BMSC335 Lecture 3 Week 1

Pregunta	Respuesta
In terms of signaling to the brain, what does the term 'afferent' mean?	Afferent: The direction a signal travels when it is travelling into the brain.
In terms of signaling to the brain, what does the term 'efferent' mean?	Efferent: The direction a signal is travelling in when it is leaving the brain.
What are the two main pathways in the CNS for response?	1. Corticospinal (also known as Pyramidal) tract. 2. Extrapyramidal System.
What is another name for the Corticospinal tract?	The Pyramidal tract.
Is the Extrapyramidal system involved in A) Sensory input or B) Response output	B. Response output.
Is the Corticospinal tract involved in A) Sensory input or B) Response output?	B. Response output.
In the Somatosensory pathway, how many 'orders' or groups of Neurons are there?	Four.
What are 'First Order Neurons'?	- Primary afferents whose peripheral endings for the sensory receptors (or receive inputs from them). - Transmit information from environment to CNS, and have their cell bodies in the dorsal root (or cranial nerve) ganglia.
What are 'Second Order Neurons'?	- Neurons located in the spinal cord or brainstem. - Transmit information from the first order neurons to the Thalamus (usually contralateral Thalamus).
What are 'Third Order Neurons'?	- Neurons that transmit information from one of the sensory nuclei in the Thalamus to a sensory region of the cerebral cortex.
What are 'Fourth Order Neurons'?	- Neurons located in the sensory regions of the Cerebral Cortex. - May synapse with higher order neurons (higher processing).
Where are 'Higher Order Neurons' located in relation to 'Fourth Order Neurons'?	- Higher order neurons can be located in either the same, or other, cerebral cortical regions.
What does Dr. Kivell mean when she refers to the 'spatial organisation' of the CNS?	- All nerve tracts in the spinal cord are arranged in specific spatial conformations. - Deep touch and vibration are sensed by tracts running through the dorsal surface of your SC. - Pain/Temperature/Light touch/Voluntary motion are all sensed or actioned by tracts running through the ventral surface of your SC.
What is another name for the Dorsal Column Pathway?	Medial Lemniscus Pathway.
What happens to reaction output when the Dorsal column pathway (in Dorsal surface of SC) is damaged?	- Impaired muscle control. - Loss of sensation of vibration. - Loss of discriminatory touch below the level of the lesion.
How can lesions of the somatosensory pathways be used in a therapeutic setting?	Anterolateral cordotomy (surgical lesion of the spinothalamic tract) can be used to reduce pain in certain patients.
How might a clinician or neurologist assess a patient for spine damage?	By prodding/poking him or her in various places around the body to determine sensation/ability to feel pain.
Is it common to suffer a lesion that affects only one tract?	No. More common to suffer a lesion such as hemisection of the cord which leads to the loss of fine touch/vibration and loss of crude touch/pain and temperature.
Name four major differences between the Anterolateral Pathway and the Dorsal Column Pathway:	1. Velocities of transmission are slower in the ALP. 2. Poor spatial localization in ALP. 3. Less graduations of strength. 4. Crude system compared to dorsal column pathway.
Do any of the sensory pathways travel directly from receptor to the cortex?	No.
What part of the brain is also known as the 'gateway to the cortex'?	The Thalamus.
What type of nuclei transmit signals from rest of body to the Cortex?	The Thalamus' relay nuclei.
What role, other than transmission, might the relay nuclei play in the transmission of signal to and from the Cortex?	- Attenuates/regulates signals - Increases or decreases sensory input as necessary (most important sensory input emphasized). - Reduces irrelevant activity and sharpens contrast.
Where is the Somatic Sensory Cortex located?	In the postcentral gyrus.
Is each part of the body equally represented by a portion of the Somatic Sensory cortex?	- No, the representation is unequal. - Lips have the greatest area of representation followed by the face and thumb. - Trunk and lower body have the least area.
How many 'areas' make up the Somatosensory Cortex?	2. Somatosensory Area I & II
Are responses stimulated in the Somatosensory cortex as the same side as the stimulated receptor?	No. Opposite side. The body feels pain on one side, it stimulates the opposing side of the brain.
What is a Homonculus?	- Diagrammatic representation of the amounts of the cortex that are dedicated to controlling/sensing certain parts of your body.
How many layers are there in the cortex?	6.
Briefly describe the cellular organization of the cortex:	- 6 layers, with neurons in the layers arranged into columns. - Each column serves a specific sensory modality. - Different columns are interspersed among each-other (interwoven complexity of the brain)
List some of the symptoms a patient might experience if his or her Somatic Area I was destroyed:	- Loss of discrete localization ability. - Inability to judge the degree of pressure. - Inability to determine the weight of an object. - Inability to determine the shape or form of objects (astereognosis). - Inability to judge texture.
What is astereognosis?	The inability to determine the shape or form of objects.
Where are the Somatic Association Areas located?	Behind the somatic sensory cortex in the parietal area of the cortex.
Where do Somatic Association Areas receive input from?	- Sensory cortex. - Ventrobasal nuclei of the Thalamus. - Visual and auditory cortex.
What is the primary function of the Somatic Association Areas?	To decipher sensory meaning.
What happens when a patient loses their Somatic Association Areas?	Inability to recognize complex objects or loss of self.
How did Neuroscientists come to understand the importance of the Somatic Association Areas in interpreting input information?	A WW1 soldier was wounded by a bullet which pierced his dorsolateral parietal lobe and exited through the right ventrolateral parietal lobe - resulting in a visualspatial deficit. He was unable to copy images exactly - ignoring one half of the image completely.
What are corticofugal fibres?	- Fibres that run from the cortex to the sensory relay areas of the Thalamus, Medulla and SC. - Inhibitory fibres which can inhibit sensory input.
What are the main functions of Corticofugal Fibers?	- Decrease the spread of a signal - Sharpen the degree of contrast and adjust the sensitivity of the system.
What neurological condition is associated with the malfunction or damage of Corticofugal fibers?	Autism.
What parts of brain provide output to be relayed through the Corticospinal Tract?	- Primary Motor Cortex - Supplementary and Pre-motor Cortex - Somatosensory Cortex
At what level does the Corticospinal Tract cross over?	Crosses over at level of Medulla.
Which system controls sensory output directly: Corticospinal or Extrapyramidal?	Corticospinal.
What is the main function of the Corticospinal tract?	To carry the motor commands that drive voluntary movement.
What muscles does the lateral Corticospinal tract control: distal or proximal?	Distal muscles.
What muscles does the anteruor Corticospinal tract control: distal or proximal?	Proximal.
What is the major symptom of a damaged Corticospinal tract?	Permanent loss of fine control of the extremities.
What parts of the brain contribute output to the Extrapyramidal system?	- Basal Ganglia. - Reticular formation (Brainstem). - Vestibular Nuclei (BS). - Red Nuclei (BS)
What are the 4 Nuclei of the Basal Ganglia?	1. Striatum (caudate and putamen) 2. Globus Pallidus. 3. Substantia nigra. 4. Subthalamus.
What is the primary purpose of the Basal Ganglia?	To link the Thalamus to the Cerebral Cortex.
What is the Caudate circuit?	- Circuit of signaling formed by the Caudate which extends into all lobes of the Cortex and receives a large input from association areas of the Cortex. - Mostly projects to the Globus Pallidus (no fibers to subthalamus or substantia nigra). - Believed to play a role in cognitive control of motor functions (thinking about moving).
What are the symptoms of lesions on the Globus Pallidus?	Athetosis - spontaneous writing movements of the hand, arm, neck, and face.
What are the symptoms of lesions on the Putamen?	Chorea - flicking movements of the hands, face and shoulders.
What are the symptoms of lesions on the Substantia Nigra?	- Parkinson's Disease - rigidity, tremor and akinesia. - Loss of dopaminergic input from substantia nigra to the caudate and putamen.
What are the symptoms of lesions on the Subthalamus?	Hemisballismus - sudden flailing movements of the entire limb.
What are the symptoms of lesions on the Caudate Nucleus or Putamen?	Huntington's Disease - loss of GABA containing neurons to Globus Pallidus and Substantia Nigra.

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