neuronal communication paper 1

what are neurones

specialised nerve cells vital for transmitting electrical impulses quickly through the body

list the key structural components of the mammalian neurone

1. dendrons

2. dendrites

3. cell body

4. axon

describe the cell body of the mammalian neurone

contains the nucleus and cytoplasmic organelles, such as mitochondria and the endoplasmic reticulum, which are crucial in the production of neurotransmitters

describe dendrons in the mammalian neurone

short branches extending from the cell body, further branching into highly branched dendrites to receive nerve impulses from many other neurones and transmit them towards the cell body

describe the axon in the mammalian neurone

a singular long nerve fibre responsible for carrying impulses away from the cell body to other neurones or effectors

what do myelinated neurones contain

Schwann cells

what are the three functions of Schwann cells

1. their membranes form the Myelin Sheath

2. they remove debris via phagocytosis

3. they aid regeneration

what is the myelin sheath and what does it do

in myelinated neurones, it surrounds part of the axon, acting as an insulator that prevents the passage of ions into or out of the axon at the regions it covers.

what is ‘saltatory conduction’

the process at which myelinated axons conduct conduct impulses rapidly

what happens in ‘saltatory conduction’

the electrical impulse ‘jumps’ between gaps in the myelin sheath known as the nodes of Ranvier, increasing transmission speed.

out of myelinated axons and non-myelinated axons, what transmits impulses the slowest?

non-myelinated axons

what is the function of sensory neurones

carry impulses from the sensory receptors to the central nervous system

what is the function of relay neurones (intermediate neurones)

carry impulses within the central nervous system, between other neurones

what is the function of motor neurones

carry impulses from the central nervous system to effectors

what is the structure of sensory neurones

• one axon and one dendron

• dendron leads to several smaller dendrites

what is the structure of relay neurones

• numerous short axons and dendrons

what is the structure of motor neurones

• one long axon and multiple dendrites

what is the typical pathway of an impulse

receptor - sensory neurone - relay neurone - motor neurone- effector

what is a sensory receptor

a specialised cell that detects stimuli from the environment

what are photoreceptors and where are they located

detect light and are located in the eyes

what are chemoreceptors and where are they located

detect chemicals and are located in the nose, tongue and blood vessels

what are mechanoreceptors and where are they located 

detect pressure and movement, and they are located in the skin, muscles and inner ear 

what are thermoreceptors and where are they located

detect temperature and located in skin

list the four types of receptor cell

1. photoreceptors

2. chemoreceptors

3. mechanoreceptors

4. thermoreceptors

ADD SECTION ON HOW RECEPTOR CELLS WORK AND THE STRUCTURE AND FUNCTION OF PACINIAN CORPUSCLES

what is the typical value of resting potential

-70 mV

what state is the cell-surface membrane in during resting potential

a state of polarisation

during resting potential is there a difference in voltage across the membrane

yes

what are sodium potassium pumps

active transporters that move three sodium ions out of the neurone for every two potassium ions they move in.

what are potassium ion channels

they are channel proteins that allow the diffusion of potassium down its concentration gradient

what are sodium ion channels 

channel proteins that allow sodium ions to diffuse down their concentration gradient

how is resting potential achieved

• sodium-potassium pumps actively transport three sodium ions out of the neon for every two potassium ions they move in

• potassium ions allow for the diffusion of potassium ions down their concentration gradient out of the neurone

• sodium channels are closed, preventing the movement of sodium into the neurone

during resting potential, what happens to the extracellular space outside the axon

it accumulates more positive ions, so the axon becomes negatively charged in comparison, causing the membrane to become polarised

what happens when the neurone in resting potential receives a strong stimulus 

1. voltage-gated sodium ions open, so more sodium ions flow into the axon making the inside less negative 

what happens if the threshold potential is reached by a stimulus

more sodium channels open, causing an influx of sodium ions into the axon. This process is called depolarisation

what is the threshold value 

-55 mV

what happens at around 30 mV (after depolarisation)

at around 30 mV, sodium channels close and potassium channels open, so potassium ions flow out of the axon and the membrane starts repolarising 

what happens after repolarisation

an excess of potassium ions leave the axon, dropping the potential to below the -70mV resting potential. This process is called hyper polarisation

wg=hat happens during the refractory period 

various ion pumps and channels work together to restore the membrane back to the resting potential 

how is the generation of an action potential an example of a positive feedback mechanism

the initial sodium ion influx depolarises the axon membrane, which opens more sodium channels and leads to a greater influx of sodium ions, further depolarising the membrane

what characterises the all-or-nothing principle

1. the threshold phenomenon

2. no partial response

3. action potentials are always the same size

what is the threshold phenomenon 

once the threshold potential is reaches, an action potential is always triggered, regardless of the stumulus’ strength 

what does “no partial response” mean

without reaching the threshold potential, no action potential is initiated

what does a stronger stimulus do to the size ad the frequency of an action potential

the size does not increase, however the frequency of action potentials generated does increase

why can another action potential not be generated during the refractory period 

sodium ion channels remain closed during repolarisation, preventing depolarisation 

list the roles of the refractory period

• ensuring that action potentials don’t overlap

• limiting the frequency at which impulses are transmitted

• guaranteeing that impulses travel in only one direction

describe the steps of an action potential

1. the opening of sodium channels results in local depolarisation, allowing positive ions to spread sideways

2. adjacent voltage-gated sodium channels open in response to this change

3. this action leads to the depolarisation of nearby membrane areas

4. as each patch of membrane activates the next, an advancing wave is formed

5. areas of the membrane that have just experienced depolarisation are in the refractory period and remain unresponsive while they repolarise

6. this ensures that the wave moves in one direction, preventing the backward flow of the nerve impulse

does an action potential change in size 

no, as it self-propagates through local currents along the axon, its size stays the same 

give the three factors that effect the speed of an action potential

1. myelination

2. axon diameter 

3. temperature 

how does myelination affect the speed of transmission of an action potential

• myelinated neurones are insulated be a myelin sheath, which enables saltatory conduction

• this process involves action potentials ‘jumping’ between nodes of Ranvier, which is faster than continuous depolarisation

how does axon diameter affect the speed of transmission of an action potential

• a larger axon diameter means there is less resistance to flow, so the way of depolarisation travels faster along the axon

• therefore, broader axons transmit impulses faster

how does temperature affect the speed of transmission of an action potential 

• higher temperatures accelerate the diffusion of ions, leading to faster depolarisation and faster impulse transmission 

• however, temperatures above 40 *C can cause proteins to denature, which results in slower impulse transmission due to membrane damage 

define a synapse

a junction where information is transferred from one neurone to another neurone or to an effector cell.

what are the roles of synapses in neural communication

1. they transmit information through the release of neurotransmitter chemicals

2. a single impulse from a presynaptic neurone can initiate impulses in multiple postsynaptic neurones or effector cells

3. impulses from several presynaptic neurones can be combines into a single postsynaptic response

list key structures of a synapse 

• presynaptic neurone

• synaptic knob 

• synaptic vesicles 

• synaptic cleft 

• postsynaptic neurone 

• neurotransmitter receptors 

what is a presynaptic neurone

a neurone that releases neurotransmitters into the synapse

what is the synaptic knob

the section at the end of the presynaptic neurone that contains the organelles needed for neurotransmitter production, such as mitochondria to release energy

what are synaptic vesicles 

sacs within the synaptic knob that store neurotransmitters until their are released 

what is the synaptic cleft

the gap between the presynaptic and postsynaptic neurones’ membranes

what is the postsynaptic neurone

the neurone that receives the neurotransmitters and can generate new action potentials

what are neurotransmitter receptors

specific molecules on the postsynaptic membrane that bind with neurotransmitters

depending on the synapse, what two categories could the same neurotransmitter be 

excitatory or inhibitory 

what is the effect of excitatory and inhibitory neurotransmitters on the postsynaptic membrane

excitatory- depolarisation

inhibitory- hyperpolarisation

do excitatory neurotransmitter generate an action potential

they may trigger an action potential if the threshold is reached

what type of neurotransmitter prevent action potentials 

inhibitory 

what might happen if a synapse is weakly stimulated

it may not release enough neurotransmitter to reach the threshold necessary to be generated on a postsynaptic neurone or effector cell

what does summation do

makes the generation of an action potential more likely.

give the two types of summation 

spatial and temporal 

what is spatial summation

• multiple presynaptic neurones converge on a single postsynaptic neurone or effector cell

• the combines input of neurotransmitters can trigger postsynaptic firing

• inhibitory inputs have the potential to prevent this firing

what is temporal summation

• repeated firing by a presynaptic neurone leads to continuous neurotransmitter release

• an increased amount of neurotransmitter makes it more likely to trigger postsynaptic firing

in what type of summation do inhibitory inputs have the potential to prevent firing in the postysnapic neurone

spatial 

describe the key steps in synaptic transmission

1. an action potential arrives at the presynaptic knob

2. this cause voltage gated calcium ion channels to open and calcium ions flow into the presynaptic knob

3. this causes synaptic vesicles, which contain neurotransmitters, to move towards and fuse with the presynaptic membrane

4. the vesicles release neurotransmitters into the synaptic cleft through exocytosis, and the neurotransmitters rapidly diffuse across the synaptic cleft

5. on reaching the other side, the neurotransmitters bind to receptor proteins on the postsynaptic membrane, causing the receptors to change shape

6. this opens sodium ion channels in the postsynaptic membrane, leading to the depolarisation of the postsynaptic membrane

7. if this depolarisation reaches a threshold level, an action potential is triggered in the postsynaptic neurone.

what is the charge of calcium ions in the presynaptic neurone

2+

in what specific synapse is acetylcholine (ACh) used as their neurotransmitter

Cholinergic synapses

what are the two parts of the mammalian nervous system 

• central nervous sytem

• peripheral nervous system 

what does the CNS consist of

the brain and the spinal cord

what is the function of the CNS

serves as the primary command centre of the body

what does the PNS consist of 

all the nerves that connect the CNS to the rest of the body 

what does the PNS facilitate

bi-directional communication

what are the two further divisions of the peripheral nervous system

• the sensory nervous system

• the motor nervous system

what is the sensory nervous system 

consists of sensory neurones that carry nerve impulses from receptors to the CNS

what is the motor nervous system

consists of motor neurones that carry nerve impulses from the CNS to effectors like muscles or glands

where is the hypothalamus located and what are its general functions

1. homeostasis

2. water balance

3. hormonal regulation

how does the hypothalamus help with homeostasis

• it helps to regulate body temperature by sensing changes and initiating appropriate responses, such as triggering sweating or shivering

how does the hypothalamus control water balance

• it monitors and helps to regulate the composition of blood plasma, like the concentration of water and glucose in blood.

how does the hypothalamus regulate hormones

• it regulates hormone secretion from the pituitary gland

what is the largest part of the brain

the cerebrum

what are the two halves of the cerebrum called

the left and the right cerebral hemispheres

what is the outer layer of the cerebrum called and what does its structure have

it is called the cerebral cortex and it has many folds

where are receptor cells in the sensory areas of the cerebrum located

sense organs

give the two functions of the cerebrum

1. it processes sensory input, and so is crucial for processes like vision and hearing

2. it is involved in learning, memory, and higher-level thinking

where is the pituitary gland found

just below the hypothalamus

give the functions of the pituitary gland and what it is triggered by

1. it produces, stores, and secretes hormones when triggered by the hypothalamus

2. the hormones it secretes prompt other glands, like the adrenal glands, to secrete their hormones

what are the two main sections of the pituitary gland called

1. the anterior pituitary gland

2. the posterior pituitary gland

what is the function of the anterior pituitary gland

it produces six hormones including FSH, which is involved in reproduction, and growth hormones

what is the function of the posterior pituitary gland

it stores and releases hormones produced by the hypothalamus including ADH, which is involved in urine production

where is the medullar oblongata located

at the base of the brain, connecting it with the spinal cord

list the functions of the medulla oblongata

1. it involuntarily regulates breathing rate

2. it involuntarily regulates heart rte and blood pressure

3. it controls other autonomic nervous system functions like swallowing, peristalsis, and coughing.

where is the cerebellum located

underneath the cerebrum

give the functions of the cerebellum

1. it is important for coordinating and fine-tuning skeletal muscle contractions

2. it is essential for maintaining unconscious functions like posture, balance, and involuntary muscle movement