Nervous System Organization Flashcards
Describe the relationship between sensory neuron/interneuron and excitatory/inhibitory
If the sensory neuron is excitatory then the interneuron must be inhibitory
Can neural tissue be repaired or replaced if it is damaged? (in the PNS/CNS)
If you cut a neuron’s axon, it will usually regrow if it is in the PNS (if the Schwann cells are still there), but will not regrow if it is in the CNS
If you cut the axon far enough from its cell body, there is a chance that it will regrow!
What makes up the CNS and the PNS?
CNS and PNS make up most of the nervous system
CNS - mostly interneurons and synapses (white and gray matter / neurons and glial cells)
PNS - mostly sensory and motor neurons (neurons and glial cells)
Describe the organization of the CNS
The CNS has the MAJORITY of the neurons and synapses
Contains majority of neuron cell bodies
Also contains layers of extra protection for its tissues inside the skull and vertebral column
White matter in the CNS acts as a highway connecting/sending information from one place to another
What is cerebrospinal fluid (CSF)
Different from extracellular fluid - specialized for the central nervous system
Fluid that continually flows in the cavities of the brain’s ventricles and around the brain/spinal cord
What are the four characteristics of CSF?
- CSF is produced by the ependymal cells in the brain’s ventricles (get the fluid from blood supply)
- CSF drains wastes from CNS tissue through glymphatic pumping
- assisted by astrocytes
- pumped through every bit of brain tissue
- takes away toxins that are harmful for the brain (happens when sleeping) - CSF cushions impact between CNS and skull
- fills space between the spinal cord and vertebra / brain and skull
- contained in layers of membrane called meninges - Returns CSF to bloodstream
- constantly being produced, so it needs to be drained or else pressure will build up
- valves coming out of the second/third layers of meninges where fluid can be drained out
- fluid is circulated, taking away wastes and returning to the bloodstream
What is the blood brain barrier (BBB)?
A barrier that restricts the transport of water and molecules between the blood and CNS
There is a tight epithelium/endothelium lining blood vessels that only allows lipophilic molecules or hydrophilic molecules with specific transport proteins to reach the CNS
Materials can only pass from brain to blood if they can pass through the walls of the epithelium
Endothelial cells in the CNS express high numbers of what kind of transporters?
Endothelial cells in the CNS express high numbers of glucose transporters and co-transporters
What kind of glial cell controls blood vessel diameter?
Astrocytes!
Astrocytic processes control blood vessel diameter, and thus can rapidly adjust local blood flow
Determines how much oxygen can get to a particular section
What do functional MRI (fMRI) scans do?
Estimate activity in different CNS locations based on the amount of blood flow under different conditions
Whether the astrocytes are dilating the blood vessels for increased blood flow
What are the two main components of the central nervous system?
- Spinal cord
- Brain
What is the function of the PNS?
- collect and relay sensory/afferent info
- relay motor/efferent commands
- contains the sensory and motor nerves
- path for nerves to go to and from the spinal cord
- nerves carrying commands to efferent organs coming from CNS
- system of wireless relaying
What is the function of the CNS (brain/spinal cord)?
BRAIN
- contains the majority of the (inter)neurons and synapses
- comparing all sorts of sensory info coming through
- complex processing/remembering/etc
- conscious awareness
- source of voluntary control (movements)
SPINAL CORD
- initial processing of sensory/afferent info
- executes motor/efferent commands to skeletal muscles
- in charge of reflexes (action potentials in skeletal muscles that do not pass through the brain)
- most motor neurons making NMJ can be found here
- generating streams of action potentials
The destination or source of the most efferent(motor) and afferent(sensory) axons of the PNS are located at the _____________
Spinal cord
And it is topographically organized by regions
What are the four regions of the spinal cord?
- Cervical
- Thoracic
- Lumbar
- Sacrum
Each spinal cord segment shows the same organization of afferent and efferent nerve roots: Describe the two types of roots
Note: Roots enter and leave the spinal cord
- Dorsal root = ENTERING
- contains afferent axons
- has a bulge (ganglia)
- sensory axons entering the spinal cord - Ventral root = LEAVING
- contains efferent axons
- handles motor information
What would happen if your dorsal root was damaged?
Since the dorsal root is in charge of handling sensory information (afferent neurons)
If it was damaged, then that would result in sensation deficit = numbness
What would happen if your ventral root was damaged?
Since the ventral root is in charge of handling motor information (efferent neurons)
If it was damaged, then that would result in movement deficit = paralysis
(You would not be able to move your skeletal muscles)
What region does the cervical spinal cord segment process information to and from?
Upper limbs
What region does the lumbar spinal cord segment process information to and from?
Lower limbs
What region does the thoracic spinal cord segment process information to and from?
Trunk
What region does the sacral spinal cord segment process information to and from?
Lower limbs / ano-genital region
Describe the ratio of white matter to grey matter as you get closer to the brain up the spinal cord
Amount of white matter increases as you get closer to the brain
Ex: Sacral segment has the least white matter: grey matter, where the cervical segment has the most white matter: grey matter
White matter thickness increases steadily as you go from inferior to superior segments, but there are enlargements of gray matter in the cervical and lumbar regions
What symptom would be experienced if:
There was a squeezing of VENTRAL ROOT from the bulging CERVICAL intervertebral disc
Motor neuron damage = Paralysis in the upper limbs
Weakness/paralysis of upper limbs or hand
What symptom would be experienced if:
There was DORSAL ROOT avulsion (detachment) in SUPERIOR SACRAL segments
Sensory neuron damage = Numbness in the lower limbs/ano-genital region
Numbness of posterior surface of lower limb
What symptom would be experienced if:
There was a rupture of the L1 or L2 spinal nerve
The spinal nerve connects to both the dorsal and ventral root
Would result in both motor and sensory neuron damage = weakness, paralysis, and numbness
Numbness of proximal thigh AND lower limb weakness or paralysis
What are the two regions of gray matter?
Dorsal horn
Ventral horn
What is the dorsal horn? Characteristics and functions
Sensory processing
- affects sensation
What is the ventral horn? Characteristics and functions
Contains motor neurons, dendrites, and somata (cell bodies)
Dorsal regions of the spinal cord refer to the front / back
back / upperside
Ventral regions of the spinal cord refer to the front / back
front / underside
Does the withdrawal reflex arc take place in white or gray matter?
Simple spinal reflexes such as the withdrawal reflex are contained within circuits in the spinal segment’s GRAY MATTER
Trace the path of a spinal withdrawal reflex
Sensory neuron -> dorsal root
Interneuron
Motor neuron -> ventral root
What kind of information does the dorsal column (white matter) of the spinal cord segment carry?
GOING UP!
Ascending sensory relay to brain
- carrying sensory information
- affecting arms and legs
- only way info can go from lower limbs to the brain
What kind of information does the lateral column (white matter) of the spinal cord segment carry?
GOING DOWN!
Descending motor commands from brain to motor neurons
- affecting everything in the lower limbs
White matter columns are largest in the ______ levels of the spinal cord
They are smallest in the ________________________
Largest in superior levels of the spinal cord
- axons relaying between the brain & all spinal levels
Smallest in the sacral spinal cord
- only containing axons communicating with sacral nerves/sacral motor neurons
What is the function of white matter in spinal cord segments?
To act as highways communicating what is coming in and going out of the spinal cord
What symptoms would be experienced if there was:
Damage in dorsal column
Dorsal column = ascending white matter
- sensory information relay to brain affecting arms and legs
Numbness in arms, legs, and torso
(anything ascending up the spinal cord)
What symptoms would be experienced if there was:
Damage in dorsal horn
Dorsal horn = gray matter
- in charge of spinal reflexes
- sensation
Impaired withdrawal reflexes (sensory)
What symptoms would be experienced if there was:
Damage in lateral column
Lateral column = white matter
- descending motor commands
- affects lower limbs
Paralysis in lower limbs
What symptoms would be experienced if there was:
Damage in ventral horn
Ventral horn = gray matter
- in charge of motor neurons, dendrites, and cell bodies
Impaired withdrawal reflexes (motor)
What are the anatomical regions of the brain?
- Forebrain
- Midbrain
- Hindbrain
What are the physiological regions of the brain?
- Cerebrum
- Diencephalon
- Cerebellum
- Brainstem
What is the telencephalon of the brain?
Commonly known as the cerebral hemispheres
There are three main components to the telencephalon:
- Limbic system
- Basal ganglia
- Cerebral cortex
Where are the neuron cell bodies in the human brain found?
Most neuron cell bodies in the human brain are found within the CEREBRAL CORTEX of the telencephalon
What are the 5 lobes of the cerebral cortex
- parietal lobe
- occipital lobe
- frontal lobe
- temporal lobe
- insula
What are the 6 primary cortical areas of the cerebral cortex?
M1: primary motor cortex
G1: gustatory cortex
O1: olfactory cortex
A1: primary auditory cortex
V1: primary visual cortex
S1: primary somato-sensory cortex
What are the functions of the frontal lobe?
- executive lobe
- actions
- motor control
- problem-solving
- speech production
What are the functions of the parietal lobe?
- taste
- touch perception
- temperature
What are the functions of the temporal lobe?
- hearing / auditory perception
- memory / information retrieval
- language comprehension
What are the functions of the occipital lobe?
- vision
What are the functions of the primary motor cortex?
to generate signals to direct the movement of the body
What are the functions of the gustatory cortex?
perception of taste and flavour
What are the functions of the olfactory cortex?
processing and perception of odour
What are the functions of the primary auditory cortex?
bring about the conscious perception of sound
provide a basis for the comprehension and production of meaningful utterances
What are the functions of the primary visual cortex?
to receive, segment, and integrate visual information
What are the functions of the primary somato-sensory cortex?
to detect sensory information from the body regarding temperature, proprioception, touch, texture, and pain
What are the functions of the brainstem?
involuntary responses
What are the functions of the cerebellum?
balance and coordination
Where do most spinal descending and ascending pathways originate from or lead to?
PRIMARY CEREBRAL CORTICAL AREAS
Most spinal descending and ascending pathways terminate at or originate from the primary cerebral cortical areas
In ascending projections, what two areas relay synapses?
- thalamus
- hindbrain
Do primary cortical areas connect to spinal nerves on the same side of the body?
NO!
Primary cortical areas are directly connected to spinal nerves on opposite sides of the body
In other words, they process info coming from or going to the other side of the spinal body
What does decussation mean?
Decussation means crossing the midline
It describes how the primary cortical areas are connected to spinal nerves on the opposite sides of the body
The brain is lateralized: What does this mean?
The brain is separated so that different sides dominant certain functions
This works hand in hand with the decussation of the hindbrain, in that info coming from the left side is processed by the right hemisphere whereas info coming from the right side is processed by the left hemisphere
What is an electroencephalography (EEG) and what is its purpose?
A machine that measures electrical fields generated by the activity of neurons in the brain that can be detected from electrodes on the scalp -> used to help map the origin of epileptic seizures
How do EEGs help map out the origin of epileptic seizures?
The electrodes nearest the abnormal brain tissue that initiates the seizure will show abnormal activity before other electrodes
By surgically removing this abnormal brain tissue, some forms of epilepsy can be cured!
How does mild electrical stimulation of the cortex probe for seizure foci and map precise sub-regions within primary cortices?
Lightly stimulating the motor strip (M1) triggers twitch movements of different muscles/parts of the body, depending on exactly where you stimulate
Stimulating in a primary sensory cortex creates phantom sensations for that sensory modality
