Neuronal Communication Flashcards
What is homeostasis?
Maintenance of a stable equilibrium in the conditions inside the body
What is the basic order of the nervous pathway?
Receptor, sensory neurone, CNS (contains relay neurone), motor neurone, effector
What are the functions of the 4 general structures of neurones?
Dendron - Sends impulse to cell body
Cell body - release neurotransmitters
Axon - sends impulse away from cell body
Myelin sheath - layers of plasma membranes (lipids), acts as insulation and speeds up rate of transmission
Describe the structure and function of a sensory neurone
- Transmits impulses from a sensory receptor cell to a relay neurone, motor neurone or brain
- Have one dendron, which carries the impulse to the cell body
- One axon, which carries the impulse away from the cell body
- Nodes of Ranvier, where impulse jumps along in-between myelin sheaths.
Describe the structure and function of a relay neurone
- Transmit impulses between neurones
- For example, between sensory and motor neurones
- They have many short axons and dendrons
- Cell body in the middle of dendrites and axons
Describe the structure and function of a motor neurone
- Transmit impulses from a relay neurone or sensory neurone to an effector, such as a muscle or a gland
- One long axon and many short dendrites, as well as nodes of Ranvier
- Cell body at beginning of the neurone structure
What is the function of the myelin sheath?
- Acts as an insulating layer
- Speeds up nerve impulse transmission (saltatory conduction) at nodes of Ranvier
- Produced by Schwann cell
Why are sensory receptors described as transducers?
- Can turn a stimulus into an electrical impulse
- Generator potential
What are the 4 sensory receptors and what do they each detect?
Mechanoreceptor - Pressure and movement
Chemoreceptor - Chemicals (smell/taste)
Thermoreceptor - Heat (eg on tongue/skin)
Photoreceptor - light
What is the outer layer of a pacinian corpuscle and the layers inside?
- Capsule
- Layers of connective tissue with viscous gel between to help transmit vibrations
What are stretch mediated sodium ion channels in a pacinian corpuscle?
- On outside of neurone ending
- Sensitive to any changes within their physical structure, can be stretched open
- Only sodium ions can diffuse across them
What occurs in the pacinian corpuscle at a resting state?
- Sodium ion channels are closed, so sodium on outside cannot enter neurone
- Outside of neurone is more positive, so membrane is polarised
What happens when pressure is applied to the pacinian corpuscle?
- The corpuscle changes shape and the neurone membrane is stretched
- Sodium ion channels stretched open so sodium ions diffuse down the electrochemical gradient into the sensory neurone
- Depolarises membrane as sensory neurone becomes more positive than outside
- Initiates generator potential, and action potential triggered when enough sodium ions enter
- Signal sent across sensory neurone causing for example a reflex action
At the resting potential in a cell, what ions get pumped in and out at what proportion and through what pump/channel, and through what process?
3 Sodium ions out
2 Potassium ions in
Through sodium Potassium pump
Through active transport (ATP –> ADP + Pi)
Through what process do potassium ions leave the cell and move through the potassium channel during resting potential?
Facilitated diffusion
When does the action potential take place?
When a stimulus has been detected by a sensory receptor
Name and describe the first stage of the action potential
Depolarisation
- First sodium channels will detect nerve impulse and receive energy, so open
- Sodium ions enter cell through facilitated diffusion increasing sodium conc in cells
- Threshold potential of -55mV is reached so more sodium channels are stimulated to open
- Big sodium ion influx, so cell becomes positive and outside becomes negative
- Occurs until +40mV is reached
Name and describe the second stage of the action potential, after depolarisation
Repolarisation
- Sodium channels close and potassium channels open, so potassium ions leave the cell by facilitated diffusion
- Overshoot of potential difference leading to hyperpolarisation
- Sodium potassium pumps reopened
Name and describe the third stage of the action potential, after repolarisation
Hyperpolarisation
- Potential difference is lower than -70mV
What is a synapse?
The junction (gap) between 2 neurones, containing neurotransmitters which diffuse across
Explain the two types of neurotransmitter, and give an example of each
Excitatory (eg acetylcholine) - triggers new action potential to be generated in post synaptic neurone
Inhibitory (eg GABA) - does not trigger action potential
Explain the stages in the pre synaptic neurone when an impulse/action potential enters the pre synaptic neurone?
- Polarisation of membrane causes voltage gated calcium channels to open, so calcium ions enter the pre synaptic neurone down the electrochemical gradient
- The calcium ions move the acetylcholine vesicles to the cell surface membrane and it fuses with it
- Acetylcholine released into syanptic cleft, where they diffuse across to the post synaptic neurone
Explain what happens once the acetylcholine reaches the post synaptic neurone
- Acetylcholine binds to receptors on the sodium channels
- Sodium ion channels open, so sodium ions enter the post synaptic neurone down the electrochemical gradient
- Membrane depolarises, causing a new action potential
Why is constant action potentials not good, and simply, how is this stopped?
- You would go into a seizure because constantly receiving excitatory impulse
- Stop the release of new action potential by breaking acetylcholine down
How is acetlycholine broken down?
- Using the very efficient enzyme acetylcholinesterase, acetylcholine is removed from the receptor
- And is broken down into two parts called choline and acetate
- They diffuse back into the pre synaptic neurone
- Mitochondria in the pre synaptic neurone does respiration to release ATP, which is used to combine these two parts back into actylcholine
Explain the three main functions of synapses
Unidirectional transmission - Nerve impulse/action potential moves in one direction (from sensory to motor neurone)
Can cause multiple responses from one stimulus
Can receive multiple stimuli from one response
What is summation?
- The effect of the build up of neurotransmitters in the synapse
- A new action potential can only be triggered if the neurotransmitters have built up to the threshold
Explain spatial summation
- Multiple neurones connected to one synapse
- More than one presynaptic neurone releases neurotransmitters to trigger new action potential in one postsynaptic neurone
- If only one presynaptic neurone recieves signal, no action potential will be generated
Explain temporal summation
- High frequency of action potentials reach the presynaptic neurone, causing a higher concentration of neurotransmitters being released to trigger a new action potential in the postsynaptic neurone
- No action potential triggered on the postsynaptic neurone if only one action potential sent along the pre synaptic neurone
What is the difference between the CNS and Peripheral nervous system?
CNS - consists of the brain and spinal cord
PNS - consists of the neurones that connect the CNS to the rest of the body (sensory and motor neurones)
What is the difference between the somatic and autonomic nervous system and give an example for each
Somatic - under conscious control. For example, when you decide to move a muscle to move your arm, the somatic nervous system carries impulses to the body’s muscles
Autonomic - works constantly, under subconscious control and is involuntary. For example, causing the heart to beat, or digesting food. Carries nerve impulses to glands, smooth muscle and cardiac muscle
What two nervous systems is the autonomic nervous system further divided into?
Sympathetic - increases activity
Parasympathetic - decreases activity
What is the function of the cerebrum?
Controls
- voluntary action
- personality
- memory
- learning
- conscious thoughts
What is the function of the cerebellum, medulla oblongata, hypothalamus and pituitary gland?
Cerebellum - controls unconscious functions such as posture and balance
Medulla - used in autonomic control, controls heart rate for example
Hypothalamus - regulatory centre for temperature and water balance (homeostasis)
Pituitary gland - stores and releases hormones that regulate many body functions
Explain the stages of the knee jerk reflex and state what type of reflex it is
Spinal reflex
1. Tap under kneecap causes patellar tendon to stretch, which also stretches extensor
2. Sends reflex arc through sensory neurone
3. Reflex signal goes along one motor neurone, causing extensor muscle to contract
4. Relay neurone inhibits the other motor neurone of flexor muscle, to relax
5. Leg kicks due to antagonistic muscle action
When may the blinking reflex be used?
- To assess if unconscious patients are brain dead, as it is a cranial reflex (involves the brain)
- Done by shining a light or touching cornea
Explain the blinking reflex
- Cornea irritated
- Triggers impulse along sensory neurone
- Relay neurone in lower brain stem passes impulse along
- Signal branches off in motor neurone to eyelid muscles
- Both eyes shit as a consensual response
Define a sarcomere, sarcolemma, sarcoplasm, sarcoplasmic reticulum and myofibril
Sarcomere- Basic functional unit of a fibre
Sarcolemma - plasmic membrane around fibres
Sarcoplasm - shared cytoplasm within fibres
Sarcoplasmic reticulum - endoplasmic reticulum within sarcomere
Myofibril - Long cylindrical organelles made of proteins actin and myosin
What is the Z line, dark band, light band and H zone?
Z line - Lines found in between light bands, distance between two Z lines is the sarcomere
Dark band - areas that appear dark because of thick myosin filaments, edges particularly dark where actin overlaps
Light band - appear light as not where they overlap, just actin
H zone - found in the centre of each dark band, only mysoin filaments present here, decreases when muscle contracts
Describe the structure of actin
- Protein tropomyosin wraps around it and is held in place by troponin
- Troponin can bind to calcium ions leading to a conformational (shape) change, moving the tropomyosin to stop covering the actin myosin binding site
Describe the structure of myosin
- Much thicker than actin
- Contains myosin heads which bind to actin myosin binding sites on the actin
- In resting state, ADP binds to the myosin head
- Contains an ATPase component to hydrolyse ATP into ADP + Pi
- Can form cross bridges with actin at AM binding site
Explain how the interaction of myosin and actin is stimulated to begin muscle contraction
- Action potential arrives and depolarises sarcolemma and sarcoplasmic reticulum
- Voltage gated calcium ion channels on sarcoplasmic reticulum open to release calcium ions into sarcoplasm
- Calcium ions bind to troponin, causing a conformational change
- It pulls on tropomyosin and exposes AM binding site
Explain the attachment and movement stage in muscle contraction
- Myosin head binds to actin myosin binding site, forming cross bridges
- Myosin filament flexes, pulling actin along and releasing ADP from the myosin head
Explain the detachment stage in muscle contraction
- ATP binds to myosin head, causing it to detach from the actin myosin binding site on actin
- Calcium ions activates ATPase in myosin head so the ATP is hydrolysed to form ADP +Pi once again
- Energy releases from ATP hydrolysis returns the myosin head back to its original position
