Module 5 :neuronal Communication Flashcards
Homeostasis
Maintenance of our internal environment relatively stable through negative feedback- monitored & controlled by nervous/ hormonal system
Structure and functions of sensory, relay and motor neurones
General structures of neurones :
- dendron - send impulse to cell body
- cell body - releases neurotransmitters
- Axon - sends impulses away from cell body
- myelin sheath - layers of plasma membranes (lipids) - insulation-speed rate of nervous impulses
- sensory N - dendrites - dendrons - cell body ( middle ) - axon , (blocks are myelin sheath , and spaces - node of ravier ) - when there’s an action potiential , diffuses to next node of ravier
- Motor N - ( impulse from relay neurons or CNS) dendrites - cell body - axon - myelin sheath and node of ravier
- relay N - cell body / myelin sheath ( acts as insulating layer - speeds up nerve impulse transmission- saltatory conduction ) at nodes of ravier - contains Schwann cells
the roles of mammalian sensory receptors in converting different types of stimuli into nerve impulses
Sensory receptors - specific to 1 type of stimulus, Acts as a transducer ( convert from one energy to another - generator potential)
Types : Mechanoreceptors ( movement, pressure ) , chemoreceptors (chemicals) , thermoreceptors ( heat), photoreceptors (light)
- pacinian corpuscles- surface of skin , contains stretch- mediated sodium channel ion ;
- At normal resting state , stretched-mediated sodium channels are closed , maintaining resting potential , with higher Na+ concentration outside neurone
- Pressure applied - the corpuscle changes shape , causing neurone membrane to stretch as well , opens channels
- Na+ diffuse into sensory neurone , down electrochemical gradient -depolarises membrane , initiates generator p , lead to action p along neurone
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the generation and transmission of nerve impulses in mammals( resting potiental )
Resting potential - state at which the cell (membrane) can be stimulated
- Sodium-potassium pump moves more sodium in and less potassium out by AT
- SoNa + channels are closed to prevent entry of Na+
3.K+ channels open allow K+ leave cell by facilitated diffusion - Permanent negative ion in cell (-70mv )
the generation and transmission of nerve impulses in mammals ( action potential)
- Depolarisation- nerve impulse along neurone - allow na+ channels to open -diffuse in na+ by facilitated diffusion- na+ ion conc increase reach threshold-55mv-voltage gated na+ channels open - na-influx till +40mv (positive feedback)
- Repolarisation- na+ channels close , k+ voltage gated channels open, k+ ion leave
- Hyper-polarisation - k+ leave till +70mv or lower - sodium/potassium pumps reopen - back to resting potiental
the structure and roles of synapses in neurotransmission
Roles of synapse: unidirectional transmission (always in single direction), multiple response from one stimulus , receive multiple stimuli from one response
the importance of synapses in summation:
Summation - effect of build up of neurotransmitters in synapse(new AP only triggered if neurotransmitter build to threshold level)
Spatial summation - more than 1 presynaptic neurone release NT to trigger new AP in one postsynaptic neurone
Temporal summation - high frequency of AP reach presynaptic neurone - high conc of NT released trigger AP in post
the structure of a cholinergic synapse
Synapse - gap between neurones - transmit impulse by neurotransmitters
Excitatory - (e.g. ach) triggers new AP in postsynaptic neurone
Inhibitory - ( e.g. GABA) does not trigger new AP
Action of neurotransmitters at synapse:
1. AP arrives at presynaptic neurone - cause voltage gated ca2+ channels open
2. Calcium ions diffuse into presynaptic neurone - down electrochemical gradient
3. Ca2+ ions cause synaptic vesicles with ACh to fuse with presynaptic membrane
4. ACh is released into synaptic cleft and diffuses across ‘ the synapse towards postsynaptic neurones
5. ACh binds to receptor sites of postsynaptic Na+ - they open
6. Na+ diffuse into postsynaptic neurone - down electrochemical gradient - causing depolarisation of postsynaptic select the membrane & trigger AP
- ACh broken down by enzyme (AChE) - acetylcholinesterase - into choline and acetate - Na+ channels close prevent continuous AP generation
The organisation of the nervous system
structure :
Central NS- brain, spinal cord , relay neurone
Peripheral NS: receptors, sensory , motor neurones
Function:
- somatic - concious actions e.g. moving
- autonomic - unconcious actions e.g. heart rate,breathing ( sympathetic - increase activity / parasympathetic - reduce activity )
Reflex arc
Reflexes - involuntary actions ,naturally born(innate), fast , everyday actions
structure: receptor-sensory n- relay n - motor n - motor n - effector
- knee jerk: patellar tendon, flexor muscle, extensor muscle (sensory, motor, relay connected)
1. Tap under the kneecap causes the patellar tendon to stretch, and stretches the the extensor.
2. sends reflex are impulses through sensory N
3. reflex signal goes along one motor neurone, causing extensor muscle to contract.
4. Relay N inhibits the other motor neurone of flexor muscle -> relax
5. leg kicks due to antagonistic muscle action
Blinking reflex(cranial reflex)- unconscious patients are brain-dead(brain stem function or not)
1. cornea irritated, triggers impulse along a sensory neurone
2. relay N in the lower brain stem pass impulse along
4. Signal branches off in motor neurone to eyelid muscles
5. Both eyes shut as a consensual response
Structure of sliding filament model (Definitions)
- Sarcomere: Basic Functional unit of a fibre
- sarcolemma: Plasmic membrane around fibres
- Sacroplasm: Shared cytoplasm within fibres
- Sarcoplasmic reticulum: Endoplasmic Reticulum in sacromere
- Myofibril - long cylindrical organelles
- sacromere structure - myosin (line - thicker), actin (place - thin ), sarcomere (whole section), dark band ( overlap), H-zone(Gap), light band (rest space)
- Actin structure - tropomyosin (line rapped), troponin (bind to ca2+, conformational change in shape- spot)- actin-myosin binding site(dent)
- myosin structure (brush) - myosin head and ADP (relaxed), ATPase components(ATP-> ADP+P) - forms cross-bridges at AM binding site
