Chap 13 - Neural Communication Flashcards
What are examples of internal changes
- blood glucose concentration
- internal temperature
- water potential
- cell pH
What are examples of external changes
- humidity
- external temperature
- light intensity
- new or sudden sound
How do animals respond to internal/external changes?
- electrical responses (neurones)
- chemical responses (hormones)
How do plants respond to changes?
- number of chemical communication systems (including hormones)
- communication systems must be coordinated to produce required response
What does MRS GREN stand for?
Movement, Respiration, Sensitivity, Growth, Reproductivity, Excretion, Nutrition
Why do organisms need to coordinate?
- as organisms have evolved, they have become specialised to perform specific functions.
- coordination enables effective operation
What is an example of a body system that can work in isolation?
the heart can continue to beat if placed in correct bathing solution
What is an example of body systems working in coordination? (RBC)
red blood cells - transport oxygen effectively but have. no nucleus - so can’t replicate. constant supply of RBC is maintained by haematopoietic stem cells
What is an example of body systems working in coordination? (muscle)
for muscles to contract, they must constantly respire, requiring constant oxygen supply - cannot transport oxygen so from RBC
What is an example of body systems working in coordination (in plants)
flowering plants need to coordinate with the seasons, pollinators coordinate with plants - light-sensitive chemicals in plants enables them to coordinate development of flower buds with longer/shorter days
Define homeostasis
maintaining a constant internal environment - the functions of organs need to be coordinated
Give an example of homeostasis
digestive organs (eg. exocrine pancreas), duodenum, ileum, endocrine pancreas and liver work to maintain constant blood glucose concentration
What systems coordinate activities of organisms
nervous and hormonal systems
Give 3 other examples of homeostasis
- temperature
- blood glucose
- water
What does the coordination rely on
cell signalling on a cellular level
How does cell signalling work?
one cell releases a chemical that effects another cell (known as a target cell)
What 2 things can cells do through the process of cell signalling
- transfer signals locally (eg. between neurones and synapses - signal is used as a neurotransmitter)
- transfer signals across large distances using hormones (eg. cells of pituitary gland secret antidiuretic hormone (ADH) - acts on cells in kidneys to maintain water balance)
Give an example of how plants respond to changes in internal/external environment
- plant stems grow towards a light source to maximise rate of photosynthesis - achieved through hormones
Define stimulus
a detectable change in environment
What are neurones?
specialised cells that transmit impulses in the form of action potentials
What is the role of neurones
transmit electrical impulses rapidly around the body so that the organism can respond to changes in its internal and external environment
What are the 3 key features of neurones
- cell body
- axon
- dendrons
Describe the structure of the cell body of a neuron
- contains nucleus surrounded by cytoplasm
- cytoplasm has endoplasmic reticulum and mitochondria involved in neurotransmitter production
Describe the structure of dendrons in a neuron
- short extensions from the cell body
- divide into smaller brances = dendrites
- transmit electrical impulses towards the cell body
Describe the structure of axons in a neuron
- singular, elongated nerve fibres
- transmit impulses away from the cell body
- can be long (eg. transmit impulse from tip of toes to spinal cord)
- cylindrical shape with narrow regin of cytoplasm surrounded by plasma membrane
What are the 3 types of neurones?
- sensory neurones
- motor neurones
- relay neurones
Describe sensory neurones and their function
- transmit impulses from sensory receptor cell to relay & motor neurones or the brain
- one dendron - carries impulse to cell body
- one axon - carries impulse away from cell body
Describe motor neurones and their function
- transmit impulses from relay neuron or sensory neuron to an effector
- one long axon and many short dendrites
Name 2 types of effectors
- muscles
- glands
What is the myelin sheath made of?
layers of plasma membrane
How are the layers of plasma membrane made?
- schwann cells grow around the axon many times
- each time they grow around the axon, a dounle layer of phospholipid bilayer is laid down
- when it stops, there will be >20 layers of membrane
What does the myelin sheath do?
- acts as an insulating layer
- allows myelinated neurones to conduct electrical impulse at faster speed
How fast can myelinated neurones transmit impulses
100 metres per second
How fast can non-myelinated neurones transmit impulses
1 metre per second
How big is the gap between schwann cells (node of Ranvier)
2-3 micrometers
What is saltatory conduction?
where the electrical impulse jumps from one node to the next in myelinated neurones
What does the central nervous system include?
the brain and the spinal cord
What does the peripheral nervous system include?
all neurones that connect the CNS to the rest of the body
What is the somatic nervous system?
when you voluntarily decide to do something under conscious control
What is an example of the somatic nervous system
when you decide to move a muscle in your arm - impulses are carried to the muscles
What is the autonomic nervous system
when the body does something automatically under sub-conscious control
What is an example of the autonomic nervous system
- heart beat
- carrying nerve impulses to glands, smooth muscle and cardiac muscle
What happens in the parasympathetic nervous system
outcomes decrease activity (eg. decrease in heart rate after exercise)
What happens in the sympathetic nervous system
outcome increases activity (eg. fight-or-flight response)
How many neurones does the human brain contain?
approx. 86 billion
What is the brain responsible for?
processing information collected by receptor cells
- receives info from hormonal system through molecules in the blood - then produces coordinated response
What is a benefit of having one central control centre?
communication between neurones is faster than if multiple were placed around the body (exludes reflex actions)
Where are all nervous reactions processed?
in the brain - excluding reflex actions
What is the brain surrounded by
the skull and protective membranes - meninges
What are the 5 main areas of the brain?
- cerebrum
- cerebellum
- medulla oblongata
- hypothalamus
- pituitary gland
What does the cerebrum do?
receives sensory information, interprets it and sends impulses along motor neurones to effectors - produces effective response
The cerebrum is highly convoluted, why is this important?
it increases surface area and therefore space for complex activity
How thick is the outer layer of the cerebrum
2-4mm thick
Where do sophisticated processes (eg. reasoning + decision making) occur?
in the frontal/prefrontal lobe
What are the two halves of the cerebrum called and what do they control
cerebral hemispheres - each controls one half of the body (mirrored)
The size of the sensory area is proportional to…
the number of receptor cells present in the body part
What happens to info in the cerebrum?
- each sensory area receives info from receptors in sense organs
- info passed on to other areas (association areas) to be analysed and acted upon.
- impulses move into motor areas where motor neurones send impulse (eg. to move skeletal muscles)
The size of the motor area is proportional to…
the number of motor endings in it
What is the primary region that controls movement
primary motor cortex in the back of the frontal lobe
How do impulses cross?
left hemisphere receives impulses from the right side of the body (vice versa)
- eyes help with the collection of the information - helps judge balance and perspective
What does the cerebullum control?
muscular movement, body posture, balance
- does not initiate movement but coordinates it
What happens if the cerebellum becomes damaged?
causes jerky and uncoordinated movement
How does the cerebellum work
- receives info from organs of balance (in ears) and about tone of muscles and tendons
- info is relayed to areas of cerebral cortex involved in motor control
What does the medulla oblongata contain?
important regulatory centres of the ANS
How is the body able to detect changes in environment?
sensory receptors
Where are sensory organs located?
eyes and ears
What are the 2 features of sensory receptors
- specific to single type of stimulus
- act as a transducer - convert stimulus into nerve impulses
What types of stimuli do sensory receptors detect?
light, heat, sound, pressure
Describe mechanoreceptors
stimulus: pressure and movement
example of receptor: Pacinian corpuscle
detects: pressure
sense organ: skin
Describe chemoreceptor
stimulus: chemicals
receptor: olfactor receptor
detects: smell
sense organ: nose
Describe thermoreceptors
stimulus: heat
receptor: end-bulbs of Krause
sense organ: tongue
Describe photoreceptors
stimulus: light
receptor: cone cell
detects: different light wavelengths
sense organ: eye
What is a generator potential?
the nerve impulse that has been converted from the stimulus
What is an example of generator potential
a rod cell (in the eye) responds to light and produces a generator potential
What is a transducer?
converts stimulus into a nerve impulse
What are Pacinian corpuscles?
specific sensory receptors that detect mechanical pressure
Where are Pacinian corpuscles located? Where are they most abundant?
- deep in the skin
- most abundant in fingers and soles of feet
- also in joints - enables you to know which joints are changing direction
What is resting potential
when a neurone is not transmitting an impulse, the potential difference is known as resting potential
What is potential difference?
the difference in charge between the inside and outside of the axon
What are the charges of a neurone in resting potential
outside of the membrane is more positive than the inside (slightly negative)
Why is the membrane considered polarised?
because it has a potential difference across it
Whaty is the sodium channel called
stretch-mediated sodium ion channel
How does the Pacinian corpuscle convert mechanical pressure into a nervous impulse
- in resting state, stretch-mediated sodium channel are too narrow to allow sodium ions to pass through - the neuron has a resting potential
- when pressure is applied, corpuscle changes shape - membrane surrounding neurone stretches
- when membrane stretches, sodium ion channels widen. sodium can diffuse into neurone now
- influx of Na+ changes potential of membrane - becomes depolarised - results in generator potential
- generator potential creates action potential that passes along sensory neurone
what is a synapse
gaps between axon end of one neuron and dendrite of an adjacent neurone
how are synapses involved in action potentials?
the action potential is transmitted as a neurotransmitter which diffuses across a synapse
what does axon terminal button contain?
- vesicles containing neurotransmitters
- neurotransmitter reuptake pump
- gated Ca2+ channels
why are impulses at synapses unidirectional
- neurotransmitters are only released from presynaptic neurones
- receptors for neurotransmitters are only on post synaptic neurones
- so neurotransmitters can only activate action potentials in the post synaptic neurone
what is a neuromuscular junction
the synapse between a motor nerve and a muscle
what is a sarcolemma
plasma membrane which surrounds a muscle cell
what is the motor end plate
the part of the sarcolemma which faces the synapse
how does transmission work at a neuromuscular junction
- action potential reaches neuromuscular junction
- vesicles of acetylcholine fuse with presynaptic membrane
- acetylcholine diffuses across synapse and binds with receptors of post synaptic neurone
- allows Na+ to enter muscle which brings about contraction
what is divergence
one neurone releases neurotransmitter to many neurones
what is convergence
many neurones release neurotransmitters to one neurone
what is an excitatory post synaptic potential?
- action potential passes down axon to synapse
- causes a few vesicles to move and fuse with pre synaptic membrane
- small number of acetylcholine molecules produces small depolarisation
- alone not sufficient enough to cause action potential
what is summation
the combined effect of several EPSPs to increase membrane depolarisation to reach threshold and cause action potential
what is spatial summation
when two or more presynaptic neurones converge and release neurotransmitters at the same time onto the same post synaptic neurone
- small amount released from each can be enough altogether to reach threshold and trigger action potential
what is temporal summation
when two or more nerve impulses arrive in quick succession from same presynaptic neurone
- action potential is more likely because more NT is released into synapse
how is the potential difference across a membrane achieved?
distribution of ions (Na+, K+)
what is the role of the sodium potassium ion pump
uses ATP to pump 3 sodium ions out of the cell and 2 potassium ions into the cell
- net movement of one cation outwards
…… potassium ion channels allow K+ out by facilitated diffusion
…… sodium ion channels allow Na+ in by facilitated diffusion
many
fewer
how do metabolic poisons work
blocks respiratory pathways and prevent formation of ATP so K+/Na+ pump cannot function
describe how the resting potential of a neurone is maintained
- active transport of Na+ out and K+ in
- membrane less permeable to Na+
- less Na+ come in and more K+ leave
what are voltage gated channels
open and close depending on potential differences across membrane
during action potential, the voltage gated Na+ channels open which changes ………
permeability of membrane so Na+ ions rush into axon
what happens when the sodium channels open
- depolarisation
- Na+ enter and membrane becomes more positive
what is the change in voltage of depolarisation
-70 to +40mV
describe depolarisation
- Na+ channels open
- increased Na+ ions diffuse in
- triggers more channels to open and more Na+ to enter
what is meant by an action potential
when the neurones voltage increases beyond a set point from the resting potential, generating a nervous impulse
when will an action potential be generated
if a threshold is reached
-55mV
describe repolarisation
- Na+ channels close
- no more Na+ entering but K+ still leaving so voltage decreases
describe hyperpolarisation
- more K+ channels are open
- voltage becomes more negative than resting potential
why is there no stimulation in the refractory period
- ensures discrete impulses are produced separately
- ensure action potential travels in one direction
- limits number of impulse transmission which prevents overreaction
what is the status of the K+ and Na+ channels at resting potential
closed
when do Na+ channels open
depolarisation
when do K+ channels open
repolarisation
what is meant by the all or nothing principle
a stimulus only causes voltage gated ion channels to open if it exceeds the threshold level
- all Na+ channels open if threshold reaches
- all action potentials are always same size (level of depolarisation is always +40mV) no matter the stimulus intensity
what is the difference between intense and weak stimuli
intense stimuli cause many frequent action potentials
