Neuronal Communication Flashcards
Why multicellular organisms need communication systems
- To respond when their internal and external environment changes
- To co-ordinate organ function
What is cell signalling
Communication between cells: electrical signals carried by neurones or chemical signals as hormones.
What is homeostasis
Internal environment is maintained within set limits around an optimum.
Negative feedback
Self regulatory mechanisms return internal environment to optimum when there is a fluctuation
Positive feedback
A fluctuation triggers changes that results in an even greater deviation from the normal level
Receptors
Specialised cells located in sense organs that detect a specific stimulus
Effectors
Usually muscles or glands which enable a physical response to a stimulus
What is an ectotherm
Organism that cannot increase its respiration rate to increase the internal production of heat is it relies on external sources to regulate its body temperature. Responds to temp. changes behaviourally e.g. orientation of body to minimise/maximise sun exposure
What is an endotherm
Organism that can regulate its own body temperature independently of external sources. Thermo-receptors send signals to the hypothalamus which’s triggers a physiological or behavioural response
Behavioural methods endothermic use to regulate body temperature
- Basking in the sun
- Pressing against warm surfaces
- Digging burrows
- Hibernation
- Panting (water evaporation from mouth)
How does the autonomic nervous system enable endothermic to regulate
Negative feedback- Thermo-receptors detect changes in skin temperature. Thermo-receptors in hypothalamus detect changes in the blood temperature sending impulses to effectors in skin and muscles.
Role of skin in thermal regulation
Vasolidation- Constriction of arterioles supplying skin capillaries controls heat loss to skin surface
- Hair erector muscles contract and follicles protrude to trap air for insulation
- Evaporation of sweat cools skin surface
What is excretion?
Process of removing metabolic wastes e.g. CO2 and nitrogen based byproducts to maintain metabolism. Enables organisms to maintain pH balance and regulate osmotic pressure
Features common to all sensory receptors
- Act as energy transducers which establish a generator potential
- Respond to specific stimuli
Basic structure of pacinian corpuscle
- Single nerve fibre surrounded by layers of connective tissue which are separated by viscous gel and contained in a capsule
- Stretch mediated sodium channels on plasma membrane
- Capillary runs along base layer of tissue
What stimulus does a pacinian corpuscle respond to and how
- Pressure deforms membrane causing stretch-mediated sodium ion channels to open
- If influx of sodium ions raises membrane to threshold potential a generator potential is produced
- Action potential moves along a sensory neurone
Describe features of all neurones
Cell body - contains organelles and high proportion of RER
Dendrons - branch into dendrites which carry impulses towards the cell body
Axon - long unbranded fibre carries nerve impulses away from cell body
Structure and function of sensory neurone
- Usually unipolar
- Transmits impulses from receptors to CNS
Structure and function of a relay neurone
- Usually bipolar
- Transmits impulses between neurones
Structure and function of a motor neurone
- Usually multipolar
- Transmits impulses from relay neurones in the CNS to effectors
Additional features of myelinated neurone
Schwann cells - wraps around axon multiple times
Myelin sheath - made from myelin-rich membranes of Schwann cells
Nodes of ranvier - very short gaps between neighbouring Schwann cells where there is no myelin sheath
3 processes Schwann cells are involved in
- Electrical insulation
- Phagocytosis
- Nerve regeneration
Why myelinated axons conduct impulses faster than unmyelinated axons
Saltatory conduction - impulses jump from one node of Ranvier to another. Depolarisation cannot occur where myelin sheath act as an electrical insulator so impulse doesn’t travel along the whole axon length
Where are myelinated neurones found in the body
Most neurones are found in central and peripherals nervous systems e.g. in spinal reflex
Where are non-myelinated neurones found?
Groups C nerve fibres involved in transmitting secondary pain
What is resting potential?
PD across neurone membrane when it’s not stimulated (-70mV in humans)
How is resting potential established
- Membrane is more permeable to K+ than Na+
- Sodium-potassium pump actively transports 3Na+ out of cell and 2K+ into cell
This establishes an electrochemical gradient - cell contents more negative than extra cellular environment
Name the stages in generating an action potential
- Depolarisation
- Repolarisation
- Hyperpolarisation
- Return to resting potential
Outline the steps of depolarisation
- Facilitated diffusion of sodium ions into cell down electrochemical gradient
- PD across membrane becomes more positive
- If membrane reaches threshold potential (-50mV) voltage gated sodium ion channels open
- Significant infusion of sodium ions reverses PD to +40mV
Outline the steps of repolarisation
- Voltage gated sodium ion channels close and voltage gated potassium ion channels open
- Facilitated diffuse of K+ out of cell down their electrochemical gradient
- PD across membrane becomes more positive
Outline the steps of hyperpolarisation
- Overshoot - K+ ions diffuse out so PD becomes more negative than resting potential
- Refractory period - no stimulus is larger enough to raise membrane potential to threshold
- Voltage-gated K+ channels close to and sodium potassium pump re-establishes resting potential
Explain the importance of the refractory period
- No action potential cha be generated in hyperpolarised sections of a membrane*
- Ensures unidirectional impulse
- Ensures discrete impulses
- Limits frequency of impulse transmission; larger stimuli have higher frequency
Why is the frequency of impulse transmission significant?
- Enables organism to distinguish size of stimulus although all APs have the same magnitude
- Larger stimuli result in higher frequency of transmission since they overcome hyperpolarisation more quickly
Function of synapses
- Electrical impulse cannot cross junction
- Neurotransmitters send impulses between neurones. From neurones to effectors for excitatory or inhibitory response
- Summarion of sub-threshold impulses
- New impulses can be initiated in several different neurones for simultaneous responses
Describe the structure of a synapse
Presynaptic neurone ends in synaptic knob: contains lots of mitochondria, endoplasmic reticulum and vesicles of neurotransmitters
Synaptic cleft - 20-30 nm gap between neurones
Postsynaptic - has complementary receptors to neurotransmitters
What happens in the presynaptic neurone when an AP is transmitted between neurones
- Wave of depolarisation travels down presynaptic neurone, causing voltage gated calcium ion channels to open
- Vesicles mode towards and fuse with the presynaptic membrane
- Exocytosis of neurotransmitter into synaptic cleft
How do neurotransmitters cross the synaptic cleft
Simple diffusion
What happens in the postsynaptic neurone when an AP is transmitted between neurones?
- Neurotransmitter binds to specific receptor on postsynaptic membrane
- Ligand-gated Na channels open
- An influx of sodium ions raises membrane to its threshold potential, action potential is generated
Ligand gated ion channel
Transmembrane protein complex that conduct ion flow in response to binding of a neurotransmitter
What happens in an inhibitory synapse
- Neurotransmitter binds to and opens Cl- Channels on postsynaptic membrane and triggers K+ channels to open
- Cl- moves in and K+ moves out via facilitated diffusion
- PD becomes more negative - no AP is generated
Define summation and name both types
Neurotransmitters form several sub-threshold impulses accumulates to generate action potential. These do not occur at neuromuscular junctions
- Temporal summation
- Spatial summation
Difference between temporary and spatial summation
Temporal summation involves the several release of neurotransmitters in quick succession by one presynaptic neurone whereas a spatial summation is when presynaptic neurones release neurotransmitters
What happens to acetylcholine form the synaptic cleft?
- Hydrolysis into acetyl and choline by acetylcholinesterase
- Acetyl and choline diffuse back into presynaptic membrane
- ATP is used to reform acetylcholine for storage in vesicles
Gross structure of mammalian nervous system
Peripheral - voluntary, autonomic (sympathetic and parasympathetic)
Central - spinal cord and brain
Two main divisions of nervous system
Central nervous system - Brain and spinal cord. Specialised system of nerve cells
Peripheral nervous system - All other neurones that are not part of CNS
Two main divisions of peripheral nervous system
Somatic - under conscious control
Autonomic - under unconscious control
Two main divisions of autonomic nervous system
Sympathetic - Often stimulates effectors (fight or flight response ), neurotransmitter noradrenaline, ganglia near CNS
Parasympathetic - Often inhibits effectors (rest/digest response), neurotransmitter acetylcholine, neurotransmitter acetylcholine, ganglia far from CNS.
Gross structure of the Brain
2 hemispheres joined by band of nerve fibres called corpus callosum
Parietal lobe - Top of the brain : movement, orientation, memory, recognition
Occipital lobe - Back of the brain : visual cortex processes signals from the eye
Temporal lobe - Beneath the temples : process auditory signals
Cerebellum function
- Controls execution of movement e.g. balance, co-ordination, posture
- Possible role in cognition e.g. attention and language
Function of medulla oblongata
Controls a range of autonomous functions including breathing and heart rate
Function of the cerebrum
Controls voluntary actions e.g. initiating movement, speech, thought
Function of hypothalamus
Includes pituitary gland (secretes hormones)
Involved in thermo/osmo regulation
Outline the steps in a simple reflex arc
Receptor - Detects stimulus and creates AP in the sensory neurone
Sensory neurone - Carries impulse to spinal chord
Relay neurone - Connects sensory neurone to the motor neurone with spinal chord/ brain
Motor neurone - Carries impulse to the effector to carry out response
How many neurones are there in the human brain
Approximately 86 billion
How many neurones are there in Alen’s brain
Like 2
Describe the knee jerk reflex
- Stretch receptor in quadricep muscle detect stretch
- Nerve impulse is passed along a sensory neurone to relay neurone
- Relay neurone communicates with motor neurone
- Motor neurone carries nerve impulse to appropriate effector
Describe the blinking reflex
- Cornea of the eye is initiated by a foreign body
- Stimulus triggers an impulse along a sensory neurone
- Impulse then passes through a relay neurone in the lower brain stem
- Impulses are then sent along branches of the motor neurone to initiate a motor response to close the eyelids
What is the fight or flight response?
Example : When Nijel sees Jiyeon
Nijels brain perceives a stimulus, which involves production of adrenaline.
Triggers physiological changes to prepare body: pupil dilation for clearer view of jiyeon, inhibition of digestive system to prevent stomach rumbling, higher heart rate for greater supply of oxygen, greater blood flow to penis (initiates boner) and brain for mental awareness so that he doesn’t miss his chance!
Describe the skeletal muscles
- Striated
- Consists of multinucleated cells
- Muscle cells fused together to form bundles of parallel muscle fibres (myofibrils)
- Surrounded by endomycium - loose connective tissue with many capillaries
Described the involuntary muscles
- Smooth
- Enables walls of blood vessels and intestines to contract
Cardiac muscles
- Specially striated
- Branched uninucleated cells
- Myogenic contraction
Components such of myofibrils
Z-line, I-band, A-band, H-zone
What are Z-lines
Boundary between sarcomeres
What is in I- bands
Only actin which appears light under optical microscope
What is the A-band
Overlap of actin and myosin (appears dark under optical microscope)
What’s in the H-zone
Only myosin
How is a muscle contraction stimulated
- Action potential causes voltage gated calcium ion channels to open
- Vesicles move towards and fuse with presynaptic membrane
- Exocytosis of acetyl choline which diffuses across synaptic cleft
- ACh binds to receptor on sodium channel proteins in skeletal muscle cell membrane
- Influx of sodium ions - depolarisation
Outline the steps in the sliding filament theory
- Myosin head with ADP attached forms cross bridge with actin
- Power stroke: my sodium head changes shape and loses ADP, pulling actin over myosin
- ATP attaches myosin head, causing it to detach from actin
- ATPase hydrolyses ATP to ADP so myosin head CNS return to original position
- Myosin head re-attaches to actin further along filament
Describe the structure of a neuromuscular junction
Synaptic cleft between a presynaptic motor neurone and skeletal muscle cell. Acts as end of neural pathway and always stimulates an excitatory response
