White Matter Flashcards
What does white matter refer to?
Large expanses of myelinated tracts
What do projection fibres do?
form tracts that transmit APs between the cerebrum and other parts of the CNS. Can refer to ascending or descending fibres
______ connect and transmit impulses between gyri in the same hemisphere
association fibres
______ transmit impulses from gyri in one cerebral hemisphere to corresponding gyri in opposite cerebral hemisphere
Commissural fibres
The largest of the commissural tracts
Corpus callosum
In patients with severe epileptic seizures what is cut to prevent the spreading of the seizure from one hemisphere to the other?
What is one outcome?
Corpus callosum is cut.
Alien hand sign. - left hand won’t allow you to smoke
APs in C-nerve fibres travel at what speed?
Slow walk
APs in A-delta nerve fibres travel at what speed?
Fast sprint
1a/1b nerve fibre APs travel at what speed?
Near airplane
Order of the fibre speed is…
C fibre (slowest) - non myelinated
A-delta - myelinated
Beta- myelinated
1a/1b (fastest)- myelinated
When you stub your toe you will feel which sensation first? Which second? Which last?
Touch sensation first (beta nerve fibres) Sharp pain (A-delta) Dull throb (C fibres)
Between stimulus and experience is series of 4 complex electrical and chemical events.
1) transduction
2) transmission
3) modulation
4) perception
What is transduction?
Stimuli are converted to APs by sensory receptors
What is transmission?
Nerve signals enter and ascend the CNS in various pathways
What is modulation?
The process by which accompanying neural activity ( from other ascending inputs or signal descending from brain) can modify sensory transmission.
Intensity of sensory input can be controlled
What is perception?
Final process - results in subjective feelings.
Combo of transmission and modulation
Can be altered by emotions such as fear, rage, depression
What are the parallel ascending (sensory) tracts?
1) Posterior columns aka dorsal columns (DC) and CN V
2) Spinocerebellar tracts
3) Spinothalamic tract (neospinothalamic and paleospinothalamic divisions)
4) Spino-hypothalamic tract
The posterior column relays what ?
Somatosensory information entering the spinal cord to the brain except for face mouth and head
Aka dorsal columns (DC) and CN5
Somatosensory information from the face mouth and head is supplied by what?
Primarily by afferent unipolar axons of the trigeminal nerve (CN V)
Posterior column sensory information includes what?
Fine (well localized, discriminative) touch, conscious proprioception and vibratory sensations
The posterior column is made up of what?
Gracile fasciculus (lower limb) Cuneate fasciculus (upper limb)
Spinocerebellar tracts transmit impulses for what?
Subconscious muscle and joint position sense (proprioception) to the cerebellum
Proprioceptive information is obtained by what?
Golgi tendon organs and muscle spindles
What does information from GTO and muscle spindles tell?
How long each muscle is, how fast each muscle in moving, how much tension is in each muscle.
Cerebellum compares info to what higher motor centres want muscles to do - then a correction can occur via pathways that leave the cerebellum to influence motor performance
Spinothalamic tracts relay what?
Pain, temperature and crude touch (person won’t be able to tell where they are touched, just that they are touched)
Spinothalamic tract - neospinothalamic division does what?
Carries first aka fast aka discriminative aka well localized pain and crude touch directly to the sensory cortex.
Signals are consciously interpreted as sharp, acute, well localised pain
Spinothalamic tract - paleospinothalamic division does what?
Carries second aka slow aka poorly localized pain via unmyelinated C-fibres
Nerve signals consciously interpreted as dull, aching, deep, poorly localized chronic pain of insidious onset.
What do Commissural fibres do?
Transmit impulses from gyro in one hemisphere to the corresponding gyri in the opposite cerebral hemisphere
What do association fibres do?
Connect and transmit impulses between gyri in the same hemisphere
Neospinothalamic division has how many major neurons?
Is associated with what?
3 major neurons
Associated with superficial cutaneous and withdrawal reflexes and escape behaviour.
Paleospinothalamic division has how many major neurons?
Is associated with what?
More than 3 neurons in relaying signals from dorsal horn to the brain stem, hypothalamus, thalamus, and limbic-forebrain system
In both divisions of the spinothalamic tract, neurons attaches to which type of fibre?
Neo: 1st order neuron attaches to A-delta nociceptor
Pales: unipolar neuron is attached to C-PMN nociceptor
Signal crosses over to opposite side
Spino-hypothalamic tract produces what?
Fight or flight response. Includes increased HR, sweating, breathing rate, core muscular contraction etc
Descending pathways (motor pathways) are divided into 2 main divisions:
Direct: motor cortex directly to LMN (corticobulbar and corticospinal)
Indirect: motor cortex via other tracts to LMN (rubrospinal, tectospinal, vestibulospinal)
The DIRECT pathway, is a 2 neuron pathway consisting of what?
UMNs from the motor cortex
LMNs from SC or brainstem (CN V, VII) that inner ate skeletal muscle
The direct motor tract (aka what?) controls what?
Aka corticospinal
Controls voluntary movements of our body. Only direct connection between the motor cortex and the spinal cord
90% of corticospinal tract axons decussate where?
To the other side of the body in the distal medulla
What is the elevated area of the direct pathway known as?
What does this area do?
Pyramidal decussation
It separates the medulla from the spinal cord
Neospinothalamic division has how many major neurons?
Is associated with what?
3 major neurons
Associated with superficial cutaneous and withdrawal reflexes and escape behaviour.
Paleospinothalamic division has how many major neurons?
Is associated with what?
More than 3 neurons in relaying signals from dorsal horn to the brain stem, hypothalamus, thalamus, and limbic-forebrain system
In both divisions of the spinothalamic tract, neurons attaches to which type of fibre?
Neo: 1st order neuron attaches to A-delta nociceptor
Pales: unipolar neuron is attached to C-PMN nociceptor
Signal crosses over to opposite side
Spino-hypothalamic tract produces what?
Fight or flight response. Includes increased HR, sweating, breathing rate, core muscular contraction etc
Descending pathways (motor pathways) are divided into 2 main divisions:
Direct: motor cortex directly to LMN (corticobulbar and corticospinal)
Indirect: motor cortex via other tracts to LMN (rubrospinal, tectospinal, vestibulospinal)
The DIRECT pathway, is a 2 neuron pathway consisting of what?
UMNs from the motor cortex
LMNs from SC or brainstem (CN V, VII) that innervate skeletal muscle
The direct motor tract (aka what?) controls what?
Aka corticospinal
Controls voluntary movements of our body. Only direct connection between the motor cortex and the spinal cord
90% of corticospinal tract axons decussate where?
To the other side of the body in the distal medulla
What is the elevated area of the direct pathway known as?
What does this area do?
Pyramidal decussation
It separates the medulla from the spinal cord
What is the internal capsule of the direct pathway?
A massive layer (8-10mm thick) of white matter. Consists of ascending and descending projection fibres
Major route by which cerebral cortex is connected to brainstem and spinal cord
What is the most common stroke location?
The part of the internal capsule which carries the corticospinal tract
Cortical strokes usually cause what?
Because body parts in cortex are spread so widely Rarely big enough to effect entire half of body - instead hands and face which take up the most cortical area are usually affected
What is the internal capsule of the direct pathway?
A massive layer (8-10mm thick) of white matter. Consists of ascending and descending projection fibres
Major route by which cerebral cortex is connected to brainstem and spinal cord
What is the most common stroke location?
The part of the internal capsule which carries the corticospinal tract
Cortical strokes usually cause what?
Because body parts in cortex are spread so widely Rarely big enough to effect entire half of body - instead hands and face which take up the most cortical area are usually affected
In the Internal capsule - what is a common stroke?
A small stroke can effect the entire side of the body because fibres are bundles so closely together (Hemiplegia or hemiparesis)
If a stroke occurs in the brain stem what will usually happen?
The hemiparesis will often be accompanied by other symptoms because the brainstem is very tightly packed
What are warning signs of a stroke?
Sudden numbness or weakness of face arms or leg especially on one side
Confusion, rouble talking or understanding speech, trouble seeing in one or both eyes, trouble walking, dizziness,
Loads of balance or coordination, severe headache with no known cause
Indirect pathways (extra pyramidal) consist of which fibres ?
Projection fibres from basil ganglia and cerebellum also influence LMNs but they do so indirectly
What are examples of people with extrapyramidal disorders? What would they have trouble with?
Parkinson’s, frequently have trouble with balance, issues with involuntary movements such as pill rolling
Exteapyramidal system is lied with which types of movements?
Gross rather than fine voluntary movement.
What is a communicative behaviour mediated by the extrapyramidal tract?
Fascial expression
T/f postural pathways originate in the Cortex
False - however they are controlled to some degree by cortical structures,
In the CNS information being carried by neurons is often sent to many different neurons. This process is called…
Divergence
Information from many different sources sent to the same neuron or nucleus is called
Convergence
If several sources compete for the final common pathway (aka LMN, Alpha motor neuron) to converge at any one time what will happen?
Compatible signals will reinforce each other
Incompatible signals for example those which are initiated by painful stimuli for example protective reflexes take precedence
