Topic 6 Flashcards
Stimulus
-Detectable change in the environment
-detected by cells called receptors
Nervous system structure
Central nervous system = brain and spinal cord
peripheral nervous system = receptors, sensory and motor neurones
Simple reflex arc
Stimulus (touching hot object)
-> receptor
-> sensory neurone
-> coordinator (CNS / relay
neurone
-> motor neurone
-> effector (muscle)
-> response (contraction)
Importance of simple reflexes
-Rapid - short pathway only three neurones & few synapses
-autonomic -conscious thought not involved - spinal cord coordination
-protect from harmful stimuli e.g., burning
Tropism
-Response of plants to stimuli via growth
-can be positive (growing towards stimulus) or negative (growing away from stimulus)
-controlled by specific growth factors (IAA)
Specific tropisms
Response to light -phototropism
response to gravity-gravitropism
response to water- hydrotropism
Indoleacetic acid
-Type of auxin (plant hormone)
-controls cell elongation in shoots
-inhibits growth of cells in roots
-made in tips of roots / shoots
-can diffuse to other cells
Phototropism in shoots
-Shoot tip produces IAA
-diffuses to other cells
-IAA accumulates on shaded side of shoot
-IAA stimulates cell elongation so plant bends towards light
-positive phototropism
Phototropism in roots
-Root tip produces IAA
-IAA concentration increases on lower (darker) side
-IAA inhibits cell elongation
-root cells grow on lighter side
-root bends away from light
-negative phototropism
Gravitropism in shoots
-Shoot tip produces IAA
-IAA diffuses from upper side to lower side of shoot in response to gravity
-IAA stimulates cell elongation
-so plant grows upwards
-negative gravitropism
Gravitropism in roots
-Root tip produces IAA
-IAA accumulates on lower side of root in response to gravity
-IAA inhibits cell elongation
-root bends down towards gravity and anchors plant
-positive gravitropism
Taxis
-Directional response by simple mobile organisms
-move towards favourable stimuli (positive taxis) or away from unfavourable stimuli (negative taxis)
Kinesis
-When an organism changes its speed of movement and rate of change of direction in response to
a stimulus
-if an organism moves to a region of unfavourable stimuli it will increase rate of turning to return to origin
-if surrounded by negative stimuli, rate of turning decreases - move in straight line
Receptors
-Responds to specific stimuli
-stimulation of receptor leads to establishment of a generator potential - causing a response
-pacinian corpuscle
-rods
-cones
Pacinian corpuscle
Receptor responds to pressure changes
occur deep in skin mainly in fingers and feet
sensory neurone wrapped with layers of tissue
Pacinian corpuscle structure
-Single sensory neurone wrapped around by layers of connective tissue each layer separated by a gel
-It has special stretch mediated Na+ channels which gets deformed when pressure is applied and causes depolarisation.
-Neurone also contains Schwann cells
How pacinian corpuscle detects pressure
-When pressure is applied, stretch mediated sodium ion channels are deformed
-sodium ions diffuse into sensory neurone
-influx increases membrane potential - establishment of generator potential
Rod cells
-Concentrated at periphery of retina
-contains rhodopsin pigment connected in groups to one bipolar cell (retinal convergence) - Spatial summation
- do not detect colour
Cone cells
-Concentrated on the fovea
-fewer at periphery of retina
-3 types of cones containing different iodopsin pigments - red,green and blue
-one cone connects to one neurone - Temporal summation
- detect coloured light
Rods and cones: describe differences in sensitivity to light
-Rods are more sensitive to light
-cones are less sensitive to light
Rods and cones: describe differences in
visual acuity
-Cones give higher visual acuity
-rods have a lower visual acuity
Visual acuity
-Ability to distinguish between separate sources of light
-a higher visual acuity means more detailed, focused vision
Rods and cones: describe differences in
colour vision
-Rods allow monochromatic vision (black and white)
-cones allow colour vision
Why rods have high sensitivity to light
-Rods are connected in groups to one bipolar cell
-retinal convergence
-spatial summation
-stimulation of each individual- cell alone is sub-threshold but because rods are connected in groups more likely threshold potential is reached