Physiology Flashcards
What are dendrites?
Terminals that receive electrical impulses and convey these to the soma.
What is the metabolic centre of a neuron also known as?
The soma.
It is the cell body.
What occurs at the axon hillock?
Action potential initiation.
Where information received is assimilated.
Once the APs have left the soma, where do they head?
Presynaptic cleft
An AP heading from the soma to the presynaptic cleft is said to be what?
Anterograde
An AP heading from the presynaptic cleft to the soma is said to be what?
Retrograde
What occurs at the synapse?
Chemical communication.
Give examples of viruses that exploit retrograde transport.
Herpes
Polio
Rabies
What are the 4 main functional regions of a neuron?
Input
Integrative
Conductive
Output
What are the 4 different types of neuron?
Unipolar
Pseudounipolar
Bipolar
Multipolar
In AP generation, does Na+ influx precede K+ efflux?
Yes
What is the length constant?
The distance a current can spread before it diminishes to 0.
Is conduction faster in myelinated or non-myelinated axons?
Myelinated axons.
In myelinated axons, what are the areas that APs jump between referred to as?
Nodes of Ranvier
What occurs at the Nodes of Ranvier?
Na+ influx.
Give 2 examples of demyelinating conditions?
Guillain-Barre syndrome
Multiple sclerosis
What effect does demyelination have on AP conduction?
Slows it down.
Can lead to compete cessation in severe disease.
What ion is responsible for the release of the neurotransmitters into the synaptic cleft following AP conduction?
Ca2+
Enters the presynaptic cleft via the voltage-gated channels.
What is found in the presynaptic cleft area?
Vesicles
These contain inactive neurotransmitters, awaiting release.
What is found in the postsynaptic cleft area?
Many receptors to bind the neurotransmitters upon their release.
What neurotransmitter most commonly activates excitatory synapses?
Glutamate
What are the 2 main roles a synapse can play?
Excitatory
Inhibitory
What neurotransmitters are inhibitory in the CNS?
GABA
Glycine
What is temporal summation?
When a single pre-synaptic neuron fires many times, resulting in a postsynaptic neuron reaching its threshold.
What is the role of the somatosensory system?
Detecting stimuli from across the body.
May be of internal or external origin.
What do low threshold receptors respond to?
Non-harmful stimuli.
These include fine discriminatory touch.
What do high threshold receptors respond to?
Noxious stimulation.
How many neurons are typically involved in a somatosensory pathway?
3 neurons.
1st order is in the PNS.
2nd and 3rd order is in the CNS.
Where does all sensory information collected travel to?
The primary somatosensory cortex.
What is meant by adaptation rate?
The intensity of stimulation needed to excitate the receptor.
Receptors with a high threshold are responsible for what?
Pain or other noxious stimuli.
What is the function of slow adapting sensory units?
Provide continuous information to the CNS.
What is adaptation?
A feature of sensory units that determines whether the rate of AP discharge changes, or remains constant, due to a stimulus.
What do fast adapting sensory units do?
Rapid movements.
The area supplied by peripheral nerve endings is called what?
The receptor field.
This varies in size dependent on where it is located on the body.
What is the relationship between sensory acuity and the size of the receptor field?
As receptor field decreases, sensory acuity increases (converse also applies).
What is the benefit of having many receptors close together?
Allows for a greater degree of discrimination between receptor fields - higher sensitivity.
Where is the area of highest innervation density?
The fingers.
What is the name of the mechanoreceptor responsible for fine touch and pressure?
Meissner’s corpuscle
Where is the cell body of a spinal nerve located?
Dorsal root ganglion
What is found within a dorsal root?
Sensory neurons that innervate a single dermatome.
What test is used to test somatosensory function?
Two-point discrimination
How many pairs of spinal nerves are there?
31 sets.
What is the virus responsible for shingles and chickenpox?
Varicella zoster
Once infected with varicella zoster, where does it live?
The dorsal root ganglion.
What does grey matter contain?
Neuronal cell bodies
Afferent terminals
What does white matter contain?
Fibre tracts
Where does crossover of the DCML tract fibres occur?
The brainstem.
The process of nerve fibres crossing to their contralateral side is called what?
Decussation
What is the DCML pathway responsible for?
Fine touch
Pressure
Vibration
Proprioception
Where does decussation of the spinothalamic tract occur?
Within the spinal column, prior to reaching the thalamus.
Where does information from the DCML and spinothalamic tract head to?
Primary somatosensory cortex
In the spinothalamic tract, does decussation occur at every spinal level?
Yes
The medial tract of the DCML is called the gracile. What information is carried here?
Sensory afferents of the legs and lower trunk.
Input from T6 and above is carried in the DCML via the lateral tract. What is it called?
Cuneate tract.
Where do the gracile tracts of the DCML synapse?
Gracile nucleus of the brainstem.
Where do the cuneate tracts of the DCML synapse?
Cuneate nucleus of the brainstem.
Name 5 abilities conveyed by the DCML.
Stereognosis Fine touch Conscious proprioception Vibration detection Weight discrimination
What is contrast enhancement?
The process by which one neuron in a sensory pathway, when activated, can amplify the difference in activity in the surrounding neurons.
This allows the exact neuron triggered to be ascertained.
What is lateral inhibition?
When one neuron is active, it inhibits the surrounding neurons.
This sharpens perception of stimulus, allowing localisation of the sensation.
Where is the somatosensory cortex located?
Post central gyrus.
What are the subdivisions of the PSC called?
Brodmann bands
There are 4 of these - 1, 2, 3a, and 3b.
What are Brodmann bands 3a and 3b responsible for?
Proprioception and other touch information.
What areas have the greatest representation within the PSC?
The hands and face due to high levels of receptors in these areas (high sensitivity).
What is the role of the posterior parietal cortex in somatosensation?
Receive and integrate information from the PSC, allowing the deeper meaning of the information to be deciphered.
What is the role of cerebral pattern generators?
To allow simple activities to be carried out without thought.
An example is walking.
Where are UMNs found?
Within the brain.
Where are LMNs found?
Within the brainstem or the ventral horn of the spinal cord.
What are LMNs made of?
Alpha-MNs
Gamma-MNs
What sources supply information to LMNs?
UMNs
Proprioception
Interneurons
What is the role of alpha-MNs?
To innervate the bulk of muscle fibres in order to generate a force.
What is the role of gamma-MNs?
To innervate a sensory organ within the muscle.
The sensory organ is a muscle spindle.
What is the name given to a group of muscles that work together in order to carry out a function?
Synergists
What are antagonistic muscles?
Those that work to oppose each other.
What do axial muscles do?
Maintain posture.
What do proximal muscles do?
Mediate locomotion.
Where do the axons of LMNs exit the spinal cord?
The ventral roots.
Anterior/Ventral roots consist of which fibres?
Motor fibres
Posterior/Dorsal roots consist of which fibres?
Sensory fibres
At which points is there a greater distribution of motor neurons?
Cervical enlargement
Lumbar enlargement
Between which vertebrae levels is the cervical enlargement found?
C5-T1
Between which vertebrae levels is the lumbar enlargement found?
L1-S3
What comprises a motor unit?
Alpha-MN
All of the skeletal muscle it innervates
What is a motor pool?
The collection of motor neurons that innervate a single muscle.
What 2 factors influence the strength of a muscle contraction?
The frequency of AP discharge
The recruitment of additional motor units
What differs between slow-twitch and fast-twitch fibres?
The rate at which ATP is hydrolysed.
Which type of muscle fibres are fatigue-resistant?
Type 1 fibres
Can a muscle contract if only alpha-MNs are activated?
No, they will be inhibited by gamma-MNs.
Co-activation is key to contraction.
