APPP 02: Gross Anatomy of the CNS – Gross Anatomy and Cellular Anatomy Flashcards
What are the major cell types of the CNS? (3)
- neurons
- glial cells
- cells of the blood brain barrier (BBB)
What is the basic unit of the nervous system?
nerve cell (neuron)
Describe the structure of nerve cells (neurons).
- cell body: contains nucleus and cytoplasm, site of transcription and translation
- dendrites: (nerve fibre) branched extensions of cell body, function to conduct impulses towards the cell
- axon: (nerve fibre) one elongated extension, functions to send messages as electrical impulses
What are oligodendrocytes?
myelinating glia of the central nervous system
- extend dendritic processes and wrap around the axon of nerve fibres to create myelin sheaths
- myelin is unique among plasma membrane equivalents in its usually high lipid content (around 70%)
What is the function of myelin?
insulates and supports CNS axons
- insulation increases the speed of nerve conduction
- results in the accumulation of voltage-gated Na+ channels at the nodes of Ranvier
What are nodes of Ranvier?
gaps on the axon in between the myelin sheaths
Defects in myelination and myelin structure have been observed in what population?
adults exposed to cocaine, cannabinoids, alcohol, methamphetamines
- affects nerve conductivity
- usually reversible, but depends on the length of drug use
- high dose of cannabinoids deteriorates myelination (causes inflammation), but low dose supports myelination
What is multiple sclerosis (MS)?
immune-mediated destruction of myelin that results in interrupted electrical nerve signals
- the most common demyelinating disease of the CNS
What are the symptoms of multiple sclerosis (MS)?
- numbness
- weakness
- cognitive difficulties
What is the therapy for multiple sclerosis (MS)?
aimed at slowing disease progression and improving quality of life
- high-dose corticosteroids are used to dampen inflammation
What are the 3 most common neuron structures?
- multipolar neuron
- bipolar neuron
- pseudounipolar neuron
What are multipolar neurons?
characterized by one axon and many dendrites that can originate from different regions of the cell body
- vary greatly in size, shape, and complexity of their dendritic tree
- the most common type of neuron in the central nervous system – ie. motor neurons
What are bipolar neurons?
two processes – one axon, one dendrite
- dendrite that receives signals usually from the periphery and an axon that propagates the signal to the central nervous system
- found in sensory organs – ie. retina, olfactory epithelium, auditory system
- least common type of neuron
What are pseudounipolar neurons?
variations of bipolar neurons – have two processes which fuse during their development into one short common axon
- axon splits into one branch that terminates in the periphery while the second branch terminates in the spinal cord – this way, stimuli from the periphery bypass the cell body and reach the axon terminal without delay
- found in sensory ganglion of cranial and spinal nerves
What are the 3 classifications of neurons?
(based on function)
- sensory neurons
- motor neurons
- interneurons
What is the function of sensory neurons?
convey signals from sensory receptors to the CNS via afferent nerves
What is the function of motor neurons?
convey information from CNS or ganglia to effector cells via efferent nerves
What is the function of interneurons?
form a communicating network between sensory and motor neurons
- make up > 99.9% of all neurons
Briefly describe the flow of information through neurons.
communication between neurons in the CNS occur through synapses
- dendrites collect
- cell body integrates
- axon passes
What are the 3 main types of ion channels and receptors that control synaptic transmission?
- voltage-gated ion channel
- ligand-gated ion channel
- metabotropic receptor
What are voltage-gated channels?
- respond to changes in membrane potential
- directly opens ion channels
What are ligand-gated channels?
- respond to neurotransmitters
- directly opens ion channels
What are metabotropic receptors?
- respond to neurotransmitters
- indirectly opens ion channels
Describe the membrane potential at resting state of a neuron.
- all voltage-gated Na+ channels and most voltage-gated K+ channels closed
- resting membrane potential: -70 mV
- Na+/K+ transporter pumps K+ ions into the cell and Na+ ions out
- inside net negative
- outside net positive
How does an action potential get generated?
- ligands bind receptors (ligand-gated ion channel or metabotropic receptor)
- changes to membrane potential as channels open
- when net charge increases to -55 mV, this sensitizes Na+ voltage-gated ion channels
- concentration of Na+ channels at axon hillock initiates action potential
- depolarization spreads down the axon, repolarization follows
- depolarization of presynaptic terminal opens Ca2+ channels, resulting in neurotransmitter release
How do voltage-gated Na+ ion channels work?
- open at -55 mV
- inactivated at +40 mV
- after inactivation, it takes time for the protein to return to resting state (unavailable for reactivation)
How do voltage-gated K+ ion channels work?
- slow to open
- once open, K+ flows out
- causes hyperpolarization
- occurs during repolarization stage
What do Na+/K+ pumps do?
active transport ions to maintain resting levels
How does synaptic transmission occur?
- Ca2+ binds to specific proteins (SNARE proteins), which triggers the complete fusion of the vesicle with the target membrane
- this results in neurotransmitter release from vesicles at the terminal bouton into the synaptic cleft, and either activation or inhibition of the neuron
How does vesicle loading (monoamine/amino acid) occur?
- carrier vesicles containing membrane transporter proteins are moved along microtubules
- small molecule (ie. acetylcholine) produced in the cell are taken into vesicles
- loaded vesicles are store at the presynaptic membrane
- depolarization leads to docking of vesicles and exocytosis into the synapse
What is orexin?
one of the many neuropeptides functioning in the CNS
Neurotransmitters
Dopamine
- mechanism
- type
- mechanism: inhibitory or excitatory
- type: monoamine
Neurotransmitters
Norepinephrine
- mechanism
- type
- mechanism: inhibitory or excitatory
- type: monoamine
Neurotransmitters
Serotonin
- mechanism
- type
- mechanism: inhibitory or excitatory
- type: monoamine
Neurotransmitters
Acetylcholine
- mechanism
- type
- mechanism: inhibitory or excitatory
- type: amino acid
Neurotransmitters
GABA
- mechanism
- type
- mechanism: inhibitory
- type: amino acid
Neurotransmitters
Glutamate
- mechanism
- type
- mechanism: excitatory
- type: amino acid
Neurotransmitters
Glycine
- mechanism
- type
- mechanism: inhibitory
- type: amino acid
Neurotransmitters
Histamine
- mechanism
- type
- mechanism: inhibitory or excitatory
- type: monoamine
Neurotransmitters
Orexin
- mechanism
- type
- mechanism: excitatory
- type: neuropeptide
What is the cerebrum?
forms the bulk of the brain
Describe the structure of the cerebrum.
- gyri (bumps) and sulci (grooves)
- large sucli called the fissure
- these ridges increase surface area
- top layer is the cortex (cerebral cortex) – made up of grey matter
- 4 lobes
What are the 4 lobes of the cerebrum?
- frontal
- parietal
- occipital
- temporal
What are the functions of the cerebrum?
- perception
- higher motor functions
- cognition
- memory
- emotion
What is the frontal lobe?
- contains motor areas
- controls intellectual activities, such as the ability to organize
- controls personality, behaviour, and emotional control
What is the parietal lobe?
- contains somatosensory areas
- controls the ability to read, write, and understand spatial relationships
What is the temporal lobe?
- contains auditory areas
- controls memory, speech, and comprehension
What is the occipital lobe?
- contains visual areas
- controls sight
Describe the left and right hemispheres of the brain.
- information is constantly being transferred between the hemispheres
- hemispheres are connected by the corpus callosum
What is the corpus callosum?
thick bundle of nerve fibres that ensures both sides of the brain can communicate and send signals to each other
- approximately 300 million axons (nerve fibres) in an average corpus callosum
What is the limbic system?
involved in behavioural and emotional responses
What are the 3 major components of the limbic system?
- hippocampus
- amygdala
- thalamus and a portion of they hypothalamus (mammillary body)
What is the amygdala?
region of the brain primarily associated with emotional processes
- involves fear and other emotions related to aversive (unpleasant) stimuli, fight or flight
- now known to be involved in positive emotions elicited by appetitive (rewarding) stimuli
What is the hippocampus?
- responsible for processing long term memory, spatial navigation, regulation of hypothalamic function, and emotional responses
- also responsible for the memory of the location of objects or people
What is the thalamus?
acts as a relay between a variety of subcortical areas and the cerebral cortex
- processing sensory and motor signals relay to cerebral cortex
- regulating consciousness, sleep, and alertness
- every sensory system (with the exception of the olfactory system) has a thalamic nucleus that receives sensory signals and sends them to the associated primary cortical area
What does the hypothalamus do?
coordinates hormonal and behavioural circadian rhythms, complex patterns of neuroendocrine outputs, and homeostatic mechanisms
What is the brainstem?
connects the brain to the spinal cord and the rest of the body
What are the 3 parts of the brainstem?
- midbrain
- pons
- medulla
What is the midbrain responsible for?
- auditory and visual signals
- arousal
- human consciousness
What is the pons responsible for?
carries signals that control basic functions – ie. sleep
What is the medulla responsible for?
control of involuntary functions – ie. breathing and heart rate
What is the neocortex?
top layer of the cerebrum is the cortex – 6 layer structure called the neocortex
What does the amygdala comprised of?
group of nuclei, or clusters of neurons
How does the amygdala work?
uses interconnections with limbic and sensory cortex to form associations (ie. good or bad) and trigger appropriate responses
What is the lateral nucelus (LA)?
the sensory interface of the amygdala – key site of plasticity
What is the central nucleus (CE)?
viewed as the output region
Amygdala
Describe a normal physiological state.
- balance between glutamate and GABA maintains emotional responses at the level appropriate to external stimuli
- regulated by activation of either glutamatergic neurons or GABAergic neurons
What is the amygdala essential for?
the acquisition and storage of a memory of a conditioned experience and the expressed response
Amygdala
What is fear conditioning?
procedure in which an emotionally neutral conditioned stimulus (CS) is presented in association with an aversive unconditioned stimulus (US)
- auditory thalamic and prefrontal input pathways onto the LA can lead to fear memory formation
What happens in the event of amygdala dysfunction?
- anxiety disorders – ie. generalized anxiety disorder, phobias, panic attacks, PTSD, more
- seizures
- pain conditions – ie. neuropathic pain
What is the treatment for amygdala dysfunction?
- benzodiazepines, sedative/anti-anxiety drugs (valium) – enhances GABA-mediated synaptic inhibition and increases inhibitory signals to balance activation
- serotonin levels are low in patients with emotional disorders – enhanced glutamatergic activity in the lateral nucleus (LA) of the amygdala and potentiated fear behaviours
- SSRI – decreases the amygdala response to fear and other aversive stimuli
What is the entorhinal cortex (EC)?
the major input and output structure of the hippocampal formation
- spatial information relays through the medial entorhinal cortex (MEC)
- non-spatial information relays through lateral entorhinal cortex (LEC)
What type of neurons does LEC and MEC have?
cholinergic (acetylcholine)
What are the 4 sections/sub-structure of the hippocampus?
- MEC and LEC project into the hippocampus dentate gyrus (DG) region
- project into the CA3 region (cornu ammonis)
- CA3 projects to the CA2 and CA1
- CA1 projects back to the entorhinal cortex
What neurotransmitters do hippocampal neurons mainly release?
glutamate or GABA
What is Alzheimer disease?
progressive neurodegenerative disease most often associated with memory deficits and cognitive decline
- related to hippocampus
- damage to cholinergic neurons
- LEC and MEC contain cholinergic neurons
- progressive loss of neurons
- progressive memory impairment and cognitive dysfunction
What is the damage to cholinergic neurons caused by in Alzheimer disease?
- Aβ plaques (generated from amyloid precursor protein cleavage)
- Tau protein aggregates
Clinical diagnosis of Alzheimer disease is based on what symptoms?
- memory impairment
- irritability
- paranoia and delusional thinking
- *loss of sense of smell is often an early indicator
What is the treatment for Alzheimer disease?
- cholinesterase inhibitors
- agents that block the breakdown of acetylcholine
What essential role does the thalamus and brainstem play?
a role in sleep-wake regulation and role
What is one of the most important functions of the hypothalamus?
linking the nervous system to the endocrine system via the pituitary gland
What are some other functions of the hypothalamus?
- temperature regulation
- appetite
- sexual dimorphism (difference between males/females during gestation)
What can disorders of the hypothalamus result in?
appetite, temperature, and sleep disorders
What is hypothalamic obesity?
can develop from major hypothalamic injury/damage affecting the centers of appetite regulation and energy balance
