Weeks 7, 8, 9, 10 and 11 Flashcards
(159 cards)
1
Q
What are ciliated CNS neuroglia that play an active role in moving the cerebrospinal fluid called?
A
ependymal cells
2
Q
A group of neuron cell bodies in the PNS is a…
A
Ganglion
3
Q
An example of an unencapsulated receptor is a…
A
tactile disc
4
Q
What is the role of acetylcholinesterase?
A
destroy ACh a brief period after its release by axon endings
5
Q
Broca’s area is important in coordinating muscles involved in…
A
speech
6
Q
The term central nervous system refers to the…
A
brain and spinal cord
7
Q
Which of the brain regions is a major convergence area for most sensory input before it is sent on to the cerebral cortex?
A
Thalamus
8
Q
The part of a neuron that conducts impulses away from its cell body is called an…
A
Axon
9
Q
Which ion channel opens in response to a change in membrane potential and participates in the generation and conduction of action potentials?
A
voltage-gated channel
10
Q
Week 8 overview: Functions of the nervous system • Neuroglia, Neurons, Neuron Processes • Classification of Neurons • Membrane Potentials • Basic Principles of Electricity • Changing the Resting Membrane Potential • Graded Potential vs Action Potential • Generating an Action Potential • Synapses
A
Yes.
11
Q
Divisions of Peripheral Nervous System PNS has two functional divisions Sensory (afferent) division o Somatic sensory fibers: o Visceral sensory fibers: Motor (efferent) division o Somatic (voluntary) nervous system o Autonomic nervous system
A
Yes.
12
Q
Nervous tissue histology: 2 main cell types
• Neurons (nerve cells):
excitable cells that transmit
electrical signals
• Neuroglia (glial cells): small
cells that support, surround
and wrap delicate neurons
• Four main neuroglia types support CNS neurons
Oligodendrocytes, Astrocytes, Microglial cells, Ependymal cells
• Two main neuroglia types support PNS neurons
Schwann cells, Satellite cells
A
Yes.
13
Q
Neurons
• Neurons are basic structural units of nervous system
• Large, highly specialized cells that conduct impulses
• Special characteristics
– Excitable
– Extreme longevity (lasts a person’s lifetime)
– Amitotic, with few exceptions
– High metabolic rate: requires continuous supply of
oxygen and glucose
• All have cell body and one or more “processes” extending
from it.
A
Yes.
14
Q
Neuron Cell Body and Processes
Neuron Cell body
Clusters of neuron cell bodies are termed:
− Nuclei in the CNS
− Ganglia in the PNS
Neuron Processes (axons & dendrites)
• Arm like structures that extend from cell body
• Bundles of neuron processes are termed:
− Tracts in CNS
− Nerves in PNS
• Different mix of cell bodies & processes between CNS and PNS
− CNS: mainly neuron cell bodies & their processes
– PNS: mainly neuron processes
A
Yes.
15
Q
Myelination of neurons (cont)
– Myelin: a whitish, protein-lipid substance
• Wraps around some axons in PNS and CNS
• Protects and electrically insulates axon
• Increases speed of nerve impulse transmission
– Myelinated fibers: sheath is segmented in most
long or large-diameter axons
• Gaps in the sheath (Nodes of Ranvier)
• Further assists nerve transmission
− Nonmyelinated fibers:
• Small diameter neurons not sheathed by myelin
• Conduct impulses more slowly
A
Yes.
16
Q
Myelin Sheaths in the CNS
• Myelinated fibres in the CNS
– Formed by processes of oligodendrocytes
– Each cell can wrap up to 60 axons at once
– Myelin sheath gap is present
– “White matter” in the CNS
• Nonmyelinated fibres in the CNS
– Thinnest fibers are unmyelinated, but covered by long
extensions of adjacent neuroglia
– “Gray matter” in the CNS: mostly neuron cell bodies
and nonmyelinated fibers
A
Yes.
17
Q
Membrane potentials and nerve impulses
• Like all cells, neurons have a resting
membrane potential
• Neurons are highly excitable
• Unlike most other cells, neurons can rapidly
change resting membrane potential
• Their function is to generate and conduct
nerve impulses
• These impulses are essentially “electricity”
A
Yes.
18
Q
Basic Principles of Electricity Apply
• Batteries: a useful example
• Opposite charges are attracted
to each other
• Energy required to keep opposite
charges separated
• Potential energy or potential difference (ie a voltage)
• Energy liberated when the charges move toward one another (ie
circuit complete)
• Electrical current flows as electrons flow around the circuit wire
• In the body, electrical current flows as ions move across a
membrane
A
Yes.
19
Q
Membrane potential in neurons (cont).
• Changes in Resting Membrane Potential (+/-) can be
mediated through:
• Chemically gated (ligand-gated) channels
• Open only with binding of a specific chemical
(example: neurotransmitter)
• Voltage-gated channels
• Open and close in response to changes in
membrane potential
• Mechanically gated channels
• Open and close in response to physical
deformation of receptors, as in sensory receptors
A
Yes.
20
Q
Changing the Resting Membrane Potential
• Changes in membrane potential are used as signals to
receive, integrate, and send information
• Membrane potential changes when:
• Concentrations of ions across membrane change
• Membrane permeability to ions changes
• Changes can produce two types of membrane potentials
• Graded potentials
− Short-distance signals on affected membrane
• Action potentials
− Long-distance signals along axons
A
Yes.
21
Q
Changing the Resting Membrane Potential (cont.)
• Depolarization: relative decrease in membrane
potential (-70mV +30mV)
• Inside of membrane becomes less negative than resting
membrane potential
• Moves toward zero and beyond (+30mV)
• Probability of producing impulse increases
• Hyperpolarization: relative increase in membrane
potential (-75mV -70mV)
• Inside of membrane becomes more negative than resting
membrane potential
• Moves away from zero
• Probability of producing impulse decreases
A
Yes.
22
Q
Graded Potentials
• Short-lived, localized changes in membrane potential
– The stronger the stimulus, the more voltage changes and
the further current flows
• Triggered by stimulus that opens gated ion channels
– Results in depolarization or sometimes hyperpolarization
• Named according to location and function
– Receptor potential (within a receptor after stimulus)
– Postsynaptic potential
A
Yes.
23
Q
Action Potentials (APs)
• In neurons, also referred to as a nerve impulse
• Involves opening of specific voltage-gated channels
• Brief reversal of membrane potential with a positive
change in voltage of around 100 mV
• Principal way neurons send signals
– Means of long-distance neural communication
− Action potentials (APs) do not decay over distance as
graded potentials do
− AP travels in one direction only
A
Yes.
24
Q
Threshold and All-or-None Phenomenon
• Not all depolarization events produce APs
• For an axon to “fire,” depolarization must reach
threshold voltage to trigger AP
• At threshold:
– Membrane is depolarized by 15 to 20 mV
– Na+ permeability increases
– Na+ influx exceeds K+ efflux
– More Na+ channels open - positive feedback cycle
• All or None
– An AP either happens completely, or not at all
A
Yes.
25
Conduction Velocity (“speed” of impulse along nerve)
• AP conduction velocities along axons vary widely:
− Fast: pathways for balance
− Slow: most gut pathways
• Conduction velocity depends on two factors:
Axon diameter
− Larger diameter axons usually faster
Degree of myelination
− Two types of conduction depending on presence or
absence of myelin
Continuous conduction (slow – nonmyelinated)
Saltatory conduction (fast – myelinated)
Yes.
26
Electrical Synapses
• Less common than chemical synapses
• Neurons are electrically coupled
– Joined by gap junctions that connect cytoplasm of
adjacent neurons
– Communication is very rapid and may be unidirectional
or bidirectional
– Found in some brain regions responsible for eye
movements or hippocampus in areas involved in
emotions and memory
– Most abundant in embryonic nervous tissue
Yes.
27
Chemical Synapses: Postsynaptic Potentials
• Postsynaptic neurotransmitter receptors cause
graded potentials - via chemically gated channels
• Graded potentials vary in strength based on:
– Amount of neurotransmitter released
– Time neurotransmitter stays in cleft
• Neurotransmitters can cause two types of
postsynaptic potentials
– EPSP: excitatory postsynaptic potentials
– IPSP: inhibitory postsynaptic potentials
Yes.
28
Integration & Modification of Synaptic Events:
• (1) Summation by the postsynaptic neuron
– Most neurons receive both excitatory and inhibitory
inputs from thousands of other neurons
– A single EPSP cannot induce an AP in a neuron
• EPSPs and IPSPs can summate to influence
postsynaptic neuron
• If EPSPs predominate and bring to threshold, an AP will be
generated
• Two types of summations:
− Temporal: quick succession of impulses
− Spatial: many impulses simultaneously
Yes.
29
(2) Synaptic potentiation “Neuron workout”
− Repeated use of synapse increases ability of
presynaptic cell to excite postsynaptic neuron
• Ca2+ concentration increases in
presynaptic terminal
• More neurotransmitter released
• More EPSPs in postsynaptic
neuron
• More Ca2+ activates postsynaptic
receptors to be more effective
Integration & Modification of Synaptic Events (cont)
− Long-term potentiation: facilitates learning and memory
Yes.
30
Presynaptic inhibition
− Release of excitatory neurotransmitter by one neuron is inhibited
by another neuron via an axoaxonal synapse
– Less neurotransmitter is released, leading to smaller EPSPs
Yes.
31
```
Neurotransmitters
− Classification by chemical structure
− Classification by function
− Neurotransmitter receptor types
• Neural processing & circuitry
```
Yes
32
Neurotransmitters: “language of the nervous system”
• 50 or more neurotransmitters have been
identified
• Each binds with a fairly specific receptor
• A neuron can release more than one
neurotransmitter
• different neurotransmitters released at different
stimulation frequencies
• Classified by:
– Chemical structure
– Function
Yes
33
```
Classification of Neurotransmitters:
by Chemical Structure
• Acetylcholine (Ach)
– First identified and best understood
– Released in:
• neuromuscular junctions (Somatic NS)
• neurons in the Autonomic Nervous System
• some CNS regions
– Degraded by enzyme acetylcholinesterase
(AChE)
```
Yes
34
Classification of Neurotransmitters:
by Chemical Structure (cont)
• Biogenic amines
– Catecholamines (CA)
• Dopamine, norepinephrine (NE), and epinephrine (E)
– Indolamines
• Serotonin:
• Histamine:
– All active in brain: roles in emotional behaviors and
biological clock, learning, motor control.
– CA’s released by some ANS neurons
• Especially NE and E
– Imbalances in CNS can be associated with mental
illness, movement disorders etc
Yes
35
Classification of Neurotransmitters:
by Chemical Structure (cont)
Amino acids
– Amino acids make up all proteins: therefore, it is
difficult to prove which are neurotransmitters
– Amino acids that are proven neurotransmitters
• Glutamate
• Aspartate
• Glycine
• GABA: gamma (γ)-aminobutyric acid (inhibitory in CNS)
Yes.
36
Classification of Neurotransmitters:
by Chemical Structure (cont)
Peptides (neuropeptides)
• Endorphins act as natural opiates
• Purines
• ATP, the energy molecule, is now considered
a neurotransmitter
• Gases and lipids
• Endocannabinoids
• Believed to be involved in learning and memory,
controlling appetite, and suppressing nausea
Yes.
37
```
Classification of Neurotransmitters:
by functions (then receptor types)
• Neurotransmitters exhibit a great diversity of
functions
• Neurotransmitter functions can be
grouped into two classifications:
– Effects: Excitatory vs Inhibitory
– Actions: Direct vs Indirect
```
Yes.
38
Classification of Neurotransmitters by function:
(1) Effects
• Effects: excitatory versus inhibitory
– Neurotransmitter effects can be excitatory
(depolarizing) and/or inhibitory
(hyperpolarizing)
– Effect determined by receptor to which it
binds
– ACh is excitatory at neuromuscular junctions in
skeletal muscle
– ACh is inhibitory in cardiac muscle
Yes.
39
Classification of Neurotransmitters by function:
(2) Actions
• Actions: direct versus indirect
– Direct action: neurotransmitter binds directly
to, and directly open, ion channels
• Promotes rapid responses by altering membrane potential
• Example: Ach on neuromuscular junction receptors
– Indirect action: neurotransmitter acts through
intracellular second messengers, usually G
protein pathways
• Similar mechanism on G proteins as some hormones
• Example: Ach on muscarinic receptors in the ANS
Yes.
40
Neurotransmitter Receptor Types:
(1) Ion channel-linked receptors
– Excitatory receptors - channels for small
cations
• Na+ influx contributes most to depolarization
• Postsynaptic Ach receptors at the neuromuscular
junction are an example
– Inhibitory receptors - allow Cl– influx that
causes hyperpolarization
• GABAA receptors in the CNS
− Action is immediate and brief
Yes.
41
Neurotransmitter Receptor types:
(2) G protein-linked receptors
• G protein–linked receptors
– Responses are indirect, complex, slow, and often prolonged
– Involves transmembrane protein complexes
– Some indirectly open ion channels
– Others can cause widespread metabolic changes. These are
termed “metabotropic” receptors
– Examples:
• Muscarinic ACh receptors (heart muscle)
• Dopamine receptors in CNS (pleasure, memory, learning,
motor control) - “metabotropic”
Yes.
42
Neurotransmitter Receptor types:
G protein-linked receptors (cont.)
• G protein–linked receptors (cont.)
– Mechanism:
• Neurotransmitter binds to G protein–linked receptor, activating
G protein
• Activated G protein controls production of second
messengers, such as cyclic AMP, cyclic GMP,
diacylglycerol, or Ca2+
• Second messengers can then:
– Open or close ion channels
– Activate kinase enzymes
– Phosphorylate channel proteins
– Activate genes and induce protein synthesis
Yes.
43
```
Neural Integration
• Neural integration:
– neurons functioning together in groups
• Neuronal pool:
– functional groups of neurons
• Patterns of processing
– Serial processing (reflex arcs)
– Parallel processing
• Types of neural circuits
```
Yes.
44
Patterns of Neural Processing
• Serial processing
– Input travels along one pathway to a specific
destination
• One neuron stimulates next one, which stimulates
next one, etc.
– System works in all-or-none manner to produce
specific, anticipated response
– Best example is a spinal reflex
Yes.
45
Patterns of Neural Processing (cont.)
Example: CNS overlay on the
withdrawal reflex (boiling hot coffee)
– Do I want to drop it?
– How long can I bear it?
– Where can I put it down (visual input etc.)?
!?
Parallel processing
– Input travels along several pathways
– Different parts of circuitry deal simultaneously with the information
– One stimulus promotes numerous responses
– Important for higher-level mental functioning
Yes.
46
```
Types of Neuronal Circuits
• Circuits: patterns of synaptic connections in
neuronal pools
• Four types of circuits
1. Diverging
2. Converging
3. Reverberating
4. Parallel after-discharge
```
Yes.
47
Brain Regions and Organization (cont.)
• Gray matter: short, nonmyelinated neurons and
cell bodies
• White matter: myelinated and nonmyelinated
axons
• Basic pattern found in CNS: central cavity
surrounded by gray matter, with white matter
external to gray matter
Yes.
48
Cerebral Cortex
• Cerebral cortex is “executive suite” of brain
• Site of conscious mind: awareness, sensory perception,
voluntary motor initiation, communication, memory storage,
understanding
• Thin (2–4 mm) superficial layer of gray matter
– Composed of neuron cell bodies, dendrites, glial cells, and
blood vessels, but no axons
• 40% of mass of brain
• Functional imaging (PET and MRI) of brain show specific
motor and sensory functions are located in discrete cortical
areas called domains
– Higher functions are spread over many areas
Yes.
49
Cerebral Cortex (cont.)
• Four general considerations of cerebral cortex:
1. Contains three types of functional areas:
• Motor areas:
• Sensory areas:
• Association areas:
2. Each hemisphere is concerned with
contralateral (opposite) side of body
3. Lateralization (specialization) of cortical
function can occur in only one hemisphere
4. Conscious behavior involves entire cortex in
one way or another
Yes.
50
Motor areas
– Located in frontal lobe, motor areas act to control
voluntary movement
– Primary motor cortex in precentral gyrus
– Premotor cortex anterior to precentral gyrus
– Broca’s area anterior to inferior premotor area
– Frontal eye field within and anterior to premotor
cortex; superior to Broca’s area
Yes.
51
Cerebral Cortex (cont.)
– Premotor cortex
• Helps plan movements
– Staging area for skilled motor activities
• Controls learned, repetitious, or patterned motorskills
• Coordinates simultaneous or sequential actions
• Controls voluntary actions that depend on sensory feedback
– Broca’s area
• Present in one hemisphere (usually the left)
• Motor speech area that directs muscles of speech production
• Active in planning speech and voluntary motor activities
– Frontal eye field
• Controls voluntary eyemovements
Yes
52
Cerebral Cortex (cont.)
– Primary (somatic) motor cortex
• Located in precentral gyrus of frontal lobe
• Pyramidal cells: large neurons that allow conscious
control of precise, skilled, skeletal muscle movements
• Pyramidal (corticospinal) tracts: formed from long
axons that project down spinal cord
• Somatotopy: all muscles of body can be mapped to
area on primary motor cortex
– Motor homunculi: upside-down caricatures represent
contralateral motor innervation of body regions
Yes.
53
Clinical – Homeostatic Imbalance 12.1
• Damage to areas of primary motor cortex, as seen in a
stroke, paralyzes muscles controlled by those areas
• Paralysis occurs on opposite side of body from damage
• Muscle strength or ability to perform discrete individual
movements is not impaired; only control over movements is lost
– Example: damage to premotor area controlling movement of
fingers would still allow fingers to move, but voluntary control
needed to type would be lost
• Other premotor neurons can be reprogrammed to take over skill
of damaged neurons
– Would require practice, just as the initial learning process did
Yes.
54
Cerebral Cortex (cont.)
• Sensory areas
– Areas of cortex concerned with conscious
awareness of sensation
– Occur in parietal, insular, temporal, and occipital
lobes
– Eight main areas include primary
somatosensory cortex, somatosensory
association cortex, visual areas, auditory
areas, vestibular cortex, olfactory cortex,
gustatory cortex, and visceral sensory area
Yes.
55
Cerebral Cortex (cont.)
– Primary somatosensory cortex
• Located in postcentral gyri of parietal lobe
• Capable of spatial discrimination: identification of
body region being stimulated
• Somatosensory homunculus: upside-down
caricatures represent contralateral sensory input from
body regions
– Somatosensory association cortex
• Posterior to primary somatosensory cortex
• Determines size, texture, and relationship of parts of
objects being felt
Yes.
56
Cerebral Cortex (cont.)
– Visual areas
• Primary visual (striate) cortex located on extreme
posterior tip of occipital lobe
– Most buried in calcarine sulcus
– Receives visual information from retinas
• Visual association area surrounds primary visual
cortex
– Uses past visual experiences to interpret visual stimuli
(color, form, or movement)
» Example: ability to recognize faces
– Complex processing involves entire posterior half of
cerebral hemispheres
Yes.
57
Cerebral Cortex (cont.)
– Auditory areas
• Primary auditory cortex
– Superior margin of temporal lobes
– Interprets information from inner ear as pitch, loudness,
and location
• Auditory association area
– Located posterior to primary auditory cortex
– Stores memories of sounds and permits perception of
sound stimulus
– Vestibular cortex
• Posterior part of insula and adjacent parietal cortex
• Responsible for conscious awareness of balance
(position of head in space)
Yes.
58
Cerebral Cortex (cont.)
– OIfactory cortex
• Primary olfactory (smell) cortex
– Medial aspect of temporal lobes (in piriform lobes)
– Part of primitive rhinencephalon, along with olfactory
bulbs and tracts
– Remainder of rhinencephalon in humans becomes part
of limbic system
– Involved in conscious awareness of odors
Yes.
59
```
Cerebral Cortex (cont.)
– Gustatory cortex
• In insula just deep to temporal lobe
• Involved in perception of taste
– Visceral sensory area
• Posterior to gustatory cortex
• Conscious perception of visceral sensations, such as
upset stomach or full bladder
```
Yes.
60
Clinical – Homeostatic Imbalance 12.2
• Damage to the primary visual cortex results in
functional blindness
• By contrast, individuals with a damaged visual
association area can see, but they do not
comprehend what they are looking at
Yes.
61
Cerebral Cortex (cont.)
• Multimodal association areas
– Receive inputs from multiple sensory areas
– Send outputs to multiple areas
– Allows us to give meaning to information
received, store in memory, tie to previous
experience, and decide on actions
– Sensations, thoughts, emotions become
conscious: makes us who we are
– Broadly divided into three parts: anterior
association area, posterior association area,
and limbic association area
Yes.
62
Cerebral Cortex (cont.)
– Anterior association area
• Also called prefrontal cortex
• Most complicated cortical region
• Involved with intellect, cognition, recall, and
personality
• Contains working memory needed for abstract ideas,
judgment, reasoning, persistence, and planning
• Development depends on feedback from social
environment
Yes.
63
Cerebral Cortex (cont.)
– Posterior association area
• Large region in temporal, parietal, and occipital lobes
• Plays role in recognizing patterns and faces and
localizing us in space
• Involved in understanding written and spoken
language (Wernicke’s area)
– Limbic association area
• Part of limbic system
• Involves cingulate gyrus, parahippocampal gyrus, and
hippocampus
• Provides emotional impact that makes a scene
important to us and helps establish memories
Yes.
64
Clinical – Homeostatic Imbalance 12.3
• Tumors or other lesions of the anterior association area may
cause mental and personality disorders, including loss of
judgment, attentiveness, and inhibitions
– Affected individual may be oblivious to social restraints,
perhaps becoming careless about personal appearance,
or take risks
• Different problems arise for individuals with lesions in the
part of the posterior association area that provides
awareness of self in space
– Individual may refuse to wash or dress the side of the
body opposite to lesion because “that doesn’t belong to
me
Yes.
65
Cerebral Cortex (cont.)
• Lateralization of cortical functioning
– Lateralization: division of labor between
hemispheres
• Hemispheres are not identical
– Cerebral dominance: refers to hemisphere that
is dominant for language
• 90% of humans have left-sided dominance
• Usually results in right-handedness
• In other 10%, roles of hemispheres are reversed
Yes.
66
Cerebral Cortex (cont.)
• Lateralization of cortical functioning (cont.)
– Left hemisphere
• Controls language, math, and logic
– Right hemisphere
• Visual-spatial skills, intuition, emotion, and artistic and
musical skills
– Hemispheres communicate almost
instantaneously via fiber tracts and functional
integration
Yes.
67
Cerebral White Matter
• Responsible for communication between
cerebral areas, and between cortex and lower
CNS
• Consists of myelinated fibers bundled into large
tracts
Yes.
68
Basal Nuclei (Ganglia)
• Functions of basal nuclei are thought to:
– Influence muscle movements
– Play role in cognition and emotion
– Regulate intensity of slow or stereotyped
movements
– Filter out incorrect/inappropriate responses
– Inhibit antagonistic/unnecessary movements
• Parkinson’s disease and Huntington’s disease
are disorders of the basal nuclei
Yes.
69
Thalamus (cont.)
• Makes up 80% of diencephalon
– Contains several nuclei, named for location
• Main thalamic function is to act as relay station for
information coming into cortex
– Sorts, edits, and relays ascending input such as:
• Impulses from hypothalamus for regulating emotion and visceral
function
• Impulses from cerebellum and basal nuclei to help direct motor
cortices
• Impulses for memory or sensory integration
• Overall, it acts to mediate sensation, motor activities,
cortical arousal, learning, and memory
Yes
70
Hypothalamus
• Located below thalamus
• Forms cap over brain stem and forms
inferolateral walls of third ventricle
• Contains many important nuclei such as:
– Mammillary bodies: paired anterior nuclei that
act as olfactory relay stations
• Infundibulum: stalk that connects to pituitary
gland
Yes.
71
Hypothalamus (cont.)
• Located below thalamus
• Contains many important nuclei such as:
– Mammillary bodies: paired anterior nuclei that act as
olfactory relay stations
• Infundibulum: stalk that connects to pituitary gland
• It is the main visceral control and regulating center that is
vital to homeostasis
• Chief homeostasis controls:
– Controls autonomic nervous system
– Initiates physical responses to emotions
Yes.
72
Hypothalamus (cont.)
• The hypothalamus also:
– Regulates body temperature: sweating or shivering
– Regulates hunger and satiety in response to nutrient
blood levels or hormones
– Regulates water balance and thirst
– Regulates sleep-wake cycles
– Suprachiasmatic nucleus of thalamus sets our biological
clock
– Controls endocrine system functions such as:
• Secretions of anterior pituitary gland
• Production of posterior pituitary hormones
Yes.
73
```
Clinical – Homeostatic Imbalance 12.4
• Hypothalamic disturbances cause a number of
disorders such as:
– Severe body wasting
– Obesity
– Sleep disturbances
– Dehydration
– Emotional imbalances
• Implicated in failure to thrive: delay in growth or
development
– Occurs when child is deprived of a warm,
nurturing relationship
```
Yes.
74
```
Epithalamus
• Most dorsal portion of diencephalon
• Forms roof of third ventricle
• Contains pineal gland (body)
– Extends from posterior border
– Secretes melatonin that helps regulate sleepwake cycle
```
Yes.
75
```
Midbrain (cont.)
– Substantia nigra: functionally linked to
basal nuclei
• Parkinson’s disease is degeneration
of this area
– Red nucleus: relay nuclei for some
descending limb flexion motor pathways
• Part of reticular formation
```
Yes.
76
Pons
• Located between midbrain and medulla oblongata
• Fourth ventricle separates pons from cerebellum
• Composed of conduction tracts:
– Longitudinal fibers connect higher brain centers and
spinal cord
– Transversal/dorsal fibers relay impulses between motor
cortex and cerebellum
• Origin of cranial nerves V (trigeminal), VI
(abducens), and VII (facial)
• Some nuclei play role in reticular formation, and
some help maintain normal rhythm of breathing
Yes.
77
Medulla Oblongata
• Also known as medulla
• Blends into spinal cord at foramen magnum
• Contains fourth ventricle
– Continuation of central canal of spinal cord
– Medulla and pons form ventral wall
– Contains choroid plexus
Yes.
78
```
Medulla Oblongata (cont.)
• Structures of the medulla oblongata
– Pyramids:
– Decussation of the pyramids:
– Olives:
– Cranial nerves VIII, IX, X, and XII
– Vestibular and cochlear nuclei:
– Nucleus cuneatus and nucleus gracilis:
```
Yes.
79
```
Medulla Oblongata (cont.)
• Functions of the medulla oblongata
– Medulla is an autonomic reflex center
• Many functions overlap with hypothalamus
– Hypothalamus relays instructions via medulla
– Functional groups of medulla include:
• Cardiovascular center
– Cardiac center
– Vasomotor center
• Respiratory centers
• Various other centers regulate:
– Vomiting ,Hiccupping ,Swallowing ,Coughing&Sneezing
```
Yes.
80
Cerebellum and its Anatomy
• Cerebellar hemispheres connected by wormlike vermis
• Folia: transversely oriented gyri
• Each hemisphere has three lobes
– Anterior, posterior, and flocculonodular
• Contains thin cortex of gray matter with distinctive treelike
pattern of white matter called arbor vitae
• Purkinje fibers originate in cortex, synapse with cerebellum
• Cerebellar homunculi show sensory maps of entire body
Yes.
81
Cerebellar Processing
• Cerebellum fine-tunes motor activity as follows:
1. Receives impulses from cerebral cortex of intent to
initiate voluntary muscle contraction
2. Receives signals from proprioceptors throughout
body, as well as visual and equilibrium pathways that:
• Pathways continuously “inform” cerebellum of body’s
position and momentum
3. Cerebellar cortex calculates the best way to smoothly
coordinate muscle contraction
4. Sends “blueprint” of coordinated movement to cerebral
motor cortex and brain stem nuclei
Yes.
82
Cognitive Functions of Cerebellum
• Neuroimaging suggests that cerebellum plays
role in thinking, language, and emotion
• As it does for motor processes, it may compare
actual output of higher functions with expected
output and adjust accordingly
Yes.
83
```
Functional Brain Systems
• Networks of neurons that work together but
span wide areas of brain
– Limbic system
– Reticular formation
```
Yes.
84
Limbic System
• Limbic system puts emotional responses to odors
– Example: skunks smell bad
• Most output relayed via hypothalamus
– Hypothalamus plays a role in psychosomatic illnesses
• Limbic system interacts with prefrontal lobes
– Allows us to react emotionally to things we consciously
understand to be happening
– Makes us consciously aware of emotional richness in our
lives
• Hippocampus and amygdaloid body also play a role in
memory
Yes.
85
Reticular Formation (cont.)
• Reticular activating system (RAS)
– Sends impulses to cerebral cortex to keep it conscious and alert
– Filters out repetitive, familiar, or weak stimuli (~99% of all stimuli is
not relayed to consciousness)
– Inhibited by sleep centers, alcohol, drugs
– Severe injury can result in permanent unconsciousness (coma)
• Motor function of reticular formation helps control coarse limb
movements via reticulospinal tracts
• Reticular autonomic centers regulate visceral motor
functions
– Vasomotor centers
– Cardiac center
– Respiratory centers
Yes.
86
```
Higher Mental Functions
Analysis of higher mental functions include:
– Language
– Memory
– Brain waves and EEGs
– Consciousness
– Sleep and sleep-wake cycles
```
Yes.
87
Language
• Language implementation system involves
association cortex of left hemisphere
• Main areas include:
– Broca’s area: involved in speech production
• Patients with lesions in Broca’s understand
words, but cannot speak
– Wernicke’s area: involved in understanding
spoken and written words
• Patients with lesions in Wernicke’s can
speak, but words are non sensible
• Corresponding areas on right side are involved
with nonverbal language components
Yes.
88
```
Memory
• Memory:
• Different kinds of memory
– Declarative memory of facts
– Procedural memory of skills
– Motor memory memory of motor skills
– Emotional memory memory of experiences
• Two stages of declarative memory storage:
– Short-term memory
– Long-term
Emotional state:
Rehearsal: repetition and practice
Association:
Automatic memory:
Memory consolidation
```
Yes.
89
Clinical – Homeostatic Imbalance 12.5
• Damage to hippocampus or surrounding temporal lobe
structures on either side result in only slight memory loss
• Bilateral destruction causes widespread amnesia
• Anterograde amnesia: consolidated memories are not lost,
but new inputs are not associated with old one
– Person lives in the here and now
– Memory of conversations from just 5 minutes before
would not be remembered
Retrograde amnesia: loss of memories formed in the
distant past
Yes.
90
Brain Wave Patterns and the EEG
• Brain waves reflect electrical activity of higher mental
functions
• Normal brain functions are continuous and hard to
measure
• Electroencephalogram (EEG) records electrical activity that
accompanies brain function
– Used in diagnosis of disease conditions, in research and
also to determine brain death
– Electrodes placed on scalp measure electrical potential
differences between various cortical areas
Yes.
91
Brain Wave Patterns and the EEG (cont.)
• Measures wave frequency in Hertz (Hz), numbers
of peaks per second (1 Hz = 1 peak per second)
• Can be grouped into four classes based on Hz:
Yes.
92
Clinical – Homeostatic Imbalance 12.6
• Epileptic seizure:
• Victim of epilepsy may lose consciousness, fall stiffly, and
have uncontrollable jerking
• Aura (sensory hallucination) may precede seizure
• Absence seizures (formerly petit mal)
– Mild seizures of young children: expression goes blank
for few seconds
• Tonic-clonic seizures (formerly grand mal)
• Control of epilepsy includes anticonvulsive drugs, vagus
nerve stimulator or deep brain stimulator implantations that
deliver pulses to vagus nerve or directly to brain to stabilize
brain activity
Yes.
93
Consciousness
• Consciousness involves:
– Perception of sensation
– Voluntary initiation and control of movement
– Capabilities associated with higher mental processing
(memory, logic, judgment, etc.)
• Clinically defined on continuum that grades behavior in
response to stimuli: alertness, drowsiness (lethargy), stupor,
and coma
• Current suppositions on consciousness
– Involves simultaneous activity of large cortical areas
– Superimposed on other neural activities
– Holistic and totally interconnected
Yes.
94
Clinical – Homeostatic Imbalance 12.7
• Except during sleep, loss of consciousness signals that
brain function is impaired
• Fainting or syncopy: brief loss of consciousness
– Most often due to inadequate cerebral blood flow
– Due to low blood pressure or ischemia from hemorrhage
or sudden, severe emotional stress
• Coma: unconsciousness for extended period
– Not the same as deep sleep; oxygen consumption is
lowered
• Brain death: irreversible coma
– Ethical and legal issues surround decisions on whether
person is dead or alive
Yes.
95
Sleep and Sleep-Wake Cycles (cont.)
• Sleep regulation
• Importance of sleep
– Slow-wave sleep (NREM stages 3 and 4) presumed to be restorative
stage
– People deprived of REM sleep become moody and depressed
– REM sleep may:
1. Give brain opportunity to analyze day’s events and work
through emotional events or problems
2. Eliminate unneeded synapses that were formed (dream to
forget)
3. Daily sleep requirements decline with age
4. Stage 4 sleep declines steadily and may disappear after age
60
Yes
96
```
Clinical – Homeostatic Imbalance 12.8
• Sleep disorders include:
• Narcolepsy: abrupt lapse into sleep
from awake state
– Orexins (“wake-up” chemicals from
hypothalamus) may be being
destroyed by immune system
• Offer key to possible treatment
• Insomnia: chronic inability to obtain
amount or quality of sleep needed
– May be treated by blocking orexin
action
```
Yes.
97
Clinical – Homeostatic Imbalance 12.9
• Meningitis: inflammation of the meninges
• May spread to CNS, which would lead to
inflammation of the brain, referred to as
encephalitis
• Meningitis is usually diagnosed by observing
microbes in a sample of CSF obtained via
lumbar puncture
Yes.
98
Cerebrospinal Fluid (CSF)
Cerebrospinal fluid (CSF)
• Composed of watery solution formed from blood plasma, but with less
protein and different ion concentrations from plasm
Choroid plexus:
• CSF is filtered from plexus at constant rate
– Ependymal cells use ion pumps to control composition of CSF and
help cleanse CSF by removing wastes
– Cilia of ependymal cells help to keep CSF in motion
• Normal adult CSF volume of ~150 ml is replaced every 8 hours
Yes.
99
Blood Brain Barrier
• Helps maintain stable environment for brain
• Substances must past through three layers before gaining entry into
neurons
1. Continuous endothelium of capillary walls
2. Thick basal lamina around capillaries
3. Feet of astrocytes surrounding neuronsBarrier is selective, but not
absolute
• Allows certain nutrients to move by facilitated diffusion
• Metabolic wastes, proteins, toxins, most drugs, small
nonessential amino acids, K+ denied
• Allows any fat-soluble substances to pass, including alcohol,
nicotine, and anesthetics
• Absent in some areas, such as vomiting center and
hypothalamus
• Necessary to monitor chemical composition and temperature of
blood
Yes.
100
```
Brain Injuries and Disorders
Traumatic Brain Injuries
– Concussion
– Contusion
– Subdural or subarachnoid hemorrhage
– Cerebral edema
```
Yes.
101
Cerebrovascular Accidents (CVAs)
• Also referred to as “strokes”
• Ischemia:
– Glutamate acts as excitotoxin, worsening
condition
• Hemiplegia
• Transient ischemic attacks (TIAs): temporary
episodes of reversible cerebral ischemia
• Tissue plasminogen activator (TPA) is only
approved treatment for stroke
Degenerative Brain Disorders
Yes.
102
```
Overview of ANS Lecture
• ANS vs Somatic Nervous System
− Differences (effectors, pathways, ganglia, neurotransmitters)
− Functional overlap
• Parasympathetic vs Sympathetic Divisions (overview)
− Functional differences
− Anatomical differences
− ANS (“visceral”) Reflexes
• Neurotransmitters in the ANS
− Cholinergic and Adrenergic fibres
− Receptor types
• Parasympathetic and Sympathetic Divisions
− Effects on various organs and systems
− Levels of neural control of the ANS
```
Yes.
103
ANS versus Somatic Nervous System
– Effectors
– ANS: smooth muscle, cardiac muscle, glands
– SNS: skeletal muscle
– Efferent (motor) pathways and ganglia
– ANS: two neuron chain with postganglionic neuron outside CNS
(ie cell body and axon)
– SNS: Cell body in CNS with long fibre extending to skeletal
muscle effector
Target organ responses to neurotransmitters
– ANS: ACh at all ganglia. ACh at Parasymapthetic effectors (+/-).
NE at Sympathetic effectors
– SNS: ACh at neuromuscular junction (+)
Yes.
104
Overlap of Somatic and Autonomic Function
• Higher brain centers regulate and coordinate both systems
• Most spinal and many cranial nerves contain both somatic
and autonomic fibers
• Adaptations usually involve both skeletal muscles and
visceral organs
– Example: Active muscles require more oxygen and glucose, so
ANS nerves speed up heart rate and open airways
Yes.
105
Role of the Parasympathetic Division
• Keeps body energy use as low as possible, even while carrying out
maintenance activities
– Directs digestion, diuresis, defecation
• Referred to as “rest-and-digest” or “house keeping” system
• Example: person relaxing and reading after a meal
– Blood pressure, heart rate, and respiratory rates are low
– Gastrointestinal tract activity is high
– Pupils constricted, lenses accommodated for close vision
Yes.
106
Role of the Sympathetic Division
• Mobilizes body during activity
• Referred to as “fight-or-flight” system
• Exercise, excitement, emergency, embarrassment activates sympathetic
system
– Increased heart rate; dry mouth; cold, sweaty skin; dilated pupils
• During vigorous physical activity:
– Shunts blood to skeletal muscles and heart
– Dilates bronchioles
– Causes liver to release glucose
Yes.
107
Cholinergic Receptors
• Two types of cholinergic receptors bind ACh
1. Nicotinic receptors – always stimulatory
2. Muscarinic receptors- stimulatory or inhibitory
• Named after drugs that bind to them and mimic
ACh effects: nicotine and muscarine
Yes.
108
```
Adrenergic Receptors
• Two major classes that respond to
Noradrenaline NE or epinephrine E
– Alpha (α) receptors
• Divided into subclasses: α1, α2
– Beta (β) receptors
• Divided into subclasses: β1, β2, β3
```
Yes.
109
Parasympathetic and Sympathetic Interactions
• Most visceral organs have dual innervation
• Action potentials fire along axons of both ANS divisions:
– producing a dynamic antagonistic interaction
– works to precisely control visceral activity
• Both ANS divisions are partially active, resulting in a basal
sympathetic and parasympathetic tone
• One division usually predominates but change can be rapid:
− e.g. changes in heart rate with exercise
• In a few cases, divisions have a cooperative effect
− e.g. male erection (parasympathetic) and ejaculation (sympathetic)
Yes.
110
Unique Roles of the Sympathetic Division
• Exclusive innervation of some effectors:
− Adrenal medulla, sweat glands, arrector pili muscles, kidneys,
and almost all blood vessels receive only sympathetic fibers
• Thermoregulatory responses to heat
− Dilatation of skin blood vessels, allowing heat to escape
− Activate sweat glands
− (When body temperatures drop, blood vessels constrict)
• Release of renin from kidneys
− Sympathetic system causes release of renin from kidneys that in turn
activates a system that increases blood pressure
• Metabolic effects
− Increases metabolic rates of cells
− Raises blood glucose levels
− Mobilizes fats for use as fuels
Yes.
111
Localized vs Diffuse Effects
• Parasympathetic division tends to elicit short-lived and
highly localized control over effectors
– ACh is quickly destroyed by acetylcholinesterase
– In some cases, effects are sustained e.g. vagal tone at rest
• Sympathetic division tends to be longer-lasting with
body wide effects
– NE is inactivated more slowly than ACh
– NE and epinephrine hormones from adrenal medulla have
prolonged effects that last even after sympathetic signals stop
• “Diffuse/Systemic effects”
Yes.
112
Levels of motor control: Types of reflex activity
5
• Inborn (intrinsic) reflex: rapid, involuntary, predictable motor response to
stimulus
− Examples: maintain posture, control of visceral activities
− Can be modified by learning and conscious effort
• Learned (acquired) reflexes result from practice or repetition
− Example: driving skills
Yes.
113
Components of a Reflex Arc (cont.)
8
• Reflexes are classified functionally as:
– Somatic reflexes
• Activate skeletal muscle
– Autonomic (visceral) reflexes
• Activate visceral effectors
− smooth muscle (blood vessels, lungs, gut etc.)
− cardiac muscle
− glands including the adrenal medulla, sweat glands, salivary
glands etc.
Yes.
114
Spinal Reflexes
9
• Spinal reflexes occur without direct involvement of higher
brain centers
– Brain is still advised of spinal reflex activity and may have an effect
on the reflex
• Testing of somatic reflexes important clinically to assess condition of
nervous system
– If exaggerated, distorted, or absent, may indicate degeneration or
pathology of specific nervous system regions
– Most commonly assessed somatic reflexes are stretch, flexor, and
superficial reflexes
Yes.
115
Stretch and Tendon Reflexes
10
• To smoothly coordinate skeletal muscle, nervous system must receive
proprioceptor input regarding:
– Muscle Length sent from muscle spindles
– Muscle Tension sent from tendon organs
• Tendon organs also have protective function
− Length and stretch information is dynamic
Yes.
116
Stretch Reflexes (cont.)
15
• Stretch Reflex
− Stretch Reflex sets skeletal muscle’s length and tone
− Basic pathway of stretch reflex is monosynaptic and ipsilateral
(motor activity is on same side of body)
− Example: postural muscles maintain specific tone through the stretch
reflex
• Reciprocal inhibition can also occur
− Afferent fibers synapse with interneurons that inhibit motor neurons of
antagonistic muscles
− This component is polysynaptic and ipsilateral
− Overall example: In patellar reflex, stretched muscle (quadriceps)
contracts (monsynaptic), and antagonists (hamstrings) relax
(polysynaptic)
Yes.
117
Stretch Reflexes (cont.): Spindle sensitivity
17
• Adjusting muscle spindle sensitivity
– When neurons are stimulated by brain, spindle is stretched, and
contraction force is maintained or increased
• Example: Gymnast on balance beam – razor sharp balance reflexes.
Important as speed and difficulty increase.
– If neurons are inhibited, spindle becomes less responsive, and muscle
relaxes
• Example: Pitching a baseball. Winding back with “loose spindle” allows
muscle to load more by stretching more. Greater force with forward
pitch.
Yes.
118
Tendon Reflexes
18
• Tendon reflex
– Involves polysynaptic reflexes
– Helps prevent damage due to excessive stretch
– Important for smooth onset and safe termination of
muscle contraction
• Contraction or passive stretch activates tendon reflex
• Afferent impulses transmitted to spinal cord
– Contracting muscle relaxes; antagonist contracts
(reciprocal activation)
• Information transmitted simultaneously to cerebellum and used to adjust
muscle tension
Yes.
119
```
The Flexor (Withdrawal) Reflex
20
• Initiated by painful stimulus
• Automatic withdrawal of threatened body part
• Ipsilateral and polysynaptic
- Many different muscles may be called into play, so needs to be
polysynaptic
• Protective and important to survival
• Brain can override
```
Yes.
120
The Crossed-Extensor Reflex
21
• Crossed extensor reflex occurs with flexor reflexes in
weight-bearing limbs to maintain balance
− Accompanies the ipsilateral withdrawal reflex
− Essentially a contralateral extensor reflex
• Taken together:
− Stimulated side is withdrawn (ipsilateral flexor reflex)
− Opposite side extended (contralateral crossed
extensor)
• Example:
− Stepping barefoot on broken glass causes
damaged leg to withdraw and opposite leg to
extend to support weight shift and balance
Yes.
121
Superficial Reflexes
23
• Superficial reflexes are usually elicited by cutaneous stimulation of
area
• Clinically important reflexes signal problems in upper motor pathways or
cord-level reflex arcs
• Best known:
– Plantar reflex (a withdrawal reflex)
• Many others:
– Corneal reflex (cranial reflex with complex CNS overlays)
Yes.
122
```
Spinal Nerves
3
• 31 pairs of spinal nerves
• All are mixed nerves named for point of issue from spinal cord
• Supply all body parts except head and part of neck
– 8 pairs of cervical nerves (C1–C8
)
– 12 pairs of thoracic nerves (T1–T12)
– 5 pairs of lumbar nerves (L1–L5
)
– 5 pairs of sacral nerves (S1–S5
)
– 1 pair of tiny coccygeal nerves (C0
)
```
Yes.
123
Somatic innervation of Specific Body Regions:
Roots, Rami and nerve plexuses
9
• Roots (dorsal and ventral)
− Lie medial to spinal nerve - fuse to form each spinal nerve
− Each root is purely sensory or motor
• Rami (dorsal and ventral)
− Lie distal to spinal nerves - are lateral branches of spinal nerve
− Each ramus carries both sensory and motor fibres
• Dorsal rami supply posterior body trunk
• Ventral rami supply rest of trunk and limbs
• Nerve plexuses are interlacing networks of ventral rami
• Only ventral rami form plexuses
• Found in cervical, brachial, lumbar, and sacral areas
• Not found in T2-T12
Yes.
124
Homeostatic Imbalance:
Phrenic nerve within the cervical plexus
13
• Irritation of the phrenic nerve causes spasms of the diaphragm,
also called hiccups
• If both phrenic nerves are severed, or if C3–C5
region of spinal
cord is destroyed:
− Diaphragm becomes paralyzed
− Respiratory arrest occurs
− Mechanical respirator required to stay alive
Yes.
125
```
Homeostatic Imbalance: Ulnar & radial nerves
17
• Ulnar nerve is very vulnerable to injury
− Striking the “funny bone,” the spot
where this nerve rests against
medial epicondyle, can make the
little finger tingle.
• Radial Nerve
− Falling asleep with arm extended
compresses nerve and impairs
blood supply
− “Saturday night paralysis”:
```
Yes.
126
Alcoholism and the Peripheral N.S
27
• Alcoholism can indirectly lead to toxic polyneuropathy in PNS
− Essentially axonal degeneration
− Mainly occurs from inadequate nutrition (thiamine and other B vitamins)
− Thiamine/B vitamins essential for metabolism in nerve and glial cells
− Thinning of myelin sheath and impaired conduction results
• Direct neurotoxicity due to alcohol metabolites can also occur
• Overall, symptoms include:
− Distal sensory disturbances with pain, paresthesia and numbness
− Weakness and atrophy of distal muscles, especially lower limbs
− Loss of tendon jerk reflexes
• CNS symptoms can also be severe
Yes.
127
Receptor level processing in Somatosensory NS
7
• Transduction – “signal generation”: where the stimulus is converted to
graded potentials (two types)
− Generator Potential - directly generates AP within the sensory neuron
− Receptor Potential – indirectly generates AP in another neuron
(postsynaptic)
• Adaptation – “change in sensitivity”
− Rapidly adapting – (e.g. Temperature receptors)
− Slowly adapting – (e.g. Pain receptors)
Yes.
128
Pain
8
• Slowly adapting – warns and requires action
• Caused by various physical or chemical events
− Mediated by a whole range of body chemicals – histamine, K+
, kinins
and prostaglandins, acids (lactic acid);
− Impulses carried at various speeds by small myelinated and nonmyelinated fibres;
− “Centrally” - perception of pain is reduced through blockage of
ascending sensory pathways (endorphins, enkephalins, opiates)
− “Peripherally” - pain is reduced through blocking pain substances (eg
aspirin and prostaglandins)
Yes.
129
Perception of pain (many different “types”)
10
• Slowly adapting – warns and requires action
• Caused by various physical or chemical events
− Mediated by a whole range of body chemicals – histamine, K+
,
kinins and prostaglandins, acids (lactic acid);
− Impulses carried at various speeds by small myelinated and nonmyelinated fibres;
− “Centrally” - perception of pain is reduced through blockage of
ascending sensory pathways (endorphins, enkephalins, opiates)
− “Peripherally” - pain is reduced through blocking pain substances (eg
aspirin and prostaglandins)
Yes.
130
Spinal Cord Cross-sectional Anatomy
• Two lengthwise grooves that run length of cord
partially divide it into right and left halves
– Ventral (anterior) median fissure
– Dorsal (posterior) median sulcus
• Gray matter is located in core, white matter
outside
• Central canal runs length of cord
– Filled with CSF
Yes.
131
Spinal Cord Cross-sectional Anatomy (cont.)
• Gray matter and spinal roots
– Cross section of cord resembles butterfly or letter
“H”
– Three areas of gray matter are found on each
side of center and are mirror images:
• Dorsal horns: interneurons that receive somatic and
visceral sensory input
• Ventral horns: some interneurons; somatic motor
neurons
• Lateral horns (only in thoracic and superior lumbar
regions): sympathetic neurons
Yes.
132
Spinal Cord Cross-sectional Anatomy (cont.)
• Gray matter and spinal roots (cont.)
– Gray commissure: bridge of gray matter that
connects masses of gray matter on either side
• Encloses central canal
– Ventral roots: bundle of motor neuron axons
that exit the spinal cord
– Dorsal roots: sensory input to cord
– Dorsal root (spinal) ganglia: cell bodies of
sensory neurons
– Spinal nerves: formed by fusion of dorsal and
ventral roots
Yes.
133
Spinal Cord Cross-sectional Anatomy (cont.)
• Gray matter and spinal roots (cont.)
– Gray matter divided into four groups based on of
somatic or visceral innervation
• Somatic sensory (SS), visceral sensory (VS),
visceral (autonomic) motor (VM) and somatic
motor (SM)
Yes.
134
Spinal Cord Cross-sectional Anatomy (cont.)
• White matter
– Myelinated and nonmyelinated nerve fibers allow
communication between parts of spinal cord, and
spinal cord and brain
– Run in three directions
• Ascending: up to higher centers (sensory inputs)
• Descending: from brain to cord or lower cord levels
(motor outputs)
• Transverse: from one side to other (commissural
fibers)
Yes.
135
Spinal Cord Cross-sectional Anatomy (cont.)
• White matter (cont.)
• White matter is divided into three white
columns (funiculi) on each side
– Dorsal (posterior)
– Lateral
– Ventral (anterior)
• Each spinal tract is composed of axons with
similar destinations and functions
Yes.
136
Spinal Cord Trauma and Disorders
• Spinal cord trauma
– Localized injury to spinal cord or its roots leads
to functional losses
• Paresthesias: caused by damage to dorsal roots or
sensory tracts
– Leads to sensory function loss
• Paralysis: caused by damage to ventral roots or
ventral horn cells
– Leads to motor function loss
– Two types of paralysis: flaccid or spastic
Yes.
137
Spinal Cord Trauma and Disorders (cont.)
• Spinal cord trauma (cont.)
– Flaccid paralysis: severe damage to ventral
root or ventral horn cells
• Impulses do not reach muscles; there is no voluntary
or involuntary control of muscles
• Muscles atrophy
– Spastic paralysis: damage to upper motor
neurons of primary motor cortex
• Spinal neurons remain intact; muscles are stimulated
by reflex activity
• No voluntary control of muscles
• Muscles often shorten permanently
Yes.
138
Spinal Cord Trauma and Disorders (cont.)
• Spinal cord trauma (cont.)
– Transection (cross sectioning) of spinal cord at
any level results in total motor and sensory loss
in regions inferior to cut
• Paraplegia: transection between T1 and L1
• Quadriplegia: transection in cervical region
– Spinal shock: transient period of functional loss
caudal to lesion
Yes.
139
Spinal Cord Trauma and Disorders (cont.)
• Poliomyelitis
– Destruction of ventral horn motor neurons by
poliovirus
– Muscles atrophy
– Death may occur from paralysis of respiratory
muscles or cardiac arrest
– Survivors often develop postpolio syndrome
many years later from neuron loss
Yes.
140
Spinal Cord Trauma and Disorders (cont.)
• Amyotrophic lateral sclerosis (ALS)
– Also called Lou Gehrig’s disease
– Destruction of ventral horn motor neurons and
fibers of pyramidal tract
– Symptoms: loss of ability to speak, swallow, and
breathe
– Death typically occurs within 5 years
– Caused by environmental factors and genetic
mutations involving RNA processing
• Involves glutamate excitotoxicity
Yes.
141
Spinal Cord Trauma and Disorders (cont.)
• Amyotrophic lateral sclerosis (ALS) (cont.)
– Drug riluzole interferes with glutamate signaling:
only treatment
Yes.
142
Neuronal Pathways
• Major spinal tracts are part of multineuron
pathways
• Four key points about spinal tracts and
pathways:
– Decussation: Most pathways cross from one
side of CNS to other at some point
– Relay: Consist of chain of two or three neurons
– Somatotopy: precise spatial relationship in CNS
correspond to spatial relationship in body
– Symmetry: pathways are paired symmetrically
(right and left)
Yes.
143
Ascending Pathways
• Conduct sensory pathways upward through a
chain of three neurons:
– First-order neuron
• Conducts impulses from cutaneous receptors and
proprioceptors
• Branches diffusely as it enters spinal cord or medulla
• Synapses with second-order neuron
Yes.
144
```
Ascending Pathways (cont.)
– Second-order neuron
• Interneuron
• Cell body in dorsal horn of spinal cord or medullary
nuclei
• Axons extend to thalamus or cerebellum
– Third-order neuron
• Also an interneuron
• Cell bodies in thalamus
• Axon extends to somatosensory cortex
• No third-order neurons in cerebellum
```
Yes.
145
Ascending Pathways (cont.)
• Somatosensory signals travel along three main
pathways on each side of spinal cord:
– Two pathways transmit somatosensory
information to sensory cortex via thalamus
• Dorsal column–medial lemniscal pathways
• Spinothalamic pathways
• Provide for discriminatory touch and conscious
proprioception
– Third pathway, spinocerebellar tracts,
terminate in the cerebellum
Yes.
146
Ascending Pathways (cont.)
– Dorsal column–medial lemniscal pathways
• Transmit input to somatosensory cortex for
discriminative touch and vibrations
• Composed of paired fasciculus cuneatus and
fasciculus gracilis in spinal cord and medial lemniscus
in brain (medulla to thalamus)
– Spinothalamic pathways
• Lateral and ventral spinothalamic tracts
• Transmit pain, temperature, coarse touch, and
pressure impulses within lateral spinothalamic tract
Yes.
147
```
Ascending Pathways (cont.)
– Spinocerebellar tracts
• Ventral and dorsal tracts
• Convey information about muscle or tendon stretch to
cerebellum
– Used to coordinate muscle activity
```
Yes.
148
```
Descending Pathways and Tracts
• Deliver efferent impulses from brain to spinal
cord
• Two groups
– Direct pathways: pyramidal tracts
– Indirect pathways: all others
• Motor pathways involve two neurons:
– Upper motor neurons
• Pyramidal cells in primary motor cortex
– Lower motor neurons
• Ventral horn motor neurons
• Innervate skeletal muscles
```
Yes.
149
Descending Pathways and Tracts (cont.)
• Direct (pyramidal) pathways
– Impulses from pyramidal neurons in precentral
gyri pass through pyramidal (lateral and ventral
corticospinal) tracts
– Descend directly without synapsing until axon
reaches end of tract in spinal cord
– In spinal cord, axons synapse with interneurons
(lateral tract) or ventral horn motor neurons
(ventral tract)
– Direct pathway regulates fast and fine (skilled)
movements
Yes.
150
Descending Pathways and Tracts (cont.)
• Indirect pathways
– Also referred to as multineuronal pathways
– Complex and multisynaptic
– Includes brain stem motor nuclei and all motor
pathways except pyramidal pathways
– These pathways regulate:
• Axial muscles, maintaining balance and posture
• Muscles controlling coarse limb movements
• Head, neck, and eye movements that follow objects in
visual field
Yes.
151
Descending Pathways and Tracts (cont.)
• Indirect pathways (cont.)
– Consist of four major pathways:
• Reticulospinal and vestibulospinal tracts:
– maintain balance by varying tone of postural muscles
• Rubrospinal tracts: control flexor muscles
• Tectospinal tracts: originate from superior colliculi
and mediate head movements in response to visual
stimuli
Yes.
152
Developmental Aspects of Central Nervous
System
• Starting in a 3-week old embryo:
1. Ectoderm thickens, forming neural plate
• Invaginates, forming neural groove flanked by neural
folds
2. Neural crest forms from migrating neural fold
cells
3. Neural groove deepens, edges fuse forming
neural tube
Yes.
153
Developmental Aspects of Central Nervous
System
• Neural tube, formed by week 4, differentiates
into CNS
– Brain forms rostrally
– Spinal cord forms caudally
• By week 6, both sides of spinal cord bear a
dorsal alar plate and a ventral basal plate
– Alar plate becomes interneurons
– Basal plate becomes motor neurons
– Neural crest cells form dorsal root ganglia
Yes.
154
Developmental Aspects of Central Nervous
System
• Gender-specific areas appear in both brain and
spinal cord
– Depends on presence or absence of fetal
testosterone
• Maternal exposure to radiation, drugs, or
infection can harm developing CNS
– Example: alcohol or opiates, various infections
such as rubella
• Smoking decreases oxygen in blood, which can
lead to neuron death and fetal brain damage
Yes.
155
Developmental Aspects of Central Nervous
System
• Hypothalamus is one of last areas of CNS to
develop
– Premature infants have poor body temperature
regulation
• Visual cortex develops slowly over first 11
weeks
• Neuromuscular coordination progresses in
superior-to-inferior and proximal-to-distal
directions along with myelination
Yes.
156
Developmental Aspects of Central Nervous
System
• Age brings some cognitive declines, but not
significant in healthy individuals until 80s
• Shrinkage of brain accelerates in old age
• Excessive alcohol use and boxing cause signs
of senility unrelated to aging process
Yes.
157
Clinical – Homeostatic Imbalance 12.2
• Cerebral palsy: neuromuscular disability
involving poorly controlled or paralyzed
voluntary muscles
– Due to brain damage, possibly from lack of
oxygen during birth
– Spasticity, speech difficulties, motor impairments
can be seen
– Some patients have seizures, are intellectually
impaired, and/or are deaf
– Visual impairment is common
Yes.
158
Clinical – Homeostatic Imbalance 12.2
• Anencephaly: cerebrum and parts of brain
stem never develop
– Neural fold fails to fuse
– Child is vegetative
– Death occurs soon after birth
• Spina bifida: incomplete formation of vertebral
arches
– Spina bifida occulata: least serious, involves only
one or few missing vertebrae
• Causes no neural problems
Yes.
159
Clinical – Homeostatic Imbalance 12.2
– Spina bifida cystica: more severe and most
common
• Saclike cyst protrudes dorsally from spine
• Cyst may contain CSF (meningocele) or portions of
spinal cord and nerve roots (myelomeningocele)
– Larger cysts cause neurological impairment
• Usually also see hydrocephalus
– Most cases caused by lack of B vitamin folic acid
• U.S. incidence has dropped with mandatory
supplementation
Yes.
