Nervous systems

Dendrites

recieves input from other neurons

Cell body

intergration of synaptic potentials

Axon

conduction component of the neuron, propagates action potentials to the axon terminals 

action potential 

transmits information and triggers synaptic output 

Synaptic terminals

output of the neuron, secretion of neurotransmitter, alters activities of other cells

resting membrane potential concentrations

Na+ is more concentrated outside the cells and K+ more concentrated inside the cell

Resting membrane potential first part 

Mainly K+ channels open, NA+/K+ pump maintains high intracellular K+ conc. and creates chemical conc. gradient, K+ ions diffuse in both directions across the membrane

Resting membrane potential second part 

Higher probability of K+ ions hitting channels from inside neuron creating net outward current of K+, an excess of negative ions inside creates an electrical gradient which opposes K+ outflow. 

Equilibrium with gradients

Electrical gradient counteracts chemical concentration gradient

Before an action potential

Most voltage-gated sodium and potassium channels are closed

Depolarisation

Voltage gated Na+ channels open first and Na+ flows into the cell

Rising phase of action potential 

When reaching the threshold, membrane potential becomes more positive, more Na+ channels open and so on, this is a self sustaining process 

falling phase of action potential

Voltage gated Na+ channels become inactivated, Voltage gated K+ channels open and K+ flows out of the cell

Undershoot/hyperpolarisation

Voltage gated K+ channels are still open (in addition to permanently opened ones), more K+ flows out than during rest

Electrical synapse

Cytoplasmic channels (gap junctions) directly connect adjacent neurons, allow direct electrical current flow for rapid transmission, transmission is bidirectional

Chemical synapse

Neurotransmitter cross cleft and bind postsynaptic receptors, slower than electrical synapses but more flexible, transmission is unidirectional, excitatory or inhibitory 

Chemical synapse processes 1 and 2

1) synthsis and packaging neurotransmitter in synaptic vesicles 2) Action potential causes Ca2+ influx which triggers fusion of the vesicle with the presynaptic, results in neurotransmitter release 

Chemical synapse process 3 

3) Neurotransmitter diffuses across the synaptic cleft and binds to and activates receptors in postsynaptic cell 

Natural toxins often block synaptic transmission

Botox blocks neurotransmitter release, bungarotoxin preventing binding of neurotransmitter at receptor 

two mechanisms of terminating synaptic transmission

enzymatic breakdown of neurotransmitter in the synaptic cleft, reuptake of neurotransmitter by presynaptic neuron 

Chemical synapse can be …

excitatory or inhibitory

Synaptic integration

Neuron combines synaptic inputs to determine its output, summation of postsynaptic potentials

IPSP

Inhibitory postsynaptic potential, decrease probability of action potential generation

EPSP

Excitatory postsynaptic potential, increase probability of action potential generation 

Stretch reflex inhibitory interneuron

Sensory neuron also activates inhibitory interneurons, these inhibits antagonistic motor neurons, prevents antagonistic muscle contraction, sensory neuron of stretch receptor synapses on motor neurons to the same muscle

Stretch reflex 

Motor neuron excited, extensor muscle contracts, leg extensor muscle stretched, muscle spindle generates action potentials 

Reflexes 

a model for how circuits generate behaviour, automatic responses, often mediated by spinal cord or brainstem, simple and reproducible, clear input-output pathways

Reflexes are useful for

studying information processing, synaptic plasticity, and basic learning, less suited for complex cognition but form essential building blocks for larger networks

Sensory neurons, afferent neurons

detect stimuli and convert them to electrical signals

Interneurons 

integrate and modulate information 

Efferent neurons, motor neurons

send signals to muscles or glands causing action

Acrosome 

Sperm must be able to penetrate the protein layer surrounding the eggs, it does by secreting enzymes from the acrosome 

sensation definition

Detection of external or internal stimuli

Sensation mechanism and function

Stimulus →receptor activated → Transduction → signal transmission to brain, provides raw sensory data

Perception definition

Process of interpreting and giving meaning to sensory input

Perception mechanism

Brain integrates sensory input with attention, memory, prior knowledge, context and emotion

Perception function

creates a coherent, meaningful, and emotionally coloured representation of the world, supports recognition, decision making and behaviour 

Fish lateral line system

Detects water movement and sel-motion

What is the lateral line system essential for…

Orientation, hunting, schooling, defense

What do mechanosensory hair cells transduce 

Water movement, vibration, pressure gradients 

Sharks hunt by…

Following preys hydrodynamic wake sensed with their lateral line system

Cupula

Jelly-like structure surrounding hair cells sensory hairs

Cupula functions

Acts as mechanical bridge between water and hair cells, Transmits water movement to sensory hairs, Extends through boundary layer where water movement is reduced, amplifies sensitivity to water disturbances

Sensory transduction

Stimulus arrives and activates receptor, stimulus energy is converted into a receptor potential, signal passed on by neurotransmitter release or by change in action potential rate

Tip Links

Connect adjacent stereocilia, maintain tension for sensitivity, transmit deflection forces, gate mechanosensitive ion channels

Sensory transduction process

1) stimulus arrives and activates receptor 2) receptor activated, 3) stimulus energy converted to receptor potential, change in membrane potential 4) signal passed on by neurotransmitter release 

Receptor potentials signal type and amplitude

Continuous and graded, proportional to stimulus

Action potentials signal types and amplitude

proportional to stimulus, all or none

Receptor potentials propagation, threshold and function

Local and decremental, none, encode stimulus strength

Action potentials propagation, threshold and function 

long-distance and non-decremental, required, reliable transmission 

decremental

gradual reduction or decrease

Hair cells…

Encode the direction of water movement

Muscles

Produce movement

Glands 

Secrete substances

Muscles and glands together

turn neural signals into actions and body responses

Exocrine glands

Salivary, mammary, sweat

Exocrine glands delivery, secretion, target, and examples

Through ducts to surface/cavities, non-hormone substances, local environment, sweat, salivary, mammary

Exocrine glands Function, onset and duration

Lubrication, digestion and cooling, immediate, generally short-term 

Endocrine gland delivery, secretion, target and examples 

into the bloodstream, hormones, distant cells in whole body, thyroid, pituitary and adrenal 

Endocrine gland function, onset and duration 

Regulate metabolism, growth, homeostasis, relatively slow, often long-lasting 

Muscle Fibres 

Long cylindrical cells, formed by fusion of many embryonic cells (myoblasts), contain multiple nuclei, can span the full length of a muscle 

Sarcomeres 

Smallest contractile units of muscle, arranged in repeating patterns along myofibrils, responsible for the striated appearance of skeletal

Myofibril structure

Thin filaments attached to Z line, thick filaments anchored at M lines, in relaxed state there is partial overlap between thick and thin filaments

Muscle contraction

Muscle shortens during contraction, filament lengths remain constant, thin and thick filaments slide past each other 

Myosin 

tails aggregate to form thick filaments, heads are motile, extending from filament 

Myosin head contraction 1-3

1) myosin head bound to ATP, 2) Myosin head hydrolyzes ATP →ADP and inorganic P 3) Myosin head attaches to actin

Myosin head contraction 4-5 

4) Power stroke, ADP and P relase, myosin head pivots pulling actin 5) New ATP binds to myosin, myosin releases from actin 

Muscle contraction involves …

Repeated cycles of binding and release

Why do dead animals become stiff

After death, ATP production stops, Without ATP, myosin heads cannot detach from actin, Result, muscles lock in a contracted state 

Neuromuscular junction signalling in vertebrates 1-3

1) Release of acetylcholine 2) Action potential propagation 3) Action potential triggers Ca2+ release

Neuromuscular junction signalling in vertebrates 4-7

4) Ca2+ bind to troponin exposing the myosin-binding sites 5) contraction 6) Removal of Ca2+ 7) Tropomyosin blocks myosin-binding sites 

Vertebrate Skeletal muscle fibers

Innervation: one excitatory motor neuron per muscle fiber, Neurotransmitters: Acetylcholine, excitatory, Contraction Control: All-or-none action potential propagates along the whole fibre 

Insect muscle fibres 

Innervation: Multiple excitatory and inhibitory motor neurons per muscle fibres, Neurotransmitters: Glutamate, excitatory, GABA, inhibitory Contraction control: graded excitatory and inhibitory postsynaptic potentials sum

Neuron type vertebrates and insects

vertebrate:Excitatory only, Insects: Excitatory and inhibitory, insects evolved inhibitory inputs for finer control 

Precision of control Vertebrate and insects 

Vertebrates: lower, all or nothing contraction, Insects: higher, graded contraction, insect flight and complex terrestrial locomotion required more precise movements 

Metabolic efficiency For vertebrates and insects 

Vertebrates: lower, Insects: higher, graded control conserves energy in small bodies 

Body plan adaptation Vertebrates and insects

Vertebrates: centralised control for non-segmented body, Insects: distributed control for segmented body, different body plans shaped neural strategies 

Animal cognition

study of mental processes in non-human including perception, learning, memory, and decision making

Classical conditioning first trial

Conditioned stimulus along does not elicit the unconditioned reaction, Unconditioned stimulus elicits an unconditioned response, Temporal coupling makes Conditioned stimulus predictive for the unconditioned

Waggle dance

Allows bees to communicate food location, bee learns to associate flower with food, bee must translate where the food is located

How the waggle dance communicates

All relative to position of sun, Straight upwards means towards the sun, 60 degrees is 60 from the sun etc, Number of waggles is distance in km

Is the waggle dance an example of cognition

dance is innate/not cognition, forager bees must learn and remember food locations/cognition, nestmates must remember and navigate/cognition

How to test abstract thinking bees

1) sample presentation 2)retention 3) comparison 4)selection

Testing abstract thinking bees

Bees learn to associate same colours with food stimulus, does not require abstract thinking

To actually bees test abstract thinking…

swap colours out for patterns, shows abstraction, bees distinguish same vs difference