Central Nervous System Flashcards
(163 cards)
1
Q
3 Main Components of the Brain
A
Cerebrum
Cerebellum
Brainstem
2
Q
Cerebrum
A
The largest part of the brain
Divided into the left and right hemispheres
Divided into two layers = white and gray matter
3
Q
Corpus Callosum
A
Part of the cerebrum
Nerve axons that link the right and left hemispheres of the cerebrum so that the two hemispheres can communicate
4
Q
Cerebral Cortex
A
The outer layer of the gray matter of the cerebrum
4 lobes make up the cerebral cortex
Functions: sensory perception, motor control, language, cognitive functions
5
Q
Frontal Lobe
A
Functions in personality, emotions, control of movement
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Parietal Lobe
A
Mediates skin and muscle sensation
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Q
Occipital Lobe
A
Vision
8
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Temporal Lobe
A
Hearing and memory functions
9
Q
Forebrain
A
Comprises the cerebrum and diencephalon
10
Q
Cerebellum
A
Controls balance and voluntary movement
11
Q
Brainstem
A
composed of the: midbrain pons medulla oblongata controls: respiration locomotion cardiovascular functions
12
Q
Basal Ganglia
A
functions: movement inhibition, inhibition of muscles antagonistic to the desired movement
13
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Thalamus
A
functions: sensory switchboard which selects and relays sensory signals to the cortex
14
Q
Hypothalamus
A
functions: homeostasis, emotions
15
Q
Spinal Cord
A
locomotor pattern generator
16
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Limbic System Structures
A
Includes: thalamus, hypothalamus, hippocampus, olfactory bulbs in the nose, and septal nuclei
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Limbic System Functions
A
Involved in learning, emotion, appetite, sex functions, and endocrine integration
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Meninges
A
3 layers of membranes that cover the brain and spinal cord
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Dura Mater
A
Tough outer layer
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Arachnoid Mater
A
Spidery intermediary mesh
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Pia Mater
A
Delicate inner layer
22
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Meningitis
A
infection of the meninges
23
Q
Cerebrospinal Fluid
A
Produced in brain ventricles
Reabsorbed into the blood in the venous system at the same rate it is produced
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Q
Cerebrospinal Fluid Function
A
Maintain an appropriate electrolyte balance around neurons
Bathe and support neural tissue
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4 Types of Glial Cells
Astrocytes
Oligodendrocytes
Ependymal Cells
Microglia
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Astrocytes
```
Physically supports neurons
Form the blood-brain barrier
Form scar tissue which inhibits regeneration of axons
Recycling of neurotransmitter molecules
Maintain electrolyte balance
```
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Oligodendrocytes
cells with relatively few branches that form the myelin sheath around neuronal axons
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Ependymal Cells
Produce the cerebrospinal fluid
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Microglia
scavengers
| ingest bacteria and cellular fluid
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Do Neurons Form Tumors?
No
| neurons cannot divide so brain tumors do not develop from neuronal cells
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Types of brain tumours
Arise from glial cells = gliomas
| Arise in the meninges = meningioma
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Hydrocephalus
Occurs when the reabsorption of CSF is blocked and CSF builds up
Treated with drainage tubes
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Blood-Brain Barrier
Capillaries of the BBB are less porous than in the rest of the body
Protects neurons from chemical fluctuations and large molecules
Provides oxygen and glucose
Selectively transports molecules needed by the brain while excluding harmful molecules
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CNS
the brain and spinal cord
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Afferent Neurons
sensory input conveyed to the CNS by the peripheral nervous system
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Efferent Neurons
motor commands conveyed from the CNS to the peripheral nervous system
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Somatic Nervous System
Voluntary movement
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Vertebra Column
Boney structure that supports the trunk and the head on the legs. Inside the vertebrae is where the spinal cord is found
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Spinal Cord
Conveys signals from sensory receptors to the brain and signals from the brain to the effector organs
Each spinal nerve innervates a specific area of skin (dermatome) and a specific set of muscles (myotome)
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Dorsal Root Ganglion
A cluster of neurons in a dorsal root of a spinal nerve
| cell bodies of sensory neurons are located in the dorsal root ganglion
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PNS and CNS interface
Sensory afferent axons enter the spinal cord through the dorsal roots
Sensory afferent axons bifurcate (split) into ascending and descending axons
Motorneurons are located in the ventral horn
The efferent axons of motorneurons leave the spinal cord through the ventral roots and innervate the muscles
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Central Gray Matter
comprised of motoneurons, interneurons, dendrites, and axons
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Surrounding White Matte
Comprised of bundles of axons (tracts) that convey sensory signals
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Dermatomes
The 31 spinal nerves on each side of the body provide sensory innervation to skin areas
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Cervical Nerves
mediate sensory input from the arms
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Thoracic Nerves
mediate sensory information from the abdomen
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Lumbar, Sacral, and Coccygeal Nerves
mediate sensory information from the legs and feet
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Spinal Cord Injury
When the spinal cord is damaged at a particular level, sensation and motor functions below that level are absent or abnormal depending on how severe the damage is
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Spinal Damage at C6 or C7
Quadriplegia
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Spinal Damage at L1 or L2
Paraplegia
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You can only control what you see
Sensory information is important in the control of movement
| Everything that is controlled requires sensory input
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Modality
The structure of a sensory receptor determines which modality of stimulus it responds to
The modality activating a given receptor is called the receptor's adequate stimulus
Different modalities are processed in different brain regions
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Meissner's Corpuscles
responds to light touch of the skin
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Merkel's Corpuscles
responds to touch
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Free Nerve Ending
responds to pain
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Pacinian Corpuscles
distributes and amplifies the mechanical deformation of the nerve endings that are right in the middle of the receptor - respond vigorously to vibrations
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How Pacinian Corpuscles Work
slippery layers called lamellae slide over each other as the pressure of the corpuscles rises
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Ruffini Corpuscles
slow adapting mechanoreceptors that respond to skin stretch and also function as thermoreceptors
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Warm receptors
Increase firing rate as their temperature rises
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Cold receptors
Increase firing rate as their temperature falls
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Sensory receptor A
Specialized endings of afferent axons that project directly to the spinal cord
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Sensory receptor B
Separate cells that respond to stimulus and transmit signals via synapses with afferent neurons
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Examples of sensory receptor B
Cochlear hair cells, retinal photoreceptor cells
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Examples of sensory receptor A
Skin and muscles receptors
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Somatosensory receptors
cover the surface of the body and signal a variety of sensory modalities to the CNS
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Mechanoreceptors
sense local tissue deformation in skin and viscera
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Thermoreceptors
sense temperature in the skin and brain
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Nociceptors
Sense pain (tissue damage) in skin, viscera, and muscle
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Proprioceptors
sense movement and force muscles and joints
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Vestibular receptors
senses head acceleration and tilt
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Conduction Velocities of Axons
Muscle spindle primary endings/Golgi tendon has the fastest conduction
Nociceptors/warmth receptor/preganglionic fibres/postganglionic fibres have the slowest conduction
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Stimulus Intensity
As stimulus intensity increases, the membrane potential at the initial segment of the sensory receptor's afferent axon increases until action potentials are generated
Further increases cause increases in action potential rate and the recruitment of more sensory receptors
Changes in the regularity of firing rates may also encode stimulus properties
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Spinal Cord Tracts
Relationship between the intensity of mechanical stimuli sensed in the PNS and release of the transmitter within the CNS
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Frequency Coding
The bigger the stimulus, the more the membrane channels in the sensory ending are distorted, the greater the number of action potentials
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Population Coding
The bigger the stimulus, the more sensory neurons are recruited into activity = more APs
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Temporal Pattern Coding
Variability of firing rate may mediate certain types of sensations
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Duration
Some receptors adapt rapidly to stimuli while others adapt very slowly
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Slow adapting receptors
tonic receptors = generate action potentials throughout the whole duration of the stimulus
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Rapidly adapting receptors
respond only briefly each time the stimulus changes
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Adaptation
reduction in response in the continuous presence of a stimulus
Different sensory receptors vary in their speed of adaptation to stimuli
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Location
Depends on:
the density of receptors and the sizes of their respective fields
convergence and divergence
lateral inhibition focuses ascending sensory signals, enhancing spatial acuity
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Two-point discrimination
```
receptors = tightly packed: the receptive fields of the receptors are small and sensory acuity is high
receptors = not tightly packed: the receptive fields of receptors are larger and sensory acuity is low
```
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Overlapping Receptive Fields
overlapping stimulation between neighbouring receptive fields provides general information about the location of a stimulus
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Divergence
each sensory afferent sends branches to many neurons in the CNS
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Convergence
a given neuron in the CNS receives inputs from many sensory afferents
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Lateral Inhibition
sharpens contrast by focusing activation of CNS neurons
| stimulus location is perceived more precisely
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Sensation
the conscious awareness of a stimulus
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Perception
when a sensation is combined with an understanding of its meaning
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Topographic Maps
within the sensory cortex
projection area is related to functional importance
maps change according to use - dynamic plasticity
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Descending Inhibition
Activity descending from higher centers in the brain + brainstem can screen out certain types of sensory information by inhibiting neurons in the afferent pathway
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Presynaptic Inhibition
acts by reducing transmitter release at the synapse between first-order and second-order sensory neurons
inhibits specific sensations
lasts several milliseconds
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Postsynaptic Inhibition
acts by hyperpolarizing membrane of second-order sensory neurons
non-selective - reduces the effect of all synaptic inputs
lasts less than 1 millisecond
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Process of Pain
damaged tissue releases prostaglandins and histamine which activate pain receptors
activity in pain fibres causes the release of substance P in the spinal cord
signals in projection neurons ascend to pain centers in the brain
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Aspirin
Blocks production and release of prostaglandins by damaged tissue
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Gabapentin
Blocks conduction in C-fibre axons
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Opioids
Cause opioid receptors in pain fibre-endings to block the release of substance P onto projection neurons in the spinal cord
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Referred Pain
the sensation of pain is experienced at a site other than the injured or damaged tissue
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Supraspinal Centres Controlling Movement
```
Involved in generating motor commands
Includes:
-sensorimotor cortex
-brainstem
-cerebellum
-cerebral cortex
-thalamus
-basal ganglia
```
99
Feedback Control
The brain, cerebellum, and brainstem issue a motor command (desired limb position) to neuronal networks in the spinal cord
Sensory receptors in the muscles, etc, signal the actual position back to the spinal cord, which compares this to the desired position and generates an output to the muscles so that the difference between actual and desired states is minimized
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Muscle Spindle
sensory receptor that signals changes in muscle length
| located in parallel with the force-producing muscle fibres
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Tendon Organs
respond to force produced by muscle
| tendinous fascicles at the ends of muscle fibres
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Intrafusal Muscle Fibres
inside the muscle spindle
connective tissue capsule and stretch receptors
generate only tiny amounts of force
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Extrafusal Muscle Fibres
main muscle fibres found outside the muscle spindle that produce all the measurable force
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Alpha Motor Neurons
Activate the main muscle extrafusal fibres to contract
| muscle shortening
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Gamma Motor Neurons
Activate intrafusal muscle fibres
activates at the end of each muscle spindle, the middle part of the spindle is non-contractile
Gamma NM activity increases the sensitivity of muscle spindles to length changes
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Alpha-Gamma Coactivation (Theory)
intrafusal contraction compensates for extrafusal muscle shortening, tightening the spindle up so that the afferents maintain or even increase their firing
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Alpha-Gamme Coactivation (Actual)
In normal movements, coactivation of gamma NMs is usually not that strong, so spindle afferent firing actually decreases
BUT less so than in the absence of gamma NM activity
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Activation of Golgi Tendon Organs
Passive stretching of a muscle causes Golgi tendon organ afferents to respond with small increases in their rate of firing
109
Stretch Reflex
| Stimulus = muscle stretch
Response:
1. spindle-afferent-mediated monosynaptic excitation of agonist MNs and disynaptic inhibition (via interneurons) of antagonist MNs
opposes change in muscle length
2. GTO-mediated disynaptic inhibition of agonist MNs and disynaptic excitation of antagonist MNs
opposes change in muscle force
110
Flexor Withdrawl Reflex
noxious stimulus evokes flexion of ipsilateral leg and extension of the contralateral leg
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Primary Motor Cortex
also called the sensorimotor cortex
| highlights the importance of sensory signals in motor control
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Somatotopic Maps
By stimulating specific parts of the brain surface, movements of body parts can be elicited
Hand and face representations are very large
Neurons in the primary motor cortex can be activated by TMS
113
Corticospinal Tract
Axons from neurons in the sensorimotor cortex form the CST
CST neurons make monosynaptic connections with spinal alpha motoneurons, whose axons, in turn, activate muscles
CST neurons are only one CNS synapse away from muscle
114
CST lesions
(stroke, cerebrovascular accident, brain attack)
| results in spastic hemiplegia
115
Symptoms of CST lesions
weakness (paresis) or paralysis
exaggerated stretch reflexes
spasms
speech deficits (dysarthria) - particularly in the left side of the brain
attentional deficits (aphasia, apraxia, hemineglect)
116
Aphasia
inability to understand the meaning of sensory inputs
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Apraxia
Problem using day to day objects
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Hemineglect
occurs when patients fail to be aware of items to one side of their body
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Broca's Area
Motor aspects of speech
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Lesions of Broca's Area
motor aphasia (slurring speech)
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Wernicke's Area
comprehension of language
| association of visual, auditory, and tackle input with words
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Lesions of Wernicke's Area
sensory aphasia (difficulty understanding the meaning of sensory input) and dyslexia
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Cerebellum Inputs
sensory input from spinal cord
| motor commands from the cerebral cortex
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Cerebellum Functional Divisions
Vermis = posture, neck and axial musculature
Intermediate Zone = locomotion
Lateral Zone = coordinating complex, skilled movements of arms, hands, and fingers
Flocculonodular Lobe = balance
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Basal Ganglia Anatomy
large, deep cerebral nuclei
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Basal Ganglia Functions
involved in initiating movement
| involved in suppressing the activity of muscles that would resist the intended movement
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Basal Ganglia Dysfunction
Poverty of movement = bradykinesia
eg Parkinson's disease
Involuntary movement = dyskinesia
eg Tourette's syndrome
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Brainstem functions
- control of respiratory and cardiovascular musculature
- control of transmission in sensory, motor, reflex, and pain pathways
- initiation of locomotion
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Alert Wakefulness
high frequency, low amplitude rhythm called the beta rhythm
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Relaxed Wakefulness
lower frequency, higher amplitude called the alpha rhythm
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Relaxed Drowsiness
decrease in the alpha wave amplitude and frequency
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NREM Sleep
divided into three stages
each stage is characterized by an EEG pattern with a lower frequency and larger amplitude than the previous one
harder to wake someone up as it progresses
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N1 - Light Sleep
alpha waves become reduced in frequency and amplitude and the percentage of time that they are present
some theta waves
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N2 - Further Lack of Sensitivity
alpha waves are replaced by random waves of greater amplitude
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N3 - Deep Sleep
more theta and delta activity
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REM Sleep
stage of sleep associated with dreaming and rapid eye movement, muscles of the body are relaxed and the brain is very active
brain waves mimic the beta waves of alert wakefulness
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Timing of Sleep States
The EEG reveals 5 cycles of deep and light sleep in 8 hours
-90-minute cycles
REM sleep gets longer and longer the closer to morning
N1-> N2 -> N3 -> N2 -> REM
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Glasgow Coma Scale
```
used to classify the level of consciousness of a person
based on:
-eye movements
-responses to questions
-voluntary movements
```
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Criteria for Brain Death
1. nature and duration of the coma must be known
2. cerebral and brainstem function are absent
3. supplementary criteria include a flat EEG for 30 minutes
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Reticular Activating System
= a set of nuclei in the brainstem and hypothalamus
- during wakefulness, visual and other sensory inputs activate neurons in the reticular activating system
- the neurons release monoamines to the hypothalamus and other brain areas
- hypothalamus supplies orexins to the thalamus and cortex to maintain wakefulness
141
Suprachiasmatic Nucleus
activates orexin-producing neurons in the morning to promote wakefulness
secretes melatonin at dusk
sets the circadian rhythm
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Sleep Centre
a nucleus
found in the preoptic nucleus of the hypothalamus
causes GABAergic inhibition to the reticular activating system to reduce orexin
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Awake
suprachiasmatic nucleus, negative energy balance, limbic system activity
144
Sleep
high blood concentration of adenosine inhibits orexin, reduced drive to thalamus and cortex
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Selective Attention
attraction shifts from one focus or attractor to another
coincident attractors are more likely to trigger a shift than separate attractors
thalamus and locus ceruleus in brainstem RAS triggers shifts
146
Conscious Perception
specific sets of neurons in different parts of the brain work together to generate the consciousness experience
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Primary Motivated Behaviour
directly related to homeostasis
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Secondary Motivated Behaviour
results in pleasure
| can be disadvantageous (overeating)
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Reward
a pathway in the brainstem nuclei releases dopamine within the frontal lobe of the brain which elicits pleasure or a reward
150
Emotions
internal attitudes towards events and the environment
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Emotional Behaviour
external response to internal attitudes
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Emotion: Neuroanatomical Mechanisms
Different parts of the brain can be stimulated electrically to elicit particular types of emotions
- stimulating hypothalamus = rage
- lesion of amygdala = absence of fear
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Drug Dependence Diagnosis
There are 7 criteria and substance dependence is diagnosed when three or more of the specified criteria occur within a twelve-month period
154
Depression Treatment
act by maintaining levels of serotonin and norepinephrine at synapses in the CNS
thought to cause neurogenesis
155
Working/Short-Term Memory
easily acquired, easily lost
episodic = recent events, places
visuospatial = recent sights, locations
phonological = recent words, sounds
156
Long-Term Memory
```
A slower period of acquisition lasts maybe even a lifetime
declarative = conscious
-semantic = facts
-episodic = personal experiences
procedural = sub-conscious
-stimulus-response behaviours
-motor skills
```
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Consolidation
Transfer from the stm to the ltm probably happens in the temporal lobe
158
Caudate Nucleus
implicated in consolidating stimulus-response associations taught during operant conditioning and in solving sequence tasks
159
Concussion
measured by type and duration of amnesia
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Retrograde Amnesia
loss of memory of events prior to the injury
161
Anterograde Amnesia
loss of memory of event after the injury
162
Korsakoff's Syndrome
damage to the hippocampus
| complete anterograde amnesia
163
Alzheimer's Disease
degeneration of memory-holding neurons (overexcitation)
