L4 - Nerve Flashcards
1
Q
Nervous system subdivisions
A
- CNS: brain, spinal cord (and optic nerve)
- PNS: all nervous tissue outside CNS
2
Q
Nervous system function
A
- Maintain homeostasis (works closely along with endocrine system)
- Initiate voluntary movements
- Responsible for perception, behaviour and memory
3
Q
Nervous tissue functions
A
- Sensory: detection of internal and external stimuli and transfer to CNS
- Integrative: analysis and storing of information
- Motor (effector): stimulation of effectors (muscle and glands) through PNS - Control muscle activity, Regulate glandular secretions
4
Q
Nervous tissue composition
A
Two types of cells:
1) neurons
2) neuroglia
5
Q
Neuron features
A
- Can be very large - longest cells in the body (up to 1 m - spinal cord to toe)
- Conscious and unconscious control
- Sensitive to stimuli - convert stimuli to electrical signals (action potentials)
- Do NOT divide (once damaged, they’re damaged)
- High metabolic rate (die rapidly without oxygen)
6
Q
Neuron structural components
A
Dendrites, axon, cell body (soma/perikaryon), cytoskeleton
7
Q
Dendrite appearance
A
Short, tapering, highly branched
8
Q
Dendrite function
A
Receiving/input part of the neuron - convey nerve impulses into cell body
9
Q
Axon appearance
A
Long, single, thin, cylindrical
10
Q
Axon function
A
Output portion of the neuron - carries nerve impulses away from neuron/cell body
11
Q
Axon composition
A
Axoplasm, axolemma
12
Q
Cell body/soma/perikaryon
A
Contains nucleus and organelles
13
Q
Cytoskeleton composition
A
Neurofibrils, Microtubules (, Lipofuscin)
14
Q
Neurofibrils
A
bundles of intermediate filaments that provide cell shape and support
15
Q
Microtubules
A
assist moving materials between cell body and axon
16
Q
Lipofuscin
A
pigment occurring as yellowish brown granule clumps in aging neurons
- Product of neuronal lysosomes that accumulate as neuron ages but doesn’t seem to harm neuron
17
Q
Structural classification of neurons
A
Multipolar, bipolar, unipolar, anaxonic
18
Q
Multipolar. Features
A
Some of longest (spinal cord to toes muscles)
19
Q
Multipolar. Structure
A
- multiple dendrites
- single axon
- cell body among (centre of) dendrites
20
Q
Multipolar. Location
A
- Most common neurons in CNS (brain, spinal cord)
- All motor neurons which control skeletal muscles
21
Q
Bipolar. Features
A
Rare and small (30 µm)
22
Q
Bipolar. Structure
A
- single dendrite (can branch at tip but not at the cell body)
- single axon
- cell body between axon and dendrite
23
Q
Bipolar. Location
A
Special sense organs (sight - retina of eye, smell - olfactory area of brain, hearing - inner ear)
- Relay information from receptor to neurons
24
Q
Unipolar. features
A
- Very long (1 m) like motor nerves from CNS to toe tip (periphery back to CNS)
- Begin as bipolar neurons in embryo and then dendrites and axon fuse together during development
25
Unipolar. Structure
- Dendrites and axon are continuous (whole thing from where dendrites converge is the axon)
- cell body is off to one side
26
Unipolar. Location
Most sensory nerves (touch, pressure, pain, thermal)
27
Types of sensory receptors
Corpuscle of touch, type 1 cutaneous mechano-receptor, lamellated receptor, nociceptor
28
Corpuscle of touch
- touch receptor
| - Mass of dendrites enclosed by capsule of connective tissue
29
Type 1 cutaneous mechano-receptor
- touch receptor
| - Free nerve endings (bare dendrites) that make contact with tactile epithelial cells of the stratum basale of skin
30
Lamellated receptor
- pressure receptor
| - Multilayered connective tissue capsule encloses dendrite
31
Nociceptor
- pain receptor
| - Free nerve endings (bare dendrites)
32
Other sensory receptors
Thermo receptors, itch receptors, tickle receptors are also unipolar neurons with free nerve endings that serve as sensory receptors (resemble nociceptors)
33
Anaxonic. Features
Rare and function is poorly understood
34
Anaxonic. Structure
Anatomy cannot distinguish dendrites from axons
35
Anaxonic. Location
Brain and special sense organs
36
Functional classification of neurons
Sensory/afferent, motor/efferent, interneurons
37
Sensory/afferent function
Info TO the CNS
- stimulus activates sensory receptor = sensory neurons forms action potential in its axon = impulse conveys into CNS via cranial/spinal nerves
38
Sensory/afferent structure
- Contain sensory receptors at dendrites or located just after sensory receptors
- most are unipolar
39
Motor/efferent function
Info FROM CNS to organs (muscles and glands)
40
Motor/efferent structure
Multipolar
41
Interneurons function
Within CNS BETWEEN sensory and motor neurons
| - incoming sensory information from sensory neurons = elicit motor response by activating appropriate motor neurons
42
Interneurons structure
Most are multipolar
43
Neuroglia location
Both in CNS and PNS
44
Neuroglia features
- Make up ~50% the volume of CNS (structural glue)
- Smaller than neurons but more numerous (5 - 50x)
- Do not propagate action potentials, but can communicate chemically
- Can divide within mature nervous system
45
Neuroglia function
- Physical structure of nervous tissue (support and protect)
- Repair framework of nervous tissue (nourish)
- Undertake phagocytosis (vacuum cleaner for brain)
- Nutrient supply to neurons
- Regulate interstitial fluid in neural tissue
46
CNS neuroglia types
Atrocytes, oligodendrocytes, microglia, ependymal cells
47
Astrocytes structure
- Star-shaped, largest, most numerous neuroglia
| - Syncytium network: complicated family of cells linked together in coordinated way
48
Astrocyte function
- Support (have microfilaments that give strength)
- Repair (scar)
- Communicate (chemically) with neurons via gliotransmitters (neurotransmitters) - e.g glutamate
- Maintain environment around neuron (surrounding tissue) - e.g regulating ions
- Maintain blood-brain barrier - protects brain + other areas of CNS from being exposed to toxins/poisons carried in blood by wrapping around vessels and influencing/controlling their permeability
- Learning/memory by influencing formation of neural synapses
- In embryo, secrete chemicals that appear to regulate growth, migration, interconnection among neurons in the brain
49
Types of astrocytes
Protoplasmic, fibrous
50
Protoplasmic astrocytes
short branching processes found in grey matter
51
Fibrous astrocytes
long unbranched processes located in white matter
52
Oligodendrocytes
Resemble astrocytes but smaller and contain fewer processes
53
Oligodendrocyte function
Form myelin sheath (multilayered protein lipid cover) around CNS axons
- Can myelinate more than one neuron cell’s axon
54
Myelin sheath function
Insulates/protects neuron and accelerates action potential
55
Microglia
Phagocytes (resident macrophages) - protection
- If there is an infection, breakdown/damage of cells, microglia migrate to consume cellular debris, microbes (bacteria), damaged nervous tissue
56
Ependymal cells structure
Single layer of predominantly cuboidal cells with cilia (flow) and microvilli (absorb and turn over CSF for sampling to monitor/adjust CSF composition)
57
Ependymal cells function
- Produce, possibly monitor and assist circulation of CSF (Cerebrospinal fluid)
- Line CSF-filled ventricles of brain and central canal of spinal cord
- CSF mechanical buffer
- Moves (cilia) nutrients and waste
58
Ependymal cells location
Ventricles of brain, central canal of spinal cord, other locations where CSF found
59
PNS neuroglia
Schwann cells, satellite cells
60
Schwann cells
PNS version of CNS oligodendrocyte
61
Schwan cell types
Myelinating, non-myelinating
62
Myelinating schwann cells ratio
One schwann cell per axon
63
Myelinating schwann cell function
Form insulating myelin sheath around axons
64
Myelinated PNS neuron structure
Myelinated internodes (axon and schwann cell nucleus side by side), nodes of Ranvier, neurolemma
65
Neurolemma
- very outer membrane of myelinating schwann cells
- only in axons of PNS
- aids regeneration
66
Non-myelinating schwann cells ratio
Multiple axons per cell
67
Non-myelinating schwann cell function
Support and surround axons
68
Non-myelinating PNS neuron structure
Unmyelinated internodes (axons surround schwann cell nucleus), nodes (fewer than myelinated), absense of neurolemma
69
Myelin features
Amount increases from birth to maturity and its presence greatly increases the speed of nerve impulse conduction
- during infancy, myelination is still in progress so response to stimuli is neither as rapid nor coordinated as those of older child or adult
70
Satellite cell location
Surround neuron cell bodies
71
Satellite cell function
Support and regulate fluid exchange between neuronal cell bodies and interstitial fluid
72
Synapse
site of communication between two neurons or between a neuron and an effector cell
73
Synaptic end bulbs
tips of some axon terminals that swell in bulb-shaped structures
74
Synaptic vesicles
tiny membrane-enclosed sacs contained by synaptic end bulbs and varicosities
75
Neurotransmitter
chemical stored and released from synaptic vesicle that excites or inhibits another neuron, muscle fibre or gland cell
