Response To Stimuli Flashcards
What is kinesis?
A rapid movement and rapid change of direction in response to a stimulus. In a positive stimulus, the movement and direction changes slow down so the organism is more likely to stay in a favourable environment
What are tropisms?
Plant growth in response to a directional stimulus
What are the two major divisions in the nervous system?
CNS - made up of the brain and spinal cord
PNS - made up of pairs of nerves that originate from the brain or spinal cord
What is the PNS divided into?
• Sensory neurones (impulses from receptors to CNS)
• Motor neurones (impulses from CNS to effectors)
- VNS (impulses to muscles)
- ANS (impulses to glands)
What are the stages of a reflex arc?
1) Stimulus
2) Receptor (creates impulse to send to sensory neurone)
3) Sensory neurone (passes impulse to spinal cord)
4) Intermediate neurone (links sensory neurone to motor)
5) Motor neurone (carries impulse from spinal cord to effector
6) Effector
7) Response
Why is the reflex arc so fast?
The neurone pathway is short with few synapses
What is the ANS divided into?
The sympathetic NS - stimulates effectors and speeds up an activity
Parasympathetic NS - Inhibits effectors and slows down activity (concerned with conserving energy)
What is heart rate controlled by and what are the two centres?
Medulla Oblongata
- A centre which increases heart rate, linked to SAN by SNS
- A centre which decreases heart rate, linked to SAN by PSNS
How does pH affect heart rate?
- More CO2 in blood = lower pH
- Chemoreceptors on wall of carotid arteries and the aorta detect this and increase the frequency of impulses to the medulla to the centre that decreases heart rate
- The centre increases the frequency of impulses via the SNS to SAN to increase heart rate
- Increased blood flow leads to more CO2 being removed from the lungs so the inverse happens
- If you have low blood pressure, you need to increase your heart rate
What are the characteristics of sensory receptors (Pacinian corpuscle)?
- Specific to one type of stimulus (mechanical pressure for PC)
- Convert one form of energy into another e.g. Mechanical into nerve impulse (greater potential) by acting as a transducer
What is the structure of the Pacinian corpuscle?
- Occur deep in the skin
- Arranged in layers with a single sensory neurone at the centre
- Sensory neurone has a stretch-mediated sodium channel which is permeable to sodium when stretched
What are the functions of the Pacinian corpuscle?
- In the resting state the sodium channels are too narrow to allow sodium ions in and out so a resting potential is maintained
- When pressure is applied to the receptor, it changes shape and the neurone becomes stretched
- Sodium ions diffuse in
- The membrane becomes depolarised and produces a generator potential
- This created an action potential that passes along neurones to the CNS
What are the characteristics of rod cells?
- Cannot distinguish between different wavelengths of light
- Share a single sensory neurone so respond to light of a low intensity because a certain threshold must be exceeded before a generator potential is created in the bipolar cells attached
- To create a generator potential, the rhodopsin pigment must be broken down, which can happen in low light intensities
- Low visual acuity because so many rod cells share the same sensory neurone
What are the features of Cone cells?
- Three different types, each responding to a different wavelength of light
- Each connected to a sensory neurone attached to a bipolar cell
- Only respond to high LI because threshold is not reached
- Iodopsin will only be broken down in high LI to create generator potential
- Can distinguish between separate sources of light so produce high visual acuity
What is the distribution of rod and cone cells?
- Cone cells found at the fovea which receives the highest intensity of light
- Rod cells found at peripheries of the retina
