5.1.3 Neuronal communication Flashcards
What is a sensory receptor?
Specialised cells which detect stimuli from the environment.
What is a transducer?
Transducers converts one form of energy into another.
How do receptors act as transducers?
In a receptor a transducer converts the stimulus energy into a nerve impulse which is transmitted to the CNS.
Name four types of receptor cell.
Photoreceptor, Chemoreceptor, Mechanoreceptors and Thermoreceptors.
Name the stimulus detected and the location of photoreceptors.
Light
Eyes
Name the stimulus detected and the location of chemoreceptors.
Chemicals
Nose, tongue, blood vessels
Name the stimulus detected and the location of mechanoreceptors.
Pressure, movement
Skin, muscles, inner ear
Name the stimulus detected and the location of thermoreceptors.
Temperature
Skin
What Pacinian Corpuscles?
Mechanoreceptors in the skin that detect pressure and vibrations.
Describe the structure of Pacinian Corpuscles.
Contain the ending of a sensory neuron wrapped in layers of connective tissue called lamellae. There is viscous gel between each layer.
What happens when Pacinian Corpuscles are stimulated?
- Lamellae deform pressing on the sensory neuron ending
- This stretches the neuron ending causing it to change shape
- This opens stretch mediated Na+ channels increasing permeability to Na+
- Na+ diffuses into the neuron, depolarising it and resulting in a generator potential
- If this signal reaches a threshold action potential is triggered.
How does increasing the strength of a stimulus affect a receptor cell?
It increases the size of the generator potential.
What is a resting potential?
When a neuron is not transmitting signals, its membrane is in a state of polarisation meaning there is a difference in voltage across the membrane.
What value is resting potential?
-70mv
Describe how membrane proteins achieve resting potential
Sodium potassium ion pumps - pump 3 Na+ out for every 2 K+ in.
Potassium ion channels - allow K+ to diffuse out of the neuron down concentration gradient.
Sodium ion channels - closed preventing Na+ entering neurons.
How is resting potential achieved?
The extracellular space outside of the axon accumulates negative ions making the axon cytoplasm more negatively charged causing the membrane to be polarised.
What are the stages involved in generating action potential?
Resting potential
Stimulus
Depolarisation
Repolarisation
Hyperpolarisation
Refractory period
What happens at the resting potential stage?
The membrane is at rest and is polarised at -70mV.
What happens during the stimulus stage?
Voltage gated Na+ ion channels open so more Na+ ions flow into the neuron making it less negatively charged.
What happens in depolarisation?
A threshold potential of -55mv is reached causing more Na+ channels to open resulting in Na+ influx.
What happens during repolarisation?
At +30mv Na+ channels close and K+ channels open causing K+ to flow out of the axon repolarising the membrane
What happens in hyperpolarisation?
An excess of K+ ions leave the membrane causing the potential to drop below -70mv (resting potential)
What happens in the refractory period?
Ion pumps/channels restore resting potential.
What are the parts of the all or nothing response?
The threshold phenomenon, no partial response, action potentials are always the same size
Describe the threshold phenomenon
Once threshold potential is reached an action potential is always triggered regardless of stimulus strength
Describe no partial response
Without a threshold being reached no action potential is initiated
Describe action potentials are always the same size
Stronger stimulus doesn’t increase action potential strength but increases frequency of action potentials generated
What is a synapse?
A junction where information is transferred from one neuron to another/to an effector cell.
What are the key roles of synapses?
- Transmit information (through release of neurotransmitter chemicals)
- A single impulse in the presynaptic neuron can initiate multiple impulses on the postsynaptic neuron.
- Impulses from several presynaptic neurons can be combined to form one postsynaptic response.
Name two types of neurotransmitter
Excitatory and Inhibitory
How do excitatory neurotransmitters effect the post synaptic membrane, do they generate action potential, provide examples
- Depolarises
- May trigger AP if threshold potential reached
- Acetylcholine in the CNS and at neuromuscular junctions
How do inhibitory neurotransmitters effect the post synaptic membrane, do they generate action potential, examples
- Hyperpolarisation
-Prevent action potential - Acetylcholine at cardiac synapses
Name two types of summation
Spatial and Temporal
Describe spatial summation
- Multiple presynaptic neurons converge on a single postsynaptic neuron/ effector cell
- Combined input of neurotransmitters can trigger postsynaptic firing
- Inhibitory inputs have potential to prevent firing
Describe temporal summation
Repeated firing by a presynaptic neuron leads to continuous neurotransmitter release.
An increased amount of neurotransmitter makes the postsynaptic neuron more likely to fire.
Describe the key steps in synaptic transmission
- Action potential arrives
- Ca 2+ channels open
- Synaptic vesicles fuse with the presynaptic membrane
- Neuotransmitters diffuse across the synaptic cleft
- Neurotransmitters bind to receptors.
- Depolarisation
- If depolarisation reaches a threshold AP triggered
What are cholinergic synapses?
Specific types of synapse which use acetylcholine (ACh) as their neurotransmitter.
What happens when ACh binds to receptors?
- ACh is broken down by acetylcholinesterase to choline and ethanoic acid (acetate)
- These products are reabsorbed into the presynaptic knob by active transport
- They are recycled to synthesise ACh
- ACh is transported to synaptic vesicles for another AP
What two parts is the mammalian nervous system divided into?
The central nervous system (CNS) and the peripheral nervous system (PNS)
What is the CNS?
Consists of the brain and spinal cord and serves as the primary command centre for the body.
What is the PNS?
Consists of all of the nerves (made up of neurones) that connect the CNS to the rest of the body which facilitates bi-directional communication.
What are the divisions of the PNS?
The sensory nervous system and the motor nervous system.
Describe the sensory nervous system
Consists of sensory neurons that carry nerve impulses from receptors to the CNS
Describe the motor nervous system
Consists of motor neurons that carry nerve impulses from the CNS to effectors (e.g. muscles and glands)
What are the functional divisions of the nervous system?
The somatic nervous system and the autonomic nervous system.
Describe the somatic nervous system
Controlled consciously for voluntary movement.
Describe the autonomic nervous system
Controlled subconsciously for involuntary movements
What are the divisions of the autonomic nervous system?
Sympathetic and parasympathetic nervous system
Describe the sympathetic nervous system
Activates the fight/flight response, increases activity levels, uses the neurotransmitters noradrenaline and adrenaline
Describe the parasympathetic nervous system
Activates the rest/digest system, decreases activity levels, uses the neurotransmitters acetylcholine.
What are the key functions of the brain?
- Receives sensory information from receptor cells and the hormonal system about internal/external environment and coordinates a response.
- Controls movement, physiological functions, emotion and cognition
Where is the hypothalamus located?
Just below the middle part of the brain
What is the function of the hypothalamus?
Homeostasis
Water balance
Hormonal regulation
What is the cerebrum?
The largest part of brain and consists of two halves called the left and right cerebral hemispheres that receive sensory information. Has an outer layer called the cerebral cortex.
Functions of the cerebrum
- Processes sensory information (crucial for vision and hearing)
- Involved in learning, memory and higher level thinking
Where is the pituitary gland?
What are the functions of the pituitary gland?
- Produces, stores and secretes hormones when triggered by the hypothalamus.
- The hormones is secretes prompt other glands.
What are the two sections of the pituitary gland?
Anterior and posterior pituitary gland
Describe the anterior pituitary gland
Produces six hormones including follicle stimulating hormone (FSH) which is involved in reproduction and growth hormones.
Describe the posterior pituitary gland
Stores and releases hormones produced by the hypothalamus including ADH (involved in urine production)
Where is the medulla oblongata and describe its functions.
- At the base of the brain, connecting with the spinal cord.
- It involuntarily regulates breathing rate, heart rate and blood pressure. It controls autonomic functions e.g. swallowing, coughing and peristalsis
Where is the cerebellum and what is its function?
- Located underneath the cerebrum
- Coordinate skeletal muscle contraction, maintain posture, balance and involuntary muscle movement.
Key features of the reflex arc
Involuntary, innate, protective, rapid
Describe the knee-jerk (patellar) reflex
Spinal reflex that causes the leg to kick when it is tapped just below the knee cap. Helps maintain posture and balance.
What are the steps in the reflex arc?
Stimulus
Receptor
Sensory
Relay
Motor
Effector
Response
What is a reflex arc?
A neural pathway that causes an involuntary and immediate reaction to a stimulus, typically designed for protection
What are the three types of muscle?
Skeletal, cardiac and smooth muscle
Describe skeletal muscle
- Tubular, striated
- Multiple nuclei
- Regular, parallel bundles of myofibrils
- Voluntary control
- Neurogenic stimulation
- Fast contraction speed, short duration
Describe cardiac muscle
- Branched, striated
- Single nuclei per fibre
- Branching network of myofibrils
- Involuntary control
- Myogenic stimulation
- Intermediate contraction speed and duration
Describe smooth muscle
- Spindle shaped, non striated
- single nuclei
- Unorganised, no myofibrils
- Involuntary control
- Neurogenic stimulation (can also respond to pressure)
- Slow contraction speed and long duration
Name the components of muscle fibre
Sarcolemma (cell surface membrane)
Sarcoplasm (cytoplasm)
Transverse tubules (extensions of sarcolemma)
Sarcoplasmic reticulum (release Ca2+)
Myofibrils
Multiple nuclei
Mitochondria
Describe myofibrils
Made up of repeating units called sarcomeres that slide past each other enabling muscle contraction
What are the two main filaments in a sarcomere?
Myosin (thick)
Actin (thin)
Name the key sections of a sarcomere
A band (dark band)
I band (light band)
Z- line
M -line
H -zone
Describe the A band
Area with both myosin and overlapping actin filaments (darker in colour)
Describe the I band
Area containing only light actin filaments (lighter in colour)
Describe Z-lines
Mark the boundaries of each sarcomere unit
Describe the M-line
The central line of a sarcomere
Describe the H-zone
Area with only myosin filaments (central lighter region within the A band)
What changes occur in the sarcomere during muscle contraction?
I band and H-zone shorten in length due to increased overlap of actin and myosin, A band remains constant in length
Outline the main steps in the sliding filament theory
- Ca2+ ions bind to troponin altering its shape
- This moves tropomyosin away from actin’s binding sites, making them available for myosin
- Myosin attaches to exposed actin filaments forming actin-myosin cross bridges
- Myosin heads execute a power stroke, pulling actin along and releasing ADP
- ATP binds to myosin head so it detaches from actin
- Ca2+ activates myosin’s ATPase activity, breaking down ATP to ADP and phosphate, releasing energy
- Energy resets myosin head to original position
- Myosin head reattaches to a new actin site further along the filament.
How can ATP for muscle contraction be generated?
Aerobic respiration, anaerobic respiration, The ATP-creatine phosphate system
Describe the ATP Creatine phosphate system
Quick source of energy, broken down to immediately replenish ATP without oxygen
What is a neuromuscular junction?
Where a motor neuron meets a skeletal muscle fibre
What is a motor unit?
A motor unit consists of all of the muscle fibres supplied by a single motor neurone
How does the number of motor units determine the force of contraction?
To exert a strong force, large number of motor units are stimulated. (Small forces require only the stimulation of a few motor units)
What provides energy for the reformation of Acetylcholine?
Mitochondria in the neurone
Stages in neuromuscular transmission
- AP arrives at the end of the neuron
- Ca2+ channels open and Ca2+ enters the neuron
- Acetylcholine vesicles release contents into the synaptic cleft
- Acetylcholine diffuses across synaptic cleft
- ACh binds to receptors on the sarcolemma leading to opening of sodium channels
- This results in depolarisation of the sarcolemma
Describe the role of the sarcoplasmic reticulum
When stimulated by arrival of action potential, Ca2+ channels open in the sarcoplasmic reticulum membrane, releasing Ca2+ into the sarcoplasm.
