Nervous systems Flashcards
Squid giant axon
What did Hodgkin & Huxley, 1963 do?
What properties were observed?
fast or jet propulsions=escape response
radial muscle contraction to hyper-inflate mantle cavity, then stronger contraction
0.5-1.5mm diameter axon
They isolated a squids giant axon and first people to describe an action potential, so the properties you have for an action potential includes
*Lipid bilayer (capacitor)
*Discontinuity in ion distribution
*Sets up a potential gradient
What is the donnan equilibrium? (tissue disalysis)
*negatively charged proteins too big to diffuse
*Attracts cations (+) exclude mobile anions
Donnan potential= passive properties of ions/proteins cause voltage
explain a resting membrane potential (in the phospholipid bilayer)
2 potassium ions in
3 sodium ions out
Potassium leak channels “More permeable to K+” diffusion of K+ on gradient
Explain an action potential
When a nerve is not being stimulated we have resting potential.
In the membrane we have a phospholipid bilayer separating outside and inside the cell.
This membrane prevents ions that are water soluble from passively entering.
There are 4 different channels
1) sodium potassium pump that requires energy and when an ATP binds it causes a conformational change it picks up 3 sodiums and transports them outside and 2 potassiums to the inside.
2) The potassium leak channel (more permeable to K ) this diffuses potassium creating a concentration gradient of its own distribution. This creates more positive charge on the outside than on the inside
on average the charge inside the membrane is -70
When there is a stimulus the inside of the cell becomes more positive
3)Voltage-gated Na+ channel opens and Na+ diffuses into cell making it even more positive.
4)voltage gated channel allows more k+ to move out but slower making it more negative again
IF A THRESHOLD IS REACHED
DEPOLARISATION= More positive as voltage-gated Na+ channel opens and this hits action potential.
REPOLARISATION= then k+ channel opens slowly releasing K+
REFRACTORY PERIOD= The k+ channels close slowly so there is a delay and an overshoot meaning the cell becomes way more negative inside
HYPERPOLARISATION= but will then go back to normal resting state.
What is;
absolute refractory period
relative refractory period
absolute refractory period= When threshold is reached it causes an action potential so this period shows an all or nothing response
relative refractory period=It very difficult to stimulate the cell in this period as you need even more positive charge than normally. But a strong stimulus can be conveyed by number of action potentials in succession rather than the size of them.
What’s the difference between a neuron and a nerve?
Neuron= specialised cell that conducts nerve impulses
-Sensory neuron
-Motor neuron
-Interneuron
Nerve= bundle of neurons, connective tissue & blood, they are vessels to transmit a signal between two body parts
Explain the structure of a myelinated neuron
In a neuron there can be Schwann cells and in between there are tiny patches of bare membrane called the nodes of Ranvier. Sodium ion channels are concentrated at the nodes so this is where depolarisation occurs. The neuron’s soma conducts enough electrical charge to depolarise the next node, so the impulse jumps from node to node called saltatory conduction.
In what responses do you think you might find myelinated nerves?
reflex responses, things that need tight coordination between left and right nerves so that there is no asynchrony.
What is;
Temporal summation
Spatial summation
Temporal summation= converts a rapid series of weak pulses from a SINGLE source into one large signal.
Spatial summation= occurs when several weak signals from different locations are converted into a single larger one.
there can also be inhibition
What are the two types of synapses
Electrical= Fast reflexes/synchronisation This has Gap junction which is lots of aligned channels (pore for ions) for a fast response
Chemical= neurotransmitters and varied actions
Voltage-gated Ca+ channels opens and the calcium through a series of steps causes migration of synaptic vesicles and they fuse to membrane called exocytosis. They contain chemical and they release contents into the gap where they bind to the next receptor on the next cell membrane or it can bind to Ligand/G-protein gated channels which then bind to the next cell.
This response can be a more specialised response as flexibility with different chemicals
What does synapses response depend on?
Give an example of some of the neurotransmitters
Synapses Response to action potential in chemical neurotransmitters depends on
* Post - synaptic tissue ( e.g. muscle , gland )
*Inhibitory or excitatory
►Acetylcholine ( “ Cholinergic nerve fibres “ ; muscles ) ➤GABA ( brain )
►Dopamine ( motivation reward system / emotional arousal ) > Serotonin ( intestine / regulates appetite / impulsivity )
> Norepinephrine ( noradrenaline ; CNS / SNS , “ adrenergic nerve fibres “ )
> Epinephrine ( adrenaline ; brainstem / adrenal glands ; “ adrenergic “ )
► Presence of drugs ( agonists / antagonists )
Describe the nervous system anatomy of sponges a radiata
Sponges: no cells with synaptic junctions But e.g. Ca+ waves synchronise contraction
“Radiata” (lack bilateral symmetry)
nerve net, no centralised brain, sensory & motor neurons connected by intermediates
Describe an earthworm nervous system
Earthworm nervous system
Dual nerve cords connected by transverse nerves
Nerve ring - simple brain?
*Integrates photoreception, coordinates contraction
*Central nervous system (CNS) v peripheral (PNS)
They have;
buccal receptors
Photosensitive cells= (“lights of hess”)
epidermal receptors
Explain some parts of the human brain
*Frontal lobe= Cognition, emotion, memory, decision-making, movement
*Parietal lobe= Sensory –> Motor integration
*Lateral lobe= Language/hearing/memory (hippocampus)
*Occipital lobe= Visual processing
Vertebrate nervous system
*Afferent ( sensory ) : PNS → CNS
*Efferent ( motor ) : CNS → PNS
Somatic nervous system =voluntary and reflex movements of skeletal muscles → Acetylcholine ( cholinergic )
Autonomic nervous system = Sympathetic ( mostly adrenergic , catecholamines ) and Parasympathetic ( cholinergic )
