Week 3 The Nervous Sytem

Question 1

Neuroscience

Answer 1

Neuroscience is the study of the nervous system
• Includes structure, function, health and disease
• Understanding the structure and function of the nervous system requires integration of the knowledge of various scientific disciplines

Question 2

Neurones

Answer 2

Fundamental units of the nervous system
• Human brains contain ~86 billion neurons
• Neuron development ceases before birth
• Under influence of various factors
• How do they connect with each other and other parts of the nervous system

Question 3

Neurons - Structure

Answer 3

typical neuron has three regions:
1) Cell body (Soma)
Contains organelles and cell processes radiate out from the cell body.
2) The dendrites = Neuron’s receivers. Receives impulses and carries the impulse towards cell body
3) The axon = Neuron’s transmitter. Conducts electrical impulses away from cell body.

Question 4

Neurons - Function

Answer 4

• Neurons are responsible for sending and receiving information around the body
•Depending on location, neurons can be:
Sensory
Motor
Interneuron

Question 5

Sensory (afferent) neurons

Answer 5

Make up sensory division of the PNS

Question 6

Motor (efferent) neurons

Answer 6

Connect to muscle fibres at distal end of axon Can have Upper and Lower neurons
Upper from brain
Lower arise from spinal cord an attach to muscles

Question 7

Motor Unit

Answer 7

Motor neuron + muscle fibres

Question 8

Interneurons

Answer 8

between motor and sensory neurons

Question 9

Nerve Impulses

Answer 9

Neurons are excitable tissue converting a stimulus to nerve impulses, similar to electricity travelling through wires.
• Resting Membrane potential (RMP)
• Cell membrane of a typical neuron at rest has negative electrical
potential ~ -70mV (Inside v Outside)
• This electrical potential difference = RMP
• Caused by uneven separation of charged ions (↑ conc. K+ inside membrane & ↑ conc. Na+ outside) = polarised
• Imbalance is maintained by i) differences in cell membrane permeability & ii) sodium-potassium pump

Question 10

Polarisation

Answer 10

Depolarisation:
• If the inside of cell becomes less negative in relation to outside = ↓ in potential difference across membrane = membrane less polarised.
• Occurs when charge difference is more +ve than RMP (- 70mV)

• Repolarisation:
• Membrane potential returns to its resting state after an AP towards a more –ve value (cell membrane more polarized), but continues past RMP

• Hyperpolarisation:
• Charge moves back to RMP (-70mV)

Question 11

Graded potentials

Answer 11

Localised change in membrane potential of depolarization or hyperpolarisation.
• Not ‘all or none’
• Local event and depolarisation doesn’t spread along neuron – need action potential.
Slight change in membrane potential

Question 12

Action Potentials

Answer 12

• Action Potential = Rapid (~1ms) & substantial neuron membrane depolarisation.
• Membrane potential changes from RMP (- 70mV) to +30mV and back again.

All Action Potentials begin as Graded Potentials
• If GP does not reach depolarization threshold, nothing happens.
• If threshold ~15-20mV reached (mV from RMP of -70 to ~ -55mV), AP will occur
• ‘All-or-none’ principle

• When an axon is in the process of generating an action potential – unable to respond to another stimulus – absolute refractory period. Won’t be able to respond to anothing else

• Once an axon has dealt with a stimulus, it can deal with a new one if the new stimulus is of a greater magnitude than the one it is dealing with – relative refractory period can react but stimulus has to bigger than the one its dealing with

Question 13

Synapse

Answer 13

A synapse is the place where neurons connect and communicate to continue transmitting APs
Each neuron has between a few to hundreds of thousands of synaptic connections Site of AP transmission from axon terminals of 1 neuron to dendrites of another.
• Synapse between 2 neurons includes:

i) Axon terminals of presynaptic neuron

ii) Receptors on postsynaptic neuron

iii) Spacebetweenthetwo structures = synaptic cleft

Question 14

Neurotransmitters

Answer 14

Endogenous chemicals that allow neurons to communicate
• Carry messages from one neuron to the next nerve or effector organ cell
• Located in axon terminal in sacs called synaptic vesicles
• Neurotransmitters released from vesicles into synaptic cleft to carry messages across
• More than 50 neurotransmitters have been identified

Question 15

Neuromuscular junction

Answer 15

Junction of motor neurone and the muscles fibres it innovates
Axon terminals protrude to motor end plate
Neurotransmitters released from motor neurone a on terminals bind to receptors on plasma

Question 16

One-Way Signals

Answer 16

Presynaptic terminals contain saclike structures = synaptic vesicles containing neurotransmitters.
When never impulse reaches presynaptic axon terminals, vesicles release neurotransmitters into synaptic cleft

Question 17

Organisation of the nervous system

Answer 17

Human nervous system divided into 2 parts:
i) CNS (Central Nervous System) - Includes the brain & Spinal Cord.

ii) PNS (Peripheral Nervous System)
—somatic
—autonomic nervous system
— sympathetic NS — parasympathetic NS — enteric NS

Question 18

Peripheral nervous system

Answer 18

PNS further subdivided into Sensory (afferent) or Motor (efferent)
• Sensory = Sends signals from periphery to CNS afferent
• Motor = Send signals from CNS to effector organs. Efferent

Question 19

Peripheral nervous system - Motor

Answer 19

Sensory (afferent) and Motor (efferent)
Motor nerves can also be divided into Somatic (voluntary) or Autonomic (Involuntary) control

• Somatic = Conscious processes
• Autonomic = Regulates bodily processes at subconscious level

Question 20

Sensory-Motor Integration

Answer 20

How does a sensory stimulus result in a motor response?
Sensory-Motor Integration

PNS relays sensory info to CNS

CNS interprets info and sends out appropriate motor signals

Question 21

Sensory Input

Answer 21

Sensory input from receptors in the body can terminate at varying levels in the CNS The area where sensory impulses terminate = Integration Centre

• Spinal cord – response is typically a simple motor reflex

• Lower brain stem – result in subconscious motor reactions of a
more complex nature e.g. postural control during sitting

• Cerebellum – subconscious control of movement (smoothing)

• Thalamus – Enter conscious level & person can distinguish various sensations
• Cerebral cortex – This part of conscious brain allows us to be aware of our surroundings & our relationship to them.

Degree of movement complexity increase I
V

Question 22

Peripheral nervous system

Answer 22

Autonomic system further subdivided
Into:
Sympathetic
Parasympathetic
Enteric Nervous Systems

Question 23

The Central Nervous System

Answer 23

The CNS consists of the brain and spinal cord.

• Brain
• Has 4 major regions:
• i)Cerebrum
• ii)Diencephalon
• iii)Cerebellum
• iv) Brain Stem

Question 24

CNS - Cerebrum

Answer 24

Right & Left hemispheres connected by fibre bundles = corpus callosum
Cerebral cortex = outer layer of cerebral hemispheres
• Houses the Primary Motor Cortex & Basal Ganglia

Consists of 5 lobes:
Frontal Lobe: General Intellect & motor control
Temporal Lobe: Auditory input & interpretation
Parietal Lobe: General sensory input & interpretation
iv) Occipital Lobe: Visual input & interpretation
v) Insular Lobe: Diverse functions linked to emotion &
self-perception

Question 25

CNS - Diencephalon

Answer 25

Composed of thalamus & hypothalamus

• Thalamus – All sensory input (except smell) comes here to be relayed to appropriate area of cortex.
Regulates what sensory input reaches conscious brain

• Hypothalamus – Directly below thalamus & maintains homeostasis Neural centres here assist in control and regulation of BP, HR, Breathing and Digestion

Question 26

CNS - Cerebellum

Answer 26

Located behind brain stem & crucial in coordinating timing of motor activities, progression from one movement to the next & smoothing out movements
• Compares expected/intended movement with actual changes in the body and initiates corrective adjustments
• PMC decides on movement & relays decision to cerebellum
• Cerebellum notes desired action and compares to actual movement based on sensory feedback If actions are different, cerebellum sets in process corrective action

PRIMARY motor cortex -> cerebellum

Question 27

CNS – Brain Stem

Answer 27

• Connects brain to spinal cord
• Sensory & motor neurons pass through brain stem
• Made up of midbrain, the pons & medulla oblongata
• Houses a specialised group of neurons: the reticular formation
• They are involved in many vital functions including:
i) Control CV & respiratory function
ii) Coordinate skeletal muscle function & maintain muscle tone
iii) Influence arousal & consciousness
iv) Circadian rhythm
v) Pain control system

Question 28

CNS – Spinal Cord

Answer 28

Joins onto the lowest part of the brain stem (medulla oblongata)
• Nerve fibres in spinal cord allow 2-way conduction of nerve impulses
• Sensory (afferent) fibres carry signals from the sensory receptors such as those on the skin and muscles to the upper levels of the CNS
• Motor (efferent) fibres carry signals from the brain and upper spinal cord to the end organs (e.g. muscle)