Physiology (Peters) Flashcards
What is the role of a dendrite?
Receive inputs from other neurones
Convey graded electrical signals passively to the soma
What is the role of the cell body (soma)?
Intergrate incoming electrical signals that are conducted passively to axon hillock
What is the role of the axon hillock and initial segment?
The site of initiation of the “all or none” action potential
What is the role of the axon?
To conduct output signals as action potentials to presynaptic terminal.
If the axon mediates transport of materials between the soma and presynaptic terminal what is this called?
Anterograde
Opposite direction is retrograde
What occurs at the synapse?
Point of chemical communication between neurones
What is the clinical importance of retrograde transport of material?
Several viruses (herpes, polio, rabies) can exploit this transport to infect neurones
Where are unipolar neurones (one neurite) usually found?
Peripheral autonomic system
Where are pseudounipolar (one neurone that bifurcates) neurones usually found?
Dorsal root ganglion
Where are bipolar (two neurites) neurones usually found?
Retina
Where are multipolar neurones (three or more neurites) usually found?
Lower motor neurones
What are the four functional regions of the neuron?
Input
Intergrative
Conductile
Output
What type of neurone transmits information from skin to dorsal horn of spinal cord?
Sensory neuron
What type of neurone transmits information from ventral horn to spinal cord to skeletal muscle?
Motor neurone
What type of neurone transmits information between neurones in CNS
Local interneurone
What type of neurone transmits information from dorsal of spinal cord to brain structures?
Projection neurones
Describe the action potential
Stimulus arrives Membrane passively depolarised up to a point where Na channels open Threshold is reached Na enters cells Upstroke of membrane potential so fast Cascade of opening of Na channels Positive feedback Reaches +40 at the same time voltage K are open but slight delay Allows membrane potential to decrease Afferent hyper-polarisation
What happens to the strength of the passive signal as it travels from it’s site of origin along the axon?
Strength of signal diminishes
Passive signals do not spread far due to loss across the membrane
Opening of which ion channel causes depolarisation of the membrane?
Na channel
What two factors will determine how long the distance that the current will spread?
Membrane resistance
Axial resistance of axoplasm
How can passive current spread be increased?
Increasing axon diameter
Add insulating material
Which cell provides myelin in the PNS?
Schwann cells
Which cell provides myelin in the CNS?
Oligodendrocytes
Many Schwann cells surround a single axon and only one oligodendrocyte surround many axons. True/False?
True
Conduction in myelinated axons is much slower/faster than in non-myelinared axons of the same diameter?
Faster!
What is the name of the site that action potentials ‘jump’ to and from?
Node of Ranvier
Name two demyelinating disorders
Multiple sclerosis (CNS) Guillian-Barré (PNS)
What are the 3 morphological classes of synapses?
Axodendritic (Most common)
Axosomatic
Axoaxonic (Least common)
What is commonly the transmitter for excitatory synapses in the CNS?
Glutamate
What are the three major amino acid neurotransmitters in the CNS?
Glutamate, GABA and glycine
What is commonly the transmitter for inhibitory synapses in the CNS?
GABA
What are the sensations covered by the somatosensory system?
Fine discriminatory touch Proprioception Thermosensation Nociception (Pain) Pruriception (Itch)
What are 3 divisions of the somatosensory system?
Exteroceptive- cutaneous senses
Proprioceptive- posture and movement from sensors in muscle, tendons and joints
Enteroceptive- internal state of body (autonomic function closely linked)
What are the 3 neurones that comprise the somatosensory pathway?
1st order neurone in PNS (primary sensory afferent)
2nd order neurone in CNS (projection neurone)
3rd order neurone in CNS (projection neurone)
Somatosensory cortex
How does a stimulus (mechanical, thermal or chemical) elicit a depolarising receptor potential?
Stimulus opens cation selective ion channels in peripheral terminal or primary sensory afferent
What is modality?
Primary afferent neurones are especially ‘tuned’ to respond to a specific type of energy (stimulus) that normally excited them
What is meant by threshold?
Relates to the intensity of a stimulus required to excite a sensory unit
What do low threshold mechanoreceptors sense?
Fine discriminatory touch
What do low threshold thermoreceptors sense?
Cold, cool, indifferent warm and hot
What do high threshold units (nociceptors) sense?
High, noxious (potentially damaging), not low intensity stimuli
What do high threshold mechanoreceptors (mechanical nociceptors) sense?
High intensity mechanical stimuli
What do thermal nociceptors sense?
Extreme degrees of heat (>45C) or cold (<10-15C)
What do chemical nociceptors sense?
Substances in tissue (inflammation, prostaglandins, bradykinin, serotonin, histamine etc)
What is adaptation?
Changing of firing rate in response to a stimulus of changing intensity
What are factors that differ between primary sensory afferent fibres?
Axon diameter
Extent of myelination
Conduction velocity
Associated sensory receptor
Name the groups of primary sensory afferent fibres from thickest to thinnest
Group 1–>Group IV
Aα, Aβ, Aδ, C
What is the sensory receptor for Aα fibres?
Proprioceptors of skeletal muscle
What is the sensory receptor for Aβ fibres?
Mechanoreceptors of skin
What are the sensory receptors for Aδ fibres?
Pain and temperature
What are the sensory receptors for C fibres?
Temperature, pain, itch
