Lecture 15 Flashcards
(100 cards)
1
Q
What are the 3 overall functions of the nervous system?
A
- Stimulate muscle and glands
- Produce quick effects by electrochemical mechanisms
- Contributes to to homeostatic feedback loops
2
Q
What are the 2 parts of the CENTRAL nervous system (CNS)?
A
- Brain
- Spinal cord
3
Q
What does the brain do for the CNS?
A
It is the central processing center
4
Q
What does the spinal cord do for the CNS?
A
It is the gateway between the brain and trunks/limbs
5
Q
What are the 2 parts of the PERIPHERAL nervous system (PNS)?
A
- Nerves
- Ganglia
6
Q
What are nerves?
A
Cordlike structures that conduct information
7
Q
What are nerves composed of?
A
Axons and neurons
8
Q
What are ganglia?
A
Knot-like swelling in a nerve (contain neuron cell bodies)
9
Q
What do ganglia serve as in the PNS?
A
It serves as relay centers, where neurons synapse and transmit information to each other
10
Q
What does the CNS do?
A
Receives and processes information, initiates action
11
Q
What does the PNS do?
A
Transmits signals between the CNS and the rest of the body
12
Q
What do sensory neurons do?
A
Relay information about stimuli such as temp, pressure, light, pain, and certain chemicals back to the brain
13
Q
What does the somatic sensory division do?
A
Sensory nerves from the skin, skeletal muscles, bones, and joints
14
Q
What does the visceral sensory division do?
A
Detects changes in the viscera (the organs in the thoracic and abdominal cavities)
15
Q
What does the somatic motor division do?
A
- Voluntary muscle contractions
- Involuntary somatic reflexes
Motor nerves that innervate skeletal muscles
16
Q
What does the visceral motor division do?
A
AKA autonomic NS (it is largely autonomous)
- Controls cardiac muscle
- Controls smooth muscle
- Glands
sympathetic and parasympathetic
17
Q
What are the 3 functional properties found in all neurons?
A
- Excitability (irritability)
- Conductivity
- Secretion
18
Q
What is excitability in a neuron?
A
Respond to environmental changes (stimuli)
19
Q
What is conductivity in a neuron?
A
Produce electrical signals that travel along nerve fibers (axons) to reach other cells at distant locations
20
Q
What is secretion in a neuron?
A
Nerve fiber endings (axon terminals) release chemical neurotransmitters that influence other cells
21
Q
What are the 2 differential structures in the PNS?
A
- ganglia
- nerves
22
Q
What are ganglia in the PNS?
A
Collections of neuron cell bodies in the PNS
23
Q
What are nerves in the PNS?
A
Bundles of axons in the PNS
24
Q
What are the 5 differential structures in the CNS?
A
- neural cortex
- nuclei
- tracts
- columns
- centers
25
What are nuclei in the CNS?
Collections of neuron cell bodies in the interior of the CNS?
26
What are tracts in the CNS?
Bundles of CNS axons that share a common origin, destination, and function
27
What are columns in the CNS?
Several tracts that form an anatomically distinct mass
28
What are the centers in the CNS?
The integrate of all the information
Lower centers (incl spinal cord): carry out essential body functions
Higher centers:control more sophisticated information processing
29
What are the 3 functional categories of neurons?
1. *PNS* Sensory (afferent which is input) neurons conduct signals from receptors for the CNS
2. *inbetween* Interneurons are confined to the CNS (integrative function)
3. *PNS* Motor (efferent which is output) neurons conduct signals from the CNS to effectors such as muscles and glands
30
What are dendrites on a neuron?
Chemically regulated ion gates respond to stimulation by NTs
Receive signals from other neurons
31
What happens when a neuron has more dendrites?
The neuron can receive more information
32
What is the soma (neurosoma, cell body, perikaryon) on a neuron?
The neuron’s control center (metabolic and regulatory functions)
Produces NTs
33
What is the trigger zone on a neuron?
Axon hillock + initial segment
Plays important role in initiating nerve signal
34
What is an axon (nerve fiber)on a neuron?
Only the axon has voltage voltage regulated ion gates - “the conducting region”
Originate from the axon hillock
35
What shape are axons?
Cylindrical and relatively unbranched (few branches near the soma, called axon collateral)
36
What is terminal arborization?
Axons branching extensively at their distal end
37
What is the terminal button?
Each branch ends in a bulbous axon terminal which is the terminal button
38
What are neurofibrils?
Actin filaments
39
What are chromatophilic substances (nissl bodies)?
Stained masses if rough (granular) ER & ribosome separated by the bundles of neurofibrils (involved in protein synthesis)
40
What are lipofuscin granules?
Products of lysosomal activity
41
What is “aging pigment”
They accumulate with age and push the nucleus to one side of the cell instead of in the middle of the cell
42
What are the 4 structural classes of a neuron?
*According to number of processes extending from the soma
Multipolar
Bipolar
Unipolar
Anaxonic
43
What are multipolar neurons?
Most neurons of the brain and spinal cord
44
What are bipolar neurons?
Sensory neurons that are located in some special sense organs
45
What are unipolar neurons?
Most are primary or first-order sensory neurons (touch and pain)
46
What are anaxonic neurons?
No axon
They communicate locally (no AP)
47
What are microtubules?
They are the track for organelle transport in neurons
48
What is retrograde transport?
Inward transport
Up the axon toward the soma
49
What is anterograde transport?
Outward transport
Down the axon away from the soma
50
What direction does axonal transport happen?
In each direction
51
What has fast anterograde transport?
Organelles
Enzymes
Synaptic vesicles
Small molecules
52
What has slow anterograde transport?
Enzymes
Cytoskeleton components
Supplies new axoplasm
53
What has fast retrograde transport?
Recycled materials
Pathogens (& toxins)
54
How many neurons are in the nervous system?
About 1 trillion
55
Neuroglia (glial cells) outnumber neurons by at least ___
10 to 1 (non-neuronal cells)
56
What are the 4 general functions of neuroglia cells?
Bind neurons together (the word glia means glue)
In fetus, guide migrating neurons to their destination
Cover mature neurons (except at synapses) - gives precision to conduction pathways
Provide physical and metabolic support to neurons
57
What are the 2 neuroglia cells in the PNS?
Schwann cells
Satellite cells
58
What is the function of Schwann cells?
Myelin are certain axons in the PNS
Assist in regeneration of damaged fibers
59
What is the function of satellite cells?
Surround and support cell bodies
Provide electrical insulation
Regulate the chemical environment
60
What are the 4 cell types in the CNS?
Olygodendrocytes
Ependymal cells
Astrocytes
Microglial cells
61
What do olygodendrocytes do?
Their processes form myelin sheaths around CNS nerve fibers
62
What do ependymal cells do?
Line cavities
Produce cerebrospinal fluid (CSF)
Cilia help circulate CSF
63
What do astrocytes do?
*the most abundant*
Convert glucose to lactate; supply this to neurons
Produce growth factors
Regulate the extracellular environment (chemical composition)
Form the blood-brain barrier
64
What do microglial cells do?
Defensive cells (phagocytic)
They remove damaged neurons and infections
Specialized populations of macrophages
65
What is the insulation of the myelin sheath around the axon?
20% protein and 80% lipid
66
What is the myelin sheath formed by?
Formed by plasma mb of glial cells
- Schwann cell in the PNS
- Oligodendrocytes in CNS
67
What does the myelin sheath increase?
Increases action potential conduction velocity
68
In the CNS, where does each oligdendrocyte reach out to?
Reaches out to myelinate several nerve fibers
69
In the PNS, what is spiraled repeatedly around a single nerve fiber?
Schwann cells
Each segment of axon wrapped by a different Schwann cell
70
What is the neurilemma?
The outermost nucleated cytoplasmic layer of Schwann cells
71
How can regeneration of damaged PNS nerve fiber (axon) occur?
If the soma is intact and at least some of the neurilemma remains
72
In an unmyelinated peripheral axon, what does a Schwann do?
A Schwann cell folds its plasma membrane around several fibers
Only fold once around each fiber
73
What is needed for an action potential to occur?
An initial grade of depolarization
74
What is action potential?
A sudden, fast transitory, and propitiating change of the resting membrane potential
75
What happens at resting membrane potential?
Ligand gated sodium channels open in response to ACh, allowing for Na+ influx inside the cell and depolarization cell to threshold
76
What is depolarization?
The increase in the positivity of the membrane potential
77
What happens during depolarization?
When the cell reaches threshold, voltage-gated Na+ channels open, causing an action potential
78
What happens at repolarization?
At this high membrane potential, Na+ channels close, and voltage0-gated K+ channels open, repolarizing the cell
79
What is hyperpolarization?
Refers to the increase in negativity of membrane potential
80
K+ leak channels are always ___
Always open
As K+ leaks out, inside of membrane becomes more negative
81
What is local potential produced by?
Produced by ligand-gated Na+ channels on the dendrites and soma
82
What is action potential produced?
Produced by voltage-gated ion channels on the trigger zone and axon
(Occurs only where there is a increase in density of these channels)
83
Local potential may be ___ or ____
Excitatory (depolarizing, to more + voltages)
Inhibitory (hyperpolarizing, to more - voltages)
84
Action potential always begins with what?
Depolarization
85
Local potential is graded. What is graded?
Proportional to stimulus strength
Stronger stimuli open more Na+ channels
86
Action potential is all-or-none law. What is that?
If a stimulus depolarizes the neruon to threshold, the neruon fires at its maximum voltage (not graded); if not reached: not action potential
87
Local potential is reversible. What is reversible?
Returns to RMP if stimulation ceases before threshold is reached
88
Action potential is irreversible. What is irreversible?
Goes to completion once it begins (it can’t be stopped once it begins)
89
Local potential is local. What does this mean?
Has effects for only a short distance from point of origin
Incoming Na+ diffuses for short distances along the inside of the plasma membrane
90
Action potential is self propagating. What does this mean?
It has effects at a great distance from point of origin
91
Local potential is decremental. What does this mean?
Signal grows weaker with distance
92
Action potential is nondecremental. What does this mean?
Signal maintains same strength regardless of distance
93
How is a nerve signal conducted down an axon?
When the local current arrives at the axon hillock, it depolarizes that membrane at that point
If reaches the threshold voltage: the neuron now ‘fires’ (produces an action potential)
94
What are the 2 factors that affect the conduction velocity of nerve signals? (How fast a nerve signal traversals down an axon)
Diameter
Presence of absence of myelin
95
How does diameter affect nerve signal speed?
Large axons have more surface area and conduct signals
(The conduction velocity is proportional to fiber diameter)
96
We have a lot of ions flooding into the axon, so ____
So the more space they have to travel, the more likely they will be able to keep going in the right direction
97
How does the presence or a sense of myelin affect nerve signal speed?
Myelin increases signal conduction (and myelin thickness)
98
What kind of conduction do nonmyelinated axons have?
Continuous
Uninterrupted wave of electrical excitation all along the fiber
99
What other conduction can myelinated axons have?
Saltatory conduction
100
What does saltatory conduction create?
Since APs occur only at the nodes, saltatory conduction creates a false impression that the nerve signal jumps from node to node
