SNS - Biology - Nervous System Flashcards
Invertebrates
Protozoa
Unicellular organisms possess no organized nervous system
May respond to stimuli including touch, heat, light and chemicals
Invertebrates
Cnidarians
Simple nervous system - nerve net
Network of nerve cells which may have limited centralisation
Some jellyfish have clusters of cells and pathways that coordinate the relatively complex movements required for swimming
Invertebrates
Annelida
Earthworms possess primitive nervous system consisting of defined ventral nerve chord and anterior ‘brain’ of fused ganglia
Definite nerve pathways lead from receptors to effectors
Invertebrates
Arthropoda
Brains similar to annelids but more specialised sense organs present (eg compound or simple eyes, tympanum for detecting sound)
Neuronal Resting Membrane Potential
-70mV
Inside of neuron more negative than outside
Due to selective ionic permeability of Na-K pump - uses ATP to transport 3 Na+ out for every 2K+ transported into the cell
Neuron is also selectively permeable to K+, allowing it to diffuse outwards along conc gradient, decresing neuronal resting potential
Neuronal Threshold Membrane Potential
Level at which an AP generated
Usually ~ -50mV
Action Potential Mechanism
- Soma receives excitatory and inhibitory impulses from other nerve cells
- Depolarised above threshold membrane potential, VGSCs open - Na+ enters further depolarising cell
- VGPCs open, VGSCs close, repolarises as K+ leaves cell
- Cell hyperpolarises
- VGPCs close, resting potential restored
Diameter and Action Potential Velocity
Greater the diameter, greater the speed of AP
Drugs and Synapses
Curare
Blocks postsynaptic ACh receptors
Leads to paralysis by blocking nerve impulses to muscles
Drugs and Synapses
Botulinium Toxin
Blocks presynaptic release of ACh
Resluts in paralysis
Drugs and Synapses
Anticholinesterases
Inhibit acetylcholinesterase
ACh not degraded at synapse and continues to act, preventing coordinated muscle contractions
Used as nerve gases and insecticides (parathion)
CNS
Brain
Forebrain
- Telencephalon - cerbral cortex, olfactory bulb
- Diencephalon - thalamus and hypothalamus
CNS
Brain
Mesencephalon
Midbrain
Relay centre for visual and auditory impulses
Important role in motor control
CNS
Brain
Hindbrain
Brainstem :
- Cerebellum - modulates motor impulses initiated by cerebral cortex and important in the maitentance of balance, hand eye coordination and timing of rapid movements
- Pons - relay centre between cortex and cerebellum
- Medulla - many functions including breathing, heart rate and GI activity
PNS
Divisions
- Somatic
- Autonomic : (A) Sympathetic, (B) Parasympathetic
The Eye
Sclera
Thick opaque layer covering the surface of the eyeball
The Eye
Choroid
Layer beneath the sclera
Helps to supply the retina with blood
Dark, pigmented area that reduces reflection in the eye
The Eye
Retina
Innermost layer
Contains the photoreceptors:
- Cone cells - respond to high intensity light, sensitive to colour. Contain three pigments that absorb red, blue and green wavelength
- Rods - respond to low intensity light, importnat in night vision. Contains a single pigment - rhodopsin - which absorbs single wavelength
These synapse with bipolar cells which synapse with ganglion cells. Axons of ganglion cells bundle into optic nerve
The Eye
Cornea
Transparent outer layer at front of eye
Bends and focuses light which then travel via the pupil through the lens suspended behind it and image forms on retina
The Eye
Iris
Pigmented. muscular structure
Controls pupil diameter
The Eye
Ciliary Muscles
Control the shape and focal length of the lens
The Eye
Blind Spot
Point at which the optic nerve exits the eye - photoreceptors not present
The Eye
Fovea
Small are of the retina, densely packed with cones
Important for high-acuity vision
The Eye
Vitreous Humour
Jellylike material which helps maintain shape and optical properties of eye
Is formed by the eye and exits it via ducts to join the venous blood
