CNS Flashcards
Classify synapses
1) Upon nature of transmission
-chemical
-electrical
-conjoint
2) Upon anatomical
-axosomatic
-somatic
-axoaxonic
3) Physiological classification
-Exictatory
-Inhibitory
Components at end of synapse
-vesicles containing neurotransmitter
- mitochondria
- voltage gated calcium channels
Transmission
-impulse arrive at presynaptic terminal causing depolarisation
- voltage gated Ca channels open and influx of Ca ions.
- Fusion of synaptic vesicles with presynaptic neurons.
- Neurotransmitter released by exocytosis in synaptic cleft.
- Neurotransmitter combined with Ach gated Na channels.
- Na ions diffuse into postsynaptic membrane and cause decrease in negativity.
- This decreased negativity is called excitatory post synaptic potential.
- In case of inhibitory synapse glycine and GABA open Cl channels and potential is called inhibitory post synaptic potential.
- After completion of action, they are removed by enzymes like acetyl choline esterase.
Applied physiology-
1) Drugs like anaesthetics depress synaptic transmission and produce anaesthesia.
Receptors properties and classification
Receptor is a biological transducer which converts external and internal stimuli into nerve impulse.
1) On basis of nature of stimulus
a) Mechanoreceptors
-Cutaneous- Pacinian corpuscles , ruffini endings, meissners corpuscles, merkels disc, hair end organs , free nerve endings.
-deep tissue - muscle tendon and Golgi tendon organs.
- baroreceptors in vascular tree
- hair cells in cochlea, otolith organs and semicircular canals.
2) Thermoreceptors
- ruffini organ and Krause bulb
3) Nocioreceptors - free nerve endings
4) Chemoreceptors - taste and smell receptors.
5) Electromagnetic - rods and comes Emw
6) Osmoreceptors - respond to osmotic changes in hypothalamus and duodenum.
Upon situation of receptors:
1) Exteroreceptors - cutaneous recep.
2) Interoreceptors - Baroreceptors and teloreceptors
3) Teloreceptors - visual and auditory receptor (detect distant signals)
On basis of adaptability
1) Rapidly adapting/phasic- hair end organs, pacinian corpuscles , olfactory receptors and missners corpuscles.
2) Slowly adapting receptors/tonic - baro and pain receptors.
Properties
1) Specificity - Each receptor is stimulated by a specific stimulus.
2) Adaptation - Stimulating a receptor continuously decreases the impulses and then stop.
3) Labeled line principle - Impulses arising from specific receptors pass through a discrete tract carrying a specific modality sensation and have specific termination in brain .
4) Law of projection - When a sensory pathway from receptor to cerebral cortex is stimulated on any particular site along its pathway , the sensation caused by stimulus is always felt at the site of receptors.
Basal Ganglia
Consists of caudate nucleus, putamen, Globus pallidus, subthalamic nucleus of luys, substantia nigra, claustrum and red nucleus.
Connections:
Afferents -
1) From motor cortex, premotor, supplementary, motor area to caudate nucleus and putamen.
2) From thalamus to putamen
3) From raphe nucleus of brain to putamen.
4) From motor cortex to substantia nigra.
5) From motor and premotor areas, vestibular nucleus and cerebellum to red nucleus.
EFFERENTS-
1) From Globus pallidus to ventroanterior and ventrolateral nucleus of thalamus.
2) From Globus pallidus to reticular formation and segmental nuclei.
3) From substantia nigra to spinal cord.
4) Subthalamic nigra to thalamus.
5) Subthalamic nucleus to thalamus.
6) From red nucleus to VA and VL nucleus of thalamus.
Interconnections
1) Putamen to Substantia nigra
2) Substantia nigra to Putamen
3) Putamen to Globus pallidus
4) Substantia nigra to red nucleus
5) Globus pallidus with sub thalamic nucleus.
∆ Functions
1)Control of voluntary movements
2) Caudate circuit involved in planning the timing and sequencing of complex motor patterns
3) Initiation and control of gross voluntary movements
4) Responsible for automatic and associated movements like facial expressions and swinging of arms.
5) Control posture through extrapyramidal fibresm
6) Caudate nucleus has inhibitory effect on muscle tone of body
7) Globus pallidus and Subthalamic nucleus control movements of axial and girdle muscles
Sleep
It is a naturally occurring reversible state of unconsciousness. Characterised by reduced sensitivity to changes in sorrounding and can be aroused by appropriate stimuli.
NREM and REM sleep occurs in cycles in which NREM is 60m and REM is 30m.
NREM:
1) Deep restful sleep
2) Dreams occur but not consolidated
3) Decrease heart rate, cardiac output and blood pressure.
4) Fall in BMR
5) Decrease in muscle tone and muscles relaxed.
6) Babinski sign present.
4 stages
1) beta waves replaced by alpha waves which are replaced by theta waves.
2) Presence of sleep spindles or K complex.
3) High amplitude theta waves and few delta waves.
4) Theta waves replaced by delta waves.
Occurs by active inhibition of reticular activating system by raphe nuclei.
REM sleep
1) More deep and intense
2) Rapid movements of eyeballs
3) Dreams occur and are remembered
4) Extreme inhibition of muscle tone
5) Threshold for arousal from sleep increased
6) Heart rate and respiration becomes irregular.
Also called as paradoxical sleep because of high frequency low wavelength beta waves.
Discharge from neurons of locus serulus.
Memory
Memory can be defined as the ability to store information and recall it when needed.
3 types:
1) Immediate memory
2) Short term memory
3) Long term memory
1) Immediate memory
Memory of facts, number or words lasting from few seconds to few minutes.
Mechanism
• Reverberating circuit theory in which sensory impulses coming to set up in Reverberating oscillatory circuit between neurons of cortex and available as long as reverberations continue.
• Post tetanic potentiation theory in which passage of repeated impulses facilitate these circuits due to prolonged release of neurotransmitters
2) Short term memory
Information is retained from few minutes to few days or weeks.
Recall is rapid.
Memory is lost by blow on head or electric shock.
Mechanism - Presynaptic facilitation mechanism
Occurs due to temporary physical and chemical changes in synapses. Facilitatated circuits are formed which can be exicted for recall of information.
3) Long term memory
Is retained and can be recalled after weeks, months and years.
Takes some time to recall.
Not lost by concussion or electrical loss.
Mechanism
Storage of this type of memory occurs by anatomical changes in synapses.
Increase in number of release sites, increase in number of transmitter vesicles, increase in Presynaptic terminals and change in numbe rof neurons. Storage of memory is associated with RNA synthesis.
Consolidation of memory.
It is processes of fixation of immediate into short term and then into long term memory.
Takes 10 minutes to 1 hour and occurs by rehearsal of information.
Consolidation is done by hippocampus and thalamus helps to recall it.
Damage to hippocampus leads to anterograde amnesia and to thalamus causes retrograde amnesia.
