CH2 Nervous System Functioning

Question 1

Central Nervous System (CNS)

Answer 1

• Three main roles: to receive sensory information from the body, to send motor information to the body, to process information.
• Carries messages to and from PNS.
• Made up of the brain and spinal cord

Question 2

The brain

Answer 2

• Is an intricate network of cells that processes information received through neural pathways from the body and directs/coordinates actions within the body.

A neural pathway comprises one or more circuits of interconnected neurons that form a communication network.

Question 3

The spinal cord and its roles

Answer 3

• Is a cable-like bundle of nerve fibres that extends from the base of the brain to the lower back.
• Has two main roles:
  
  • To receive sensory information from the body via the PNS and send these messages to the brain for processing.
  • To receive motor information from the brain and send it to relevant parts of the body via the PNS to control muscles, glands and internal organs so that appropriate actions can be taken.

Question 4

The Spinal Reflex

Answer 4

• Is an unconscious, automatic response controlled solely by neural circuits in the spinal cord; bypasses the brain

Question 5

Why is the spinal reflex considered adaptive?

Answer 5

Something is considered to be adaptive when it assists in the sruvival of the organism. An immediate withdrawal response initiated by the spinal cord enables a faster reaction time (i.e. a fraction of a second before the sensory information reaches the brain). Thus, it allows an organism to save time while evading a possibly harmful situation.

Question 6

Peripheral Nervous System (PNS)

Answer 6

• A system comprised of muscles, organs and glands
• Subdivisions: autonomic NS and somatic NS
• Has two main roles
  
  • Receive motor information from the CNS
  • Send sensory information to the CNS

Question 7

6 steps in the spinal reflex

Answer 7

1. Receptor cells within the skin of your feet detect a sharp poke from a pin left on the ground. A neural message is sent to a sensory neuron.
2. Sensory neurons carry the message along a sensory, afferent pathway to the spinal cord.
3. Interneurons relay the message to motor neurons
4. Motor neurons carry the message along a motor, efferent pathway to the leg muscle, causing a withdrawal reflex (whereby the foot withdraws from the pin).
5. Simultaneously, the message is carried up the spinal cord to the brain.
6. The message is received in the brain (specifically in the area that processes this type of sensory information). Pain is consciously interpreted in the foot.

Question 8

The Somatic NS

Answer 8

• Is responsible for initiating skeletal muscle movement
• Controls voluntary, goal-directed movements.
• Sensory information is received at sensory receptor sites in the body (skin, muscles, joints and tendons) and carried along sensory neural pathways by sensory neurons to the CNS.
• Motor information from the CNS is carried along motor neural pathways by motor neurons to skeletal muscles to control their activity by causing them to contract or relax.

Does NOT involve visceral muscles, organs or glands. Skeletal muscles are attached to our bones and respond to messages from the CNS to initiate, change or stop movement.

Question 9

The Autonomic NS

Answer 9

• Regulates the activity of the visceral muscles (i.e. internal organs and glands).
• Connects the CNS to the body’s internal organs (e.g. the heart, stomach, liver etc.) and glands (such as sweat, salivary and adrenal glands), providing feedback to the brain about their activities.
• Primarily self-regulating (not entirely); without conscious awareness
• Split into three further sub-divisions: sympathetic NS, parasympathetic NS, enteric NS

Question 10

Sympathetic NS

Answer 10

Activates muscles, organs and glands to prepare for action

Question 11

Parasympathetic NS

Answer 11

• Maintains the body’s internal environment
• Counterbalances activity of the sympathetic nervous system

(Para)lysed; NOTE: The sympathetic NS and the parasympathetic NS are NOT at all separate from each other. Rather, one is dominant over the other at any given time depending on the situation.

Question 12

Enteric NS

Answer 12

Dedicated to the functioning of the gastrointestinal tract

Question 13

Structure of a neuron and the roles of each part

Answer 13

• Dendrites – convert neurotransmitters to action potential (i.e. receives neural information) and sends it to the soma
• Soma – processes info
• Axon – site of travelling action potential
• Myelin sheath – protects axon; speeds up action potential
• Axon terminal/terminal button – converts action potential into neurotransmitters before releasing the neural information into the synapse.

Question 14

A neurotransmitter (Nt)

Answer 14

• Is a chemical substance released by a presynaptic neuron to send signals to the post-synaptic neuron.
• Its role is to transmit chemical signals to the adjacent neuron.
• Can be either:
  
  • Excitatory – make postsynaptic neurons more likely to fire (i.e. release action potential)
  • Inhibitory – make postsynaptic neurons less likely to fire

Question 15

Neural information as electrochemical

Answer 15

• Communication between neurons may be electrical.
  
  • E.g. axons transmit messages directly to other axons or directly to the cell body (soma) of other neurons; dendrites of one neuron communicate directly with the dendrites of other neurons via an electrical impulse.
  • E.g. action potential.
• Communication can be chemical (i.e. neurotransmitters).

Question 16

Excitatory v inhibitory neurotransmitters

Answer 16

• Excitatory – makes postsynaptic neurons more likely to fire (i.e. release action potential)
• Inhibitory – makes postsynaptic neurons less likely to fire
• Whether a neurotransmitter is excitatory or inhibitory depends on the properties of the receptor at the synapse, where it is released and on the receptor’s location in the brain.

Question 17

The neural synapse

Answer 17

• Is the site where adjacent neurons communicate by transmitting neural signals to one another.
• Made up of the synapatic gap/cleft, the terminal buttons of the presynaptic neuron and the dendrites of the postsynaptic neuron

Question 18

Neurohormones

Answer 18

• Are neurotransmitters that are also hormones.
  
  • E.g. noradrenaline is secreted as a hormone by the adrenal glands into the blood, and as a neurotransmitter from neurons.

Question 19

Glutamate (Glu)

Answer 19

• The main excitatory neurotransmitter in the CNS.
• Involved in normal brain function (i.e. learning, memory, perception, thinking and movement)
• Its excitatory effects promote the growth and strengthening of synaptic connections, subsequently improving memory of what as been learnt.
• Abnormally high concentrations of Glu can result in overexcitation of receiving neurons.
  
  • Neuronal damage and/or death by overstimulating them.

Glu(cose) = gives energy; excitatory

Question 20

Gamma-amino butyric acid (GABA)

Answer 20

• The main inhibitory neurotransmitter in the CNS.
• Fine-tunes neurotransmission in the brain and maintains neurotransmission at an optimal, or ‘best possible’, level.
• Low concentrations of GABA
  
  • May cause seizures due to a lack of controlled activation
  • Anxiety symptoms

Question 21

A neuromodulator (Nm)

Answer 21

• Is a chemical (i.e. Nt) that is released by neurons to modulates, or influences, the effectiveness of other neurotransmitters.
• Altering neural transmission can be done by changing the reactivity of receptors to enhance their excitatory or inhibitory responses or controllling the synthesis + release of Nts.

Question 22

A conscious response

Answer 22

• Involves awareness
• Is voluntary; intentional; goal-directed
• Exercises some degree of control
  
  • e.g. speaking to a friend, picking up a water bottle

Question 23

An unconscious response

Answer 23

• Does not involve awareness
• Involuntary; unintentional; automatic
• Is not typically controlled
  
  • e.g. bodily responses regulated by the autonomic NS like digesting, blinking, breathing

Question 24

Visceral muscles

Answer 24

• Are the muscles involved in the activity of internal organs and glands.
• Have built-in mechanisms for generating activity and do not depend on voluntary control from the brain.
• Are an important feature of the ANS → allows the ANS to function continuously - whether we are awake, active, asleep, under an anaesthetic or in a coma.

Question 25

Neurotransmitters v neuromodulators

Answer 25

• Site of release: Nts are released into a single synapse, Nms are released outside of the synapse into neural tissue in the brain.
• Target: Nts target a single post-synaptic neuron, Nms target groups of neurons
• Speed of action: Nms’ effects take longer to become established and last longer than Nts.

Question 26

Dopamine

Answer 26

• Is primarily an excitatory neuromodulator
  
  • Can be inhibitory depending on location or on the type of receptors that are present.
• Dopaminergic systems associated with voluntary movement and the dopamine reward system.

Question 27

Dopamine in controlling voluntary movemtns

Answer 27

• Pathways in the substantia nigra: dopamine released to cerebellum and spinal cord (involved in movement) for voluntary movements.
• Low levels due to a damaged substantia nigra is associated with Parkinson’s disease.

Question 28

Dopamine reward system

Answer 28

• Is along pathways in the limbic system
• Release of dopamine brings feelings of pleasure and happiness.
• Involved in reward-based learning; may influence us to engage in certain behaviours to attain the pleasurable experience it can cause, based on previous experience with that type of reward.
• Associated with addictive behaviours.
• High levels associated with schizophrenia.

Question 29

Serotonin

Answer 29

• Only has inhibitory effects.
  
  • Helps counterbalance excessive excitatory effects of other neurotransmitters, as GABA does with glutamate.
• Regulates the sleep-wake cycle; produced in brain stem and gut and then released in the pineal gland to trigger melatonin production.
• Is a mood stabiliser
• Not enough = depression and anxiety
• Too much = serotonin syndrome
• Optimal levels associated with positive, calm and stable moods.

Question 30

Symptoms of serotonin syndrome

Answer 30

Fever, elevated heart rate, restlessness, agitation, confusion, hallucinations, delirium and seizures

Question 31

Synaptic Plasticity

Answer 31

• Refers to the ability of the synapse to change in response to experience.
  
  • Enables a flexible, efficient and effectively functioning nervous system.
  • Is the biological basis of learning and memory formation.

This model is highly simplified; a memory of a single bit of information may be stored within many connections, and each connection may be involved in several different memories.

Question 32

Sprouting

Answer 32

• Is the creation of new extensions (i.e. sprouts on axons or dendrites) on a neuron to allow it to make new connections with other neurons. This occurs enables new links to be made, including rerouting of existing connections.
  
  • The dendritic branch refers to bushier dendrites on the post-synaptic neuron that have more branches to make new connection.
  • Filigree appendages refer to the growth of pre-synaptic axon terminals towards the dendrite of post-synaptic neurons.

Question 33

Rerouting

Answer 33

• Is the reorganisation of neural connections into more effective or necessary pathways
  
  • May be entirely new neural pathways or connections to other pathways in the brain.
  • The rerouting may involve the existing synaptic connections and/or new connections from the sprouts.

Question 34

Pruning

Answer 34

• Is the elimination of weak, ineffective or unused synapses.
  
  • Determined by usage – synapses that are frequently used are retained and those that are not decay and disappear.
  • May be a way of fine-tuning the brain’s neural circuits to maintain efficient brain functioning.

Question 35

Functions of sprouting, rerouting and pruning

Answer 35

These make it possible to adapt to changing and increasingly complex environments, enable neurons to restore or compensate for a lost function following a brain injury and to maximise remaining functions.

Question 36

Long-term depression (LTD)

Answer 36

• Is the long-lasting decrease in the strength of synaptic transmission and neuronal response due to prolonged lack of stimulation.
  
  • The weakening or elimination of unused synapses through LTD may result in the pruning, leaving only the important connections that have been strengthened through repeated use by LTP.

NOTE: LTD and LTP refer to effects; they are not processes

Question 37

Long-term potentiation (LTP)

Answer 37

• Refers to the long-lasting enhancement of synaptic transmission due to repeated strong stimulation.
  
  • The postsynaptic neurons become more and more responsive (i.e. more sensitive) to the presynaptic neuron release due to additional growth of receptor sites.
  • The presynaptic neurons releases more neurotransmitters.

NOTE: LTD and LTP refer to effects; they are not processes

Question 38

Similarities between LTD and LTP

Answer 38

• Both are activity dependent; that is, more or less activity
• Both involve glutamate (excitatory neurotransmitter)
• Both occur at glutamate synapses
• Both involve changes in excitability
• Both have long-lasting effects

Question 39

Using biofeedback

Answer 39

• Biofeedback is a type of mind-body technique you use to control some of your body’s functions
• Sympathetic responses can be switched to parasympathetic responses (despite being part of the autonomic NS) using biofeedback
• I.e. Controlling high heart rate (an otherwise sympathetic response) by consciously slowing down breathing rate.