WEEK 4: Nervous System - TISSUE Flashcards
What is the function of the NS?
Sensory function: receptors in the PNS detect stimuli. Sensory information is transmitted to CNS.
Integrative function: CNS processes sensory information via integration and analysis. An appropriate outcome is decided.
Motor function: CNS transmits motor information to peripheral NS. Action carried out by effectors.
What is the organisation of the NS?
CNS:
- Brain
- Spinal cord
PNS:
* Cranial nerves
* Spinal nerves
* Ganglia
* Enteric plexuses in the small intestine
* Sensory receptors in skin
THREE FURTHER DIVISIONS OF THE PNS
What are the three divisons of the PNS?
Somatic NS:
- voluntary movement
- skeletal muscle
Autonomic NS:
- involuntary movement
- smooth muscle, cardiac muscle, glands
TWO DIVISIONS: sympathetic parasympathetic (associated with flight or fight response)
Enteric NS:
- new discovery
- involuntary movement
- smooth muscle, glands and endocrine cells in GI tract
What is a neuron?
= the fundamental units of the brain and nervous system.
Consist of =
- soma
- dendrites
- axon
- axon terminal
- synaptic end bulbs
- axon hillock
- schwann cells
- node of ranvier
What is a cell body (soma)?
- contains nuclei and organelles.
- Receives information from other neurons.
What are dendrites?
- extensions from the cell body
- site of input for neuron
What is an axon?
- projection from cell body
- impulses are conducted along here
What is an axon terminal?
- the area where the electrical impulse is transferred to another cell
What is a synaptic end bulb?
- The area that synapses with other cells
- They don’t touch but come close to touching
What is an axon hillock?
= area between the cell body and the axon.
- It integrates all information that the cell receives from the dendrite. It must determine a response.
- Determines if it is positive and stimulatory or if it’s negative and inhibitory; essentially should the impulse continue.
What is a schwann cell?
- cells that wrap around the axon
- produce the myelin sheath
- is a glial cell
What are nodes of ranvier?
= specialized axonal segments that lack myelin, allowing the saltatory conduction (skipping of the impulse) of action potentials.
What is the myelin sheath?
= an insulating layer, or sheath that forms around nerves, including those in the brain and spinal cord.
- is a lipid and protein cover around axons
- only in CNS
- increases the speed of electrical impulse transfer
Structural classification of neurons
MULTIPOLAR:
- several dendrites, one axon
- all motor neurons
BIPOLAR:
- one main dendrite and one axon
- eye, ear and olfactory area
UNIPOLAR:
- a continuous process with a cell process of the side.
- most sensory neurons
Functional classification of neurons
SENSORY =
- From receptor to the CNS
- AFFERENT NEURONS (ARRIVE)
MOTOR =
- From CNS to effectors
- EFFERENT NEURONS (EXIT)
INTERNEURONS =
- In the CNS
- Process and integrate the information from the electrical impulse
What are neurogila?
- All non-neuronal cells in the NS
- Not electrically excitable
- Able to multiply and divide (neurons can’t)
- Make up half of the NS.
Types of neuroglia?
6 TYPES:
CNS HAS 4:
- astrocytes
- oligodendrocytes
- microglia
- ependymal cells
PNS HAS 2:
- schwann cells
-satellite cells
What do astrocytes cells do?
- star shaped
- Most numerous neuroglia
- Provide support to neurons (contain fibers that make them strong)
- Maintain blood-brain-barrier (they wrap around capillaries around blood vessels in brain to protect them)
- Maintain local chemical environment (they store glucose because the brain can’t or struggles to)
What do oligodendrocytes do?
- Octopus-like and extensions wrap around the axons.
- Fewer processes than an astrocyte
- Form and maintain myelin sheath (Schwann cells produce myelin in PNS and these cells produce myelin in the CNS)
- Can wrap around multiple axons (up to 50 from one cell)
What are microglia?
- Small cells with thin, spine like projections.
- Function as phagocytes.
- Remove cellular debris, microbes, damaged NS.
What are ependymal cells?
- Cuboidal cells with microvilli and cilia
- Line ventricles and the central canal (the brain)
- Produce and circulate CSF (cerebral spinal fluid)
What are schwann cells?
- Form and maintain myelin sheath.
- Each Schwann cell myelin one axon and one specification
- Involved in axon regeneration.
What are satellite cells?
- Surround cell bodies of neurons of PNS ganglia.
- Provide structural support (cushion cell body)
- Exchange material between cell bodies and interstitial fluid (fluid that surrounds the cells).
What is neurogeneration?
= regrowth or repair of the NS or cells (neurons, axons, myelin, synapses)
Difference between CNS and PNS nerve repair
CNS = little to no repair due to inhibitory influences from neuroglia, absence of growth-stimulating cues, and rapid formation of scar tissue.
PNS = repair possible if the cell body is intact; if Schwann cells are functional, and if the scare tissue formation doesn’t occur too rapidly.
Steps of PNS regeneration steps
- Chromatolysis
- Wallerian degeneration
- Formation or a regeneration tube
PNS regeneration: chromatolysis
- 24/48 hours after injury, Nissl bodies in cell body break up into different pieces
- Are essentially rough endoplasmic reticulum which produce proteins (chromatolysis)
PNS regeneration: wallerian degeneration
- Day 3-5, the distal axon with swell and break up. The myelin will also begin to break.
- The degeneration of the axon sheath = Wallerian degeneration.
PNS regeneration: formation or regeneration tube
- Macrophages phagocytize the damaged tissue.
- Synthesis of RNA and protein accelerates, and this allows for the rebuilding of the axon.
- Schwan cells divide and grow to form regeneration tube = this tube will guide the formation of the axon from proximal to distal side.
Various collections of nervous tissue:
- clusters of neuronal cell bodies
- bundles of axons
- white and grey matter
What are CLUSTERS OF NEURONAL CELL BODIES?
PNS = ganglion
CNS = Nucleus
What are BUNDLES OF AXONS?
PNS = nerve
CNS = tract
What are WHITE AND GREY MATTER?
WHITE (only myelinated axons) AND GREY MATTER (everything by myelinated axon):
BRAIN AND WHITE = inner layers
SPINAL AND WHITE = outer layers
