Week 1 Flashcards
What is the definition of Afferent?
Neurons that receive information from our sensory organs and transmit this input to the central nervous system
Define Efferent
Neurons that send impulse from central nervous system to your limbs and organs
Define peripheral afferent receptors
Stimulation of specialised receptor endings produces a receptor potential
Physical stimulus is then transfixed to electrical signal by activation of specific ion channels on the receptors
What does mechanoreceptors sense stimuli due to?
Physical deformation of their plasma membranes
What does mechanoreceptors Contain?
Mechanically gated ion channels Gates open/close in response to pressure Touch Stretching Sound
What are mechanoreceptors in the skin described as?
Encapsulated
Unencapsulated
What are free nerve endings sensitive to?
Painful stimuli
Hot and cold
Light touch
What are 4 primary tactile mechanoreceptors in human skin?
Merkel’s disk
Meissner’s Corpuscle
Ruffini endings
Pacinian Corpuscle
What are 2 types of mechanoreceptors?
Slowly-adapting
Rapidly-adapting
What is slow adapting nerve fibres?
Send information about ongoing stimulation
What is rapidly adapting nerve fibre?
Send information related to changing stimuli
What is epidermis?
The outermost later of skin
Provides a waterproof barrier
Creates skin tone
What is the dermis?
Beneath the epidermis
Contain tough connective tissue
Hair follicles, sweat glands
What are the properties of Merkel’s disk?
Location: upper layer of skin, base of epidermis
Distribution: fingertips and lips
Function: slowly adapting, unencapsulated nerve endings - respond to light touch
Receptive field: small, well defined borders - sensitive to edges - typing on keyboard
What are the propertied of Meissner’s Corpuscle?
Location: upper dermis - project to epidermis
Distribution: fingertips and eyelids
Function: respond to fine touch and pressure - low frequency vibration
Type: rapidly-adapting, fluid filled, encapsulated nerve endings with well defined border - responsive to fine detail
What are the properties of Ruffini endings?
Location: deeper in the dermis, near base - bulbous corpuscles
Distribution: glabrous and hairy skin
Function: slow-adapting, encapsulated mechanoreceptors - detect skin stretch and deformations within joints - gripping objects and controlling finger position and movements
Contribute to proprioception and kinaesthesia
Detect warmth
What are the properties of Pacinian Corpuscles ?
Location: deep in the dermis of both glabrous and hairy skin
Distribution: bone periosteum, joint capsules, pancreas and other viscera, breast and genitals
Function: rapidly adapting mechanoreceptors, sense deep, transient pressure - high frequency vibration
What does nerve consist of?
Sensory afferent axon
Motor efferent axon
What are nerve axons and their associated Schwann cells bound together by?
Connective tissue - endoneurium
What are fascicles enclosed in?
Connective tissue sheath called perineurium
What is the whole nerve enclosed in?
Tough coat —> epineurium
What does epineurium provide to the nerve?
Mechanical strength
Support
What is epineurium continuous with?
Dura Mater
What forms the outer and inner components of the perineurial sheath?
Arachnoid and Pia Mater
What does cerebrospinal fluid contribute to?
Endoneurial fluid via pial tissue space
What are sensory nerve fibres?
Pseudo-unipolar
What does pseudo-unipolar neuron consist of?
One axon with two branches: central and peripheral
Why are sensory neurons an exception?
They do not have separate dendrites and an axonal process, rather one branched process that serves both function
Where are the soma of each pseudo-unipolar neuron located within?
Dorsal root ganglion
Where does the axon leave the cell body?
Into dorsal root where it splits into 2 branches
Where does the central branch go to?
Dorsal column of the spinal cord where it forms synapses with other neurons
Where does the peripheral branch travel through?
Distal dorsal root into the spinal nerve all the way until skin, joint and muscle
What can medium-sized DRG neurons give rise to and what can it innervate?
Myelinated axons
Innervate skin or muscle structures
Muscle structures: Golgi tendon organ or muscle spindles
What does peripheral processes of some DRG cells release?
Vasoactive mediators
What does the cell body located in the dorsal root Ganglia mediate?
Touch and conscious proprioception
What does cell body size of DRG correlate with?
Axon diameter
Degree of myelination
Conduction velocity
Action potential shape
What does large sensory cells give rise to?
Myelinated axons
What does small sensory cells give rise to?
Unmyelinated axons
For cells that are clearly large what is the conduction velocity?
Greater than 2.5 m/s
For cells that are clearly small, what is the conduction velocity?
Less than 2.5 m/s
What are the two populations of DRG neurons which can be distinguished based on their cytoplasmic appearance?
Small dark neurons
Large light neurons
What is white matter?
Surrounds grey matter
Contain myelinated and unmyelinated nerve fibres
Where do the white matter fibres conduction information?
Up or down the cord
What is white matter divided into?
Dorsal (posterior) column
Lateral column
Central column
Where do A fibre axons ascend to?
Dorsal column nuclei (DCN)
Where does C-fibres run in?
Lissauer’s tract and ascend 1-2 segments within cord
What are the 4 different regions the spinal cord is divided into?
- Cervical
- Thoracic
- Lumbar
- Sacral regions
What are the 2 enlargements of the spinal cord that can be visualised?
- Cervical enlargement (C3-T1)
2. Lumbar enlargement (L1 to S2)
How many segments are the spinal cord divided into?
31 segments
31 pairs of nerves
What are the nerves divided into?
8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal
What is the function of afferents?
Pain (ad)
Touch (ab)
What is lamina pattern?
Modality specific
What are 3 types of spinal cord neurons?
Projections
Motoneurons
Interneurons
What is spinothalamic tract split into?
Lateral spinothalamic: transmit pain and temperature sensation to thalamus
Anterior spinothalamic: transmit pressure and crude touch sensation to the thalamus
Schwann cells
1:1 axon ratio
PNS myelination
Oligodendrocytes
1:many
CNS myelination
Astrocytes
Homeostasis
Microglia
Immune surveillance
What is somatotopy?
Point-for-point correspondence of an area of body to a specific point on CNS
