CNS sensory Flashcards
Describe the structure of the spinal cord from inside to outside:
Central canal
Gray matter
White matter
Roots (dorsal and ventral)
Spinal nerve
What is role of the gray matter in the spinal cord?
It’s where information can be processed
What is the role of the white matter in the spinal cord?
it’s where axons travel through the spinal cord
How does the structure of grey and white matter vary in the spinal cord as compared to the brain?
Unlike the brain, the white matter is on the outside layer of the spinal cord with gray matter inside of it
What is the role of the central canal in the spinal cord?
It’s where CSF travels
What are the two main segments of the grey matter in the spinal cord? Describe their functions.
There is the dorsal horn and the ventral horn. The dorsal horn receives sensory inputs, while the ventral horn sends out signals.
What is the difference between the dorsal root and the ventral root of the spinal tract?
The ventral roots carry axons from motor neurons in the CNS. The dorsal roots are the way through which afferents send their axons into the dorsal horn.
What is the other way that information gets in and out of the CNS aside from the spinal cord?
It can travel through one of the 12 cranial nerves
Where are cranial nerves located?
They all go into and out of the brain stem except for two: the olfactory nerve and the optic nerve.
Describe the development of the nervous system in week 1.
during week one, it’s simply a blastocyte that starts to have some structure
Describe the development of the nervous system in week 2.
On week two, the blastocytes start to develop cavities which will become different parts of the body.
Describe the development of the nervous system in week 3.
On week three, we can see the appearance of an embryonic disk
The top of the embryonic disk is called […]
the neural plate
Describe the structure of the neural tube as of week 3 of development. Include the embryonic disk.
The neural plate (top layer of the disk) will become the neural groove and finally close to creating a tube, part of the CNS and PNS. This happens with the ectoderm layer. In between that one and the mesoderm, we have the appearance of the neural crest which will be part of the PNS.
Describe how the neural tube develops during week 4
There a vesicles that start forming: the forebrain, the midbrain and the hindbrain followed by a tube
The neural crest cells formed during week […] become […]
3, PNS
Describe how the different segments of the neural tube develop into different parts of the CNS.
Forebrain: central hemispheres and thalamus
Midbrain: Midbrain
Hindbrain: Cerebellum, pons and medulla
Tube: spinal cord
Cavity: ventricles and central canal
What is the function of the ventricles in the brain?
It’s where the CSF can circulate
How much cerebral spinal fluid do the ventricles contain?
150 ml
Name the 3 major types of ventricles.
Lateral ventricles
Third ventricle
Fourth ventricle
How is the cerebrospinal fluid formed?
It’s produced by the choroid plexus in the four ventricles (mostly lateral as they are bigger).
What is the rate of production of CSF per day?
500 ml/day
Name the 3 functions of the CSF.
- Supports and cushions the CNS
- Provide nourishment to the brain
- Remove metabolic waste through absorption at the arachnoid villi
What is the composition of the CSF?
It’s a sterile, colorless and acellular fluid that contains glucose
What type of circulation does CSF undergo?
Passive
Describe the route of CSF to the spinal cord after its production.
It goes from the lateral ventricle through the Foramen or Monro to reach the 3rd ventricle. Then, it goes through the cerebral aqueduct to reach the 4th ventricle. It can then exit to the spinal cord
The CSF can enter the subarachoid space via what 2 methods?
The LUSHKA or MAGENDIE foramen
What are arachnoid villi and where are they located?
They are bulges that let veinous drainage absorb CSF after the circulation
What are the 3 meninges of the CNS?
Where are the meninges of the CNS located with respect to skin and bone?
Dura
Arachnoid
Pia
They start under the bone and stay close to white or gray matter.
CSF returns to the blood at the […]
dural sinus
Where is the dural sinus located?
It’s an opening of the dura matter at the level of the midline, between both hemispheres
What is the major substrate metabolized by the brain?
Glucose
The brain needs a constant supply of […]
glucose
Does the brain require insulin to receive nutrients?
No
What are the possible consequences of a blood supply interruption to the brain?
A few seconds will lead to loss of consciousness
A few minutes will lead to neuronal death (stroke)
The brain receives […]% of total blood and is […]% of total mass.
15%
2%
Describe the path that blood takes from the heart to the brain.
Goes up with the Aorta and then through the vertebral or the common carotid. The later then splits in to the internal and external carotid.
How many vertebral arteries and internal carotid arteries do we have?
2 of each
Describe the structure of the arteries that carry blood to the brain once arrived at the base of the brain.
Internal carotid: base of the brain
External: outside of the head
What is the purpose of the circle of willis?
If there is a blockage or damage at any of the vessels that supply the brain, the circle provides another way for blood to get to the brain.
What is the blood brain barrier?
It’s a very tight capillary wall to control what goes in and out of the blood circulation going to the brain (specific needs)
What types of substances can cross the blood brain barrier?
Lipid-soluble
Active transport
Give 3 examples of substances that can pass the blood brain barrier.
Water
Respiratory gasses
Glucose
Explain why heroine is so harmful.
Heroine is lipid-soluble and so can get into the brain. Once it’s in, it will become morphine (morphine can’t originally get into the blood-brain barrier)
What is sensation?
Awareness of sensory stimulation
What is perception?
The understanding of a sensation’s meaning
What is the law of specific nerve energies?
Regardless of how a sensory receptor is activated, the sensation felt corresponds to that of which the receptor is specialized.
Give an example of the law of specific nerve energies.
Rubbing the eyes hard enough will cause to see lights
What is the law of projection?
Regardless of where in the brain you stimulate a sensory pathway, the sensation is always felt at the sensory receptor location
The phenomenon of phantom limb pain corresponds to which law of perception? Explain why.
It’s an example of the law of projection. Even if the end of the axon is cut, it can be re-activated when it connects to something else. When it’s stimulated lower down the axon, the sensation will be felt at the end of the amputated limb.
What is labeled-line code?
It is the notion that the brain knows the modality (class of stimulus) and location of every sensory afferent.
What is an exception to labeled-line code?
In certain instances dealing with pain - this is referred pain.
Name the 5 steps of sensory receptor functioning.
- Stimulus energy is received.
- The corresponding receptor membrane reacts with the stimulus energy
- The energy is used for the transduction of ion channels
- The ion channels activate
- The signal is sent to the CNS via afferent neurons.
Stimulus energy gets converted into […]
Afferent activity
Name and explain the steps involved in the conversion of stimulus energy into afferent activity.
- Start with stimulus energy
- Membrane depolarization takes place, affecting receptor potential.
- If the threshold is met, action potentials are produced.
- Action potentials are propagated along the body to the brain.
- Neurotransmitters are released.
What happens if the membrane depolarization caused by stimulus energy doesn’t meet the threshold for an action potential?
No action potential will be fired. So even though something is touching you, for example, you won’t feel it.
What are the 3 levels of stimulus intensity?
Subthreshold, weak, strong
Describe how a subthreshold stimulus intensity will affect…
a) The magnitude of receptor potential
b) The frequency of action potentials
c) The magnitude of neurotransmitters release
a) The magnitude of the receptor potential will be small
b) No action potentials will be sent out
c) No neurotransmitter release
Describe how a weak stimulus intensity will affect…
a) The magnitude of receptor potential
b) The frequency of action potentials
c) The magnitude of neurotransmitters release
a) Medium receptor potential
b) A few action potentials released
c) Some neurotransmitter released
Describe how a strong stimulus intensity will affect…
a) The magnitude of receptor potential
b) The frequency of action potentials
c) The magnitude of neurotransmitters release
a) High magnitude of receptor potential
b) High frequency of action potential
c) High magnitude of neurotransmitters released
Explain the purpose of adaptation of afferent response.
The majority of afferents show adaptation, which allows us to be sensitive to changes in the sensory input.
How does adaptation of afferent response work? Compare non-adapting, slowly adapting, and rapidly adapting
Adaptation is the ability of a neuron to be sensitive to changes in the sensory input.
Non-adapting: the same AP will be fired till the stimulus goes away
Slowly adapting: There will be a slow decrease in frequency even if the stimulus stays the same.
Rapid adapting: an AP will only be when the stimulus starts and ends. These neurons are interested in the stimulus change.
What is a receptive field?
The region that activates one single sensory receptor or neuron
The response across a receptor field can be described as […]. Explain why.
gradual. If a stimulus is sent in the middle of the RF, the AP will be stronger (more frequent) whereas the same stimulus on the periphery will result in a lower frequency AP
Overlapping receptive fields produce […]
population code
What is a population code?
It’s when more than one neuron is activated (middle and periphery) which allows the brain to know exactly what the stimulus and where it’s happening.
What is stimulus acuity?
Ability to differentiate one stimulus from another
Compare the relationship between acuity and location based on acuity for lips vs back.
Lips: small RF gives higher acuity since touching 1 mm to the side will activate a new neuron
Back: Larger RF gives lower acuity since touching 1 mm to the side could be activating the same neuron
What is the relationship between lateral inhibition and sensory acuity?
Lateral inhibition sharpens sensory acuity because excited neurons reduce the activity of neighbouring neurons, enhancing contrast and sharpening sensory perception.
Lateral inhibition occurs at the […] level of processing
second-order
Explain how lateral inhibition works (using the example of three afferents A, B, and C where the stimulus affects B).
If neuron B is excited, it will send inhibitory AP to neurons A and C so the brain has a better contrast of which neuron is activated.
Lateral inhibition is a […] process
neurophysiological
Descending pathways is a […] process
neuro communication
Explain how descending pathways works.
Axons from neurons in the CNS can stop or block sensory axons (ex. pain)
The inhibition can be presynaptic or on the second-order neuron
What are astrocytes?
They are part of the nervous system, but they do not carry any information
Name 3 functions of astrocytes.
Phagocytosis of debris
Structural support
Tight junction of the blood-brain barrier
Describe the general structure of touch receptors.
They are Mecano receptors with specialized end organs that surround the nerve terminals. They allow only selective mechanical information to activated the nerve terminal
Name 2 superficial touch receptors.
Meissner’s corpuscle and the Merkel disk
Describe the structure and function of the Meissner’s corpuscle.
It’s a fluid-filled structure enclosing the nerve terminal
It’s a rapidly adapting neuron that reacts to light stoking and fluttering
Describe the structure and function of the Merkel neuron.
They have small epithelial cells that surround the nerve terminal
They are slowly adapting neurons that react to pressure and texture
Name 2 deep touch receptors.
Pacinian corpuscle and the Ruffini endings
Describe the structure and function of the Pacinian corpuscle
Large concentric capsules of connective tissue surround the nerve terminal
They are rapidly adapting neurons that react to strong vibration
Describe the structure and function of the Ruffini endings.
The nerve endings are wrapped around a spindle like structure
They react to the stretch and bending of the skin to understand shapes
What is proprioception?
a sense that lets us perceive the location and movements of our body parts.
What is the role of the end organs in tranduction?
translation of a sensory signal to an electrical signal in the nervous system.
Explain how the mechanoreceptors in the somatosensory system get activated.
The mechanoreceptor is covered in cytoskeletal stands that connect all the ion channels. When there is a mechanical deformation, the stands pull on the ion channels to open them
What type of ion channels are involved in the somatosensory system?
Mechanically gated ion channels
Explain how the somatosensory systems deals with temperature.
There are thermoreceptors on free nerve endings with ion channels that respond to different temperature ranges. They can also be activated by certain chemicals
What are the 2 main types of thermoreceptors? State their range and the chemicals that can activate them.
Cold afferents: 0-35° also activated by menthol
Warm afferents: 30-50° also activated by capsaicin and alcool
Nociceptors open in response to […]
INTENSE mechanical deformation, EXCESSIVE temperature or chemicals
Are pain afferents highly modulated or minimally modulated?
Highly (enhanced and suppressed)
What are visceral pain receptors activated by?
inflammation
When nociceptors are activated, they release […] in the […].
Substance P, spinal cord
What is the function of substance P?
It is a neurotransmitter, so it activates second order neurons that send the pain signal up to the brain.
What are the two ways in which nociceptors are enhanced?
Substance P also activate:
1. Enhancement of surrounding nociceptors by injured tissue and afferent feedback onto mast cells
2. Dilation of nearby blood vessels
Explain how enhancement of surrounding nociceptors by injured tissue works.
When substance P is released, mast cells are prompted to release histamine. The cells around the injury become more susceptible to injury, and when they burst, they release bradykinin, 5-HT, and Prostaglandin. This creates a feedback loop that increases the sensitivity of the injury and continues the release of histamine and the other substances.
Explain how enhancement of nociceptors by dilation of nearby blood vessels works.
The dilation of blood vessels causes swelling, further enhancing injury due to a more sensible somatosensory stimulation.
What is the purpose of somatosensory enhancement?
To tell you not to use the injured part of your body until healing has occurred.
Nociceptor enhancement is a […] mechanism called […]
Bottom-up, hyperalgesia
What are the 2 pathways that carry somatosensory information?
Dorsal columns and anterolateral pathway
What type of stimulus do the dorsal columns and anterolateral pathways transport?
Dorsal columns: touch and proprioception
Anterolateral: temperature and pain
Describe the 4 steps of the travel of a signal up the dorsal columns pathway.
- signal travels along the nerve through the dorsal root ganglion
- Signal travels along dorsal columns on the ipsilateral side and reaches the medulla in the midbrain.
- Signal crosses at midline and travels up to the thalamus on the contralateral side.
- Signal continues to the somatosensory cortex.
Describe the 4 steps of travel of a signal up the anterolateral pathway.
- The signal travels along the spinal nerve and enters the spinal cord through the dorsal root ganglion and the dorsal horn.
- It travels to the contralateral side of the spinal cord and then goes up via the anterolateral column.
- The signal travels up and branches into the reticular formation and goes up into the thalamus.
- The signal travels on to the somatosensory cortex.
If there is a lesion on the dorsal root, what part of the nervous system will it affect?
All somatic input at the level and ipsilateral to the lesion
If there is a lesion on the spinal cord itself, what part of the nervous system will it affect?
All sensory and motor will be gone from the lesion to the toes
If someone has loss of touch and proprioception starting at the left hand and proceeding down to the toes, all else being normal, where is their lesion?
The dorsal column ipsilateral and at the level of the left hand has a lesion
If someone has bilateral loss of touch and proprioception from the bellybutton down to the toes, all else being normal, where is their lesion?
Both dorsal column’s at the level of the belly button have a lesion
If someone has bilateral loss of pain and temperature in a thin strip at the level of the lower chest, all else being normal, where is their lesion?
The middle of the gray matter at the level of the lower chest has lesions
If someone has loss of touch and proprioception on their entire left side from the belly button down, loss of temperature and pain on their entire right side from the bellow button down, and loss of touch and temperature/pain along a thin strip on their left side, where are their lesions?
- Left dorsal column of belly button
- Left anterolateral column of belly button
- Left dorsal root
What is a somatotopic map?
A representation of receptor fields for different areas of the body (acuity of each body part)
Put the following body parts in order on a somatotopic map: genitals, face, tongue, hands, legs, back, arms, feet
Medial to lateral:
Genital, Feet, Leg, Back, Arms, Hands, Face, Tongue
What body parts occupy the most space on a somatotopic map? What does this say about their acuity?
Fingers: they have a high acuity
What is referred pain? Give an example
It’s when a visceral pain will be felt as somatic pain
Explain the cause of referred pain.
Because visceral and somatic pain afferent commonly synapse on the same second-order neuron in the spinal cord
The regulation of nociceptive information is called […] and is a […] process
Analgesia, top-down
Analgesia is a form of […]
descending pathway
In analgesia, the descending pathways release […]
Opiate neurotransmitters
What is the effect of opiate neurotransmitters released during analgesia?
It will do presynaptic inhibition on the pain afferent so it doesn’t release substance P
Give an example of a pain-reduction drug and where it takes action.
Morphine acts on the same opiate receptors
If someone feels pain on the left side of their neck without reason, what is the likely source of the pain?
Lung and diaphgram
If someone feels pain on the right side of their neck without reason, what is the likely source of the pain?
Liver and gallblader
If someone feels pain on the left side of their chest without reason, what is the likely source of the pain?
Heart
If someone feels pain in their abdomen without reason, what is the likely source of the pain?
Kidneys
