Nervous Tissue Lecture 2 Flashcards
Neuroglia
- Support, nourish, and protect neurons
- Smaller but more numerous than neurons
- Neuroglia make up about half the volume of CNS
Astrocytes
- Largest and most numerous of neuroglia
- Star-shaped cells that support neurons
- Form the blood-brain barrier (BBB)
- BBB maintains selective permeability of capillaries, preventing harmful substances from entering CNS
Oligodendrocytes
- Form myelin sheath around CNS axons
- Important for speed of AP conduction
Microglia
- Phagocytes of the CNS
- Remove microbes and cellular debris during tissue repair
Ependymal Cells
- Arranged in single layer along brain ventricles and spinal cord central canal
- Produce and circulate cerebrospinal fluid (CSF)
Gliomas
- Brain tumors arising from glial cells
- Highly malignant and usually fatal
- Most common types: astrocytomas and oligodendrogliomas
Satellite Cells
- Surround cell bodies of neurons in PNS
- Provide structural support
- Regulate material exchange between neuron and interstitial fluid
Schwann Cells
- Form myelin sheaths of PNS neurons
- Similar function to oligodendrocytes in CNS
Myelination of Neurons
- Myelination = insulation of axons by neuroglia
- Oligodendrocytes in CNS, Schwann cells in PNS
- Increases rate and efficiency of electrical impulse transmission
- Saltatory conduction
CNS vs. PNS
- CNS: Oligodendrocytes myelinate multiple neurons via branches
- PNS: Schwann cells found on one neuron, wrapping around it
Neurolemma
- Outermost layer of axons in PNS
- Made of Schwann cells
- Absent in CNS
Nodes of Ranvier
- Gaps in myelination with high ion channel concentrations
- Allow action potentials to “skip” along axon, increasing speed
- Facilitate saltatory conduction
Unmyelinated Neurons
- Often found in Schwann cells
- No myelin sheath formed
- Neuron exposed to extracellular environment
- Lack saltatory conduction, slower continuous conduction
Grey and White Matter
Some regions in brain and spinal cord appear white or grey
Grey Matter
Contains: cell bodies, dendrites, axon terminals, unmyelinated axons, neuroglia cells
White Matter
Composed mainly of myelinated axons (appearing white)
Difference in Grey and White Matter:
- In the brain, grey matter is superficial and white matter is deep
- Grey matter in cerebrum called cortex
- In spinal cord, white matter is superficial and grey matter is deep
Collections of Nervous Tissue
- Cell bodies and axons typically grouped together in the body
- Different names based on location (CNS or PNS)
Ganglia
Clusters of neuronal cell bodies in PNS
Nuclei
Collection of neuronal cell bodies within CNS
Nerves
- Bundles of axons in PNS
- Can be motor, sensory, or mixed
Tracts
- Bundles of axons in CNS
- In spinal cord, ascending tracts carry sensory info to brain, descending tracts carry motor info from brain
- In brain, carry information between different brain areas
Reflexes
- Fast, automatic responses to specific stimuli involving peripheral nerves and spinal cord
- Maintain homeostasis through rapid adjustments in organ/system function
5 Components of a Reflex Arc:
- Stimulation of receptor
- Activation of sensory neuron
- Information processing in CNS via interneurons
- Activation of motor neuron
- Response of peripheral effector
Stretch Reflex
- Monosynaptic reflex involving muscle spindles
- Regulates skeletal muscle length
Postural Reflexes
Subset of stretch reflexes maintaining upright position
Withdrawal Reflexes
- Polysynaptic reflex moving away from stimulus
- Strongest with painful stimuli
- Versatile due to involvement of interneurons
Flexor Reflex
- Type of withdrawal reflex affecting limb muscles
Example: Grabbing hot pan
Crossed Extensor Reflexes
- Contralateral reflex coordinated with flexor reflex
- Accompanies flexion with extension of opposite side
- Example: Step on sharp object
General Sensation
Concious Sensation
- Complex response involving sensation, integration, and response
- Example: Feeling spider on arm
- Response influenced by past experiences, preferences, and knowledge
Integration of Sensation
Concious Sensation
Dissemination of sensory information to brain regions for decision-making
Response varies based on factors such as past experiences and preferences
Voluntary Efferent Signals
Concious Sensation
Sent to skeletal muscles for response (e.g., shaking off spider)
Involves activation of sympathetic nervous system for fight or flight response (if scared of spiders)
Multiple Sclerosis (MS)
Autoimmune disease causing degeneration of myelin sheath around CNS neurons
Cause and Symptoms:
(MS)
- Idiopathic cause, likely genetic link
- Symptoms include fatigue, visual disturbances, paresthesia, muscle weakness, other neurological deficits
Prognosis and Epidemiology
(MS)
Lower life expectancy (5 to 10 years)
High rates in Canada (over 90,000 affected, 1 in 400 people)
Possibly linked to vitamin D deficiencies
More common in females (~4x) and risk doubles with relatives
