Neuronal Coordination Flashcards
What are 4 changes in the internal environment that could elicit a response from an organism?
Blood glucose concentration
Internal temperature
Water potential
Cell pH
What are 4 changes in the external environment that could elicit a response from an organism?
Humidity
External Temperature
Light intensity
New or sudden sound
What are electrical responses made via?
Neurones
What are chemical responses made via?
Hormones
What are the two main reasons why organisms need to be coordinated?
Maintain conditions in and out of the body
Position organism in environment for optimal chance of survival
Define ‘homeostasis’
Maintenance of a constant internal environment
How does cell signalling work?
A cell releasing a chemical which has an effect on another cell called a target cell
What two things can occur due to cell signalling?
Transfer of signals locally between neurones and synapses
Transfer signals across large distances using hormones
What are stimulus?
Changes in internal and external environments that a nervous system detects
What is the role of neurones?
To 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 main parts of a neurone?
Cell body
Dendrons
Axons
What is the cell body made up of?
Nucleus surrounded by cytoplasm, with a large proportion of endoplasmic reticulum and mitochondria used in production of neurotransmitters
What are neurotransmitters?
Chemicals used to pass signals from one neurone to the next
What are dendrons?
Short extensions from the cell body which are responsible for transmitting electrical impulses towards the cell body
What is the role of axons?
Singular, elongated nerve fibres that transmit impulses away from cell body
What is the structure of an axon?
A cylindrical fibre with a narrow region of cytoplasm surrounded by plasma membrane
What are the 3 main types of neruone?
Sensory neurone
Motor neurone
Relay neurone
What is the role of a sensory neurone?
Neurones that transmit impulses from a sensory receptor cell to a relay neurone, motor neurone or the brain
What is the structure of a sensory neurone?
One dendron which carries impulse to cell body
One axon which carries impulse away from cell body
What are relay neurones?
Neurones that transmit signals between neurones
What is the structure of relay neurones?
Short axons and short dendrons
What are motor neurones?
Neurones that transmit impulses from a motor/sensory neurone to an effector.
What is the structure of a motor neurone?
A long axon and many short dendrites
What is the typical pathway an electrical impulse follows?
Receptor Sensory neurone Relay neurone Motor neurone Effector cell
How do myelin sheaths form?
Schwann cells produce layers of membrane which lay down a double phospholipid bilayer every time they grow. This creates a myelin sheath.
What is the role of myelinated sheaths?
Insulating layer
Conduct electrical impulses at a much faster speed
What is the node of Ranvier?
Small gap(1-3mm) between adjacent Schwann cells
How do electrical impulses travel on myelinated neurones?
Electrical impulse ‘jumps’ from one node to the next
Faster
How do electrical impulses travel on unmyelinated neruones?
Transmits continuously along nerve fibre
What is the role of a sensory receptor?
Convert a stimulus they detect into a nerve impulse
Explain process from sensory receptor to the effector
Convert a stimulus they detect into a nerve impulse
Impulse passed to central nervous system via nervous system
Brain coordinates response and sends an impulse to the effector
Effector initiates a response
What are the two main features of a sensory receptor?
Specific to a single type of stimulus
Act as a tranducer
What is a tranducer?
Something that converts a stimulus into a nerve impulse
What is the name of a nervous impulse produced by a sensory receptor?
Generator potential
What do Pacinian corpuscles detect?
Mechanical pressure
Where are Pacinian corpuscles located?
Deep within skin
Fingers and soles of feet
Joints to know which joints are changing direction
Explain the structure of a Pacinian corpuscle
End of sensory neurone within the centre of corpuscle
Surrounded by layers of connective tissue with viscous gel between
What specific structure is present in the Pacinian corpuscle? What is its role?
Sodium ion channel
Responsible for transporting sodium ions across the membrane
What is present in the neurone ending of a Pacinian corpsucle?
A stretch mediated sodium channel
Give one specific feature of a stretch mediated sodium channel
When the channel changes shape it also changes in permeability to sodium
Explain how a Pacinian corpuscle converts mechanical pressure into a nervous impulse
Pressure applied to a Pacinian corpuscle, meaning it changes shape.
Membrane surrounding neurones stretch
Membrane stretches, sodium channels present widen
Sodium ions diffuse into neurone
Influx of positive sodium ion changes potential of membrane causing it to become depolarised
Generator potential created
Generator potential creates an action potential that passes along sensory neurone
Action potential passed to central nervous system
What are the two stages that an axon membrane switches between?
Resting potential
Action potential
Explain the difference in charge between the inside and outside of a membrane when a neurone is in resting potential
Outside of membrane more positively charged than the inside of the membrane
What word is used to describe a membrane in resting state? Why?
Polarised
Potential difference across it
What is the potential difference across a membrane during resting potential?
-70mV
Explain the movement of sodium and potassium ions across axon
3 sodium ions are actively transported out of the axon, while 2 potassium ions are actively transported into the axon.
Occurs via a sodium potassium pump
What is an electrochemical gradient?
Concentration gradient of ions
Explain the events that result in creation of action potential
3 sodium ions actively transported out, 2 potassium ions actively transported in
More sodium ions on the outside, more potassium ions on the inside
Sodium ions move back in, and potassium out via the electrochemical gradient
Gated sodium ion channels shut limiting movement of sodium ions
Gated potassium ion channels open, so potassium diffuses out
More positively charged ions outside the axon
Creates resting potential, with inside negative relative to outside
What is the potential difference of a membrane during action potential?
+40mV
Define depolarisation
The change in potential difference from negative to positive
When does depolarisation occur?
Energy of stimulus causes some sodium voltage-gated channels to open
Membrane more permeable to sodium ions
Sodium ions diffuse into axon down electrochemical gradient
Inside less negative- depolarised
Give an example of positive feedback within action potential
Change in charge following opening of sodium voltage-gated channels causes more sodium channels to open
More sodium ions diffuse into axon
What occurs within the axon once +40mV has been reached?
Voltage gated sodium channels shut
Voltage gated potassium channels open
Membrane more permeable to potassium ions
How does repolarisation occur?
Once the membrane has reached +40mV and it becomes more permeable to potassium ions, they diffuse out via electrochemical gradient which causes outside to become more negative than inside
What is hyperpolarisation?
Excessive numbers of potassium ions diffuse out of the axon resulting in the inside of the axon becoming more negative than in the normal resting state
What is a nerve impulse?
An action potential that starts at one end of the neurone and is propagated along the axon to the other end of the neurone
How does a wave of depolarisation occur?
Initial stimulus causes a change in the sensory receptor which triggers an action potential within sensory receptor
This is the first region of axon to be depolarised
Sodium ions follow down electrochemical gradient which initiates depolarisation in the next section
What is the refractory period?
Short period of time where the axon cannot be excited again and the voltage gated sodium ion channels remain closed, preventing movement of sodium ions into axon
What is the importance of the refractory period?
Prevents propagaiton of an action potential backwards along an axon
Prevents overlap- ensures they are unidirectional
What is saltatory conduction?
Sodium ions passing through long circuits from one Node of Ranvier to another in a ‘jumping’ motion
Why is saltatory conduction more efficient?
Faster
Less channels have to open
Repolarisation uses ATP so doing this less reduces use of ATP
What are three factors which affect speed at which action potential travels?
Axon diameter
Temperature
Myelination
How does axon diameter affect speed at which action potential travels?
Bigger the axon diameter= faster impulse
Less resistance to flow of ions in cytoplasm
How does temperature affect speed at which action potential travels?
Higher temperature=faster
Ions diffuse faster
Only to 40 as protein channels denature
What is the all or nothing principle?
The nerve impulse has to reach the threshold value to initiate an action potential
What affect does size of stimulus have on action potentials?
Increases frequency of action potential but not size
What is a synapse?
The junction between two neurones or a neurone and an effector
What is the synaptic cleft?
The gap which separates the axon of one neurone from the dendrite to the next neurone
What is the presynaptic neurone?
The neurone along which the impulse has arrived
What is the postsynaptic neurone?
Neurone that receives the neurotransmitter
What is the synaptic knob?
The swollen end of the presynaptic neurone
What are the key features of the synaptic knob?
Mitochondria and large amounts of endoplasmic reticulum to enable it to manufacture neurotransmitters
What is the role of the presynaptic vesicle?
Vesicles fuse with eh presynaptic membrane and release contents into the synaptic cleft
What are the neurotransmitter receptors?
Receptor molecules which the neurotransmitter binds to in the postsynaptic membrane
What are the two types of neurotransmitter?
Excitatory and inhibitory
How do excitatory neurones work?
Neurotransmitters result in depolarisation of the postsynaptic neurone. Active potential occurs if threshold is reached
Give an example of an excitatory neurone
Acetlycholine
How do inhibitory neurones work?
Neurotransmitters result in the hyperpolarisation of the postsynaptic membrane. Prevents an action potential being triggered.
Give an example of an inhibitory neurone
GABA
Explain the process of synaptic transmission
Action potential reaches end of presynaptic neurone
Depolarisation causes the calcium voltage gated channels to open
Calcium ions diffuse into presynaptic knob
Causes synaptic vesicles to fuse with the presynaptic membrane. Neurotransmitter released into synaptic cleft by exocytosis
Neurotransmitter diffuses across synaptic cleft and binds with its specific receptor molecule on the postsynaptic membrane
Sodium ion channels open
Sodium diffuses into postsynaptic neurone
Triggers an action potential and impulse is propagated along the postsynaptic neurone
How are neurotransmitters released from the postsynaptic neurone?
Removed via enzymes
Some enzymes release neurotransmitter from receptor
Why is it important that neurotransmitters are released once they have been used?
To ensure that the stimulus is not maintained and another stimulus can arrive
What is a cholinergic synapse?
Any synapse that uses the neurotransmitter acetlycholine
What is acetylcholine broken down into?
Choline and ethanoic acid (acetyl)
Explain the process of acetyl choline being broken down
Acetylcholinesterase hydrolyses acetylcholine into choline and ethanoic acid
Products taken back to presynaptic knob where they can be reformed
What are the 3 main roles of a synapse?
Unidirectional
Allow a single stimulus to cause a number of simultaneous responses
Many stimuli can produce one response
Define summation
The building up of a specific neurotransmitter to sufficiently reach the threshold which will trigger an action potential
What are the two types of summation?
Spatial
Temporal
Explain how spatial summation occurs
Number of presynaptic neurones connect to one postsynaptic neurone. Each releases neurotransmitter which builds up to a high enough level to trigger an action potential
Explain how a temporal summation occurs
Single presynaptic neurone releases neurotransmitter as a result of an action potential occurring frequently
What 2 structural systems is the Mammalian nervous system organised into?
Central nervous system
Peripheral nervous system
What is in the central nervous system?
Brain
Spinal cord
What is in the peripheral nervous system?
Neurones that connect CNS to the rest of the body
sensory and motor
What 2 functional systems is the nervous system organised into?
Somatic nervous system
Autonomic nervous system
What is the somatic nervous system?
A system under conscious control for voluntary actions
Where does the somatic nervous system carry impulses to?
The body muscle’s
What is the autonomic nervous system?
A system that works constantly that is under subconscious control
Where does the autonomic system carry impulses to?
Glands, smooth muscle and cardiac muscles
What is the autonomic system subdivided into?
Sympathetic and parasympathetic
What is the difference between the sympathetic and parasympathetic systems?
Sympathetic is involved with an increase
Parasympathetic is involved with a decrease
What two structures protect the skull?
The brain and the mengines
What are the names of the 5 main areas of the brain?
Cerebrum Cerebellum Medulla oblongata Hypothalamus Pituitary gland
What does the cerebrum control? Give 4 examples
Controls voluntary actions
Eg. learning, memory, personality and conscious thought
What does the cerebellum control? Give 3 examples
Controls unconscious function
Eg. posture, balance and non-voluntary movement
What does the medulla control?
Used in autonomic control
Eg, heart rate and breathing rate
What does the hypothalamus control?
Regulatory centre for temperature and water balance
What is the role of the pituitary gland?
Stores and releases hormones that regulate many body functions
What are the 3 ways that brains are imaged?
Autopsies
MRI
CT scan
How are active areas of the brain identified during an MRI?
Increased blood flow in the area
How does the cerebrum process information?
Cerebrum receives sensory information, interprets it with respect to information stored from previous experiences, and then sends impulses along motor neurone to effectors with a suitable response
Why is important that the cerebrum has a large surface area?
Increases capacity for complex activity
Where do the most sophisticated processes occur?
Frontal and prefrontal lobe of the cerebral cortex
Explain the substructures of cerebrum
Two hemispheres called cerebral hemispheres
Outer layer of cerebral hemispheres called a cerebral cortex
What occurs at the base of the brain?
Impulses from each side of the body cross over so left hemisphere receives impulses from the right side of the body
What is the size of the sensory area in cerebrum proportional to?
The relative number of receptor cells present in the part of the body
What is the size of the motor area in cerebrum proportional to?
Relative number of motor endings
Which region controls movement in the cerebrum?
Primary motor cortex located at back of the frontal lobe
How does the cerebellum process information?
Receives information from organs of balance and from muscles and tendons, relays information to cerebral cortex which is involved with motor control
What are the two centres present in the hypothalamus?
Parasympathetic and sympathetic nervous system
What are the three main functions of the hypothalomus?
Controlling complex patterns of behaviour
Monitoring composition of blood plasma
Producing hormones
Where is the pituitary gland located?
Found at base of hypothalamus
What are the two sections of pituitary gland?
Anterior pituitary
Posterior pituitary
What does the anterior pituitary gland do?
Produces 6 hormones including FSH
What does the posterior pituitary gland do?
Stores and releases hormones produced by hypothalamus such as ADH
What is reflex action?
A response to a situation without conscious thoughT
Define a reflux
An involuntary response to a sensory stimulus
What is the reflex arc?
Pathway of neurones involved in a reflex action
What is the order of neurones in a reflex response? What does each one do?
Receptor- detects stimulus and creates action potential in sensory neurone
Sensory neurone- carries impulse to spinal cord
Relay neurone- connects sensory neurone with motor neurone via CNS
Motor neurone- carries response to effector
What is the spinal cord?
A column of nervous tissues running up the back surrounded by the spine for protection
What type of reflex is the knee-jerk reflex?
A spinal reflex
What type of reflex is a blinking reflex?
A cranial reflex
Why are reflexes important?
Avoid body being harmed or the severity of the damage
Which 3 ways do reflexes increase chances of survival?
Involuntary
Innate
Fast
What are the three types of muscle in the body?
Skeletal
Cardiac
Involuntary
What is the role of skeletal muscle and where are they found?
Responsible for movement
For example biceps and triceps
What type of muscle is cardiac muscle?
Myogenic muscle which means they contract without nervous stimuli
Where is cardiac muscle found?
Heart
Give 2 examples where involuntary muscle is found
Walls of hollow organs such as stomach and bladder
Walls of blood vessels and digestive tract
Explain the fibre appearance in the three types of muscle
Skeletal- striated, tubular and multinucleated
Cardiac- specialised striated, branched, unnucleated
Involuntary- non-striated, spindle shaped, unnucleated
Explain how each of the three types of muscles are controlled
Skeletal- conscious/voluntary
Cardiac- involuntary
Involuntary- involuntary
Explain the arrangement of muscles within the three different types of muscle
Skeletal- regularly arranged so muscle contracts in one direction
Cardiac- cells branch and interconnect resulting in simultaneous contraction
Involuntary- no regular arrangement
Explain the contraction speed for each of the three different types of muscles
Skeletal- rapid
Cardiac- intermediate
Involuntary-slow
Explain the length of contraction for each of the three different muscle types
Skeletal- short
Cardiac- intermediate
Involuntary- contracted for relatively long time
What are bundles of muscle fibres enclosed in?
A plasma membrane called a sarcolemma
What is the shared cytoplasm within a muscle cell called?
Sarcoplasm
What is the shared cytoplasm within a muscle cell called?
Sarcoplasm
What are T tubules made up of and why are they important?
Parts of the sarcolemma folded inwards
Spread electrical impulse throughout sarcoplasm
What is the name of the specialised endoplasmic reticulum in the muscle cell? What is its role?
Sarcoplasmic Reticulum
Contains calcium ions required for muscle contraction
What are myofibrils?
Long cylindrical organelles made of protein which are specialised for contraction
How are myofibrils arranged?
Lined up in parallel
What two protein filaments make up myofibrils?
Actin
Myosin
Describe the structure of actin
Two polypeptide strands twisted around each other
Thinner filament
Describe the basic structure of myosin
Long rod shaped fibres with bulbous heads that project to one side
Why do myofibrils have a striped appearance?
Alternating bands of light and dark
How do light bands form?
Areas where actin and myosin do not overlap
What is the alternative name for light bands?
I bands
How do dark bands form?
Presence of thick myosin filaments, edges particularly dark due to overlap with actin
What is the alternative name for dark bands?
A bands
What is the sarcomere?
Distance between two Z lines
What happens to a sarcomere when a muscle contracts?
Shortens
What is the Z line?
The line found at the centre of each light band
What is the H zone?
The area in the centre of each dark band where only myosin filaments are present
What happens during contraction of a muscle?
Myosin filaments pull actin filaments towards the centre of the sarcomere
What is the result of muscle contraction on the bands/zones?
Light band decreases in size
The Z zones become closer together reducing the length of the sarcomere
H zone becomes narrower
Explain how changes in the sarcomere cause bone movement
Simultaneous contraction of sarcomeres cause the contraction of myofibrils and muscle fibres
Causes enough force on the bone to cause movement
Describe the structure of a myosin filament
Tails arranged aligned to create myosin filament
Globular heads present which are hinged so can move back and forward
Binding site for actin and ATP
What is the structure of actin?
Actin have binding sites for myosin
What are the binding site for myosin blocked by?
Tropomyosin which is held in place by troponin
What happens between actin and myosin when a muscle is in resting state?
Nothing
The myosin binding site is blocked
Can’t bind to myosin so there is no movement
Can’t slide over each other
What is a neuromuscular junction?
Where a motor neurone and a skeletal muscle meet
Describe the process of events that occurs when an action potential reaches a neuromuscular junction
Stimulates calcium ion channels to open
Calcium ions diffuse into synaptic knob
Synaptic vesicles fuse with presynaptic membrane
Acetyl choline is released into synaptic cleft by exocytosis and diffuses across synapse
Acetylcholine binds to sarcolemma which opens the sodium ion channels and causes depolarisation
Acetylcholine is broken down by acetylcholinesterase which prevents the muscle being over stimulated
Explain the interaction of myosin and actin during muscle contraction
1) Tropomyosin molecule prevents myosin head from attaching to the binding site on the actin molecule
2) Calcium ions released from endoplasmic reticulum cause tropomyosin molecule to pull away from the binding site on the actin molecule
3) Myosin head now attaches to binding site on actin filament
4) Head of myosin changes angle, moving the actin filament. ADP is released.
5) ATP molecule fixes to myosin head, causing it to detach from actin filament
6) Hydrolysis of ATP to ADP by myosin provides energy for myosin head to resume its normal position
7) Head of myosin reattaches to a binding site further along the actin filament and cycle is repeated
What are the three ways that ATP is generated?
Aerobic respiration
Anaerobic respiration
Creatine phosphate
Where is most of the ATP in muscle cells produced from?
Regenerated from ADP using oxidative phosphorylation
