MICROANATOMY Flashcards
What is the nissil stain
- compromised of a basic dye (cresol violet) - stains the nuclei and nissil bodies of neurones
What is the Golgi stain
- compromised of silver chromate solution - stains heroines and their projections
What is the structure of prototypical neurone
- cell body (soma)
- axon
- dendrites
- dendrites receive synaptic input from other neurones
axon + dendrites = neurites
20 micrometres
What are the names of neurones thr/ough number of projections
unipolar - one
bipolar - two
multipolar - 3
How are dendrites classified
pyramidal - shape of pyramid
stellate - all over
What are the classification of axon length?
Golgi type 1 - neurones that extend from one part of the brain to other (pyramidal cells)
Golgi type 2 - dont extend (Stellae)
What does GAT do?
intake of GABA into presynaptic neurone from synapse
What are glial cells?
support cells within the NS and can be classified into four categories based on structure
- astrocytes
- microglia
- ependymal cells
- ogligodendrocytes/schwann cells
What are astrocytes
star-shaped glial cells that function to regulate the extracellular environment of the brain
e.g. enclosing synaptic junctions and actively removing neurotransmitters from synaptic cleft
- most numerous type of glial cells
What are microglia
type of glial cells that function as phagocytes within the NS to remove neuronal and glial debris
- 5-15% of total CNS number
- distributes in brain and spinal cord
What do microglia function in?
- phagocytosis of neuronal and glial debris
- synaptic connection remodelling via scavenging and removing unnecessary synapses
- directing neuronal migration during brain development
what are ependymal cells
type of glial cells that provide the lining of the ventricular system of both the brain and spinal cord
What are the function of ependymal cells
- act as barrier separating brain tissue from cerebrospinal fluid
- osmotic regulation of cerebrospinal fluid via uptake of ions and water molecules
- flow of cerebrospinal fluid from lateral ventricles into 3rd + 4th ventricles before being absorbed in the subarachnoid space
- direction cell migration during brain development
What is associated with deficits in ependymal cell function
severe neurological condition - hydrocephalus
= excessive accumulation of cerebrospinal fluid within ventricular system = enlargement of 3rd/4th ventricles = severe pressure on brain
What are oligodendrocytes and Schwann cells?
glial cells that function to provide myelin - membranous sheath around axons
oligodendrocytes in CNS = contribute to lots of axons
Schwann cells in peripheral NS = myelinated only 1 axon
What is cytoskeleton?
internal scaffolding that gives neurones its charatersitic shape, compromised of microtubules, microfilaments and neurofilaments
What are microtubules
a polymer of tubular - located in axons and dendrites and important in axoplasmic transport
What are microfilaments
polymer of actin - found throughout neurones but particularly abundant in axons and dendrites
What are neurofilaments
type of immediate filament - particularly abundant in a axons and important in regulating axonal shape
- promising biomarker for neurodegenerative disorders (Alzheimers)
What are axons compromised of
- highly specialised in neuronal projectection that conduct nerve impulses for AP within NS
- axon hillock - tapers away from soma to form initial segment of axon
- axon ‘proper’ - axon can branch to form axon collaterals and recurrent collaterals
- axon terminal - site where axon comes into contact with other neurones at a synapse
What are the specialties of dendrites
- receives synapse inputs from other neurones
- dendrites of a single neurones collectively termed dendritic tree
- covered with dendritic spines - small sacs of membrane that protrude from dendrites of some cells to receive synaptic input
- sensitive to type and amount of synaptic activity
What are afferent neurones?
- carry info away from periphery towards brain or spinal cord
- carry info from somatic (skin skeletal muscle) or visceral (smooth muscle/glands) towards brain/spinal cord
What are the primary afferent axons? - diameters, conduction speeds and function
- Aa-fibres - 13-20microm, 80-120m/sec, proprioceptors of skeletal muscle
- Ab-fibres - 6-12microm, 35-75m/sec, mechanoreceptors of skin
- Adelta-fibres, 1-5microm, 5-30m/sec, pain/temp
- C-fibres, 0.2-1.5microm, 0.5-2 m/sec, temp/pain/itch
What are efferent neurons
carry info away from brain/spinal cord to peripheral organs and tissues
How does the knee-jerk reflex work?
- hammer tap stretches tendon = stretches sensory receptor in leg extensor muscle
- sensory neuron synapses excites motor neuron in the spinal cord
2b. sensory neruon also excites spinal interneuron
2c. interneuron synapse inhibits motor neuron to flexor muscles
3a. motor neuron conducts AP to synapses on extensor muscle fibres, causing contraction
3b. flexor muscle relaxes because activity of its motor neurone has been inhibited - leg extends
What is neurotransmission?
fundamental process that drives info transfer between neurones and their targets
What is membrane potential?
defines as voltage difference in charge across a cell membrane
negative membrane potential?
- higher conc of cations outside cell (extracellular fluid) than inside (in cytoplasm)
positive membrane potential?
- higher conc inside cell relative to outside
resting potential?
-70mv
- when AP is not being fired , resting state
ION PUMPS? HOW MANY NA OUT AND K IN?
3 NA OUT
2 K IN
What is hyper polarisation?
displacement of membrane potential towards a more negative value resulted from opening of K gated ion channels, k moves out making cell more negative
what is depolarisation
displacement of membrane potential towards more positive, NA gated ion channels open = movement of NA into cell = more positive
WHAT IS AP?
membrane potential of a neurones when firing, transmitting info between two cells within NS
- depolarisation requires summation of excitatory post-synaptic potentials - can be temporal or spatial
What is saltatory conduction
propagation of an action potential along a myelinated axon
