Module 4: Neurology Flashcards
Three types of neurons?
Sensory Interneurons Efferent
Two types of sensory neurons?
Psuedounipolar and bipolar
What are psuedounipolar neurons?
Psuedounipolar neurons have a single process called the axon. During development, the dendrites fuse with the axon.
What are bipolar neurons?
Bipolar neurons have two relatively equal fibres extending off the central body.
Two types of interneurons?
Anaxonic and multipolar
What are anaxonic interneurons?
Anaxonic CNS interneurons have no apparent axon
What are multipolar interneurons?
Multipolar CNS interneurons are highly branches but lack long extensions
What are efferent neurons?
A typical multipolar efferent neuron has five to seven dendrites, each branching four to six times. A single long axon may branch several times and end at the enlarged axon terminal
What cells support neurons? What ratio do they uphold?
Glial cells support neurons. The ratio of glial cells to neurons is 50:1
If an axon is damaged, what occurs?
Under some circumstances, the proximal axon may regrow through the existing sheath of Schwann cells and reform a synapse with the proper target
What is a resting membrane potential determined primarily by?
K+ concentration gradient, and the cell’s resting permeability to K+, Na+ and Cl-
What channels control ion permeability?
Gated channels
Three types of gated channels?
Mechanically gated Chemically gated Voltage-gated
Two types of graded potentials?
Sub-threshold and supra-threshold graded potentials
What is a sub-threshold graded potential?
A graded potential starts above threshold (T) at its initiation point but decreases in strength as it travels through the cell body. At the trigger zone, it is below the threshold and therefore does not initiate an action potential
What is a supra-threshold graded potential?
A stronger stimulus at the same point on the cell body creates a graded potential that is still above threshold by the time it reaches the trigger zone, so an action potential results
What is conduction in action potentials?
Conduction is the high-speed movement of an action potential along an axon
What are the nodes of the axon called in nerves?
Nodes of Ranvier
Can signals in gap junctions be bi-directional?
Yes
What are the excitatory and inhibitory amino acids of the brain?
Excitatory: Aspartate Inhibitory: GABA
What is the excitatory amino acid of the CNS?
Glutamate
How does aspartate excite a brain cell?
By depolarising target cells
How does aspartate inhibit a brain cell?
By hyper-polarising target cells by opening Cl- gates
What enzyme breaks down neurotransmitters?
Acetylcholinesterase
What determines how much of a neurotransmitter is released?
Frequency of action potentials
What is a divergent pathway?
One pre-synaptic neuron branches to affect a larger number of post-synaptic neurons
What is a convergent pathway?
Many pre-synaptic neurons provide input to influence a smaller number of post-synaptic neurons
(Advanced Question) How many capillaries are in the brain?
400 miles worth
(Advanced Question) What promotes a tight junction in the blood brain barrier?
The astrocyte foot secretes paracrines that promote tight junction formation, and tight junctions prevent solute movement between endothelial cells.
What is responsible for joining the two halves of the brain? What function does this utilise?
The corpus callosum allows for cerebral laterilisation
Three structural types of sensory receptors?
Simple Complex Special
What are simple receptors?
Simple receptors are neurons with free nerve endings. They may have myelinated or unmyelinated axons
What are complex neural receptors?
Complex neural receptors have nerve endings enclosed in connective tissue capsules
What are special neural receptors?
Most special senses receptors are cells that release neurotransmitter onto sensory neurons, initiating an action potential
What are the four main types of sensory receptors?
Chemoreceptors Mechanoreceptors Photoreceptors Thermoreceptors
What type of receptors are baroreceptors?
Mechanoreceptors
What type of receptors are osmoreceptors? What do they detect?
Mechanoreceptors - detect cell stretch length
What determines the amount of space on the somatosensory cortex?
The amount of space on the somatosensory cortex devoted to each body part is proportional to the sensitivity of that part
(Advanced Question) What gland secretes tears?
The lacrimal gland
(Advanced Question) What duct connects the eyes to the nasal cavity?
The nasolacrimal duct
What is the pupil?
An opening that widens and shrinks when pupillary muscles contract
What is the iris?
The coloured ring of pigment around the eye
What are the two chambers in the eye?
One is in front of the lens and is filled with an aqueous humor covered by the cornea The second is behind the lens and is a larger, vitreous chamber filled with a vitreous body
What is vitreous?
Glass-like
What is the retina?
The retina layer lines the back of the eye and contains photoreceptors
What is the blind spot in the eye called? Where is it?
The optic disk (blind spot) is the location where neurons join into the optic nerve
Where do optic nerves cross over?
In the optic chiasm
Where does the optic tract end?
At the visual cortex in the occipital lobe
How does the eye produce vision?
Light enters the eye, focused on the retina by the lens Photoreceptors transduce light energy into electrical signals Neural pathways process electrical signals into visual images
What does the size of the pupil modulate?
The amount of light that reaches the photoreceptors
What is the pupil’s reflex called? What type of reflex is it?
The pupillary reflex is a consensual reflex
What is the pupillary reflex?
Light in one eye causes constriction in the other eye
What are the differences between parasympathetic and sympathetic fibres in the eye?
Constriction occurs in response to parasympathetic fibres in bright light Dilation occurs in response to sympathetic nervous system in dim light
Where does light entering the eye refract?
At the cornea and lens
What influences refraction?
The angle at which light meets the lens
Two types of lens? What type of lens is the eye lens?
Concave lens Convex lens (eye)
What does a concave lens do?
Scatters light rays
What does a convex lens do?
Causes light rays to converge
What is the focal length of the lens?
The focal length of the lens is the distance from the centre of the lens to the focal point
What is a photon?
A discrete packet of energy
What is light?
A photon with a certain portion of electromagnetic spectrum
What is accommodation?
A process by which the eye adjusts lens shape to keep objects in focus
Where is the near point of accommodation?
The closest distance at which the lens can focus on an object
How does the lens keep an object in focus as it moves closer?
It becomes more rounded
Why can a close object be blurry?
The light rays are no longer parallel. The lens and its focal length have not changed, and thus the light beam is not focused on the retina
What is the difference between myopia and hyperopia?
Myopia is when the focal point falls in front of the retina Hyperopia is when the focal point falls behind the retina
What is a loss of accommodation called in vision?
Presbyopia
What is astigmatism?
A distorted image usually caused by a cornea that is not a perfectly shaped dome