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Define the nervous system

Primary internal communication system in the body, based on electrical and chemical signals, which is split into two parts (CNS + PNS)


What are the two main functions of the nervous system?

- To collect, process + respond to info in the environment
- To coordinate the workings of bodily organs + cells


What two parts is the nervous system split into?

- Central Nervous System (CNS)
- Peripheral Nervous System (PNS)


What is the CNS split into?

- Brain
- Spinal cord


What is the PNS split into?

- Autonomic Nervous System (ANS), which is further split into the Sympathetic Nervous System (SNS) + Parasympathetic Nervous System (PNS)
- Somatic Nervous System (SNS)


What is the role of the CNS?

- To control higher functioning processes e.g. decision making (brain)
- To deal with reflex actions + relay info between the brain and rest of the body (spinal cord)


How does the brain (in the CNS) process + respond to info?

- Receptor cells take in environmental info
- Sensory neurones pass this info to spinal cord
- In spinal cord, relay neurones receive info and pass it to brain
- Brain decides how to respond + passes this info through relay neurones in the spinal cord to motor neurones in the body
- Motor neurones send info about response to effector cells, causing them to respond appropriately


What is a reflex action?

A quick, involuntary bodily response that bypasses the use of the brain by triggering an unconscious ‘relay arc’


Outline the reflex arc as a quick unconscious means of response

- The reflex arc is triggered when the receptor cells detect environmental stimuli that requires a quick response
- Sensory neurones transmit the info to the spinal cord
- Relay neurones in the spinal cord receive the info + coordinate a quick response
- This info on how to respond is sent to the motor neurones
- The motor neurones trigger a quick response in the effector cells


Give 2 examples of a reflex action

- Knee jerk reflex
- Touching hot plate and immediately removing hand


What is the role of the PNS?

- Varies in function between the ANS + SNS
- To transmit info to and from the CNS


Outline the function of the Somatic Nervous System (branch on the PNS)

To control conscious bodily activities
- E.g. voluntary muscle movement
- Mainly controls skeletal muscles


Outline the function of the Autonomic Nervous System (branch on the PNS)

To control unconscious bodily activities that are vital for survival
- E.g. digestion, stress response, breathing, sexual arousal
- Mainly controls smooth muscles + glands
- Split into 2


What is the Autonomic Nervous System (branch of PNS) divided into?

- Sympathetic Nervous System
- Parasympathetic Nervous System


What is the function of the Sympathetic Nervous System?

- Prepares + excites body for action when faced with danger
- Actions include: increased heart rate, increased breathing rate, decreased saliva flow
- Involved in the fight or flight response


What is the function of the Parasympathetic Nervous System?

- Calms body after being faced with danger to return it to resting state
- Actions include: slows heart rate, slows breathing rate, stimulates saliva flow
- Involved in ‘rest and digest’


Which neurones are predominant in the Autonomic Nervous System?

Motor neurones (responding to info from CNS unconsciously)


Which neurones are predominant in the Somatic Nervous System?

Sensory + motor neurones (taking in and responding to info consciously)


List 2 similarities between the autonomic + somatic branches of the PNS

- Both part of PNS
- Both conduct nerve impulses from CNS to other parts of body


List 2 differences between the autonomic + somatic branches of the PNS

- ANS controls unconscious activities + CNS conscious
- ANS uses mainly motor neurones + CNS motor and sensory


Define neurones

Nerve cells that are the basic building blocs of the nervous system, processing + transmitting messages through the body


What are the three types of neurone?

- Sensory
- Relay
- Motor


What is the role of sensory neurones?

Carry messages from the PNS to the CNS


What is the role of relay neurones?

Carry messages through the CNS (brain + spinal cord), as the connection between sensory neurones + motor neurones


What is the role of motor neurones?

Carry messages from the CNS to effector muscles + glands, which can respond


Briefly describe the structure of sensory neurones

- Long dendrite
- Short axon


Briefly describe the structure of relay neurones

- Short dendrites
- Short axon


Briefly describe the structure of motor neurones

- Short dendrites
- Long axon


Where are sensory neurones located?

In the PNS (in clusters: ‘ganglia’)


Where are relay neurones located?

In the CNS (brain + spinal cord)


Where are motor neurones located?

Cell body in the the CNS, with long axon stretching into the PNS towards effector cells and organs


How big are neurones?

Vary in size (less than mm - m)


List the basic components all neurones share

- Cell body
- Nucleus
- Dendrites
- Axon
- Myelin sheath
- Nodes of Ranvier
- Terminal buttons


What makes the three types of neurones different?

Their: structure (size of basic components), function + location


What is a cell body?

The metabolic centre of the cell, containing the nucleus + intercellular structures


What is a nucleus?

Control centre of cell, containing its genetic info (chromosomal DNA)


What are dendrites?

Branchlike structures that carry nerve impulses from neighbouring neurones TOWARDS the cell body


What is an axon?

Branchlike structure that carries nerve impulses AWAY from the cell body


What is a myelin sheath?

Fatty layer that covers the axon to protect it + speed up electrical transmission of the impulse


What are Nodes of Ranvier?

Gaps that segment the myelin sheath to speed up the electrical impulse transmission by forcing it to ‘jump’ along the axon


What would happen if the myelin sheath was continuous (no Nodes of Ranvier)?

Electrical impulse transmission along the axon would be slower


What are terminal buttons?

End of axon where signal is sent to adjacent neurone across the synapse


What is action potential?

Explosion of electrical activity in an impulse which travels down the axon towards the end of the neurone (terminal button + synapse)


In resting state, what charge does the inside of a neurone have?



When activated, what charge does the inside of a neurone have?



What is a synapse?

Three components that make up the area connecting neurones
- Presynaptic terminal (end of one neurone)
- Postsynaptic terminal (end of next neurone)
- Synaptic cleft (gap between the terminals)


Define synaptic transmission

The process by which neighbouring neurones communicate by sending chemical messages across the synapse between them


How are signals transmitted within neurones?



How are signals transmitted between neurones (across the synapse)?



Outline the process of synaptic transmission

- Action potential (electrical explosion) travels along neurone’s axon until it reaches the end: presynaptic terminal
- The AP triggers the release of neurotransmitters from synaptic vesicles
- The neurotransmitters diffuse across the synaptic cleft (down the conc. gradient) as a chemical signal
- The neurotransmitters fit into specifically shaped postsynaptic receptor sites on the dendrite of the next neurone
- Any neurotransmitters that don’t fit into these sites are either: reuptaken into the presynaptic terminal OR broken down by enzymes
- At the postsynaptic terminal, the signal is converted back to electrical
- If the summation is positive, the postsynaptic terminal fires, passing this electrical impulse down the neurone


Define neurotransmitters

Brain chemicals released from synaptic vesicles that relay signals between neurones across the synapse


What is different between different types of neurotransmitters?

- Specialist function
- Specialist molecular shape
- Either classified as excitatory or inhibitory


What model can be used to describe how neurotransmitters fit into receptor sites?

Lock and key model


What are excitatory neurotransmitters? Give an example?

Increase the positive charge of the postsynaptic neurone, increasing the likelihood it will fire + pass on action potential
- Nervous systems’ “on switch”
- E.g. Adrenaline


What are inhibitory neurotransmitters? Give an example

Increase the negative charge of the postsynaptic neurone, decreasing the likelihood it will fire + pass on action potential
- Nervous systems’ “off switch”
- E.g. Serotonin


What is summation?

The net calculation of excitatory post-synaptic potential (EPSP) and inhibitory post synaptic potential (IPSP)


What must summation be for a neurone to fire?

Net positive