stimuli and responses and nervous coordination

what is a stimulus and what are receptord and effectors

• stimulus= change in environment

• receptor= detect stimuli

• effector= brings about a response- muscles or glands

order of a reflex arc

• Stimulus

• Receptors

• Sensory neurone

• Relay neurone

• Motor neurone

• Effectors

• Response

CNS

• brain and spinal chord

• sensory neurone —→ CNS—→ Motor neurone

peripheral nervous system

• neurones that connect CNS to body

somatic nervous system

• controls conscious activities

autonomic nervous system

• controls unconscious activities

• sympathetic- gets body ready for action (fight or flight)

• parasympathetic- calms body

plant responses

phototropism

• response to light

• shoots grow towards light- positive

• roots grow away from light- negative

plant responses

gravitropism

• response to gravity

• shoots grow upwards- negative

• roots grow downwards- positive

plant responses

IAA- growth factor

• IAA= auxin produced in tips of shoots in flowering plants

• moves by diffusion, active transport or phloem for long distances

• moves to shaded side

• elongates cells- bends towards light in shoots

• roots bend away from light- inhibits growth

animals responses

taxis

• directional stimulus

• e.g moving towards or away from light

animal responses

kinesis

• rate of turning

• non-directional

• e.g humidity

choice chamber

• how animals react to certain conditions

• have each chamber in different conditions

• e.g cover some with black paper

• after a certain amount of time count how many are in each chamber

pacinian corpuscle

• mechanoreceptors in the skin to detect pressure

• end of sensory neurone wrapped in layers of connective tissue (lamellae)

• pressure- deforms lamellae

• stretch mediated sodium ion channels open

• Na+ move into cell by facilitated diffusion

• if enouhg sodium enters to reach threshold an action potential is triggered

where are photoreceptors in the eye found

• retina

• fovea= area of retina with lots of photoreceptors

how is an action potential triggered in the eye

• light enters eye

• hits photoreceptors on retina

• absorbed by light sensitive optical pigments

• light bleaches the pigments

• altering membrane permeability to sodium ions

• if enough sodium ions moce across membrane to reach threshold

• action potential

rods

• black and white

• many rods to one bipolar cell

• highly sensitive- many weak potentials combine

• low acuity- brain can’t distinguish between close points

cones

• colour- red, gree, blue sensitive

• one cone to one bipolar cell

• low sensitivity- takes more light to reach threshold

• high acuity- brain can distinguish between points- one action potential per cone

cardiac muscles involved in heart beat

• SAN (pacemeaker found in walll of right atrium) sends electrical impulses to atria walls

• atria contract at same time

• AVN- slight delay

• bundle of his

• splits into purkinje tissue

• ventricle walls

• contract from apex upwards

what part of the brain controls heart rate

• medulla oblongata controls rate at which SAN fires

• unconscious

controlling heart rate

high blood pressure

• baroreceptors detect high blod pressure

• send signals to medulla

• parasympathetic

• secretes acetylcholine that binds to SAN

• heart rate slows

• reduced pressure

controlling heart rate

low blood pressure

• detected by baroreceptors

• medulla

• sympathetic

• noradrenaline binds SAN

• speeds up rate

• increase pressue

controlling heart rate

high pH, low CO₂

• chemoreceptor

• medulla

• parasympathetic

• acetylcholine binds to SAN

• rate slows

controlling heart rate

low pH, high CO₂

• chemoreceptors

• medulla

• sympathetic

• noradrenaline binds to SAN

• rate speeds up

structure of neurone

• cell body- contains nucleus, RER and neurotransmitters

• axon- single, long fibre that carries nerve impulses away from cell body

• mylein sheath- covers axon, made of membrane of schwann cells that wrap around axon many times to provide insulation

• dendrons- carry impulses towards cell body

• nodes of ranvier- gaps between adjacent schwann cells where there is no mylein sheath

resting potential

• 3 Na+ move out of axon, 2 K+ move in via sodium potassium pump

• pump requires ATP to change shape

• higher conc of Na+ out of axon, higher conc of K+ in

• some K+ move out of axon due ot leaky membrane via K+ channel proteins

action potential

• voltage gated sodium ion channels open

• Na+ flood into cell by facilitated diffusion

• wave of depolarisation- positive feedback

• voltage gated potassium ion channels open

• K+ moves out of cell by facilitated diffusion

• repolarisation

• more K+ move put due to leaky membrane- hyperpolarisation

• back to resting

what is refractory period and all or nothing

• refractory period= time taken to go back to resting

• all or nothing= once threshold is reached the same action potential always fire no matter the strength of stimulus

factors affecting speed of action potential

• temperature

  • higher temp= faster rate of diffusion of ions

  • not too high or else proteins in membrane will denature

• axon diameter

  • bigger diameter= less resistance for ions to flow

• myelination

  • an action potential can jump from one node of ranvoer to aother so it doens’t have to travel the whole length of axon- saltatory conduction

synapse= gap between neurones

e.g neuromuscular junction

• incoming action potential

• calcium ion channels open in presynaptic knob

• Ca²⁺ flood in

• calcium channels close

• causes vesicles to move and fuse with presynaptic membrane

• neurotransmitter (acetylcholine) released and diffises across synaptic cleft

• binds to complementary receptors on postsynaptic membrane

• opens ligand gated sodium ion channels on postsynaptic membrane

• Na⁺ move into postsynaptic neruone- depolarisation

• acetylcholinesterase hydrolysis acetylcholine back into acetyl and choline so they can diffuse back to presynaptic neurone

• sodium ion channels close

excitatory and inhibitory neurotransmitters

• excitatory- depolarises postsynaptic membrane- action potential if threshold reached

• inhibitory- hyperpolarise postsynaptic membrane- prevents action potential

summation

spatial and temporal

• temporal

  • two or more impulses arrive in quick succession from the same neurone- action potential more likely becuase there is more neurotransmitter in synaptic cleft

• spatial

  • many neurones connect to one neurone

  • small amounts of neurotrasnmitters from each neurone is enough to reach threshold

effects of drugs at synapses

• same shape as neurotransmitters so mimic action at receptors- more receptors activated

• drugs can block receptors- no action potential

• inhibit enzymes that hyrolyse neurotransmitters e.g acetylcholinesterase- more neurotransmitters left in cleft- loss of muscle control

• stimulate release of neorutransmitters

• inhibit release of neurotransmitters

structure of skeletal muscle

different bands in myofibrils

• z line

• A band = myosin and actin

• I band= just actin

• H zone = just myosin

• M line- down middle

sliding filament theory

• sarcomere shortens

• A band- no change

• I band- shortens

• H zone- dissapears

• z line- no change

muscle contraction

• action potential depolarises sarcolemma

• sarcoplasmic reticulum releases calcium ions into sarcoplasm

• calcium ions bind to protein attached to tropomyosin- changes shape

• pulls tropomyosin out of actin myosin binding site

• allows myosin head to bind to actin- forms an actin myosin cross bridge

• calcium ions activate ATP hydrolase

• causes myosin head to bend- pulling actin filament

• more ATP breaks cross bridge

• myosin head reattaches to bidning site further along actin

• repeats as long as calcium ions present

ways to make ATP

• aerobic respiration- oxidative phosphorylation

• anaerobic respiration- glycolysis

• phosphocreatine stored in cells and a phosphate from it binds to ADP

slow twitch muslces

• contract slowly

• good for endurance activities

• long time

• aerobic respiration

• lots of mitochondria

• red colour- lots of myoglobin

fast twitch muscles

• contract quickly

• for fast movements

• short bursts of energy

• tired quickly

• anaerbic respiration

• few mitochondria

• white colour- less myoglobin