chapter 13 - neuronal communication

why is coordination needed ?

organisms need to coordinate the function of difference specialised cells and systems to operate effectively

what is coordination a response to

a change in an organisms external or internal environment for survival

what is homeostasis?

the coordination of organs in order to maintain a relatively constant internal environment

what is cell signalling

communication at a cellular level that occurs when one cell releases a chemical which has an effect on another target cell

what are the two purposes of cell signalling

1- transfer signals locally between neurones at synpases

2- transfer signals across large distances using hormones

what is the role of the nervous system

detecting changes in the internal and external environment (stimuli) and processing this information to produce an appropriate response

what is the role of neurones

to transmit electrical impulses rapidly around the body so that organisms can respond to stimuli

what is the cell body made up of

a nucleus surrounded by cytoplasm

what occurs in the cytoplasm of the cell body

large amounts of endoplasmic reticulum and mitochondria are involved in the production of neurotransmitters

what are dendrons

short extensions form the cell body which divide into dendrites.

what direction do dendrons transmit

towards the cell body

what are axons

singular elongated nerve fibres consisting of a narrow region of cytoplasm surrounded by a plasma membrane

what direction do axons transmit

away from the cell body

role of the sensory neurone

transmit impulses from sensory receptor cells to relay neurones motor neurones or the brain

structure of sensory neurone

• central cell body

• one dendron, one axon

role of relay neurone

transmit impulses between neurones

structure of relay neurone

they have many short axons and dendrons

role of a motor neurone

transmit impulses from relay neurones or sensory neurones to an effector

structure of a motor neurone

• one long axon

• many short dendrites

2 types of effector

muscle and gland

what is the myelin sheath

layers of plasma membrane (produced by schwann cells) which insulate the neurone, allowing them to conduct electrical impulses at a faster speed

what is the role of the Node of Ranvier

its a small gap between myelin sheath, which force the impulse to ‘jump’ from one node to another which allows the impulse to travel quicker

what is the issue with non-myelinated neurones

• having no myelin sheath means there is no neurone insulation

• having no nodes of ranvier mean impulses travel continuously along the nerve fibre which is much slower

what is the role of sensory receptors

to convert stimuli into a nerve impulse

two main features of a sensory receptors

• they are specific to a single stimulus

• they are a transducer (convert stimulus into a nerve impulse)

what is the pacinian corpuscle

a sensory receptor that detects mechanical pressure (located in your feet and fingers)

how does the pacinian corpuscle

1- at rest the stretch mediated sodium ion channels are too narrow to allow sodium to pass

2- when pressure is added the stretch mediated sodium ion channels widen and sodium ions can diffuse into the neurone

3-positive influx change the potential of the membrane (generator potential)

4- the generator effect creates an action potential that pass along the sensory neurone

what type of channel does the pacinian corpsucle use

stretch mediate sodium ion channels

what is the resting potential

the state in which the outside of the neurone is more positive than inside the axon

what is the typical value of resting potential

-70mV

what causes a resting potential (bi-layer)

• Na+ and K+ ions cant diffuse through the phospholipid bilayer and so must be transported through channel proteins

steps of a resting potential

• Na+ are actively transported out in groups of 3

• K+ are actively transported in in groups of 2

• as a result outside the membrane is more positive

• Na+ diffuse back in down their electrochemical gradient

• K+ diffuse back out down their electrochemical gradient

• K+ channels are all open but most of the sodium ion channels are shut

• therefore more positively charged ions remain outside the axons

what occurs when a stimulus is detected by sensory receptor

• the energy of the stimulus temporaril reverse the charge of the axon membrane, making it positive +40mV

what is depolarisation

change from negative to positive

eg, the start of an action potential when a stimulus is detected by sensory receptor turning the axon to +40 from -70

is depolarisation permanent in action potentials

No

as the impulse passes repolarisation occurs to change from positive to negative

when do action potentials occur

when the voltage in a membrane is enough to change the shape of proteins resulting in the opening or closing of channels

what type of ion channels are in action potentials

voltage gated ion channels

what is happening in voltage gated ion channels are resting potential

• some K+ channels are open

• all Na+ channels are closed

how does an action potential occur

1- stimulus energy cauuses Na+ channels to open

2- Na+ diffuse in down their electrochemical gradient

3- inside of the axon becomes more positive

4- positive feedback causes more Na+ channels to open

5- this stops when it reaches +40mV

6-now all Na+ shut and voltage gated K+ open

7- K+ leave down their electrochemical gradient

8- hyperpolarisation occurs when initially lots of K+ leave

9- K+ shut

10- sodium-potasium pumos balance again and repolarise

example of positive feedback in action potentials

the influx of Na+ into the axon when volatge gated ion channels open causes more to open

what three factors affect the speed of action potential travel

• myelination

• axon diameter

• temperature

how does axon diameter affect speed of action potential

the bigger the diameter the faster the impulse is transmitted because there is less ion resistance in the cytoplasm

how does temperature affect speed of action potential

the higher the temo the fast the impulse because ions diffuse faster at higher temperatures

synaptic cleft

the gap which separates the axon of one neurone from the dendrite of the next neurone

presynaptic neurone

neurone along whch the impulse has arrived from

postsynaptic neurone

neurone that recieves the neurotransmitter

synaptic knob

the swollen end of the presynpatic neurone

what does the synpatic knob contain

a large number of mitochondria and endoplasmic reticulum to enable the manufacture of neurotransmitters

synaptic vessicles

vesicles containing neurotransmitters

neurotrasmitter receptors

recpector molecules which the neurotransmitters bind to on the postsynpatic membrane

what is a synpase

junction between two neurones

two types of neurotransmitter

• excitatory

• inhibitory

what is a excitatory neurotransmiiter

result in the depolarisation of a postsynaptic neurone

• if the threshold is met an action potential is triggered

example of a excitatory neurotransmitter

acetylcholine

what is an inhibitory neurotransmitter

result in the hyperpolarisation of the postsynaptic membrane to prevent an action potential

exmaple of a inhibitory neurotransmitter

GABA

how are impulses trasmitted across a synpase

• actional potential reaches the end of the presynaptic neurone

• depolarisation causes Ca channels to open

• Ca diffuse into the presynaptic knob

• synpatic vesicles fuse with the presynaptic membrane

• they release neurotransmitters

• diffuse across the synpatic cleft

• Na channels open

• Na diffuse into the post synaptic neurone

• triggers an action potential in the post synpatic neurone

mnemonic for transmission of impulses across synapses

Angry Dogs Can Snarl, Never Snap Suddenly

Angry Dogs Can Snarl, Never Snap Suddenly

1- action potential in the presynaptic

2-depolarisation opens Ca channels

3-calcium ions diffuse into the presynaptic knob

4-synaptic vesicles fuse and release neurotransmitters

5-neurotransmitters diffuse and bind on the postsynaptic membrane

6- sodium channels opens

7-sodium ions diffuse to create an action potential

what are cholinergic synpases

synapses used by aceytlcholine

steps of a cholinergic synapse

• action potential arrives at the end of the presynpatic

• depolarisation opens Ca channels

• these channels open and Ca diffuse into the presynaptic knob

• synaptic vesicles fuse and release acetylcholine into the cleft

• these fuse to Na channels on the post synaptic nurone

• Na channels open and the influx causes a new action potential

• acetylcholine hydrolyses into choline and ethanoic acid

• choline and ethanoic acid is recycled back into the cleft

• mitochondria release ATP to recombine choline and ethanoic acid to stores for future use

what are the 3 main roles of a synapse

• ensure impulses are unidirectional

• they allow allow an impulse from one neurone to be transmitted across multiple synpases

• they allow multiple synapses to feed one neurone

what is summation

• a single impulse of neurotransmitters may not be enough to reach the threshold for an action potential

• summation is when these neurotransmitters build up to sufficiently reach the threshold

what are the two types of summation

• spatial

• temporal

what is spatial summation

when a number of presynaptic neruones connect to one postsynaptice neurone and they all contribute to the build up for propogation along the one postsynaptic neurone

what is temporal summation

when a single presynaptic neurone releases neurotransmitters as a result of an action potential that builds up over several times

what is the CNS

your brain and spinal cord

what is your PNS

all the neurones that connect the CNA to the rest of the body

somatic nervous system 

the conscious control used for voluntary movement

example of somatic control 

when you decide to move a muscle to move your arm 

what is the autonomic nervous system

the subconcious system that constantly works to fufil involuntary action

example of autonomic control

heart rate

how can the autonomic nervous system be divided

sympathetic and parasympathetic 

general rule for sympathetic nervous system

if something increases (eg, fight or flight)

general rule for parasympathetic nervous system

if something decreases (eg, relaxing responses)

what is the neurotransmitter for the somatic nervous system

acetylcholine  

what is the neurotransmitter for the sympathetic nervous system

noradrenaline

what is the neurotransmitter for the parasympathetic nervous system

acetylcholine

role of the cerebrum

controls voluntary actions such as learning and memory 

structure of the cerebrum

• split into two halves

• each half controls one half of the body 

what is the role of the cerebellum

muscular control like movement, body posture and balance 

what is the role of the medulla

regulatory sector of the autonomic nervous system, eg heart and ventillation rate

what is the role of the hypothalamus (3)

controlling sleep patterns 

monitoring blood plasma composition

producing hormones 

where is the pituiatry gland

found at the base of the hypothalamus 

how can the pituitary gland be split 

• anterior pituitary 

• posterior pituitary 

role of the anterior pituitary gland

FRONT SECTION produces 6 hormones including FSH

role of the posterior pituitary

BACK SECTION stores and releases hormones produced by the hypothalamus, including ADH

what type of reflex is a knee jerk

a spinal reflex, meaning it involves no brain participation and is mediated by the spinal cord, resulting in a quick response to stimulus.

steps of a knee jerk

• a tap of the leg acts as a stimulus

• the stimulus triggers a reflex arc

• extensor muscle on the top contracts and the flexor muscle motor neurone is inhibted and so relaxes

• this causes a leg kick

how do reflexes aid survival

• the brain doesn’t have to deal with decisions as these reflexes are involuntary

• you dont have to learn the reflexes

• extremely fast

• help to fufil daily actions, eg keeping upright

3 types of muscle

• skeletal

• smooth

• cardiac

what is skeletal muscle

cells responsible for movement and make up the bulk of body muscle tissue 

what is cardiac muscle

a collection of myogenic cells only found within the heart

what is involuntary/smooth muscle

muscle that operates without conscious control, found in walls of hollow organs and blood vessels.

what type of muscle fibre is in skeletal muscle

striated muscle which makes up the muscles that attach to bones and facilitate movement.

what type of muscle fibre is in cardiac muscle

specialised striated

what type of muscle fibre is in smooth muscle

non-striated 

what type of control is skeletal muscle

conscious

what type of control is cardiac muscle

involuntary 

what type of control is smooth muscle

involuntary