Protect blood vessels
• Dura mater – 2 layers of fibrous tissue mostly attached, fibrous outer attached to skull and an inner enclosing the Central Nervous System
• Arachnoid mater– separated from the dural by the sub-dural space and covers the pia mater. Connects to this by web like extensions forming the
sub-arachnoid space. This is a large space filled with CSF and blood vesssels
• Pia mater – innermost layer attaches to the brain
Meninges – Dura mater
• Dura mater
• Separation of layers forms:
• Dural partition of brain:
• Falx cerebri, tentorium cerebelli, Falx cerebelli.
• Intracranial venous structures (sinuses) Superior sagittal sinus, inferior sagittal sinus, confluence of sinuses, straight sinus, transverse sinus
• Extradural space between periosteal (outer) layer and bone of skull
• Subdural space between meningeal (inner) layer and arachnoid mater.
Spinal cord
• Extends as a loose sheath from foramen magnum to the 2nd sacral vertebra.
Meninges – Arachnoid mater
• Arachnoid mater
• Passes over the convolutions of the brain.
• Merges with the dura mater to at the 2nd sacral vertebra.
• Arachnoid mater separated from :
• Dura mater by subdural space
• Pia mater by subarachnoid space
Meninges – Pia mater
• Pia mater
• Connective tissue
• Adheres to brain covering dipping into fissures
• Continues beyond spinal cord with filum terminale
• Sheaths blood vessels
• Fuses to periosteum of the coccyx with dura mater
Ventricles
Irregular shaped cavities located within the brain.
• Contain cerebrospinal fluid (CSF)
• CSF: Suspends brain cells – provides buoyancy
and a fluid environment for biochemical activity.
Thus protects and maintains viability.
• CSF is like plasma with less protein and a
different electrolyte composition. It is essential
for brain function, e.g. very sensitive to pH,
affecting breathing and perfusion of blood.
• Consist of defined aspects:
• Left and right lateral ventricles
• Third ventricle
• Fourth ventricle
CSF
• Is produced in the choroid plexuses.
• Located in lateral ventricles, 3rd ventricle roof and 4th ventricle
• Clusters of fine capillaries hanging from the
ventricles.
• Ependymal cells filter blood and modify
composition.
• CSF locates between the pia mater and arachnoid mater, within the sub- arachnoid space.
• CSF secreted continuously
• Volume of CSF constant (150 ml)
Functions of CSF
• Keeps brain moist.
• Supports and protects brain and spinal cord
•Transports glucose, oxygen and other needed chemicals from blood to neurons and waste product removal
The brain structure
Brain structure:
Cerebrum
Diencephalon
• Epithalmus
• Thalamus
• Hypothalamus
Cerebellum
Brain stem
• Midbrain
• Pons
• Medulla oblongata